Bandeau LBPB

Chimie des métaux du groupe 11 (Cu et Au)

  • β-Hydride Elimination at Low-Coordinate Gold(III) Centers
    Rekhroukh, L. Estevez, S. Mallet-Ladeira, K. Miqueu*, A. Amgoune*, D. Bourissou*
    Am. Chem. Soc., 2016, 138, 11920–11929.

    JACS 2016 beta-H

    This Article reports the first comprehensive study of β-hydride elimination at gold(III). The stability/fate of gold(III) alkyl species have been investigated experimentally and computationally. A series of well-defined cationic cyclometalated gold(III) alkyl complexes [(P,C)gold(III)(R)][NTf2] [(P,C) = 8-diisopropylphosphino-naphthyl; R = Me, nPr, nBu] have been synthesized and spectroscopically characterized. While the cationic gold(III) methyl derivative 3c is stable for days at room temperature, the gold(III) n-propyl and n-butyl complexes 3a,b readily undergo β-hydride elimination at low temperature to generate propylene and 2-butenes, respectively. The formation of internal olefins from the gold(III) n-butyl complex 3b shows that olefin isomerization takes place after β-hydride elimination. Computational studies indicate that this isomerization proceeds through a chain-walking mechanism involving a highly reactive gold(III) hydride intermediate and a sequence of β-hydride elimination/reinsertion into the Au–H bond. The reaction of the cationic gold(III) methyl complex 3c with ethylene was also explored. According to 1H and 13C NMR spectroscopy, a mixture of propylene, 1-butene, and 2-butenes is formed. DFT calculations provide detailed mechanistic insights and support the occurrence of migratory insertion of ethylene, β-hydride elimination, and olefin exchange at gold(III).

  • Coordination–Insertion of Norbornene at Gold: A Mechanistic Study
    Rekhroukh, L. Estevez, C. Bijani, K. Miqueu*, A. Amgoune*, D. Bourissou*
    Organometallics, 2016, 35, 995–1001.

    toc OM

    A detailed experimental/theoretical study of the migratory insertion of norbornene into gold(III)–carbon bonds of discrete (P,C)-cyclometalated gold(III) alkyl complexes is reported. The generation of cationic gold(III) methyl complex 2 by methide abstraction with B(C6F5)3 has been confirmed spectroscopically at low temperature. The DFT-optimized structure of this highly electrophilic species indicates a three-coordinate gold(III) species with T-shaped geometry. In the presence of norbornene, the corresponding gold(III)–olefin complex 3 is formed, and it has been fully characterized by NMR spectroscopy at low temperature. Bonding analysis of this key intermediate confirmed the significantly weaker contribution of metal-to-olefin back-donation with gold compared with the other late transition metals. Upon warm-up, the π complex 3 evolves by insertion of the olefin into the Au(III)–Me bond to form the cationic (P,C)gold(III)–norbornyl complex 4. The mechanism of the double addition has been extensively explored by DFT calculations, and the results strongly support a two-step coordination–migratory insertion pathway. The influence of the unsymmetrical (P,C) bidentate ligand on the kinetic and thermodynamic parameters of the reaction is also discussed. This comprehensive organometallic study provides new important insights into the coordination, structure, and reactivity of gold(III) complexes. It highlights some fundamental similarities but also points out some significant differences with isolobal Pd(II) alkyl complexes.

  • Experimental and Theoretical Evidence for an Agostic Interaction in a Gold(III) Complex
    Rekhroukh, L. Estévez, C. Bijani, K. Miqueu*, A. Amgoune*, D. Bourissou*
    Angew. Chem. Int. Ed. 2016, 55, 3414-3418.

    ACIE toc agostic

    The first agostic interaction in a gold complex is described. The presence of a bonding C−H⋅⋅⋅Au interaction in a cationic “tricoordinate” gold(III) complex was suggested by DFT calculations and was subsequently confirmed by NMR spectroscopy at low temperature. The agostic interaction was analyzed computationally using NBO and QTAIM analyses (NBO=natural bond orbital; QTAIM=quantum theory of atoms in molecules).

  • Reactivity of Gold Complexes towards Elementary Organometallic Reactions
    Joost, A. Amgoune*, D. Bourissou*
    Angew. Chem. Int. Ed. 2015, 54, 15022-15045.

