Phosphinimide−Phosphinimide Ligands: New Bulky Ligands for Ethylene Polymerization Catalysts

The phosphinimide−phosphines PPh 2 (NPR 3 ) (R = i -Pr 1, t- Bu 2 ) were readily prepared in 80−98% yield. These species react with AlMe 3 or B(C 6 F 5 ) 3 to form Me 3 AlPPh 2 (NPR 3 ) (R = i -Pr 3, t- Bu 4 ) and (C 6 F 5 ) 3 B(PPh 2 (NP i -Pr 3 )) ( 5 ), respectively. Oxidation of compounds 1 and 2 with Me 3 SiN 3 yields Me 3 SiNPPh 2 (NPR 3 ) (R = i -Pr 6, t- Bu 7 ). These species react with CpTiCl 3 to give titanium(IV) complexes CpTiCl 2 (NPPh 2 (NPR 3 ) (R = i -Pr 8, t- Bu 9 ) and subsequently the alkylated complexes CpTiMe 2 (NPPh 2 (NPR 3 )) (R = i -Pr 10, t- Bu 11 ). Compounds 8 − 11 were tested for activity in ethylene polymerization. In the presence of excess methylalumoxane, the species 8 and 9 gave rise to active single-site catalysts, generating 299 and 34 gPE mmol - 1 h - 1, respectively. In contrast, activation of 10 and 11 by [Ph 3 C][B(C 6 F 5 ) 4 ] showed negligible polymerization activity. Reaction of 11 with B(C 6 F 5 ) 3 was shown to give numerous products, one of which was the dicationic species [CpTi(μ-Cl)(NPPh 2 (NP t -Bu 3 )] 2 [BC 6 F 5 ) 4 ] 2, 12 . The formation of this species and the implications of these results for catalyst and ancillary ligand design are considered and discussed. X-ray crystallographic data are reported for 1, 3, 4, 8, and 12 .