Structure and Reactivity Studies on Dinuclear Copper Complexes of the Ligand α,α′-Bis{bis[1-(1′-methyl-2′-benzimidazolyl)methyl]amino}-m-xylene

✍ Scribed by Giuseppe Battaini; Luigi Casella; Michele Gullotti; Enrico Monzani; Giorgio Nardin; Angelo Perotti; Lucio Randaccio; Laura Santagostini; Frank W. Heinemann; Siegfried Schindler

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 185 KB
• Volume: 2003
• Category: Article
• ISSN: 1434-1948
• DOI: 10.1002/ejic.200390155

✦ Synopsis

Abstract

The ligand α,α′‐bis{bis[1‐(1′‐methyl‐2′‐benzimidazolyl)methyl]amino}‐m‐xylene (L‐55) forms the complexes Cu^I^~2~(L‐55)(MeCN)~2~~2~ (1) and [Cu^II^~2~(L‐55)(OMe)~2~][ClO~4~]~2~ (2), in which an extremely weak axial amine interaction is imposed by the small five‐membered benzimidazole chelating ring units. This structural feature has been characterized by X‐ray crystal structure determination. In 1, the Cu^I^ centers are three‐coordinate with ligation from two benzimidazolyl and one acetonitrile N‐donors, in a slightly distorted trigonal arrangement. In 2, each Cu^II^ center has a distorted square‐planar geometry and coordinates to the benzimidazolyl N atoms and the bridging methoxy groups in the basal positions, with a much weaker interaction with the tertiary amine N in an apical position. These structural features affect the reactivities of the copper(I)− and copper(II)−L‐55 complexes toward dioxygen and hydrogen peroxide, respectively. [Cu^I^~2~(L‐55)(MeCN)~2~]^2+^ does not produce a stable peroxo complex, but undergoes an irreversible oxidation to copper(II) species, while [Cu^II^~2~(L‐55)(H~2~O)~2~]^4+^ reacts slowly with hydrogen peroxide to undergo regiospecific hydroxylation of the ligand at one benzylic carbon atom, which causes decomposition of the complex. [Cu~2~(L‐55)(H~2~O)~2~]^4+^ is easily converted into its bis(μ‐hydroxo) adduct [Cu~2~(L‐55)(OH)~2~]^2+^. This pH‐driven equilibrium was monitored by paramagnetic ^1^H NMR spectroscopy, and the solution magnetic properties of the complexes were determined by the Evans susceptibility method. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)