SINGLE-COMPONENT N-O CHELATED ARYLNICKEL(II) COMPLEXES AS ETHENE POLYMERIZATION AND CO ETHENE COPOLYMERIZATION CATALYSTS - EXAMPLES OF LIGAND-INDUCED CHANGES TO THE REACTION PATHWAY/
Sy. Desjardins et al., SINGLE-COMPONENT N-O CHELATED ARYLNICKEL(II) COMPLEXES AS ETHENE POLYMERIZATION AND CO ETHENE COPOLYMERIZATION CATALYSTS - EXAMPLES OF LIGAND-INDUCED CHANGES TO THE REACTION PATHWAY/, Journal of organometallic chemistry, 544(2), 1997, pp. 163-174
Arylnickel(II) phosphine complexes containing substituted N-O bidentat
e ligands, of the type [NiR(N-O)L] [N-O = 4-nitropyridine-2-carboxylat
e (4-NO2-pyca), R = o-tolyl, L = PPh3; N-O = 2-pyrazinecarboxylate (py
zca), R = o-tolyl, L = PPh3; and N-O = 4-methoxypyridine-2-carboxylate
(4-MeO-pyca), R = o-tolyl, L = PPh3] have been prepared and character
ised. Single crystal X-ray studies of the complexes [Ni(o-tolyl)(pyca)
PPh3], 1, and the isomorphous analogue [Ni(o-tolyl)(4-NO2-pyca)PPh3],
3, show the expected square planar coordination about the nickel centr
es, with the pyridine nitrogens being trans to the phosphine ligand fo
r both compounds. The coordination spheres of the two complexes are ve
ry similar, no elongation of the Ni-N bond for complex 3, which contai
ns the 4-NO2-pyca ligand, being evident. In complex 3 the o-tolyl liga
nd is disordered over two sites indicating the presence, in the solid
state, of two conformers in which the o-methyl groups of o-tolyl are l
ocated to either side of the coordination plane. The complexes with su
bstituted pyca ligands form single component catalysts for the convers
ion of ethene to high molecular weight polyethene and for the copolyme
risation of ethene and carbon monoxide to polyketone under mild condit
ions. The nature of the product, whether predominantly high molecular
weight polymer or a mixture of polymer and lower oligomer, is dependen
t on the basicity of the N-O chelate ligand. From an NMR study of the
effect of added ethene on the complex [Ni(o-tolyl)(4-NO2-pyca)PPh3], a
mechanism involving alkene promoted ligand dissociation is suggested.
(C) 1997 Elsevier Science S.A.