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Mono- and polynuclear Ag(I) complexes of N-functionalized bis(diphenylphosphino)amine DPPA-type ligands: synthesis, solid-state structures and reactivity† Alessio Ghisolfi,*‡a Christophe Fliedel,*b Pierre de Frémontc and Pierre Braunstein*a The reactivity of the N-functionalized DPPA-type ligands (Ph2P)2N( p-Z)C6H4 [Z = H (1a), SMe (1b), OMe (1c)] with AgBF4 was investigated and revealed an unexpected influence of the para substituent Z of the N-aryl ligand. In acetone, the mononuclear bis-chelated [Ag{(1a–1c)-P,P}2]BF4 (2a·BF4–2c·BF4) and dinuclear bridged [Ag2{μ2-(1a–1c)-P,P}2](BF4)2 [3a·(BF4)2–3c·(BF4)2] complexes were obtained with a 1 : 2 and 1 : 1 AgBF4/ligand molar ratio, respectively. While the molecular structures of 2a·BF4 and 2b·BF4 determined in the solid-state by X-ray diffraction revealed their mononuclear nature and the absence of cation/anion interaction, complexes 3b·(BF4)2 and 3c·(BF4)2 form 2D coordination polymers through intermolecular Ag–S or Ag–O interactions, respectively, involving the N-function of the respective DPPAtype ligand, and display direct interactions between one BF4 anion and both Ag(I) cations. Surprisingly, the equimolar reaction between ligands 1a–1c and AgBF4 in CH2Cl2 led to different proportions of the dinuclear complexes 3a·(BF4)2–3c·(BF4)2 and clusters [Ag3(μ3-Cl)2{μ2-(1b–1c)-P,P}3]BF4 (4b·BF4–4c·BF4), depending on the nature of the para substituent Z of the N-aryl ligand. The trinuclear complexes resulted

Received 16th December 2016, Accepted 9th March 2017 DOI: 10.1039/c6dt04755f rsc.li/dalton

from C–Cl bond activation of the chlorinated solvent and were characterized by NMR spectroscopy and X-ray diffraction, and could be selectively produced by addition of 2/3 equiv. of [NMe4]Cl to the corresponding dinuclear complexes or by a one-pot procedure involving the correct amount of each reagent. A series of experiments and kinetic NMR investigations were performed to gain further insight into the formation of the trinuclear Ag3Cl2 core clusters.

Introduction a Université de Strasbourg, CNRS, CHIMIE UMR 7177, Laboratoire de Chimie de Coordination, 4 rue Blaise Pascal, CS 90032, 67081 Strasbourg, France. E-mail: [email protected], [email protected] b Laboratoire de Chimie de Coordination (LCC), CNRS – UPR 8241, 205 route de Narbonne, F-31077 Toulouse Cedex 4, France. E-mail: [email protected] c Université de Strasbourg, CNRS, CHIMIE UMR 7177, Equipe de Synthèse, Réactivité et Catalyse Organométallique, 4 rue Blaise Pascal, CS 90032, 67081 Strasbourg, France † Electronic supplementary information (ESI) available: 31P{1H} NMR spectra (Fig. S1–S5) and crystallographic and experimental details for all the structures (Tables S1–S7). CCDC 1497150–1497155 and 1497157 for 2a·BF4, 2b·BF4, 3b·(BF4)2, 3c·(BF4)2, 3c·(BF4)2·(THF)3, 4a·BF4·3(CH2Cl2) and 4c·BF4·CH2Cl2. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/ c6dt04755f ‡ Present address: Groupe Photocatalyse et Photoconversion, Institut de Chimie et des Procédés pour l’Energie, l’Environnement et la Santé (ICPEES), UMR 7515 CNRS/Université de Strasbourg, 25 rue Becquerel, 67087 Strasbourg Cedex, France.

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The coordination chemistry of short-bite ligands such as Ph2PCH2PPh2 (bis(diphenylphosphino)methane = DPPM) and Ph2PNHPPh2 (bis(diphenylphosphino)amine = DPPA, Chart 1, top) has been widely studied over the past years.1–4 However, this topic remains of continuing interest because of the often unique structural features and physical and chemical properties of their metal complexes and their numerous applications, e.g. in homogeneous and heterogeneous catalysis and materials science.5 These diphosphine ligands can act as chelates, forming strained four-membered rings, or as monodentate or bridging ligands, allowing in the latter case the stabilization of homo- and hetero-dinuclear complexes and metal clusters.6 This ability to bring metal centres in close proximity can promote metal–metal interactions and/or chemical transformations involving two or more metal centres.7–9 An advantage of DPPA over DPPM resides in the easy deprotonation of the N–H function, leading to a monoanionic P,P-bidentate or P,P,N-tridentate ligand (DPPA–H−, Chart 1, top),1,10,11 and

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Chart 1 Top: Short-bite DPPM and DPPA, and deprotonated DPPA–H− ligands. Bottom: N-substituted (1a) and N-functionalized (1b and 1c) DPPA-type ligands studied in this work.

facilitating derivatization of the nitrogen atom by various hydrocarbyl groups (such as 1a) or chemical functions (i.e. ligands 1b–1d), thus offering a myriad of possibilities (Chart 1, bottom).5,11 The terminology “N-substituted” and “N-functionalized” DPPA-type ligands may be conveniently used to distinguish the type of N-substituent, referring to pure hydrocarbyl groups in the former case or to a chemical function in the latter. The nature of the N-substituent can lead to specific reactivity or original coordination assemblies.5,12 In most cases, the synthesis of N-substituted/functionalized DPPA-type ligands is readily achieved by a one pot reaction between chlorodiphenylphosphine and the corresponding amine and allows an easy fine-tuning of the stereo-electronic properties of the resulting ligand. Over the last years, we examined the influence of the nature of the spacer between the PNP fragment and the additional donor function in N-thioether-functionalized DPPA-type ligands (1b, 1d and others) on their resulting metal complexes13–18 and their performances in catalytic oligomerization of ethylene19 or activation of Csp3–Cl bonds.20 We have also used S-functionalized DPPA-type ligands to anchor coordination complexes onto partially gold-covered Janus-type microspheres for a rapid, straightforward visual identification at the micrometer scale of suitable candidates for molecular electronics applications at the nanometer scale.21 Furthermore, alkoxysilyl-functionalized DPPA-type ligands and their metal complexes and clusters22,23 were successfully employed to functionalize inorganic mesoporous matrices.24,25 Short-bite diphosphine ligands are candidates of choice to support metallophilic d10–d10 interactions,26,27 and the broad impact of aurophilic28,29 and argentophilic30 interactions has been widely demonstrated. In particular, several recent reports deal with the synthesis of polynuclear gold complexes containing DPPA-type ligands and the study of their luminescence properties as a function of the nature of N-substituent.31–37 Furthermore, numerous silver complexes are efficient catalysts for organic transformations, and gaining more insight into the coordination chemistry of Ag ions and the stability/reactivity/

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solution behaviour of their complexes with such types of phosphorus ligands might lead to further developments.38,39 We recently investigated the coordination chemistry of the N-thioether-functionalized DPPA-type ligands (Ph2P)2N( p-SMe) C6H4 (1b) and (Ph2P)2N(CH2)3SMe (1d) towards Ag(I) ions, with the objective to determine the influence of a rigid phenylene or a flexible n-propyl spacer between the PNP moiety and the S-donor, respectively, on the nature of the resulting metal complexes (Chart 1).40,41 Given that the stoichiometric reaction between AgBF4 and the PNP ligands 1b and 1d did not lead to a similar outcome, and that the presence of an aromatic-based N-substituent appeared to influence the stability/reactivity of the resulting silver complexes, we extended our investigations by varying the nature of the N-aryl substituent and the ligand/ metal molar ratio. Herein, we report the synthesis and unambiguous characterization, both in solution and in the solid state, of mono-, diand tri-nuclear Ag(I) complexes containing the N-substituted/ functionalized DPPA-type ligands (Ph2P)2N( p-Z)C6H4 [Z = H (1a), SMe (1b), OMe (1c), Chart 1]. Despite their very similar structures, ligands 1a–1c, in combination with AgBF4, were found to exhibit a different reactivity in chlorinated solvents, clearly highlighting the non-innocent role of the para-substituent of the N-aryl group.

Results and discussion Synthesis, spectroscopic and structural characterization The known N-substituted/functionalized DPPA-type ligands 1a–1c were readily prepared by aminolysis of the corresponding primary amines.19,42,43 The reactions between 1a–1c and AgBF4 in a 2 : 1 molar ratio afforded the mononuclear, cationic bis-chelated complexes [Ag(P,P)2](BF4) (2a–2c), respectively, in good yield (75–91%, Scheme 1). The 31P{1H} NMR spectrum of 2a·BF4–2c·BF4 contains, in each case, two wellresolved doublets centred at 97.6, 97.9 and 97.8 ppm, respectively, with coupling constants of 1J (109Ag,31P) = 255 Hz and 1 107 J ( Ag,31P) = 221 Hz, corresponding to a gyromagnetic ratio γ(109Ag)/γ(107Ag) = 1.15, and in the expected range (200–1000 Hz) for such compounds.44,45 This spectral pattern is consistent with four equivalent phosphorus centres forming a tetrahedral coordination environment around the metal.

