Reactivity of Co 4(CO) 12 with polydentate ligands. Fragmentation kinetic studies of the substituted derivatives

Abstract

The reaction of Co 4(CO) 12 with the polydentate phosphines (Ph 2Ppy (2-(dihenylphosphino)pyridine), t-dppv ( trans-1,2-vinylenebis(diphenylphosphine) and dpmp (bis((diphenylphosphino)methyl)phenylphosphine) yield the tetrasubstituted Co 4(CO) 8L 4 complexes (L  Ph 2Ppy and t-dppv) in which the ligand behaves as monodentate, trisubstituted Co 4(CO) 9(dpmp) complex in which the ligand behaves as tridentate, and pentasubstituted Co 4(CO 7(dpmp) 2 in which the ligands behave as di- and tridentate. All the compounds have been characterized by elemental analysis and IR, 1H and 31P NMR spectroscopy. The kientics of fragmentation in DCE (dichloroethane) of Co 4(CO) 8(PPh 2Py) 4 to form Co 2(CO) 6(Ph 2Ppy) 2 has been studied under a N 2 or CO atmosphere. The rate constants are independent of the concentration of Ph 2Ppy and are lower under CO. This suggests that the reaction proceeds by a CO-dissociative (D) mechanism. The complexes Co 4(CO) 8( t-dppv) 4, Co 4(CO) 9(dpmp) and Co 4(CO) 7(dpmp) 2 are stable towards fragmentation.