Nickel(II) Complexes with Three-Dimensional Geometry α-Diimine Ligands: Synthesis and Catalytic Activity toward Copolymerization of Norbornene

Abstract

A series of three-dimensional geometry 9,10-dihydro-9,10-ethanoanthracene-11,12-diimines (L1–L4) and their nickel(II) dibromide complexes (C1–C4) were synthesized and characterized. The nickel complexes C1–C4, with three-dimensional geometry, exhibited very high activities for norbornene (NB) homopolymerization with only B(C6F5)3 as cocatalyst,: for C2 even up to 5.53 × 107 g of polymer/((mol of Ni) h). To investigate the activation of polar monomer, complexes C2 and C3 were selected for copolymerization of NB and 5-norbornene-2-yl acetate (NB-OCOMe) in relatively high activities (1.6–5.8 × 105g of polymer/((mol of Ni) h)) and high molecular weights ((0.2–2.8) × 105 g/mol) as well as narrow molecular weight distributions (MWD < 2 for all polymers) depending on the variation of feed ratios. The reactivity ratios of the NB and NB-OCOMe monomers for C2/B(C6F5)3 system by the Kelen–Tüdös method were determined to be r NB‑OCOMe = 0.05 and r NB = 6.72, respectively. Moreover, the mechanism of polymerization catalyzed by the novel three-dimensional geometry nickel(II) complexes was presented and supported by an end group analysis of the polymer and density functional theory (DFT) calculations of the reaction. The substituent effect of the catalysts and the interaction between Ni2+ and NB were discussed, and the results showed that α-diimine nickel complexes with greater steric hindrance and smaller HOMO–LUMO gaps could achieve higher reactivity.

Revisiting Benzylidenequinolinylnickel Catalysts through the Electronic Effects on Catalytic Activity by DFT Studies

“…Based on the previous study, the HOMO–LUMO energy gap in catalyst molecule itself has no clear correlation with catalytic activity . In recent report by Huo et al, the HOMO–LUMO energy gap values between pre‐catalyst and norbornene monomer were calculated and showed qualitatively correlation with catalytic activity, higher reactivity achieved by smaller HOMO–LUMO gaps …”

“…[ 18 ] In recent report by Huo et al, the HOMO-LUMO energy gap values between pre-catalyst and norbornene monomer were calculated and showed qualitatively correlation with catalytic activity, higher reactivity achieved by smaller HOMO-LUMO gaps. [ 19 ] In the present study, the DFT calculations were performed to study the reactivity for a series of nickel complex pre-catalyst containing eleven different substituents (as shown in Scheme 1 ). Systematic experimental studies to evaluate the activity of these pre-catalysts for ethylene oligomerization were provided in our previous paper.…”

New nickel(II) diimine complexes bearing phenyl and sec‐phenethyl groups: synthesis, characterization and ethylene polymerization behaviour

“…The key feature of these complexes lies in the bulky α ‐diimine ligand that has steric hindrance in the axial direction of the metal coordination plane to suppress the associative chain transfer . Since the earlier studies, investigations have increasingly focused on improvement of the catalytic properties through modification of the structures of catalysts, especially on changes of the backbone substituents on the carbon atoms of imine groups and replacement of the aniline moiety as well as the resultant influence on ethylene polymerization. For instance, Rhinehart et al .…”

Vinylic copolymerization of norbornene and higher 1-alkene with three-dimensional geometry binickel catalyst

“…Toluene was dried over sodium/benzophenone and distilled under nitrogen before use. The three-dimensional geometry binickel catalyst was synthesized according to the method reported in our previous work [36]. Tris(pentafluorophenyl)borane (B(C 6 F 5 ) 3 , 97 %) was purchased from J&K (Tianjing, China).…”

“…Meanwhile, in comparison to late transition monometallic catalysts, many of multinuclear polymerization catalysts have been reported to incorporate higher levels of polar comonomers in copolymerizations with norbornene [31][32][33][34][35]. Therefore, Our group have addressed binickel catalysts on the reactivity of NB polymerization and successfully explored a thermostable α-diimine binickel catalyst with three-dimensional geometry backbone [36,37]. The bulky backbone can enhance the stability of α-diimine nickel complexes by hindering the rotation of aniline moieties and protecting the metal center effectively, which lead to the good catalytic properties.…”