Fluxional behaviour of the clusters Os 3(μ-H) 2(CO) 9(L), L = PMe 2Ph, PMe 3, P iPr 3, P( o-tolyl) 3 and PPh(1-naphthyl) 2. Crystal structure of Os 3(μ-H) 2(CO) 9(P iPr 3)

Abstract

The variable temperature 1H, 13C and 31P NMR spectra of the phosphine-substituted clusters Os 3(μ-H) 2(CO) 9(L) ( 2a, L = PMe 2Ph; 2d, L = PMe 3; 2e, L = P iPr 3; 2f, L = P( o-tolyl) 3; and 2g, L = PPh(1-naphthyl) 2) are reported. The crystal structure of 2e shows that the phosphine is substituted at an equatorial site on the Os(μ-H) 2Os unit, and in solution this isomer (2 eq) is the major species for all derivatives. 2a and 2d show minor amounts of the pseudo-axially subsituted isomer (2 ax), which exchanges with the major species. No detectable concentrations of 2 ax were found with the more bulky phosphines, but for 2a and 2e minor amounts of a non-exchanging third isomer were observed, and this was judged to be a species with phosphine substitution at an equatorial site on the Os(CO) 4 group. Tripodal rotation of the Os(CO) 3 group is found in all derivatives. Clusters 2f and 2g show temperature-dependent effects that may be attributed either to a slowed rotation about the OsP bond or to a slowed inversion of chirality of the propellor configuration of the aryl groups.