Intermediates and Elementary Reactions in Gold Catalysis

The success of homogeneous gold catalysis [1] was accompanied by intensive efforts to understand the mechanisms of the new conversions [2]. None of the many new gold-catalyzed reactions proceeds through only one transition state, we always deal with multistep mechanisms. Many of the reactions have the first steps in common, and then diverge at a later stage of the sequence of elementary steps of the catalytic cycles, which ultimately leads to the manifold of different products that can be obtained. 

These initial steps involve the Jt-coordination of the unsaturated substrate which activates the substrate for the attack of an intra- or intermolecular nucleophile. At the other end of the catalytic cycle, typically the last step is a proto-deauration, setting free the LAu fragment for the next turnover of the catalytic cycle. 

By a detailed computational investigation, including relativistic treatment, insights into the mechanism of activation by x-complexation to gold could be obtained. For both goldfl) and goldfni), the x-coordination to propyne has been 

Molecular Catalysts Structure and Functional Desiffi, First Edition. Edited by Lutz H Gade and Peter Hofmann. 2014 Wiley-VCH Verlag GmbH Co. KGaA. Published 2014by Wiley-VCH VerIagGmbH Co. KGaA. 

Only in 2009/2010, a proof for their participation in catalytic cycles could be obtained by isolation of some of these species. This, in the end, opened up a preparative access to these species, which for the first time enabled chemists to expand this aspect of organogold chemistry in new directions. 

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