BIS(ETA-CYCLOPENTADIENYL)-MOLYBDENUM AND -TUNGSTEN IMIDO COMPLEXES - X-RAY STRUCTURES OF [MO(ETA-C5H5)2(NBU(T))] AND [MO(ETA-C5H4ME)2(NBU(T))ME]I

The pseudo-trigonal bis(eta-cyclopentadienyl)-molybdenum and -tungsten imido complexes [M(eta-C5H4R)(eta-C5H4R')(NBut)] (M = Mo or W; R = R' = Me or H, R' = Pr(i) R = H) are reported together with the ring-slipped indenyl analogue [Mo(eta-C5H4Pri)(eta3-C9H7)(NBut)] and the metal-methylated salts [Mo(eta-C5H4Me)2(NBut)Me]X (X = I or BF4); the X-ray structures of [Mo(eta-C5H5)2(NBut)] and [Mo(eta-C5H4Me)2(NBut)Me]BF4 suggest that the NBu(t) ligand acts as a strong pi-donor to the metal centre; photoelectron studies identify an unusually low ionization-energy band largely localized on the ligands.