Bandeau LBPB

Chemistry of the coinage metals

  • Gold(I)/Gold(III) Catalysis Merging Oxidative Addition and π-Alkene Activation
    M. Rigoulet, O. Thillaye du Boullay, A. Amgoune, D. Bourissou
    Angew. Chem. Int. Ed., 2020, Ahead Printing

    The hetero‐arylation of alkenes with aryl iodides has been efficiently achieved with the (MeDalphos)AuCl complex via Au(I)/Au(III) catalysis. The possibility to combine oxidative addition of aryl iodides and π‐activation of alkenes at gold is demonstrated for the first time. The reaction is robust and general (>30 examples including internal alkenes, 5, 6 and 7‐membered rings). It is regioselective and leads exclusively to trans addition products. The (P,N) gold complex is most efficient with electron‐rich aryl substrates, which are troublesome with alternative photoredox / oxidative approaches. In addition, it actuates a very unusual switch in regioselectivity from 5‐exo to 6‐endo cyclization between the Z and E isomers of internal alkenols.

  • Gold(III) π‐Allyl Complexes
    J. Rodriguez, G. Szalóki, E. D. Sosa Carrizo, N. Saffon‐Merceron, K. Miqueu, D. Bourissou
    Angew. Chem. Int. Ed., 2020, 59, 1511-1515.

    Gold(III) π‐complexes have been authenticated recently with alkenes, alkynes, and arenes. The key importance of PdII π‐allyl complexes in organometallic chemistry (Tsuji–Trost reaction) prompted us to explore gold(III) π‐allyl complexes, which have remained elusive so far. The (P,C)AuIII(allyl) and (methallyl) complexes 3 and 3′ were readily prepared and isolated as thermally and air‐stable solids. Spectroscopic and crystallographic analyses combined with detailed DFT calculations support tight quasi‐symmetric η3‐coordination of the allyl moiety. The π‐allyl gold(III) complexes are activated towards nucleophilic additions, as substantiated with β‐diketo enolates.

  • Versatility and adaptative behaviour of the P^N chelating ligand MeDalphos within gold(I) π complexes
    M. Navarro, A. Toledo, S. Mallet-Ladeira, E. D. Sosa Carrizo, K. Miqueu, D. Bourissou
    Chem. Sci., 2020, 11, 2750-2758.

    The hemilabile P^N ligand MeDalphos enables access to a wide range of stable gold(I) π-complexes with unbiased alkenes and alkynes, as well as electron-rich alkenes and for the first time electron-poor ones. All complexes have been characterized by multi-nuclear NMR spectroscopy and whenever possible, by X-ray diffraction analyses. They all adopt a rare tricoordinate environment around gold(I), with chelation of the P^N ligand and side-on coordination of the alkene, including the electron-rich one, 3,4-dihydro-2H-pyrane. The strength of the N → Au coordination varies significantly in the series. It is the way the P^N ligand accommodates the electronic demand at gold, depending on the alkene. Comparatively, when the chelating P^P ligand (ortho-carboranyl)(PPh2)2 is used, gold(I) π-complexes are only isolable with unbiased alkenes. The bonding situation within the gold(I) P^N π-complexes has been thoroughly analyzed by DFT calculations supplemented by Charge Decomposition Analyses (CDA), Natural Bond Orbital (NBO) and Atoms-in-Molecules (AIM) analyses. Noticeable variations in the donation/back-donation ratio, C C weakening, alkene to gold charge transfer and magnitude of the N → Au coordination were observed. Detailed examination of the descriptors for the Au/alkene interaction and the N → Au coordination actually revealed intimate correlation between the two, with linear response of the MeDalphos ligand to the alkene electronics. The P^N ligand displays non-innocent and adaptative character. The isolated P^N gold(I) π-complexes are reactive and catalytically relevant, as substantiated by the chemo and regio-selective alkylation of indoles.

  • Au(I)/Au(III)-Catalyzed C–N coupling
    J. Rodriguez, N. Adet, N. Saffon-Merceron, D. Bourissou
    Chem. Commun., 2020,56, 94-97.

