Volume 43 Number 48 28 December 2014 Pages 17873–18148
Dalton Transactions An international journal of inorganic chemistry www.rsc.org/dalton
ISSN 1477-9226
PAPER Yan Z. Voloshin et al. Copper(I)- and copper(0)-promoted homocoupling and homocoupling– hydrodehalogenation reactions of dihalogenoclathrochelate precursors for C–C conjugated iron(II) bis-cage complexes
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Copper(I)- and copper(0)-promoted homocoupling and homocoupling– hydrodehalogenation reactions of dihalogenoclathrochelate precursors for C–C conjugated iron(II) bis-cage complexes† Oleg A. Varzatskii,a Sergey V. Shul’ga,a Alexander S. Belov,b Valentin V. Novikov,b Alexander V. Dolganov,b Anna V. Vologzhaninab and Yan Z. Voloshin*b Iron(II) dibromo- and diiodoclathrochelates undergo copper(I)-promoted reductive homocoupling in HMPA at 70–80 °C leading to C–C conjugated dibromo- and diiodo-bis-clathrochelates in high yields. Under the same conditions, their dichloroclathrochelate analog does not undergo the same homocoupling reaction, so the target dichloro-bis-cage product was obtained in high yield via dimerization of its heterodihalogenide iodochloromonomacrobicyclic precursor. The use of NMP as a solvent at 120–140 °C gave the mixture of bis-clathrochelates resulting from a tandem homocoupling–hydrodehalogenation reaction: the initial acetonitrile copper(I) solvato-complex at a high temperature underwent resolvatation and disproportionation leading to Cu(II) ions and nano-copper, which promoted the hydrodehalogenation process even at room temperature. The most probable pathway of this reaction in situ includes hydrodehalogenation of the already formed dihalogeno-bis-clathrochelate via the formation of reduced anion radical intermediates. As a result, chemical transformations of the iron(II) dihalogenoclathrochelates in the presence of an acetonitrile copper(I) solvato-complex were found to depend both on the nature of halogen atoms in their ribbed chelate fragments and on reaction conditions (i.e. solvent and temperature). The C–C conjugated iron(II) dihalogeno-bis-clathrochelates easily undergo nucleophilic substitution with various N,S-nucleophiles giving ribbed-functionalized bis-cage species. These iron(II) complexes were characterized by elemental analysis, MALDI-TOF mass spectrometry, IR, UV-Vis, 1H and C NMR spectroscopy, and by X-ray diffraction; their electrochemical properties were studied by cyclic
13
voltammetry. The isomeric shift values in Received 27th May 2014, Accepted 8th July 2014
57
Fe Mössbauer spectra of such cage compounds allowed
identifying them as low-spin iron(II) complexes, while those of the quadrupole splitting are the evidence for a significant TP distortion of their FeN6-coordination polyhedra. As follows from CV data, the C–C
DOI: 10.1039/c4dt01557f
conjugated iron(II) bis-clathrochelates undergo stepwise electrochemical reduction and oxidation giving
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mixed-valence FeIIFeI and FeIIFeIII bis-cage intermediates.
Introduction Iron(II) clathrochelates have been reported1 to effectively inhibit the action of T7 RNA polymerase in vitro (thus being prospective antiviral and antitumor drug candidates), and the inhibition constant depended strongly on the shape of the
a
Vernadskii Institute of General and Inorganic Chemistry NASU, 03680 Kiev, Ukraine Nesmeyanov Institute of Organoelement Compounds RAS, 119991 Moscow, Russia. E-mail:
[email protected]; Fax: +7-499-135-50-85 † Electronic supplementary information (ESI) available: The X-ray diffraction and UV-vis spectral tables. CCDC 1004068–1004070. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt01557f b
17934 | Dalton Trans., 2014, 43, 17934–17948
inhibitor’s molecule. Tighter binding can be obtained by expanding the surface of a cage metal complex while maintaining the complementarity of its shape to that of a biomolecular target. Indeed, we recently2 boosted the activity of such cage compounds by direct joining of two macrobicyclic fragments with a covalent bond. The first C–C conjugated iron(II) bis-clathrochelates obtained in ref. 2 via a copper-promoted reductive homocoupling reaction had incredible chemical stability, were easy to synthesize from available and inexpensive initial reagents and reactive clathrochelate precursors and had favorable geometry, allowing introduction of up to fourteen different apical and ribbed substituents. They were prone to limited torsion mobility, allowing them to accommodate them-
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selves to the shape of a binding site while keeping the number of conformational states low to ensure higher selectivity; the activity of these low-toxic iron(II) bis-clathrochelates falls in the submicromolar range.2 Moreover, the mono- and bis-macrobicyclic iron(II) complexes have been reported in ref. 3 as versatile guests in supramolecular assemblies with blood transport proteins and serum albumins that discriminated other globular proteins. Such binding depends on the size and the nature of a guest cage molecule: monoclathrochelates give more stable assemblies than bis-clathrochelates, and functionalization with carboxyphenylsulfide ribbed substituents at a macrobicyclic framework substantially improves the binding.3 They have also been proposed in ref. 4 as structure- and concentration-dependent antifibrillogenic agents; the latter is important, as aggregation of protein molecules into highly ordered beta-pleated structures (amyloid fibrils) is associated with Alzheimer’s and Parkinson’s diseases, systemic amyloidoses and diabetes type II. As followed from fluorescence spectroscopy, AFM and flow cytometry data,3,4 the presence of such cage compounds changed the kinetics of fibrillization reaction and reduced the amount of fibrils with a substantial decrease in their diameter. Here, we report the detailed synthetic procedures, X-ray structures and spectral data for a series of C–C conjugated iron(II) bis-clathrochelates, their unexpected chemical reactions and electrochemical characteristics.
Results and discussion Synthesis Chemical transformations of the iron(II) dihalogenomonoclathrochelate precursors in the presence of an acetonitrile copper(I) solvato-complex depend both on the nature of halogen atoms in their ribbed chelate fragments and on reaction conditions (i.e. solvent and temperature). Dibromo- and
Scheme 1
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diiodoclathrochelates FeBd2(Br2Gm)(BF)2 and FeBd2(I2Gm)(BF)2 in HMPA at 70–80 °C underwent copper(I)-promoted reductive homocoupling as shown in Schemes 2 and 3 leading to C–C conjugated dibromo- and diiodo-bis-clathrochelates {FeBd2(BrGm)(BF)2}2 and {FeBd2(IGm)(BF)2}2 in high yields, respectively. Their dichloroclathrochelate analog FeBd2(Cl2Gm)(BF)2 did not undergo such homocoupling under the same reaction conditions, so the target dichloro-biscage product {FeBd2(ClGm)(BF)2}2 was obtained in high yield via dimerization of the heterodihalogenoclathrochelate FeBd2(IGmCl)(BF)2 as shown in Scheme 4. The use of NMP as a solvent at 120–140 °C gave a mixture of bis-clathrochelate products resulting from tandem homocoupling–hydrodehalogenation reactions of the dihalogenomonoclathrochelate precursors (Scheme 1). It seems that the initial acetonitrile copper(I) solvato-complex at a high temperature in NMP media undergoes re-solvatation and disproportionation as shown in Scheme 5 leading to copper(II) ions and nano-copper (this causes an additional red coloration of the reaction mixture, characteristic of nanometals;5 such colloidal systems are stable for a long time under anaerobic conditions), promoting the hydrodehalogenation process even at room temperature. The plausible pathways I and II of this tandem process are shown in Scheme 6. First one ( pathway I) includes the formation of a very reactive monobromoclathrochelate anion radical that abstract hydrogen atoms from a solvent or reactants giving the iron(II) monomethinomonobromoclathrochelate. The following reduction–hydrodehalogenation of this intermediate complex with nano-copper may give a monomethine anion radical easily undergoing dimerization with the formation of a C–C conjugated bis-clathrochelate. Such a highly reactive radical species should also abstract hydrogen atoms from solvents or reactants, giving the dimethinomonoclathrochelate FeBd2(H2Gm)(BF)2. The latter complex, however, was not detected in appreciable amounts among the
Copper-promoted reactions of the iron(II) dihalogenomonoclathrochelates.
