Synthesis and structural characterization of isocyanate, amido and imido niobocene derivatives:: crystal structures of [Nb(η5-C5H4Si-Me3)2Cl(κ2N,C-OCNPh] and [{Nb(η5-C5H4SiMe3)2Cl}2-(μ-1,3-N2C6H4)]

The niobium complex [{Nb(eta(5)-C5H4SiMe3)(2)Cl}(2)] 1 reacted with phenyl isocyanate, 1,3- and 1,4-phenylenediisocyanate to give the corresponding complexes [Nb(eta(5)-C5H4SiMe3)(2)Cl(kappa(2)N, C-OCNPh)] 2, [{Nb(eta(5)-C5H4SiMe3)(2)Cl}(2){kappa(2)N,C-mu-1,3-(OCN)(2)C6H4}] 3 and [{Nb(eta(5)-C5H4SiMe3)(2)Cl}(2){kappa(2)N,C-mu-1,4-(OCN)(2)C6H4}] 4, respectively. The spectroscopic data were not sufficient unequivocally to differentiate between the presence of a kappa(2)C,N or kappa(2)C,O co-ordination mode. However the crystal structure of 2 showed it to have kappa(2)C,N co-ordination. Complexes 3 and 4 have an analogous structure in which two metal centres are linked through an aryl ring containing a diisocyanate ligand. The reactivity of these complexes under reduction and thermal decomposition conditions was examined. Complexes 2-4 with Na/Hg underwent a reduction at each metal centre followed by protonation to afford the corresponding [Nb(eta(5)-C5H4SiMe3)(2)(OCHNPh)] 5, [{Nb(eta(5)-C5H4SiMe3)(2)}(2){mu-1,3-(OCHN)(2)C6H4}] 6 and [{Nb(eta(5)-C5H4SiMe3)(2)}(2){mu-1,4-(OCHN)(2)C6H4}] 7. The imido [Nb(eta(5)-C5H4SiMe3)(2)Cl(NPh)] 8 and diimido derivatives [{Nb(eta(5)-C5H4SiMe3)(2)Cl}(2)(mu-1,3-N2C6H4)] 9 and [{Nb(eta(5)-C5H4SiMe3)(2)Cl}(2)(mu-1,4-N2C6H4)] 10 were isolated by heating 2, 3 or 4 or alternatively by treating 1 with the appropriate amount of the corresponding aniline, 1,3- or 1,4-phenylenediamine, respectively. The molecular crystal structure of 9 was determined by single-crystal diffractometry. It contains two bent niobocene units linked by a 1,3-diimidophenylene ligand, with the niobium atoms slightly deviating from the plane formed by this ligand. Complexes 8-10 reacted with Grignard reagents MgRCl (R = Me, Et or Pr-1) or MgMe2 in tetrahydrofuran solution to give the corresponding substitution products [Nb(eta(5)-C5H4SiMe3)(2)R(NPh)] (R = Me 11, Er 12 or Pr-1 13), [{Nb(eta(5)-C5H4SiMe3)(2)R}(2)(mu-1,3-N2C6H4)] (R = Me 14, Et 15 or Pr-1 16) and [{Nb(eta(5)-C5H4SiMe3)(2)R}(2)(mu-1,4-N2C6H4)] (R = Me 17, Et 18 or Pr-1 19). The reaction of 8-10 with Na/Hg in appropriate molar ratios afforded the corresponding hydride complexes [Nb(eta(5)-C5H4SiMe3)(2)H(NPh)] 20, [{Nb(eta(5)-C5H4SiMe3)(2)H}(2)(mu-1,3-N2C6H4)] 21 and [{Nb(eta(5)-C5H4SiMe3)(2)H}(2)(mu-1.4-N2C6H4)] 22. Finally, the monoimido complexes 8 and 11-13 were easily protonated with 1 equivalent of HBF4 . OEt2 to give, in one step, the corresponding amido cationic complexes [Nb(eta(5)-C5H4SiMe3)(2)X(NHPh)](+) [BF4](-)(X = Cl 23, Me 24, Et 25 or Pr-1 26). The structures of the different families of complexes isolated were determined by spectroscopic methods.