Tetranuclear Gold(I) Complexes Bearing Imidazo[1,5- b ]pyridazin-7-ylidene Ligands: Synthesis and Catalytic Applications in Nucleophilic Addition to Alkynes

Imidazo[1,5- b ]pyridazin-7-ylidene, which is composed of a carbene site and a proximate 2e-σ-donor N -heteroaromatic site, was developed as a rigid scaffold for constructing multinuclear metal complexes. Gold(I) chloride was introduced to the carbene site, giving an η 1 -carbene-gold(I) complex containing a noncoordinated N-σ-donor site. The chloride ligand on the gold(I) complex was then abstracted by a cationic silver salt, enabling the N-σ-donor to coordinate to another cationic gold center and affording a tetranuclear gold(I) complex. SC-XRD analysis revealed that the tetranuclear gold complex had a bent square Au 4 core bearing gold(I)–gold(I) interactions. These interactions were further assessed using DFT calculations. The catalytic performance of the tetranuclear gold complexes was evaluated in four types of nucleophilic addition reactions to alkynes.