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Activation of M−Cl Bonds with Phosphine−Alanes: Preparation and Characterization of Zwitterionic Gold and Copper Complexes Marie Sircoglou, †,∥ Nathalie Saffon,‡ Karinne Miqueu,*,§ Ghenwa Bouhadir,*, † and Didier Bourissou*, † †

Université de Toulouse, UPS, LHFA, 118 route de Narbonne, 31062 Toulouse, France, and CNRS, LHFA, UMR 5069, 31062 Toulouse, France ‡ Université Paul Sabatier, Institut de Chimie de Toulouse (FR 2599), 118 route de Narbonne, 31062 Toulouse cedex 9, France § Institut Pluridisciplinaire de Recherche sur l’Environnement et les Matériaux UMR-CNRS 5254, Université de Pau et des Pays de l′Adour, Hélioparc, 2 avenue du Président Angot, 64053 Pau Cedex 09, France S Supporting Information *

ABSTRACT: The triphosphine−alane [iPr2P(o-C6H4)]3Al (1) was prepared by coupling ortho-lithiated diisopropylphenylphosphine with AlCl3. Reactions of 1 with gold and copper chlorides afforded the zwitterionic cage complexes 2 and 3. The three phosphine arms coordinate symmetrically to the coinage metal, while the aluminum center abstracts the chloride. Coordination of the related diphosphine−alane [iPr2P(o-C6H4)]2AlCl (4) to CuCl is also accompanied by a shift of the chloride atom from copper to aluminum. However, the ensuing highly electrophilic Cu+ center engages in weak intraand intermolecular Cl→Cu interactions, resulting in the original polymeric complex 5. The structures of all complexes have been ascertained spectroscopically and crystallographically, and their bonding situations have been analyzed by DFT calculations.

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INTRODUCTION Over the past few years, the coordination properties of ambiphilic ligands have been investigated intensively.1 The Lewis acid moiety was found to readily participate in the coordination, giving rise to unusual bonding situations. In this context, we have been particularly interested in phosphine ligands featuring a group 13 element in close proximity. Typically, diphosphine− and triphosphine−boranes were found to engage in P→M→B bridging coordination, in which the borane moiety behaves as a σ-acceptor ligand. 2 The corresponding ligands based on heavier group 13 elements (Al, Ga, In) behave quite differently and tend to favor M−Cl activation processes.3 Ionization of M−X bonds with ambiphilic ligands represents an interesting and direct entry to zwitterionic complexes. Zargarian and Fontaine first proposed the formation of complexes I4 and II5 upon activation of Ni−Me and Rh−Me bonds with the simple phosphine−alane Me2PCH2AlMe2 (Figure 1). In 2008, Tilley reported the zwitterionic Ni complex III,6 providing unambiguous evidence for the cleavage of a M−X bond with an ambiphilic ligand. Simultaneously, we disclosed the ionization of Au−Cl bonds with a diphosphine− alane (complex of type IV)3a and subsequently prepared related zwitterionic gold complexes with phosphine−gallane and −indanes (complexes IV and V).3b,c Very recently, Stephan further extended this methodology and isolated complex VI upon coordination of a diphosphine−borane to RuCl2.7 In this paper, we report the coordination and ionization of AuCl and CuCl with phosphine−alanes. This was envisioned to provide zwitterionic complexes that are relatively rare, in © XXXX American Chemical Society

Figure 1. Zwitterionic complexes derived from M−X bond activations with ambiphilic ligands.

Special Issue: Applications of Electrophilic Main Group Organometallic Molecules Received: June 20, 2013

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particular for copper. These complexes usually derive from the coordination of preformed anionic ligands.8 Copper is intrinsically more electrophilic than gold, and thus abstraction of chloride by the aluminum center is a priori less favorable with copper than with gold. The synthesis of the new triphosphine−alane 1 and its coordination to gold and copper leading to the zwitterionic cage complexes 2 and 3 are described. The formation of the original polymer copper complex 5 from the related diphosphine−alane 4 is also discussed.

