Preparation, structure and decomposition of gold(I) and gold(III) acetylide complexes

1-Alkynyl-dimethyl(triorganophosphine)gold(III) complexes of the type cis-Me2(Ph3P)Au–Ctriple bond; length of mdashC–R with R = H, Me, Ph (1–3) have been prepared from the cis-Me2(Ph3P)AuX (X = Cl, I) complexes and lithium alkynyls. The crystal structures of 1 and 2 have been determined together with those of the reference compounds cis-Me2(Ph3P)AuX (X = Cl, I) and cis-Me2(Me3P)AuI. The molecules have a standard square planar geometry and are not associated into oligomers. Due to the different hybridization of the carbon orbitals, the Au–C(triple bond; length of mdashCR) bonds are found significantly shorter than the Au–CH3 bonds. Compounds 1–3 are stable colourless, crystalline solids at 20 °C but decompose on heating with selective (cis) reductive elimination of ethane and formation of the gold(I) alkynyls (Ph3P)Au–Ctriple bond; length of mdashC–R thus retaining the stronger gold-alkynyl bonds. Two complexes of this type have also been prepared by conventional routes from (R3P)AuX complexes and the crystal structures of (Me3P)Au–Ctriple bond; length of mdashC–Ph and [(p-Tol)3P]Au–Ctriple bond; length of mdashC–H have been determined. The former with the small Me3P ligand is associated into two different trimers via aurophilic bonding and further aggregated into chains via weak inter-trimer contacts, while the latter is a monomer owing to the steric bulk of the (p-Tol)3P ligand.