A dynamic tetranuclear gold()-cyclophane - gold()-centred chirality and fluxionality arising from an intramolecular shift of Au-S bonds

A tetranuclear gold( i ) complex [Au 4 (μ-PAnP) 2 (μ-L) 2 ] (PAnP = 9,10-bis(diphenylphosphino)anthracene and L = benzene-1,2-dithiolate) has been synthesized and characterised by multinuclear NMR and X-ray crystallography. The molecule has a cyclophane-like structure which can be considered to be composed of two [Au 2 (μ-PAnP)(μ-L)] units held together by Au-S bonds and aurophilic interactions (Au-Au = 3.0712(2) Å). L acts as a chelating and bridging ligand with one of its S atoms bonded to two Au ions as sulfonium ions and there are two Au 2 S 2 cores on each side of the cyclophane. A sulfur atom in each Au 2 S 2 core is a chiral sulfonium ion, being bonded to two chemically distinct Au ions. Two Au ions are bonded to four atoms (2S, P and Au) in an asymmetric environment, making them a rare example of gold( i )-centred chirality. The two Au 2 S 2 cores have R Au , R S and S Au , S S configurations, and the chiralities of the sulfonium ion and the gold ion are correlated. Variable-temperature NMR spectroscopy showed that the metallacyclophane undergoes rapid exchange in solution. A bond shift mechanism involving simultaneous cleavage and formation of Au-S bonds is proposed for the exchange. A dynamic tetranuclear gold( i )-cyclophane which shows gold( i )-centred chirality and fluxionality arising from ligand exchange.