Aldehyde hydrosilylation with ethylzinc complexes of bulky β-thioketiminate ligands

We report the synthesis of a novel β-thioketiminate ligand, H-SacNacAr* (3), featuring a bulky 2,6-bis(benzhydryl)-4-methylphenyl substituent, and its zinc ethyl complex [(SacNacAr*)ZnEt] (4). Complex 4 catalyses the hydrosilylation of benzaldehyde with PhSiH3, showing enhanced activity relative to the less bulky analogue [(SacNacDipp)ZnEt] 2, particularly upon addition of MeOH as an activator. Under these conditions, 4 exhibits high selectivity towards dialkoxysilane product (B), over monoalkoxysilane (A) or trialkoxysilane (C) products. Density functional theory (DFT) calculations support a mechanism involving pre-catalyst 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.