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 η1-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 Au4 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.