Chelating ether–phosphine complexes of the cobalt group metals. Crystal structures of bis[benzylbis(2-ethoxyethyl)-phosphine]-bis(trifluoromethanesulfonato)cobalt(II) and -trichlororhodium(III)

Abstract

New Group 9 metal complexes have been prepared using the trifunctional ligand benzylbis(2-ethoxyethyl)phosphine (L). Reactions of this potentially hemilabile ligand with CoCl₂, and CoCl₂·6H₂O with AgCF₃SO₃, have been studied, resulting in the isolation of [CoCl₂L₂]1 and [CoL₂(O₃SCF₃)₂]2 respectively. In the former complex L acts as a monodentate P-bonding ligand with the metal adopting a tetrahedral geometry, but in the latter it acts as an O,P chelate. The crystal structure for 2 has been determined and shows the metal to have a distorted-octahedral geometry with trans ligands (P and O) and trans triflates. The ³¹P-{¹H} NMR spectrum of 2 suggests the formation of a dimeric species in solution. Reactions of L with RhCl₃·3H₂O, [{RhCl(CO)₂}₂] and [{RhCl(cod)}₂](cod = cycloocta-1,5-diene) resulted in the isolation of [RhCl₃L₂]3, [RhCl(CO)L₂]4 and [RhCl(cod)L]5 respectively, where L acts as a monodentate P-bonding ligand in 4 and 5. Complex 4 is shown to be trans by NMR studies. In 3 the ligand bonds as a monodentate phosphorus donor in one case and as a bidentate O,P chelate in the other. The crystal structure of 3 has been determined and shows the metal to have a slightly distorted-octahedral mer arrangement with cis phosphorus donors. The fluxional nature of this complex has been monitored by variable-temperature ³¹P-{¹H} and ¹H NMR spectroscopy which shows that these ligands readily interchange at high temperatures. The iridium analogue of 5 has been prepared from [{IrCl(cod)}₂] resulting in the isolation of [IrCl(cod)L]6. The reaction of 3 with cyclohexene gave an unstable alkene complex 7 which could not be isolated, but was identified by variable-temperature ³¹P-{¹H} NMR studies.