Nickel Complexes Based on Tridentate Pyrazolyl Ligands for Highly Efficient Dimerization of Ethylene to 1-Butene

Abstract

A series of new pentacoordinated nickel complexes NiCl 2 (NZN) based on nitrogen-, oxygen-, or sulfurbridged bis(pyrazolyl) ligands (NZN) were synthesized and characterized by elemental analysis and an X-ray diffraction study for NiCl 2 {bis[2-(3,5-dimethylpyrazolyl)ethyl)]amine} (1). Upon activation with methylaluminoxane (MAO), these complexes show high activity in ethylene oligomerization (TOF ) 7-80 × 10 3 h -1 ), which varies according to the ligand environment. Up to 92% selectivity for 1-butene, combined with a TOF of 60 × 10 3 h -1 , has been obtained under moderate conditions (30 °C, 40 bar, MAO-to-Ni ) 250) using NiCl 2 {bis[2-(5-phenylpyrazolyl)ethyl)]ether} (3) as the catalyst precursor.

Substituted tridentate pyrazolyl ligands for chromium and nickel-catalyzed ethylene oligomerization reactions: effect of auxiliary ligand on activity and selectivity

“…Upon activation with methylaluminoxane (MAO), these pre-catalysts showed high turnover frequencies for ethylene oligomerization under optimized conditions 3 mol C 2 H 4 (mol Cr In parallel, the use of nickel complexes such as NiCl 2 {bis [2-(3,5-dimethyl-1-pyrazolyl)methyl] benzylamine} (3) and NiCl 2 {bis [2-(3,5-dimethyl-1-pyrazolyl)ethyl)]ether} (5) in oligomerization reactions carried out in the presence of triphenylphosphine (PPh 3 ) afforded highly active catalytic systems with turnover frequencies (TOFs) varying from 36. 4 …”

“…These results are consistent with those observed in 6-membered ring nickel and chromium catalysts bearing an analogous tridentate sulfur-bridged ligand. 4,6 The chromium complexes 1a and 2a produce oligomers ranging from C 4 to C 14+ with a high selectivity for a-olefins attaining 67.71 and 73.47%, respectively. Both catalyst systems show similar behaviour for production of a-olefins as shown in Figure 1.…”

“…This result is consistent with those ones found for MAO-activated nickel and chromium complexes bearing analogous tridentate ligands. 4,6 It is interesting to note that the presence of phenyl groups at 3-position of the pyrazolyl rings in CrCl 3 {bis[2-(3-diphenyl-1-pyrazolyl)ethyl)]amine} (1a) determines a dramatic effect on activity and selectivity as compared to the similar complex CrCl 3 {bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl)]amine} (1b) 6 (compare entries 1 and 3, Table 1). For instance, catalyst 1a (22,900 mol(ethylene) mol(Cr)…”

“…The molecular geometry and atom-labeling scheme are shown in Figure 2. Complex 4 has a cubane-type {Ni 4 (m 3 -Cl) 4 The Cl-Ni-Cl angles involving the bridging chlorine ligands are systematically lower than 90°, ranging from 82.73(2) to 86.4(2)°. On the other hand, Ni-Cl-Ni angles are significantly higher, tipically in the range of 93.17-97.40°.…”

Palladium Complex Bearing 3,5-Bis(benzotriazol-1-Ylmethyl)toluene Ligand Catalyzes Oxidative Amination of Allyl Butyl Ether

“…[4][5][6][7][8] Another family of active late transition metal polymerization catalysts based on pyrazol and poly(pyrazolyl) ligands has been described. [9][10][11][12][13][14][15][16] These types of ligands are attractive since their steric and electronic properties can be changed by the appropriate selection of the substituents in the pyrazol ring.…”