A Thermally Stable Gold(III) Hydride: Synthesis, Reactivity, and Reductive Condensation as a Route to Gold(II) Complexes

摘要

Transition-metal hydride complexes are well-established as key intermediates in numerous homogeneously and hetero-geneously catalyzed reactions. Hydride complexes of plat-inum(II), for example, have been known for over 50 years. Analogous complexes of the isoelectronic gold(III), on the other hand, appear to be unknown. This is all the more surprising as gold complexes have attracted much attention as catalysts and catalyst precursors in recent years. For example, heterogeneous gold catalysts are used for selective hydrogenations ; for zirconia-supported gold hydrogenation catalysts, surface Au~(3+) ions have been proposed as active sites. Both gold(I) and gold(III) hydrides have been postulated as intermediates in numerous homogeneously catalyzed hydrogenations, hydrosilylations, dehydrogen-ative alcohol silylations, hydroborations,1 and other organic transformations. Corma and co-workers used immobilized gold(III) chelate complexes as hydrogenation catalysts and explored the possible involvement of Au~(III) hydride intermediates in detail by kinetic and computational methods. On the other hand, the highly positive standard redox potentials for gold (Au~(3+)/Au~+ = 1.36 V; Au~(3+)/Au~0 = 1.52 V) might suggest facile reduction of Au~(III) in the presence of hydride. Binary hydrides, including AuH, (H2)AuH, (H2)AuH3, and [AuH4]~-, have been detected in frozen gas matrices below 5 K. We report herein the synthesis and reactions of a thermally stable gold(III) hydride, [(C^N^C)~*AuH], wherein (C^N^C)~* is a doubly cyclometa-lated 2,6-bis(4'-tert-butylphenyl)pyridine ligand.