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Figure 2. Molecular views of complexes 2 (left) and 3 (right). The isopropyl groups are simplified, and the hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg) are as follows. Complex 2: P1−Au, 2.370(1); P2−Au, 2.388(1); P3−Au, 2.376(1); Al−Cl, 2.266(2); Au−Al, 3.026(1); P3−Au−P2, 119.29(3); P2−Au− P1, 119.02(3); P1−Au−P3, 120.62(3); Au−Al−Cl, 179.60(6). Complex 3: P1−Cu, 2.278(2); P2−Cu, 2.297(2); P3−Cu, 2.290(2); Al−Cl, 2.255(3); Cu−Al, 3.044(2); P3−Cu−P2, 120.13(8); P2−Cu− P1, 118.88(8); P1−Cu−P3, 120.25(8); Cu−Al−Cl, 179.3(1).

RESULTS AND DISCUSSION The triphosphine−alane (TPA) 1 (Scheme 1) was obtained by reacting AlCl3 with 3 equiv of ortho-lithiated diisopropylpheScheme 1. Synthesis of the Zwitterionic Complexes 2 and 3 upon Coordination of the Triphosphine−Alane 1

sum of C−Al−C bond angles 354.3°). The cage structure maintains a relatively short Al−Au distance of 3.026(1) Å (28% shorter than the sum of van der Waals radii (4.2 Å)11 and 18% longer than the sum of covalent radii (2.57 Å)12). A weak interaction between the metal center and the chloroaluminate is conceivable, and indeed an NBO analysis carried out on the optimized structure revealed the presence of weak Au→Al interactions (ΔENBO = 16.6 kcal/mol). The corresponding neutral form (without transfer of chloride from Au to Al) is found to be slightly higher in energy computationally (+2.1 kcal/mol at the B3PW91/SDD+f (M), 6-31G** (other atoms) level of theory, taking into account solvent effects).13 In solution, it may coexist or be in equilibrium with the corresponding zwitterionic form. For a detailed discussion on the coexistence/interconversion of neutral/zwitterionic forms of the related diphosphine− and triphosphine−gallane AuCl complexes, see ref 3b. With the aim of generalizing the process of M−Cl ionization with ambiphilic ligands, we then became interested in preparing zwitterionic copper complexes. To this end, the TPA ligand 1 was reacted with CuCl and the ensuing complex 3 was characterized spectroscopically and crystallographically. The 31P NMR spectrum displays a unique resonance signal at δ 14.3 ppm, indicating the symmetric coordination of the three phosphine arms. An X-ray diffraction study substantiated the shift of Cl from copper to aluminum in 3, resulting in a zwitterionic structure very similar to that of 2. The copper center is surrounded by the three phosphorus atoms (CuP distances ∼2.29 Å) and adopts a trigonal-planar geometry (sum of P−Cu−P bond angles 359.3°). The most salient features of the aluminum environment are (i) the short Al−Cl distance (2.255(3) Å) and quasi-linear CuAlCl arrangement (179.3(1)°), (ii) the outward pyramidalization of the C3Al framework (sum of C−Al−C bond angles 352.3°), and (iii) the enforced transannular Cu−Al distance (3.044(2) Å), associated with a very weak Cu→Al interaction according to NBO analysis (ΔE = 3.5 kcal/mol).14,15 Thus, the higher Lewis acidity of copper in comparison to gold does not prevent the splitting of the M−Cl bond and zwitterionic complexes are obtained in both cases. Zwitterionic complexes of copper are rare,8 and the coordination of ambiphilic ligands to copper halides appears to be an efficient and straightforward route to such complexes. As a further

nylphosphine in toluene at room temperature. According to 31P NMR spectroscopy, compound 1 is formed in nearly quantitative yield. Its 31P NMR chemical shift at δ 15 ppm suggests the existence of some degree of P→Al interactions, as previously observed in related ambiphilic compounds.1d,3a,9,10 After filtration and evaporation, the TPA 1 was obtained as a white solid (90% crude yield). The extreme sensitivity of 1 precluded its isolation, and it was thus engaged into coordination without further purification. First, the TPA ligand 1 was treated with a suspension of [AuCl(SMe2)] in dichloromethane (DCM). A white precipitate instantaneously formed, and complex 2 was readily isolated (85% yield) (Scheme 1). The presence of a unique 31P NMR signal at δ 60.0 ppm indicates the symmetric coordination of the three phosphine arms and thus the formation of a cage structure. To further assess the coordination mode of the TPA ligand, crystals of 2 were grown from a saturated dichloromethane solution at −30 °C and analyzed by X-ray diffraction (Figure 2). Similarly to that observed in the related diphosphine−alane complex,3a the coordination of 1 mainly proceeds with transfer of the chloride from Au to Al. In the solid state, the TPA complex 2 adopts a zwitterionic structure analogous to that of the corresponding triphosphine−gallane and −indane complexes.3b,c The gold center is coordinated by the three phosphine side arms organized together in a trigonal-planar environment (average P−Au−P bond angle 119.4°). The chlorine atom at Al sits trans to gold (Au−Al−Cl bond angle 179.60(6)°), and the Al−Cl distance (2.266(2) Å) is in the typical range for a chloroaluminate. The aluminum center slightly deviates from the plane defined by the three carbon atoms of the o-phenylene linkers and points opposite to gold (outward pyramidalization, B

