Structure and chemical properties of zirconium(IV) complexes containing a rigid naphthalene diamide ligand ([1,8-C 10 H 6 (NSiMe 3 ) 2 ] 2 - ) or flexible propylene diamide ligands ([1,3-C 3 H 6 (NR) 2 ] 2 -, R = SiMe 3, Si( i -Pr) 3 ) are described. The reaction of 1,8-C 10 H 6 (NHSiMe 3 ) 2 with Zr(NMe 2 ) 4 in refluxing toluene yields [1,8-C 10 H 6 (NSiMe 3 ) 2 ]Zr(NMe 2 ) 2 ( 1 ), and the product 1 is converted to [1,8-C 10 H 6 (NSiMe 3 ) 2 ]ZrCl 2 ( 2 ) in a moderate isolation yield by the treatment with excess ClSiMe 3 . X-ray crystallographic analysis establishes that 2 forms a dimer associated through two chloride bridges in the solid state and has a highly puckered six-membered ring with a small N−Zr−N bite angle (91.05°). The reaction of 1,3-C 3 H 6 (NHR) 2 (R = SiMe 3, Si( i -Pr) 3 ) with Zr(NMe 2 ) 4 also affords [1,3-C 3 H 6 (NR) 2 ]Zr(NMe 2 ) 2 . Treatment of the amide complex with excess ClSiMe 3 results in [1,3-C 3 H 6 (NR) 2 ]ZrCl 2 ( 4, R = SiMe 3; 5, R = Si( i -Pr) 3 ) in a facile manner. The crystal structure of 5 shows that the molecule is monomeric, featuring a mirror plane that passes the zirconium atom and two chloride atoms, and the chelate and the metal form a boatlike six-membered ring with a large N−Zr−N angle (104.31°). While these zirconium(IV) diamide complexes ( 2, 4, and 5 ) exhibit moderate ethylene polymerization activity (10−90 kg of PE/(mol cat ·atm·h)) in the presence of methylalumoxane, the diamide dimethyl compound [1,3-C 3 C 6 (NSi( i -Pr) 3 ) 2 ]ZrMe 2 ( 6 ) shows a high activity (300 kg of PE/(mol cat ·atm·h)) for the ethylene polymerization when it is activated with Ph 3 CB(C 6 F 5 ) 4 .
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Lee et al. (2000) studied this question.