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

•Double-alkoxy-supported cyclodimeric copper(II) complexes were self-assembled.•The horseshoe-type ligand plays a pivotal role in forming the cyclodimeric complexes.•The cyclodimeric complexes show the catalytic oxidation of catechol.•The present catalytic effects can be explained by the steric hindrance.

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 2.92–2.98 Å 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.

Graphical abstractThe series of new doubly-alkoxy-supported cyclodimeric species, [Cu(μ-OR)(L)]2(X)2 (R = Me, Et, iPr; X− = ClO4−, BF4−), with appropriate intracyclic Cu⋯Cu distances are a good model system for catecholase mimetics. The catalysis is depending on the catalytic steric hinderance in the order [Cu(μ-OMe)(L)]2(X)2 > [Cu(μ-OEt)(L)]2(X)2 > [Cu(μ-OiPr)(L)]2(X)2 and substrates in the order 4-BuCat > 4-ClCat > 3,5-DBuCat > Cat.Figure optionsDownload full-size imageDownload as PowerPoint slide