Scheme 1

Synthesis of complexes 2a·BF4–2c·BF4.

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The 1H NMR spectrum of 2a·BF4 exhibits two triplets and one doublet at 7.11, 6.91 and 6.20 ppm (3JH,H = 7.5 Hz), for 2Hpara, 4Hmeta and 4Hortho, respectively. The 1H NMR spectra of 2b·BF4 and 2c·BF4 are very similar, and display two doublets at 6.81 and 6.19 ppm (3JH,H = 8.6 Hz) and 6.47 and 6.18 ppm (3JH, H = 8.6 Hz), respectively, for the AB spin system corresponding to the four Hortho and four Hmeta, respectively. The SMe and OMe protons in 2b·BF4 and 2c·BF4 give rise to singlets at 2.33 and 3.62 ppm, respectively, close to the chemical shift values observed for the free ligands, indicating no intermolecular interactions involving the (thio)ether moieties in solution. The solid-state structures of complexes 2a·BF4 and 2b·BF4 were established by single crystal X-ray diffraction analysis. They are very similar and in agreement with those found in solution (Fig. 1 and 2). Upon crystallization, the silver(I)

Fig. 1 View of the molecular structure of the cation in 2a·BF4. The BF4 anion and the hydrogen atoms have been omitted for clarity. Selected bond distances (Å): P1–Ag1 = 2.522(2), P2–Ag1 = 2.503(2), P3–Ag1 = 2.492(2), P4–Ag1 = 2.555(2). Selected angles (°): P1–Ag1–P2 = 68.11(6), P3–Ag1–P4 = 68.33(6), P1–Ag1–P3 = 123.33(1), P1–Ag1–P4 = 125.07(6), P2–Ag1–P3 = 138.37(6), P2–Ag1–P4 = 142.81(6), P1–N1–P2 = 110.4(3), P3–N2–P4 = 110.8(3).

Fig. 2 View of the molecular structure of the cation in 2b·BF4. The BF4 anion and the hydrogen atoms have been omitted for clarity. Selected bond distances (Å): P1–Ag1 = 2.521(2), P2–Ag1 = 2.476(2), P3–Ag1 = 2.506(2), P4–Ag1 = 2.512(2). Selected angles (°): P1–Ag1–P2 = 68.51(6), P3–Ag1–P4 = 68.39(6), P1–Ag1–P3 = 132.47(7), P1–Ag1–P4 = 128.20(7), P2–Ag1–P3 = 138.49(7), P2–Ag1–P4 = 132.74(7), P1–N1–P2 = 109.8(3), P3–N2–P4 = 110.1(3).

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cations retain a tetrahedral coordination environment, which is highly distorted due to the small P–Ag–P bite angles of the diphosphine ligands [ranging from 68.11(6) to 68.51(6)°]. There is no interaction between silver(I) cations and tetrafluoroborate anions, or thioether pendant groups in 2b·BF4. Noteworthy, the three complexes 2a·BF4–2c·BF4 are stable for hours in acetone-d6 solution. However, the crystallization conditions which successfully afforded single crystals of 2a·BF4 and 2b·BF4, failed to provide analytically pure 2c·BF4. They led instead to the isolation of the dinuclear complex 3c·(BF4)2 (see below and Scheme 2). This surprising observation clearly shows the influence of the remote para-substituent of the aryl group linked to the N atom of DPPA-type ligands on the stability/reactivity of the resulting complexes. The solid state structure of complex 3c·(BF4)2 was established by single crystal X-ray diffraction analysis and features two equivalent silver(I) cations generated by a C2 axis of symmetry. The metals are in a distorted linear coordination environment, with the P1–Ag1–P2′ angle equal to 157.15(7)°, and both diphosphine ligands are on the same side of a plane including the metals and orthogonal to the Ag1,Ag1′,F1 plane (Fig. 3 and 4, left). The separation of 3.0755(8) Å between the silver(I) cations is compatible with d10–d10 argentophilic interactions.30 One tetrafluoroborate anion interacts strongly with both silver(I) cations in a bridging mode.46 The Ag⋯F1 distance of 2.317(6) Å falls in the lower limit for van der Waals interactions which are usually found between 2.30 and 2.90 Å,47 while dative fluorine–silver bonds are usually encountered around 2.10 Å.48 Both the P1–Ag1–P2′ angle, which corresponds to a linear rather than a Y-shape coordination geometry, and the Ag⋯F1 distance are consistent with electrostatic interactions rather than dative Ag–F bonds. The second tetrafluoroborate anion does not interact with any silver(I) cation. Finally, both silver(I) ions interact weakly with one OMe group of two distinct complexes 3c·(BF4)2 via long range intermolecular van der Waals

Scheme 2 Possible routes for the synthesis of the dinuclear complexes 3a·(BF4)2–3c·(BF4)2.

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Fig. 3 Top view of the molecular structure of 3c·BF4 in 3c·(BF4)2 (monomeric unit). One non-coordinated BF4 anion and the hydrogen atoms have been omitted for clarity. Selected bond distances (Å): P1–Ag1 = 2.567(2), P2–Ag1 = 2.522(2), Ag1–F1 = 2.317(6), Ag1–O1 = 3.103(6). Selected angles (°): P1–Ag1–F1 = 115.1(2), P2–Ag1–F1 = 87.5(2), P1–N1–P2 = 124.1(3).

interactions, with an Ag⋯O1 distance equal to 3.103(6) Å. Each dinuclear complex unit has thus four possible Ag/O grafting sites, resulting in the formation of a 2D coordination polymer (Fig. 4, right). As stated above, various attempts were made to crystallize the mononuclear complex 2c·BF4 and they always led to the dinuclear complex 3c·(BF4)2. Furthermore, the crystals grown from a 1 : 2 mixture of THF/n-pentane were shown to correspond to the solvated complex 3c·(BF4)2·(THF)3. Its solid-state structure is remarkably different from that of 3c·(BF4)2 and features two silver(I) cations, in different distorted coordination environments, with P1–Ag1–P4 and P2–Ag2–P3 angles of 147.98(4) and 155.32(4)°, respectively. The separation of 2.9034(6) Å between the silver(I) cations is compatible with d10–d10 interactions, and in contrast to the non-solvated derivative 3c·(BF4)2, the P donors of the diphosphine ligands are arranged on both side of the Ag1,Ag1′,N1,N2 plane to lower steric hindrance due to the coordination of the BF4 ions (Fig. 5 and 6). Each tetrafluoroborate anion interacts strongly with a silver(I) cation in a monodentate mode. The Ag1⋯F1 and Ag2⋯F5 distances of 2.681(6) and 2.791(6) Å are in the typical range for van der Waals/electrostatic interactions. In contrast to the solid state structure of 3c·(BF4)2, no interaction involving

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Fig. 5 View of the molecular structure of 3c·(BF4)2·THF in 3c·(BF4)2·(THF)3. Solvent molecules and hydrogen atoms have been omitted for clarity. Selected bond distances (Å): P1–Ag1 = 2.415(1), P4–Ag1 = 2.414(1), P2–Ag2 = 2.411(1), P3–Ag2 = 2.405(1), Ag1–F1 = 2.681(6), Ag2–F5 = 2.791(6), Ag1–O3 = 2.565(5). Selected angles (°): P1–Ag1–P4 = 147.98(4), P2–Ag2–P3 = 155.32(4), P1–N1–P2 = 120.6(2), P3–N2–P4 = 121.5(2).

Fig. 6 ORTEP representation showing the coordination environment of the silver cations in 3c·(BF4)2·(THF)3. Only the ipso carbon atoms of the aryl rings are represented.

the OMe pendant group of ligand 1c and silver was observed in 3c·(BF4)2·(THF)3. In the crystal, there are 3 molecules of THF in the asymmetric unit and one of them interacts with a silver(I) cation (Ag1). The Ag1–O3 distance of 2.565(6) Å falls in the

Fig. 4 Left: ORTEP side view of the coordination environment of the silver cations in 3c·(BF4)2. Only the ipso carbon atoms of the aryl rings are represented. Right: View of the 2D coordination polymer assembly (the blue arrows highlight the directions of expansion).

