Lewis Acid Catalysis with Cationic Dinuclear Gold(II,II) and Gold(III,III) Phosphorus Ylide Complexes

Abstract

The dinuclear gold­(II,II) and gold­(III,III) complexes [Au2(μ-PY)2(MeCN)2]­OTf2 (2-OTf 2 ) and [Au2(μ-PY)2(μ-CH2)­(MeCN)2]­OTf2 (3-OTf 2 ) (PY = [(CH2)2PPh2]−) have been synthesized and evaluated as Lewis acid catalysts for Mukaiyama addition and alkyne hydroamination reactions. 2-OTf 2 and 3-OTf 2 provide similar or improved catalytic activity for these reactions compared to the commonly used gold­(I) Lewis acids Ph3PAuOTf and IPrAuOTf. The versatile Lewis acidity of 2-OTf 2 was further demonstrated by its superior performance in a cascade reaction involving intramolecular hydroamination followed by intermolecular conjugate addition to generate a 2,3-substituted indole.

An Antimony(V) Dication as a Z‐Type Ligand: Turning on Styrene Activation at Gold

“…In conclusion, we describe the synthesis and characterization of ag old chloride complex, [3][NTf 2 ] 2 ,f eaturing ad icationic Z-type antimony ligand. Formation of this complex is made possible by the coordination of an eutral phosphine oxide donor that attenuates the reactivity of the dicationic antimony center.D espite its electron-deficient nature,the gold center of [3] 2+ can be activated by conversion into the proposed triflimide complex [4] 2+ .Generation of this complex is accompanied by the emergence of atypical reactivity [18] toward styrene which is readily polymerized or converted into the hydroamination Markovnikov product when in the presence of p-toluenesulfonamide.These unusual reactions highlight the unique activation resulting from the coordination of the dicationic antimony Z-type ligand to the gold center.…”

Recent Advances in Gold(III) Chemistry: Structure, Bonding, Reactivity, and Role in Homogeneous Catalysis

“…The gold-catalyzed Mukaiyama addition of silyl enol ethers to α,β unsaturated aldehydes was also achieved by Wade and coworkers with the dimeric phosphorus ylide complex 343. 555 Compound 343 led to the formation of a mixture of 1,2 and 1,4 adducts in a 73:27 ratio in the case of crotonaldehyde, while only the 1,4 adduct was obtained in the case of cyclohexanone (Scheme 150). The catalytic performance of 343 was however found to be inferior to the corresponding Au II dimer with a direct Au−Au bond.…”

Recent Progress in the Transition Metal Catalyzed Synthesis of Indoles

“…The reaction was widely applicable, but with two notable exceptions: 8-aminoquinoline and an alkyne substituted with a trimethylsilyl group were unreactive. Gold complexes were tested in the cascade reaction of 2-(phenylethynyl)aniline and cyclohexanone [48]. The hydroamination to afford 2-phenylindole was exclusively obtained (95% yield) with 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I) triflate (IPrAuOTf).…”

“…complexes were tested in the cascade reaction of 2-(phenylethynyl)anil none [48]. The hydroamination to afford 2-phenylindole was exclusively obtain ith 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I) triflate (IPrAuOT catalysts 3-OTf2 and 2-OTf2 (Scheme 24) a mixture of 2-phenylindole and the as obtained in a 78 and 14% yield and a 25 and 75% yield, respectively.…”