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

Dalton Transactions Pub Date: 2012-03-29 DOI: 10.1039/C2DT30151B

Abstract

A series of α-aminopyridines in the form of (2,6-C6H3N)(R1)(CHR2NR3R4) (R1 = R2 = H R3 = H R4 = iPr (L1a), R4 = tBu (L1b), R4 = Ph (L1c), R4 = 2,6-Me2C6H3 (L1d), R4 = 2,6-iPr2C6H3 (L1e), R1 = R2 = H R3 = R4 = Et (L1f), R1 = H R2 = Me R3 = H R4 = iPr (L2a), R4 = Ph (L2c), R4 = 2,6-Me2C6H3 (L2d), R4 = 2,6-iPr2C6H3 (L2e), R1 = Me R2 = H R3 = H R4 = 2,6-iPr2C6H3 (L3e)) and β-aminopyridines in the form of (2-C6H4N)(CH2CH2NR1R2) (R1 = H R2 = iPr (4a), R2 = tBu (L4b), R1 = R2 = Et (L4f)) have been prepared. Their corresponding halonickel complexes 1a–4f are synthesized by ligand substitution from (DME)NiBr2 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 105 g PE mol?1 Ni h. The PE products with high branching and high crystallinity have Mn ～ 103 with PDI < 2.

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