Spectroscopic Properties, Electrochemistry, and Reactivity of Mo0, MoI, and MoII Complexes with the [Mo(bpa)(CO)3] Unit [bpa = bis(2-picolyl)amine] and Their Application for the Labelling of Peptides

Abstract

The synthesis of the complexes [Mo(bpa)(CO)3] (1) and [Mo(Bz-bpa)(CO)3] (2) [bpa = bis(2-picolyl)amine; Bz-bpa = N-benzylbis(2-picolyl)amine] is described. These compounds have been characterized by spectroscopic techniques including multinuclear NMR spectroscopy (1H, 13C, and 95Mo), and also by X-ray crystallography. Complexes 1 and 2 underwent reversible one-electron oxidations in acetonitrile and dichloromethane with Bu4NPF6 as supporting electrolyte to yield the 17-electron organometallic compounds 1+ and 2+. With Bu4NBr as supporting electrolyte in dichloromethane, on the other hand, 1 and 2 underwent electrochemically irreversible two-electron oxidations, resulting in the formation of [Mo(bpa)(CO)3Br]+ and [Mo(Bz-bpa)(CO)3Br]+. Infrared spectra and electronic spectra of these oxidized species were recorded in spectro-electrochemical studies. The electrochemical behaviour and the infrared spectroscopic data of 1, 2, and their oxidized derivatives are compared in detail with those of analogous tricarbonylmolybdenum complexes with the ligands 1,4,7-triazacyclononane and hydridotris(pyrazolyl)borate. The complex [Mo(bpa)(CO)Br]Br3 (3) could be prepared by oxidation of 1 with elemental bromine. Under aerobic aqueous conditions, 3 reacted further to yield the dinuclear diamagnetic MoV complex [Mo2(bpa)2(O)2(μ-O)2](Br,PF6) (4). The identity of 4 was confirmed by a single-crystal X-ray crystallographic study. Finally, the syntheses of two bioconjugates of [Mo(bpa)(CO)3], in which bpa ligands are covalently linked to the N-termini of an amino acid (Phe-OMe, 8a) and of a dipeptide (Ala-Phe-OMe, 8b), are described. These bioconjugates were comprehensively characterized (including elemental analysis, 1H, 13C, and 95Mo NMR, IR, MS, and electrochemistry). All analytical data supported the proposed constitution and underscore the potential of the Mo(bpa)(CO)3 group as a robust marker group in bioorganometallic chemistry. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)