    Cycling between Au(I) and Au(III) is challenging, so gold-catalyzed cross-couplings are rare. The (MeDalphos)AuCl complex, which we showed was prone to undergo oxidative addition, is reported here to efficiently catalyze the C–N coupling of aryl iodides and amines. The transformation does not require an external oxidant or a directing group. It is robust and works with a wide scope of aryl iodides and N-nucleophiles under mild conditions. Mechanistic studies, including the NMR and MS characterization of a key aryl amido Au(III) complex, strongly support a 2e redox cycle in which oxidative addition precedes transmetalation and reductive elimination is the rate-determining step.

  • Catalytic Au(I)/Au(III) arylation with the hemilabile MeDalphos ligand: unusual selectivity for electron-rich iodoarenes and efficient application to indoles
    J. Rodriguez, A. Zeineddine, E. D. Sosa Carrizo, K. Miqueu, N. Saffon-Merceron, A. Amgoune, D. Bourissou
    Chem. Sci., 2019, 10, 7183-7192.

    The ability of the hemilabile (P,N) MeDalphos ligand to trigger oxidative addition of iodoarenes to gold has been thoroughly studied. Competition experiments and Hammett correlations substantiate a clear preference of gold for electron-enriched substrates both in stoichiometric oxidative addition reactions and in catalytic C–C cross-coupling with 1,3,5-trimethoxybenzene. This feature markedly contrasts with the higher reactivity of electron-deprived substrates typically encountered with palladium. Based on DFT calculations and detailed analysis of the key transition states (using NBO, CDA and ETS-NOCV methods in particular), the different behavior of the two metals is proposed to result from inverse electron flow between the substrate and metal. Indeed, oxidative addition of iodobenzene is associated with a charge transfer from the substrate to the metal at the transition state for gold, but opposite for palladium. The higher electrophilicity of the gold center favors electron-rich substrates while important back-donation from palladium favors electron-poor substrates. Facile oxidative addition of iodoarenes combined with the propensity of gold(III) complexes to readily react with electron-rich (hetero)arenes prompted us to apply the (MeDalphos)AuCl complex in the catalytic arylation of indoles, a challenging but very important transformation. The gold complex proved to be very efficient, general and robust. It displays complete regioselectivity for C3 arylation, it tolerates a variety of functional groups at both the iodoarene and indole partners (NO2, CO2Me, Br, OTf, Bpin, OMe…) and it proceeds under mild conditions (75 °C, 2 h).

  • Cyclometalated AuIII Complexes for Cysteine Arylation in Zinc Finger Protein Domains: towards Controlled Reductive Elimination
    M. N. Wenzel, R. Bonsignore, S. R. Thomas, D. Bourissou, G. Barone, A. Casini
    Chem. Eur. J., 2019, 25, 7628-7634.

    With the aim of exploiting the use of organometallic species for the efficient modification of proteins through C‐atom transfer, the gold‐mediated cysteine arylation through a reductive elimination process occurring from the reaction of cyclometalated AuIII C^N complexes with a zinc finger peptide (Cys2His2 type) is here reported. Among the four selected AuIII cyclometalated compounds, the [Au(CCON)Cl2] complex featuring the 2‐benzoylpyridine (CCON) scaffold was identified as the most prone to reductive elimination and Cys arylation in buffered aqueous solution (pH 7.4) at 37 °C by high‐resolution LC electrospray ionization mass spectrometry. DFT and quantum mechanics/molecular mechanics (QM/MM) studies permitted to propose a mechanism for the title reaction that is in line with the experimental results. Overall, the results provide new insights into the reactivity of cytotoxic organogold compounds with biologically important zinc finger domains and identify initial structure–activity relationships to enable AuIII‐catalyzed reductive elimination in aqueous media.

  • Evidence for genuine hydrogen bonding in gold(I) complexes
    M. Rigoulet, S. Massou, E. D. Sosa Carrizo, S. Mallet-Ladeira, A. Amgoune, K. Miqueu, D. Bourissou
    Proc. Natl. Acad. Sci. U. S. A., 2019, 116, 46-51.

    The ability of gold to act as proton acceptor and participate in hydrogen bonding remains an open question. Here, we report the synthesis and characterization of cationic gold(I) complexes featuring ditopic phosphine-ammonium (P,NH+) ligands. In addition to the presence of short Au∙∙∙H contacts in the solid state, the presence of Au∙∙∙H–N hydrogen bonds was inferred by NMR and IR spectroscopies. The bonding situation was extensively analyzed computationally. All features were consistent with the presence of three-center four-electron attractive interactions combining electrostatic and orbital components. The role of relativistic effects was examined, and the analysis is extended to other recently described gold(I) complexes.