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Scheme 2
Synthesis of a C–C conjugated iron(II) dibromo-bis-clathrochelate precursor and its nucleophilic substitution.
Scheme 3
Synthesis of a C–C conjugated iron(II) diiodo-bis-clathrochelate.
clathrochelate products of this reaction. Therefore, pathway II seems to be the most probable, as it includes in situ hydrodebromination of the already formed dibromo-bis-clathrochelate. This suggestion was confirmed by almost quantitative (with a yield of approximately 95%) conversion as shown in Scheme 7 of the preliminary isolated complex {FeBd2(BrGm)(BF)2}2 into the product of its hydrodebromination {FeBd2(HGm)-(BF)2}2 in the presence of nano-copper and copper(II) ions in NMP at 140 °C (see the Experimental section); similar stepwise hydrodehalogenation of the diiodomonoclathrochelate FeBd2(I2Gm)(BF)2 with copper(I) cyanide in DMF has earlier been reported in ref. 6. The C–C conjugated iron(II) dihalogeno-bis-clathrochelates obtained as reactive bis-macrobicyclic precursors easily undergo nucleophilic substitution with various N,S-nucleo-
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philes leading to ribbed-functionalized bis-cage complexes; the examples of such reactions performed for the precursor {FeBd2(BrGm)(BF)2}2 are shown in Scheme 2. The iron(II) complexes synthesized were characterized by elemental analysis, MALDI-TOF mass spectrometry (Fig. S5 and S6†), IR, UV-Vis, 1H and 13C NMR spectroscopy, and X-ray diffraction; their electrochemical properties were studied by cyclic voltammetry (CV). X-ray structures Molecular structures of four C–C conjugated iron(II) bis-clathrochelates {FeBd2(HGm)(BF)2}2·3C6H6, {FeBd2(BrGm)(BF)2}2· 3C6H6, {FeBd2(IGm)(BF)2}2·6C6H5Cl, {FeBd2((CH2)5NGm)(BF)2}2·5C6H6 and a new polymorph of their dibromomonoclathrochelate precursor FeBd2(Br2Gm)(BF)2·CH2Cl2 are shown
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Scheme 4 Synthesis of a C–C conjugated iron(II) dichloro-bisclathrochelate.
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in Fig. 1–5. The asymmetric part of the unit cells for the dimethino- and dihalogeno-bis-clathrochelates contain half of their molecules, while the piperidinyl-functionalized complex occupies a general position. Average Fe–N distances (Table 1) fall in the narrow range 1.90–1.92 Å and are characteristic of low-spin iron(II) complexes with N-donor ligands. The FeN6polyhedra of macrobicyclic entities possess a distorted trigonal prismatic (TP, the distortion angle φ = 0°) – trigonal antiprismatic (TAP, φ = 60°) geometry with the φ angles from 24.3 to 27.8°; these values are also characteristic of aromatic tris-dioximate iron(II) clathrochelates. The encapsulated iron(II) ions are situated almost in the centres of these polyhedra; their heights h and the bite angles α (half of the chelate N–Fe–N angle) are 2.24–2.32 Å and approximately 39°, respectively. The chelate C–C distances in the functionalized ribbed fragments (1.47–1.49 Å) are greater than those in their α-benzyldioximate chelate moieties (1.43–1.45 Å), and the C–C distances between the C–C conjugated macrobicyclic frameworks (1.46–1.47 Å) are close to the average value for a C(sp2)–C(sp2) bond (1.45 Å).7 The torsion CvC–CvC angle ψ between them decreases from the bis-clathrochelates {FeBd2(HGm)(BF)2}2 (160°) and {FeBd2(BrGm)(BF)2}2 (122°) to
Scheme 5
Transformations of an initial acetonitrile copper(I) solvato-complex in different media.
Scheme 6
Plausible pathways of tandem homocoupling–hydrodehalogenation reaction.
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Scheme 7
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Hydrodehalogenation of the iron(II) dibromo-bis-clathrochelate leading to its dimethine-containing analog.
Fig. 3 General view of the bis-clathrochelate {FeBd2(IGm)(BF)2}2 given in thermal ellipsoids drawn at p = 50%.
Fig. 1 General view of the dibromomonoclathrochelate FeBd2(Br2Gm)(BF)2 in its new polymorphic modification II given in thermal ellipsoids drawn at p = 50%.
Fig. 4 General view of the bis-clathrochelate {FeBd2(BrGm)(BF)2}2 given in thermal ellipsoids drawn at p = 50%.
Fig. 2 General view of the bis-clathrochelate {FeBd2(HGm)(BF)2}2 given in thermal ellipsoids drawn at p = 50%.
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their piperidinyl- and iodo-containing analogs {FeBd2(IGm)(BF)2}2 (88°) and {FeBd2(((CH2)5N)Gm)(BF)2}2 (53°). Surprisingly, the latter bis-clathrochelate with the most bulky ribbed substituents shows the lowest ψ value. This may be explained by hindrances between them in the chair conformation with nitrogen lone pairs directed towards each other. A variation in
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Fig. 5 General view of the bis-piperidinyl-functionalized bis-clathrochelate {FeBd2(((CH2)5N)Gm)(BF)2}2 given in thermal ellipsoids drawn at p = 50%.
ψ values suggests that a rotation around the C–C bridging bond between the π-conjugated macrobicyclic polyazomethine frameworks allows these bis-clathrochelates to adopt the conformations that are complementary to the binding pockets in biological macromolecules and their macromolecular complexes.2 Fig. 6 shows that overlapping of one of the two macrobicyclic fragments of the bis-clathrochelates {FeBd2(HGm)(BF)2}2 and {FeBd2(((CH2)5N)Gm)(BF)2}2 makes the C3-symmetry pseudoaxes of their other cage frameworks almost perpendicular. Crystal packing of these rigid polyazomethine bis-clathrochelates suggests the formation of vacant cavities suitable for inclusion of solvate molecules. Indeed, the X-rayed crystals of the iron(II) complexes contain up to six guests of this type.
Table 1
Fig. 6 Comparison of molecular structures of the bis-clathrochelates {FeBd2(HGm)(BF)2}2 (solid violet line) and {FeBd2(((CH2)5N)Gm)(BF)2}2 (green dashed line); the atoms Fe1, B1, B2, C1 and C2, and Fe1, B1, B2, C5 and C6 in the first and second molecules, respectively, are overlapped. Hydrogen atoms, except for those of the methine groups, are omitted for clarity.
