Synthesis and catalytic activity of heterobimetallic Au/M (M = Rh^III, Ir^III) complexes with ditopic mono- and triphosphane ligands

A series of heterobimetallic complexes Au/M (M = Rh^III, Ir^III) were prepared on the basis of two ditopic ligands: a monophosphane ligand L1H and a triphosphane ligand L2H. The complexes were fully characterised, including single-crystal X-ray diffraction studies. Catalytic activity of cationic L1/Au^I/Ir^III and L2/Au^I/Ir^III bis(trifluoromethane)sulfonimide was analysed through their capacity to induce allenyl ether rearrangement and cycloisomerisation of N-propargyl benzamide. While cationic L1/Au^I/Ir^III showed some ability to induce allenyl ether rearrangement, no conversion was observed for cationic L2/Au^I/Ir^III. Similarly, N-propargyl benzamide could undergo cycloisomerisation in the presence of cationic L1/Au^I/Ir^III, whereas cationic L2/Au^I/Ir^III was again inactive. These findings highlight how crucial the surroundings of the metal centre are to the catalytic activity. Catalytic activity is only possible when Au has a free coordination site; the gold complex becomes inactive when the tridentate ligand is present.