Abstract
Herein we describe the isolation and characterisation of the first "gold-allenylidene" complexes [Au&z.dbd; C&z.dbd; C&z.dbd; CR sub(2)] super(+) X super(-) (R = N(CH sub(2)) sub(n), OMe; n= 3, 4; X super(-) = OTf super(-)) and present a bonding model for these species based on an experimental and theoretical analysis. Heteroatom stabilisation (oxygen and nitrogen donors) overpowers the ligand effect on gold and has a large impact on the distribution of electron density in the allenylidene fragment. The description of a gold-stabilised propargylic cation rather than a gold-vinylidene complex is favoured, clearly indicated by experimental and theoretical work. Removing this heteroatom stabilisation by means of a theoretical analysis shows that the choice of ligand can fine-tune the electronics ranging from a gold-stabilised carbocation towards a Au-allenylidene. This observation is in excellent agreement with the recent gold "carbene vs.carbocation" discussion and expands the understanding of Au-carbocation interactions to include gold-cumulene systems.