N-0 Chelated Nickel(II) Complexes as Catalysts for Ethene Oligomerisation, Polymerisation and Ethene/Carbon Monoxide Co-Polymerisation

This thesis reports on the use of square planar nickel(II) complexes containing N-0 chelates as homogeneous catalyst precursors for carbon-carbon bond formation reactions. A series of new arylnickel phosphine complexes have been prepared. Complexes are of the type [NiR(N-0)L] [R = o-tolyl, N-0 = 2- pyridinecarboxylate pyca, L = PPh3 (la); R = o-tolyl, N-0 = p y c a, L = P(CH2Ph)3 (lb); R = o-tolyl, N-0 = pyca, L = PMePh2 (lc); R = o-tolyl, N-0 = PYca, L = PMe2Ph (1d); R = o-tolyl, N-0 = pyca, L = PCy3 (le); R = mesityl, NO = pyca, L = PMePh2 (10; R = phenyl, N-0 = pyca, L = PPh3 (lg); R = p-tolyl, N-0 = pyca, L = PPh3 (lh); R = mesityl, N-0 = 2-pyridineacetate pyac, L = PMePh2 (2a); R = o-tolyl, N-0 = 2-pyrazinecarboxylate pyzca, L = PPh3 (3a); R = o-tolyl, N-0 = pyzca, L = P(CH2Ph)3 (3b); R = o-tolyl, N-0 = 4-nitro-2- pyridinecarboxylate 4-NO 2-pyca, L = PPh3 (4a); R = o-tolyl, N-0 = 4-methoxy- 2-pyridinecarboxylate 4-Me0-pyca, L = PPh3 (5a)]. The complexes differ in the steric and electronic nature of the monodentate phosphine ligand, the size of the metallacycle (5-membered or 6-membered (2a)) and in the basicity of the N-0 -chelate. Crystal structure for the complexes [Ni(o-tolyl)pycaPPh3], [Ni(o-toly1)4- NO2 -pycaPPh3], [Ni(mesityl)pycaPMePh2] and [Ni(mesityl)p y a cPMePh2] indicate that the complexes have a square planar coordination with the phosphine ligand trans to the nitrogen atom. Upon warming, the complexes form moderately active single component catalysts for the oligomerisation of ethene. Products are 95-98% linear containing 60-80% a-olefins and show a geometric distribution of chain lengths. The effects of phosphine ligands, chelate ring size and chelate basicitS, on the catalytic performance have been studied. Catalyst activities and product distributions are highly dependant on the phosphine ligand present. Highest activities are obtained with complexes [Ni(o-tolyl)pycaPPh3 ] and [Ni(o-tolyl)pycaP(CH2Ph)31 and the highest percentage of linear a-olefins in the product is generated by [Ni(otolyl)pycaPMe2Ph]. Addition of excess PPh3 to the catalysts derived from [Ni(otolyl)pycaPPh3] provides mechanistic information on the oligomerisation process. The results are interpreted in terms of an associative insertion mechanism for the oligomerisation catalysts. The catalytic behaviour of the complexes vary greatly when the bidentate ligand is substituted in the 4-position of the pyridyl ring. It was found that complexes [Ni(o-toly1)4-NO2-pycaPPh3 ], [Ni(o-tolyl)pyzcaPPh 3 ] and [Ni(otoly1)4-Me0-pycaPPh 3 ] act as polymerisation catalysts and produce high molecular weight polyethylene. The possibility of two different insertion pathways being followed for the oligomerisation catalysts and the polymerisation catalysts may explain the different products obtained. Remarkably, the polymerisation catalysts are active for the copolymerisation of ethene with carbon monoxide and produce high molecular weight perfectly alternating polyketone. The complexes also form a moderately active catalytic system for the dimerisation of propene in the presence of alkyl aluminium co-catalysts such as A1Et2 C1 ' A1EtC1 2 and methylaluminoxane (MAO). The reaction has been examined as a function of catalyst, co-catalyst, and solvent. The activity and isomer distribution are shown to depend on the phosphine and bidentate ligands. The nature of the co-catalyst greatly affects the catalytic performance. The results are consistent with a bimetallic Ni-Al catalytic intermediate in equilibrium with excess co-catalyst.