Azo-complexes of bis(cyclopentadienyl)-titanium and -vanadium; model systems for N–N multiple bond activation

Abstract

Azobenzenebis(η⁵-cyclopentadienyl)-titanium and -vanadium and some titanium and vanadium analogues have been synthesized from [Ti(CO)₂(cp)₂] and [V(cp)₂](cp =η⁵-C₅H₅) respectively. In the mononuclear structure of [Ti(cp)₂(PhNNPh)] the conformation and bond data of the cis-azobenzene ligand differ considerably from those of the free molecule. The complex consists of a Ti(cp)₂ moiety bridged in an edge-on fashion to the azo-group with the most significant bond data being : N–N 1.339(8), N–C 1.395(10), Ti–N 1.968(6), Ti–cp(centroid) 2.077 Å, N–Ti–N 39.8(5), and cp–Ti–cp 133.0°. The metal–nitrogen and –azo bonding characteristics are evaluated in connection with related compounds. A quantitative ab initio molecular orbital treatment of the related model complex [TiCl₂(MeNNMe)] is consistent with the main conformational data and indicates strong interaction of of the azo-group and the metal. Formation of the complex gives rise to a lowering of the N–N bond order and an increase of the titanium oxidation state.