Studies on the reactivity of alkoxo-niobium(V) compounds towards O,O- or S,S-enolate ligands. Synthesis and structural characterisation of (alkoxo)(beta-diketonato)- and (alkoxo)[dialkyl(aryl)dithiocarbamato] complexes of niobium(V)

Reaction of the alkoxo-containing niobium complexes [NbCl3(OR)(2)](2) (R=Me , Et, Pr-i) with beta-diketones R'COCH2COR' [R' = Me (Hacac); R' = Bu-t (Hd pm); R' = Ph (Hdbm)] in a 1:2 molar ratio, afforded the corresponding (alko xo)(beta-diketonato) complexes [NbCl2(OR)(2)(O,O'-R'COCHCOR')] (R = Me, R' = Me 1; R = Et, R' = Me 2; R = Pr-i, R' = Me 3; R = Me 3; R' = Bu-t 4; R = Et, R' = Bu-t 5; R = Pr-i, R' = Bu-t 6; R = Me, R' = Ph 7; R = Et, R' = Ph 8; R = Pr-i, R' = Ph 9). The molecular structure of 8 was elucidated by an X-ray diffraction study. The kinetics of the displacement reaction of 5 and 8 with Hacac to give complex 2 and the corresponding P-diketone Hdpm or Hd bm have also been studied by H-1-NMR spectroscopy. Finally, the complexes [ NbCl3(OR)(2)](2) reacted with reagents of the type Na(S2CNR2'), in a 1:4 mo lar ratio, to give the corresponding (alkoxo)[dialkyl(aryl)dithiocarbamato] complexes [NbCl(OR)(2)(S,S'-S2CNR')(2)] (R = Me, R' = Me 10; R = Me, R' = Et 11; R = Me, R' = Bz 12; R = Et, R' = Me 13; R = Et, R' = Et 14; R = Et, R' = Bz 15; R = Pr-i, R' = Me 16; R = Pr-i, R' = Et 17; R = Pr-i, R' = Bz 1 8). All complexes were characterised spectroscopically. (C) 2000 Elsevier S cience S.A. All rights reserved.