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O ‐Acylated 2‐Phosphanylphenol Derivatives – Useful Ligands in the Nickel‐Catalyzed Polymerization of Ethylene
Author(s) -
Yakhvarov Dmitry G.,
Basvani Kaleswara R.,
Kindermann Markus K.,
Dobrynin Alexey B.,
Litvinov Igor A.,
Sinyashin Oleg G.,
Jones Peter G.,
Heinicke Joachim
Publication year - 2009
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200801121
Subject(s) - chemistry , ethylene , catalysis , nickel , polymerization , acylation , polymer chemistry , phenol , nuclear magnetic resonance spectroscopy , medicinal chemistry , stereochemistry , organic chemistry , polymer
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, t Bu, 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 P‐coordinated Ni 0 complexes, which are formed at room temperature, such as 4d obtained from 3d and Ni(cod) 2 (in a 2:1 molar ratio), and characterized by multinuclear NMR spectroscopy. Upon heating in the presence of ethylene, the precatalysts are activated. Catalysts 2 Ni and 3a – d Ni convert ethylene nearly quantitatively, 2 Ni slowly, and 3a – d Ni rapidly, into linear polyethylene with vinyl and methyl end groups, and in the latter case, C(O)R end groups are also detectable. This proves insertion of Ni 0 into the O–C(O)R bond of 3a – d ligands for formation of the primary catalyst. Termination of the first chain growing cycle by β‐hydride elimination changes the mechanism to the phosphanylphenolate–NiH initiated polymerization providing the main body of the polymer. A small retardation in the ethylene consumption rate with 3a – d Ni catalysts relative to that observed for 1 Ni and stabilization of the catalyst, which gives rise to reproducibly high ethylene conversion, is observed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)