Single-Step Synthesis of Dinuclear Neutral Gold(I) Complexes with Bridging Di(N-heterocyclic carbene) Ligands and Their Catalytic Performance in Cross Coupling Reactions and Alkyne Hydroamination

We report on a single step procedure for the synthesis of dinuclear gold(I) complexes with bridging diNHC (di(N-Heterocyclic carbene)) ligands of general formula Au2Br2L1-9 (L = diNHC). The obtained complexes differ for the bridging group between the carbene donor and for the terminal wingtip substituents at the imidazole-2-ylidene rings. The complexes have been characterized by means of elemental analysis, NMR spectroscopy, ESI-MS spectrometry and single crystal X-ray structure analysis. The dinuclear gold(I) complexes have been tested as homogeneous catalysis in technological relevant reactions, such as the cross coupling between phenylboronic acid and aryl bromides and the intermolecular hydroamination of al-kynes. They exhibit moderate activity in the former reaction, whereas their efficiency is much higher in the latter, though the substrate scope of the hydroamination appears largely limited to terminal alkynes and primary arylamines. The catalytic performance of complexes Au2Br2L1-9 has been also compared with that of the benchmark mononuclear complex IPrAuCl with the aim of highlighting the presence of cooperative effects in the gold(I) catalyzed reactions between the two gold cen-ters in the complexes.