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To gain further insight into the structure of complex 5, DFT calculations were performed on the monomeric unit. At the B3PW91/SDD+f (Cu), 6-31G** (other atoms) level of theory, the geometric features of the zwitterionic moiety determined crystallographically are fairly well reproduced (Figure 4). Two

extension of this work, we were intrigued by the behavior of the related diphosphine−alane (DPA) 4 toward copper, several scenarios being conceivable. On the one hand, we have shown previously that the corresponding diphosphine−borane ligands engage in multicenter BCC interactions upon coordination to copper.16 On the other hand, M−Cl activation with DPA, as observed in the related gold complex,3a would lead to a highly electrophilic diphosphine Cu+ moiety.17 Reaction of the DPA ligand 4 with CuCl readily afforded complex 5 (Scheme 2). 31P NMR spectroscopy (δ 22.7 ppm) Scheme 2. Synthesis of the Polymeric Complex 5 upon Coordination of the Diphosphine−Alane 4

Figure 4. Optimized structures of complexes 5 ZI* (left) and 5 N* (right) at the B3PW91/SDD+f (Cu), 6-31G** (other atoms) level of theory. Selected bond lengths (Å) and angles (deg) are as follows. Complex 5 ZI*: P−Cu, 2.236; Al−Cl1, 2.253; Al−Cl2, 2.179; Cl1− Cu, 2.536; Cu−Al, 3.037; P−Cu−P, 157.75; Cl1−Al−Cl2, 102.96; Al−Cl1−Cu, 76.54. Complex 5 N*: P−Cu, 2.291; Al−Cl1, 2.173; Cu−Al, 2.552; P−Cu−P, 152.31; Cl2−Cu−Al, 161.11.

indicates the formation of a symmetric diphosphine complex. Crystals of 5, obtained from a saturated DCM solution at −30 °C, were analyzed by X-ray diffraction (Figure 3). Accordingly,

very close Al−Cl distances are found computationally (2.253 and 2.179 Å), and one of the Cl atoms still interacts with the copper center (Cu···Cl1, 2.536 Å). Consistently, a weak Cl→ Cu interaction is found at the second-order perturbation level in the NBO analysis (ΔENBO = 19.0 kcal/mol). The zwitterionic form 5 ZI* is the global minimum on the potential energy surface. The corresponding neutral form 5 N* corresponds to a local minimum and is located 8.3 kcal/mol higher in energy. The short CuAl distance (2.552 Å, in comparison with 2.53 Å for the sum of covalent radii) and the inward pyramidalization of the aluminum environment (sum of C−Al−C and C−Al−Cl1 bond angles 346.1°) are diagnostic of a substantial Cu→Al interaction in 5 N*. The corresponding NBO delocalization energy is estimated as 12.8 kcal/mol. In conclusion, direct formation of zwitterionic complexes upon activation of M−X bonds with ambiphilic ligands has been expanded to copper. Reaction of the triphosphine−alane 1 with copper chloride gives the zwitterionic cage complex 3. The three phosphine arms coordinate symmetrically to copper, while the aluminum center abstracts chloride. The related diphosphine−alane 4 also forms a zwitterionic complex with copper chloride. However, the ensuing Cu+ center is highly electrophilic and engages in weak intra- and intermolecular Cl→Cu interactions, resulting in the original polymeric complex 5. These results substantiate further the versatility of ambiphilic ligands. The generation of electrophilic metal centers upon such internal M−X ionization opens interesting perspectives, and the reactivity of zwitterionic complexes derived from ambiphilic ligand is worth exploring.18

