DOI: 10.1002/chem.201400285
Full Paper
& Supramolecular Chemistry
Anionic Bipyridyl Ligands for Applications in Metallasupramolecular Chemistry Mirela Pascu,[a] Mathieu Marmier,[a] Clment Schouwey,[a] Rosario Scopelliti,[a] Julian J. Holstein,[b] Grard Bricogne,[b] and Kay Severin*[a]
Abstract: The facile synthesis of anionic bipyridyl ligands with dinuclear clathrochelate cores is described. These metalloligands can be obtained in high yields by the reactions of M(ClO4)2(H2O)6 (M: Zn, Mn, or Co) with 4-pyridylboronic acid and 2,6-diformyl-4-methylphenol oxime or 2,6-diformyl-4-tert-butylphenol oxime, followed by deprotonation.
The ligands are interesting building blocks for metallasupramolecular chemistry, as evidenced by the formation of a Ptbased molecular square and four coordination polymers with 2D or 3D network structures. Competition experiments reveal that the utilization of anionic bipyridyl ligands can result in significantly more stable assemblies.
Introduction Bipyridyl ligands are among the most frequently used building blocks for supramolecular coordination chemistry.[1] The simple 4,4’-bipyridine (bpy) ligand has been employed for a long time, as exemplified by the molecular square [{(en)Pd(bpy)}4]8 + (en: ethylenediamine) published in 1990.[2] Today, one can find more than 1000 entries for structures of the type LnM(bpy)MLn in the Cambridge Structural Database.[3] Of course, many structural variants of 4,4’-bipyridine have been explored over time. Bipyridyl ligands containing metal ions (“metalloligands”) are an interesting subclass in this context.[1, 4] The metal ions can add novel properties, such as color, redox activity, magnetism, molecular-recognition sites, or catalytic activity. Furthermore, the metal ions can facilitate the synthesis of the bipyridyl ligand if metal-templated reactions are employed. Some representative examples of metal-containing bipyridyl ligands are depicted in Figure 1. Complexes of type A have mainly been used as “expanded ligands” for structural investigations.[4a,e] Metallaporphyrins of type B[4d,f] and salen-type complexes of type C possess accessible metal sites, which can be used for molecular recognition (for example, in sensing applications)[5] or for catalysis.[6] We have recently introduced clathrochelatebased bipyridyl ligands of types D and E.[7] These ligands are rigid, long (approximately 3.2 nm for E with n = 2), well soluble, and easily accessible in a one-pot reaction from commercially [a] Dr. M. Pascu, M. Marmier, C. Schouwey, Dr. R. Scopelliti, Prof. K. Severin Institut des Sciences et Ingnierie Chimiques cole Polytechnique Fdrale de Lausanne (EPFL) 1015 Lausanne (Switzerland) E-mail: [email protected] [b] Dr. J. J. Holstein, Dr. G. Bricogne Global Phasing Ltd., Sheraton House Castle Park, Cambridge CB3 0AX (UK) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201400285. Chem. Eur. J. 2014, 20, 5592 – 5600
Figure 1. Examples of metal-containing bipyridyl ligands.
available starting materials. Below, we describe a different class of clathrochelate complexes with terminal pyridyl groups. The new bipyridyl ligands display an interesting characteristic for applications in metallasupramolecular chemistry: they are negatively charged.
Results and Discussion In 2006, Chaudhuri and co-workers reported the synthesis and structure characterization of a dinuclear MnII clathrochelate 5592
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Full Paper complex with bridging phenolatodioximato ligands and capping methylboronate esters.[8] We hypothesized that similar dinuclear complexes could be used to build bipyridyl ligands. Indeed, macrobicyclic MII tris(dioximato) complexes (M: Zn, Co, or Mn) with terminal pyridyl groups were obtained by subcomponent self-assembly[9] of three compounds, M(ClO4)2(H2O)6, 4-pyridylboronic acid, and 2,6-diformyl-4-methylphenol oxime (L1) or 2,6-diformyl-4-tert-butylphenol oxime (L2), in dichloromethane/ethanol (Scheme 1). Products 1–6 precipitated from
Single-crystal X-ray structure analyses of 4 and 5 confirmed the presence of dinuclear clathrochelate cores with terminal pyridyl groups. A graphical representation of the structure of complex 4 is given in Figure 2, and selected bonds lengths and angles for 4 and 5 are summarized in Table 1. The two MII
Figure 2. Molecular structure of complex 4 in the crystal. Most of the hydrogen atoms have been omitted for clarity.
Table 1. Selected distances [] and angles [8] for the complexes 4, 5, 7, and 8.
4 5 7 8
Scheme 1. Synthesis of the clathrochelates 1–6.
the reaction mixtures in the form of microcrystalline materials. All of the complexes were obtained in high yield (> 80 %), with the exception of complex 6, for which a somewhat lower yield of 65 % was observed. The reactions were performed without the addition of a base, so the products were obtained in the diprotonated form with perchlorate as the counteranion. The cationic complexes are only soluble in polar organic solvents such as DMF or DMSO. Clathrochelates 1–6 were analyzed by elemental analysis and mass spectrometry. The diamagnetic Zn complexes 1 and 4 were also characterized by NMR spectroscopy. As expected, only one set of signals was observed for the three phenolatodioximato ligands. The “free” ligands L1 and L2 showed luminescence with emission maxima at 392 nm (L1) and 387 nm (L2; in DMF; lex = 340 nm). Solutions of the Co and Mn complexes did not show significant luminescence, presumably due to quenching by the paramagnetic metal ions. The Zn complexes 1 and 4 however, were highly emissive, with maxima at 451 nm for 1 and 445 nm for 4 (in DMF; lex = 340 nm). Due to the inert character of the Zn2 + ions, the photoluminescence can be assigned to intraligand (IL) and/or ligand-to-ligand charge transfer (LLCT) emissions. The magnetic properties of the Co and Mn complexes were not investigated. However, it is expected that the Mn complexes 3 and 6 show very similar behavior to that of the previously reported clathrochelate with methylboronate ester end groups. For the latter, a magnetic moment of 7.13 mB (290 K) and antiferromagnetic exchange coupling between the two paramagnetic MnII centers was observed.[8]
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M···M []
M Nav []
M Oav []
M O Mav [8]
N M Oav [8]
2.9401(17) 2.9591(10) 2.9436(8) 2.9080(10)
2.12 2.10 2.12 2.18
2.10 2.10 2.10 2.14
88.9 89.6 88.8 85.6
82.4 83.0 82.4 80.7
ions in 4 and 5 are coordinated in a trigonal prismatic fashion by three nitrogen and three oxygen atoms. The latter bridge the two metal ions, which results in M···M distances of 2.9401(17) (4) and 2.9591(10) (5). At 1.490 , the average B O bond length of the tetragonal boronate esters is similar to what is found for mononuclear chlathrochelates with boronate ester caps.[7, 10] The N atoms of the pyridyl groups in 4 and 5 are 17.91 and 17.87 apart from each other, respectively. The clathrochelate ligands are thus substantially longer than mononuclear clathrochelates of type D (14.95 ; Figure 1). The NH groups of the protonated pyridyl groups are involved in hydrogen bonding to the perchlorate anion (NH···O in 4: 2.729 ; NH···O in 5: 2.817 ). The cationic clathrochelates can be deprotonated by the addition of a base: when triethylamine or tetraethylammonium hydroxide was added to a solution of 1, 3, or 4 in acetonitrile/ methanol, the anionic complexes 7–9 were obtained in high yield (Scheme 2). The solubility of the anionic complexes is higher than that of the cationic perchlorates: the complexes display a good solubility (> 10 mg mL 1) in acetonitrile/methanol (1:1), acetone, or CHCl3. Crystallographic analyses of 7 and 8 show that the deprotonation has only a minor influence on the structure: the bond lengths and angles observed for the anions of 7 and 8 are very similar to those of the cations of 4 and 5 (Figure 3). The N···N distances in 7 (17.99 ) and 8 (17.98 ) are marginally longer than those found for 4 and 5.
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Scheme 2. Synthesis of the anionic bipyridyl ligands 7–9.
Figure 3. Molecular structure of complex 8 in the crystal. Most of the hydrogen atoms have been omitted for clarity. Scheme 3. Synthesis of the molecular square 10.
After having established a facile synthetic route for the synthesis of anionic clathrochelates with pyridyl end groups, we examined the potential of these bipyridyl ligands in structural supramolecular chemistry. It is well known that rigid, linear bipyridyl ligands react with cis-protected square-planar Pd and Pt complexes to form square-shaped structures.[1e, 11] We postulated that our new ligands would react in a similar fashion, and we therefore studied the reaction of 9 with Pt(dppp)(OTf)2 (dppp: 1,3-bis(diphenylphosphino)propane; OTf: trifluoromethanesulfonate). Complex 9 was chosen because it is diamagnetic and because of its superior solubility compared to that of 7. Multinuclear NMR analysis of a 1:1 solution of 9 and Pt(dppp)(OTf)2 in DMSO indicated the formation of a single product possessing a high degree of symmetry. Isolation of the product as a pale yellow amorphous powder was achieved by precipitation upon addition of CHCl3. Complex 10 displays poor solubility in most common solvents, with the exception of polar aprotic solvents such as DMSO and DMF. The analytical data of 10 (NMR, elemental analysis, and ESI-MS) confirmed the formation of a molecular square (Scheme 3). The presence of a negative charge on the clathrochelate ligand was expected to result in a more stable assembly.[12] To investigate this hypothesis, we compared the stability of 10 with that of the known bpy analogue [(dppp)Pt(bpy)]4(OTf)8 (11).[13] Increasing amounts of the N-donor [D5]pyridine were added to solutions of 10 or 11 in [D6]DMSO (Scheme 4). Pyridine competes with the bridging ligand for complexation to the Pt centers and therefore results in rupture of the assembly. The amount of remaining square complex was then deterChem. Eur. J. 2014, 20, 5592 – 5600
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Scheme 4. Disruption of the molecular squares 10 and 11 by addition of pyridine ([D5]pyridine was used for the NMR experiments).
mined by 1H or 31P NMR spectroscopy. The results are summarized in Figure 4. Addition of only one equivalent of [D5]pyridine to a solution of 11 resulted in significant ligand exchange, and no starting material could be observed after the addition of approximately seven equivalents. In contrast, more than 50 % of square 10 was still present after addition of approximately 10 equivalents of [D5]pyridine, and more than 100 equivalents
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Full Paper upon heating to generate a basic medium.[14] The base can deprotonate the pyridyl groups of 1 and 4. In this way, the network is formed slowly and crystallizes directly from the reaction mixture. Attempts to perform the same reaction with the deprotonated metalloligands 7 or 9 resulted in the immediate formation of powders. Crystallographic analyses of the coordination polymers 12 and 13 revealed 2D square-grid-type layer structures with square dimensions of 22.3 22.3 (Figure 5). Four metallo-
Figure 4. Ratio of starting material 11 (*) or 10 (*) present in solution relative to the initial 2.0 mm concentration in [D6]DMSO upon an increase in the concentration of the competitor [D5]pyridine.
