Ethylene pressure has been used to control the competition between isomerization (chain walking) and monomer insertion processes for ethylene coordination polymerization catalyzed by a palladium-alpha-diimine catalyst. The topology of the polyethylene varies from linear with moderate branching to "hyperbranched" structures. Although the overall branching number and the distribution of short-chain branching change very slightly, the architecture or topology of the polyethylene changes from linear polyethylene with moderate branches at high ethylene pressures to a hyperbranched polyethylene at low pressures.

The α-diimine ligand ArNC(Me)C(Me)NAr (Ar = 2,6-C6H3-iPr2) reacts with Pd(OAc)2 in the presence of HBF4·Et2O, or [Pd(MeCN)4](BF4)2 in the absence of acid, to give ethylene polymerization catalysts. The reactions of a related β-diimine ligand with [Pd(MeCN)4](BF4)2 and (1,2-dimethoxyethane)NiBr2, and the polymerization activity of catalysts derived from it, are discussed.