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

Reaction of the alkoxo-containing niobium complexes [NbCl3(OR)2]2 (R=Me, Et, iPr) with β-diketones R′COCH2COR′ [R′=Me (Hacac); R′=tBu (Hdpm); R′=Ph (Hdbm)] in a 1:2 molar ratio, afforded the corresponding (alkoxo)(β-diketonato) complexes [NbCl2(OR)2(O,O′-R′COCHCOR′)] (R=Me, R′=Me 1; R=Et, R′=Me 2; R=iPr, R′=Me 3; R=Me, R′=tBu 4; R=Et, R′=tBu 5; R=iPr, R′=tBu 6; R=Me, R′=Ph 7; R=Et, R′=Ph 8; R=iPr, 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 β-diketone Hdpm or Hdbm have also been studied by 1H-NMR spectroscopy. Finally, the complexes [NbCl3(OR)2]2 reacted with reagents of the type Na(S2CNR′2), in a 1:4 molar 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=iPr, R′=Me 16; R=iPr, R′=Et 17; R=iPr, R′=Bz 18). All complexes were characterised spectroscopically.