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lower limit of van de Waals interactions, which are usually above 2.60 Å, while dative oxygen (from THF)–silver bonds are usually encountered around 2.35 Å (survey of the CSD database).49 This interaction is likely responsible for the different values of the P2–Ag2–P3 and P1–Ag1–P4 angles, and Ag2 is in a distorted T-shape coordination environment, while the coordination geometry around Ag1 might be better described as distorted tetrahedral.50 The dinuclear complexes 3a·(BF4)2–3c·(BF4)2 can be selectively synthesized in acetone or THF, by reacting either ligands 1a–1c with an equimolar amount of AgBF4, or the isolated mononuclear complexes 2a·BF4–2c·BF4 with 0.5 equiv. of AgBF4. Upon crystallization of the crude reaction mixtures, all complexes were collected in good to high yields (68–94%), as colourless crystals (Scheme 2). The 31P{1H} NMR spectra of complexes 3b·(BF4)2 and 3c·(BF4)2 revealed a similar pattern, composed of two pseudo triplets at 89.8 and 86.4 ppm flanking a broad signal at 88.3 ppm for 3b·(BF4)2, and at 91.60 ( pseudo t), 87.04 ( pseudo t) and 89.36 (br) ppm for 3c·(BF4)2, analogous to that observed for 3a·(BF4)2.40 Such patterns have been reported in the literature for diphosphine/Ag(I) systems and correspond to an AMM′ spin system (A = 31P, M and M′ = 107/109Ag) with the expected mixture of isotopomers in the following proportions: 26.9 : 49.9 : 23.2 corresponding to (107Ag)2, 2 × (107Ag)(109Ag) and (109Ag)2, respectively. Furthermore, a dynamic behaviour involves coordination/decoordination of the phosphine(s) donor(s).40,44,45,51 We highlighted this phenomenon by recording low-temp 31P{1H} NMR on similar [Ag2(P,P)2](BF4)2 complexes of N-substituted/functionalized DPPA-type ligands, which showed the splitting of the central broad signal into several well-defined peaks.40 A very similar pattern was observed by Pettinari and co-workers for [Ag2(DPPM)2](NO2)2, which has a solid-state structure similar to that of 3a·(BF4)2.52 The similarities between the 1H NMR spectra of the dinuclear complexes 3a·(BF4)2–3c·(BF4)2 and their corresponding mononuclear bis-chelate complexes 2a·BF4–2c·BF4 emphasize the need for X-ray diffraction analyses in this chemistry. However, structures in the solid-state and in solution are often not identical due to the occurence of solvent effects, intermolecular interactions, etc. The solid-state structure of complex 3b·(BF4)2 was established by single crystal X-ray diffraction (Fig. 7) and is very similar to that of 3c·(BF4)2 (see above). It features two equivalent silver(I) cations generated by a C2 axis of symmetry, which are in a distorted linear coordination environment, with the P1–Ag1–P2′ angle equal to 150.10(5)°. The arrangement of the diphosphine ligands with respect to a plane containing the silver atoms and orthogonal to the Ag1,Ag1′,F1 plane, is similar to that observed in 3c·(BF4)2 (Fig. 7 and 8, top). The separation of 2.9111(1) Å between the silver(I) cations is compatible with d10–d10 interactions. A tetrafluoroborate anion interacts with both silver(I) cations in a bridging mode. The Ag⋯F1 distance of 2.622(4) Å corresponds to van der Waals interactions. The second tetrafluoroborate anion does not interact with any silver(I) cation. Finally, both silver(I) centres

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Fig. 7 View of the molecular structure of 3b·BF4 in 3b·(BF4)2. One noncoordinated BF4 anion and the hydrogen atoms have been omitted for clarity. Selected bond distances (Å): P1–Ag1 = 2.420(2), P2–Ag1 = 2.433(2), Ag1–F1 = 2.622(4), Ag1–S1 = 2.622(4). Selected angles (°): P1–Ag1–P2’ = 150.10(5), P1–Ag1–F1 = 97.4(1), P2–Ag1–F1 = 112.0(1), P1–N1–P2 = 122.7(2).

Fig. 8 Top: ORTEP representation of the coordination environment of the silver cations in 3b·(BF4)2. Only the ipso carbon atoms of the aryl rings are represented. Bottom: View of the coordination polymer present in the solid-state (the blue arrows highlight the directions of expansion).

interact weakly with a thioether group via long range intermolecular van der Waals interactions, with Ag⋯S1 distances of 2.884(2) Å. As a result, each dinuclear complex unit has four possible Ag/S grafting sites, leading to a 2D coordination

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polymer (Fig. 8, bottom). A comparison between the metrical parameters (P–Ag–P angles, Ag⋯F, Ag⋯O/S) of 3b·(BF4)2 and 3c·(BF4)2 tends to indicate that the thioether groups interact more strongly with the silver(I) cations than the ether groups. From the single resonance observed for the four equivalent F atoms of the BF4 anion (δ = ca. 151 ppm) in their 19F{1H} NMR spectra, it can be concluded that complexes 3a·(BF4)2– 3c·(BF4)2 exist in solution as dissociated BF4 salts. This observation contrasts with their solid state structures, in which Ag⋯F (from BF4 anion) interactions are present. C–Cl bond activation When the reaction of ligand 1b or 1c with an equimolar amount of AgBF4 was performed in a chlorinated solvent (CH2Cl2 or CDCl3) instead of THF or acetone, the formation of the dinuclear complexes 3b·(BF4)2 and 3c·(BF4)2, was accompanied with that of the trinuclear complexes 4b·BF4 and 4c·BF4, respectively, in different ratios (Scheme 3). In contrast, the reaction between ligand 1a and AgBF4 in a 1 : 1 molar ratio only afforded 3a·(BF4)2, even in CH2Cl2.40 Considering the complexity of their 31P{1H} NMR spectra resulting from inequivalent P atoms, and the numerous 2+3 J (31 P, 31 P), 1 31 107/109 J ( P, Ag) and 2+3J (31P,107/109Ag) couplings, the identity and connectivity of the trinuclear complexes had to be unambiguously established by X-ray diffraction (see below). In our previous report describing the trinuclear complex 4b·BF4, the 31P{1H} NMR spectrum attributed to this complex corresponded to a sample isolated after recrystallization for two days from a CH2Cl2/pentane mixture, while the structure of 4b·BF4 resulted from the analysis of a unique crystal.40 Unfortunately, this crystal was not representative of the whole sample and the 31P{1H} NMR spectrum was erroneously assigned to 4b·BF4. This has now been clearly evidenced and corrected (see Experimental section). Nevertheless, the unexpected activation of a C–Cl bond of the solvent, induced by the presence of the N-arylthioether moiety, triggered further investigations with the N-Ph, N-(p-SMe)C6H4 and N-( p-OMe) C6H4 functionalized ligands. The equimolar reactions between

Fig. 9 31P{1H} NMR of the reaction mixtures of 1a–1c and AgBF4 (1 : 1 molar ratio) in CD2Cl2 recorded at room temp. after 1 h.

ligands 1a–1c and AgBF4 in CD2Cl2 were monitored by 31P{1H} NMR and allowed to estimate the proportion of complexes 3 vs. 4 formed in each case (Fig. 9). This proportion dramatically depends on the nature of the N-substituent, since 1a only afforded the dinuclear complex 3a·(BF4)2 (Fig. 9, top), 1b led to a ca. 90 : 10 mixture of the complexes 3b·(BF4)2 and 4b·BF4 (Fig. 9, middle), respectively, while ligand 1c afforded a ca. 10 : 90 ratio of the complexes 3c·(BF4)2 and 4c·BF4 (Fig. 9, bottom), respectively. Interestingly, these ratios were established after a short reaction time (1 h) and did not evolve over a prolonged period (up to 3 days). Both the mononuclear bis-chelate (2·BF4) and the dinuclear bridged [3·(BF4)2] complexes, once isolated in pure form, could be ruled out as direct precursors to the Ag3 clusters (4·BF4) since their dissolution in chlorinated solvents (CD2Cl2 or CDCl3, Scheme 4) did not lead to any transformation (see Fig. S1 and S2 in ESI†). These observations highlight a complex mechanism and/or the formation of a more reactive species, able to activate a C–Cl bond of CH2Cl2 (or CHCl3), upon mixing ligands 1b (or 1c) and AgBF4.

Scheme 3 Equimolar reaction between ligands 1a–1c and AgBF4 in CH2Cl2 or CDCl3, affording a mixture of the dinuclear 3a·(BF4)2–3c·(BF4)2 and trinuclear 4b·BF4–4c·BF4 complexes in different ratios (determined by 31P{1H} and 1H NMR), depending on the N-substituent of the DPPA-type ligand used.

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Scheme 4 Experiments performed to control the stability/non-reactivity of isolated mononuclear bis-chelated and dinuclear bridged Ag(I) complexes of ligand 1b in dichloromethane.

