The stability of organogold compounds. Hydrolytic, thermal, and oxidative cleavages of dimethylaurate(I) and tetramethylaurate(III)

Abstract

The decomposition of the anionic permethyl derivatives of gold(1) and gold( I 11) are btudied to contrast their stability with other methylgold complexes. The hydrolytic, (hernial. and oxidative cleavage of dimethblaurate(1) and tetrnmethyluu- rate(lll) are examined in two series of complexes: (I) lithium pentamethyldiethylenetriamine (PMDT) chclates and (2) lithi- um complexes in the presence of triphenylphosphine. First, hydrolysis leads to cleavage of only a single methyl-gold bond from either dimethylaurate or tetramethylaurate, but the gold products depend on the availability of ligands. Thus, in the presence of phosphine, CH3AuPPh3 and (CH3)?.AuPPh3 are obtained. whereas metallic gold (and ethane) are produced from the Li(PMDT) complexes. Second, the thermal decompositions of both dimethll- and tetramethylaurates proceed at much sloucr rates than those of the corresponding neutral methyl- and trimethylgold species examined previously. Molecular orbital calcu- lations suggest that fragmentation of the coordinatively saturated tetramethylaurate (which is a symnietrb-allo\~cd procw) is more difficult than that of trimethylgold owing to unavoidable ligand-ligand interactions. Finally. both diniethll- and te- tramcthylaurates, in contrast to their neutral counterparts. undergo rapid decomposition in the presence of dioxggen ;is well as methyl iodide to produce unusual products. For example. (CH3)2AuLi(PPh3) is converted by dioxygcn to a niixture ofoniy CHAAuPPh3 and (CH3)3AuPPh3 in high yields; and (CH3)uignctic intermediates.