Migratory Insertion of Carbenes into Au(III)–C Bonds

Abstract

Migratory insertion of carbon-based species into transition-metal–carbon bonds is a mechanistic manifold of vast significance: it underlies the Fischer–Tropsch process, Mizoroki–Heck reaction, Ziegler–Natta and analogous late-transition-metal-catalyzed olefin polymerizations, and a number of carbonylative methods for the synthesis of ketones and esters, among others. Although this type of reactivity is well-precedented for most transition metals, gold constitutes a notable exception, with virtually no well-characterized examples known to date. Yet, the complementary reactivity of gold to numerous other transition metals would offer new synthetic opportunities for migratory insertion of carbon-based species into gold–carbon bonds. Here we report the discovery of well-defined Au(III) complexes that participate in rapid migratory insertion of carbenes derived from silyl- or carbonyl-stabilized diazoalkanes into Au–C bonds at temperatures ≥ −40 °C. Through a combined theoretical and experimental approach, key kinetic, thermodynamic, and structural details of this reaction manifold were elucidated. This study paves the way for homogeneous gold-catalyzed processes incorporating carbene migratory insertion steps.

Chiral N-heterocyclic Carbene Gold Complexes: Synthesis and Applications in Catalysis

“…Recently, the application of NBu4(acac) as a base has been reported for the efficient preparation of sterically unhindered complexes [59]. In addition, stronger bases are occasionally used, such as KHMDS [potassium bis(trimethylsilyl)amide] [60] or the mixture of NaH/KOtBu [61] (NaH is used as the stoichiometric base, whereas KOtBu acts Considering all the above aspects, N-heterocyclic carbene gold complexes offer an excellent opportunity for the development of efficient enantioselective processes. Although many excellent reviews devoted to the synthesis of phosphines (and related ligands) and N-heterocyclic carbene complexes have been published, no separate review covering the synthesis of chiral N-heterocyclic carbene gold(I) and gold(III) complexes has appeared to date.…”

“…Recently, the application of NBu 4 (acac) as a base has been reported for the efficient preparation of sterically unhindered complexes [59]. In addition, stronger bases are occasionally used, such as KHMDS [potassium bis(trimethylsilyl)amide] [60] or the Catalysts 2019, 9,890 3 of 40 mixture of NaH/KOtBu [61] (NaH is used as the stoichiometric base, whereas KOtBu acts as a phase transfer catalyst) in ethereal solvents. The combination of AuCl•SMe 2 /acetone constitutes arguably one of the most popular methods, widely used nowadays also for the synthesis of enantiomerically pure complexes.…”

A Dinuclear Mechanism Implicated in Controlled Carbene Polymerization

“…Inspired by our recent studies into migratory insertion in carbenoid gold intermediates, 25 we began our investigation with ( π -allyl)palladium chloride dimer (l), known to initiate the polymerization of EDA. 26 We hypothesized that the low-moderate yields of polymer resulted from the low nucleophilicity and Lewis basicity of the chloride ligand, detrimental to its migratory aptitude.…”

Architectural Stabilization of a Gold(III) Catalyst in Metal-Organic Frameworks

“…10 Despite these advances in mechanochemistry, the static force provided by rigid materials has, to the best of our knowledge, previously not been utilized toward the preservation of ligand geometry that are sensitive to bending effects. In cases where reductive elimination is problematic in transition-metal catalysis, [11][12][13] rigidification of ligands could potentially suppress such unimolecular decomposition pathways. Traditionally, solid-state supports have addressed bimolecular decomposition pathways of catalysts; [14][15][16] however, unimolecular decomposition pathways of homogeneous catalysts have previously not been suppressed with solid-state supports.…”

“…As a model system, we were interested in leveraging architectural stabilization to prevent a unimolecular decomposition pathway of IPrAu(III)(biphenyl)X (where IPr is [1,3-bis (2,6-diisopropylphenyl) imidazole-2-ylidene] and Xis a non-coordinating counteranion), which is known to undergo reductive elimination to yield biphenylene and IPrAu(I)X (Scheme 1B). 13 We reasoned that a bifunctionalized IPrAu(III)(biphenyl)X catalyst could be incorporated into a robust porous material to architecturally lock the geometry of the catalyst. Contrary to common solid-state supports, metal-organic frameworks (MOFs) allow for the precise placement of molecules in a well-ordered…”