    ACIE Revue Gold

    For a while, the reactivity of gold complexes was largely dominated by their Lewis acid behavior. In contrast to the other transition metals, the elementary steps of organometallic chemistry—oxidative addition, reductive elimination, transmetallation, migratory insertion—have scarcely been studied in the case of gold or even remained unprecedented until recently. However, within the last few years, the ability of gold complexes to undergo these fundamental reactions has been unambiguously demonstrated, and the reactivity of gold complexes was shown to extend well beyond π-activation. In this Review, the main achievements described in this area are presented in a historical context. Particular emphasis is set on mechanistic studies and structure determination of key intermediates. The electronic and structural parameters delineating the reactivity of gold complexes are discussed, as well as the remaining challenges.

  • Oxidative Addition of Carbon-Carbon Bonds to Gold
    M. Joost, L. Estevez, K. Miqueu,* A. Amgoune,* D. Bourissou*
    Angew. Chem. Int. Ed. 2015, 54, 5236-5240.

Add Ox ACIE 2015

The oxidative addition of strained C[BOND]C bonds (biphenylene, benzocyclobutenone) to DPCb (diphosphino-carborane) gold(I) complexes is reported. The resulting cationic organogold(III) complexes have been isolated and fully characterized. Experimental conditions can be adjusted to obtain selectively acyl gold(III) complexes resulting from oxidative addition of either the C(aryl)[BOND]C(O) or C(alkyl)[BOND]C(O) bond of benzocyclobutenone. DFT calculations provide mechanistic insight into this unprecedented transformation.

  •  Coordination of a Triphosphine-Silane to Gold: Formation of a Trigonal Pyramidal Complex Featuring Au+→Si Interaction
    P. Gualco, S. Mallet-Ladeira, H. Kameo, H. Nakazawa, M. Mercy, L. Maron, A. Amgoune, D. Bourissou
    Organometallics 2015, 34, 1449-1453.

OM 2015 TPsi

Coordination of the triphosphine–fluorosilane [o-(iPr2P)C6H4]3SiF to AuCl results in the formation of a trigonal pyramidal cationic complex. Though cationic, the gold center acts as a Lewis base and is engaged in significant Au→Si interaction, as substantiated by X-ray diffraction and NMR spectroscopy. In solution, the P,P,P,Si tetracoordinate cationic complex coexists with a neutral P,P,Cl tricoordinate form, with a pendant phosphine buttress and without Au→Si interaction. The bonding situation in the two isomeric forms has been assessed by DFT calculations. Coordination of the third phosphine arm is shown to induce cationization and to play a key role in the presence of the Au→Si interaction.

  •  Cationic Gold(III) Alkyl Complexes: Generation, Trapping and Insertion of Norbornene.
    F. Rekhroukh, R. Brousses, A. Amgoune,* D. Bourissou.*
    Angew. Chem., Int. Ed. 2015, 54, 1266-1269.

Coinage 1

Migratory insertion of alkenes into gold–carbon bonds, a key, yet unprecedented organometallic reaction, is evidenced. Methide abstraction from a (P,C) cyclometallated gold(III) dimethyl complex with B(C6F5)3  is shown to generate a highly reactive cationic Au(III) complex. In the presence of norbornene, migratory insertion into the Au–C bond proceeds at low temperature. The resulting norbornyl complex was trapped with pyridines and chloride.

  • Enhanced π-Backdonation from Gold(I): Isolation of Original Carbonyl and Carbene Complexes.
    M. Joost, L. Estevez, S. Mallet-Ladeira, K. Miqueu,* A. Amgoune,* D. Bourissou*
    Angew. Chem., Int. Ed. 2014, 53, 14512-14516.

Coinage 2

Bending was shown to significantly enhance π-backdonation in gold(I) complexes. This strategy gives access to the first classical carbonyl complex of gold and allows the isolation of a diphenyl carbene complex that is stabilized by the gold fragment rather than the carbene substituents. The structures of these new complexes were thoroughly analyzed by spectroscopic, crystallographic, and computational means.

  • Facile Oxidative Addition of Aryl-iodides to Gold(I) by Ligand Design: Bending Turns on Reactivity.
    M. Joost, A; Zeineddine, L. Estevez, S. Mallet-Ladeira, K. Miqueu, A. Amgoune,* D. Bourissou*
    J. Am. Chem. Soc. 2014, 136, 14654-14657.

