A carbon-13 NMR study of phosphine, phosphite, arsine and stibine ligands and their LNi(CO) 3, LCr(CO) 5 and η-(C 5H 5)Mn-(CO) 2L complexes

Abstract

13C NMR chemical shift and J( 13C 31P) coupling constant data are presented for PPh 3− n Me n ( n = 0, 1 and 2, P(OPh) 3, PEt 3, AsPh 3 and SbPh 3 ligands, and some corresponding LNi(CO) 3, LCr(CO) 5 and η-(C 5H 5)Mn(CO) 2L complexes. Analysis of the 13C NMR chemical shift data for the C(4) resonance in these C 6H 5X derivatives suggests: (1) a resonance substituent parameter R = 0.005 for X = PPh 2 and R = 0.09 for X = (CO) 5CrPPh 2, (2) a decrease in the resonance interaction of the Group VA atom with the phenyl ring in EPh 3 derivatives in the order E = P > As > Sb, and (3) an increase in the electron density at the phosphorus atom in PPh 3− n Me n derivatives in the order: PPh 3 < PPh 2Me < PPhMe 2. There appears tobe an anomalous shielding of the C(1) resonance in these derivatives upon complexation, and with increasing electronegativity of the Group Va atom. The electron-withdrawing character of the metal carbonyl moiety appears to increase in the order: η-(C 5H 5)Mn(CO) 2L < LNi(CO) 3 < LCr(CO) 5. The magnitude of the 1 J( 13C 31P) and 3 J( 13C 31P) coupling in trialkyl and triaryl phosphines increases upon complexation, while the magnitude of the 2 J( 13C 31P) coupling decreases. As a result, in (Me 2PhP)Ni(CO) 3, the 3 J( 13C 31P) coupling to the C(3,5) resonance of the phenyl group is larger than the 2 J( 13C 31P) coupling to the C(2,6) resonance. In contrast, complexation of triphenyl phosphite leads to an apparent increase in the magnitude of the 2 J( 13C 31P) coupling and a decrease in the magnitude of the 3 J( 13C 31P) coupling. The signs of the one-, two- and three-bond J( 13C 31P) coupling constants in Ph 3PMo(CO) 5 have been determined to be positive.