Synthesis of (1-adamantylimido)vanadium(V) complexes containing aryloxo, ketimide ligands: Effect of ligand substituents in olefin insertion/metathesis polymerization

A series of (1-adamantylimido)vanadium(V) complexes containing anionic donor ligands of the type, V(NAd)Cl-2(L) [Ad = 1-adamantyl; L = 0-2,6-Me2C6H3 (2), O-2,6-(Pr2C6H3)-Pr-i (3), N=(CBu2)-Bu-t (5), N=C(Bu-t)CH2SiMe3 (6), N=C(Bu-t)Ph (7), N=CPh2 (8)], have been prepared from V(NAd)Cl-3, which was in turn prepared from VOCl3 by treatment with 1-adamantylisocyanate in octane, by treatment with the corresponding lithium salts (lithium phenoxides, lithium ketimides) in Et2O. These complexes (2, 3, 5-8) were identified by NMR spectroscopy and elemental analysis, and the structures for 2 and 5 were determined by X-ray crystallography. The reaction of V(NAd)Cl-3 with 2,6-dimethylphenol in n-hexane afforded the tris(aryloxo) analogue V(NAd)(O-2,6-Me2C6H3)(3) (4), the structure of which was determined by X-ray crystallography. 8 gradually decomposed in toluene to give a dimeric species, [N(Ad)H-3](+)[V-2(mu(2)-Cl)(3)Cl-2(NAd)(2)(N=CPh2)(2)](-) (10), but 8 was stabilized as a PMe3 coordinated species, V(NAd)Cl-2-(N=Cph(2))(PMe3)(2) (9): the structures for 9 and 10 were determined by X-ray crystallography. These complexes were evaluated as catalyst precursors for ethylene polymerization in the presence of MAO. The ketimide analogues, especially 5, exhibited moderate catalytic activity, and the activity with a series of V(NAd)Cl-2(L)-MAO catalyst systems increased in the order: L = N=(CBu2)-Bu-t (5, 516 kg-PE/mol (.) V (.) h) > N=C(Bu-t)Ph (7, 300) > N=CPh2 (8, 105) > N=C(Bu-t)CH2SiMe3 (6, 70.8). These complexes (2, 3, 5, 6) were found to be effective as catalyst precursors for the ring-opening metathesis polymerization (ROMP) of norbomene (NBE) in the presence of MeMgBr and PMe3.