Synthesis, Structures, Dynamics, and Ethylene Polymerization Activity of Nickel Complexes Containing an <i>ortho</i>-Methoxy-aryl Diphosphine Ligand

Abstract

The Ni coordination chemistry of {(2-OMe-4-Me-Ph)2P}2NMe (2, PNP) has been studied. The reaction of (dimethoxyethane)NiBr2 with 2 yields {PNP}NiBr2 (3, 75%). The reaction of Ni(cod)2 (cod = 1,5-cyclooctadiene) with 2 equiv of 2 affords {PNP}2Ni (4, 61%). The reaction of Ni(cod)2 with 1 equiv of 2 yields {PNP}Ni(cod) (5, 90%) via initial formation of 4 (50%), followed by comproportionation with Ni(cod)2. X-ray crystallographic analyses of 3 and 4 show that the methoxy groups do not coordinate to Ni but reveal the presence of weak CH---Ni interactions involving the ortho aryl hydrogens, and weak CH−π interactions involving the OMe hydrogens and the aryl rings. The reaction of 5 with [H(OEt2)2][B(3,5-(CF3)2C6H3)4] or [H(OEt2)2][B(C6F5)4] generates a cationic species formulated as {PNP}Ni(codH)+ (6) on the basis of ESI-MS data. Cation 6, generated in situ from Ni(cod)2/2/[H(OEt2)2][B(3,5-(CF3)2C6H3)4] or 5/[H(OEt2)2][B(C6F5)4], catalyzes ethylene polymerization.