Electronic and Steric Effects in Gold(I) Phosphine ThiolateComplexes

Abstract

The unusual yellow color of Au2(dppm)(SR)2 (R = 4-tolyl; dppm = diphenylphosphinomethane) is attributed to a red-shift in the S→Au charge transfer caused by destabilization of the sulfur highest occupied molecular orbital (HOMO). Variable temperature experiments show two broad bands at -80°C in the 31P{1H} NMR spectrum of Au2(dppm)(SR)2 and the activation energy for interconversion is 10 kcal/mol. Only one sharp band is observed down to -80°C in the spectrum of the white complex, Au2(dppe)(SR)2 (dppe = diphenylphosphinoethane). Molecular mechanics calculations on Au2(dppm)(SR)2 and Au2(dppe)(SR)2 reveal that, for Au2(dppe)(SR)2, a series of maxima and minima, separated by 2.5 kcal/mol, occur every 120° which is consistent with rotation around an unhindered carbon-phosphorus single bond. The Au atoms are not within bonding distance in any conformation. Computational results for Au2(dppm)(SR)2 indicate one minimum energy structure in which the Au-P bonds are anti. There is a high energy conformation (9 kcal/mol above the global minimum) where overlap between golds is maximized. The implications of gold-gold bonding in this complex are discussed. The steric influence of the thiolate ligand has been examined by synthesizing a series of dinuclear gold(I) complexes in which the steric properties of the thiolate are varied: Au2(dppm)(SR)2 (R = 2,6-dichlorophenyl; 2,6-dimethylphenyl; 3,5-dimethylphenyl). The 2,6-disubstituted complexes are white, while the 3,5-dimethyl complex is yellow. These results, along with VT-NMR experiments, are consistent with the conclusion that the more sterically-bulky thiolates hinder the close approach of the golds in the dinuclear complexes.

Architecture of Crystalline Polymers Formed from the Binuclear Complexes XAuPh2P(CH2)nPPh2AuX through Weak Au(I)···Au(I) Interactions

“…The weakness of the Au···Au interaction facilitates this self-assembly process. Related self-assembly of linear chains of complexes of the type RSAu(μ-ditertiary phosphine)AuSR have been reported. , Recently, Schmidbaur and co-workers have been able to construct novel crystalline polymers that utilize both the auriophilic interactions utilized in this study and hydrogen bonding as the weak interactions that facilitate self-assembly …”

“…Related self-assembly of linear chains of complexes of the type RSAu(µ-ditertiary phosphine)AuSR have been reported. 25,26 Recently, Schmidbaur and co-workers have been able to construct novel crystalline polymers that utilize both the auriophilic interactions utilized in this study and hydrogen bonding as the weak interactions that facilitate self-assembly. 27 Further development of this type of intermolecular organization may be expected to develop rapidly.…”

Electrochemical and Chemical Oxidation of Gold(I) Thiolate Phosphine Complexes: Formation of Gold Clusters and Disulfide

“…However, the targets and mechanisms of action of gold complexes remain elusive. Since rheumatoid arthritis has an oxidative pathology, − we have been studying the oxidative reactivity and electronic structure of complexes of the form LAu(SC 6 H 4 CH 3 ) and LL[Au(SC 6 H 4 CH 3 )] 2 , where L and LL are mono- and bisphosphines. − These complexes are related to the antiarthritis drug, Auranofin, which contains gold(I) coordinated to triethylphosphine and tetraacetylthioglucose. The study reported below demonstrates that mild oxidation of gold−sulfur complexes produces gold clusters and disulfide by way of an electron-transfer mechanism that occurs with unexpected n values.…”