Research Projects

Designing pyridine-based pincer ligands and their metal complexes is an emerging field of metal-organic chemistry due their robust complexation, non-redox active behavior, and wide applicability towards various kinds of transformations. The current proposal is about designing two such novel pincers of NNN-type, one non-palindromic with the pyridyl donor at the side (L²H) and another palindromic and where the pyridyl moiety is the central donor (L²H₂). The acidic alpha-CH protons would make L¹ and L² mono- and dianionic, respectively, by deprotonation. In anionic pincers, it is typically the donor sites which carry the negative charge (anionic donors) forming conventional L-M sigma bonds. But in this proposed ligand framework the negative charge would be generated at the backbone and shall partially delocalize on to the pyridyl ring, and thereby avoiding a direct L-M s bond to some extent. In the coordination chemistries of electropositive metals, L-M dative coordinations are better suited than L-M sigma bonds as the latter could exhibit competitive reactivity which can be problematic when taking place from an ancillary ligand support. The current proposal would deal with the complexation of L¹ and L² with three main group electropositive metals, namely magnesium, zinc, and aluminum. The flexible nature of L¹ is expected to provide fac-coordination, imposing the favorable tetrahedral geometry on metals like Mg and Zn. The dianionic L₂ would be more suited for the trivalent Al. Appropriate variation in the substituents of L¹ and L² is under consideration to optimize the steroelectronic behavior. Sufficient kinetic protection would be necessary to prevent the Schlenk equilibrium for the divalent metals like Mg and Zn. Complexes of the types [(L¹)MX] (M = Mg, Zn) and [(L2)AlX] would be the prime objectives with a diverse range of terminal X ligands including alkyl, aryl, alkoxide, amide, silazide, and a special emphasis on the hydride. Those will be tested as catalysts in transformations like hydroelementations of unsaturated functional groups including small molecules like CO and CO₂, hydroamination, ring- opening polymerization of cyclic esters and copolymerization of CO₂ and epoxides. Earth abundant and nontoxic main group element mediated catalytic process might be advantageous over the same by the heavy, toxic, and rare Pt group metals. The reaction mechanism shall be investigated in details.