were needed before the concentration of square 10 dropped below 5 % of the initial concentration. The complexity of the equilibria involved in the formation and disruption of these molecular squares made it impossible to accurately derive the thermodynamic parameters. However, the results clearly show that the assembly between (dppp)Pt2 + and the clathrochelatebased bipyridyl ligand 9 is significantly more stable than the square formed between (dppp)Pt2 + and the standard bpy ligand. Bipyridyl ligands have been used extensively for the construction of metal–organic frameworks (MOFs).[1d] To demonstrate that our clathrochelate-based bipyridyl ligands can also be used in this area, we have investigated the reactions of 1 and 4 with Zn2 + and Cd2 + ions. Heating of a mixture of Zn(NO3)2(H2O)6 and the protonated metalloligands 1 or 4 in DMF in a sealed vial resulted in the formation of the crystalline coordination polymers 12 and 13 (yields of 66 and 89 %, respectively; Scheme 5). It is known that DMF decomposes slowly
Scheme 5. Syntheses of the two-dimensional coordination polymers 12 and 13. Chem. Eur. J. 2014, 20, 5592 – 5600
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Figure 5. Part of the layer structure of coordination polymer 12 with a view along the crystallographic z axis. Hydrogen atoms and solvent molecules have been omitted for clarity. C: grey; O: red; N: blue; B: green; Zn: cyan.
ligands are connected through ZnII ions. The latter have an octahedral coordination geometry with two additional DMF molecules in the trans positions. Overall, the networks are neutral, because the anionic clathrochelate ligands compensate for the charge of the ZnII ions. It is worth mentioning that MII-based MOFs with square-grid-type layer structures have been reported previously in the literature.[15] In contrast to 12 and 13, the square substructures are typically smaller and the anions are coordinated to the bridging M2 + ions (Figure 5). The 2D networks of 12 and 13 both show an ABAB-type packing arrangement (Figure 6). Due to the presence of the bulky tert-butyl groups, the interlayer distance of the planes defined by the bridging Zn2 + ions is larger for 13 (23.7 ) than for 12 (18.6 ). The solvent-accessible volume, as calculated by the PLATON software,[16] is larger for 12 (25 %) than for 13 (21 %).
Figure 6. Space filling representation of the structures of 12 (left) and 13 (right) highlighting the packing of two adjacent layers. Solvent molecules have been omitted for clarity.
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Full Paper In order to avoid scrambling of the metal ions, reactions of Zn-based clathrochelates with Cd2 + ions were performed under milder conditions. Large single crystals of the coordination polymers 14 and 15 (yield for both: 80 %) were obtained by slow diffusion of a methanolic solution of Cd(ClO4)2(H2O)6 into a DMF solution of the deprotonated metalloligands 7 or 9 (Scheme 6). A crystallographic analysis of the heterometallic
Scheme 6. Syntheses of the coordination polymers 14 and 15.
coordination polymer 15 revealed a layer structure that is very similar to what was observed for 13. Four metalloligands are connected through octahedral Cd(DMF)2 units to form 22.2 22.8 squares. In contrast to what was found for 13, an ABBAtype packing arrangement is observed. The interlayer distance is 10.6 , and the calculated solvent-accessible volume is 30 %. The crystallographic analysis of polymer 14 was hindered by disorder of the Cd ions and their coordinated clathrochelate ligands. Located next to a special position (inversion center), the occupancies are split 50:50. Key to a successful refinement was the utilization of stereochemical restraints for the clathrochelate ligand, which were generated by the GRADE program.[17, 18] This macromolecular refinement technique has been adapted to be used in the SHELXL program.[19] Its first application in a supramolecular chemistry context was the refinement of a tetranuclear coordination cage.[20] The method drastically increases the robustness of the refinement, especially if it is combined with the new rigid bond restraint in the SHELXL 2013 (RIGU) program.[21] The ShelXle program,[22] which supports the macromolecular residue grouping, was used as a graphical user interface (GUI). More crystallographic details can be found in the Experimental Section. Surprisingly, coordination polymer 14 shows a completely different structure than the analogous Zn network 12. A 3D network structure with two types of octahedral Cd nodes is observed. Both Cd centers are bound to four pyridyl groups, but one is bound to two DMF molecules in the trans positions (“Cd1”), whereas the other one features two DMF ligands in cis positions (“Cd2”). This arrangement gives rise to a 3D network, with layers of (Cd1)2(Cd2)2 rhombuses, which are linked through Cd2 centers by two clathrochelate metalloligands (Figure 7). The latter are oriented perpendicular to the plane defined by the Cd atoms. The network is neutral, because the anionic bipyridyl ligands compensate for the charge of the Cd2 + ions. The framework is twofold interpenetrated. The calculated solvent-accessible volume is 45 % of the unit cell volume. The Zn-based clathrochelates are luminescent, so we have also investigated the photoluminescence of the coordination polymers 12 and 15 in the solid state. The Zn-based polymer 12 exhibits an emission maximum at 467 nm (lex = 380 nm), and the heterometallic Zn/Cd coordination polymer 15 shows an emission maximum at 455 nm (lex = 390 nm). A hypsochroChem. Eur. J. 2014, 20, 5592 – 5600
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Figure 7. Part of the 3D network structure of coordination polymer 14. Hydrogen atoms and solvent molecules have been omitted for clarity. C: grey; O: red; N: blue; B: green; Zn: cyan; Cd: pink.
mic shift can be observed relative to the solid state spectra of the protonated metalloligands 1 (lmax = 515 nm) and 4 (lmax = 469 nm). This shift is probably induced by the coordination of the pyridyl groups to the Zn2 + and Cd2 + ions. Thermogravimetric analyses of 12–15 show that the structurally related networks 12, 13, and 15 are all thermally stable up to approximately 300 8C. Coordination polymer 14 was found to be more susceptible to thermal degradation, which confirmed indirectly that it possesses a unique structure. BET surface measurements (N2, 77 K) after drying under vacuum gave low values for the coordination polymers 12 (54 m2 g 1) and 14 (10 m2 g 1), both of which are based on a clathrochelate ligand with methyl substituents on the phenolatodioximato ligand. Significantly higher values were observed for the tert-butyl-containing 13 (556 m2 g 1) and 15 (700 m2 g 1; pore volume = 0.412 cm3g 1). These differences show that the lateral size of the clathrochelates can have a pronounced influence on the physical properties of the resulting assemblies.
Conclusion We have described the synthesis of dinuclear ZnII, MnII, and CoII clathrochelates with terminal pyridyl groups. These complexes were obtained in high yield by one-pot reactions of M(ClO4)2 salts with phenolatodioximato ligands and pyridylboronic acid. Upon deprotonation, anionic bipyridyl ligands are obtained. These ligands have interesting characteristics for applications in supramolecular coordination chemistry: 1) they are robust, rigid, and relatively long; 2) the lateral size and the solubility of the ligands can be modified by variation of the phenolatodioximato ligand; 3) the Zn-based clathrochelates are luminescent; and 4) it is possible to incorporate diamagnetic or paramagnetic metal ions. To demonstrate that these ligands are indeed useful building blocks in metallasupramolecular chemistry, we have synthesized the molecular square 10 as an example of a molecularly defined nanostructure, as well as the coordination polymers 12–15. By using competition experiments, we
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Full Paper were able to demonstrate that complex 10 is significantly more stable than an analogous assembly with the standard 4,4-bipyridine ligand. The increased stability is attributed to the presence of an anionic charge on the clathrochelate, which reduces the overall charge of the metallamacrocycle. The possibility to make more stable metal-based assemblies is certainly an interesting aspect of this new class of ligands. The successful synthesis of the coordination polymers 12–15 is the first evidence for the utility of clathrochelate-based pyridyl ligands in the field of metal–organic frameworks. The negative charge of the metalloligands is again an important point, because it reduces or even eliminates the need for anionic coligands to compensate for the charge of the metal ions. The lateral size of the clathrochelate ligands can be controlled by the choice of the phenolatodioximato ligands. So far, we have explored methyl- and tert-butyl substituents on the phenolato ligand. The importance of such modifications was evidenced by the pronounced differences that were observed for the specific surface areas of 12 and 13. Overall, we think that dinuclear clathrochelates are an interesting new class of metalloligands with a lot of potential for applications in molecular nanoscience.
Experimental Section General All reagents were obtained from commercial sources. Ligand L1 was prepared according to a literature procedure.[8] The synthesis of ligand L2 and Pt(dppp)Cl2 is described in the Supporting Information. Pt(dppp)(OTf)2 and the molecular square 11 were synthesized as described in the literature.[13] 1H and 13C NMR spectra were obtained on a Bruker Avance instrument (1H: 400 MHz; 13C: 100 MHz). 1H and 13C chemical shifts (d) are reported in parts per million (ppm) referenced to the internal solvent. All spectra were recorded at room temperature. Electrospray-ionization MS data were acquired on a Q-Tof Ultima mass spectrometer (Waters) operated in the positive ionization mode, and data were processed by using the MassLynx 4.1 software. APPI-FT-ICR experiments were performed on a hybrid linear ion trap Fourier transform ion cyclotron resonance mass spectrometer (LTQ FT-ICR MS, Thermo Scientific, Bremen, Germany) equipped with a 10 T superconducting magnet (Oxford Instruments Nanoscience, Abingdon, UK). Data analysis was carried out by using XCalibur software (Thermo Scientific, Bremen, Germany). IR spectra were recorded on a Perkin– Elmer Spectrum One Golden Gate FT/IR spectrometer. Combustion analysis was performed with a Thermo Scientific Flash 2000 Organic elemental analyzer. Diffuse reflectance spectra were carried out by using a Perkin–Elmer Lambda 900 UV/VIS/NIR spectrometer with a PELA-1000 accessory within the wavelength range of 200– 800 nm. Emission spectra were recorded with Varian Cary Eclipse or Perkin–Elmer LS-50 spectrofluorimeters. Thermogravimetric analysis was performed on a Mettler-Toledo TGA/SDTA851e instrument equipped with a TSO800GC1 gas control unit. Data were collected by using the STARe software and processed in Microsoft Excel. The sample was heated from 35 to 600 8C at a rate of 2 8C per minute in an alumina crucible under a 60 mL min 1 flow of N2. Nitrogensorption measurements were performed on a Quantachrome Autosorb iQ surface area analyzer. Before the measurements, the polymers were dried under a high vacuum for 12 h at 120 8C. The BET analyses were performed at 77.3 K. Note: compounds containing Chem. Eur. J. 2014, 20, 5592 – 5600
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perchlorate are potentially explosive and should be handled with care!
