Chimie organometallique du niobium: XII. Formation de nouveaux derives par clivage de liaisons soufre-soufre. Etude par resonance paramagnetique electronique de la structure electronique des complexes [Nb(η 5-C 5H 5) 2{PS 2(OR) 2} 2

Abstract

[Nb(η 5-C 5H 5) 2(CH 3) 2] (I) reacts with (RO) 2P(S)SSP(S)(OR) 2 (IIa: R = Et; IIb: R = i-Pr) and R 2NC(S)SSC(S)NR 2 (IIIa: R = Me; IIIb: R = Et) to give niobium complexes via SS bond cleavage of the organic substrates. With IIa and IIb, the paramagnetic niobium complexes [Nb(η 5-C 5H 5) 2{PS 2(OR) 2} 2] (IV) are obtained, while IIIa and IIIb give diamagnetic niobium(V) derivatives. EPR spectra of complexes IV have been recorded at 130 and 295 K and are analysed in detail. The spin Hamiltonian parameters are given and compared with the atomic orbital coefficients in the ground state molecular orbital involved in bonding. They show: (i) the unpaired electron lies essentially in the 4 d x 2− y 2 metal-ion orbital mixed with a small amount of the corresponding metal-ion 4 d z 2 orbital, the z axis coinciding with the C 2 axis of the compound; (ii) a weaker delocalization than in [Nb(η 5-C 5H 5) 2{PS 2(OR) 2}] +; and (iii) an indirect interaction via the sulphur atoms between niobium orbitals and phosphorus orbitals, mostly 3 s in character.