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

Abstract

The syntheses of group 4 metal complexes containing the picolyldicarbollyl ligand Dcab Py H [ nido-7-HNC 5H 4(CH 2)-8-R-7,8-C 2B 9H 10] ( 2) are reported. New types of constrained geometry group 4 metal complexes (Dcab Py )MCl 2, [{(η 5-RC 2B 9H 9)(CH 2)(η 1-NC 5H 4)}MCl 2] (M = Ti, 3; Zr, 4; R = H, a; Me, b), were prepared by the reaction of 2 with M(NMe 2) 2Cl 2 (M = Ti, Zr). The reaction of 2 with M(NMe 2) 4 in toluene afforded (Dcab Py )M(NMe 2) 2, [{(η 5-RC 2B 9H 9)(CH 2)(η 1-NC 5H 4)}M(NMe 2) 2] (M = Ti, 5; Zr, 6; R = H, a; Me, b), which readily reacted with Me 3SiCl to yield the corresponding chloride complexes (Dcab Py )MCl 2 (M = Ti, 3; Zr, 4; R = H, a; Me, b). The structures of the diamido complexes (Dcab Py )M(NMe 2) 2 (M = Ti, 5; Zr, 6) were established by X-ray diffraction studies of 5a, 5b, and 6a, which verified an η 5:η 1-bonding mode derived from the dicarbollylamino ligand. Related constrained geometry catalyst CGC-type alkoxy titanium complexes, (Dcab Py )Ti(O i Pr) 2 ( 7), were synthesized by the reaction of 2 with Ti(O i Pr) 4. Sterically less demanding phenols such as 2-Me-C 6H 4OH replaced the coordinated amido ligands on (Dcab Py )Ti(NMe 2) 2 ( 5a) to yield aryloxy stabilized CGC complexes (Dcab Py )Ti(OPh Me) 2(Ph Me = 2- Me–C 6H 4, 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(OPh Me) 2 ( 8).