MONO(CYCLOPENTADIENYL) AND ANSA-BIS(CYCLOPENTADIENYL)IMIDO DERIVATIVES OF GROUP-5 AND GROUP-6 TRANSITION-METALS - CRYSTAL-STRUCTURES OF [M((ETA-C5H4)CME2(ETA-C5H4))(NR)X] (M = NB, R = SIME3, X = CL, R = BU-T, X = CL, BR OR I, M = TA, R = BU-T, X = CL)

The new half-sandwich mono(cyclopentadienyl)tungsten compounds [W(eta- C5H4Me)(NBut)Cl-3] and [W(eta-C5H4Me)(NBut)(L)Cl] (L=eta-C2H4 or eta-M eC2Me) have been synthesized. In addition, the ansa-bis(cyclopentadien yl) Group 5 compounds [M{(eta-C5H4)CMe2(eta-C5H4)}(NR)X] (M=V, R=Bu-t, X=Cl; M=Nb, R=SiMe3, X=Cl; R=Bu-t, X=Cl,* Br,* I* or Me; M=Ta, R=Bu- t, X=Cl or Me) are reported. An asterisk indicates that the compound has been structurally characterized. Attempts to prepare the related d ichloride compounds by replacement of the imido functionality in [M{(e ta-C5H4)CMe2(eta-C5H4)}(NBut)Cl] (M=V, Nb or Ta) using HCl led to deco mposition, suggestive of a labilising of the cyclopentadienyl rings by the strongly bonding imido ligand.