Monitoring by 31P{1H} NMR of the reaction between ligand 1b and AgBF4 (1 : 1 molar ratio) in CDCl3 (Fig. 10) revealed the initial formation of nearly 50% of a product never observed before (Xb) which gave rise to a resonance at a similar chemical shift to the dinuclear complex 3b·(BF4)2 (1 : 1 Ag/ligand ratio), but its pattern is clearly different (two pseudo triplets vs. two pseudo triplets with a central broad peak), along with 40% of the bis-chelate species 2b·BF4 (1 : 2 Ag/ligand ratio), and less than 10% of the trinuclear complex 4b·BF4 (1 : 1 Ag/ ligand ratio) (approx. integrations of the 31P{1H} NMR spectrum, see Fig. S3 in ESI†). It can reasonably be assumed that Xb has a 2 : 1 Ag/ligand ratio and since it is present in an amount complementing that of the bis-chelate complex 2b (1 : 2 Ag/ligand ratio, approx. 31P{1H} NMR integrations), the 1 : 1 Ag/ligand ratio introduced initially would be satisfied. The intensity of the signals corresponding to 2b·BF4 and Xb rapidly decreased with time. After 3 h reaction, complex 2b·BF4 has completely disappeared, the signals corresponding to Xb have been substituted by those of 3b·(BF4)2, and those of 4b·BF4 have become more intense. A stable ratio of 1 : 0.4 in favour of

Fig. 10

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the dinuclear complex 3b·(BF4)2 is reached after 6 h (Fig. S4 in ESI†). We noticed that the formation of the trinuclear cluster 4b·BF4 is favoured in CHCl3 compared to CH2Cl2 (Fig. S5 in ESI†), which is consistent with an easier C–Cl bond activation in the former solvent. The very broad signals in the region 83–90 ppm at t = 2 and 3 h do not allow to exclude the coexistence of both complexes Xb and 3b·(BF4)2. We suggest that these complexes are not in equilibrium, but Xb converts to 3b·(BF4)2 and/or 4b·BF4 with concomitant consumption of 2b·BF4. Several experiments were then performed to shed light on the nature of Xb and the mechanism leading to 4b. The formation of the “stable” dinuclear (type 3) vs. the more “reactive” type X (in combination with bis-chelate, type 2) species was found to critically depend on the nature of the N-substituent. While ligand 1a afforded only the dinuclear complex 3a·(BF4)2, the (SMe)-functionalized ligand 1b led rapidly to a ca. 50 : 50 mixture of Xb and 2b·BF4, which further reacted to give 3b·(BF4)2 and 4b·BF4 (see Fig. S3 and S4 in the ESI†), and finally, the (OMe)-functionalized ligand 1c produced the cluster 4c·BF4 (>90%) so fast that the possible intermediate(s) could no longer be detected after 5 min (Fig. 9 and 10). Our hypothesis about the 2 : 1 Ag/ligand ratio in species Xb was supported by the following reactions. The reaction between the mononuclear complex 2b·BF4 and 1.2 equiv. AgBF4, was monitoring by 31P{1H} NMR in CD2Cl2. It led after 1 h to a mixture of 2b·BF4 and Xb, which slowly evolved until only Xb was present (Fig. 11). No further evolution to the cluster 4b·BF4 was observed, which established that Xb alone, as well as 2b and 3b, are unable to activate a C–Cl bond of dichloromethane or chloroform. Moreover, mixing 1 equiv. of ligand 1b with 2 equiv. AgBF4 in acetone only afforded 3b·(BF4)2, and 1 equiv. AgBF4 remained presumably unreacted. However, if the acetone is

In situ 31P{1H} NMR monitoring of the reaction between ligand 1b and AgBF4 (1 : 1 molar ratio) in CDCl3.

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Fig. 11

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P{1H} monitoring of the transformation of 2b·BF4 into Xb in CD2Cl2 upon addition of AgBF4.

removed under vacuum and the dry residue is dissolved in dichloromethane, then immediate and quantitative formation of complex Xb was observed (NMR evidence).53 Complex Xb can also be cleanly and quantitatively formed by addition of dichloromethane to a solid mixture of ligand 1b and AgBF4 (1 : 2 ligand/metal ratio, Scheme 5 and Fig. S7 in the ESI†). Although its solid-state structure could not be established by single crystal X-ray diffraction, complex Xb was characterized by multinuclear NMR (see Experimental section). We initially thought that complex Xb might consist of a square of four Ag ions in which two edges would be bridged by one ligand 1b each, with four µ2-bridging and/or µ3-capping Cl ions.30,56,57 Structures with cationic Ag(I) ions bridging two Ag(I) ions supported by two ligands, [Ag2(µ2-C,N)2(µ2-Ag)2](OTf )4 type complexes, have been reported.54 Further analytical data obtained by mass spectrometry (ESI-MS) and elemental analysis (EA) allowed to speculate on the molecular formula of Xb. Its EA was clearly not consistent with a [(1b)2Ag4Cl4] species, but

Scheme 5 Determination of complex Xb and involvement in the C–Cl bond activation.

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agrees better with the formulation [(1b)2Ag4][BF4]4·CH2Cl2 (see Experimental section). Several sets of peaks were observed in the ESI-MS spectrum of Xb, and in some of them the isotopic distributions were in agreement with compounds containing Ag, Cl, B and F. While most of the fragments could not be identified, one of them at m/z = 849.8 [M − 2(BF4)]2+ (M = {[(1b)2Ag4][BF4]4·CH2Cl2}) strongly supports the proposed formula for Xb. From the monitoring of the reaction between ligand 1b and AgBF4 (1 : 1 molar ratio) shown in Fig. 10 and the control experiments depicted in Scheme 4, it appears that the C–Cl bond activation leading to the trinuclear cluster 4b·BF4 (along with 3b·(BF4)2) involves both complexes 2b·BF4 and Xb. The reaction between Xb and 2b·BF4 (1 : 2 ratio, respectively in CD2Cl2) was monitored by NMR and revealed the immediate formation of a mixture of complexes 4b·BF4 and 3b·(BF4)2, in a ratio close to that found in the initial 1 : 1 reaction between ligand 1b and AgBF4 (Scheme 5 and Fig. S8† vs. Scheme 3 and Fig. 9, middle). Although multinuclear NMR spectra were always thoroughly investigated when C–Cl bond activation was observed, the fate of the organic side-product could not be determined. The abstraction of Cl atoms from chloroform or dichloromethane by d10 metal/phosphine systems has been reported several times, but the mechanism involved and the nature of the remaining organic moiety were never fully assessed.55 Noteworthy, no P-ylide (PvCH2) moiety was detected, while such species resulted from the activation of CH2Cl2 by Ni(0) complexes.20 In this section, we were able to highlight an original C–Cl bond activation, which surprinsingly depends on the nature of the N-substituent of the DPPA-type ligand and while the mechanism could not be clearly established, the species involved were clearly determined and it can be assumed that this reactivity is triggered by a coordination/decoordination mechanism typical of such Ag/DPPA species.

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Rational synthesis of the Ag3 clusters and interconversion between complexes of types 2–4 It was envisaged that the formal addition of 2/3 equiv. of Cl− ions, in the form of the ammonium salt [NMe4]Cl, to an 1 : 1 Ag/ligand mixture in acetone should allow the quantitative formation of the trinuclear complexes 4a·BF4–4c·BF4. Complexes 4b·BF4–4c·BF4 were only formed as side-products so far, and access to the N-Ph analogue 4a·BF4 remained to be established. The Ag3Cl2 core clusters 4a·BF4–4c·BF4 were readily obtained in good yields (75–80%), also by a direct one-pot reaction involving the addition of AgBF4 and [NMe4]Cl to a solution of the corresponding DPPA-type ligand (3 : 2 : 3 molar ratio, Scheme 6, left), or by treatment of an isolated sample of the dinuclear species 3a·(BF4)2–3c·(BF4)2 with 0.66 equiv. of [NMe4]Cl in acetone (Scheme 6, right). Noteworthy, the use of an excess of chloride source (>3 equiv.) did not lead to a complete anion exchange and the formation of any Ag3Cl3 or [Ag3Cl2]Cl core clusters, as evidenced by 19F{1H} NMR. The formation of a complex with a Ag4Cl4 core could also be envisaged, since M4X4-type clusters (M = Cu, Ag; X = halogen) have already been reported for DPPA-type ligands and other bridging ligands.30,56–60 The 31P{1H} NMR spectra of the trinuclear complexes 4a·BF4–4c·BF4 exhibit a characteristic pattern composed by two broad pseudo quadruplets centred at 77.4 and 74.5 ppm for 4a·BF4, 77.7 and 74.8 ppm for 4b·BF4 and 78.1 and 75.3 ppm for 4c·BF4. The shape of these signals results from the overlapping of the different contributions of all possible isotopomers, as observed in related systems involving DPPM as assembling ligand such as [Ag3{μ-SC(O)R-S}2(μ-DPPM)3]ClO4 (R = Me or Ph).51,61 In contrast, the 1H NMR spectra of the trinuclear complexes 4a·BF4–4c·BF4 were very similar to those of the corresponding mono- and dinuclear complexes, with the characteristic signals of the N-substituent. The solid-state structure of 4a·BF4 and 4c·BF4 were confirmed by X-ray crystallography, and are almost identical to each other and to that of 4b·BF4.40 They feature a Ag3Cl2 core, with the three Ag(I) cations forming an almost equilateral triangle, likely stabilized by d10–d10 interaction, with Ag⋯Ag distances comprised between 3.0265(4) and 3.1619(8) Å, and by two capping μ3-Cl ligands, with Ag–Cl distances between 2.6632(7) and 2.765(2) Å (Fig. 12 and 13).

