Oxidative addition of Pd/Au vinylene species with iodobenzene reveals the effect of a strong metallophilic Pd⋯Au interaction on phenyl transmetalation from PdIV to AuI, which allows subsequent reductive elimination of LAuI at Pd and Au.

Metal-bound isobenzopyrylium species are proposed as reactive intermediates in transition-metal-catalyzed [3 + 2] or [4 + 2] cyclizations of o-alkynylbenzaldehydes (enynals) or o-alkynylarylketones (enynones). Because of their high reactivity, isolation and structural characterization of such intermediates have remained elusive. Herein, we report the isolation of such gold­(I)- and gold­(III)-bound isobenzopyrylium intermediates, and two of them have been characterized by X-ray diffraction analysis. When reacting with reaction partners, such as styrene and phenyl acetylene, the Au­(I) intermediate exhibited a reaction rate much faster than that of the Au­(III) species. A degradation pathway of active Au­(III)–carbene intermediate was observed, leading to release of Au­(I) species and consequent formation of a dichloride compound. In other related catalytic reactions, the Au­(I) intermediate could react well with a range of cyclization partners, whereas the Au­(III) intermediate did not work. The above observations indicate that Au­(I) species is probably the real catalyst in such gold-catalyzed transformations of o-alkynylbenzaldehydes and o-alkynylarylketones.

Heterotrimetallic complexes (NiAuAg, PdAuAg, PtAuAg, and NiAuCu) containing a tritopic N-heterocyclic carbene (NHC) have been synthesized for the first time through the deprotonation and metalation of heterodimetallic complexes and were structurally characterized by single-crystal X-ray diffraction. The carbene character of the donor groups in the tritopic NHC complexes was established on the basis of structural and NMR analyses.

The facile synthesis of tetrahydroquinoline-based chiral carbene precursors is reported. A rare Au⋯H–C(sp3) interaction between Au(i) and the hydrogen atom was observed in the crystal structure of a related NHC–gold complex.