General procedure for the synthesis of 1–3 A mixture of ligand L1 (201 mg, 108 mmol) and 4-pyridylboronic acid (88 mg, 720 mmol) was heated in a mixture of dichloromethane/ethanol (1:1, 20 mL) until all of the boronic acid had dissolved. Solid M(ClO4)2(H2O)6 (M: Zn, 268 mg, 720 mmol; M: Co, 263 mg, 720 mmol; M: Mn, 260 mg, 720 mmol) was then added, and the solution was stirred for 1 h. The yellow (1 and 3) or orange (2) microcrystalline precipitate was filtered, washed with cold ethanol, and dried under vacuum. Complex 1: Yield: 0.31 g, 81 %; 1H NMR (400 MHz, [D7]DMF): d = 2.20 (s, 9 H, CH3), 7.21 (s, 6 H, CHar), 8.38 (d, 4 H, J = 6.4 Hz, CHpy), 8.42 (s, 6 H, CHim), 9.00 ppm (d, 4 H, J = 6.6 Hz, CHpy); 13C NMR (100 MHz, [D7]DMF): d = 163.77 (C OPh), 155.51 (C=N), 139.97 (CHar), 136.96 (Car), 130.39 (CHar), 124.34 (Car), 119.29 (CHar), 19.55 ppm (CH3) (B C was not observed); ESI-MS: m/z: 883.0644 [M + 2 H] + ; elemental analysis: calcd (%) for Zn2C37H31N8B2O9(ClO4)(CH2Cl2) (1068.47 g mol 1): C 42.71, H 3.11, N 10.48; found: C 42.83, H 3.42, N 10.47; FTIR: n˜ max : 3413 (br), 2928 (br), 1615 (m), 1594 (m), 1554 (m), 1445 (s), 1321 (s), 1186 (m), 1084 (s), 997 (vs), 935 (vs), 815 (vs), 758 (s), 621 cm 1 (s). Complex 2: Yield: 0.30 g, 83 %; ESI-MS: m/z: 871.1042 [M + 2 H] + ; elemental analysis: calcd (%) for Co2C37H31N8B2O9(ClO4)(CH2Cl2)0.5 (1013.09 g mol 1): C 44.45, H 3.18, N 11.06; found: C 44.60, H 3.32, N 11.07; FTIR: n˜ max : 3248 (br), 1614 (m), 1591 (m), 1556 (m), 1445 (s), 1313 (s), 1201 (m), 1089 (s), 1000 (vs), 937 (vs), 816 (vs), 761 (s), 620 cm 1 (s). Complex 3: Yield: 0.25 g, 87 %; ESI-MS: m/z: 861.1017 [M + 2 H] + ; elemental analysis: calcd (%) for Mn2C37H31N8B2O9(ClO4)(CH2Cl2)2 (1132.50 g mol 1): C 41.36, H 3.11, N 9.89; found: C 41.39, H 3.08, N 10.31; FTIR: n˜ max : 2982 (br), 1603 (m), 1578 (m), 1545 (m), 1473 (s), 1321 (s), 1200 (m), 1181 (m), 1029 (s), 991 (vs), 927 (vs), 819 (vs), 758 (s), 684 cm 1 (s).
General procedure for the synthesis of 4–6 A mixture of ligand L2 (0.66 g, 2.79 mmol) and 4-pyridylboronic acid (0.23 g, 1.86 mmol) was heated in a mixture of dichloromethane/ethanol (1:1, 20 mL) until all of the boronic acid had dissolved. Solid M(ClO4)2(H2O)6 (M: Zn, 0.69 g, 1.86 mmol; M: Co, 0.68 g, 1.86 mmol; M: Mn, 0.67 g, 1.86 mmol) was then added, and the solution stirred for 1 h. The yellow (4 and 6) or orange (5) microcrystalline precipitate was filtered, washed with cold ethanol, and dried under vacuum. Complex 4: Yield: 0.98 g, 88 %; X-ray-quality crystals were formed by slow evaporation of the mother liquor; 1H NMR (400 MHz, [D6]DMSO): d = 1.22 (s, 27 H, (CH3)3), 7.37 (s, 6 H, CHar), 8.20 (d, 4 H, J = 6.5 Hz, CHpy), 8.44 (s, 6 H, CHim), 8.79 ppm (d, 4 H, J = 6.5 Hz, CHpy); 13C NMR (100 MHz, [D6]DMSO): d = 162.56 (C OPh), 155.10 (C=N), 139.17 (CHar), 137.36 (Car), 132.97 (CHar), 129.46 (Car), 117.99 (CHar), 33.44(C(CH3)3), 31.11 ppm (C(CH3)3), (B C was not observed); ESI-MS: m/z: 1009.2392 [M + H] + ; elemental analysis: calcd (%) for Zn2C46H49N8B2O9(ClO4) (1109.78 g mol 1): C 49.79, H 4.45, N 10.10; found: C 50.35, H 4.51, N 10.23; FTIR: n˜ max : 3242 (br), 2949 (m), 1612 (m), 1550 (m), 1444 (s), 1326 (s), 1221 (s), 1198 (s), 1075 (s), 1035 (s), 998 (vs), 938 (vs), 838 (m), 771 (s), 695 (s), 618 cm 1 (s). Complex 5: Yield: 0.90 g, 89 %; X-ray-quality crystals were formed by slow evaporation of the mother liquor; ESI-MS: m/z: 499.1277 [M + 2 H]2 + ; elemental analysis: calcd (%) for Co2C46H49N8O9(ClO4) (1075.44 g mol 1): C 51.38, H 4.59, N 10.42; found: C 51.00, H 4.40,
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Full Paper N 10.41; FTIR: n˜ max : 2955 (br), 1610 (m), 1550 (m), 1445 (s), 1365 (m), 1325 (s), 1285 (m), 1200 (m), 1080 (s), 1035 (vs), 940 (vs), 840 (vs), 770 (s), 620 cm 1 (s). Complex 6: Yield: 0.57 g, 65 %; ESI-MS: m/z: 989.2579 [M + 2 H] + ; elemental analysis: calcd (%) for Mn2C46H49N8B2O9(ClO4) (1088.87 g mol 1): C 50.74, H 4.54, N 10.29; found: C 50.91, H 4.62, N 10.44; FTIR: n˜ max : 2955 (br), 1630 (m), 1580 (m), 1545 (m), 1445 (s), 1330 (s), 1280 (m), 1195 (m), 1020 (s), 990 (vs), 935 (vs), 805 (vs), 780 (s), 690 cm 1 (s).
General procedure for the synthesis of 7 and 8 Et3N (88 mL, 0.6 mmol) was added to a suspension of 1 (0.33 g, 0.31 mmol) or 3 (0.27 g, 0.31 mmol) in acetonitrile/methanol (1:1, 20 mL). The mixture was stirred until all of solid had dissolved. The volume of the solvent was reduced under vacuum to 3 mL, and a yellow solid formed. The product was filtered, washed with cold acetonitrile, and dried under vacuum. Complex 7: Yield: 0.29 g, 85 %; 1H NMR (400 MHz, [D7]DMF): d = 1.29–1.35 (m, 12 H), 2.18 (s, 9 H, CH3), 3.43 (q, J = 7.3 Hz, 8 H), 7.14 (s, 6 H, CHar), 7.66 (d, 4 H, J = 5.7 Hz, CHpy), 8.35 (s, 6 H, CHim), 8.46 ppm (d, 4 H, J = 5.6 Hz, CHpy); 13C NMR (100 MHz, [D7]DMF): d = 164.25 (C OPh), 155.20 (C=N), 148.95 (CHar), 136.91 (Car), 128.49 (CHar), 124.53 (Car), 120.11 (CHar), 53.01 (CH2), 20.16 (CH3), 7.95 ppm (CH3) (B C was not observed); ESI-MS: m/z: 883.1703 [M + 2 H] + ; elemental analysis: calcd (%) for Zn2C37H31N8B2O9(C6H16N)(CH2Cl2) (1060.13 g mol 1): C 49.84, H 3.61, N 11.89; found: C 48.66, H 4.89, N 11.37; FTIR: n˜ max : 3208 (br), 2988 (br), 1613 (m), 1592 (m), 1553 (m), 1444 (s), 1322 (s), 1202 (s), 1085 (m), 1034 (vs), 998 (vs), 935 (vs), 817 (s), 761 (s), 688 cm 1 (s). Complex 8: Yield: 0.25 g, 87 %; ESI-MS: m/z: 861.1017 [M + 2 H] + ; elemental analysis: calcd (%) for Mn2C37H31N8B2O9(C6H16N)(CH2Cl2) (1039.23 g mol 1): C 50.85, H 3.68, N 12.13; found: C 50.01, H 3.52, N 12.30; FTIR: n˜ max : 2982 (br), 1603 (m), 1578 (m), 1545 (m), 1473 (s), 1321 (s), 1200 (m), 1181 (m), 1029 (s), 991 (vs), 927 (vs), 819 (vs), 758 (s), 684 cm 1 (s). Complex 9: Et4NOH (1.0 mL, 1.7 mmol, 25 % in MeOH) was added to a suspension of 4 (0.98 g, 0.88 mmol) in acetonitrile/methanol (1:1, 20 mL). The mixture was stirred until the entire solid had dissolved. A few more drops of the Et4NOH solution were added, and a yellow solid started to form. The product was filtered, washed with cold methanol, and dried under vacuum. Yield: 0.92 g, 92 %; 1 H NMR (400 MHz, [D7]DMF): d = 1.27 (s, 27 H, (CH3)3), 1.32 (t, J = 8.2 Hz, 12 H, CH3), 3.43 (q, J = 7.3 Hz, 8 H, CH2), 7.38 (s, 6 H, CHar), 7.67 (d, 4 H, J = 5.6 Hz, CHpy), 8.42 (s, 6 H, CHim), 8.46 ppm (d, 4 H, J = 5.7 Hz, CHpy); 13C NMR (100 MHz, [D7]DMF): d = 164.15 (C OPh), 155.53 (C=N), 148.92 (CHar), 138.41 (Car), 133.61 (CHar), 128.51 (Car), 119.79 (CHar), 52.94 (CH2), 34.55 (C(CH3)3), 31.93 (CH3), 7.94 ppm (CH3) (B C was not observed); ESI-MS: m/z: 1009.2791 [M + H] + ; elemental analysis: calcd (%) for Zn2C46H48B2N8O9(C8H21N)(H2O)2.5 (1186.62 g mol 1): C 54.86, H 6.18, N 10.66; found: C 54.73, H 5.98, N 10.66; FTIR: n˜ max : 2949 (m), 1611 (m), 1590 (m), 1550 (m), 1446 (s), 1331 (s), 1221 (s), 1202 (s), 1079 (s), 1036 (s), 996 (vs), 919 (vs), 781 (vs), 772 (s), 696 cm 1 (s).
Molecular square 10 A solution of Pt(dppp)(OTf)2 (100 mg, 110 mmol) and complex 9 (125 mg, 110 mmol) in DMSO (10 mL) was stirred for 1 h. CHCl3 (20 mL) was then added, which caused the precipitation of a paleyellow amorphous powder. The product was isolated by centrifugation, washed with CHCl3 (3 5 mL) and Et2O (3 5 mL), and dried under vacuum. Yield: 133 mg, 68 %; 1H NMR (600 MHz, [D6]DMSO): Chem. Eur. J. 2014, 20, 5592 – 5600
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d = 1.10 (s, 108 H, CH3), 1.98 (br, 8 H, CH2), 3.26 (br, 16 H, CH2), 7.25 (s, 24 H, Ar-H), 7.30 (d, 16 H, Ar-H), 7.47 (t, 32 H, Ar-H), 7.60 (t, 16 H, Ar-H), 7.73 (t, 32 H, Ar-H), 8.26 (s, 24 H, CH), 8.49 ppm (d, 16 H, ArH); 13C NMR (150 MHz, [D6]DMSO): d = 17.3 (CH2), 21.5 (CH2), 31.1 (CH3), 33.3 (Cq), 118.0 (Cq), 125.0 (Cq), 125.4 (Cq), 129.2 (CH), 129.3 (CH), 132.4 (CH), 132.6 (CH), 132.9 (CH), 137.1 (Cq), 147.1 (CH), 154.7 (CH), 162.4 ppm (Cq); 31P NMR: d = 12.7 (t, 1JPt P = 1512 Hz); HRMS (ESI + ): m/z calcd for [C292H292B8N32O36P8Pt4Zn8]4 + : 1615.5895; found: 1615.5914 [M (OTf)4]4 + ; elemental analysis: calcd (%) for C296H292B8F12N32O48P8Pt4S4Zn8 (7059.6 g mol 1): C 50.36, H 4.17, N 6.35; found: C 50.50, H 4.12, N 6.33.