Fig. 12 Top: View of the molecular structure of 4c in 4c·BF4·CH2Cl2. The non-coordinated BF4 anion, the solvent molecule and the hydrogen atoms have been omitted for clarity. Bottom: ORTEP representation of the Ag3Cl2(P,P)3 core. Selected bond distances (Å): P1–Ag2 = 2.452(2), P2–Ag1 = 2.463(2), P3–Ag2 = 2.458(2), P4–Ag3 = 2.426(2), P5–Ag3 = 2.421(2), P6–Ag1 = 2.454(2), Ag1–Cl1 = 2.765(2), Ag1–Cl2 = 2.667(2), Ag2–Cl1 = 2.709(2), Ag2–Cl2 = 2.705(2), Ag3–Cl1 = 2.655(2), Ag3–Cl2 = 2.711(2), Ag1⋯Ag2 = 3.1619(8), Ag2⋯Ag3 = 3.0823(8), Ag3⋯Ag1 = 3.0710(7). Selected angles (°): P2–Ag1–P6 = 125.61(7), P1–Ag2–P3 = 124.47(7), P4–Ag3–P5 = 117.96(7), Ag1–Ag2–Ag3 = 58.90(2), Ag2–Ag3– Ag1 = 61.84(2), Ag3–Ag1–Ag2 = 59.26(2).

The global positive charge of the metal cluster is balanced by the presence of a non-coordinated BF4 anion. The silver(I) cations exhibit a distorted tetrahedral coordination environ-

Scheme 6 Rational synthesis of the trinuclear complexes 4a·BF4–4c·BF4 using a one-pot procedure (left) or starting from the isolated dinuclear complexes 3a·(BF4)2–3c·(BF4)2 (right).

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Fig. 13 Top: Top view of the molecular structure of 4a in 4a·BF4·3 (CH2Cl2). The non-coordinated BF4 anion, solvent molecules and the hydrogen atoms have been omitted for clarity. Bottom: ORTEP representation of the Ag3Cl2(P,P)3 core. Selected bond distances (Å): P1–Ag1 = 2.4293(9), P2–Ag2 = 2.4371(9), P3–Ag2 = 2.4245(8), P4–Ag3 = 2.4422(8), P5–Ag3 = 2.437(1), P6–Ag1 = 2.431(1), Ag1–Cl1 = 2.6904(7), Ag1–Cl2 = 2.7200(8), Ag2–Cl1 = 2.735(1), Ag2–Cl2 = 2.6632(7), Ag3–Cl1 = 2.6726(7), Ag3–Cl2 = 2.7450(9), Ag1⋯Ag2 = 3.0334(4), Ag2⋯Ag3 = 3.0265(4), Ag3⋯Ag1 = 3.1083(3). Selected angles (°): P1–Ag1–P6 = 120.51(3), P2–Ag2–P3 = 119.98(3), P4–Ag3–P5 = 123.86(3), Ag1–Ag2–Ag3 = 61.72(1), Ag1–Ag3–Ag2 = 59.25(1), Ag2–Ag1–Ag3 = 59.03(1).

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ment, with P–Ag–P and P–Ag–Cl angles comprised between 117.96(7)–125.61(7)° and 105.55(6)–114.32(7)°, respectively. Various μ3-anionic ligands are known from the literature to stabilize such types of M3 cores (M = Ag, Cu).62–65 Although the mechanism leading to the formation of the clusters 4b–4c·BF4 in chlorinated solvents could not be unambiguously determined, we developed a simple, stepwise approach to access the mono-, di- and trinuclear complexes of the three series a–c (Scheme 7), which was monitored by 31P {1H} NMR (Fig. 14 for the (SMe)-functionalized derivatives b). The reaction of ligand 1b with AgBF4 in a 2 : 1 molar ratio afforded the mononuclear, bis-chelate complex 2b·BF4 (A), further addition of 0.5 equiv. of AgBF4 to this solution yielded the dinuclear complex 3b·(BF4)2 (B), and finally, addition of 2/ 3 equiv. of [NMe4]Cl resulted in the quantitative formation of the cluster 4b·BF4 (C). Noteworthy, the addition of 2 equiv. of ligand 1b to the corresponding dinuclear complex 3b·(BF4)2 afforded solely the bis-chelate complex 2b·BF4 (B′). The latter experiment highlights the importance of the stoichiometry of the reagents in Ag/DPPA systems and their “versatility”, with facile interconversions from 1 : 2 to 1 : 1 to 1 : 2 (again) metal/ ligand ratios. Further attempts to increase the nuclearity of the silver(I) clusters by using a 1 : 2 : 2 ligand/Ag/Cl− ratio, targeting a Ag4Cl4 core supported by two diphosphine ligands, remained unsuccessful and only the trinuclear complexes of type 4 were formed (31P{1H} NMR evidence).

Conclusion The characterization of mono-, di- and trinuclear silver(I) complexes (2, 3 and 4) obtained with three DPPA-type ligands (1a–1c) differing only by the nature of the para substituent Z of the N-aryl group, i.e. a hydrogen (1a, no functional group), a

Scheme 7 Possible access to mono-, di- and trinuclear Ag(I) complexes of N-substituted/functionalized DPPA-type ligands (1a–1c). Note: Reaction B’ leads to 2 equiv. of complexes 2a·BF4–2c·BF4.

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Fig. 14

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P{1H} NMR monitoring of the in situ transformations A–C depicted in Scheme 7.

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thioether (1b) or an ether group (1c), has established the importance of this para substituent and of the reaction solvent. In acetone, the expected mononuclear bis-chelated 2a·BF4–2c·BF4 and dinuclear bridged 3a·(BF4)2–3c·(BF4)2 complexes were obtained with a 1 : 2 and 1 : 1 AgBF4/ligand molar ratio, respectively. In the solid-state, 3b·(BF4)2 and 3c·(BF4)2 form bi-dimensional coordination polymers involving the chalcogen atom from N-aryl group and the BF4 anions interact with the two silver cations while 19F{1H} NMR evidenced no interaction in solution. With a similar 1 : 1 Ag/ligand molar ratio, trinuclear Ag3Cl2 core clusters were selectively formed (rather than dinuclear complexes) via Cl/BF4 anion metathesis, upon addition of the suitable amount of [NMe4]Cl as chloride source. We could establish a surprising influence of the N-aryl para substituent Z in DPPA-type ligands, because when a stoichiometric amount of AgBF4 and diphosphine ligand were reacted in a chlorinated solvent, a mixture of dinuclear (type 3) and trinuclear (type 4) complexes was obtained in a relative ratio dependent on the ligand. While the N-phenyl DPPA-type ligand afforded only the dinuclear complex 3a·(BF4)2, the N-aryl DPPA-type ligands functionalized in para-position by a SMe or a OMe group led to mixtures of 3 and 4, in 90 : 10 and 10 : 90 ratios, respectively. A precise reaction mechanism accounting for the activation of C–Cl bonds and the formation of the trinuclear complexes 4b·BF4 and 4c·BF4 (without addition of [NMe4]Cl) could not be established, but we demonstrated that pure mononuclear bis-chelated and dinuclear complexes (type 2 and 3, respectively), isolated from acetone, are unable to activate C–Cl bonds of chlorinated solvents. However, the involvement of intermediate species Xb of 2 : 1 : x AgBF4/ligand/Cl molar ratio (1 Ag per P donor) was clearly established. Interestingly, the Csp3–Cl bond activation observed in this work results in the formation of stable silver clusters of type 4 rather than in the precipitation of AgCl. At variance with the Ag(I) chemistry reported here, when two ligands 1b were chelated to Ni(II), reaction with CH2Cl2 in the presence of Zn

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metal also led to Csp3–Cl bond activation but in this case, CH2 insertion into a P–Ni bond was observed,20 similarly to reactions previously observed with functional monophosphines in cobalt chemistry.66 The unexpected reactivity of the 1b–1c/AgBF4 system, leading to the formation of the trinuclear [Ag3Cl2(P,P)3]BF4 (4·BF4) complexes resulted from (i) the use of a chlorinated solvent (as Cl− source) and (ii) a specific functionalization of the N-aryl substituent.

