title: Gold carbenoids: lessons learnt from a transmetalation approach.
abstract: Carbophilic catalysts that are based on Au(I) allow a host of different nucleophiles to be added across various π systems. Although many of these reactions are thought to proceed via gold carbenoids, the challenge to observe and characterize these putative intermediates has basically been unmet. The current mechanistic interpretation therefore largely relies on indirect evidence and computational data, some of which are subject to debate. In an attempt to fill this gap, we pursued a potential route to gold carbenoids by formal transmetalation of chromium or tungsten Fischer carbene complexes with [LAu](+). Whereas this transformation proceeds with exceptional ease as long as a stabilizing heteroelement is present on the carbene center, it stops half-way in its absence. Rather unusual bimetallic arrays are formed, which allow the charge density to delocalize over several positions. The obvious difficulty of releasing an "unstabilized" gold carbenoid has potential mechanistic implications for the understanding of π-acid catalysis in general.
authors.affiliation: Max-Planck-Institut für Kohlenforschung, 45470 Mülheim/Ruhr (Germany).
authors.forename: Günter
authors.initials: G
authors.lastname: Seidel
authors.forename: Barbara
authors.initials: B
authors.lastname: Gabor
authors.forename: Richard
authors.initials: R
authors.lastname: Goddard
authors.forename: Berit
authors.initials: B
authors.lastname: Heggen
authors.forename: Walter
authors.initials: W
authors.lastname: Thiel
authors.forename: Alois
authors.initials: A
authors.lastname: Fürstner
keywords: carbene complexes; chromium; dimetalation; gold; tungsten