Synthesis of Heterodinuclear Hemisalen Complexes on a Hexaarylbenzene Scaffold and their Application for the Cross-Pinacol Coupling Reaction

Intermolecular cross-pinacol coupling reaction between aliphatic and aromatic aldehydes by using heterodinuclear hemisalen complexes 1(cis) with vanadium(V) and titanium(IV) on a hexaarylbenzene scaffold is reported. Our ligand design is based on the individual activation of two aldehydes by vanadium and titanium, which are positioned with a suitable space on the rigid scaffold. Ligands such as 1(cis) were synthesized by Diels-Alder addition and decarbonylation reaction, followed by condensation of dialdehyde 3(cis) with various aminophenols. The influence of the substituents on the ligands on the pinacol coupling reaction was investigated. As a result, the reductive coupling reaction between aliphatic and aromatic aldehydes by using a catalytic amount of 1(cis) in the presence of Me3SiCl and Zn provided the corresponding cross-coupled 1,2-diol in good yields with high cross-selectivity.