Moreover, benzene and chlorobenzene molecules form a system of van der Waals π⋯π, C–H⋯π and C–H⋯X intermolecular interactions with bis-clathrochelate species. According to molecular docking calculations,2 such interactions of their bulky phenyl substituents govern the efficient binding of bisclathrochelate transcription inhibitors with a T7 RNA polymerase – matrix DNA – RNA macromolecular complex. As supramolecular architecture of their crystals is formed by van der Waals interactions, we studied them using Hirshfeld
Main geometrical parameters of the C–C conjugated iron(II) bis-clathrochelates and their dihalogenomonoclathrochelate precursors
Complex
{FeBd2(HGm)(BF)2}2
1.906(5)a 1.899(5)a 1.906(5) 1.916(5) 1.909(5) 1.920(5) 1.459(8)–1.497(8) av. 1.479 N–O (Å) 1.368(5)–1.385(6) av. 1.375 CvN (Å) 1.291(7)–1.314(7) av. 1.302 C–C (Å) chelate 1.449(8)–1.482(8) av. 1.465 φ (°) 24.3 α (°) 39.0 ψ (°) 160 h (Å) 2.32
Fe–N1 (Å) Fe–N2 (Å) Fe–N3 (Å) Fe–N4 (Å) Fe–N5 (Å) Fe–N6 (Å) B–O (Å)
{FeBd2(BrGm)(BF)2}2 2
{FeBd2(IGm)(BF)2}2
FeBd2(Br2Gm)(BF)2 {FeBd2(((CH2)5N)Gm)- polymorph I (this work)/ b2 FeBd2(I2Gm)(BF)2 6 (BF)2}2 polymorph II2
1.893(3)a 1.876(3)a 1.896(3) 1.890(3) 1.903(3) 1.899(3) 1.481(5)–1.497(5) av. 1.488 1.366(4)–1.386(4) av. 1.376 1.308(5)–1.317(5) av. 1.313 1.434(5)–1.471(5) av. 1.454 27.7 39.3 122 2.29
1.912(5)a 1.904(6)a 1.922(7) 1.913(3) 1.909(3) 1.907(5) 1.483(8)–1.501(6) av. 1.489 1.352(8)–1.380(7) av. 1.370 1.303(8)–1.312(6) av. 1.306 1.45(1)–1.47(1) av. 1.460 24.7 39.1 88 2.32
1.927(9)/1.850(10)a 1.829(9)/1.925(9)a 1.831(9)/1.853(10) 1.880(9)/1.901(9) 1.836(9)a/1.928(9) 1.947(10)a/1.896(10) 1.40(1)–1.60(1) av. 1.48 1.35(1)–1.42(1) av. 1.39 1.27(2)–1.36(1) av. 1.30 1.43(1)–1.49(1) av. 1.45 27.8/26.3 38.9/39.2 53 2.24/2.29
a
1.918(4)a/1.914(3)a 1.921(5)a/1.920(3)a 1.903(4)/1.907(3) 1.910(4)/1.912(3) 1.905(4)/1.910(3) 1.910(4)/1.897(3) 1.471(5)–1.506(5) av. 1.491 1.355(6)–1.377(4) av. 1.368 1.287(5)–1.318(5) av. 1.306 1.450(6)–1.476(6) av. 1.459 24.9/25.8 39.2/39.4
1.902(8)a 1.914(8)a 1.912(9) 1.910(8) 1.904(9) 1.917(9) 1.451(15)–1.531(15) av. 1.492 1.359(10)–1.375(10) av. 1.370 1.294(13)–1.337(13) av. 1.313 1.429(15)–1.456(14) av. 1.444 24.7 39.3
2.32/2.33
2.33
b
The Fe–N distances for the functionalized ribbed fragments. This bis-cage molecule contains two independent encapsulated iron(II) ions; the parameters of both of its nonequivalent clathrochelate frameworks are presented.
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surfaces and their 2D projections. As can be seen from Fig. 7, approximately 60%, 58% and 71% of molecular surfaces of the bis-clathrochelates {FeBd2(BrGm)(BF)2}2, {FeBd2(IGm)(BF)2}2 and {FeBd2(((CH2)5N)Gm)(BF)2}2 are formed by the intermolecular C–H⋯X interactions; such calculations cannot be performed for the dimethino-bis-clathrochelate {FeBd2(HGm)(BF)2}2, as its X-ray structure was obtained using the SQUEEZE/ PLATON procedure. The supramolecular interactions of the ribbed functionalizing substituents in these bis-clathrochelates are determined by their nature. In particular, the piperidinyl substituents are included in the same C–H⋯X interactions, while diiodo- and dibromo-bis-clathrochelates form halogen bonds as well. Together with C–H⋯Hal (Hal = Br, I) hydrogen bonds, which are the shortest intermolecular interactions involving these halogen atoms (see Fig. 7, the de and 2D fingerprint plots), halogen bonds C–I⋯Cl, C–Br⋯O and C–B⋯π were found in the crystals of {FeBd2(IGm)(BF)2}2·C6H5Cl and {FeBd2(BrGm)(BF)2}2·3C6H6. A similar situation is observed in the case of two polymorphs of the dibromomonoclathrochelate precursor FeBd2(Br2Gm)(BF)2·CH2Cl2 (Table 1). Its more dense polymorph I (this work) and less dense polymorph II2 have the same geometries of their macrobicyclic frameworks: the corresponding k–Φ criteria8 are very similar (see Table S2†), and a small difference between them may be explained by different orientation of their phenyl ribbed substituents. These changes only slightly affect the relative contribution
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of the C–H⋯X contacts to the molecular Hirshfeld surface (52% and 53%, respectively). At the same time, intermolecular interactions for the dibromine-containing chelate fragments of these polymorphs are substantially different, while the clathrochelate molecules of polymorph I form infinite layers via C–Br⋯O halogen bonds (Fig. S1†), and those of polymorph II are included only in weak C–Br⋯π and C–H⋯Br intermolecular interactions (visualized in Fig. 8 by the color of de on the Hirshfeld surface and by elongations of the intermolecular contacts on the 2D fingerprint plot). Spectra The values of the isomeric shift (IS) in the 57Fe Mössbauer spectra of the mono- and bis-clathrochelates synthesized (Table 2, Fig. S3 and S4†) allowed identifying them as the lowspin iron(II) complexes, while the values of the quadrupole splitting (QS) are the evidence for a significant trigonal-prismatic distortion of the N6-coordination polyhedra of an encapsulated iron(II) ion; the low-spin state of a caged metal ion can be explained by an influence of the high field strength polyazomethine macrobicyclic ligands (the so-called “macrobicyclic effect”12). These data are in good agreement with the X-ray diffraction data for four of the compounds synthesized. The deduced QS values (0.41, 0.28, 0.32 and 0.22/0.30 mm s−1, Table 2) for the complexes FeBd2(Br2Gm)(BF)2, {FeBd2BrGm(BF)2}2, {FeBd2IGm(BF)2}2 and {FeBd2(((CH2)5N)Gm)(BF)2}2 were estimated from their X-ray diffraction data (vide supra) using the partial QS (PQS) concept,13 while the experimental
Fig. 7 Hirshfeld surfaces and selected neighborhood for the C–C conjugated iron(II) bis-clathrochelates mapped with de and the corresponding 2D fingerprint plots; a range of 1.0 (red) and 2.5 (blue) was used for mapping of the de on the Hirshfeld surfaces. For both the de and 2D maps, the regions corresponding to the C–H⋯X and C–Hal⋯X intermolecular interactions are highlighted. de and di are the closest distances from the point to nuclei, respectively, exterior and interior to the Hirshfeld surface.
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Fig. 8 Hirshfeld surfaces and selected neighborhood for two polymorphs (I and II) of the clathrochelate FeBd2(Br2Gm)(BF)2·CH2Cl2, mapped with de and the corresponding 2D fingerprint plots; a range of 1.0 (red) and 2.5 (blue) was used for mapping of the de on the Hirshfeld surfaces. For both the de and 2D maps, the regions corresponding to the C–H⋯X and C–Hal⋯X intermolecular interactions are highlighted.
Table 2 Base spacings h (Å), bite α and distortion φ angles (°), IS and QS (mm s−1), and f values for the C–C conjugated iron(II) bis-clathrochelates and their monoclathrochelate analogs
Experimental
Deduced
Compound
h
α
φ
IS
QS
f
f × PQSb
QS − f × PQS
FeBd2(Br2Gm)(BF)2 {FeBd2BrGm(BF)2}2 {FeBd2IGm(BF)2}2 FeBd2Gm(BF)2 9 {FeBd2(((CH2)5N)Gm)(BF)2}2 a
2.33 2.29 2.32 2.35 2.24 2.29 2.33 2.36 2.33
39.4 39.3 39.1 39.0 38.9 39.2 39.3 39.0 39.3
22.5 27.7 24.7 20.7 27.8 26.3 24.8 17.1 24.7
0.33 0.35 0.30 0.32 0.35
0.47 0.51 0.36 0.44 0.44
0.35 0.37 0.32
0.62 0.64 0.34
0.82 0.56 0.64 0.76 0.44 0.60 0.70 0.88 0.70
0.41 0.28 0.32 0.38 0.22 0.30 0.35 0.44 0.35
+0.07 +0.23 +0.04 +0.06 +0.22 +0.14 +0.3 +0.2 −0.01
FeBd2(Cl2Gm)(BF)2 10 Fe(Cl2Gm)3(BF)2 11 FeBd2(I2Gm)(BF)2 6 a
This bis-cage molecule contains two independent encapsulated iron(II) ions; the parameters of both of its nonequivalent clathrochelate frameworks are presented. b PQS = +0.5 mm s−1.12
ones are equal to 0.47, 0.51, 0.36 and 0.44 mm s−1, respectively. The distortion angle φ values for the complexes studied were calculated using a simple model13: QS = PQS(12–18 cos2α/cos2(φ/2)), where PQS is partial quadrupole splitting with an approximate value of +0.5 mm s−1 for macrobicyclic tris-diazomethines. The slightly higher experimental QS values for the iron(II) mono- and bis-clathrochelates compared to those theoretically deduced from this PQS concept can be accounted for by the fact that the molecules have no C3 symmetry axis passing through the apical boron atoms and an encapsulated iron(II) ion, resulting in an additional increase in the electric field gradient.
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In most cases, dimerization of the π-conjugated quasiaromatic polyazomethine frameworks causes a new band metalto-ligand charge transfer (MLCT) Fed → Lπ* to appear in the visible range (Table S3†) or results in a substantial longwaveshift of the intensive bands of this type. This suggests a dramatic redistribution of electronic density as a result of the C–C conjugation and the extension of the quasiaromatic systems. NMR spectra of these bis-cage complexes confirm the influence of their ribbed substituents on the preferential conformational state around the torsion CvC–CvC angle between their macrobicyclic entities. For all of them (except for the dimethino-bis-clathrochelate), four types of ribbed phenyl sub-
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stituents were observed in 13C NMR spectra, showing the absence of an additional mirror plane, which would be determined by ψ close to 0 or 180° (Fig. S2†). The same nonequivalence is induced in the azomethine region of these spectra, with its level depending on the value of ψ in a non-linear manner. In contrast, the spectrum of the iron(II) dimethinobis-clathrochelate shows half as much signals in the aromatic region, which is in line with its higher symmetry (vide supra) and the corresponding angle ψ close to 0 or 180°; the latter being in good agreement with its crystallographic value of 160.85(5)° (Table 1).
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Electrochemistry Electrochemical properties of the C–C conjugated iron(II) bisclathrochelates were studied by cyclic voltammetry (CV); the CV data are summarized in Table 3. All redox waves in these CVs are characteristic of the diffusion-controlled current processes (as follows from the linear plot of Ip versus v1/2, where v is the scan rate). They have similar shapes and contain two one-electron waves both in their anodic and cathodic ranges; a typical CV curve is shown in Fig. 9. The first one, which is in the cathodic range and assigned to the redox processes Fe2+/+, is quasireversible with the current Ic/Ia ratio for direct and backward redox processes equal to 1. This indicates that the anionic FeIIFeI bis-clathrochelate species shown in Scheme 8 resulting from the metal-centered Fe2+/+ reductions are stable on the CV time scale. In the backward scanning of potentials, the re-oxidation Fe+/2+ wave is observed in all CVs; ΔE = Ecp − Eap values that characterize the reversibility of a redox process are in the range 110–140 mV. This suggests significant structural rearrangements after the one-electron reduction. The second reduction wave is irreversible; so the double-reduced dianionic FeIFeI bis-macrobicyclic species are chemically unstable and undergo further irreversible reaction of a complete decomposition of only one of their two cage frameworks. As can be seen from Fig. 9, in the backward scanning of potentials after the second reduction process the re-oxidation peak characteristic of the iron(II) monoclathrochelates is observed in the CVs of the iron(II) bis-clathrochelates.
Fig. 9 CV for a 1 mM dichloromethane solution of the bis-clathrochelate {FeBd2(BrGm)(BF)2}2 at a scan rate of 200 mV s−1.
Electrochemical oxidation can proceed either simultaneously at both the redox-active metallocenters to give the dicationic FeIIIFeIII bis-clathrochelate species or stepwise to the cationic mixed-valence FeIIIFeII binuclear complex and then to the above homobinuclear FeIIIFeIII compound. Indeed, all these CVs contain two one-electron quasi-reversible oxidation waves in their anodic ranges that suggest stepwise metalcentered FeIIFeII → FeIIFeIII → FeIIIFeIII oxidation as shown in Scheme 9. These oxidation potentials depend on the nature of the ribbed functionalizing substituent, and they shift to the anodic range with an increase in their electromeric Hammett σpara constants. CV is also a convenient method to study electronic interactions between two redox-active metallocenters of a binuclear complex. Its conproportionation constant Kcon is a quantitative characteristic of the thermodynamic stability of the mixedvalence compounds formed on the first stage of this stepwise nFðΔEÞ process and can be calculated as follows: lg K con ¼ . RT
Table 3 Oxidation (Eox) and reduction (Ered) potentials (mV) and Kcom values for the iron(II) bis-clathrochelates and their monoclathrochelate analogs
Oxidation, Eox
Reduction, Ered
Complex
E01
E02
ΔE
Kcon
Ep1c
Ep1a
ΔE
Ep2c
{FeBd2(BrGm)(BF)2}2 {FeBd2(IGm)(BF)2}2 {FeBd2(HGm)(BF)2}2 {FeBd2((para-HOOCC6H4S)Gm)(BF)2}2 {FeBd2(NH2Gm)(BF)2}2 {FeBd2(((CH2)5N)Gm)(BF)2}2 {FeBd2((meta-HOOCC6H4S)Gm)(BF)2}2 {FeBd2(ClGm)(BF)2}2 {FeBd2(CH3O(CH2)2NHGm)(BF)2}2 FeBd2(I2Gm)(BF)2 FeBd2(Br2Gm)(BF)2 FeBd2(Cl2Gm)(BF)2 FeBd2Gm(BF)2
1670 1690 1680 1660 1410 1540 1660 1740 1430 1350 1420 1580 1290
1760 1790 1780 1740 1520 1660 1740 1860 1550
90 100 100 80 110 120 80 120 120
33.34 49.22 49.22 22.58 84.22 107.3 22.58 107.3 107.3
−770 −710 −590 −600 −880 −950 −600 −650 −920 −1100 −945 −870 −1230
−660 −600 −460 −485 −760 −800 −485 −560 −800 Irreversible −840 −770
110 110 130 115 120 150 115 85 120
−1310 −1350 −1200 −1000 −1250 −1380 −1000 −1110 −1360
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105 100
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Scheme 8
Stepwise electrochemical reduction of the C–C conjugated iron bis-clathrochelates.
Scheme 9
Stepwise electrochemical oxidation of the C–C conjugated iron bis-clathrochelates.
If the Kcon value approaches zero, the metallocenters do not interact with each other. One of the possible reasons for this effect can be the absence of suitable pathways for charge transfer between them; these systems belong to Class I by classification of Robin and Day.14 Low values of Kcon constants suggest a weak electronic interaction between their metallocenters and are characteristic of the binuclear complexes with a small overlap between the orbitals of one metallocenter either with those of the second ligand
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system or with the orbital localized on the second metallocenter (Class II of the same classification). High Kcon values suggest complete delocalizion of the electron density with substantial differences between the two reversible waves and strong interactions between the metallocenters (Class III). As in our case all these redox processes are quasireversible or irreversible, the E values obtained by CV are not exactly the thermodynamic redox potentials. As this hampers the esti-
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clathrochelate entity are practically the same: the remoteness of a given substituent at a distance of one σ-bond (i.e. the C–C bond between the clathrochelate entities in our case) decreases its electronic effect by a factor of 2.5–3.16 Therefore, the electron-withdrawing effects of polyazomethine cage substituents are more similar to that of the chlorine atom rather than to that of the iodine atom.
