Isolation, structural and spectroscopic investigations of complexes with tridentate [O,P,O] and [O,O,O] donor ligands

A phosphorus-containing potentially tridentate ligand bis(3,5-di-tert-butyl-2-hydroxyphenyl)phenylphosphine H2L, 1, was prepared. 1 reacts directly in solution with aerial oxygen or hydrogen peroxide to form bis(3,5-di-tert-butyl-2-hydroxyphenyl)phenylphosphine oxide H2LO, 2. It yields complexes [NiII(HL)2] 3, [CoIII(OH2)(HL)(L)] 4, [RhIIICl(H2L)(L)] 5, and [RhIII(HL)(L)(H2O)] 6 characterized by various physical techniques, including IR, MS, UV-vis, 1H and 31P-{1H} NMR and electrochemical methods. The crystal structures of 3, 4 and 5 show tridentate [O,P,O] and bidentate [O,P,OH] coordination of deprotonated 1 and the coordination geometry of the metal centre. The structure of 2 reveals strong hydrogen bonding between the phenolic hydroxyl groups and the OP group in the solid state. That the ligand 2 produces a weak ligand field providing tridentate [O,O,O] coordination sites has been evidenced by the structure and paramagnetism of [CoII2(LO)2(C2H5OH)3] 7.