Imido-supported borohydrides of titanium, vanadium and molybdenum
Résumé
New imido bis(borohydride) complexes [(RN=)M(PMe3)2(η2-BH4)2] [R = Ar, M = Ti (3); R = Ar, M = V (5); R = Ar, M = Mo (6); R = Ar', M = Mo (7); Ar = 2,6-iPr2C6H3, Ar' = 2,6-Me2C6H3] were prepared by the reaction of dichlorides [(RN=)MCl2(PMe3)n] (M = Ti, n = 2; M = V, n = 2, M = Mo, n = 3) with LiBH4 (2 equiv) in THF. Compounds 3, 5, 6 and 7 were studied by IR spectroscopy and X-ray diffraction, and an EPR spectroscopy study was performed for paramagnetic compound 5. In 3, the two borohydride units are orthogonal to each other as a result of the overlap of an antiphase combination of B-H orbitals with the empty dxy orbital of Ti. In contrast, the dxy orbital of the metal atom is singly occupied in 5 and fully occupied in 6 and 7, and both borohydride ligands are oriented in the same way, with the B(μ-H2)M moieties orthogonal to the P-M-P vector.