New transition metal imido chemistry with diamido-donor ligands

This short review presents an account of the synthesis and chemistry to date of new Groups 4, 5 and 6 imido complexes derived from the diamido-pyridine or diamido-amine ligand precursors MeC(2-C5H4N)(CH2NHSiMe2R)(2) (abbreviated as H2N2Npy for R = Me or H2N2N*(py) for R = Bu ') and Me3SiN(CH2CH2NHSiMe3)(2) (abbreviated as H2N2Nam). Reaction of the dilithium salts Li2N2Npy, Li2N2N*(py) or Li2N2Nam with metal imido synthons of the general type [M(NR)(x)Cl-y(L-B)(z)] (M=Groups 4-6 transition metals; R = alkyl or aryl substituents: L, = Lewis base) gives a diverse range of products among which are the following complexes: [Ti(NR)(N2Npy)]. [M(NR)(L-N2N)(L-B)] (M = Ti or Zr; L-N2N = a general diamido-donor ligand), [M(NR)(N2Npy)Cl(py)] (M = Nb or Ta), [Nb(mu -NBu ')(N2Nam)(mu -Cl)](2) [W(NR)(L-N2N)Cl-2] (L-N2N = N2Npy or N2Nam), [Mo(NR)(2)(L-N2N)] (L-N2N = N2Npy or N2Nam). The diamidopyridine supported titanium imido complexes [Ti(NR)(N2Npy)] and [Ti(NR)(N2Npy)(py)] in particular have reactive Ti = NR linkages and these undergo a wide range of coupling reactions with the following unsaturated organic substrates: RNC, MeCN, Bu ' CP, ArNCO, RC2Me, and RCHCCH2. Many of these transformations are the first, or among the first, of their type in transition metal imido chemistry. The combined diamido-pyridine-imido donor set also forms a useful supporting ligand environment for new chemistry at Groups 5 and 6 metal centres, especially in the Group 5 complexes [M(NR)(N2Npy)Cl(py)] (M = Nb or Ta) in which the chloride can be substituted by a range of N-. O- and C-donor ligands. (C) 2001 Elsevier Science B.V. All rights reserved.