Pyridinecarboxamidato-nickel(II) complexes

The synthesis, characterization, and reactivity toward ethylene of pyridine carboxamidato complexes of nickel are reported. These compounds are isoelec tronic to a-iminocarboxamidato complexes, which are useful ethylene polymer ization catalysts. Addition of a benzene solution containing N-phenyl-2-pyr idinecarboxamide and B(C6F5)(3) to bis(methallyl)nickel results in the form ation of [N-phenyl-2-pyridinecarboxamidatotris(pentafluorophenyl)borate-kap pa N-2,N]-Ni(eta (3)-CH2CMeCH2) (3) in 93% yield. A similar procedure using N-(2,6-diisopropyl)phenyl-2-pyridinecarboxamide provides [N-(2,6-diisoprop yl)phenyl-2-pyridinecarboxamidatotris(pentafluorophenyl)borate-kappa N-2,N] -Ni(eta (3)-CH2CMeCH2) (4) in 92% yield. The solid-state structures of 3 an d 4 were determined by X-ray diffraction techniques. The intramolecular met rical parameters are consistent with substantial partial positive charge at the nickel atom. Deprotonation of N-(2,6-diisopropyl)phenyl-2-pyridinecarb oxamide in THF with KH, followed by addition to Ni(eta (3)-CH2C6H5)Cl(PMe3) and subsequent treatment with 2 equiv of B(C6F5)(3), produces [N-(2,6-diis opropyl)phenyl-2-pyridinecarboxamidatotris(pentafluorophenyl)borate-kappa N -2,N]Ni(eta (3)-CH2C6H5) (5). Compound 5 is obtained as a mixture of isomer s. Deprotonation of N-(2,6-diisopropylphenyl)-6-triisopropylsilyl-2-pyridin ecarboxamide, followed by addition to Ni(eta (3)-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 liga nd takes place. The reactivity of 3, 4, 5, and 7 toward ethylene is present ed. 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.