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Conclusions
Fig. 10 DPV for a 1 mM dichloromethane solution of the bis-clathrochelate {FeBd2(BrGm)(BF)2}2 at a scan rate of 200 mV s−1.
mation of such interactions between their redox-active metallocenters, we used differential pulse voltammetry (DPV) to obtain the standard redox potentials for these bis-cage systems. The difference between the potentials of two reversible waves (Fig. 10) characterizes the thermodynamic stability of the corresponding bis-macrobicyclic mixed-valence complex FeIIFeIII.15 For the C–C conjugated iron(II) bis-clathrochelates, the Kcon values calculated by the above equation are relatively low and fall in the range 33–107; these complexes belong to Class II according to the Robin–Day classification. Therefore, the encapsulated iron ions in their mixed-valence FeIIFeIII bis-cage compounds interact only slightly and may be divided into two groups. For those with Kcon less than 50, the interaction between their caged metallocenters is negligible and an electronic conjugation between the macrobicyclic entities is practically absent; their ribbed substituents do not affect the magnitudes of Kcon. For those with Kcon three times higher, an electronic conjugation is observed and their encapsulated metallocenters have mutual electronic effects. The molecular orbitals of these cage frameworks are substantially overlapped causing an additional electronic exchange between the encapsulated redox-active metallocenters of these binuclear complexes. We also compared the redox properties of the C–C conjugated iron(II) bis-clathrochelate complexes with those of the parent iron(II) monoclathrochelates (Table 3). Going from these mononuclear complexes to their bis-cage analogs causes a shift of both the metal-centered oxidation Fe2+/3+ and reduction Fe2+/+ potentials to the anodic range. This suggests the electron-withdrawing effect of a polyazomethine cage framework that depends on the nature of a ribbed substituent in its C–C conjugated chelate fragment. For the methine- and iodine-containing cage complexes, the shift is 390 and 320 mV, respectively. For their bromine- and chlorine-containing analogs it decreases to 250 and 160 mV. Thus, the anodic shift decreases with an increase in the electronegativity of the ribbed substituents. The electronic effects of the second
17944 | Dalton Trans., 2014, 43, 17934–17948
Chemical transformations of the iron(II) dihalogenoclathrochelates in the presence of an acetonitrile copper(I) solvatocomplex depend on both the nature of halogen atoms in their ribbed chelate fragments and reaction conditions (i.e. solvent and temperature). Under ambient reaction conditions, dibromine- and diiodine-containing macrobicyclic precursors undergo copper(I)-promoted homocoupling to give the corresponding C–C conjugated dihalogeno-bis-clathrochelates. Under vigorous reaction conditions, the initial copper(I) solvato-complex undergoes re-solvation and disproportionation leading to Cu2+ ions and nano-copper; a tandem copper(0)-promoted homocoupling–hydrodehalogenation reaction, giving the C–C conjugated iron(II) dimethino-bis-clathrochelate, takes place even at room temperature. The most probable pathway of this reaction in situ includes hydrodehalogenation of the already formed dihalogeno-bis-clathrochelate via the formation of reduced anion radical intermediates. Nucleophilic substitution with various N,S-nucleophiles under mild reaction conditions of the C–C conjugated iron(II) dihalogeno-bis-clathrochelates obtained led to ribbed-functionalized bis-cage complexes. These binuclear compounds undergo stepwise electrochemical reduction and oxidation resulting in the mixed-valence FeIIFeI and FeIIFeIII bis-cage intermediates.
Experimental section General considerations The reagents used, FeCl2·4H2O, α-benzyldioxime (denoted as H2Bd), BF3·O(C2H5)2, 2-methoxyethylamine, piperidine, metaand para-mercaptobenzoic acids, triethylamine, sorbents, acids, bases, and organic solvents were obtained commercially (SAF). The solvato-complex [Cu(CH3CN)4](BF4) was prepared as described in ref. 17. The diiodoclathrochelate and heterohalogenide iodochloroclathrochelate precursors FeBd2(I2Gm)(BF)2 and FeBd2(IGmCl)(BF)2 were obtained as described elsewhere.6,18 Analytical data (C, H, N contents) were obtained using a Carlo Erba model 1106 microanalyzer. The iron content was determined spectrophotometrically. The bromine content was determined by titrimetry using the Shoeniger method. MALDI-TOF mass spectra were recorded in both the positive and negative spectral regions using a MALDI-TOF-MS Bruker Autoflex mass spectrometer in reflecto-mol mode. The ionization was induced using a UV-laser with a wavelength of
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336 nm. The sample was applied on a nickel plate, and 2,5dihydroxybenzoic acid was used as a matrix. The accuracy of measurements was 0.1%. IR spectra of the solid sample (KBr tablets) in the range 400–4000 cm−1 were recorded with a Nicolet Magna-IR 750 FTIR-spectrophotometer. UV-vis spectra of the solutions in dichloromethane were recorded in the range 230–800 nm with a Lambda 9 Perkin Elmer spectrophotometer. The individual Gaussian components of these spectra were calculated using the SPECTRA program. 1 H and 13C{1H} NMR spectra of the complexes obtained were recorded from their CD2Cl2 solutions using Bruker Avance 400 and Bruker Avance 600 spectrometers. 57 Fe Mössbauer absorption spectra were recorded at 77 and 298 K using a NP-255 spectrometer (Hungary) with a constant acceleration mode and a symmetrical triangular change in the velocity of a γ-quantum source (57Co in a rhodium matrix with an activity equal to 5 mCu and with a line emission width equal to 0.11 mm s−1). The spectra were collected with a 511-multichannel analyzer. The speed scale of the spectrometer was calibrated using the spectrum of sodium nitroprusside as a standard. The isomeric shift (IS) values were obtained relative to the center of this spectrum. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) experiments were carried out in dichloromethane solutions with 0.1 M ((n-C4H9)4N)(BF4) as the supporting electrolyte using a model Parstat 2273 (Princeton Applied Research, USA) potentiostat with a conventional and one-compartment threeelectrode cell (10 ml of solution). A platinum disk electrode with an active surface area of 0.125 cm2 was used as a working electrode. The electrode was thoroughly polished and rinsed before measurements. A platinum counter electrode and a standard Ag/AgCl/KClaq. reference electrode (RE) were applied. All solutions were thoroughly deaerated by passing argon through the solution before the CV experiments and above the solution during the measurements. Synthesis Preparation of FeBd2(Br2Gm)(BF)2. This complex was prepared as described in ref. 2. Anal. calc. for C30H20N6O6B2F2Br2Fe (%): C, 43.11; H, 2.41; N, 10.06; Fe, 6.68; Br, 19.12. Found (%): C, 43.04; H, 2.35; N, 10.13; Fe, 6.77; Br, 18.91. MS (MALDI-TOF): m/z (I, %) ( positive range) 676(15) [M − 2Br]+•, 836(100) [M]+•, 859(20) [M + Na+]+, 875(10) [M + K+]+; (negative range) −836 [M]−•. 1H NMR (CD2Cl2) δ ( ppm): 7.32 (m, 20H, Ph). 13C{1H} NMR (CD2Cl2) δ ( ppm): 123.41 (s, BrCvN), 127.98, 130.05, 130.44, 130.80 (all s, Ph), 157.46 (PhCvN). IR (KBr), ν/cm−1 914, 1000, 1066 ν(N–O), 1219m ν(B–O) + ν(B–F), 1546 ν(BrCvN), 1579 ν(PhCvN). UV-vis (CH2Cl2): λmax/nm (ε 10−3 mol−1 L cm−1) 264(28), 285 (6.2), 299(10), 329(3.4), 386(3.5), 440(3.4), 470(30). 57Fe Mössbauer (mm s−1): IS = 0.33; QS = 0.47. Preparation of {FeBd2(BrGm)(BF)2}2. This complex was prepared as described in ref. 2. Anal. calc. for C60H40N12O12B4F4Br2Fe2 (%): C, 47.63; H, 2.64; N, 10.06; Fe,
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7.40. Found (%): C, 47.54; H, 2.70; N, 10.00; Fe, 7.23. MS (MALDI-TOF): m/z (I, %) ( positive range, matrix: DHB) 1512(5) [M]+•, 1535(100) [M + Na+]+, 1551(25) [M + K+]+, 1597(70) [M + Rb+]+, 1645(100) [M + Cs+]+; (negative range, matrix: nitroaniline) −1512 [M]−•. 1H NMR (CD2Cl2) δ ( ppm): 7.26 (m, 40H, Ph). 13C{1H} NMR (CD2Cl2) δ ( ppm): 119.58 (s, BrCvN), 128.30, 128.19, 128.12, 128.10 (all s, meta-Ph), 128.99, 128.91, 128.84, 128.81 (all s, ipso-Ph), 130.63, 130.57, 130.50 (all s, para-Ph), 130.78, 130.72, 130.67 (all s, ortho-Ph), 157.92, 157.85, 157.82, 157.44 (all s, PhCvN). IR (KBr), ν/cm−1 932m, 1066, 1110, 1142 ν(N–O), 1219m ν(B–O) + ν(B–F), 1549m ν(BrCvN) + ν(C–CvN), 1581 ν(PhCvN). UV-vis (CH2Cl2): λmax/ nm (ε 10−3 mol−1 L cm−1) 239(33), 263(21), 282(18), 301(12), 388(7.0), 435(9.8), 461(18), 509(25). 57Fe Mössbauer (mm s−1): IS = 0.35; QS = 0.51. Preparation of {FeBd2(ClGm)(BF)2}2. Complex FeBd2(IClGm)(BF)2 (0.22 g, 0.26 mmol) was dissolved/suspended in HMPA (5 ml) and the solvato-complex [Cu(CH3CN)4](BF4) (0.4 g, 1.3 mmol) was added to the stirring reaction mixture under argon. The reaction mixture was stirred for 40 min at 80 °C, the reaction course was controlled by TLC (SiO2 foil, eluent: dichloromethane–hexane 3 : 1 mixture). Then the reaction mixture was cooled to r.t. and precipitated with 2% aqueous HCl (50 ml). The precipitate was filtered off, washed with methanol and extracted with dichloromethane (5 ml). The extract was dried with Na2SO4 and filtered through a silica gel (Silasorb SPH-300, 10-mm layer; eluent: dichloromethane). The filtrate was precipitated with hexane; the precipitate formed was washed with methanol, diethyl ether and hexane, and dried in vacuo. Yield: 0.054 g (29%). Anal. calc. for C60H40N12O12B4F4Cl2Fe2 (%): C, 50.65; H, 2.83; N, 11.81. Found (%): C, 49.83; H, 2.70; N, 11.48. MS (MALDI-TOF): m/z (I, %) ( positive range) 1423(30%) [M]+•, 1446(100%) [M + Na+]+, 1462(40%) [M + K+], (negative range) −1423 [M]−•. 1H NMR (CD2Cl2) δ 7.50–7.30 (m, 40H, Ph). 13C{1H} NMR (CD2Cl2) δ ( ppm) 128.03, 128.08, 128.09, 128.12 (meta-Ph), 128.80, 128.87, 128.92 (ipso-Ph), 130.54, 130.56, 130.61, 130.62 ( para-Ph), 130.63, 130.67, 130.68, 130.70 (ortho-Ph), 139.50 (Cl–CvN), 142.87 (Cl–C–CvN), 157.36, 157.69, 157.79, 157.91 (PhCvN). IR (KBr), ν/cm−1 939, 1068, 1109, 1147 ν(N–O), 1221 ν(B–O) + ν(B–F), 1551 ν(ClCvN) + ν(C–CvN), 1581 ν(PhCvN). UV-vis (CH2Cl2): λmax/nm (ε10−3 mol−1 L cm−1) 262(45), 283(20), 304(17), 390(8.7), 445(13), 465(26), 519(25). Preparation of {FeBd2(IGm)(BF)2}2. Complex FeBd2(I2Gm)(BF)2 (0.345 g, 0.37 mmol) was dissolved/suspended in HMPA (5 ml) and the solvato-complex [Cu(CH3CN)4](BF4) (0.58 g, 1.85 mmol) was added to the stirring reaction mixture under argon. The reaction mixture was stirred for 30 min at 70 °C. The product was isolated and purified as described above for the complex {FeBd2(ClGm)(BF)2}2. Yield: 0.26 g (88%). Anal. calc. for C60H40N12O12B4F4I2Fe2 (%): C, 44.84; H, 2.49; N, 10.46; Fe, 6.96. Found (%): C, 44.56; H, 2.46; N, 10.00; Fe, 6.81. MS (MALDI-TOF): m/z ( positive range) 1606 [M]+; (negative range) −1606 [M]−•. 1H NMR (CD2Cl2) δ 7.50–7.25 (m, 40H, Ph). 13C{1H} NMR (CD2Cl2) δ ( ppm) 97.67 (s, ICvN), 128.29,
