Crowded diphosphinomethane ligands in catalysis: [(R2PCH2PR′2-κ2P)-NiR″]+ cations for ethylene polymerization without activators

摘要: The preparation of a series nickel dichloride complexes with bulky diphosphinomethane chelate ligands R2PCH2PR′2 is reported. Reaction the appropriate Grignard reagent leads to corresponding dimethyl and dibenzyl complexes. Cationic monomethyl mono-η3-benzyl are generated from these dialkyl by protonation [H(OEt2)2]+[B(3,5-(CF3)2C6H3)4]−, while complex [(dtbpm κ2P)Ni(η3-CH(CH2Ph)Ph]+[B(3,5-(CF3)2C6H3)4]−is obtained Ni(0) olefin (dtbpm-κ2P)N(η2-trans-stilbene). Crystal structures examples dichlorides, dimethyl, dibenzyl, cationic methyl, η3-benzyl Solutions cations polymerize ethylene under mild conditions without necessity an activating agent, form polyethylene having high molecular weights low degrees chain branching. In comparison Ni methyl cations, cation more stable somewhat less active but still very efficient in C2H4 polymerization. effect on resulting varying substituents R, R′ phosphine ligand has been examined, clear trend for longer PE branching presence diphosphine found. Density functional calculations have used examine rapid suprafacial η3 haptotropic shift processes the[(R2PCH2PR′2)Ni] fragment η3−η1 change coordination mode benzyl group required polymerization those cations.