Chromium and Molybdenum Carbonyl Derivatives of N2O2 Schiff Base and 2(2'-Pyridyl) Benzimidazole

Abstract

The chemistry of Schiff bases is an area of increasing interest. Importance of these bases and their metal complexes is retained to their applications in biological, analytical and industrial fields as well as to their roles in catalysis and organic synthesis [1–9]. On the other hand, transition metal complexes having oxygen and nitrogen donor Schiff bases mostly possess unusual configuration, structural lability and are sensitive to molecular environment [10]. For example, the environment around the metal centre (such as coordination geometry, number of coordinated ligands and their donor groups) is the key factor for metalloproteins to carry out specific physiological functions [11]. The design and synthesis of symmetrical Schiff bases have been of interest due to their preparative accessibility, structural variability and tunable electronic properties allowing carrying out systematic reactivity studies based on ancillary ligand modifications [12]. Moreover, Schiff base ligands that are able to form binuclear transition metal complexes are useful to study the relation between structures and magnetic exchange interactions [13,14]. In addition, transition metal complexes with tetradentate Schiff bases have been extensively investigated as catalysts for a number of organic redox reactions and electrochemical reduction processes [15-17]. The chemistry of metal complexes containing salen-type (N2O2) Schiff base ligands derived from condensation of aldehydes and diamines are of enduring significance. These complexes have been used as synthetic oxygen carriers [18], catalysts for the asymmetric epoxidation [19-24] and the synthesis of optical and magnetic materials [25,26]. Salen complexes have also been recently used as catalytically active materials to develop surface-modified electrodes for sensoring applications [27,28]. On the other hand, transition metal complexes with 2-substituted benzimidazole ligands are progressively used to model important bioinorganic systems [29,30] and act as cytotoxic [31], antiviral [32] and antiamoebic [33] agents. Our interest in investigation of the reactions of metal carbonyls with Schiff bases [34-39] has prompted us to investigate the reactions of M(CO)6 (M=Cr or Mo) with bis(salicylaldehyde) ethylendiimine (salenH2) in presence of 2(2'-pyridyl) benzimidazole (PbiH) (Scheme 1).