Bis[(amidomethyl)pyridine] Zirconium(IV) Complexes: Synthesis, Characterization, and Activity as Olefin Polymerization Catalysts

This contribution describes the synthesis, characterization, and olefin polymerization reactivity of bis(chelate)zirconium complexes bearing (amidomethyl)pyridine ligands [(6-X-C5H3N)CH2NC6F5, X = CH3 (Lig1H), Br (Lig2H), H (Lig3H)]. Metathesis reaction, alkane elimination, and amine elimination provided routes to compounds (Lig1)2ZrCl2 (1), (Lig1)2ZrBz2 (4; Bz = CH2C6H5), and (Lig2)2Zr(NMe2)2 (5). Attempts to prepare (Lig1)2Zr(NMe2)2 in a reaction between Zr(NMe2)4 and Lig1H led instead to compound (Lig1)(Lig1*)ZrF(NMe2) (2), in which one dimethylamino group had been exchanged with one ortho fluoride on the perfluorophenyl ring of the ligand via an aromatic nucleophilic substitution reaction. Halide displacement reaction performed on compound 2 afforded the dichloride compound (Lig1)(Lig1*)ZrCl2 (3). Reaction between Zr(NMe2)4 and Lig3H provided a mixture of (Lig3)2Zr(NMe2)2 and (Lig3)(Lig3*)ZrF(NMe2), the latter being analogous to 2. X-ray crystallographic analysis showed for compound 1 a distorted octahedral geometry with C1 symmetry and for compound 2 a 7-coordinate species. Variable-temperature NMR studies established for compound 1 an inversion of metal configuration through dynamic interchange of the all-cis enantiomers. Fluxional behaviors in solution were also observed for compounds 2, 3, and 4. Treatment of complexes with AliBu2H and methylalumoxane (MAO) yields active, multisite ethylene and propylene polymerization catalysts.