Sandwich and half-sandwich niobium imido complexes: X-ray crystal structure of [Nb(=NAr)(Cp2Cl)-Cl-'] (Cp '=eta(5)-C5H4SiMe3, Ar=C6H4OMe-4)

The imido niobium complexes [Nb(=NAr)Cl-3(dme)] (Ar =C6H4Me-4 (1), C6H4OMe- 4 (2)) have been prepared and characterised. The half-sandwich complex [Nb( =NBu')CpCl2] (3) (Cp = eta(5)-C5H5) has been synthesised by a new method vi a the reaction of NaCp and [Nb(=NBu')Cl-3(py)(2)] and in a similar manner t he novel complex [Nb(=NC6H4Me-4)CpCl2] (4) was prepared by the reaction of NaCp with 1. The preparation of [Nb(=NBu')Cp'Cl-2] (5) (Cp' = eta(5)-C(5)h( 4)SiMe(3)) yielded an essentially inseparable mixture of 5 and [Nb(=NBu')Cp -2'Cl] (6). The imido niobocene(V) complex 6 was prepared and isolated as t he unique product by a new synthetic pathway via the reaction of two equiva lents of LiCp' and [Nb(=NBu')Cl-3(py)(2)] and in a similar manner the novel complexes [Nb(=NAr)Cp'Cl-2] (Ar= C6H4Me-4 (7), C6H4OMe-4 (8)) were prepare d. The molecular structure of 8 has been determined by X-ray diffraction st udies. The mixed metallocene complex [Nb(=NBu')CpCp'Cl] (9) was prepared by the reaction of Li(C(5)H(4)iMe(3)) and 3. The alkylation of 6-8 by CIMgCH2 CH=CP2 yielded the eta(1)-allyl complexes [Nb(=NR)Cp'(2)(CH2CH=CH2)] (R = B u' (10), C6H4Me-4 (11), C6H4OMe-4 (2)). (C) 1999 Elsevier Science S.A. All rights reserved.