Cobalt(II)‐based ethylene dimerization catalysts with silicon‐bridged diphosphine ligands

Abstract

A series of ligands and cobalt complexes were synthesized and characterized using NMR spectroscopy, elemental analysis and single-crystal X-ray diffrac-features a monomeric structure with κ 2 coordination of the silicon-bridged diphosphine ligand to the cobalt center.Using dried methylaluminoxane (DMAO) and AlEt 3 as co-catalysts and methylcyclohexane as solvent, the Co(II) complex proved to be moderately active and highly selective for ethylene dimerization. The effects of ligand structure, catalyst loading, reaction temperature, Al/Co molar ratio, DMAO/ AlEt 3 molar ratio and reaction time were investigated with respect to the catalytic activity and product selectivity of ethylene dimerization. Cobalt complex C1 exhibited moderate catalytic activity of 2.3 × 10 5 g (mol Co ) −1 h −1 , with 100% selectivity towards C 4 (87% 1-C 4 in the C 4 fraction).

Ethylene Oligomerization Catalyzed by Different Homogeneous or Heterogeneous Catalysts

“…Complexes 46 and 47, activated by MMAO, were capable of producing ethylene oligomers with moderate activity (up to 5.1 × 10 5 g•mol −1 Co •h −1 for complex 47) in which α-C 8 was the major product. Jiang and co-workers [139] reported a series of cobalt complexes featuring a monomeric structure with the silicon-bridged diphosphine ligand to the cobalt center (Figure 14). Transition metals supported with diphosphine ligands can exhibit good catalytic performance due to their singly and weakly coordinating moieties that can readily dissociate to create a vacant site for coordination, thereby enhancing the catalytic activity [140,141].…”

“…Transition metals supported with diphosphine ligands can exhibit good catalytic performance due to their singly and weakly coordinating moieties that can readily dissociate to create a vacant site for coordination, thereby enhancing the catalytic activity [140,141]. Jiang and co-workers [139] reported a series of cobalt complexes featuring a monomeric structure with the silicon-bridged diphosphine ligand to the cobalt center (Figure 14). Transition metals supported with diphosphine ligands can exhibit good catalytic performance due to their singly and weakly coordinating moieties that can readily dissociate to create a vacant site for coordination, thereby enhancing the catalytic activity [140,141].…”

Chromium catalysts based on PNP(NR2)2 ligands for selective ethylene oligomerization

“…We recently found that the ligands having PNP scaffolds such as PNSiP, PNSiCP, and PN (CH 2 ) n P behave as efficient catalytic systems for selective ethylene tri-/ tetramerization. [13][14][15][16][17][18] To further elucidate the potential role of the PNP scaffold toward ethylene oligomerization, we, herein, reported three new PNP-based L 1 -L 3 ligands with PNP (NR 2 ) 2 scaffold, which upon coordination with CrCl 3 (THF) 3 correspondingly afforded 1-3 chromium complexes (Scheme 1). Upon activation with MMAO-3A, the 1-3 complexes when scrutinized for ethylene oligomerization offered efficient catalysts for selective ethylene tri-/tetramerization.…”