Deuterio-ethylene labeling studies on two homogeneous chromium ethylene oligomerization catalysts show that chain propagation proceeds via metallacyclic intermediates; reactions performed in the presence of 1-nonene show no incorporation of the higher olefin, strongly implicating the involvement of large ring metallacycles.

A series of co-oligomerization and co-polymerization reactions of C 2 H 4 /C 2 D 4 (1:1) mixtures have been carried out using various transition metal catalysts based on Cr, Co and Fe in combination with MAO. The oligomeric α-olefin products have been analysed by GC and GC/MS and the experimental results have been compared with the theoretical mass spectra derived from mathematical models. Solid polymer samples have been analysed by 13 C{ 1 H} and 13 C DEPT-135 NMR spectroscopy. C 2 H 4 /C 2 D 4 co-oligomerization can be used as a method to differentiate between a metallacyclic or a Cossee-type chain growth mechanism in oligomerization systems. In the case of a metallacyclic mechanism, no H/D scrambling is observed whereas for a Cossee-type mechanism, similar rates of chain propagation and chain termination (β-H elimination) result in rapid H/D scrambling of the C 2 H 4 /C 2 D 4 feed. This method is therefore limited to oligomerization systems and cannot be applied in polymerization systems where the rate of chain propagation is much faster than the rate of chain termination.

Treatment of the bis(benzimidazolyl)amine chromium complex 2 with ethylene in the presence of MAO affords an exceptionally active oligomerization catalyst and an unprecedented distribution of 1-olefin products in which the C4n series is much more abundant than the C4n+2 series. Deuterium labeling studies are consistent with a metallacyclic chain growth mechanism in which the unusual product distribution arises from the interplay of two sites.

A series of bis(phosphanylphenoxide) group 4 metal dichloride complexes has been synthesized via treatment of MCl4(THF)2 (M = Ti, Zr, Hf) with sodium salts of the phosphanylphenols. The complexes bearing diphenylphosphine donors adopt C 1-symmetric, all-cis ground-state structures as determined by X-ray crystallography. In solution an O,P ligand exchange process is observed. Eyring analyses indicate a nondissociative process proposed to proceed via a 120° rotation of the P,P,Cl or the O,P,Cl trigonal faces. A zirconium complex containing diisopropylphosphine donors adopts a configurationally rigid trans-P2 geometry. In ethylene polymerization studies (methylaluminoxane (MAO) activation), bis(6-tert-butyl-2-diphenylphosphanylphenoxide) zirconium and hafnium catalysts gave activities up to 49 000 and 2000 g/mmol·h·bar, respectively. Both of these catalysts also afforded efficient catalyzed chain growth using ZnEt2. The zirconium derivative afforded activities up to 13 300 g/mmol·h for propylene polymerization using “dried”-MAO (DMAO) as the cocatalyst. The polymer had a slight syndiotactic bias and is formed by a chain-end control mechanism. A dibenzyl analogue of the highly active zirconium catalyst revealed an all-cis structure by crystallography, but a mixture of isomers in solution by NMR spectroscopy. Cationic monoalkyl complexes were synthesized using either [CPh3][B(C6F5)4] or DMAO and suggest a highly fluxional structure for the catalytically active species.