Structure and ligand exchange reactions of the complexes CpUCl 3L 2 in solution (L = hexamethylphosphoramide, tetrahydrofuran, triphenylphosphine oxide)

Abstract

The dynamic behaviour in solution of the compounds CpUCl 3L 2 (L = HMPA, I: THF, II; OPPh 3, III) was studied by 1H and 31P NMR (variable temperature and spin saturation transfer experiments). Two isomers of I in equilibrium (IA and IB) were detected in CDCl 3 ( E a = 92 kJ mol −1). The two HMPA ligands of the major (70%) isomer IA are relatively cis in a mer pseudo-octahedral configuration whereas in IB (30%), the two ligands are in trans equatorial positions. For all the complexes CpUCl 3L 2, the equatorial ligand of isomer A was found to exchange with free added L molecules. In the case of I ( k = 7.0 ± 0.2 mol −1 1 s −1 at 260 K), this reaction proceeded by an associative mechanism; at 240 K, the intermediate CpUCl 3L 3 was observed. Addition of chloride ions to a solution of I led to the formation of CpUCl 4(HMPA) −.