(Pyrazol-1-ylmethyl)pyridine Nickel Complexes: Ethylene Oligomerization and Unusual Friedel−Crafts Alkylation Catalysts

Abstract

The reactions of 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L1) and 2,6-bis(3,5-di-tert-butylpyrazol-1-ylmethyl)pyridine (L2) with NiCl 2 or NiBr 2 gave the nickel(II) complexes [NiCl 2 (L1)] (1), [NiBr 2 (L1)] (2), [NiCl 2 (L2)] (3), and [NiBr 2 (L2)] (4) in high yields. Compounds 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L3) and 2-(3,5-di-tert-butylpyrazol-1-ylmethyl)pyridine (L4) on the other hand gave either mononuclear or dinuclear nickel(II) complexes, depending on the steric bulk of the substituents on the pyrazolyl unit. While L3 gave the dinuclear complexes [Ni 2 (µ 2 -Cl) 2 Cl 2 (L3) 2 ] (5) and [Ni 2 (µ 2 -Br) 2 Br 2 (L3) 2 ] (6), L4 gave the mononuclear complexes [NiCl 2 (L4)] ( 7) and [NiBr 2 (L4)] ( 8). Activation of 1-8 with EtAlCl 2 resulted in the oligomerization of ethylene to C 4 , C 6 , and C 8 alkenes, followed by subsequent Friedel-Crafts alkylation of the toluene solvent. Activities as high as 15 660 kg of alkylated products/mol Ni/h were observed for 5 at 40 bar. However, when hexane was used as solvent, only trace amounts of alkylated toluene products were observed.

Symmetrically and unsymmetrically substituted bis(pyrazole)-palladium(II) and nickel(II) halides as Pre-catalysts for ethylene dimerization and Friedel-Crafts alkylation of toluene and benzene

“…Nickel catalysts are generally known for dimerizing ethylene, and since low amounts of butenes in these reactions resulted in more ethyltoluenes, it is not surprising the nickel catalyst produced mainly butyltoluenes. But compared to other pyrazolyl nickel catalysts reported in the literature 11,12 that convert all ethylene oligomers from ethylene to alkyltoluenes, the current nickel catalysts are not able to convert all the butenes produced to butyltoluenes in spite of the large amount of EtAlCl 2 used in these reactions. This suggests that the Friedel-Crafts alkylation is not catalyzed by the excess EtAlCl 2 alone, otherwise all the ethylene reactions with the nickel complexes 6-10 would have produced exclusively butyltoluenes from butenes present in the product mix.…”

“…But in these dimerization and trimerization reactions, the role of alkylaluminium co-catalysts has only recently been brought into focus following reports by Dyer et al, 9 Gao et al, 10 Ojwach et al 11 and Budhai et al 12 These reports on ethylene oligomerization and post-oligomerization Friedel-Crafts alkylation of toluene show the importance of EtAlCl 2 as a co-catalyst and the solvent in which the ethylene oligomerization reactions are run. Dyer et al, 9 Gao et al, 10 Ojwach et al 11 and others 12 have all reported the formation of alkyltoluenes as secondary products. However, only selected nickel catalysts from the Dyer 9 and Gao 10 systems gave Friedel-Crafts alkylation secondary products.…”

“…However, only selected nickel catalysts from the Dyer 9 and Gao 10 systems gave Friedel-Crafts alkylation secondary products. But what is unique about the nickel catalysts reported by Ojwach et al 11 and Budhai 12b is that they all catalyze ethylene oligomerization followed by the formation of large amounts of alkyltoluenes via the Friedel-Crafts alkylation of toluene with the ethylene oligomers formed in the reaction. This points to the possible role the pyrazolyl ligands in the nickel catalysts play in promoting the alkylation reactions; although the exact nature of how this promotes the Friedel-Crafts alkylation remains a subject of much speculation.…”

Complejos pincer y su comportamiento como iniciadores en polimerización de etileno

“…En 2009 Darkwa et al, informaron que complejos derivados de ligandos 2,6-bis(pirazolilmetil)piridina y activados con EtAlCl2, son activos en reacciones de oligomerización de etileno (Ojwach et al, 2009). …”

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.…”