Experimental section General procedures All operations were carried out using standard Schlenk techniques under an inert atmosphere. Solvents were purified and dried under nitrogen by conventional methods. CD2Cl2, CDCl3 and acetone-d6 were dried over 4 Å molecular sieves, degassed by freeze–pump–thaw cycles, and stored under argon. NMR spectra were recorded at room temperature on Bruker AVANCE 300 and 400 spectrometers and referenced using the residual solvent (1H or 13C) resonance. Chemical shifts (δ) are given in ppm. For complexes of type 3, 4 and X, 31P signals appear as pseudo triplets or quadruplets and the J values given represent the separation between two consecutive lines since the precise spin system cannot be determined (see text). IR spectra were recorded in the region 4000–100 cm−1 on a Nicolet 6700 FT-IR spectrometer (ATR mode, SMART ORBIT accessory, Diamond crystal). Elemental analyses were performed by the “Service de microanalyses”, Université de Strasbourg. Electrospray mass spectra (ESI-MS) were recorded on a microTOF (Bruker Daltonics, Bremen, Germany) instrument using nitrogen as drying agent and nebulizing gas. For the X-ray diffraction studies, the intensity data were collected at 173(2) K on a Siemens Kappa CCD diffractometer 88 or Bruker Apex II diffractometers (Mo-Kα radiation, λ =

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0.71073 Å). The structures were solved by direct methods (SHELXS-97) and refined by full-matrix least-squares procedures (based on F2, SHELXL-97/14) with anisotropic thermal parameters for all the non-hydrogen atoms.67 The hydrogen atoms were introduced into the geometrically calculated positions (SHELXL-97/14 procedures) and refined riding on the corresponding parent atoms. Crystallographic and experimental details for all the structures are summarized in the ESI (Tables S1–S7†). The ligands 1a–1c were prepared according to literature methods.19,42,43 All other reagents were used as received from commercial suppliers. Complex 3a·(BF4)2 was prepared as described previously.40 The crystal structure of the trinuclear cluster 4b·BF4 was also reported in the latter paper, however at that time we attributed to 4b·BF4 a 31P{1H} NMR spectrum consisting in two well resolved doublets centered at 98.15 ppm, with values of 1J (109Ag–P) = 254 Hz and 1J (107Ag–P) = 220 Hz consistent with the gyromagnetic ratio γ(109Ag)/γ(107Ag) = 1.15. Unfortunately, the single crystal analysed by X-ray diffraction was not representative of the sample analysed by NMR, and in the light of our new investigations, we could establish that this 31 1 P{ H} NMR spectrum corresponds to the mononuclear bischelated complex 2b·BF4 (see text).40 Mononuclear bis-chelate [Ag(P,P)2]BF4 complexes (2a–2c·BF4) Complex 2a·BF4. Solid AgBF4 (0.042 g, 0.22 mmol) was added in one portion to a stirred solution of 1a (0.200 g, 0.43 mmol) in 20 mL of acetone at room temp. The reaction mixture was stirred at room temp for 4 h with exclusion of light. Addition of n-pentane led to the precipitation of a colourless powder, isolated by sedimentation and dried under vacuum, yielding 2a·BF4 as a colourless solid (0.204 g, 0.18 mmol, yield: 87%). Colourless crystals suitable for single-crystal X-ray diffraction were grown from a mixture of acetone/n-pentane. Anal. Calcd for C60H50AgBF4N2P4 (1117.62): C, 64.48; H, 4.51; N, 2.51. Found: C, 64.11; H, 4.52; N, 2.57. FTIR: νmax(solid)/cm−1: 3055vw, 1586w, 1485m, 1436ms, 1309vw, 1278vw, 1215vw, 1204m, 1186vw, 1161vw, 1095ms, 1050vs, 1024vw, 996w, 940s, 920vw, 912w, 880s, 740s, 690vs, 666w. 1H NMR (CD2Cl2, 400 MHz) δ: 7.52–7.48 (m, 8H, aromatic), 7.35–7.29 (m, 32H, aromatic), 7.11 (t, 2H, 3JH,H = 7.5 Hz, N(C6H5), Hpara/N), 6.91 (t, 4H, 3JH,H = 7.5 Hz, N(C6H5), Hmeta/N), 6.20 (d, 4H, 3JH,H = 7.5 Hz, N(C6H5), Hortho/N) ppm. 13C{1H} NMR (CD2Cl2, 75.5 MHz) δ: 139.95 (br, N(C6H5), Cipso/N), 133.08 (br, Cortho, aromatic), 132.78 (br, Cipso, aromatic), 131.71 (s, Cpara, aromatic), 130.06 (s, N(C6H5), Cortho/N), 129.09 (br, Cmeta, aromatic), 128.58 (s, N(C6H5), Cmeta/N), 127.73 (s, N(C6H5), Cpara/N) ppm. 31P{1H} NMR (CD2Cl2, 121.5 MHz) δ: 97.61 (dd, 1J (109Ag, P) = 255 Hz, 1 107 J ( Ag, P) = 221 Hz) ppm. 19F{1H} NMR (CD2Cl2, 282.4 MHz) δ: 152.1 (BF4) ppm. MS (ESI): m/z = 1031.20 [M − BF4]+. Complex 2b·BF4. Following the same procedure as described for compound 2a·BF4, using 1b (0.220 g, 0.43 mmol) and AgBF4 (0.042 g, 0.22 mmol), yielded 2b·BF4 as a colourless solid (0.242 g, 0.20 mmol, yield: 91%). Colourless crystals suitable for single-crystal X-ray diffraction were grown from a mixture of acetone/n-pentane. Anal. Calcd for C62H54AgBF4N2S2P4 (1209.81): C, 61.55; H, 4.50; N, 2.32. Found: C, 60.35; H, 4.51;

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N, 2.08. The difference between calculated and experimental values may result from the presence of traces of water in the sample, which could originate from the hygroscopic acetone solvent.68 Although very weak, the presence of characteristic H2O absorptions in the IR spectrum of 2b·BF4 could indeed be detected. For information the calculated EA for a water adduct of 2b·BF4, closer to the experimental values, are: C62H54AgBF4N2S2P4·H2O (1227.83): C, 60.65; H, 4.60; N, 2.28. FTIR: νmax(solid)/cm−1: 3067vw, 3049vw, 2985vw, 2921w, 1583w, 1566w, 1487vw, 1478ms, 1433s, 1399w, 1309w, 1282vw, 1217ms, 1181w, 1160w, 1094ms, 1049vs, 1012w, 992mw, 961vw, 945m, 862vs, 803m, 748s, 736vw, 710w, 696vs. 1H NMR (acetone-d6, 400 MHz) δ: 7.59–7.55 (m, 8H, aromatic), 7.43 (br, 24H, aromatic), 7.19–7.14 (m, 8H, aromatic), 6.81 (A part of a AB spin system, 4H, 3JH,H = 8.6 Hz, N(C6H4)S, Hmeta/N), 6.19 (B part of a AB spin system, 4H, 3JH,H = 8.6 Hz, N(C6H4)S, Hortho/N), 2.33 (s, 6H, SCH3) ppm. 13C{1H} NMR (acetone-d6, 75.5 MHz) δ: 139.02 (br, N(C6H4)S, Cpara/N), 136.61 (br, N(C6H4) S, Cipso), 133.12 (br, Cortho, aromatic), 132.84 (br, Cipso, aromatic), 131.85 (s, Cpara, aromatic), 130.44 (s, N(C6H4)S, Cortho/N), 129.22 (s, Cmeta, aromatic), 125.36 (s, N(C6H4)S, Cmeta/N), 14.06 (s, SCH3) ppm. 31P{1H} NMR (acetone-d6, 121.5 MHz) δ: 97.79 (dd, 1J (109Ag, P) = 255 Hz, 1J (107Ag, P) = 221 Hz) ppm. 19F{1H} NMR (acetone-d6, 282.4 MHz) δ: 149.9 (BF4) ppm. MS (ESI): m/z = 1123.16 [M − BF4]+. Complex 2c·BF4. Following the same procedure as described for compound 2a·BF4, using 1c (0.200 g, 0.41 mmol) and AgBF4 (0.040 g, 0.20 mmol), yielded 2c·BF4. This complex could be unambiguously characterized as the sole reaction product in solution by multinuclear NMR techniques. However, all attempts to isolate 2c·BF4 by crystallization/precipitation led to the formation of 3c·(BF4)2 along with free ligand 1c, as shown by NMR analysis. Therefore, no yield nor EA could be provided (see text). Moreover, in an attempt to crystalize 2c·BF4 from THF, crystals of 3c·(BF4)2·(THF)3, were grown from a 1 : 2 mixture of THF/n-pentane. FTIR: νmax(solid)/ cm−1: 3054vw, 2832vw, 1602w, 1581vw, 1502ms, 1481w, 1462vw, 1436m, 1292w, 1252m, 1211w, 1195m, 1098s, 1053s, 1026vw, 997w, 953m, 910vw, 894vs, 793m, 741vs, 720mw, 694vs. 1H NMR (acetone-d6, 400 MHz) δ: 7.57–7.53 (m, 8H, aromatic), 7.40 (br, 28H, aromatic), 7.15 (br, 4H, aromatic), 6.47 (A part of a AB spin system, 4H, 3JH,H = 9.1 Hz, N(C6H4)O, Hmeta/N), 6.18 (B part of a AB spin system, 4H, 3JH,H = 9.1 Hz, N(C6H4)O, Hortho/N), 3.62 (s, 6H, OCH3) ppm. 13C{1H} NMR (acetone-d6, 75.5 MHz) δ: 158.87 (br, N(C6H4)O, Cpara/N), 133.13 (br, Cortho, aromatic), 132.52 (br, Cipso, aromatic), 131.73 (s, Cpara, aromatic), 131.17 (s, N(C6H4)O, Cortho/N), 129.16 (s, Cmeta, aromatic), 113.48 (s, N(C6H4)O, Cmeta/N), 57.77 (s, OCH3) ppm. 31P{1H} NMR (acetone-d6, 121.5 MHz) δ: 97.90 (dd, 1J (109Ag, P) = 255 Hz, 1J (107Ag, P) = 221 Hz) ppm. 19F{1H} NMR (acetone-d6, 282.4 MHz) δ: 151.2 (BF4) ppm. MS (ESI): m/z = 1091.23 [M − BF4]+. Dinuclear [Ag2(μ2-P,P)2](BF4)2 complexes (3b–3c·BF4) Complex 3a·(BF4)2. This complex has been previously obtained from CH2Cl2 and we have now found that a similar result is obtained when acetone or THF is used as solvent.40

