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)

A series of complexes [MX(CO)2(PP)(η3-R)] [M=Mo or W; X=halide, NCO or NCS; PP=Ph2P(CH2)nPPh2 (n=1−3)] have been prepared. Variable temperature 31P{1H}-NMR investigations reveal the operation of a trigonal twist fluxional process in complexes where R=cycloheptatrienyl (C7H7), cyclohexenyl (C6H9) or cyclooctenyl (C8H13) with ΔGC‡ (the free energy of activation at the temperature of coalescence) strongly R-dependent. Using the cycloheptatrienyl complexes [MX(CO)2{Ph2P(CH2)nPPh2}(η3-C7H7)] detailed investigations have been made to establish the effect on ΔGC‡ of variation of X, n and M.