Titanium and Zirconium Benzyl Complexes Bearing Bulky Bis(amido)cyclodiphosph(III)azanes: Synthesis, Structure, Activation, and Ethene Polymerization Studies

Benzyl-substituted bis(amido)cyclodiphosph(III)azane complexes [(RN)(t-BuNP)]2M(CH2Ph)nCl2-n (M = Zr, Ti; n = 1, 2) bearing t-Bu or bulky aryl substituents on amido nitrogens were prepared by direct alkylation of corresponding dichloro derivatives with PhCH2MgCl. The alkylation of Zr complexes proceeded selectively. In the solid state of [(t-BuN)(t-BuNP)]2Zr(CH2Ph)2 the zirconium atom adopts a distorted trigonal-bipyramidal configuration. The alkylation of [(t-BuN)(t-BuNP)]2TiCl2 with PhCH2MgCl in the presence of THF led to [(t-BuN)(t-BuNP)]2Ti(CH2Ph)2 simultaneously with [(t-BuN)(t-BuNP)]2Ti(CHPh)(THF). According to NMR and X-ray single-crystal studies, the latter contains a Ti−C double bond. Activation of the benzyl complexes with B(C6F5)3 led to the generation of the corresponding “cationic” species, which were further investigated by 1H, 13C, 31P, and 19F NMR methods. In the solid state the metal center of {[(t-BuN)(t-BuNP)]2Zr(η2-CH2Ph)(Et2O)}+[PhCH2B(C6F5)3]- has a distorted trigonal bipyramidal configuration, where the benzyl group coordinates to Zr in a η2-fashion. In ethene polymerization the mono- and dibenzyl Ti and Zr derivatives showed moderate to high catalytic activities (up to 4600 kg/(mol × h)). The correlation between polymerization results and activation experiments, especially in terms of electrophilicity of the metal center, is discussed.