Nickel phenyl complexes with chelating κ2-P,O ligands as catalysts for the oligomerization of ethylene into linear α-olefins (1998)

Starting from [Ni(COD)2] and the phosphorus ylide Ph3P(o-C6H4O), the complexes [N wiPh{Ph2P(o-C6H4Oz)}- (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-C6H4Oz)}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([Oz)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-C6H4NzH)}(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([Oz)Ph}(PR3)] [PR3=PMe3 (1a), PCy3 (1b), PPh3 (1c)], the corresponding nickel phosphino phenolates [N wiPh{Ph2P(o-C6H4Oz)}(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-C6H4NzH)}(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-C6H4Oz)}(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-C6H4Oz)}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([Oz)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-C6H4NzH)}(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([Oz)Ph}(PR3)] [PR3=PMe3 (1a), PCy3 (1b), PPh3 (1c)], les complexes phosphino phe′nolates correspondants [N wiPh{Ph2P(o-C6H4Oz)}(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-C6H4NzH)}(PTol3)] (6), par contre, n'a montre′ aucune activite′ catalytique en oligome′risation de l'e′thylène.