Preparation of Phosphine-Amido Hafnium and Zirconium Complexes for Olefin Polymerization

Aniline (N-R-C6H5­NH) and 1,2,3,4-tetrahydroquinoline (2-R-C9H9­NH) derivatives were ortho-lithiated via
conversion of the respective −NH groups to −N­(COOLi),
followed by treatment with tBuLi. The resulting ortho-lithiated
compounds were transformed to ortho-Ph2P-substituted derivatives on treatment with Ph2P­(OPh).
Further reaction of the resulting compounds with M­(CH2Ph)4 (M = Zr, Hf) afforded a series of Hf and Zr complexes:
(2-R-8-Ph2P­C9H9N)­Hf­(CH2Ph)3 (8, R = H; 9, R
= Me; 10, R = iPr; 11,
R = nBu), (N-R-2-Ph2P­C6H4N)­Hf­(CH2Ph)3 (12, R = Me; 13, R = Et; 14, R = iPr), (2-R-8-Ph2P­C9H9N)­Zr­(CH2Ph)3 (15,
R = H; 16, R = Me; 17, R = iPr; 18, R = nBu), and (N-R-2-Ph2P­C6H4N)­Zr­(CH2Ph)3 (19, R = Me; 20, R = Et)].
X-ray crystallographic studies of 9, 14, 16, and 19 revealed a distorted trigonal-bipyramidal
structure with two benzyl moieties in equatorial positions and the
remaining benzyl ligand occupying an apical position; in solution,
however, three benzyl ligands became scrambled, as evidenced by a
single set of benzyl signals in the corresponding 1H NMR
spectra. The complexes showed comparable activities (17–48
× 106 g/mol-M·h) to the Ti-based constrained
geometry catalyst (CGC) (36 × 106 g/mol-Ti·h)
in ethylene/1-octene copolymerization, despite their inferior 1-octene
incorporation capabilities (3–8 mol % versus 17 mol %). Compound 15 showed a moderate 1-octene incorporation capability (7.7
mol %), whereas the others showed low 1-octene incorporations (2–4
mol %). Compounds 9 and 16 provided high-molecular-weight
polymers with Mw > 200 000 even
at high reaction temperatures of 100–130 °C.