Coordination polymer 12 Polymer 12 was prepared in multiple batches. The individual reactions were carried out in sealed 20 mL microwave vials as follows. Zn(NO3)2(H2O)6 (6.0 mg, 20 mmol) was added to a solution of complex 1 (32 mg, 30 mmol) in DMF (6.0 mL). The resulting mixture was briefly sonicated before the vial was placed for 24 h into an oil bath at 80 8C. The vial was then allowed to cool to room temperature to induce crystallization. After 3 d, the resulting yellow crystals were washed with DMF (3 5 mL) before being isolated by filtration and dried under vacuum for 3 d. Yield: 20 mg, 62 %; elemental analysis: calcd (%) for (Zn2C37H29B2N8O9)2Zn(DMF)4(H2O)3 (2175.96 g mol 1): C 47.47, H 4.26, N 12.87; found: C 47.64, H 3.84, N 12.23; FTIR: n˜ max : 3317 (br), 2924 (m), 1650 (vs), 1613 (s), 1592 (m), 1554 (m), 1444 (vs), 1384 (m), 1321 (s), 1204 (m), 1086 (m), 1036 (s), 998 (vs), 940 (vs), 822 (s), 765 (s), 694 (s), 659 cm 1 (s).
Coordination polymer 13 Polymer 13 was prepared in multiple batches. The individual reactions were carried out in sealed 7 mL microwave vials as follows. Zn(ClO4)2(H2O)6 (20 mg, 54 mmol) was added to a solution of complex 4 (30 mg, 27 mmol) in DMF (5.0 mL). The resulting mixture was briefly sonicated before the vial was placed for 48 h into an oil bath at 120 8C. The vial was then allowed to cool to room temperature to induce crystallization. After 2 d, the resulting yellow crystals were washed with DMF (3 5 mL) before being isolated by filtration and dried under vacuum for 3 d. Yield: 31 mg, 89 %; elemental analysis: calcd (%) for sample after the heating under vacuum (Zn2C46H48B2N8O9)2Zn(H2O)4 (2156.09 g mol 1): C 51.24, H 4.86, N 10.39; found: C 51.03, H 4.84, N 12.23; FTIR: n˜ max : 2950 (m), 1670 (s), 1610 (m), 1445 (s), 1385 (m), 1329 (s), 1220 (m), 1202 (s), 1080 (m), 1035 (s), 995 (vs), 931 (vs), 838 (m), 785 (vs), 770 (vs), 700 (s), 660 cm 1 (m).
Coordination polymer 14 A solution of complex 7 (28 mg, 26 mmol) in DMF (4.0 mL) in a test tube (diameter = 15 mm) was layered with a solution of Cd(ClO4)2(H2O)6 (6.0 mg, 19 mmol) in MeOH (4.0 mL), separated by a buffer layer of DMF/MeOH (1:1, 2 mL). After 2 weeks, yellow crystals had formed. The crystals were washed with DMF (3 5 mL) before being isolated by filtration and dried under vacuum for 3 d. Yield: 20 mg, 80 %; elemental analysis: calcd (%) for (Zn2C37H29B2N8O9)2Cd(DMF)2(H2O)6 (2130.84 g mol 1): C 45.09, H 3.97, N 11.83; found: C 43.90, H 3.76, N 11.79; FTIR: n˜ max : 3344 (br), 2952 (m), 1652 (s), 1610 (s), 1552 (m), 1445 (vs), 1384 (m), 1327 (s), 1203 (m), 1080 (m), 1035 (s), 985 (vs), 929 (vs), 839 (s), 782 (vs), 698 (vs), 659 cm 1 (m).
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Full Paper Coordination polymer 15 A solution of complex 9 (30 mg, 26 mmol) in DMF (4.0 mL) in a test tube (diameter = 15 mm) was layered with a solution of Cd(ClO4)2(H2O)6 (6.0 mg, 19 mmol) in MeOH (4.0 mL), separated by a buffer layer of DMF/MeOH (1:1, 2 mL). After 1 week, yellow single crystals had formed. The crystals were washed with DMF (3 5 mL) before being isolated by filtration and dried under vacuum for 3 d. Yield: 24 mg, 80 %; elemental analysis: calcd (%) for sample after heating under vacuum (Zn2C46H48B2N8O9)2Cd(H2O)9 (2293.19 g mol 1): C 48.18, H 5.01, N 9.77; found: C 47.95, H 4.49, N 9.84; FTIR: n˜ max : 3344 (br), 2952 (m), 1652 (s), 1610 (s), 1552 (m), 1445 (vs), 1384 (m), 1327 (s), 1203 (m), 1080 (m), 1035 (s), 985 (vs), 929 (vs), 839 (s), 782 (vs), 698 (vs), 659 cm 1 (m).
[2] [3] [4]
[5]
Crystallographic analyses [6]
Intensity data were collected by using an Oxford Diffraction KM-4 CCD diffractometer, a Bruker APEX II CCD system, or a marmx system, with graphite monochromated Mo-Ka radiation (l = 0.71073 ) at low temperature. Data reductions were carried out with Crysalis PRO,[23] BYPASS,[24] EVALCCD,[25] or automar.[26] Structure solutions and refinements were performed with the SHELX software package,[18] in which ShelXle[22] was used as the GUI. The structures were refined by using full-matrix least-squares routines on F2. Stereochemical restraints for all boron, carbon, nitrogen, and oxygen atoms of the clathrochelate ligands were generated by using the GRADE program.[17, 18] It gathers stereochemical information from a Mogul search combined with QM calculations. This macromolecular refinement technique has been adapted to be used in the program SHELXL.[19] A GRADE dictionary for SHELXL contains target values and standard deviations for 1.2-distances (DFIX) and 1.3-distances (DANG), as well as restraints for planar groups (FLAT). All atoms of the clathrochelate ligands were grouped into residues. The dictionaries were applied to the structures of coordination polymers 12–15 and disordered solvent molecules for complexes 4, 5, 7, and 8. Rigid bond restraints (RIGU)[21] were applied to anisotropic displacement parameters of all non-hydrogen atoms. Hydrogen atoms were included in the model on calculated positions by using the riding model for all structures. CCDC 980630 (4), 980631 (5), 980632 (7), 980633 (8), 980634 (12), 980635 (13), 980636 (14), and 980637 (15) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[7] [8] [9] [10]
[11] [12]
Acknowledgements
[13]
The work was supported by Marie Curie fellowships for M.P. (IEF-2009-252716) and J.J.H. (ITN-2010-264645), the Swiss National Science Foundation, and by the EPFL. Oliver Smart is thanked for writing and adapting the GRADE program, which was applied in the X-ray analysis.
[14] [15]
Keywords: boronic acid · clathrochelates · coordination polymers · nanostructures · supramolecular chemistry [16] [1] Selected recent reviews: a) K. Harris, D. Fujita, M. Fujita, Chem. Commun. 2013, 49, 6703 – 6712; b) N. J. Young, B. P. Hay, Chem. Commun. 2013, 49, 1354 – 1379; c) M. M. Smulders, I. A. Riddell, C. Browne, J. R. Nitschke, Chem. Soc. Rev. 2013, 42, 1728 – 1754; d) H. Amouri, C. Desmarets, J. Chem. Eur. J. 2014, 20, 5592 – 5600
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[17]
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Moussa, Chem. Rev. 2012, 112, 2015 – 2041; e) P. Thanasekaran, T.-T. Luo, J.-Y. Wu, K.-L. Lu, Dalton Trans. 2012, 41, 5437 – 5453; f) R. Chakrabarty, P. S. Mukherjee, P. J. Stang, Chem. Rev. 2011, 111, 6810 – 6918. M. Fujita, J. Yazaki, K. Ogura, J. Am. Chem. Soc. 1990, 112, 5645 – 5647. A database search performed on July 2013 gave 1241 hits. Reviews about metalloligands: a) E. C. Constable, Chimia 2013, 67, 388 – 392; b) M. C. Das, S. Xiang, Z. Zhang, B. Chen, Angew. Chem. 2011, 123, 10696 – 10707; Angew. Chem. Int. Ed. 2011, 50, 10510 – 10520; c) M. J. Wiester, P. A. Ulmann, C. A. Mirkin, Angew. Chem. 2011, 123, 118 – 142; Angew. Chem. Int. Ed. 2011, 50, 114 – 137; d) I. Beletskaya, V. S. Tyurin, A. Y. Tsivadze, R. Guilard, C. Stern, Chem. Rev. 2009, 109, 1659 – 1713; e) E. C. Constable, Coord. Chem. Rev. 2008, 252, 842 – 855; f) S. J. Lee, J. T. Hupp, Coord. Chem. Rev. 2006, 250, 1710 – 1723. Selected examples: a) G. Li, C. Zhu, X. Xi, Y. Cui, Chem. Commun. 2009, 2118 – 2120; b) G. Li, W. Yu, J. Ni, T. Liu, E. Sheng, Y. Cui, Angew. Chem. 2008, 120, 1265 – 1269; Angew. Chem. Int. Ed. 2008, 47, 1245 – 1249; c) S. H. Chang, K.-B. Chung, R. V. Slone, J. T. Hupp, Synth. Met. 2001, 117, 215 – 217. Selected examples: a) O. K. Farha, A. M. Shultz, A. A. Sarjeant, S. T. Nguyen, J. T. Hupp, J. Am. Chem. Soc. 2011, 133, 5652 – 5655; b) Y. Huang, T. Liu, J. Lin, J. L, Z. Lin, R. Cao, Inorg. Chem. 2011, 50, 2191 – 2198; c) A. M. Shultz, O. K. Farha, J. T. Hupp, S. T. Nguyen, J. Am. Chem. Soc. 2009, 131, 4204 – 4205; d) S. J. Lee, S.-H. Cho, K. L. Mulfort, D. M. Tiede, J. T. Hupp, S. T. Nguyen, J. Am. Chem. Soc. 2008, 130, 16828 – 16829; e) S.-H. Cho, B. Ma, S. T. Nguyen, J. T. Hupp, T. E. AlbrechtSchmitt, Chem. Commun. 2006, 2563 – 2565. M. D. Wise, A. Ruggi, M. Pascu, R. Scopelliti, K. Severin, Chem. Sci. 2013, 4, 1658 – 1662. S. Khanra, T. Weyhermuller, E. Bill, P. Chaudhuri, Inorg. Chem. 2006, 45, 5911 – 5923. T. K. Ronson, S. Zarra, S. P. Black, J. R. Nitschke, Chem. Commun. 2013, 49, 2476 – 2490. Selected examples: a) W. J. Liu, W. J. Huang, M. Pink, D. Lee, J. Am. Chem. Soc. 2010, 132, 11844; b) Y. Z. Voloshin, O. A. Varzatskii, V. V. Novikov, N. G. Strizhakova, I. I. Vorotsov, A. V. Vologzhanina, K. A. Lyssenko, G. V. Romanenko, M. V. Fedin, V. I. Ovcharenko, Y. N. Bubnov, Eur. J. Inorg. Chem. 2010, 5401 – 5415; c) Y. Z. Voloshin, O. A. Varzatskii, A. S. Belov, A. Y. Lebedev, I. S. Makarov, M. E. Gurskii, M. Y. Antipin, Z. A. Starikova, Y. N. Bubnov, Inorg. Chim. Acta 2007, 360, 1543 – 1554; d) V. Z. Voloshin, O. A. Varzatskii, I. I. Vorontsov, M. Y. Antipin, A. Y. Lebedev, A. S. Belov, A. V. Palchik, Russ. Chem. Bull. 2003, 52, 1552 – 1561; e) Y. Z. Voloshin, O. A. Varzatskii, A. I. Stash, V. K. Belsky, Y. N. Bubnov, I. I. Vorontsov, K. A. Potekhin, M. Y. Antipin, E. V. Polshin, Polyhedron 2001, 20, 2721 – 2733; f) A. A. Kubow, K. J. Takeuchi, J. J. Grzybowski, A. J. Jircitano, V. L. Goedken, Inorg. Chim. Acta 1996, 241, 21 – 30. F. Wrthner, C.-C. You, C. R. Saha-Mçller, Chem. Soc. Rev. 2004, 33, 133 – 146. For the importance of charge compensation in Pd/Pt-based macrocycles, see: a) J. B. Pollock, T. R. Cook, G. L. Schneider, P. J. Stang, Chem. Asian J. 2013, 8, 2423 – 2429; b) Y.-R. Zheng, Z.-G. Zhao, M. Wang, K. Ghosh, J. B. Pollock, T. R. Cook, P. J. Stang, J. Am. Chem. Soc. 2010, 132, 16873 – 16882; c) A. K. Bar, G. Mostafa, P. S. Makherjee, Inorg. Chem. 2010, 49, 7647 – 7649. P. J. Stang, D. H. Cao, S. Saito, A. M. Arif, J. Am. Chem. Soc. 1995, 117, 6273 – 6283. a) M. Dickmeis, H. Ritter, Macromol. Chem. Phys. 2009, 210, 776 – 782; b) J. L. Neumeyer, J. G. Canon, J. Org. Chem. 1961, 26, 4681 – 4682. Selected examples: a) C. J. Adams, M. C. MuÇoz, R. E. Waddington, J. A. Real, Inorg. Chem. 2011, 50, 10633 – 10642; b) S.-I. Noro, R. Kitaura, M. Kondo, S. Kitagawa, T. Ishii, H. Matsuzaka, M. Yamashita, J. Am. Chem. Soc. 2002, 124, 2568 – 2583; c) M.-L. Tong, S.-L. Zheng, X.-M. Chen, Polyhedron 2000, 19, 1809 – 1814; d) Y.-S. Zhang, G. D. Enright, S. R. Breeze, S. Wang, New J. Chem. 1999, 23, 625 – 628; e) S. Subramanian, M. J. Zaworotko, Angew. Chem. 1995, 107, 2295 – 2297; Angew. Chem. Int. Ed. Engl. 1995, 34, 2127 – 2128; f) R. W. Gable, B. F. Hoskins, R. Robson, J. Chem. Soc. Chem. Commun. 1990, 1677 – 1678. A. L. Spek, PLATON: A Multipurpose Crystallographic Tool, 2008, Utrecht University, Utrecht, The Netherlands. G. Bricogne, E. Blanc, M. Brandl, C. Flensburg, P. Keller, P. Paciorek, P. Roversi, A. Sharff, O. Smart, C. Vonrhein, T. Womack, BUSTER version 2.13.0, 2011 Global Phasing Ltd., Cambridge, United Kingdom. 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper [18] http://grade.globalphasing.org. [19] G. Sheldrick, Acta Crystallogr. Sect. A 2008, 64, 112 – 122. [20] T. K. Ronson, C. Giri, N. K. Beyeh, A. Minkkinen, F. Topic´, J. J. Holstein, K. Rissanen, J. R. Nitschke, Chem. Eur. J. 2013, 19, 3374 – 3382. [21] A. Thorn, B. Dittrich, G. M. Sheldrick, Acta Crystallogr. Sect. A 2012, 68, 448 – 451. [22] C. B. Hbschle, G. M. Sheldrick, B. Dittrich, J. Appl. Crystallogr. 2011, 44, 1281 – 1284. [23] A. Technologies, CrysAlis PRO, 2009 – 2014, Agilent Technologies Ltd, Yarton, Oxfordshire, UK.
