Synthesis, structures of (aminopyridine)nickel complexes and their use for catalytic ethylene polymerization

摘要

A series of α-aminopyridines in the form of (2,6-C _6H _3N)(R ~1)(CHR ~2NR ~3R ~4) (R ~1 = R ~2 = H R ~3 = H R ~4 = ~iPr (L1a), R ~4 = ~tBu (L1b), R ~4 = Ph (L1c), R ~4 = 2,6-Me _2C _6H _3 (L1d), R ~4 = 2,6- ~iPr _2C _6H _3 (L1e), R ~1 = R ~2 = H R ~3 = R ~4 = Et (L1f), R ~1 = H R ~2 = Me R ~3 = H R ~4 = ~iPr (L2a), R ~4 = Ph (L2c), R ~4 = 2,6-Me _2C _6H _3 (L2d), R ~4 = 2,6- ~iPr _2C _6H _3 (L2e), R ~1 = Me R ~2 = H R ~3 = H R ~4 = 2,6- ~iPr _2C _6H _3 (L3e)) and β-aminopyridines in the form of (2-C _6H _4N)(CH _2CH _2NR ~1R ~2) (R ~1 = H R ~2 = ~iPr (4a), R ~2 = ~tBu (L4b), R ~1 = R ~2 = Et (L4f)) have been prepared. Their corresponding halonickel complexes 1a-4f are synthesized by ligand substitution from (DME)NiBr _2 and the molecular structures are characterized. Four types of coordination modes include four-coordinate mononuclear species with one ligand, five-coordinate mononuclear species with two ligands, five-coordinate dinuclear species with two ligands, and a six-coordinate polymeric framework were determined by X-ray crystallography. Using methylaluminoxanes (MAO) as the activator, the nickel complexes can catalyze ethylene polymerization under moderate pressure and ambient temperature. The activity reaches 10 ~5 g PE mol ~(-1) Ni h. The PE products with high branching and high crystallinity have M _n ～ 10 ~3 with PDI < 2.