Thermally stable gold(III) alkene and alkyne complexes: Synthesis, structures, and assessment of the trans-influence on Gold–Ligand bond enthalpies

The reaction of [C^C)Au(OEt2)2]+ with 1,5-cyclooctadiene or norbornadiene affords the corresponding olefin complexes [(C^C)Au(COD)]SbF6 and [(C^C)Au(NBD)]SbF6, which are thermally stable in solution and the solid state (C^C=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 (C^C)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 [(C^C)Au(AdC/CAd)(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 p-donor ligands to AuIII fragments and the effect of the trans influence exerted by Nand 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 p-acceptors being particularly affected. In comparison with [Me2Au]+, the [(C^C)Au]+ fragment is more polar and in bond enthalpy terms resembles Me2Pt.