A new tri-nuclear Cu-carbonate cluster utilizing CO2 as a C1-building block – reactive intermediates, a probable mechanism, and EPR and magnetic studies

Abstract

This work demonstrates that simple copper-bipyridine compounds and atmospheric CO₂ react to produce useful/complex materials under appropriate conditions. Starting from a distorted square planar copper(II) complex, [(^tbubpy)CuCl₂](^tbubpy = 4-tert-butyl-2-(4-tert-butylpyridin-2-yl)pyridine), an air-sensitive, copper(I) complex, [(^tbubpy)₂Cu^I][BF₄], which exhibits a distorted tetrahedral geometry, was synthesized and characterized. Reactions of [(^tbubpy)₂Cu^I][BF₄] with CO₂ inside a sealed tube and with air were carried out over a week and three weeks, respectively. A new tricopper(II)-carbonato cluster, [{(^tbubpy)₂Cu}₃(μ-CO₃)][PF₆]₄, was isolated with three distorted octahedral copper(II) centres bound by a carbonate-bridge formed from atmospheric CO₂. NMR and UV-Vis spectroscopic analyses coupled with previous reports point to a multi-step process in the formation of a trinuclear Cu^II-carbonato cluster that includes the probable involvement of μ-hydroxo-bridged dicopper(II) type intermediates.