Methyl(2-phosphanylphenolato[P,O])nickel(II) Complexes – Synthesis, Structure, and Activity as Ethene Oligomerization Catalysts

The impact of P substituents on the oligomerization of ethylene withBnickel 2-diphenyl and 2-dicyclohexylphosphinophenolate phosphineBcatalysts

“…The different properties of the catalyst systems based on 3a and 3b, respectively, indicate a distinct influence of the 2-diphenylphosphino and the 2-dicyclohexylphosphino group on the P-Ni bond in the P ∩ ONi chelate and the interplay with the nucleophiles, controlled by σ -bonding, π -bonding, and steric factors. Such differences were also observed for defined variously P-substituted methylnickel 2-phosphinophenolate trimethylphosphine single component oligomerization catalysts [12], and a comparison may help to understand the behavior of the in situ catalysts.…”

“…Diisopropylphosphino derivatives were found to be more fluxional (sharp 31 P NMR doublets only at −70 • C, diphenylphosphino derivatives −40 to −30 • C), to be catalytically more active (higher TON), and to give higher molecular weight oligomers than diphenylphosphino derivatives [12]. It is supposed that the more rapid replacement of PMe 3 in the complex by solvent (in absence of ethylene) and the longer oligomer chain lengths on use in ethylene oligomerization (smaller relative rate of olefin elimination versus chain growth) are due to weaker bonding or interactions of σ -donors (PMe 3 , β-hydrogen atom of Ni-alkyl in transition state) opposite to the basic iPr 2 P ligand, and that the higher catalytic productivity is due to stronger fixation of the π -acidic ethylene (higher equilibrium concentrations of intermediate ethylene complexes) and subsequent insertion of ethylene into the Ni-C bond.…”

“…In investigations of phosphinophenolate methylnickel trimethylphosphine complexes bearing varying R 2 P groups we observed a strong influence of the P substituents in addition to the PMe 3 content on the catalytic activity toward ethylene and the molecular weights of the oligomers [12].…”

“…It was shown that catalytically active and selective 2-phosphinoenolate and 2-phosphinophenolate nickel complexes are chelates with square-planar geometry [7][8][9][10][11][12]. In the single-component catalysts the activation temperature depends strongly on the nature of the ligand trans to oxygen [1,13,14] while the molecular weights are particularly influenced by substituents at phosphorus [12][13][14][15][16] and by solvents or ligands interacting or bound in trans position to phosphorus, e.g., donor solvents or pyridine [13,[16][17][18][19][20], phosphines [19,21], or ylides [22,23]. A study of the influence of various phosphines R 3 P in diphenylphosphinoenolate and -phenolate phenylnickel phosphine single-component oligomerization catalysts 1 and 2, accessible from α-keto-or o-chinone-triphenylphosphorus ylides, Ni(COD) 2 , and the Scheme 1. respective phosphine (Scheme 1) [7,8], demonstrated widely varying activities and mass distributions of the resulting ethylene oligomers, somewhat higher molecular weights, and different response toward PMe 3 and PcHex 3 ligands on the use of the phosphinophenolate as compared to the phosphinoenolate catalysts (1 C 4 -C 30 ; 2 C 4 -C 90 ) [21].…”

Tuning of nickel 2-phosphinophenolates – catalysts for oligomerization and polymerization of ethylene

“…Nickel(II) and palladium(II) salts are known to form bis(P \ O À -chelate) complexes 2 (Scheme 1) [14][15][16][17][18][19][20][21][22][23][24]. While intermediate nickel complexes could not be detected and isolated, trans-Pd(2-phosphinophenol) 2 X 2 3 and trans-Pd(phosphinophenolate-P,O)(phosphinophenol) halides 4 or l-O-bridging Pd(phosphinophenolate-P,O) di-or tetramers are reported as isolable intermediates and are characterized by crystal structure analyses [21,24,25].…”