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[24] P. van der Sluis, A. L. Spek, Acta Crystallogr. A 1990, 46, 194 – 201. [25] A. J. M. Duisenberg, L. M. J. Kroon-Batenburg, A. M. M. Schreurs, J. Appl. Crystallogr. 2003, 36, 220 – 229. [26] automar, release 2.8.0, Marresearch GmbH, Germany, 2011.
Received: January 23, 2014 Published online on April 2, 2014
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& Supramolecular Chemistry
Anionic Bipyridyl Ligands for Applications in Metallasupramolecular Chemistry Mirela Pascu,[a] Mathieu Marmier,[a] Clment Schouwey,[a] Rosario Scopelliti,[a] Julian J. Holstein,[b] Grard Bricogne,[b] and Kay Severin*[a]
Abstract: The facile synthesis of anionic bipyridyl ligands with dinuclear clathrochelate cores is described. These metalloligands can be obtained in high yields by the reactions of M(ClO4)2(H2O)6 (M: Zn, Mn, or Co) with 4-pyridylboronic acid and 2,6-diformyl-4-methylphenol oxime or 2,6-diformyl-4-tert-butylphenol oxime, followed by deprotonation.
The ligands are interesting building blocks for metallasupramolecular chemistry, as evidenced by the formation of a Ptbased molecular square and four coordination polymers with 2D or 3D network structures. Competition experiments reveal that the utilization of anionic bipyridyl ligands can result in significantly more stable assemblies.
Introduction Bipyridyl ligands are among the most frequently used building blocks for supramolecular coordination chemistry.[1] The simple 4,4’-bipyridine (bpy) ligand has been employed for a long time, as exemplified by the molecular square [{(en)Pd(bpy)}4]8 + (en: ethylenediamine) published in 1990.[2] Today, one can find more than 1000 entries for structures of the type LnM(bpy)MLn in the Cambridge Structural Database.[3] Of course, many structural variants of 4,4’-bipyridine have been explored over time. Bipyridyl ligands containing metal ions (“metalloligands”) are an interesting subclass in this context.[1, 4] The metal ions can add novel properties, such as color, redox activity, magnetism, molecular-recognition sites, or catalytic activity. Furthermore, the metal ions can facilitate the synthesis of the bipyridyl ligand if metal-templated reactions are employed. Some representative examples of metal-containing bipyridyl ligands are depicted in Figure 1. Complexes of type A have mainly been used as “expanded ligands” for structural investigations.[4a,e] Metallaporphyrins of type B[4d,f] and salen-type complexes of type C possess accessible metal sites, which can be used for molecular recognition (for example, in sensing applications)[5] or for catalysis.[6] We have recently introduced clathrochelatebased bipyridyl ligands of types D and E.[7] These ligands are rigid, long (approximately 3.2 nm for E with n = 2), well soluble, and easily accessible in a one-pot reaction from commercially [a] Dr. M. Pascu, M. Marmier, C. Schouwey, Dr. R. Scopelliti, Prof. K. Severin Institut des Sciences et Ingnierie Chimiques cole Polytechnique Fdrale de Lausanne (EPFL) 1015 Lausanne (Switzerland) E-mail: [email protected] [b] Dr. J. J. Holstein, Dr. G. Bricogne Global Phasing Ltd., Sheraton House Castle Park, Cambridge CB3 0AX (UK) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201400285. Chem. Eur. J. 2014, 20, 5592 – 5600
Figure 1. Examples of metal-containing bipyridyl ligands.
available starting materials. Below, we describe a different class of clathrochelate complexes with terminal pyridyl groups. The new bipyridyl ligands display an interesting characteristic for applications in metallasupramolecular chemistry: they are negatively charged.
Results and Discussion In 2006, Chaudhuri and co-workers reported the synthesis and structure characterization of a dinuclear MnII clathrochelate 5592
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Full Paper complex with bridging phenolatodioximato ligands and capping methylboronate esters.[8] We hypothesized that similar dinuclear complexes could be used to build bipyridyl ligands. Indeed, macrobicyclic MII tris(dioximato) complexes (M: Zn, Co, or Mn) with terminal pyridyl groups were obtained by subcomponent self-assembly[9] of three compounds, M(ClO4)2(H2O)6, 4-pyridylboronic acid, and 2,6-diformyl-4-methylphenol oxime (L1) or 2,6-diformyl-4-tert-butylphenol oxime (L2), in dichloromethane/ethanol (Scheme 1). Products 1–6 precipitated from
Single-crystal X-ray structure analyses of 4 and 5 confirmed the presence of dinuclear clathrochelate cores with terminal pyridyl groups. A graphical representation of the structure of complex 4 is given in Figure 2, and selected bonds lengths and angles for 4 and 5 are summarized in Table 1. The two MII
Figure 2. Molecular structure of complex 4 in the crystal. Most of the hydrogen atoms have been omitted for clarity.
Table 1. Selected distances [] and angles [8] for the complexes 4, 5, 7, and 8.
4 5 7 8
Scheme 1. Synthesis of the clathrochelates 1–6.
the reaction mixtures in the form of microcrystalline materials. All of the complexes were obtained in high yield (> 80 %), with the exception of complex 6, for which a somewhat lower yield of 65 % was observed. The reactions were performed without the addition of a base, so the products were obtained in the diprotonated form with perchlorate as the counteranion. The cationic complexes are only soluble in polar organic solvents such as DMF or DMSO. Clathrochelates 1–6 were analyzed by elemental analysis and mass spectrometry. The diamagnetic Zn complexes 1 and 4 were also characterized by NMR spectroscopy. As expected, only one set of signals was observed for the three phenolatodioximato ligands. The “free” ligands L1 and L2 showed luminescence with emission maxima at 392 nm (L1) and 387 nm (L2; in DMF; lex = 340 nm). Solutions of the Co and Mn complexes did not show significant luminescence, presumably due to quenching by the paramagnetic metal ions. The Zn complexes 1 and 4 however, were highly emissive, with maxima at 451 nm for 1 and 445 nm for 4 (in DMF; lex = 340 nm). Due to the inert character of the Zn2 + ions, the photoluminescence can be assigned to intraligand (IL) and/or ligand-to-ligand charge transfer (LLCT) emissions. The magnetic properties of the Co and Mn complexes were not investigated. However, it is expected that the Mn complexes 3 and 6 show very similar behavior to that of the previously reported clathrochelate with methylboronate ester end groups. For the latter, a magnetic moment of 7.13 mB (290 K) and antiferromagnetic exchange coupling between the two paramagnetic MnII centers was observed.[8]
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M···M []
M Nav []
M Oav []
M O Mav [8]
N M Oav [8]
2.9401(17) 2.9591(10) 2.9436(8) 2.9080(10)
2.12 2.10 2.12 2.18
2.10 2.10 2.10 2.14
88.9 89.6 88.8 85.6
82.4 83.0 82.4 80.7
ions in 4 and 5 are coordinated in a trigonal prismatic fashion by three nitrogen and three oxygen atoms. The latter bridge the two metal ions, which results in M···M distances of 2.9401(17) (4) and 2.9591(10) (5). At 1.490 , the average B O bond length of the tetragonal boronate esters is similar to what is found for mononuclear chlathrochelates with boronate ester caps.[7, 10] The N atoms of the pyridyl groups in 4 and 5 are 17.91 and 17.87 apart from each other, respectively. The clathrochelate ligands are thus substantially longer than mononuclear clathrochelates of type D (14.95 ; Figure 1). The NH groups of the protonated pyridyl groups are involved in hydrogen bonding to the perchlorate anion (NH···O in 4: 2.729 ; NH···O in 5: 2.817 ). The cationic clathrochelates can be deprotonated by the addition of a base: when triethylamine or tetraethylammonium hydroxide was added to a solution of 1, 3, or 4 in acetonitrile/ methanol, the anionic complexes 7–9 were obtained in high yield (Scheme 2). The solubility of the anionic complexes is higher than that of the cationic perchlorates: the complexes display a good solubility (> 10 mg mL 1) in acetonitrile/methanol (1:1), acetone, or CHCl3. Crystallographic analyses of 7 and 8 show that the deprotonation has only a minor influence on the structure: the bond lengths and angles observed for the anions of 7 and 8 are very similar to those of the cations of 4 and 5 (Figure 3). The N···N distances in 7 (17.99 ) and 8 (17.98 ) are marginally longer than those found for 4 and 5.