Figure 3. Molecular view of two repetitive units of complex 5. The isopropyl groups are simplified, and the hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg) are as follows: P1−Cu, 2.252(1); P2−Cu, 2.253(1); Al−Cl1, 2.204(1); Al−Cl2, 2.241(1); Cu−Cl1, 2.582(1); Cu−Cl2, 2.540(1); P1−Cu−P2, 141.18(3); Cl2−Cu−Cl1, 93.29(3); Al−Cl1−Cu, 78.33(3); Al− Cl2−Cu, 135.00(4).

complex 5 adopts a polymeric structure in which zwitterionic units are connected via Cu−Cl−Al bridges. The aluminum center is bound tightly to two chlorine atoms (Al−Cl1, 2.204(1) Å; Al−Cl2, 2.241(1) Å) and adopts a tetrahedral geometry. The coordination of the two phosphine arms to copper is characterized by short CuP distances (∼2.25 Å) and a wide PCuP bond angle (141.18(3)°). Two weak Cu···Cl contacts are also noticed, one with a Cl atom at the Al center of the same molecule (Cu···Cl1, 2.582(1) Å) and one with a Cl atom of the neighboring molecule (Cu···Cl2, 2.540(1) Å). Thus, coordination of DPA to copper induces the shift of the Cl atom from Cu to Al, but the resulting diphosphine Cu+ center is highly electrophilic and thus retains some weak interaction with the chlorine atom and engages in a weak bridging Cl→Cu interaction. This situation markedly contrasts with that encountered in the related DPA gold complex.3a In the latter compound, the gold center is dicoordinated and does not interact with chlorine atoms, neither intra- nor intermolecularly.

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EXPERIMENTAL SECTION

General Comments. All reactions and manipulations were carried out under an atmosphere of dry argon using standard Schlenk techniques. Dry, oxygen-free solvents were employed. Diethyl ether was dried over sodium/benzophenone, and CH2Cl2 was dried over CaH2 and distilled prior to use. 1H, 13C, 27Al, and 31P NMR spectra were recorded on Bruker Avance 300, 400WB, and AMX 500 spectrometers. Chemical shifts are expressed with a positive sign, in parts per million, relative to residual 1H and 13C solvent signals and external Al(NO3)3 and 85% H3PO4, respectively. Unless otherwise stated, NMR spectra were recorded at 25 °C. AlCl3 (anhydrous C

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Crystallographic Analyses. Crystallographic data for compounds 2, 3, and 5 were collected on a Bruker-AXS SMART APEX II diffractometer at low temperature with Mo Kα radiation (wavelength 0.71073 Å) by using ψ and ω scans. The data were integrated with SAINT, and an empirical absorption correction with SADABS was applied.21 The structures were solved by direct methods, using SHELXS-97,22 and refined using the least-squares method on F2. All non-H atoms were treated anisotropically. All H atoms attached to C atoms were fixed geometrically and treated as riding on their parent atoms with C−H = 0.95 Å (aromatic), 0.98 Å (CH3), 0.99 Å (CH2), or 1.0 Å (CH) with Uiso(H) = 1.2[Ueq(CH,CH2)] or Uiso(H) = 1.5[Ueq(CH3)].

powder, 99.999%) was purchased from Aldrich and used as received. The ortho-lithiated diisopropylphenylphosphine19 and diphosphine− alane 43a were prepared as previously described. The N values corresponding to 1/2[J(AX) + J(BX)] are provided for the secondorder AXX′ systems observed in 13C NMR.20 The following atom numbering has been used for the TPA and DPA ligands in complexes 2, 3, and 5:

