1352843-51-6Relevant articles and documents
Crowded diphosphinomethane ligands in catalysis: [(R2PCH 2PR′2-κ2P)-NiR″]+ cations for ethylene polymerization without activators
Schultz, Madeleine,Eisentraeger, Frank,Regius, Christian,Rominger, Frank,Hanno-Igels, Patrick,Jakob, Paul,Gruber, Irene,Hofmann, Peter
, p. 207 - 224 (2012)
The preparation of a series of nickel dichloride complexes with bulky diphosphinomethane chelate ligands R2PCH2PR′ 2 is reported. Reaction with the appropriate Grignard reagent leads to the corresponding dimethyl and dibenzyl complexes. Cationic monomethyl and mono-ν3-benzyl complexes are generated from these dialkyl complexes by protonation with [H(OEt2)2] +[B(3,5-(CF3)2C6H3) 4]-, while the complex [(dtbpm-κ2P) Ni(ν3-CH(CH2Ph)Ph]+[B(3,5-(CF 3)2C6H3)4]- is obtained from protonation of the Ni(0) olefin complex (dtbpm- κ2P)Ni(ν2-trans-stilbene). Crystal structures of examples of dichlorides, dimethyl, dibenzyl, cationic methyl, and cationic ν3-benzyl complexes are reported. Solutions of the cations polymerize ethylene under mild conditions and without the necessity of an activating agent, to form polyethylene having high molecular weights and low degrees of chain branching. In comparison to the Ni methyl cations, the ν3-benzyl cation complexes are more stable and somewhat less active but still very efficient in C2H4 polymerization. The effect on the resulting polyethylene of varying the substituents R, R′ on the phosphine ligand has been examined, and a clear trend for longer chain PE with less branching in the presence of more bulky substituents on the diphosphine has been found. Density functional calculations have been used to examine the rapid suprafacial ν3 to ν3 haptotropic shift processes of the [(R2PCH2PR′2)Ni] fragment and the ν3-ν1 change of the coordination mode of the benzyl group required for polymerization in those cations.
