Low Valent Complexes of Tantalum and Niobium (Trimcthylphosphine).

Abstract

The d('3) complexes, TaCl(,2)(PMe(,3))(,4) and NbCl(,2)(PMe(,3))(,4), were prepared by reduction of MCl(,5) with sodium amalgam and isolated in yields of 60 and 25%, respectively. Red-brown NbCl(,2)(dmpe)(,2) was obtained in 90% yield via reduction of NbCl(,4)(dmpe)(,2). The tantalum analogue was previously prepared in a similar manner. These complexes were studied using infrared, UV-Vis, ESR, and NMR spectroscopy, magnetic susceptibility and , in the cases of TaCl(,2)(PMe(,3))(,4) and NbCl(,2)(dmpe)(,2), by low temperature X-ray crystallography. The MCl(,2)L(,4) species are best described as low-spin, trans-octahedral complexes. These adducts, with the exception of NbCl(,2)(PMe(,3))(,4), all react readily with dihydrogen at 25(DEGREES)C to form monomeric, paramagnetic, d('1) hydrides, MCl(,2)H(,2)L(,4), in yields of 70-90%. The reaction of hydrogen with NbCl(,2)(PMe(,3))(,4) produces the dimeric product, {NbCl(,2)(PMe(,3))(,2)}(,2)((mu)-H)(,4). These hydride complexes were characterized by infrared and ESR spectroscopy, magnetic susceptibility and , in the cases of the two tantalum complexes, by low temperature X-ray crystallography. TaCl(,2)H(,2)(PMe(,3))(,4) and TaCl(,2)H(,2)(dmpe)(,2) adopt dodecahedral and square antiprismatic geometries, respectively. The reduction of TaCl(,2)H(,2)(PMe(,3))(,4) with one equivalent of sodium amalgam provides the seven-coordinate monomer, TaClH(,2)(PMe(,3))(,4), in 70% yield. The dmpe analogue, TaClH(,2)(dmpe)(,2), was prepared by the metathesis reaction of dmpe and TaClH(,2)(PMe(,3))(,4). These complexes were studied by variable temperature NMR and infrared spectroscopy. In the solid state, TaClH(,2)(PMe(,3))(,4) adopts a pentagonal bipyramidal geometry as indicated by low temperature X-ray and neutron crystallography. Carbon monoxide reacts with TaClH(,2)(PMe(,3))(,4) to provide TaCl(CO)(,3)(PMe(,3))(,3) in 80% yield. Reductive carbonylation of NbCl(,2)(PMe(,3))(,4) provides NbCl(CO)(,3)(PMe(,3))(,3) in 40% yield. They were characterized by NMR and infrared spectroscopy. An X-ray crystallographic study of TaCl(CO)(,3)(PMe(,3))(,3) shows that it adopts a capped trigonal prismatic geometry. The complexes, TaCl(,2)H(,2)(PMe(,3))(,4), TaClH(,2)(PMe(,3))(,4) and TaClH(,2)(dmpe)(,2), react with LiBH(,4) to provide TaH(,2)(BH(,4))L(,4). These complexes react with dihydrogen, carbon monoxide and PMe(,3) to produce TaH(,5)L(,4), Ta(CO)(,3)(PMe(,3)) (BH(,4)), Ta(CO)(,2)(dmpe)(,2), Ta(CO)(,2) (dmpe)(,2)H, and {Ta(CO)(,3)(PMe(,3))(,4)} {Ta(CO)(,5)(PMe(,3))}. These products were studied by variable temperature NMR and infrared spectroscopy and , in the latter case, by X-ray crystallography. The cation and anion adapt capped octohedral and octahedral geometries, respective(,ly. )