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Scheme 2. Synthesis of the anionic bipyridyl ligands 7–9.
Figure 3. Molecular structure of complex 8 in the crystal. Most of the hydrogen atoms have been omitted for clarity. Scheme 3. Synthesis of the molecular square 10.
After having established a facile synthetic route for the synthesis of anionic clathrochelates with pyridyl end groups, we examined the potential of these bipyridyl ligands in structural supramolecular chemistry. It is well known that rigid, linear bipyridyl ligands react with cis-protected square-planar Pd and Pt complexes to form square-shaped structures.[1e, 11] We postulated that our new ligands would react in a similar fashion, and we therefore studied the reaction of 9 with Pt(dppp)(OTf)2 (dppp: 1,3-bis(diphenylphosphino)propane; OTf: trifluoromethanesulfonate). Complex 9 was chosen because it is diamagnetic and because of its superior solubility compared to that of 7. Multinuclear NMR analysis of a 1:1 solution of 9 and Pt(dppp)(OTf)2 in DMSO indicated the formation of a single product possessing a high degree of symmetry. Isolation of the product as a pale yellow amorphous powder was achieved by precipitation upon addition of CHCl3. Complex 10 displays poor solubility in most common solvents, with the exception of polar aprotic solvents such as DMSO and DMF. The analytical data of 10 (NMR, elemental analysis, and ESI-MS) confirmed the formation of a molecular square (Scheme 3). The presence of a negative charge on the clathrochelate ligand was expected to result in a more stable assembly.[12] To investigate this hypothesis, we compared the stability of 10 with that of the known bpy analogue [(dppp)Pt(bpy)]4(OTf)8 (11).[13] Increasing amounts of the N-donor [D5]pyridine were added to solutions of 10 or 11 in [D6]DMSO (Scheme 4). Pyridine competes with the bridging ligand for complexation to the Pt centers and therefore results in rupture of the assembly. The amount of remaining square complex was then deterChem. Eur. J. 2014, 20, 5592 – 5600
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Scheme 4. Disruption of the molecular squares 10 and 11 by addition of pyridine ([D5]pyridine was used for the NMR experiments).
mined by 1H or 31P NMR spectroscopy. The results are summarized in Figure 4. Addition of only one equivalent of [D5]pyridine to a solution of 11 resulted in significant ligand exchange, and no starting material could be observed after the addition of approximately seven equivalents. In contrast, more than 50 % of square 10 was still present after addition of approximately 10 equivalents of [D5]pyridine, and more than 100 equivalents
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Full Paper upon heating to generate a basic medium.[14] The base can deprotonate the pyridyl groups of 1 and 4. In this way, the network is formed slowly and crystallizes directly from the reaction mixture. Attempts to perform the same reaction with the deprotonated metalloligands 7 or 9 resulted in the immediate formation of powders. Crystallographic analyses of the coordination polymers 12 and 13 revealed 2D square-grid-type layer structures with square dimensions of 22.3 22.3 (Figure 5). Four metallo-
Figure 4. Ratio of starting material 11 (*) or 10 (*) present in solution relative to the initial 2.0 mm concentration in [D6]DMSO upon an increase in the concentration of the competitor [D5]pyridine.
were needed before the concentration of square 10 dropped below 5 % of the initial concentration. The complexity of the equilibria involved in the formation and disruption of these molecular squares made it impossible to accurately derive the thermodynamic parameters. However, the results clearly show that the assembly between (dppp)Pt2 + and the clathrochelatebased bipyridyl ligand 9 is significantly more stable than the square formed between (dppp)Pt2 + and the standard bpy ligand. Bipyridyl ligands have been used extensively for the construction of metal–organic frameworks (MOFs).[1d] To demonstrate that our clathrochelate-based bipyridyl ligands can also be used in this area, we have investigated the reactions of 1 and 4 with Zn2 + and Cd2 + ions. Heating of a mixture of Zn(NO3)2(H2O)6 and the protonated metalloligands 1 or 4 in DMF in a sealed vial resulted in the formation of the crystalline coordination polymers 12 and 13 (yields of 66 and 89 %, respectively; Scheme 5). It is known that DMF decomposes slowly
Scheme 5. Syntheses of the two-dimensional coordination polymers 12 and 13. Chem. Eur. J. 2014, 20, 5592 – 5600
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Figure 5. Part of the layer structure of coordination polymer 12 with a view along the crystallographic z axis. Hydrogen atoms and solvent molecules have been omitted for clarity. C: grey; O: red; N: blue; B: green; Zn: cyan.
ligands are connected through ZnII ions. The latter have an octahedral coordination geometry with two additional DMF molecules in the trans positions. Overall, the networks are neutral, because the anionic clathrochelate ligands compensate for the charge of the ZnII ions. It is worth mentioning that MII-based MOFs with square-grid-type layer structures have been reported previously in the literature.[15] In contrast to 12 and 13, the square substructures are typically smaller and the anions are coordinated to the bridging M2 + ions (Figure 5). The 2D networks of 12 and 13 both show an ABAB-type packing arrangement (Figure 6). Due to the presence of the bulky tert-butyl groups, the interlayer distance of the planes defined by the bridging Zn2 + ions is larger for 13 (23.7 ) than for 12 (18.6 ). The solvent-accessible volume, as calculated by the PLATON software,[16] is larger for 12 (25 %) than for 13 (21 %).
Figure 6. Space filling representation of the structures of 12 (left) and 13 (right) highlighting the packing of two adjacent layers. Solvent molecules have been omitted for clarity.
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Full Paper In order to avoid scrambling of the metal ions, reactions of Zn-based clathrochelates with Cd2 + ions were performed under milder conditions. Large single crystals of the coordination polymers 14 and 15 (yield for both: 80 %) were obtained by slow diffusion of a methanolic solution of Cd(ClO4)2(H2O)6 into a DMF solution of the deprotonated metalloligands 7 or 9 (Scheme 6). A crystallographic analysis of the heterometallic
Scheme 6. Syntheses of the coordination polymers 14 and 15.
coordination polymer 15 revealed a layer structure that is very similar to what was observed for 13. Four metalloligands are connected through octahedral Cd(DMF)2 units to form 22.2 22.8 squares. In contrast to what was found for 13, an ABBAtype packing arrangement is observed. The interlayer distance is 10.6 , and the calculated solvent-accessible volume is 30 %. The crystallographic analysis of polymer 14 was hindered by disorder of the Cd ions and their coordinated clathrochelate ligands. Located next to a special position (inversion center), the occupancies are split 50:50. Key to a successful refinement was the utilization of stereochemical restraints for the clathrochelate ligand, which were generated by the GRADE program.[17, 18] This macromolecular refinement technique has been adapted to be used in the SHELXL program.[19] Its first application in a supramolecular chemistry context was the refinement of a tetranuclear coordination cage.[20] The method drastically increases the robustness of the refinement, especially if it is combined with the new rigid bond restraint in the SHELXL 2013 (RIGU) program.[21] The ShelXle program,[22] which supports the macromolecular residue grouping, was used as a graphical user interface (GUI). More crystallographic details can be found in the Experimental Section. Surprisingly, coordination polymer 14 shows a completely different structure than the analogous Zn network 12. A 3D network structure with two types of octahedral Cd nodes is observed. Both Cd centers are bound to four pyridyl groups, but one is bound to two DMF molecules in the trans positions (“Cd1”), whereas the other one features two DMF ligands in cis positions (“Cd2”). This arrangement gives rise to a 3D network, with layers of (Cd1)2(Cd2)2 rhombuses, which are linked through Cd2 centers by two clathrochelate metalloligands (Figure 7). The latter are oriented perpendicular to the plane defined by the Cd atoms. The network is neutral, because the anionic bipyridyl ligands compensate for the charge of the Cd2 + ions. The framework is twofold interpenetrated. The calculated solvent-accessible volume is 45 % of the unit cell volume. The Zn-based clathrochelates are luminescent, so we have also investigated the photoluminescence of the coordination polymers 12 and 15 in the solid state. The Zn-based polymer 12 exhibits an emission maximum at 467 nm (lex = 380 nm), and the heterometallic Zn/Cd coordination polymer 15 shows an emission maximum at 455 nm (lex = 390 nm). A hypsochroChem. Eur. J. 2014, 20, 5592 – 5600
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Figure 7. Part of the 3D network structure of coordination polymer 14. Hydrogen atoms and solvent molecules have been omitted for clarity. C: grey; O: red; N: blue; B: green; Zn: cyan; Cd: pink.
mic shift can be observed relative to the solid state spectra of the protonated metalloligands 1 (lmax = 515 nm) and 4 (lmax = 469 nm). This shift is probably induced by the coordination of the pyridyl groups to the Zn2 + and Cd2 + ions. Thermogravimetric analyses of 12–15 show that the structurally related networks 12, 13, and 15 are all thermally stable up to approximately 300 8C. Coordination polymer 14 was found to be more susceptible to thermal degradation, which confirmed indirectly that it possesses a unique structure. BET surface measurements (N2, 77 K) after drying under vacuum gave low values for the coordination polymers 12 (54 m2 g 1) and 14 (10 m2 g 1), both of which are based on a clathrochelate ligand with methyl substituents on the phenolatodioximato ligand. Significantly higher values were observed for the tert-butyl-containing 13 (556 m2 g 1) and 15 (700 m2 g 1; pore volume = 0.412 cm3g 1). These differences show that the lateral size of the clathrochelates can have a pronounced influence on the physical properties of the resulting assemblies.
