Mechanism of Insertion Polymerization of Allyl Ethers

The copolymerization of ethylene (E) with allyl ethyl ether (AEE) by [di­(2-dianisyl)­phosphine-2-yl]­benzene­sulfonato Pd­(II) as a catalyst is investigated by DFT calculations and compared with the copolymerization of E with diallyl ether (DAE). For AEE, both 1,2- and 2,1-monomer insertions lead to a very stable O-Chelate product (a five-membered and a four-membered ring, respectively) that hinders any further ethylene insertion. As for DAE, a first 2,1-insertion (favored by 1.8 kcal mol–1 vs the 1,2-insertion) leads to the four-membered O-Chelate product that easily evolves to the most stable intermediate with the second DAE CC bond coordinated to the metal promoting the following 1,2-insertion. The 2,1 + 1,2 DAE insertion product, bearing a five-membered cyclic unit, is stabilized by a β-agostic interaction that easily opens in favor of E coordination and insertion. Based on the proposed copolymerization mechanism, the stereochemistry of the E/DAE copolymer is studied and the experimental microstructure explained. Finally, [di­(2-anisyl)­phosphine-2-yl]­benzenesulfon­(methyl)­amido Pd­(II) species showing a greater regioselectivity toward a first DAE 2,1-insertion (ΔΔG of −3.6 kcal mol–1) are suggested to be a promising catalyst.