Nickel phenyl complexes with chelating κ2-P,O ligands as catalysts for the oligomerization of ethylene into linear α-olefins

Abstract

Starting from [Ni(COD)₂] and the phosphorus ylide Ph₃P(o-C₆H₄O), the complexes [N wiPh{Ph₂P(o-C₆H₄O^z)}- (PR₃)] [PR₃=PMe₃ (2a), PMe₂Ph (2b), PMePh₂ (2c), PCy₃ (2d), PPh₃ (2e), PTol₃ (2f), P(p-C₆H₄OMe)₃ (2g), P(OMe)₃ (2h), P(p-C₆H₄Cl)₃ (2i), P(p-C₆H₄F)₃ (2j), P(p-C₆H₄CF₃)₃ (2k)] were synthesized in the presence of the corresponding phosphine. The bis-chelate complex cis-[N wi{Ph₂P(o-C₆H₄O^z)}₂] (3) was formed as a minor by-product during these reactions, but was the only isolable compound when the reactions were conducted at temperatures above 60°C. Oxidative addition of a P–Ph bond to the N centre was also used to synthesize [N wiPh{Ph₂PCH[C([O^z)Ph}(PMe₃)] (1a) from the α-ketophosphorus ylide Ph₃PCHC(O)Ph and PMe₃. Reaction of [Ph₃P(o-C₆H₄NH₂)]Br with [Ni(COD)₂] and PTol₃ yielded the expected compound [N wiPh{Ph₂P(o-C₆H₄N^zH)}(PTol₃)] (6) via deprotonation of the NH₂ function by an excess of PTol₃. Experiments to study the potential of these nickel complexes as catalysts for ethylene oligomerization into linear α-olefins (>95%) showed widely varying activities [500–180000 mol C₂H₄ (mol catalyst h)^-1] and mass distributions of the α-olefins. In contrast to the nickel phosphino enolate complexes of the type [N wiPh{Ph₂PCH[C([O^z)Ph}(PR₃)] [PR₃=PMe₃ (1a), PCy₃ (1b), PPh₃ (1c)], the corresponding nickel phosphino phenolates [N wiPh{Ph₂P(o-C₆H₄O^z)}(PR₃)] (2) generally showed a marked tendency to oligomerize ethylene into α-olefins of higher molecular weight: C₄₌ to C₃₀₌ for 1 versus C₄₌ to C₉₀₌ for 2. The complex [N wiPh{Ph₂P(o-C₆H₄N^zH)}(PTol₃)] (6), on the other hand, showed no activity for ethylene oligomerization. Complexes phe′nylnickel à ligands che′latants κ²-P,O pour l'oligome′risation catalytique de l'e′thylene en α-ole′fines line′aires. Les complexes [N wiPh{Ph₂P(o-C₆H₄O^z)}(PR₃)] [PR₃=PMe₃ (2a), PMe₂Ph (2b), PMePh₂ (2c), PCy₃ (2d), PPh₃ (2e), PTol₃ (2f), P(p-C₆H₄OMe)₃ (2g), P(OMe)₃ (2h), P(p-C₆H₄Cl)₃ (2i), P(p-C₆H₄F)₃ (2j), P(p-C₆H₄CF₃)₃ (2k)] ont e′te′ obtenus par re′action de [Ni(COD)₂] avec les ylures de phosphore Ph₃P(o-C₆H₄O), en pre′sence des phosphines correspondantes. Le complexe bis-che′late cis-[N wi{Ph₂P(o-C₆H₄O^z)}₂] (3) est un produit secondaire de ces re′actions, mais il devient le seul compose′ isolable lorsque les re′actions sont effectue′es à des tempe′ratures supe′rieures à 60°C. L'addition oxydante d'une liaison P–Ph au centre N a e′galement permis de pre′parer [N wiPh{Ph₂PCH[C([O^z)Ph}(PMe₃)] (1a) au de′part de l'ylure de phosphore α-ce′tonique Ph₃PCHC(O)Ph et de PMe₃. La re′action entre [Ph₃P(o-C₆H₄NH₂)]Br, [Ni(COD)₂] et PTol₃ conduit au produit attendu [N wiPh{Ph₂P(o-C₆H₄N^zH)}(PTol₃)] (6) suite à la de′protonation de la fonction NH₂ par l'excès dePTol₃. Les tests mene′s pour e′valuer le potentiel de ces complexes du nickel pour l'oligome′risation catalytique del'ethylèneen α-ole′fines line′aires (>95%) montrent des activite′s[500–180000 molC₂H₄(mol catalyseur h^-1)] et des distributions en masse des α-ole′fines variables. Au contraire des complexes phosphino e′nolates du nickel du type [N wiPh{Ph₂PCH[C([O^z)Ph}(PR₃)] [PR₃=PMe₃ (1a), PCy₃ (1b), PPh₃ (1c)], les complexes phosphino phe′nolates correspondants [N wiPh{Ph₂P(o-C₆H₄O^z)}(PR₃)] (2) montrent en ge′ne′ral une forte tendance à oligome′riser l'e′thylène en α-ole′fines de poids mole′culaires plus e′leve′s: de C₄₌ à C₃₀₌ pour 1 contre C₄₌ à C₉₀₌ pour 2. Le complexe [N wiPh{Ph₂P(o-C₆H₄N^zH)}(PTol₃)] (6), par contre, n'a montre′ aucune activite′ catalytique en oligome′risation de l'e′thylène.