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.

The 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 as PowerPoint slide