Pyridinecarboxamidato−Nickel(II) Complexes

Abstract

The synthesis, characterization, and reactivity toward ethylene of pyridinecarboxamidato complexes of nickel are reported. These compounds are isoelectronic to α-iminocarboxamidato complexes, which are useful ethylene polymerization catalysts. Addition of a benzene solution containing N-phenyl-2-pyridinecarboxamide and B(C6F5)3 to bis(methallyl)nickel results in the formation of [N-phenyl-2-pyridinecarboxamidatotris(pentafluorophenyl)borate-κ2N,N]Ni(η3-CH2CMeCH2) (3) in 93% yield. A similar procedure using N-(2,6-diisopropyl)phenyl-2-pyridinecarboxamide provides [N-(2,6-diisopropyl)phenyl-2-pyridinecarboxamidatotris(pentafluorophenyl)borate-κ2N,N]Ni(η3-CH2CMeCH2) (4) in 92% yield. The solid-state structures of 3 and 4 were determined by X-ray diffraction techniques. The intramolecular metrical parameters are consistent with substantial partial positive charge at the nickel atom. Deprotonation of N-(2,6-diisopropyl)phenyl-2-pyridinecarboxamide in THF with KH, followed by addition to Ni(η3-CH2C6H5)Cl(PMe3) and subsequent treatment with 2 equiv of B(C6F5)3, produces [N-(2,6-diisopropyl)phenyl-2-pyridinecarboxamidatotris(pentafluorophenyl)borate-κ2N,N]Ni(η3-CH2C6H5) (5). Compound 5 is obtained as a mixture of isomers. Deprotonation of N-(2,6-diisopropylphenyl)-6-triisopropylsilyl-2-pyridinecarboxamide, followed by addition to Ni(η3-CH2C6H5)Cl(PMe3), gives a product (7) which lacks a benzyl fragment. An X-ray diffraction study shows that metalation of one of the isopropyl groups and loss of the benzyl ligand takes place. The reactivity of 3, 4, 5, and 7 toward ethylene is presented. Considerably more activity is obtained with 5, probably as a result of faster initiation. The pyridine ligand leaves an open quadrant adjacent to nickel. As a result, the molecular weight of the product is not high.