Arene-Bridged Salicylaldimine-Based Binuclear Neutral Nickel(II) Complexes:  Synthesis and Ethylene Polymerization Activities

Abstract

A series of novel m-arene-bridged salicylaldimine-based binuclear neutral nickel(II) complexes (2,4,6-(R 2 ) 3 C 6 H-1,3-[NdCH-4-X-6-R 1 C 6 H 2 ONi(Ph)(PPh 3 )] 2 (3a-i: R 1 , R 2 , X ) Me, Me, H (3a), t Bu, Me, H (3b), Me, Et, H (3c), t Bu, Et, H (3d), H, i Pr, H (3e), Me, i Pr, H (3f), t Bu, i Pr, H (3g), Ph, i Pr, H (3h), NO 2 , i Pr, NO 2 (3i), H, i Pr, NO 2 (3j)) are synthesized. The structure of complex 3h is further confirmed by an X-ray diffraction study showing that the two Ni centers adopt an unsymmetrical, distorted square planar geometry. In the presence or absence of the phosphine scavenger Ni(COD) 2 , complexes 3a-j show high catalytic activities for ethylene polymerization. The effect of substituents on ethylene polymerization is significant. The introduction of an electron-withdrawing group to the ligand framework improves the catalytic activity significantly. The influence of polymerization temperature, polymerization time, and catalyst concentration on the activities of ethylene polymerization is also investigated. Highly branched polyethylenes (46-127 branches per 1000 carbon atoms) with moderate molecular weights (M η ) (1.0-169) × 10 4 ) and narrow molecular weight distributions (M w /M n ) 2.3-2.4) are obtained by using complexes 3a-j as catalysts with or without a phosphine scavenger. In the presence of a polar solvent such as THF or Et 2 O, complex 3h polymerizes ethylene as a single-component catalyst. In comparison to the corresponding mononuclear Ni catalysts, the binuclear Ni catalysts generally show higher thermal stability, and complexes 3a, 3c, 3e, and 3f, which feature small R 1 substituents, are capable of acting as single-component ethylene polymerization catalysts.

Dinickel Bisphenoxyiminato Complexes for the Polymerization of Ethylene and α-Olefins

“…This drop in activity for 30 is similar to the three- to five-fold drop in TOF reported for polymerizations with phosphine-ligated nickel salicylaldimine complexes in the presence of excess ethers. 11,13,23 The notable lack of inhibition by THF of catalysts 25 – 28 may be due to the steric bulk of the fully substituted aryl group ortho to oxygen disfavoring ether coordination.…”

“…22 Further investigation of variants of f indicates similar tolerance for functional groups as compared to mononuclear counterparts. 23 System g displays higher ethylene polymerization activity and produces polymers with increased M w relative to the mononuclear systems studied. 17 Increased incorporation of comonomers and, most notably, of polar olefins occurs with system h relative to mononuclear analogues.…”

Olefin Polymerization with Non-metallocene Catalysts (Late Transition Metals)

“…Dinuclear Ni catalysts having salicylaldimine ligands (Chart 4.12, 12a-12c) have been reported to show higher catalytic activity for ethylene polymerization and/or to produce polyethylene with higher molecular weight compared to the mononuclear analogue [216][217][218][219][220]. The higher activity of the dinuclear catalysts is accounted for by the increased rate of insertion of the monomer as a result of steric bulkiness and electronic effect of the dinuclear structure.…”

Recent Research Progress of Branched and Functional Branched Polyethylene Prepared Using Ni- and Pd–Based Catalysts

“…The Ni-and Pd-based catalysts containing N-N , N-O [53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68] , P-N [69][70][71][72] , P-P [73][74][75][76][77] and P-O [78][79][80][81][82][83][84] ligands have been synthesized and applied in ethylene polymerization to yield branched polymer. By comparison, the Ni and Pd-based catalysts containing N-N inherit stronger branched capability than other catalyst and can catalyze ethylene polymerization to produce branched polyethylene with more than 100 branches per 1000 carbons.…”