The interaction of VCl3(thf)3with NaBH4in 1,2-dimethoxyethane (dme) gives deep purple solutions from which the only known binary vanadium tetrahydroborate [Na(dme)][V(BH4)4] can be crystallized. Solutions of this anion may also be obtained in diethyl ether or tetrahydrofuran from VOCl3, VCl4(thf)2, or VCl3(thf)3and LiBH4, but in these cases the product could not be crystallized. The [V(BH4)4]-anion is eight-coordinate with four bidentate BH4 -groups based on IR spectroscopy, and it reacts with 2 equiv of PMe3to give the neutral tris(tetrahydroborate) derivative V(BH4)3(PMe3)2. This high-spin (μ= 2.5μB) complex is bright green and possesses three bidentate BH4 -groups as shown by IR spectroscopy and confirmed by an X-ray crystal structure. The vanadium centers in V(BH4)3(PMe3)2adopt hexagonal-bipyramidal coordination geometries with the phosphine ligands in the axial sites and six hydrogen atoms from the bidentate BH4 -groups in the equatorial plane: V-P = 2.510 (1) A, V-H = 1.84 (3) A, V---B = 2.365 (6) A, P—V—P = 178.45 (5)°, and B—V—B = 118.9 (2) and 120.6 (1)°. Its structure differs fundamentally from that of the titanium analogue Ti(BH4)3(PMe3)2, and this structural difference may be attributable to a Jahn—Teller effect. Reaction of V(BH4)3(PMe3)2with the trialkylphosphine Me2PCH2CH2PMe2(dmpe) or excess PMe3leads to reduction to give the vanadium(II) tetrahydroborate complex V(η1-BH4)2(dmpe)2or [V(BH4)H(PMe3)2]2, respectively. The latter molecule is a paramagnetic vanadium(II) dimer with an edge-shared bioctahedral structure having hydride ligands in the bridging positions. Surprisingly, hydrolysis of V(BH4)3(PMe3)2does not yield a vanadium hydride but instead gives a divanadium(III) complex possessing a bridging oxygen atom, [V(BH4)2(PMe3)2]2O. The X-ray crystal structure of this species reveals a pentagonal-bipyramidal geometry about each metal center in which the BH4 -groups are still bidentate and the two vanadium atoms are joined by a linear oxo bridge: V-O = 1.780 (2) Á, V-O-V = 178.7 (1)°, V-P = 2.530 (1) A, V-H = 1.97 (3) A, and V-B = 2.383 (6) A. This is the first authentic example of a complex containing both tetrahydroborate and oxo ligands. The preparation and characterization of V(BH4)3(thf)3and [V(BH4)Cl(thf)2]2are also reported. All of the molecules described herein are notable since no structurally characterized vanadium complexes containing more than one BH4 -ligand per metal center have been reported previously.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry