Molybdenum complexes reaction with bidentate ligands

Reactions of the metallocene derivatives of molybdenum with pyrazole lead to the mononuclear complexes of the type 22. Structure 22 shows that it cannot be used as a ligand for the preparation of dinuclear complexes owing to geometric constraints [80JOM( 197)291 83JOM(253)53]. In acetone, an unusual complex 23 is formed [83JOM(253)53]. The bidentate ligand is the product of the reaction of pyrazole and acetone. 

These complexes are excellent models for theoretical studies. The octacyano complexes of molybdenum and tungsten are stable and inert toward substitution reactions and therefore very suitable for theoretical studies of redox reactions and application of the Marcus theory. The photoreactivity of these systems is also proving to be important. The 0X0- and nitridocyano complexes of Mo(IV), W(IV), Tc(V), Re(V), and Os(VI) are very good candidates for kinetic studies of substitution reactions with both mono- and bidentate ligands and are of interest especially in view of the large variations in the observed reactivity. 

The reaction of [MoO(H20)(CN)4] with 1,10-phenanthroline (211) and 2,2 -dipyridyl (215) has also been studied by means of reaction kinetics. It is clear that there are still uncertainties and questions regarding the mechanism of the reaction of these bidentate ligands For example, why is the reaction of the molybdenum complex faster at high pH values at which there is less of the aqua and more of the hydroxo) complex in solution (211) Scheme 5 was proposed for reaction with 2,2 -bipyridyl (215). 

Some simple oximes have been shown to act as N—O bidentates by side-on coordination of the oxime groups alone. The reaction of acetone with a hydroxylamido complex of molybdenum results in this bonding form for 2-propanone oxime.64,243 The N—O and C—N bond lengths indicate single and double bond character respectively. The reaction was related to the prebiotic formation of HCN from formaldehyde and hydroxylamido-Mo chelates. A similar form of bonding for this ligand was concluded with some fluorotungstate(IV) complexes.65... 

---