Thermally Stable Gold(III) Alkene and Alkyne Complexes: Synthesis, Structures, and Assessment of the trans-Influence on Gold-Ligand Bond Enthalpies

The reaction of [(CC)-C-boolean AND)Au(OEt2)(2)](+) with 1,5-cyclooctadiene or norbornadiene affords the corresponding olefin complexes [((CC)-C-boolean AND)Au(COD)]SbF6 and [((CC)-C-boolean AND)Au(NBD)]SbF6, which are thermally stable in solution and the solid state ((CC)-C-boolean AND=4,4-di-tert-butylbiphenyl-2,2-diyl). The crystal structures of these complexes have been determined. By contrast, dienones such as dibenzylideneacetone are O- rather than C=C-bonded. The reactions of ((CC)-C-boolean AND)Au(OAcF)(L) (L=PMe3 or CNxyl) with B(C6F5)(3) in the presence of bis(1-adamantyl)acetylene give the mixed-ligand alkyne complexes [((CC)-C-boolean AND)Au(AdCCAd)(L)](+), the first complexes of their type in gold chemistry. In the presence of an excess of acetylene these compounds are thermally stable in solution and as solids. The bonding of n- and pi-donor ligands to Au-III fragments and the effect of the trans influence exerted by N- and C-donors was explored with the aid of DFT calculations. Results show that the Au-L bond enthalpies trans to anionic C are 35-60% of the enthalpies trans to N, with strong pi-acceptors being particularly affected. In comparison with [Me2Au](+), the [((CC)-C-boolean AND)Au](+) fragment is more polar and in bond enthalpy terms resembles Me2Pt.