Investigations on the trigonal twist process in the pseudooctahedral complexes [MX(CO)2(PP)(η3-R)] (M=Mo or W; X=halide or pseudohalide; PP=bidentate P-donor ligand; R=cycloheptatrienyl, cyclohexenyl or cyclooctenyl)

Stereodynamics and conformational equilibria in some chiral pseudo-octahedral tungsten crotyl complexes

“…Since 2 coalesces at À40°C, it would be unlikely for 3 to be above the coalescence temperature (at the same field strength) at À85°C, since the addition of a methyl group to an allyl terminus would not be expected to cause such a drastic change in the rearrangement barrier. Also, a study done by Whiteley et al on these types of complexes with symmetrical g 3 ligands showed that the case of g 3 -allyl gave the lowest barriers to the twist rearrangement [22]. The rearrangement barriers for 2 and 3 were determined from line broadening in the 31 P NMR spectra, and are in agreement with these findings.…”

“…This class of complexes is fluxional [1,2,21,22], and so one needs to consider their solution dynamics in order to better understand their reactivity. Specifically, they exist as a pseudo-octahedral isomer in which one of the phosphorus atoms of the P-P chelate binds trans to the g 3 -allyl group.…”

“…1). It has been seen that this process occurs with a relatively low energy barrier ($8-12 kcal/mol), with the interconversion rates increasing with decreasing size of the halide ( I < Br < Cl) [1,2,22].…”