Coinage 3

Thanks to rational ligand design, the first gold(I) complexes to undergo oxidative addition of aryl iodides were discovered. The reaction proceeds under mild conditions and is general. The ensuing aryl gold(III) complexes have been characterized by spectroscopic and crystallographic means. DFT calculations indicate that the bending induced by the diphosphine ligand plays a key role in this process.

  • Mechanisms of syn-Insertion of Alkynes and Allenes into Gold–Silicon Bonds: A Comprehensive Experimental/Theoretical Study.
    M. Joost, L. Estevez, S. Mallet-Ladeira, K. Miqueu,* A. Amgoune,* D. Bourissou,*
    J. Am. Chem. Soc. 2014, 136, 10373-10382

Coinage 4

A detailed mechanistic study is reported for the syn-insertion of alkynes and allenes in the Au−Si bonds of complexes (R3P)Au−SiR′Ph2 (R = Ph, Me and R′ = t-Bu, Ph). The reaction is found to proceed via a two-step inner-sphere mechanism: (i) first, the alkyne coordinates to the gold silyl complex to form a π-complex; (ii) the subsequent migratory insertion step is rate determining and occurs in a concerted manner.

  • Activation of Aryl Halides at Gold(I): Practical Synthesis of (P,C) Cyclometallated Gold(III) Complexes.
    J. Guenther, S. Mallet-Ladeira, L. Estevez, K. Miqueu, A. Amgoune,* D. Bourissou,*
    J. Am. Chem. Soc. 2014, 136, 1778-1781

Coinage 5

Taking advantage of phosphine chelation, direct evidence for oxidative addition of Csp2−X bonds (X= I, Br) to a single gold atom is reported. NMR studies and DFT calculations provide insight into this unprecedented transformation, which gives straightforward access to stable (P,C) cyclometalated gold(III) complexes.

  • Direct Evidence for Intermolecular Oxidative Addition of s(Si-Si) Bonds to Gold.
    M. Joost, P. Gualco, K. Miqueu, C. E. Kefalidis, L. Maron,* A. Amgoune,* D. Bourissou,*
    Angew. Chem., Int. Ed. 2014, 53, 747–751.

Coinage 6

Oxidative addition is the most elusive elementary step in gold chemistry. Here, we report evidence for intermolecular oxidative addition of s(Si–Si) bonds. Phosphine gold chlorides are shown to readily react with disilanes at low temperature in the presence of GaCl3. The ensuing gold(III) bis(silyl) complexes have been characterized by quantitative 31P and 29Si NMR experiments. Their structure (distorted Y-shape) and the reaction profile of s(Si–Si) bond activation have been analyzed by DFT calculations.

  • Direct syn Insertion of Alkynes and Allenes into Au-Si Bonds.
    M. Joost, P. Gualco, S. Mallet-Ladeira, A. Amgoune,* D. Bourissou,*
    Angew. Chem., Int. Ed. 2013, 52, 7160–7163.

Coinage 7

Alkynes and allenes are shown to insert into Au–Si bonds with complete stereocontrol and in most cases complete regiocontrol. The ensuing b–silyl vinyl gold complexes have been characterized by spectroscopic and crystallographic means. These results provide unequivocal evidence for syn insertion reactions at gold.

  • Activation of a σ-SnSn Bond at Copper, Followed by Double Addition to an Alkyne.
    N. Lassauque, P. Gualco, S. Mallet-Ladeira, K. Miqueu, A. Amgoune,* D. Bourissou,*
    J. Am. Chem. Soc. 2013, 135, 13827-13834.

Coinage 8

In this contribution, we report that σ-SnSn bond of a diphosphine-distannane ligand readily undergoes oxidative addition at both gold and copper, giving bis(stannyl) Au+ and Cu+ complexes. Coordination of the ligand to CuBr leads to a neutral complex which features more σ-SnSn complex character. The reaction of the bis(stannyl) Cu+ complex with methyl propiolate afforded cleanly a bis-stannylated alkene copper complex. The structures of all complexes have been unambiguously determined by multinuclear NMR spectroscopy and crystallography. These results substantiate the ability of copper to promote the addition of apolar σ-bonds to CC multiple bonds via a 2e redox sequence and draw thereby an unprecedented parallel with the group 10 metals.


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