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

Abstract

. The presence of this auxiliary ligand has a strong impact on the selectivity towards the production of a-olefins, decreasing substantially the amount of 1-butene with a concominat increase of the 2-butene fractions. Attempts to crystallize the nickel complex 3 afforded the tetrametallic [{(L)(μ 3 -Cl)NiCl} 4 ] (4, L = 1-anilinomethyl-3,5-dimethylpyrazole) which was characterized by X-ray diffraction analysis.

Synthesis of cubane-type Ni(ii) complexes from pyridyl-alcohol ligands; their single-molecule magnet behaviour

“…13 The structures of two related complexes were only suggested on the basis of spectroscopic data, 14 whereas [Ni II Cl 2 {N-benzyl-1-(3,5-dimethyl-1H-pyrazol-1-yl)methanamine}] 4 , which belongs to this family, has been obtained in a non-measurable yield. 15 It appears that the only other Ni 4 cubane-type complex with triply-bridging halides is [Ni 4 F 4 {bis( pyrazolyl)-sulfan} 4 (µ-FAsF 4 F) 2 ](AsF 6 ) 2 • 4SO 2 , which does not however correspond to the general formulation [NiX 2 Z 2 ] 4 . 16 Mononuclear square planar (type A), 17 tetrahedral (type B) 18 and dinuclear structures [NiX 2 Z 2 ] 2 (types C and D in Scheme 4) 19 are common for Ni(II) complexes, whereas "tetramerization" of a mononuclear building block remains rarely observed.…”

Bis(pyrazolyl)thioether/amine‐chromium(III) catalysts bearing pendantO‐ andN‐donor group for oligomerization and polymerization of ethylene

“…On comparing these results with those based on MAO‐activated chromium complexes containing bis(pyrazolyl) ligands, [ 48,51 ] it is clear that the presence of a bridge soft S ‐donor atom positively affects the catalytic performance of these chromium complexes. However, the formation of more strained 5‐membered‐ring chromium complexes afford catalytic systems with lower activities.…”

“…Previous studies by our group and others have shown that pyrazolyl-based metal complexes are efficient catalysts for oligomerization of ethylene producing mostly oligomers with high selectively for α-olefins. [46][47][48][49][50][51][52][53][54][55][56] In particular, we have reported chromium complexes based on tridentate pyrazolyl ligands as highly selective and active systems for ethylene oligomerization when activated with MAO. [48,51,56] As an extension of our continuous interest in this field, we herein report the synthesis, characterization, and catalytic performance in oligomerization and polymerization of ethylene of a new set of 5-membered Cr (III) complexes supported by bis(pyrazolyl)thioether/ amine ligands containing pendant O-and N-donor groups.…”

“…[46][47][48][49][50][51][52][53][54][55][56] In particular, we have reported chromium complexes based on tridentate pyrazolyl ligands as highly selective and active systems for ethylene oligomerization when activated with MAO. [48,51,56] As an extension of our continuous interest in this field, we herein report the synthesis, characterization, and catalytic performance in oligomerization and polymerization of ethylene of a new set of 5-membered Cr (III) complexes supported by bis(pyrazolyl)thioether/ amine ligands containing pendant O-and N-donor groups. The role of central bridging atom and the pendant donor group on the activity and distribution of products (oligomer vs. polymer) were studied.…”

Chromium Complexes Supported by Phenyl Ether‐Pyrazolyl [N,O] Ligands as Catalysts for the Oligo‐ and Polymerization of Ethylene

“…[ 17–81 ] In particular, chromium catalysts stabilized by pyrazolyl‐based tridentate ligands have been successfully synthetized and their catalytic application in ethylene oligomerization explored in details. [ 51,81–91 ] Selected examples are presented in Chart 1. For instance, Tosoh Corporation reported chromium complex bearing tris(3,5‐dimethyl‐1‐pyrazolyl)methane ligand that, once activated with methylalumoxane (MAO), generate highly active oligomerization/polymerization species 526.0 x 10 3 (mol ethylene) (mol Cr) −1 ·h −1 with selectivity for 1‐hexene >99.5%.…”