Synthesis and structural characterization of a nickel(II) precatalyst bearing a β‐triketimine ligand and study of its ethylene polymerization performance using response surface methods

Abstract

The reaction of N-(4-(mesitylamino)pent-3-en-2-ylidene)-2,4,6-trimethylbenzenamine (1) with n-butyl lithium and then with N-(2,4,6-trimethyl-phenyl)-acetimidoyl chloride yields a new b-triketimine ligand, N-(4-(mesitylamino)-3-(1-(mesitylimino)ethyl)pent-3-en-2-ylidene)-2,4,6-trimethylbenzenamine, 2. The addition of 2 to nickel (II) dibromide 1,2-dimethoxyethane (NiBr 2 (DME)) in the presence of [Na] The structure of 3 has been determined by single crystal X-ray diffraction. This complex generates catalytically active species for the homopolymerization of ethylene in combination with methylaluminoxane to produce elastomeric, branched polyethylene. The effect of factors (temperature, pressure, and cocatalyst to catalyst molar ratio (CC)) on the polymerization process has been investigated using regression models of responses (catalyst activity, crystallinity, and weight-average molecular weight of polymer (M w )) and visualized via the response surface method (RSM). Activity and M w responses show a second-order variation with temperature and vary linearly with pressure. Conversely, crystallinity follows a secondorder model while varying temperature, pressure, and CC. Furthermore, a set of polymerization conditions for reaching desirable responses was predicted and then experimentally verified. The activities achieved challenge the best reported activities for Ni(II) catalysts with b-connected imine ligand supports, but fall short of those for a-diimines. V C 2013 Wiley Periodicals, Inc. J.

Bidentate forms of β-triketimines: syntheses, characterization and outstanding performance of enamine–diimine cobalt complexes in isoprene polymerization

“…14,[18][19][20] These complexes mainly employed bis-imino-pyridine and analogous cases such as bis-benzimidazolylpyridine, exclusively planar mer-N,N,N-ligands on cobalt. In contrast, in our previous work on Cr(0), Mo(0), W(0), 21 Tl(I), 22 Ni(II) 23 and Co(II), 7,24 the triketimine N,N,N ligands were found exclusively to bind in a fac tridentate manner. In our mechanistic hypotheses, we reasoned on the basis of electron counts that it was likely that bidentate forms may be found at key points in the catalytic cycle.…”

“…In the several previous examples of reaction of enamine-diimines with Co(II) and other metals, in all cases the ligands converted exclusively to the tridentate β-triketimine forms. 7,[21][22][23][24] Here, uniquely, the enamine-diimine tautomer present in the proligand is retained, though the internal hydrogen bond is lost. This different behaviour may be ascribed to the presence of alkyl substituents in both ortho positions of each aryl, a degree of bulk which appears not be tolerated in the tridentate form.…”

1‐(2,6‐dibenzhydryl‐4‐fluorophenylimino)‐2‐aryliminoacenaphthylylnickel halides highly polymerizing ethylene for the polyethylenes with high branches and molecular weights

“…It is still important to finely tune model nickel complexes through modifying the ligands with different substituents. Inspired by the simulation results as ligands containing electron‐withdrawing substituents activating their nickel pre‐catalysts, 2,6‐dibenzhydryl‐4‐chloroaniline was used instead of 2,6‐dibenzhydryl‐4‐methylaniline to form α ‐diimine ligands and prepare nickel analog pre‐catalysts ( C , Scheme ) showing high catalytic activities . (b) Further investigation is currently conducted to use 2,6‐dibenzhydryl‐4‐fluoroaniline in preparing organic compounds as extensive ligands for their nickel complexes ( D , Scheme ).…”

Synthesis and characterization of β-triketimine cobalt complexes and their behaviour in the polymerization of 1,3-butadiene

“…17,18 The most recent focus has been upon nitrogen-ligated cobalt complexes in diene polymerization, especially on those with tridentate ligands. [19][20][21] In this work we present the synthesis and characterisation of a new generation of cobalt catalysts using β-triketimine ligands recently employed to present a neutral N,N,N-ligand set in Cr, Mo, W, 22 Ni 23 and Tl complexes. 24 Our extension here to cobalt marks a departure from the recent work of others who employed exclusively planar, meridional N,N,N-ligands on cobalt, [19][20][21] since β-triketimines present a facial donor set.…”