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TPA 1. The ortho-lithiated diisopropylphenylphosphine (diethyl ether adduct, 150 mg, 0.59 mmol) was dissolved in 5 mL of toluene and was added slowly at room temperature to dry aluminum chloride (26 mg, 0.20 mmol). After filtration and elimination of volatiles under vacuum, the triphosphine−alane TPA was obtained as a white solid (107 mg, 90% crude yield). The ligand TPA proved to be extremely sensitive and was thus only characterized by 31P NMR. 31P NMR (202.5 MHz, toluene, 298 K): δ 15.0. Au Complex 2. A solution of TPA 1 (113 mg, 0.19 mmol) in toluene (5 mL) was added slowly to a suspension of [AuCl(SMe2)] (55 mg, 0.19 mmol) in dichloromethane (0.5 mL) at −78 °C. A white precipitate appeared, which persisted on warming to room temperature. Elimination of the supernatant and drying of the solid under vacuum afforded complex 2 as a white powder (114 mg, 85%). Colorless crystals of the complex suitable for X-ray crystallography were obtained from a saturated dichloromethane solution at −30 °C. Mp: 148−150 °C. 31P NMR (202.5 MHz, CD2Cl2, 238 K): δ 60.0. 1H NMR (500.3 MHz, CD2Cl2, 238 K): δ 8.70 (m, 3H, Harom), 7.47−7.31 (m br, 6H, Harom), 7.21 (m br, 3H, Harom), 3.04 (m, 3H, CHiPr), 2.02 (m, 3H, CHiPr), 1.19 (m, 18H, CH3 iPr), 0.97 (m, 9H, CH3 iPr), −0.02 (m, 9H, CH3 iPr). 13C{1H} NMR (125.8 MHz, CD2Cl2, 238 K): δ 165.4 (s br, C1), 142.9 (AXX′, N = 11.2 Hz, CHarom), 137.4 (AXX′, N = 21.0 Hz, C6), 130.9 (s, CHarom), 127.9 (s, CHarom), 125.3 (s, CHarom), 26.6 (AXX′, N = 11.4 Hz, CHiPr), 24.9 (AXX′, N = 10.9 Hz, CHiPr), 20.4 (s br, CH3 iPr), 19.5 (s br, CH3 iPr), 17.5 (s, CH3 iPr), 17.3 (s, CH3 iPr). Cu Complex 3. A solution of TPA 1 (490 mg, 0.81 mmol) in dichloromethane (6 mL) was added slowly to a suspension of anhydrous CuCl (80 mg, 0.81 mmol) in the same solvent (1 mL) at −78 °C. When it was warmed to room temperature, the solution became limpid. After evaporation of the solvent, 3 was obtained as a white powder (532 mg, 93%). Colorless crystals of the complex suitable for X-ray crystallography were obtained from a saturated dichloromethane solution at −30 °C. 31P NMR (202.5 MHz, CD2Cl2, 298 K): δ 14.3. 27Al NMR (104.13 MHz, CD2Cl2, 298 K) δ 69.9 (W1/2 ≈ 3096 Hz). 1H NMR (500.3 MHz, CD2Cl2, 298 K): δ 8.44 (d br, 3H, 3 J(H,H) = 6.4 Hz, H5), 7.32 (m, 3H, H2), 7.22 (m, 6H, H3,4), 2.70 (m, 3H, CHiPr), 1.43 (m, 12H, CH3 iPr and CHiPr), 1.38 (m 9H, CH3 iPr), 0.62 (m, 18H, CH3 iPr). 13C{1H} NMR (125.8 MHz, CD2Cl2, 298 K): δ = 165.1 (s br, C1), 142.2 (AXX′, N = 10.7 Hz, C5), 140.5 (m, C6), 129.4 (s, C2), 127.4 (s, CHarom), 125.8 (m, CHarom), 27.7 (m, CHiPr), 23.4 (m,, CHiPr), 23.2 (m, CH3 iPr), 20.9 (s br, CH3 iPr), 18.9 (s, CH3 iPr), 17.3 (s, CH3 iPr). Cu Complex 5. A solution of DPA 4 (63 mg, 0.14 mmol) in dichloromethane (2 mL) was added to a suspension of anhydrous CuCl (19 mg, 0.19 mmol) in the same solvent (0.5 mL) at −78 °C. When it was warmed to room temperature, the solution became limpid. The solution was concentrated, and the inorganic residue was eliminated by filtration. Cooling the supernatant to −30 °C allowed colorless crystals of 5 (23 mg, 20%) suitable for X-ray crystallography to be obtained. 31P NMR (202.5 MHz, CDCl3, 273 K): δ 22.7. 1H NMR (500.3 MHz, CDCl3, 273 K): δ 8.22 (d, 2H, 3J(H,H) = 7.1 Hz, H5), 7.35 (m, 4H, Harom), 7.26 (t, 2H, 3J(H,H) = 7.1 Hz, Harom), 2.50 (m, 4H, CHiPr), 1.26 (m, 12H, CH3 iPr), 1.03 (m, 12H, CH3 iPr). 13 C{1H} NMR (125.8 MHz, CDCl3, 273 K): δ 160.0 (br, C1 or C6), 139.6 (AXX′, N = 10.7 Hz, CHarom), 130.1 (s, CHarom), 128.7 (s, CHarom), 127.1 (s, CHarom), 22.6 (s, CHiPr), 19.2 (s, CH3 iPr), 18.1 (s, CH3 iPr). C1 or C6 is not observed.

