Triazamethylenemethane complexes of zirconium and tantalum

Addition of [Li 2 (THF) 4 ][C(NPh) 3 ] ( 2 ) to a THF solution of Cp * ZrCl 3 (Cp * =C 5 Me 5 ) yields, after recrystallization in Et 2 O, the zwitterionic species Cp * [C(NPh) 3 ]ZrCl 2 Li(Et 2 O)(THF) ( 3 ). Treating 3 with excess methylaluminoxane (MAO) affords a homogeneous Ziegler–Natta catalyst for ethylene polymerization. Addition of LiNPh 2 to 3 allows for Cl substitution to give the new product Cp * [C(NPh) 3 ]Zr(NPh 2 )ClLi(THF) 2 ( 4 ). A single crystal diffraction study of 4 reveals that the [C(NPh) 3 ] ligand is η 2 -bound. The group 5 complex Cp * [C(NPh) 3 ]TaMe 2 ( 5 ) was prepared by addition of 2 to Cp * TaMe 2 Cl(OSO 3 CF 3 ). The X-ray diffraction structure of 5 shows that the [C(NPh) 3 ] ligand is η 2 -bound to tantalum and that, when compared to 4 , there is less electron delocalization across the inner core of [C(NPh) 3 ].