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Complex 3b·(BF4)2. A THF solution (10 mL) of 1b (0.110 g, 0.22 mmol) was added to a mixture of AgBF4 (0.042 g, 0.22 mmol) in 5 mL of CH3CN at room temp. The reaction mixture was stirred at room temp for 4 h with exclusion of light. Layering of the resulting colourless solution with diethyl ether led to the formation of colourless crystals of the coordination polymer 3b·(BF4)2, isolated by filtration and dried under vacuum (0.145 g, 0.21 mmol, yield: 94%). Anal. Calcd for C62H54Ag2B2F8N2P4S2 (1404.47): C, 53.02; H, 3.87; N, 1.99. Found: C, 53.03; H, 4.04; N, 1.88. FTIR: νmax(solid)/cm−1: 3057w, 3028vw, 3007vw, 2989vw, 2921w, 1586w, 1560vw, 1486s, 1438s, 1433s, 1400w, 1310m, 1299vw, 1234mw, 1201m, 1181mw, 1097s, 1057s, 1014vw, 995w, 983vw, 958s, 917m, 892s, 813vw, 746m, 733vw, 691vs. 1H NMR (acetone-d6, 400 MHz) δ: 7.61 (t, 8H, 3JH,H = 7.0 Hz, aromatic), 7.44–7.34 (m, 32H, aromatic), 6.59 (A part of a AB spin system, 4H, 3 JH,H = 8.5 Hz, N(C6H4)S, Hmeta/N), 5.91 (B part of a AB spin system, 4H, 3JH,H = 8.5 Hz, N(C6H4)S, Hortho/N), 2.27 (s, 6H, SCH3) ppm. 13C{1H} NMR (acetone-d6, 75.5 MHz) δ: 140.52 (br, N(C6H4)S, Cpara/N), 133.84 (br, Cpara, aromatic), 133.00 (s, Cortho, aromatic), 131.85 (s, N(C6H4)S, Cortho/N), 129.54 (s, Cmeta, aromatic), 125.52 (s, N(C6H4)S, Cmeta/N), 15.04 (s, SCH3) ppm. 31P{1H} NMR (acetone-d6, 121.5 MHz) δ: 89.82 ( pseudo t, J (observed) = 19 Hz), 88.3 (br), 86.35 ( pseudo t, J (observed) = 19 Hz) ppm. 19F{1H} NMR (acetone-d6, 282.4 MHz) δ: 151.9 (BF4) ppm. MS (ESI): m/z = 615.04 [M − 2(BF4)]2+. Complex 3c·(BF4)2. Solid AgBF4 (0.039 g, 0.20 mmol) was added in successive portions to a stirred solution of 1c (0.100 g, 0.20 mmol) in 20 mL of acetone at room temp. The reaction mixture was stirred at room temp for 4 h with exclusion of light. Addition of n-pentane led to the precipitation of a colourless powder, isolated by decantation and dried under vacuum, yielding 3c·(BF4)2 as a colourless solid (0.103 g, 0.15 mmol, yield: 75%). Colourless crystals shown by singlecrystal X-ray diffraction to be the coordination polymer 3c·(BF4)2 were grown from an acetone/diethyl ether mixture. Anal. Calcd for C62H54Ag2B2F8N2P4O2 (1373.35): C, 54.26; H, 3.97; N, 2.04. Found: C, 54.22; H, 4.13; N, 1.91. FTIR: νmax(solid)/cm−1: 3055vw, 2840vw, 1712vw, 1602m, 1581w, 1501s, 1481w, 1465vw, 1437ms, 1363vw, 1291m, 1251ms, 1191ms, 1097m, 1054s, 1035vw, 1024m, 997m, 955s, 910s, 892vs, 826vw, 792ms, 741vs, 692vs. 1H NMR (acetone-d6, 400 MHz) δ: 7.68 (t, 8H, 3JH,H = 7.5 Hz, aromatic), 7.53 (t, 16H, 3 JH,H = 7.5 Hz, aromatic), 7.42 (br, 16H, aromatic), 6.34 (A part of a AB spin system, 4H, 3JH,H = 8.9 Hz, N(C6H4)O, Hmeta/N), 6.01 (B part of a AB spin system, 4H, 3JH,H = 8.9 Hz, N(C6H4)O, Hortho/N), 3.58 (s, 6H, OCH3) ppm. 13C{1H} NMR (acetone-d6, 75.5 MHz) δ: 159.36 (br, N(C6H4)O, Cpara/N), 133.65 (br, Cortho, aromatic), 132.60 (br, Cpara, aromatic), 132.39 (s, N(C6H4)O, Cortho/N), 130.37 (br, N(C6H4)O, Cipso), 129.33 (s, Cmeta, aromatic), 113.62 (s, N(C6H4)O, Cmeta/N), 54.85 (s, OCH3) ppm. 31P{1H} NMR (acetone-d6, 121.5 MHz) δ: 91.60 ( pseudo t, J (observed) = 21 Hz), 89.36 (br), 87.04 ( pseudo t, J (observed) = 21 Hz) ppm. 19F{1H} NMR (acetone-d6, 282.4 MHz) δ: 150.3 (BF4) ppm. MS (ESI):