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128.38, 128.50 (meta-Ph), 129.03, 129.05, 129.06, 129.17 (ipsoPh), 130.73, 130.80, 130.83 ( para-Ph), 130.90, 130.91, 130.94, 130.99 (ortho-Ph), 146.36 (s, C–CvN), 157.47, 157.75, 157.89 (PhCvN). IR (KBr), ν/cm−1 916, 940, 1064, 1108, 1137 ν(N–O), 1218 ν(B–O) + ν(B–F), 1547 ν(ICvN) + ν(C–CvN), 1580 ν(PhCvN). UV-vis (CH2Cl2): λmax/nm (ε10−3 mol−1 L cm−1) 262(44), 283(18), 298(19), 368(7.9), 428(9.7), 462(26), 495(23), 516(7.5). 57Fe Mössbauer (mm s−1): IS = 0.30; QS = 0.36. Preparation of {FeBd2(HGm)(BF)2}2. The solvato-complex [Cu(CH3CN)4](BF4) (0.31 g, 1 mmol) was dissolved in NMP (3 ml) under argon and the reaction mixture was stirred at 140 °C for 5 min; its color changed from olive to dark-brown. Then the reaction mixture was cooled to 100 °C and the complex FeBd2(Br2Gm)(BF)2 (0.30 g, 0.2 mmol) was added. The reaction mixture was stirred at 110 °C for 45 min; the reaction course was controlled by TLC (SiO2 foil, eluent: dichloromethane–hexane 3 : 1 mixture). Then an additional portion of the solvato-complex [Cu(CH3CN)4](BF4) (0.15 g, 0.48 mmol) was added. The reaction mixture was stirred at 110 °C for 30 min, cooled to r.t. and precipitated with 2% aqueous HCl (20 ml). The product obtained was isolated and purified as described above for the complex {FeBd2(ClGm)(BF)2}2. Yield: 0.115 g (85%). Anal. calc. for C60H42N12O12B4F4Fe2 (%): C, 53.23; H, 3.13; N, 12.41; Fe, 8.25; B, 3.19; F, 5.61. Found (%): C, 53.67; H, 2.92; N, 10.97; Fe, 7.94; B, 3.20; F, 4.88. MS (MALDITOF): m/z (I, %) ( positive range) 1354(100%) [M]+•, 1377(70%) [M + Na+]+, 1393(50%) [M + K+]+, (negative range) −1354 [M]−•. 1 H NMR (CD2Cl2) δ 8.92 (s, 2H, NvC–H), 7.50–7.35 (m, 40H, Ph). 13C{1H} NMR (CD2Cl2) δ ( ppm) 128.09 (meta-Ph), 128.90, 128.87 (ipso-Ph), 130.51, 130.47 ( para-Ph), 130.57, 130.55 (two s, ortho-Ph), 140.97 (s, HC–CvN), 146.26 (s, HCvN), 157.30, 156.81 (two s, PhCvN). IR (KBr), ν/cm−1 929, 1064, 1110, 1135 ν(N–O), 1218 ν(B–O) + ν(B–F), 1545 ν(HCvN) + ν(C–CvN), 1580 ν(PhCvN). UV-vis (CH2Cl2): λmax/nm (ε10−3 mol−1 L cm−1), 262(19), 279(27), 305(14), 346(6.0), 415(6.9), 465(26), 529(15), 567(24). Preparation of {FeBd2(( para-HOOCC6H4S)Gm)(BF)2}2. The complex {FeBd2(BrGm)(BF)2}2 (0.20 g, 0.13 mmol) and paramercaptobenzoic acid (0.06 g, 0.39 mmol) were dissolved in DMF (4 ml), and triethylamine (0.09 ml, 0.65 mmol) was added dropwise to the stirring reaction mixture under argon. The reaction mixture was stirred for 30 min and then precipitated with mixed 2% HCl and 4% KCl aqueous solution (50 ml). The precipitate formed was filtered off, washed with water and methanol, and dried in air. The solid was dissolved/ suspended in dichloromethane (35 ml) and precipitated with diethyl ether (70 ml). The precipitate was washed with diethyl ether and hexane, and dried in vacuo. Yield: 0.185 g (94%). Anal. calc. for C64H50N12O16B4F4S2Fe2 (%): C, 53.60; H, 3.05; N, 10.14. Found (%): C, 53.60; H, 3.09; N, 10.16; Fe. MS (MALDITOF): m/z (I, %) ( positive range) 1599(30) [M − COO− − O]+, 1643(90) [M − O]+•, 1659(100) [M]+•, 1682(50) [M + Na+]+, 1698(35) [M + K+]+; (negative range) −1586(90) [M − COOH − CO]−•, −1659(100) [M]−•. 1H NMR (CD2Cl2) δ ( ppm): 6.50 (d, 4H, C6H4), 7.18 (d, 4H, C6H4), 7.22 (m, 8H, Ph), 7.29 (m, 16H, Ph), 7.38 (m, 16H, Ph). 13C{1H} NMR (CD2Cl2) δ ( ppm): 124.28
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Dalton Transactions
(s, C6H4), 127.13 (s, C6H4), 128.07, 128.13, 128.42, 128.54 (all s, meta-Ph), 128.67, 128.74, 128.83 (all s, ipso-Ph), 130.19, 130.39, 130.67 (all s, ortho-Ph), 130.55, 130.91, 130.99 (all s, para-Ph), 138.92 (s, C6H4), 139.13 (s, SCvN), 144.60 (s, C–CvN), 156.94, 157.59, 157.76, 157.83 (all s, PhCvN), 171.58 (s, COOH). IR (KBr), ν/cm−1 930, 1068, 1110, 1144 ν(N–O), 1218m ν(B–O) + ν(B–F), 1554 ν(C–CvN) + ν(SCvN), 1593 ν(PhCvN). UV-vis (CH2Cl2): λmax/nm, (ε10−3 mol−1 L cm−1) 238(12), 269(35), 302(10), 362(4.7), 416(4.6), 458(15), 512(13), 530(5.8). Preparation of {FeBd2((meta-HOOCC6H4S)Gm)(BF)2}2. The complex {FeBd2(BrGm)(BF)2}2 (0.43 g, 0.28 mmol) and metamercaptobenzoic acid (0.13 g, 8.4 mmol) were dissolved in DMF (7 ml), and triethylamine (0.45 ml, 3.2 mmol) was added dropwise to the stirring reaction mixture under argon. The reaction mixture was stirred for 30 min and then precipitated with mixed 2% HCl and 4% KCl aqueous solution (100 ml). The precipitate formed was filtered off, washed with water, methanol and diethyl ether, and dried in vacuo. Yield: 0.43 g (92%). Anal. calc. for C64H50N12O16B4F4S2Fe2 (%): C, 53.60; H, 3.05; N, 10.14. Found (%): C, 53.49; H, 3.15; N, 10.06. MS (MALDI-TOF): m/z (I, %) ( positive range) 1599(35) [M − COO− − O]+, 1643(95) [M − O]+•, 1659(100) [M]+•, 1682(70) [M + Na+]+, 1698(6) [M + K+]+; (negative range) −1506(20) [M − HCOOC6H4S]−•, −1659(100) [M]−•. 1H NMR (CD2Cl2) δ ( ppm): 7.09 (m, 8H, Ph), 7.16 (m, 4H, C6H4), 7.21 (m, 16H, Ph), 7.29 (m, 16H, Ph), 7.63 (m, 4H, C6H4). 13C{1H} NMR (CD2Cl2) δ ( ppm): 128.13, 127.98, 127.96 (all s, meta-Ph), 128.24, 128.28 (s, C6H4), 129.15, 129.08, 129.01 (all s, ipso-Ph), 130.25, 130.18, 130.00, 129.77 (all s, para-Ph), 130.91, 130.69, 130.44 (all s, ortho-Ph), 133.24, 133.17, 133.04 (all s, C6H4), 139.44 (s, SCvN), 145.45 (s, C–CvN), 156.71, 156.83, 156.90, 157.35 (all s, PhCvN), 169.61 (s, COOH). IR (KBr), ν/cm−1 928, 1066, 1109, 1147 ν(N–O), 1218m ν(B–O) + ν(B–F), 1554 ν(C–CvN) + ν(SCvN), 1595 ν(PhCvN). UV-vis (CH2Cl2): λmax/nm, (ε10−3 mol−1 L cm−1) 245(42), 270(28), 296(21), 358(6.8), 442(14), 465(17), 519(11), 526(16). Preparation of {FeBd2(NH2Gm)(BF)2}2. The complex {FeBd2(BrGm)(BF)2}2 (0.25 g, 0.17 mmol), THF (2 ml) and liquid ammonia (2 ml) were placed in a 7 ml volume steel autoclave at −40 °C. The reaction mixture was autoclaved at 70 °C for 2 h, then cooled to −40 °C and evaporated to dryness. The solid residue was dissolved in dichloromethane, the solution was filtered through a silica gel (Silasorb SPH-300, 30-mm layer, eluent: dichloromethane) and precipitated with hexane. The precipitate formed was filtered off, washed with methanol and dried in vacuo. Yield: 0.11 g (47%). Anal. calc. for C60H44N14O12B4F4Fe2 (%): C, 52.07; H, 3.20; N, 14.17. Found (%): C, 51.96; H, 3.10; N, 14.12. MS (MALDI-TOF): m/z (I, %) ( positive range) 1337(10) [M − O − 2NH2]+•, 1369(75) [M − NH2]+•, 1385(100) [M]+•, 1408(35) [M + Na+]+, 1424(40) [M + K+]+; (negative range) −1369(90) [M − NH2]−•, −1385(100) [M]−•. 1H NMR (CD2Cl2) δ ( ppm): 5.83 (d, 4H, NH2), 7.27 (m, 40H, Ph). 13C{1H} NMR (CD2Cl2) δ ( ppm): 128.26, 128.12, 128.06 (all s, meta-Ph), 129.16, 129.09, 129.02, 128.96 (all s, ipso-Ph), 130.52, 130.37, 130.35 (all s, para-Ph), 130.74, 130.64, 130.58, 130.49 (all s, ortho-Ph), 139.01 (s, NCvN), 149.97 (s,
