Aldehyde Hydrosilylation with Ethylzinc Complexes of Bulky β-Thioketiminate Ligands

The synthesis of a novel β-thioketiminate ligand, H-SacNac^Ar* (3), featuring a bulky 2,6-bis(benzhydryl)-4-methylphenyl substituent, and its zinc ethyl complex [(SacNac^Ar*)ZnEt] (4), is reported. Complex 4 catalyzes the hydrosilylation of benzaldehyde with PhSiH3, showing enhanced activity relative to the less bulky analogue [(SacNac^Dipp)ZnEt] 2, particularly upon addition of MeOH as an activator. Under these conditions, 4 exhibits high selectivity toward dialkoxysilane product (B), over monoalkoxysilane (A) or trialkoxysilane (C) products. Density functional theory calculations support a mechanism involving precatalyst activation by MeOH to form a zinc alkoxide intermediate, followed by σ-bond metathesis with PhSiH3 affording a catalytically active zinc hydride complex. The results highlight the role of ligand sterics and alcohol activators in tuning catalytic activity and offer insights into the design of new zinc-based hydrosilylation catalysts.<p></p>