Synthesis and characterization of metal complexes containing pincer type ligands
Transition metal pincer complexes are of great interest for their wide use in catalysis and bond activation reactions in modern inorganic chemistry. Although the transition metal chemistry of many pincer ligands has been well studied, but the chemistry of the bulky electron rich mixed nitrogen phosphorus neutral tridentate pyridine-based PNP pincer ligand 2,6-bis-(di-tert -butylphosphinomethyl)pyridine with cobalt metal has been largely overlooked. This thesis describes the chemical interaction between cobalt(II)halide and PNP pincer ligand of the type 2,6-bis-(di-tert -butylphosphinomethyl)pyridine to synthesize novel cobalt halide-PNP pincer complexes. In contrast to transition metals, the use of lanthanide cations in the construction of coordination complexes with PCP and PNP type ligands is still relatively less available. Here in we also report the synthesis and characterization of first europium-PNP pincer complex. Chemical treatment of hydrated metal halide with PNP ligand of the type 2,6-bis-(di-tert-butylphosphinomethyl)pyridine in THF following 1:1 molar ratio under an inert atmosphere affords the formation of novel metal halide-PNP complexes. These cobalt and europium pincer complexes have been characterized by IR and NMR spectroscopy. The molecular geometry and structure of the complexes have been determined by single crystal X-ray crystallography. All the cobalt halide-PNP complexes are neutral and comprised of two halide ligands and one tridentate PNP ligand. The exception was for one of the cobaltiodo-PNP complexes which is cationic and consisted of one iodo ligand, one water ligand, one nitrogen atom and two oxygen atoms from the oxidized PNP ligand in the inner sphere of the complex and the outer sphere contains one iodide ion. In all the cobalt halide-PNP complexes metal center adopts a penta-coordinated system exhibiting distorted trigonal bipyramidal geometry. Structural analyses of the europium-PNP pincer complex shows that the complex is cationic and the Eu metal center exhibited a seven coordinate system comprised of two chloro ligands, three water ligands and two oxygen atoms from the modified phosphinoxide PNP ligand. Insertion of oxygen occurs between the metal and the two phosphorus atoms of the PNP ligand in cobaltiodo-PNP and europiumchloro-PNP complexes which have been confirmed from X-ray diffraction analysis. The coordination mode of the PNP ligand is observed as a tridentate pincer ligand in all metal-PNP pincer complexes. However it acted as a bidentate ligand in europiumchloro-PNP complex where the nitrogen atom of the pyridine ring of the PNP ligand is not found to coordinate to the metal.
Abdul Goni MD.,
"Synthesis and characterization of metal complexes containing pincer type ligands"
ETD Collection for Tennessee State University.