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Dalton Transactions
C–CvN), 158.59, 156.45, 156.41 (all s, PhCvN). IR (KBr), ν/cm−1 930, 1059, 1108, 1159 ν(N–O), 1213m ν(B–O) + ν(B–F), 1545 ν(C–CvN) + ν(NCvN), 1580m ν(PhCvN), 1638 δ(N–H), 3377 ν(N–H). UV-vis (CH2Cl2): λmax/nm (ε10−3 mol−1 L cm−1) 264(27), 285(10), 296(18), 323(9.0), 382(6.4), 442(8.7), 478(20), 508(14), 568(18), 598(5.8). Preparation of {FeBd2(((CH2)5N)Gm)(BF)2}2. The complex {FeBd2(BrGm)(BF)2}2 (0.060 g, 0.04 mmol) was dissolved in DMSO (2.5 ml) at 70 °C, and piperidine (0.027 g, 0.3 mmol) was added to the stirring reaction mixture under argon. The reaction mixture was stirred for 4 h and then precipitated with 4% aqueous KCl solution (20 ml). The precipitate formed was filtered off, washed with water, methanol and diethyl ether, and dried in vacuo. Yield: 0.058 g (95%). Anal. calc. for C70H60N14O12B4F4Fe2 (%): C, 55.30; H, 3.98; N, 12.90; Fe, 7.35. Found (%): C, 55.48; H, 3.83; N, 12.80; Fe, 7.24. MS (MALDI-TOF): m/z (I, %) 1521(100) [M]+•, 1544(55) [M + Na+]+, 1560(75) [M + K+]+. 1H NMR (CD2Cl2) δ ( ppm): 1.44 (m, 8H, β-piperidyl), 2.42 (m, 4H, γ-piperidyl), 3.30 (m, 8H, α-piperidyl), 7.11 (m, 4H, Ph), 7.16 (m, 4H, Ph), 7.25 (m, 4H, Ph), 7.37 (m, 4H, Ph). 13C{1H} NMR (CD2Cl2) δ ( ppm): 23.68 (s, γ-piperidyl), 26.23 (s, β-piperidyl), 50.99 (s, α-piperidyl), (s, BrCvN), 128.11, 128.09, 127.96, 127.92 (all s, meta-Ph), 129.28, 129.14, 129.11, 129.03 (all s, ipso-Ph), 130.30, 130.21, 130.11 (all s, para-Ph), 130.83, 130.69, 130.58, 130.38 (all s, ortho-Ph), 143.80 (s, C–CvN), 152.48 (s, NCvN), 158.43, 157.73, 156.91, 156.68 (all s, PhCvN). IR (KBr), ν/cm−1 923, 941, 992, 1061, 1110, 1133, 1152, 1182 ν(N–O), 1211m ν(B–O) + ν(B–F), 1589m ν(CvN). UV-vis (CH2Cl2): λmax/nm (ε10−3 mol−1 L cm−1) 253(41), 266(4.3), 288(31), 310(10), 399 (7.0), 477(12), 489(21), 545(18). 57Fe Mössbauer (mm s−1): IS = 0.35; QS = 0.44. Preparation of {FeBd2(CH3O(CH2)2NHGm)(BF)2}2. The complex {FeBd2(BrGm)(BF)2}2 (0.060 g, 0.04 mmol) was dissolved in DMF (3 ml), and 2-methoxyethylamine (0.10 ml, 1.3 mmol) was added to the stirring reaction mixture under argon. The reaction mixture was stirred for 24 h and then precipitated with 0.5% aqueous HCl solution (30 ml). The precipitate formed was extracted with chloroform, the extract was evaporated to a small volume (∼2 ml) and precipitated with hexane. The precipitate was filtered off, washed with diethyl ether and hexane, and dried in vacuo. Yield: 0.033 g (55%). Anal. calc. for C66H56N14O14B4F4Fe2 (%): C, 52.84; H, 3.76; N, 13.07. Found (%): C, 52.66; H, 3.88; N, 12.92. MS (MALDI-TOF): m/z (I, %) ( positive range) 1485(30) [M − O]+•, 1501(100) [M]+•, 1524(35) [M + Na+]+, 1540(25) [M + K+]+. 1H NMR (CD2Cl2) δ ( ppm): 3.15 (s, 6H, CH3), 3.15 (m, 8H, CH2CH2), 7.23 (m, 40H, Ph). 13C{1H} NMR (CD2Cl2) δ ( ppm): 46.20 (s, NCH2), 60.72 (s, CH3), 73.58 (s, OCH2), 130.06, 130.00, 129.93 (all s, meta-Ph), 131.32, 131.28, 131.21, 131.19 (all s, ipso-Ph), 132.21, 132.17, 132.09, 132.01 (all s, para-Ph), 132.67, 132.59, 132.56, 132.46 (all s, ortho-Ph), 141.72 (s, NCvN), 152.54 (s, C–CvN), 159.98, 159.77, 158.92, 158.25 (all s, PhCvN). UV-vis (CH2Cl2): λmax/nm (ε10−3 mol−1 L cm−1) 251(28), 276(34), 292(8.4), 357(9.1), 427(9.0), 474(140), 500(22), 555(12), 645(4.1).
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Paper
X-ray crystallography Single crystals of a new polymorph of the dibromomonoclathrochelate precursor FeBd2(Br2Gm)(BF)2·CH2Cl2 and the bisclathrochelates {FeBd2(HGm)(BF)2}2·3C6H6, and {FeBd2(IGm)(BF)2}2·6C6H5Cl, were grown from dichloromethane–hexane, benzene–iso-octane mixtures and chlorobenzene, respectively, at room temperature. The intensities of reflections were measured at 120(2) and 100(2) K, respectively, with a Bruker Apex II CCD diffractometer using graphite monochromated Mo–Kα radiation (λ = 0.71073 Å). Transmission coefficients were determined using the SADABS program.19 The structures were solved by the direct method and refined by full-matrix least squares against F2. Non-hydrogen atoms were refined in anisotropic approximation. The unit cell of the crystal {FeBd2(HGm)(BF)2}2·3C6H6 contains highly disordered solvate benzene molecules, which have been treated as a diffuse contribution to the overall scattering without specific atom positions by SQUEEZE/PLATON;20 the chemical formula, formula weight and density were calculated taking the solvate molecules into account. Positions of the H(C) atoms were calculated geometrically and included in the refinement by the riding model with Uiso(H) = 1.2Ueq(C). All calculations were made using the SHELXTL PLUS and OLEX2 software.21,22 The crystallographic data and experimental details are listed in Table S1 (see ESI†). The specific features of the intermolecular interactions in these X-rayed crystals were studied using the Hirshfeld surface partitioning23 with the CrystalExplorer3.0 program package.24
Acknowledgements The synthesis and characterisation of bis-clathrochelates were supported by RSCF project no. 14-13-00724. Y.Z. Voloshin and O.A. Varzatskii also acknowledge the support of RFBR (grants 12-03-00961, 13-03-90452, 13-03-00570 and 14-03-00384) and the Marie Curie International Research Staff Exchange Scheme (IRSES) of the 7th EU Framework Program (grant 295160).
References 1 V. V. Novikov, O. A. Varzatskii, V. V. Negrutska, Y. N. Bubnov, L. G. Palchykovska, I. Y. Dubey and Y. Z. Voloshin, J. Inorg. Biochem., 2013, 124, 42. 2 O. A. Varzatskii, V. V. Novikov, S. V. Shulga, A. S. Belov, A. V. Vologzhanina, V. V. Negrutska, I. Y. Dubey, Y. N. Bubnov and Y. Z. Voloshin, Chem. Commun., 2014, 50, 3166. 3 M. Y. Losytskyy, V. B. Kovalska, O. A. Varzatskii, A. M. Sergeev, S. M. Yarmoluk and Y. Z. Voloshin, J. Fluoresc., 2013, 23, 889. 4 V. B. Kovalska, M. Yu. Losytskyy, O. A. Varzatskii, V. V. Cherepanov, Y. Z. Voloshin, A. A. Mokhir,
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