Synthesis, characterization, and reactivity of new types of constrained geometry group 4 metal complexes derived from picolyl-substituted dicarbollide ligand systems

The syntheses of group 4 metal complexes containing the picolyldicarbollyl ligand Dcab(Py) H [nido-7-HNC5H4(CH2)-8-R-7,8-C2B9H10] (2) are reported. New types of constrained geometry group 4 metal complexes (Dcab(Py)) MCl2, [{(eta(5)-RC2B9H9)(CH2)(eta(1)-NC5H4)} MCl2] (M = Ti, 3; Zr, 4; R = H, a; Me, b), were prepared by the reaction of 2 with M(NMe2)(2)Cl-2 (M = Ti, Zr). The reaction of 2 with M(NMe2)(4) in toluene afforded (Dcab(Py))M(NMe2)(2), [{(eta(5)-RC2B9H9)(CH2)(eta(1)-NC5H4)} M(NMe2)(2)] (M = Ti, 5; Zr, 6; R = H, a; Me, b), which readily reacted with Me3SiCl to yield the corresponding chloride complexes (Dcab(Py))MCl2 (M = Ti, 3; Zr, 4; R = H, a; Me, b). The structures of the diamido complexes (Dcab(Py))M(NMe2)(2) (M = Ti, 5; Zr, 6) were established by X-ray diffraction studies of 5a, 5b, and 6a, which verified an eta(5):eta(1)-bonding mode derived from the dicarbollylamino ligand. Related constrained geometry catalyst CGC-type alkoxy titanium complexes, (Dcab(Py))Ti((OPr)-Pr-i)(2) (7), were synthesized by the reaction of 2 with Ti((OPr)-Pr-i)(4). Sterically less demanding phenols such as 2-Me-C6H4OH replaced the coordinated amido ligands on (Dcab(Py)) Ti(NMe2)(2) (5a) to yield aryloxy stabilized CGC complexes (Dcab(Py))Ti(OPhMe)(2)(Ph-Me = 2- Me-C6H4, 8). NMR spectral data suggested that an intramolecular Ti - N coordination was intact in solution, resulting in a stable piano-stool structure with two aryloxy ligands residing in two of the leg positions. The aryloxy coordinations were further confirmed by single crystal X-ray diffraction studies on complexes (Dcab(Py))Ti(OPhMe)(2) (8). (C) 2007 Elsevier B.V. All rights reserved.