Conclusion We have described the synthesis of dinuclear ZnII, MnII, and CoII clathrochelates with terminal pyridyl groups. These complexes were obtained in high yield by one-pot reactions of M(ClO4)2 salts with phenolatodioximato ligands and pyridylboronic acid. Upon deprotonation, anionic bipyridyl ligands are obtained. These ligands have interesting characteristics for applications in supramolecular coordination chemistry: 1) they are robust, rigid, and relatively long; 2) the lateral size and the solubility of the ligands can be modified by variation of the phenolatodioximato ligand; 3) the Zn-based clathrochelates are luminescent; and 4) it is possible to incorporate diamagnetic or paramagnetic metal ions. To demonstrate that these ligands are indeed useful building blocks in metallasupramolecular chemistry, we have synthesized the molecular square 10 as an example of a molecularly defined nanostructure, as well as the coordination polymers 12–15. By using competition experiments, we
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Full Paper were able to demonstrate that complex 10 is significantly more stable than an analogous assembly with the standard 4,4-bipyridine ligand. The increased stability is attributed to the presence of an anionic charge on the clathrochelate, which reduces the overall charge of the metallamacrocycle. The possibility to make more stable metal-based assemblies is certainly an interesting aspect of this new class of ligands. The successful synthesis of the coordination polymers 12–15 is the first evidence for the utility of clathrochelate-based pyridyl ligands in the field of metal–organic frameworks. The negative charge of the metalloligands is again an important point, because it reduces or even eliminates the need for anionic coligands to compensate for the charge of the metal ions. The lateral size of the clathrochelate ligands can be controlled by the choice of the phenolatodioximato ligands. So far, we have explored methyl- and tert-butyl substituents on the phenolato ligand. The importance of such modifications was evidenced by the pronounced differences that were observed for the specific surface areas of 12 and 13. Overall, we think that dinuclear clathrochelates are an interesting new class of metalloligands with a lot of potential for applications in molecular nanoscience.
Experimental Section General All reagents were obtained from commercial sources. Ligand L1 was prepared according to a literature procedure.[8] The synthesis of ligand L2 and Pt(dppp)Cl2 is described in the Supporting Information. Pt(dppp)(OTf)2 and the molecular square 11 were synthesized as described in the literature.[13] 1H and 13C NMR spectra were obtained on a Bruker Avance instrument (1H: 400 MHz; 13C: 100 MHz). 1H and 13C chemical shifts (d) are reported in parts per million (ppm) referenced to the internal solvent. All spectra were recorded at room temperature. Electrospray-ionization MS data were acquired on a Q-Tof Ultima mass spectrometer (Waters) operated in the positive ionization mode, and data were processed by using the MassLynx 4.1 software. APPI-FT-ICR experiments were performed on a hybrid linear ion trap Fourier transform ion cyclotron resonance mass spectrometer (LTQ FT-ICR MS, Thermo Scientific, Bremen, Germany) equipped with a 10 T superconducting magnet (Oxford Instruments Nanoscience, Abingdon, UK). Data analysis was carried out by using XCalibur software (Thermo Scientific, Bremen, Germany). IR spectra were recorded on a Perkin– Elmer Spectrum One Golden Gate FT/IR spectrometer. Combustion analysis was performed with a Thermo Scientific Flash 2000 Organic elemental analyzer. Diffuse reflectance spectra were carried out by using a Perkin–Elmer Lambda 900 UV/VIS/NIR spectrometer with a PELA-1000 accessory within the wavelength range of 200– 800 nm. Emission spectra were recorded with Varian Cary Eclipse or Perkin–Elmer LS-50 spectrofluorimeters. Thermogravimetric analysis was performed on a Mettler-Toledo TGA/SDTA851e instrument equipped with a TSO800GC1 gas control unit. Data were collected by using the STARe software and processed in Microsoft Excel. The sample was heated from 35 to 600 8C at a rate of 2 8C per minute in an alumina crucible under a 60 mL min 1 flow of N2. Nitrogensorption measurements were performed on a Quantachrome Autosorb iQ surface area analyzer. Before the measurements, the polymers were dried under a high vacuum for 12 h at 120 8C. The BET analyses were performed at 77.3 K. Note: compounds containing Chem. Eur. J. 2014, 20, 5592 – 5600
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perchlorate are potentially explosive and should be handled with care!
General procedure for the synthesis of 1–3 A mixture of ligand L1 (201 mg, 108 mmol) and 4-pyridylboronic acid (88 mg, 720 mmol) was heated in a mixture of dichloromethane/ethanol (1:1, 20 mL) until all of the boronic acid had dissolved. Solid M(ClO4)2(H2O)6 (M: Zn, 268 mg, 720 mmol; M: Co, 263 mg, 720 mmol; M: Mn, 260 mg, 720 mmol) was then added, and the solution was stirred for 1 h. The yellow (1 and 3) or orange (2) microcrystalline precipitate was filtered, washed with cold ethanol, and dried under vacuum. Complex 1: Yield: 0.31 g, 81 %; 1H NMR (400 MHz, [D7]DMF): d = 2.20 (s, 9 H, CH3), 7.21 (s, 6 H, CHar), 8.38 (d, 4 H, J = 6.4 Hz, CHpy), 8.42 (s, 6 H, CHim), 9.00 ppm (d, 4 H, J = 6.6 Hz, CHpy); 13C NMR (100 MHz, [D7]DMF): d = 163.77 (C OPh), 155.51 (C=N), 139.97 (CHar), 136.96 (Car), 130.39 (CHar), 124.34 (Car), 119.29 (CHar), 19.55 ppm (CH3) (B C was not observed); ESI-MS: m/z: 883.0644 [M + 2 H] + ; elemental analysis: calcd (%) for Zn2C37H31N8B2O9(ClO4)(CH2Cl2) (1068.47 g mol 1): C 42.71, H 3.11, N 10.48; found: C 42.83, H 3.42, N 10.47; FTIR: n˜ max : 3413 (br), 2928 (br), 1615 (m), 1594 (m), 1554 (m), 1445 (s), 1321 (s), 1186 (m), 1084 (s), 997 (vs), 935 (vs), 815 (vs), 758 (s), 621 cm 1 (s). Complex 2: Yield: 0.30 g, 83 %; ESI-MS: m/z: 871.1042 [M + 2 H] + ; elemental analysis: calcd (%) for Co2C37H31N8B2O9(ClO4)(CH2Cl2)0.5 (1013.09 g mol 1): C 44.45, H 3.18, N 11.06; found: C 44.60, H 3.32, N 11.07; FTIR: n˜ max : 3248 (br), 1614 (m), 1591 (m), 1556 (m), 1445 (s), 1313 (s), 1201 (m), 1089 (s), 1000 (vs), 937 (vs), 816 (vs), 761 (s), 620 cm 1 (s). Complex 3: Yield: 0.25 g, 87 %; ESI-MS: m/z: 861.1017 [M + 2 H] + ; elemental analysis: calcd (%) for Mn2C37H31N8B2O9(ClO4)(CH2Cl2)2 (1132.50 g mol 1): C 41.36, H 3.11, N 9.89; found: C 41.39, H 3.08, N 10.31; FTIR: n˜ max : 2982 (br), 1603 (m), 1578 (m), 1545 (m), 1473 (s), 1321 (s), 1200 (m), 1181 (m), 1029 (s), 991 (vs), 927 (vs), 819 (vs), 758 (s), 684 cm 1 (s).
General procedure for the synthesis of 4–6 A mixture of ligand L2 (0.66 g, 2.79 mmol) and 4-pyridylboronic acid (0.23 g, 1.86 mmol) was heated in a mixture of dichloromethane/ethanol (1:1, 20 mL) until all of the boronic acid had dissolved. Solid M(ClO4)2(H2O)6 (M: Zn, 0.69 g, 1.86 mmol; M: Co, 0.68 g, 1.86 mmol; M: Mn, 0.67 g, 1.86 mmol) was then added, and the solution stirred for 1 h. The yellow (4 and 6) or orange (5) microcrystalline precipitate was filtered, washed with cold ethanol, and dried under vacuum. Complex 4: Yield: 0.98 g, 88 %; X-ray-quality crystals were formed by slow evaporation of the mother liquor; 1H NMR (400 MHz, [D6]DMSO): d = 1.22 (s, 27 H, (CH3)3), 7.37 (s, 6 H, CHar), 8.20 (d, 4 H, J = 6.5 Hz, CHpy), 8.44 (s, 6 H, CHim), 8.79 ppm (d, 4 H, J = 6.5 Hz, CHpy); 13C NMR (100 MHz, [D6]DMSO): d = 162.56 (C OPh), 155.10 (C=N), 139.17 (CHar), 137.36 (Car), 132.97 (CHar), 129.46 (Car), 117.99 (CHar), 33.44(C(CH3)3), 31.11 ppm (C(CH3)3), (B C was not observed); ESI-MS: m/z: 1009.2392 [M + H] + ; elemental analysis: calcd (%) for Zn2C46H49N8B2O9(ClO4) (1109.78 g mol 1): C 49.79, H 4.45, N 10.10; found: C 50.35, H 4.51, N 10.23; FTIR: n˜ max : 3242 (br), 2949 (m), 1612 (m), 1550 (m), 1444 (s), 1326 (s), 1221 (s), 1198 (s), 1075 (s), 1035 (s), 998 (vs), 938 (vs), 838 (m), 771 (s), 695 (s), 618 cm 1 (s). Complex 5: Yield: 0.90 g, 89 %; X-ray-quality crystals were formed by slow evaporation of the mother liquor; ESI-MS: m/z: 499.1277 [M + 2 H]2 + ; elemental analysis: calcd (%) for Co2C46H49N8O9(ClO4) (1075.44 g mol 1): C 51.38, H 4.59, N 10.42; found: C 51.00, H 4.40,
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Full Paper N 10.41; FTIR: n˜ max : 2955 (br), 1610 (m), 1550 (m), 1445 (s), 1365 (m), 1325 (s), 1285 (m), 1200 (m), 1080 (s), 1035 (vs), 940 (vs), 840 (vs), 770 (s), 620 cm 1 (s). Complex 6: Yield: 0.57 g, 65 %; ESI-MS: m/z: 989.2579 [M + 2 H] + ; elemental analysis: calcd (%) for Mn2C46H49N8B2O9(ClO4) (1088.87 g mol 1): C 50.74, H 4.54, N 10.29; found: C 50.91, H 4.62, N 10.44; FTIR: n˜ max : 2955 (br), 1630 (m), 1580 (m), 1545 (m), 1445 (s), 1330 (s), 1280 (m), 1195 (m), 1020 (s), 990 (vs), 935 (vs), 805 (vs), 780 (s), 690 cm 1 (s).
General procedure for the synthesis of 7 and 8 Et3N (88 mL, 0.6 mmol) was added to a suspension of 1 (0.33 g, 0.31 mmol) or 3 (0.27 g, 0.31 mmol) in acetonitrile/methanol (1:1, 20 mL). The mixture was stirred until all of solid had dissolved. The volume of the solvent was reduced under vacuum to 3 mL, and a yellow solid formed. The product was filtered, washed with cold acetonitrile, and dried under vacuum. Complex 7: Yield: 0.29 g, 85 %; 1H NMR (400 MHz, [D7]DMF): d = 1.29–1.35 (m, 12 H), 2.18 (s, 9 H, CH3), 3.43 (q, J = 7.3 Hz, 8 H), 7.14 (s, 6 H, CHar), 7.66 (d, 4 H, J = 5.7 Hz, CHpy), 8.35 (s, 6 H, CHim), 8.46 ppm (d, 4 H, J = 5.6 Hz, CHpy); 13C NMR (100 MHz, [D7]DMF): d = 164.25 (C OPh), 155.20 (C=N), 148.95 (CHar), 136.91 (Car), 128.49 (CHar), 124.53 (Car), 120.11 (CHar), 53.01 (CH2), 20.16 (CH3), 7.95 ppm (CH3) (B C was not observed); ESI-MS: m/z: 883.1703 [M + 2 H] + ; elemental analysis: calcd (%) for Zn2C37H31N8B2O9(C6H16N)(CH2Cl2) (1060.13 g mol 1): C 49.84, H 3.61, N 11.89; found: C 48.66, H 4.89, N 11.37; FTIR: n˜ max : 3208 (br), 2988 (br), 1613 (m), 1592 (m), 1553 (m), 1444 (s), 1322 (s), 1202 (s), 1085 (m), 1034 (vs), 998 (vs), 935 (vs), 817 (s), 761 (s), 688 cm 1 (s). Complex 8: Yield: 0.25 g, 87 %; ESI-MS: m/z: 861.1017 [M + 2 H] + ; elemental analysis: calcd (%) for Mn2C37H31N8B2O9(C6H16N)(CH2Cl2) (1039.23 g mol 1): C 50.85, H 3.68, N 12.13; found: C 50.01, H 3.52, N 12.30; FTIR: n˜ max : 2982 (br), 1603 (m), 1578 (m), 1545 (m), 1473 (s), 1321 (s), 1200 (m), 1181 (m), 1029 (s), 991 (vs), 927 (vs), 819 (vs), 758 (s), 684 cm 1 (s). Complex 9: Et4NOH (1.0 mL, 1.7 mmol, 25 % in MeOH) was added to a suspension of 4 (0.98 g, 0.88 mmol) in acetonitrile/methanol (1:1, 20 mL). The mixture was stirred until the entire solid had dissolved. A few more drops of the Et4NOH solution were added, and a yellow solid started to form. The product was filtered, washed with cold methanol, and dried under vacuum. Yield: 0.92 g, 92 %; 1 H NMR (400 MHz, [D7]DMF): d = 1.27 (s, 27 H, (CH3)3), 1.32 (t, J = 8.2 Hz, 12 H, CH3), 3.43 (q, J = 7.3 Hz, 8 H, CH2), 7.38 (s, 6 H, CHar), 7.67 (d, 4 H, J = 5.6 Hz, CHpy), 8.42 (s, 6 H, CHim), 8.46 ppm (d, 4 H, J = 5.7 Hz, CHpy); 13C NMR (100 MHz, [D7]DMF): d = 164.15 (C OPh), 155.53 (C=N), 148.92 (CHar), 138.41 (Car), 133.61 (CHar), 128.51 (Car), 119.79 (CHar), 52.94 (CH2), 34.55 (C(CH3)3), 31.93 (CH3), 7.94 ppm (CH3) (B C was not observed); ESI-MS: m/z: 1009.2791 [M + H] + ; elemental analysis: calcd (%) for Zn2C46H48B2N8O9(C8H21N)(H2O)2.5 (1186.62 g mol 1): C 54.86, H 6.18, N 10.66; found: C 54.73, H 5.98, N 10.66; FTIR: n˜ max : 2949 (m), 1611 (m), 1590 (m), 1550 (m), 1446 (s), 1331 (s), 1221 (s), 1202 (s), 1079 (s), 1036 (s), 996 (vs), 919 (vs), 781 (vs), 772 (s), 696 cm 1 (s).
Molecular square 10 A solution of Pt(dppp)(OTf)2 (100 mg, 110 mmol) and complex 9 (125 mg, 110 mmol) in DMSO (10 mL) was stirred for 1 h. CHCl3 (20 mL) was then added, which caused the precipitation of a paleyellow amorphous powder. The product was isolated by centrifugation, washed with CHCl3 (3 5 mL) and Et2O (3 5 mL), and dried under vacuum. Yield: 133 mg, 68 %; 1H NMR (600 MHz, [D6]DMSO): Chem. Eur. J. 2014, 20, 5592 – 5600
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d = 1.10 (s, 108 H, CH3), 1.98 (br, 8 H, CH2), 3.26 (br, 16 H, CH2), 7.25 (s, 24 H, Ar-H), 7.30 (d, 16 H, Ar-H), 7.47 (t, 32 H, Ar-H), 7.60 (t, 16 H, Ar-H), 7.73 (t, 32 H, Ar-H), 8.26 (s, 24 H, CH), 8.49 ppm (d, 16 H, ArH); 13C NMR (150 MHz, [D6]DMSO): d = 17.3 (CH2), 21.5 (CH2), 31.1 (CH3), 33.3 (Cq), 118.0 (Cq), 125.0 (Cq), 125.4 (Cq), 129.2 (CH), 129.3 (CH), 132.4 (CH), 132.6 (CH), 132.9 (CH), 137.1 (Cq), 147.1 (CH), 154.7 (CH), 162.4 ppm (Cq); 31P NMR: d = 12.7 (t, 1JPt P = 1512 Hz); HRMS (ESI + ): m/z calcd for [C292H292B8N32O36P8Pt4Zn8]4 + : 1615.5895; found: 1615.5914 [M (OTf)4]4 + ; elemental analysis: calcd (%) for C296H292B8F12N32O48P8Pt4S4Zn8 (7059.6 g mol 1): C 50.36, H 4.17, N 6.35; found: C 50.50, H 4.12, N 6.33.
Coordination polymer 12 Polymer 12 was prepared in multiple batches. The individual reactions were carried out in sealed 20 mL microwave vials as follows. Zn(NO3)2(H2O)6 (6.0 mg, 20 mmol) was added to a solution of complex 1 (32 mg, 30 mmol) in DMF (6.0 mL). The resulting mixture was briefly sonicated before the vial was placed for 24 h into an oil bath at 80 8C. The vial was then allowed to cool to room temperature to induce crystallization. After 3 d, the resulting yellow crystals were washed with DMF (3 5 mL) before being isolated by filtration and dried under vacuum for 3 d. Yield: 20 mg, 62 %; elemental analysis: calcd (%) for (Zn2C37H29B2N8O9)2Zn(DMF)4(H2O)3 (2175.96 g mol 1): C 47.47, H 4.26, N 12.87; found: C 47.64, H 3.84, N 12.23; FTIR: n˜ max : 3317 (br), 2924 (m), 1650 (vs), 1613 (s), 1592 (m), 1554 (m), 1444 (vs), 1384 (m), 1321 (s), 1204 (m), 1086 (m), 1036 (s), 998 (vs), 940 (vs), 822 (s), 765 (s), 694 (s), 659 cm 1 (s).
Coordination polymer 13 Polymer 13 was prepared in multiple batches. The individual reactions were carried out in sealed 7 mL microwave vials as follows. Zn(ClO4)2(H2O)6 (20 mg, 54 mmol) was added to a solution of complex 4 (30 mg, 27 mmol) in DMF (5.0 mL). The resulting mixture was briefly sonicated before the vial was placed for 48 h into an oil bath at 120 8C. The vial was then allowed to cool to room temperature to induce crystallization. After 2 d, the resulting yellow crystals were washed with DMF (3 5 mL) before being isolated by filtration and dried under vacuum for 3 d. Yield: 31 mg, 89 %; elemental analysis: calcd (%) for sample after the heating under vacuum (Zn2C46H48B2N8O9)2Zn(H2O)4 (2156.09 g mol 1): C 51.24, H 4.86, N 10.39; found: C 51.03, H 4.84, N 12.23; FTIR: n˜ max : 2950 (m), 1670 (s), 1610 (m), 1445 (s), 1385 (m), 1329 (s), 1220 (m), 1202 (s), 1080 (m), 1035 (s), 995 (vs), 931 (vs), 838 (m), 785 (vs), 770 (vs), 700 (s), 660 cm 1 (m).
Coordination polymer 14 A solution of complex 7 (28 mg, 26 mmol) in DMF (4.0 mL) in a test tube (diameter = 15 mm) was layered with a solution of Cd(ClO4)2(H2O)6 (6.0 mg, 19 mmol) in MeOH (4.0 mL), separated by a buffer layer of DMF/MeOH (1:1, 2 mL). After 2 weeks, yellow crystals had formed. The crystals were washed with DMF (3 5 mL) before being isolated by filtration and dried under vacuum for 3 d. Yield: 20 mg, 80 %; elemental analysis: calcd (%) for (Zn2C37H29B2N8O9)2Cd(DMF)2(H2O)6 (2130.84 g mol 1): C 45.09, H 3.97, N 11.83; found: C 43.90, H 3.76, N 11.79; FTIR: n˜ max : 3344 (br), 2952 (m), 1652 (s), 1610 (s), 1552 (m), 1445 (vs), 1384 (m), 1327 (s), 1203 (m), 1080 (m), 1035 (s), 985 (vs), 929 (vs), 839 (s), 782 (vs), 698 (vs), 659 cm 1 (m).
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Full Paper Coordination polymer 15 A solution of complex 9 (30 mg, 26 mmol) in DMF (4.0 mL) in a test tube (diameter = 15 mm) was layered with a solution of Cd(ClO4)2(H2O)6 (6.0 mg, 19 mmol) in MeOH (4.0 mL), separated by a buffer layer of DMF/MeOH (1:1, 2 mL). After 1 week, yellow single crystals had formed. The crystals were washed with DMF (3 5 mL) before being isolated by filtration and dried under vacuum for 3 d. Yield: 24 mg, 80 %; elemental analysis: calcd (%) for sample after heating under vacuum (Zn2C46H48B2N8O9)2Cd(H2O)9 (2293.19 g mol 1): C 48.18, H 5.01, N 9.77; found: C 47.95, H 4.49, N 9.84; FTIR: n˜ max : 3344 (br), 2952 (m), 1652 (s), 1610 (s), 1552 (m), 1445 (vs), 1384 (m), 1327 (s), 1203 (m), 1080 (m), 1035 (s), 985 (vs), 929 (vs), 839 (s), 782 (vs), 698 (vs), 659 cm 1 (m).
[2] [3] [4]
[5]
Crystallographic analyses [6]
Intensity data were collected by using an Oxford Diffraction KM-4 CCD diffractometer, a Bruker APEX II CCD system, or a marmx system, with graphite monochromated Mo-Ka radiation (l = 0.71073 ) at low temperature. Data reductions were carried out with Crysalis PRO,[23] BYPASS,[24] EVALCCD,[25] or automar.[26] Structure solutions and refinements were performed with the SHELX software package,[18] in which ShelXle[22] was used as the GUI. The structures were refined by using full-matrix least-squares routines on F2. Stereochemical restraints for all boron, carbon, nitrogen, and oxygen atoms of the clathrochelate ligands were generated by using the GRADE program.[17, 18] It gathers stereochemical information from a Mogul search combined with QM calculations. This macromolecular refinement technique has been adapted to be used in the program SHELXL.[19] A GRADE dictionary for SHELXL contains target values and standard deviations for 1.2-distances (DFIX) and 1.3-distances (DANG), as well as restraints for planar groups (FLAT). All atoms of the clathrochelate ligands were grouped into residues. The dictionaries were applied to the structures of coordination polymers 12–15 and disordered solvent molecules for complexes 4, 5, 7, and 8. Rigid bond restraints (RIGU)[21] were applied to anisotropic displacement parameters of all non-hydrogen atoms. Hydrogen atoms were included in the model on calculated positions by using the riding model for all structures. CCDC 980630 (4), 980631 (5), 980632 (7), 980633 (8), 980634 (12), 980635 (13), 980636 (14), and 980637 (15) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[7] [8] [9] [10]
[11] [12]
Acknowledgements
[13]
The work was supported by Marie Curie fellowships for M.P. (IEF-2009-252716) and J.J.H. (ITN-2010-264645), the Swiss National Science Foundation, and by the EPFL. Oliver Smart is thanked for writing and adapting the GRADE program, which was applied in the X-ray analysis.
[14] [15]
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Received: January 23, 2014 Published online on April 2, 2014
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