Steric effects of catalysts and substrates on catechol oxidation catalysis: Cyclodimeric copper(II) complexes containing 1,4-bis(dimethyl(quinolin-3-yl)silyl)benzene

Abstract

Reaction of CuX2 with new ligand, 1,4-bis(dimethyl(quinolin-3-yl)silyl)benzene (L), in alcohol affords C2-symmetric double-alkoxy-supported cyclodimeric copper(II) complexes, [Cu(μ-OR)(L)]2(X)2 (R=Me, Et, iPr; X−=ClO4−, BF4−) in high yields. These cyclodimeric species with intracyclic Cu⋯Cu distances of 2.92–2.98Å show the significant catalytic effects on the catechol oxidation catalysis in chloroform in the order [Cu(μ-OMe)(L)]2(X)2>[Cu(μ-OEt)(L)]2(X)2>[Cu(μ-OiPr)(L)]2(X)2. Furthermore, the catalytic efficiency is strongly substrate-dependent in the order 4-BuCat>4-ClCat>3,5-DBuCat>Cat. Such notable catalytic effects potentially can be explained by the steric hindrance of both catalysts and substrates.