Gold complexes of ditelluridoimidodiphosphinate ligands - reversible oxidation of Au(I) to Au(III) via insertion of gold into a phosphorus-tellurium bond

The reaction of (THT) AuCl with (TMEDA)Na[N(TePR2)(2)] (R = Ph, i-Pr, t-Bu) produces a series of gold (III) complexes of the type [{R2PNP(Te)R-2}Au(mu-Te)](2) (4a, R = i-Pr; 4b, R = Ph; 4c, R = t-Bu) rather than the expected homoleptic Au(I) complexes of the ditelluridoimidodiphosphinate ligands. A combination of solution- and solid-state NMR studies shows that both cis and trans isomers of 4a-4c are formed in these reactions. X-ray structural determinations of the trans isomers of 4a-4c reveal a centrosymmetric arrangement with a central four-membered Au2Te2 ring formed by the formal insertion of gold into a P-Te bond; this insertion process was shown to be reversible upon addition of PPh3 to 4a to give the monomeric gold(I) complex Ph3PAu[N{TeP(i-Pr)(2)}(2)]. The X-ray structure of cis-4b is also described.