Possible Side Reactions Due to Water in Emulsion Polymerization by Late Transition Metal Complexes. 1. Water Complexation and Hydrolysis of the Growing Chain

Abstract

The transition metal catalyzed ethylene polymerization in aqueous emulsion has been increasingly successful in the last couple of years. Water however adversely affects the polymerization process by (a) competing with ethylene for the binding site at the metal and (b) hydrolyzing the growing chain. Neutral salicylaldiminato and cationic diimine complexes of Ni and Pd with different substituent patterns are studied here by density functional theory to determine their propensity toward water complexation and hydrolysis of the growing chain. Experimental NMR studies have also been carried out on the protonolysis of the Ni(II)-based Grubbs catalyst. It is found that in general that (a) ethylene coordination is preferred over water coordination for both Ni and Pd catalysts and (b) hydrolysis of the metal alkyl bond is competitive to ethylene insertion.

Synthesis, characterization and catalytic behaviors of water-soluble phosphine-sulfonato nickel methyl complexes bearing PEG-amine labile ligand

“…Secondly, the similar 1 H NMR study indicates that 2a is stable in DMSO-d 6 the NMR tubes, which can be seen from its doublet signal of NiMe. Finally, when the above DMSO-d 6 /D 2 O solution of 2a was heated to high-temperature in the presence of ethylene, Ni-Me signal disappeared quickly, which means that ethylene plays a role for the loss of activity of such neutral phosphine-sulfonato nickel methyl catalysts [37]. Moreover, unlike phosphine-sulfonato palladium methyl complexes, no nickel metal could be observed after NMR determinations at high-temperature in presence of 1 atm of ethylene [36].…”

Mechanistic Studies of Catalytic Polyethylene Chain Growth in the Presence of Water

“…That is, on an order of magnitude scale ethylene and water have a similar binding capability in the system studied; ethylene binding is slightly preferred. This finding is surprising as theoretical studies6 had pointed to a strong preference for ethylene binding 14. By comparison to other σ‐donor ligands, such as diethyl ether or THF, water competes much more effectively for coordination at the cationic palladium center.…”

“…These versatile transition‐metal‐catalyzed polymerizations in aqueous systems raise the question of fundamental underlying reaction steps, namely 1) the competition of monomer and water for binding sites at the metal center (that is, reversible blocking of active sites), 2) chain growth in the presence of water, and 3) the reactivity of higher metal alkyl species MR (R>Me) formed during polymerization towards water in general. Recent theoretical studies indicate that ethylene binding is preferred over water coordination in various catalyst systems, namely neutral nickel salicylaldiminato and cationic palladium or nickel diimine complexes 6…”

Water and Carbon Dioxide: A Unique Solvent for the Catalytic Polymerization of Ethylene in Miniemulsion

“…The resulting latex was dark‐colored (Figure S4), indicating catalyst decomposition and a low amount of polymer. Such a low rate is expected, as water has been reported to deactivate late transition metal polymerization catalysts, mostly in a reversible manner by σ coordination to the Pd atom, and also by irreversible hydrolysis of the Pd−C bond . Thus, under similar conditions, the activity in an aqueous environment was three orders of magnitude lower than that in an organic solvent.…”