A new type of monoanionic 'scorpionate' ligand. Synthesis, spectroscopic characterisation and dynamic behaviour of some niobium(III) complexes

摘要

The syntheses of novel scorpionate ligands in the form of the lithium derivative [{Li(H2O)(bdmpza)}(4)] 1 [bdmpza=bis(3,5-dimethylpyrazol-1-yl)acetate] or as the alcohol derivative 2,2-bis(3,5-dimethylpyrazol-1-yl)ethanol 2 (Hbdmpze) have been studied. These compounds are excellent precursors for the introduction of these scorpionate ligands into transition metal complexes. The complex [{NbCl3(dme)}(n)] (dme=1,2-dimethoxyethane) reacted with 1 and 2, the latter with prior addition of (BuLi)-Li-n, to give the binuclear complexes [{NbCl2(bdmpzx)}(2)] (x=a, 3; x=e, 4) [bdmpze=2,2-bis(3,5-dimethylpyrazol-1-yl)ethoxide]. Complex 3 reacted with 1 to give the complex [{NbCl(bdmpza)(2)}(2)] 5. In the same way the reaction of the mononuclear species [NbCl3(dme)(RC=CR')] with 1 and 2, the latter with prior addition of (BuLi)-Li-n, gave the appropriate [NbCl2(bdmpzx)(RC=CR')] complexes [x=a, R=R'=Me, 6; Et, 7; Ph, 8; or SiMe3, 9; R=Ph, R'=Me, 10; R=Ph, R'=Et, 11; R=Ph, R'=SiMe3, 12; x=e, R=R'=Me, 13; Et, 14; or Ph, 15; R=Ph, R'=Me, 16; R=Ph, R'=Et, 17; R=Ph, R'=SiMe3, 18]. The structures of these complexes have been determined by spectroscopic methods. Variable-temperature NMR studies were carried out in order to study their dynamic behaviour in solution. The barriers to alkyne rotation have also been calculated. Reaction of 10 with LiCp' (Cp'=C5H4SiMe3) gave the mixed Cp-bdmpza complex [NbCp'Cl(bdmpza)] 19. [References: 32]