O‐Acylated 2‐Phosphanylphenol Derivatives – Useful Ligands in the Nickel‐Catalyzed Polymerization of Ethylene

Abstract

The title ligands were prepared by O-acylation of 2-diphenylphosphanyl-4-methylphenol (1) or directly by double lithiation of 2-bromo-4-methylphenol and stepwise coupling with ClPPh 2 and ClP(O)Ph 2 or RC(O)Cl (R = Me, tBu, Ph, 4-MeOC 6 H 4 ) to afford diphenylphosphinate 2 and carboxylic esters 3a-d. X-ray crystal structure analyses of 3b-d show conformations in which the P-phenyl substituents are rotated away from the ester group and the C(O)O π planes are nearly perpendicular to the phenol ring π plane. O-Acylated phosphanylphenols 2 and 3a-d form highly active catalysts with Ni(1,5-cod) 2 (as does 1) for polymerization of ethylene, whereas phosphanylphenyl ethers do not give catalysts under the same conditions. The reason is the cleavage of the O-acyl bond upon heating with nickel(0) precursor compounds in the presence of ethylene. The precursors are Pcoordinated Ni 0 complexes, which are formed at room temperature, such as 4d obtained from 3d and Ni(cod) 2 (in a 2:1

2-Phosphinophenolate Nickel Catalysts: Formation of Ethylene Copolymers with Isolated sec-Alkyl, Aryl, and Functionally Substituted Alkyl Groups

“…Since no colloidal nickel was observed, formation of an inactive complex is assumed. It was earlier observed that ethanol is unsuitable as solvent in the PPHH/Ni -catalyzed ethylene polymerization and that it promotes the formation of catalytically inactive nickel bis(phosphinophenolates) . It is assumed that a slow but in principle similar complex formation is induced by the OH group of the comonomer which competes with the polymerization.…”

“…During our studies on tuning of 2-phosphinophenolate nickel catalysts for oligo- or polymerization of ethylene, we observed improved catalyst stability and ethylene conversion if olefins were added . A closer study showed slight to substantial incorporation of linear α-olefins if these were added as comonomers.…”

“…The first P ∩ O − -nickel chelate catalysts for oligo- and polymerization of ethylene were discovered three decades ago by Keim and co-workers and received considerable industrial importance as part of the Shell higher olefin process . This inspired extensive studies on various types of nickel catalysts with O-functional phosphine ligands , such as phosphinoalkanoates and 2-phosphinoenolates, , -phenolates, , -benzoates, and -benzenesulfonates, but also various other chelate ligands . These catalysts are more or less moisture tolerant, and the sulfonated species are even applicable in suspension polymerization .…”