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m/z = 598.01 overlap of two peaks: [C62H54Ag2N2P4O2]2+ + [C31H27AgNP2O]+. Trinuclear [Ag3(μ3-Cl)2(μ2-P,P)3](BF4) complexes (4a–4c·BF4) Complex 4a·BF4. Solid AgBF4 (0.085 g, 0.43 mmol) and [NMe4]Cl (0.031 g, 0.29 mmol) were added in one portion to a stirred solution of 1a (0.200 g, 0.43 mmol) in 20 mL of acetone at room temp. The reaction mixture was stirred at room temp for 4 h under exclusion of light. Removing of the volatiles under reduced pressure afforded a colourless solid. The crude product was re-dissolved in THF, filtrated and the solvent of filtrate removed under vacuum. The resulting colourless solid was re-dissolved in a minimum amount of CH2Cl2 and layered with n-pentane. Colourless crystals of 4a·BF4 were obtained after two days, isolated by filtration and dried under vacuum (0.208 g, 0.33 mmol, yield based on 1a: 78%). Anal. Calcd for C90H75Cl2Ag3BF4N3P6·CH2Cl2 (1950.68): C, 56.03; H, 3.98; N, 2.15. Found: C, 56.33; H, 4.15; N, 2.25. FTIR: νmax(solid)/cm−1: 3071vw, 3049w, 3005w, 1585m, 1571vw, 1561vw, 1481s, 1432s, 1315w, 1280w, 1187s, 1169vw, 1095w, 1047mw, 1029mw, 995w, 942vs, 889vs, 740vs, 689vs, 661m. 1H NMR (CD2Cl2, 400 MHz) δ: 7.37–7.32 (m, 12H, aromatic), 7.13–7.05 (m, 48H, aromatic), 6.90 (t, 3H, 3JH,H = 7.7 Hz, N(C6H5), Hpara/N), 6.60 (t, 6H, 3JH,H = 7.7 Hz, N(C6H5), Hmeta/N), 5.72 (d, 6H, 3JH,H = 7.7 Hz, N(C6H5), Hortho/N) ppm. 13C{1H} NMR (CD2Cl2, 75.5 MHz) δ: 138.06 (br, N(C6H5), Cipso), 133.36 (br s, Cortho, aromatic), 132.52 (br, Cipso, aromatic), 130.87 (s, Cpara, aromatic), 131.69 (s, N(C6H5), Cortho/N), 128.36 (br, Cmeta, aromatic), 127.77 (s, N(C6H5), Cmeta/N), 127.35 (s, N(C6H5), Cpara/N) ppm. 31P{1H} NMR (CD2Cl2 121.5 MHz) δ: 77.35 (br pseudo q, J (observed) = 11 Hz), 74.51 (br pseudo q, J (observed) = 11 Hz) ppm. 19F{1H} NMR (CD2Cl2, 282.4 MHz) δ: 152.3 (BF4) ppm. MS (ESI): m/z = 1778.09 [M − BF4]+. Complex 4b·BF4. Following the same procedure as described for compound 4a·BF4, using 1b (0.220 g, 0.43 mmol), AgBF4 (0.085 g, 0.43 mmol) and [NMe4]Cl (0.031 g, 0.29 mmol), yielded 4b·BF4 as colourless crystals (0.231 g, 0.34 mmol, yield based on 1b: 80%). Anal. Calcd for C93H81Cl2Ag3BF4N3P6S3 (2004.02): C, 55.74; H, 4.07; N, 2.10. Found: C, 55.18; H, 4.13; N, 1.94. The difference between calculated and experimental values may result from the presence of traces of water in the sample, which could originate from the hygroscopic [NMe4]Cl salt. Although very weak, the presence of characteristic H2O absorptions in the IR spectrum of 4b·BF4 could indeed be detected. For information, the calculated EA for a water adduct of 4b·BF4, closer to the experimental values, are: C93H81Cl2Ag3BF4N3P6S3·H2O (2022.04): C, 55.24; H, 4.14; N, 2.08. FTIR: νmax(solid)/cm−1: 3053w, 3005vw, 2987vw, 2922w, 2685vw, 2613vw, 2585vw, 1586w, 1481s, 1433s, 1400vw, 1314w, 1275vw, 1199m, 1178m, 1097s, 1052s, 1013vw, 997vw, 952m, 911m, 887vs, 742s, 730w, 691vs. 1H NMR (CD2Cl2, 400 MHz) δ: 7.37–7.33 (m, 12H, aromatic), 7.14–7.05 (m, 48H, aromatic), 6.44 (A part of a AB spin system, 6H, 3JH,H = 8.6 Hz, N(C6H4)S, Hmeta/N), 5.62 (B part of a AB spin system, 6H, 3 JH,H = 8.6 Hz, N(C6H4)S, Hortho/N), 2.21 (s, 9H, SCH3) ppm. 13 C{1H} NMR (CD2Cl2, 75.5 MHz) δ: 138.53 (s, N(C6H4)S, Cpara/N), 134.58 (br, N(C6H4)S Cipso/N), 133.34 (br s, Cortho,

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aromatic), 132.41 (br, Cipso, aromatic), 131.90 (s, N(C6H4)S, Cortho/N), 130.91 (s, Cpara, aromatic), 128.40 (br, Cmeta, aromatic), 124.78 (s, N(C6H5), Cmeta/N), 14.98 (s, SCH3) ppm. 31 1 P{ H} NMR (CD2Cl2 121.5 MHz) δ: 77.66 (br pseudo q, J (observed) = 11 Hz), 74.82 (br pseudo q, J (observed) = 11 Hz) ppm. 19F{1H} NMR (CD2Cl2, 282.4 MHz) δ: 152.2 (BF4) ppm. MS (ESI): m/z = 1916.06 [M − BF4]+. Complex 4c·BF4. Following the same procedure as described for compound 4a·BF4, using 1c (0.200 g, 0.40 mmol), AgBF4 (0.079 g, 0.40 mmol) and [NMe4]Cl (0.029 g, 0.26 mmol), yielded 4c·BF4 as colourless crystals (0.196 g, 0.30 mmol, yield based on 1c: 75%). Anal. Calcd for C93H81Cl2Ag3BF4N3P6O3 (1955.82): C, 57.11; H, 4.17; N, 2.14. Found: C, 57.46; H, 4.55; N, 2.09. FTIR: νmax(solid)/cm−1: 3052vw, 2950vw, 2837vw, 1600mw, 1579w, 1499m, 1480w, 1434m, 1290w, 1248m, 1190m, 1095m, 1052mw, 1024mw, 996vw, 984vw, 952ms, 908w, 890s, 821w, 791s, 739vs, 720mw, 690vs. 1H NMR (CD2Cl2, 400 MHz) δ: 7.37–7.32 (m, 12H, aromatic), 7.13–7.06 (m, 48H, aromatic), 6.11 (A part of a AB spin system, 6H, 3 JH,H = 9.0 Hz, N(C6H4)O, Hmeta/N), 5.62 (B part of a AB spin system, 6H, 3JH,H = 9.0 Hz, N(C6H4)O, Hortho/N), 3.51 (s, 9H, OCH3) ppm. 13C{1H} NMR (CD2Cl2, 75.5 MHz) δ: 158.50 (s, N(C6H4)O, Cpara/N), 133.39 (br, Cortho, aromatic), 132.62 (s, N(C6H4)O, Cortho/N), 130.79 (s, Cpara, aromatic), 128.33 (s, Cmeta, aromatic), 112.71 (s, N(C6H4)O, Cmeta/N), 57.11 (s, OCH3) ppm. 31P{1H} NMR (CD2Cl2 121.5 MHz) δ: 78.13 (br pseudo q, J (observed) = 11 Hz), 75.30 (br pseudo q, J (observed) = 11 Hz) ppm. 19F{1H} NMR (CD2Cl2, 282.4 MHz) δ: 151.6 (BF4) ppm. MS (ESI): m/z = 1868.12 [M − BF4]+. Complex Xb Method 1. Under inert atmosphere, solid AgBF4 (0.154 g, 0.78 mmol) and 1b (0.200 g, 0.39 mmol) were dissolved in 10 mL of acetone at room temp. The reaction mixture was stirred at room temp for 1.5 h under exclusion of light. NMR analysis (in acetone-d6) of an aliquot of the reaction mixture revealed the formation of 3b·(BF4)2. Evaporation to dryness of the reaction mixture and addition of dichloromethane led to a slightly pink solution. NMR analysis (in CD2Cl2) of an aliquot of the reaction mixture revealed the formation of Xb. Removing of the volatiles under reduced pressure, and washing with n-pentane (2 × 25 mL) afforded a light grey solid (0.238 g).53 Method 2. Under inert atmosphere, dry dichloromethane (10 mL) was added to solid AgBF4 (0.154 g, 0.78 mmol) and 1b (0.200 g, 0.39 mmol) and the resulting mixture was stirred at room temp for 1 h under exclusion of light. Removing of the volatiles under reduced pressure, and washing with n-pentane (2 × 25 mL) afforded a light grey solid (0.305 g, 0.16 mmol, yield based on the formula {[(1b)2Ag4][BF4]4·CH2Cl2}: 83%). Anal. Calcd for C63H56Ag4B4Cl2F16N2P4S2 (1878.76): C, 40.28; H, 3.00; N, 1.49. Found: C, 40.15; H, 3.01; N, 1.51. 1 H NMR (CD2Cl2, 400 MHz) δ: 7.62–7.55 (m, 12H, aromatic), 7.45–7.37 (m, 48H, aromatic), 6.85 (A part of a AB spin system, 6H, 3JH,H = 12 Hz, N(C6H4)S, Hmeta/N), 6.01 (B part of a AB spin system, 6H, 3JH,H = 12 Hz, N(C6H4)S, Hortho/N), 2.57 (s, 9H, SCH3) ppm. 13C{1H} NMR (CD2Cl2, 100 MHz) δ: 136.2

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(br, N(C6H4)S, Cpara/N), 134.5 (br, N(C6H4)S Cipso/N), 133.6 (br, Cortho, aromatic), 133.4 (br, Cpara, aromatic), 133.0 (br, N(C6H4) S, Cortho/N), 132.2 (br, Cipso, aromatic), 129.5 (br, Cmeta, aromatic), 128.9 (br, N(C6H4)S, Cmeta/N), 13.8 (s, SCH3) ppm. 31 1 P{ H} NMR (CD2Cl2 162 MHz) δ: 90.00 ( pseudo t, J (observed) = 21 Hz), 86.50 ( pseudo t, J (observed) = 21 Hz) ppm. 19F{1H} NMR (CD2Cl2, 282.4 MHz) δ: 152.0 (BF4) ppm. ESI-MS: m/z = 1916.1 [tentative M + K]+ (very weak intensity) and 849.8 [M − 2(BF4)]2+ with M = C63H56Ag4B4Cl2F16N2P4S2 = {[(1b)2Ag4][BF4]4·CH2Cl2}.

Acknowledgements We are grateful to the CNRS, the Ministère de la Recherche (Paris), the DFH/UFA (International Research Training Group 532-GRK532, Ph.D. grant to A. G.) for funding.

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