The isomerization of gold(I) ylide dimers and the preparation and structure of the gold(II) ylide dimers containing ligands coordinated through sulfur

Abstract

The preparation of the asymmetric gold dimer, 2, [Au(CH₂)₂P(C₆H₅)(CH₃)]₂, was carried out using Li[C₆H₅)(CH₃)P(CH₂)₂] and (C₆H₅)₃PAuCl. The trans isomer was isolated as the predominant product. Isomerization of trans-2 to an equilibrium mixture of cis and trans isomers was monitored using ¹H NMR. It was found to be first order in 2. Isomerization was suppressed by bases and enhanced by the addition of both protonic and Lewis acids. No deuterium incorporation into the ylide ligands was observed. The structures of the SO₂ adducts [Au(CH₂)₂P(C₆H₅)₂]₂[SO₂]₂ and [Au(CH₂)₂P(C₆H₅)(CH₃)]₂[SO₂]₂ were determined. The SO₂ molecules were found to be weakly coordinated at the Au centers. A mechanism for the isomerization of 2 was proposed involving activation by Lewis acids at a nucleophilic gold center of 2. The structures of the [Au(CH₂)₂P(C₆H₅)(CH₃)]₂Cl₂, [Au(CH₂)₂P(C₆H₅)(CH₃)]₂Br₂, [Au(CH₂)₂P(C₆H₅)(CH₃)]₂CH₂Cl₂, and 2 are also reported. A series of Au(II) ylide dimer compounds with ligand coordinated through sulfur were prepared using oxidative addition, ligand exchange, or proton abstraction techniques. Crystal structures for the following compounds were carried out: diethyldithiocarbamate, [Au(CH₂)₂P(C₆H₅)(CH₃)]₂[S₂CN(C₂H₅]₂; thiocyanate, [Au(CH₂)₂P(C₆H₅)(CH₃)]₂[SCN]₂; thiophenol, [Au(CH₂)₂P(C₆H₅)₂]₂[S(C₆H₅)]₂; 2-mercapto-2-thiazolin, [Au(CH₂)₂P(C₆H₅)₂]₂[SCSNC₂H₄]₂; 2-mercaptobenzothiazole, [Au(CH₂)₂P(C₆H₅)₂]₂[SCSNC₆H₄]₂; thiosalicylic acid, [Au(CH₂)₂P(C₆H₅)₂]₂[SC₆H₅CO₂H]₂; the catinated sulfur compounds [Au(CH₂)₂P(C₆H₅)₂]₂[SSC(NC₆H₅)(NHC₆H₅)]₂ and {[Au(CH₂)₂P(C₆H₅)₂]₂}₂S₄S₄. The Au(III) compound of benzenedithiol, [Au(CH₂)₂P(C₆H₅)₂]₂[S₂C₆H₄]₂ also is reported.