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A series of nickel(II) catalysts containing phenyl and chiral sec-phenethyl groups, {[(4-R1-2-R2C6H2NC)2Nap]NiBr2} (Nap: 1,8-naphthdiyl, R1 = Me, R2 = Ph (3a); R1 = Me, R2 = sec-phenethyl (3b); R1 = Cl, R2 = sec-phenethyl (3c); R1 = Me, R2 = Me (3d) were synthesized and characterized. All organic compounds were fully characterized by FT-IR and NMR spectroscopy and elemental analysis. The single crystal for X-ray crystallography was isolated from 3a in CH2Cl2/n-hexane under air; the crystal structure showed a binuclear complex 3a′, in which each nickel atom was six-coordinate. The two nickel atoms together with two bromine atoms form a planar four-membered ring, with a bromine and H2O axial ligands. These complexes, activated by diethylaluminum chloride and chiral nickel pre-catalysts rac-3c, exhibited good activities (up to 2.85 × 106 g PE (mol Ni h bar)−1) for ethylene polymerization, and produced polyethylene products with a high degree of branching (up to 117 branched per 1000 carbons) at high temperature. The type and amount of branches of the polyethylenes obtained were determined by 1H and 13C NMR spectroscopy. Copyright © 2014 John Wiley & Sons, Ltd.

A series of new chiral and achiral nickel(II) and palladium(II) complexes, {bis[N,N′-(2,6-diethyl-4-naphthylphenyl)imino]-1,2-dimethylethane}dibromonickel 3a, {bis[N,N′-(4-fluoro-2-methyl-6-sec-phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel rac-(RS)-3b, {bis[N,N′-(4-fluoro-6-sec-phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel rac-(RR/SS)-3c and {bis[N,N′-(4-fluoro-6-sec-phenethylphenyl)imino]-1,2-dimethylethane}dichloropalladium rac-(RR/SS)-3d were successfully synthesized and characterized. The molecular structures of representative ligand rac-(RS)-2b, nickel complex 3a, rac-(RR/SS)-3c and palladium complex rac-(RR/SS)-3d were determined by X-ray crystallography. The structures of complexes 3a and rac-(RR/SS)-3c have pseudo-tetrahedral geometry about the nickel center, showing C2 molecular symmetry. However, the structure of palladium complex rac-(RR/SS)-3d has pseudo-square planar geometry about the palladium center, showing C2 molecular symmetry. Complex 3e {bis[N,N′-(2,6-dimethylphenyl)imino]-1,2-dimethylethane}dibromonickel was also synthesized for comparison. Nickel complex rac-(RS)-3b bearing strong electron-withdrawing fluorine group in the para-aryl position and a chiral sec-phenethyl group in the ortho-aryl position of the ligand (one methyl group in the ortho-aryl position) displays the highest catalytic activity for ethylene and styrene polymerization, and produced highly branched polyethylene and syndiotactic-rich polystyrene. However, palladium complex rac-(RR/SS)-3d shows low catalytic activity for ethylene and styrene polymerization due to the poor leaving group, Cl, attached to palladium and the unfavorable molecular structure. Copyright © 2014 John Wiley & Sons, Ltd.

A series of new α-diimine nickel(II) catalysts bearing bulky chiral sec-phenethyl groups have been synthesized and characterized. The molecular structure of representative chiral ligand, bis[N,N′-(4-methyl-2,6-di-sec-phenethylphenyl)imino]-1,2-dimethylethane rac-1c and chiral complexes, {bis[N,N′-(4-methyl-2-sec-phenethylphenyl)imino]-2,3-butadiene}dibromidonickel rac-2a and bis{bis[N,N′-(4-methyl-2-sec-phenethylphenyl)imino]-2,3-butadiene}dibromidonickel rac-2b, were confirmed by X-ray crystallographic analysis. Complex rac-2c bearing two chiral sec-phenethyl groups in the ortho-aryl position and a methyl group in the para-aryl position, activated by diethylaluminum chloride (DEAC), showed highly catalytic activity for the polymerization of ethylene [4.12 × 106 g PE (mol Ni.h.bar)−1], and produced highly branched polyethylenes under low ethylene pressure (branching degree: 104, 118 and 126 branches/1000 C at 20, 40 and 60°C, respectively). Chiral 20-electron bis-α-diimine Ni(II) complex rac-2b also exhibited high activity toward ethylene polymerization [1.71 × 106 g PE (mol Ni · h · bar)−1]. The type and amount of branches of the polyethylenes obtained were determined by 1H and 13C NMR. Copyright © 2013 John Wiley & Sons, Ltd.