  • (P,​C) Cyclometalated Gold(III) Complexes: Highly Active Catalysts for the Hydroarylation of Alkynes
    C. Blons, S. Mallet-Ladeira, A. Amgoune, C. Bourissou
    Angew. Chem. Int. Ed. 2018, 57, 11732-11736

    TOC ACIE Charlie

    The first catalytic application of well‐defined (P,C) cyclometalated gold(III) complexes is reported. The bench‐stable bis(trifluoroacetyl) complexes 2 a,b perform very well in the intermolecular hydroarylation of alkynes. The reaction is broad in scope, it proceeds within few hours at 25 °C at catalytic loadings of 0.1–5 mol %. The electron‐rich arene adds across the C≡C bond with complete regio‐ and stereo‐selectivity. The significance of well‐defined gold(III) complexes and ligand design are highlighted in a powerful but challenging catalytic transformation.

  • Isolation of a Reactive Tricoordinate α-​Oxo Gold Carbene Complex
    A. Zeineddine, F. Rekhroukh, E. D. Sosa Carrizo, S. Mallet-Ladeira, K. Miqueu, A. Amgoune, D. Bourissou
    Angew. Chem. Int. Ed. 2018, 57, 1306-1310

    TOC ACIE Abdallah

    The [(P,P)Au=C(Ph)CO2Et]+ complex 3 [where (P,P) is an o‐carboranyl diphosphine ligand] was prepared by diazo decomposition at −40 °C. It is the first α‐oxo gold carbene complex to be characterized. Its crystallographic structure was determined and DFT calculations have been performed, unraveling the key influence of the chelating (P,P) ligand. The gold center is tricoordinate and the electrophilicity of the carbene center is decreased. Complex 3 mimics transient α‐oxo gold carbenes in a series of catalytic transformations, and provides support for the critical role of electrophilicity in the chemoselectivity of phenol functionalization (O−H vs. C−H insertion).

  • Rational development of catalytic Au(I)​/Au(III) arylation involving mild oxidative addition of aryl halides
    A. Zeineddine, L. Estevez, S. Mallet-Ladeira, K. Miqueu, A. Amgoune, D. Bourissou
    Nature Comm. 2017, 8, 1-8

    TOC Nat Comm 2017 Zeineddine

    The reluctance of gold to achieve oxidative addition reaction is considered as an intrinsic limitation for the development of gold-catalyzed cross-coupling reactions with simple and ubiquitous aryl halide electrophiles. Here, we report the rational construction of a Au(I)/Au(III) catalytic cycle involving a sequence of Csp2–X oxidative addition, Csp2–H auration and reductive elimination, allowing a gold-catalyzed direct arylation of arenes with aryl halides. Key to this discovery is the use of Me-Dalphos, a simple ancillary (P,N) ligand, that allows the bottleneck oxidative addition of aryl iodides and bromides to readily proceed under mild conditions. The hemilabile character of the amino group plays a crucial role in this transformation, as substantiated by density functional theory calculations.

  • A Nucleophilic Gold(III) Carbene Complex
    A. Pujol, M. Lafage, F. Rekhroukh, N. Saffon-Merceron, A. Amgoune,* D. Bourissou,* N. Nebra, M. Fustier-Boutignon,* N. Mezailles*
    Angew. Chem. Int. Ed., 2017, 56, 12264-12267.

    ACIE 2017
    The first AuIII carbene complex was prepared by reacting a geminal dianion with a (P,C) cyclometalated AuIII precursor. Its structure and bonding situation have been thoroughly investigated by experimental and computational means. The presence of a high-energy highest occupied molecular orbital (HOMO) centered at the carbene center suggests nucleophilic character for the AuIII carbene complex. This unprecedented feature was confirmed by reactions with two electrophiles (PhNCS and CS2), resulting in two types of C=C coupling reactions.

  • Reactivity of Gold Complexes towards Elementary Organometallic Reactions
    M. 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.

  • 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.

    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.

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