The reaction of trialkylphosphines with Ti(BH4)3(Et2O), prepared in situ from TiCl4 and LiBH4 in diethyl ether, gives dark blue adducts of stoichiometry Ti(BH4)3(PR3)2, where PR3 is PMe3, PEt3, PMe2Ph, or P(OMe)3. Magnetic susceptibility and ESR measurements indicate that these are monomeric titanium(III) species. An X-ray crystal structure of Ti(BH4)3(PMe3)2(orthorhombic; Pnma; a = 10.757 (1), b = 11.145 (2), c = 14.270 (3) Å; V= 1710.8 (8) Å3; Z = 4; RF = 6.4%; RwF = 4.8%) reveals an approximate trigonal-bipyramidal geometry, with the phosphines occupying the axial positions: Ti-P = 2.571 (3), 2.539 (3) A; P-Ti-P = 170.27 (9)°. One of the three equatorial BH4- groups is bidentate, Ti-Hb = 1.90 (6) Å, Ti—B = 2.40 (1) Å, B-Hb = 1.03 (7) Å, B-H = 1.00 (8) Å, whereas the other two BH4- groups possess unusual geometries involving interaction of the titanium center with one B-H bond in a “side-on” manner, Ti-Hb = 1.73 (7) Å, Ti-B = 2.27 (1) Å, B-Hb = 0.95 (6) Å, B-Ht= 0.96 (6) Å. This unusual interaction may be a type of Jahn-Teller distortion and closely resembles one proposed transition state for the activation of the isoelectronic molecule methane.
ASJC Scopus subject areas
- Colloid and Surface Chemistry