ASSOCIATED CONTENT

S Supporting Information *

Text, tables, figures, and CIF files giving multinuclear NMR spectra of 1−3 and 5, computational details and Cartesian coordinates for the optimized structures, and X-ray crystallographic data for CCDC 941329 (2), 941330 (3), and 941331 (5). This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*D.B.: fax, 33 (0)5 61 55 82 04; tel, 33 (0)5 61 55 68 03; email, [email protected]. Present Address ∥

Institut de Chimie Moléculaire et des Matériaux d’Orsay, UMR-CNRS 8182, Université de Paris-Sud XI, 91405 Orsay, France. Notes

The authors declare no competing financial interests.

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ACKNOWLEDGMENTS Financial support from the Centre National de la Recherche Scientifique, the Université de Toulouse, and the Agence Nationale de la Recherche (ANR-10-BLAN-070901) is gratefully acknowledged. The theoretical work was granted access to HPC resources of Idris under Allocation 2013 (i2013080045) made by Grand Equipement National de Calcul Intensif (GENCI).

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REFERENCES

(1) (a) Kuzu, I.; Krummenacher, I.; Meyer, J.; Armbruster, F.; Breher, F. Dalton Trans. 2008, 5836. (b) Fontaine, F.-G.; Boudreau, J.; Thibault, M. H. Eur. J. Inorg. Chem. 2008, 5439. (c) Braunschweig, H.; Dewhurst, R. D.; Schneider, A. Chem. Rev. 2010, 110, 3924. (d) Bouhadir, G.; Amgoune, A.; Bourissou, D. Adv. Organomet. Chem. 2010, 58, 1. (2) (a) Amgoune, A.; Bourissou, D. Chem. Commun. 2011, 47, 859. (b) Braunschweig, H.; Dewhurst, R. D. Dalton Trans. 2011, 40, 549. (3) (a) Sircoglou, M.; Bouhadir, G.; Saffon, N.; Miqueu, K.; Bourissou, D. Organometallics 2008, 27, 1675. (b) Sircoglou, M.; Mercy, M.; Saffon, N.; Coppel, Y.; Bouhadir, G.; Maron, L.; Bourissou, D. Angew. Chem., Int. Ed. 2009, 48, 3454. (c) Derrah, E. J.; Sircoglou, M.; Mercy, M.; Ladeira, S.; Bouhadir, G.; Miqueu, K.; Maron, L.; Bourissou, D. Organometallics 2011, 30, 657. (4) Fontaine, F.-G.; Zargarian, D. J. Am. Chem. Soc. 2004, 126, 8786. (5) (a) Thibault, M. H.; Boudreau, J.; Mathiotte, S.; Drouin, F.; Sigouin, O.; Michaud, A.; Fontaine, F.-G. Organometallics 2007, 26, 3807. (b) Boudreau, J.; Fontaine, F.-G. Organometallics 2011, 30, 511. (6) Fischbach, A.; Bazinet, P. R.; Waterman, R.; Tilley, T. D. Organometallics 2008, 27, 1135. (7) Boone, M. P.; Stephan, D. W. J. Am. Chem. Soc. 2013, 135, 8508.

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(8) For selected examples, see: (a) Thompson, J. S.; Harlow, R. L.; Whitney, J. F. J. Am. Chem. Soc. 1983, 105, 3522. (b) Dias, H. V. R.; Lu, H.-L.; Kim, H.-J.; Polach, S. A.; Goh, T. K. H. H.; Browning, R. G.; Lovely, C. J. Organometallics 2002, 21, 1466. (c) Thomas, J. C.; Peters, J. C. Polyhedron 2004, 23, 2901. (d) Mankad, N. P.; Peters, J. C. Chem. Commun. 2008, 1061. (e) McCormick, T.; Jia, W. L.; Wang, S. Inorg. Chem. 2005, 45, 147. (f) Cesar, V.; Barthes, C.; Farre, Y. C.; Cuisiat, S. V.; Vacher, B. Y.; Brousses, R.; Lugan, N.; Lavigne, G. Dalton Trans. 2013, 42, 7373. (9) Bontemps, S.; Bouhadir, G.; Dyer, P. W.; Miqueu, K.; Bourissou, D. Inorg. Chem. 2007, 46, 5149. (10) For triphosphine− and diphosphine−alanes featuring CH2C6H4, CH2SiMe2N, and C6H4N spacers, see: (a) Müller, G.; Lachmann, J.; Rufinska, A. Organometallics 1992, 11, 2970. (b) Fryzuk, M. D.; Giesbrecht, G. R.; Olovsson, G.; Rettig, S. J. Organometallics 1996, 15, 4832. (c) Lee, P.-Y.; Liang, L.-C. Inorg. Chem. 2009, 48, 5480. (11) Batsanov, S. S. Inorg. Mater. 2001, 37, 871. (12) Cordero, B.; Gomez, V.; Platero-Prats, A. E.; Reves, M.; Echeverria, J.; Cremades, E.; Barragan, F.; Alvarez, S. Dalton Trans. 2008, 2832. (13) The neutral form displays much stronger Au→Al interactions (53.6 kcal/mol) than the zwitterionic form. (14) (a) The corresponding neutral form, without transfer of chloride from Cu to Al, is found to be +6.3 kcal/mol higher in energy at the B3PW91/SDD+f (M), 6-31G** (other atoms) level of theory, taking into account solvent effects. (b) Copper has been shown to form significantly weaker M→Lewis acid interactions than gold: Sircoglou, M.; Bontemps, S.; Bouhadir, G.; Saffon, N.; Miqueu, K.; Gu, W.; Mercy, M.; Chen, C. H.; Foxman, B. M.; Maron, L.; Ozerov, O. V.; Bourissou, D. J. Am. Chem. Soc. 2008, 130, 16729. (15) The cationic triphosphine−borane copper complex (TPB)Cu+ was reported recently to feature a very weak Cu→B interaction: Moret, M. E.; Zhang, L.; Peters, J. C. J. Am. Chem. Soc. 2013, 135, 3792. (16) Sircoglou, M.; Bontemps, S.; Mercy, M.; Miqueu, K.; Ladeira, S.; Saffon, N.; Maron, L.; Bouhadir, G.; Bourissou, D. Inorg. Chem. 2010, 49, 3983. (17) We have recently taken advantage of this property to prepare and study σ-SiSi and σ-SiH complexes of copper: (a) Gualco, P.; Amgoune, A.; Miqueu, K.; Ladeira, S.; Bourissou, D. J. Am. Chem. Soc. 2011, 133, 4257. (b) Joost, M.; Mallet-Ladeira, S.; Miqueu, K.; Amgoune, A.; Bourissou, D. Organometallics 2013, 32, 898. (18) For selected reviews on the preparation and reactivity of zwitterionic complexes, see: (a) Chauvin, R. Eur. J. Inorg. Chem. 2000, 577. (b) Piers, W. E. Chem. Eur. J. 1998, 4, 13. (c) Stradiotto, M.; Hesp, K. D.; Lundgren, R. J. Angew. Chem., Int. Ed. 2010, 49, 494. (19) Tamm, M.; Dreβel, B.; Baum, K.; Lügger, T.; Pape, T. J. Organomet. Chem. 2003, 677, 1. (20) (a) Nuclear Magnetic Resonance Spectroscopy; Bovey, F. A. Ed.; Academic Press: New York, 1969. (b) Abraham, R. J.; Bernstein, H. J. Can. J. Chem. 1961, 39, 216. (21) (a) SAINT-NT; Bruker AXS, Madison, WI, 2000. (b) SADABS, Program for Data Correction; Bruker AXS, Madison, WI. (22) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refinement. Acta Crystallogr. 2008, A64, 112.

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