Unsymmetrical (pyrazolylmethyl)pyridine metal complexes as catalysts for ethylene oligomerization reactions: Role of solvent and co-catalyst in product distribution

(Pyrazolyl)-(phosphinoyl)pyridine iron(II), cobalt(II) and nickel(II) complexes: Synthesis, characterization and ethylene oligomerization studies

“…Consistent with our recent studies [16], attempts to activate the pre-catalysts using EtAlCl 2 in toluene solvent produced predominantly alkylated-toluenes of the pre-formed oligomers ( Table 5, entry 5). Nonetheless, the EtAlCl 2 activated system in toluene generated the most active catalyst displaying activities of 790 kg mol À1 h À1 .…”

“…As expected, increasing ethylene pressure from 10 bar to 30 bar (Table 5, entries 2, 7 and 8) resulted in an increase in activity from 360 kg mol À1 h À1 to 430 kg mol À1 h À1 respectively [16]. In addition, the selectivity for a-C 4 also increased from 65% to 77%.…”

“…The greater catalytic performance of the dibromide catalysts compared to their dichloride analogues is consistent with results obtained using 2-quinoxalinyl-6-iminopyridine [36], 2-(benzimidazol-2-yl)-1,10-phenanthroline [39] and pyrazolyliminophosphorane [52] nickel(II) complexes. Incorporation of the P]O donor group on the (pyrazolylmethyl) pyridine ligand framework changed the catalytic activities of these complexes in comparison to the 2-(chloromethyl)-6-((pyrazol-1-yl) methyl)pyridine and (pyrazolylmethyl)pyridine systems we recently reported [15,16]. The current (pyrazolyl)-(phosphinoyl) pyridine complexes exhibited lower catalytic activities compared to the previous catalysts.…”

“…Tetrabutylammonium bromide, trimethylaluminium (TMA, 2 M in toluene), ethylaluminium dichloride (EtAlCl 2 , 1.0 M in hexane), methylaluminoxane (10 wt% in toluene), 3,5-dimethylpyrazole, dibenzoylmethane, hydrazine hydrate, diphenylphosphine, nbutyllithium, thionyl chloride, 2,6-bis(hydroxymethyl)pyridine, and the metal salts were obtained from SigmaeAldrich and used as received. Compounds 2-(chloromethyl)-6-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)pyridine (L1) and 2-(chloromethyl)-6-((3,5-diphenyl-1H-pyrazol-1-yl)methyl)pyridine (L2) [16] and the starting materials 2,6-bis(chloromethyl)pyridine [25] and 3,5-diphenylpyrazole [26] were synthesized following the literature procedures. 1 H NMR and 13 C { 1 H} NMR spectra were recorded on a Bruker Ultrashield 400 ( 1 H NMR 400 MHz, 13 C { 1 H} NMR 100 MHz) spectrometer in CDCl 3 solution at room temperature and chemical shifts (d) were determined relative to internal TMS and are given in ppm.…”

“…This finding was only preceded by another report by Dyer and co-workers, even though the extent of FriedeleCrafts alkylation was minimal in their system [18]. Following this discovery, we have extensively studied FriedeleCrafts alkylation reactions [8,9,16] to establish the role of the catalyst structure, solvent and nature of co-catalysts in controlling product distribution. From our accounts, in addition to literature reports, it is apparent that the pyrazolyl ligand plays a major role in promoting FriedeleCrafts alkylation of the pre-formed oligomers.…”