Changing the chemical and physical properties of high valent heterobimetallic bis-(μ-oxido) Cu–Ni complexes by ligand effects

Abstract

Two new heterobimetallic [LNiO₂Cu(RPY2)]⁺ (RPY2 = N-substituted bis 2-pyridyl(ethylamine) ligands with R = indane, 3a or R = Me, 3b) complexes have been spectroscopically trapped at low temperatures. They were prepared by reacting the mononuclear side-on LNi^II superoxo precursor bearing a β-diketiminate ligand (L = [HC-(CMeNC₆H₃(iPr)₂)₂]) with the Cu(i) complexes. In contrast to the oxo groups in known high-valent [M₂(μ-O)₂]ⁿ⁺ (M = Fe, Co, Ni, Cu) cores that display electrophilic reactivities, 3a and 3b display rather nucleophilic oxo cores active in aldehyde deformylation reactions. However, the spectroscopic and reactivity properties of 3a/3b are found to be distinct relative to that of the previously reported [LNiO₂Cu(MeAN)]⁺ complex containing a more basic (nucleophilic) N,N,N',N',N'-pentamethyl-dipropylenetriamine (MeAN) ligand at the copper centre. The geometry and electronic properties of the copper ligands affect the electron density of the oxygen atoms of the heterodinuclear {Ni(μ-O)₂} core and 3a/3b undergo slower nucleophilic and faster electrophilic reactions than the previously reported [LNiO₂Cu(MeAN)]⁺ intermediate. The present study therefore demonstrates the tuning of the electrophilicity/nucleophilicity of the oxygen atoms of the heterobimetallic [Ni(μ-O)₂Cu]²⁺ cores by controlling the electron donation from the ancillary ligands, and underlines the significance of subtle electronic changes in the physical and chemical properties of the biologically relevant heterobimetallic metal-dioxygen intermediates.