Synthesis, electrochemistry, and thermodynamics of mononuclear and dinuclear nickel(II) diphosphine complexes.

摘要

A series of new dinuclear nickel complexes with chelating diphosphine ligands and bridging dithiolate ligands of the formula [(diphosphine)Ni] 2(μ-dithiolate)2+ have been synthesized and characterized. The chelate bite sizes of both the diphosphine and dithiolate ligands have been systematically varied in order to determine if ligand bite angles can be used to control electrochemical and chemical reduction processes in these dimeric complexes. In contrast to corresponding mononuclear complexes studied previously in our lab, no systematic trend is observed for the Ni(II/I) couples as a result of changes in the size of the chelate bite angles of these ligands.;Recent work in our lab involved the synthesis of three new complexes of the general formula [Ni(PR 2NR' 2)2](BF4)2 (where PR 2NR'2 is 1,5-diaza-3,7-diphosphacyclooctane), which were found to function as effective catalysts for the electrochemical oxidation or production of hydrogen. Here we report the complete characterization of the thermodynamic properties of the hydride derivatives of [Ni(P R 2NR'2)2](BF 4)2. The relative rates of H2 oxidation and production using these catalysts are explained in terms of the thermodynamic bias of the complexes.;Two mixed ligand complexes were also synthesized and studied in order to further probe the structural and electronic factors responsible for the reactivity of these Ni(II) diphosphine complexes. The reactivity of these and other Ni(II) diphosphine complexes toward carbon monoxide is explored in an attempt to synthesize rare Ni(II)-CO complexes and better understand the structural features responsible for CO binding in [(CO)Ni(PCy 2NBz2)2](BF4)2 .