Molybdenum(VI) borano-imido complexes and their application as Lewis acid catalysts in homocoupling of diazo compounds

Abstract

We report the synthesis, structural characterization, and catalytic activity of the borano-imido molybdenum complex featuring unique motif B-N=MoCl4(thf), prepared via reaction of a phenylpyridine-based boron azide with [MoCl₄(thf)₂]. Spectroscopic and crystallographic analyses confirmed formation of a linear B–N–Mo(VI) linkage. Reaction of formed imido complex with various neutral donors resulted in solvent assisted reduction and formation of a several structurally diverse Mo(V) derivatives, demonstrating the and adaptability of the imido framework. The Mo(VI) imido complex act as a strong Lewis acid and efficiently catalyse the homocoupling of diazo compounds under mild conditions. For diaryldiazomethanes, the product selectivity between tetraarylethylenes and azines is primarily governed by the electronic nature of the substituents: electron-donating groups favor the formation of tetraarylethylenes, whereas electron-withdrawing groups lead exclusively to 1,2-bis(diarylmethylene)hydrazines. The complex also mediated the transformation of 1-diazoindenes to afford either 1,1′-biindene or bis(1,2-indenylidene)hydrazines, with the selectivity controlled by steric effects. Furthermore, α-diazophenylacetates were efficiently coupled to yield mixtures of maleates and fumarates, accompanied by minor amounts of azine byproduct, with negligible influence of solvent or substituent variation.