A Dynamic Tetranuclear Gold(I)-Cyclophane - Gold(I)-Centred Chirality And Fluxionality Arising From An Intramolecular Shift Of Au-S Bonds

A tetranuclear gold(i) complex [Au-4(mu-PAnP)(2)(mu-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(mu-PAnP)(mu-L)] units held together by Au-S bonds and aurophilic interactions (Au-Au = 3.0712(2) angstrom). 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 Au2S2 cores on each side of the cyclophane. A sulfur atom in each Au2S2 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 Au2S2 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.