Synthesis and characterization of complexes imparting N-pyridyl bonded meso-pyridyl substituted dipyrromethanes

The meso-pyridyl substituted dipyrromethane ligands 5-(4-pyridyl)dipyrromethane (4-dpmane) and 5-(3-pyridyl)dipyrromethane (3-dpmane) have been employed in the synthesis of a series of complexes with the general formulations (η⁶-arene)RuCl₂(L)] (η⁶-arene = C₆H₆, C₁₀H₁₄) and (η⁵-C₅Me₅)MCl₂(L)] (M = Rh, Ir). The reaction products have been characterized by microanalyses and spectral studies and molecular structures of the complexes (η⁶-C₁₀H₁₄)RuCl₂(4-dpmane)] and (η⁵-C₅Me₅)IrCl₂(3-dpmane)] have been determined crystallographically. For comparative studies, geometrical optimization have been performed on the complex (η⁵-C₅Me₅)IrCl₂(4-dpmane)] using exchange correlation functional B3LYP. Optimized bond length and angles are in good agreement with the structural data of the complex (η⁵-C₅Me₅)IrCl₂(3-dpmane)]. The complexes (η⁶-C₁₀H₁₄)RuCl₂(3-dpmane)], (η⁵-C₅Me₅)RhCl₂(3-dpmane)] and (η⁵-C₅Me₅)IrCl₂(3-dpmane)] have been employed as a transfer hydrogenation catalyst in the reduction of aldehydes. It was observed that the rhodium and iridium complexes mentioned above are more effective in this regard in comparison to the ruthenium complex.