Binuclear copper complexes and their catalytic evaluation

Abstract

Two binuclear copper complexes [{Cu^I(L¹)}₂][OTf]₂ (1) and [{Cu^II(L²)Cl}₂] (2) have been synthesized and structurally characterized. The reaction of [{(5,7-dimethyl-1,8-naphthyridin-2-yl)amino}carbonyl]ferrocene (L¹) with [Cu(CH₃CN)₄][OTf] in dichloromethane afforded complex 1 in high yield and the dicopper(II) complex 2 was obtained by the overnight treatment of N-(5,7-dimethyl-1,8-naphthyridin-2-yl)-1-methylpyrrolidine-2-carboxamide (L²H) with [Cu(CH₃CN)₄][BF₄] in dichloromethane. The two copper atoms in complex 1 are bridged by two L¹ ligands in a trans disposition; the naphthyridine nitrogen atoms bridge two copper centers and the carbonyl oxygen atoms occupy sites trans to the Cu···Cu vector. The metal···metal distance is 2.4594(6) Å. In contrast, in complex 2, each of the two L² ligands bind to the two copper atoms through one naphthyridine nitrogen, a deprotonated amide, and a proline nitrogen atom to form an open-book geometry. Both dicopper complexes have been shown to be excellent catalysts for the cyclopropanation of various olefins with ethyl diazoacetate (EDA), with catalyst 1 found to be marginally superior to 2.