Science of Synthesis

Hopkinson, M. N.; Gouverneur, V., Science of Synthesis Knowledge Updates, (2011) 2, 101.

Reductive elimination from suitably substituted gold(III) complexes to afford products of homocoupling and cross coupling and gold(I) has been widely observed. A series of studies by Kochi and Komiya, among others, have focused on dialkylgold(III) complexes. Whilst the simple dimeric dimethylgold(III) complex ‌1‌ detonates violently upon melting at 78.5°C,[‌15‌] gold(III) derivatives of the form ‌2‌ {cis-[Au(Me)2X(PR13)]} stabilized by phosphine ligands thermally emit ethane with rates dependent on the nature of the phosphine and the substituent X (‌Scheme 1‌).[‌16‌–‌24‌] In some cases, complexes ‌2‌ can be prepared via oxidative addition of iodomethane to the corresponding methylgold(I) species (for X = I)[‌25‌–‌28‌] or dimethylaurate(I) (for X = Me).[‌29‌,‌30‌] Reductive elimination from ‌2‌ is thought to occur from a three-coordinate intermediate formed upon dissociation of the phosphine. The addition of excess phosphine to the reaction mixture severely retards formation of ethane. Reductive elimination of sp2-[‌19‌,‌20‌,‌31‌–‌33‌] and sp-hybridized[‌34‌] organic fragments from gold(III) complexes has also been reported. Thermolysis of triorgano-substituted species of type ‌2‌ (when X is organic) produces mixtures of coupled products resulting from Me–X and Me–Me oxidative coupling.[‌35‌] When X is aryl, hetaryl, or alkenyl, C(sp3)–C(sp2) coupling is favored, whereas ethane is generated as the major product with sp-hybridized substituents (X = alkynyl).

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References