Initiation Steps for the Polymerization of Vinyl Ethers Promoted by Cationic Palladium Aqua Complexes

Both deuterium-labeled experimental and NMR spectroscopic analyses of poly(vinyl ether) offer the mechanistic insight into the polymerization, indicating that the cationic palladium aqua imine−phosphine complexes [( P ∼ N )PdMe(H 2 O)]BF 4 ( P ∼ N = o -C 6 H 4 (PPh 2 )(N CHAr)) promote the reaction via proton-transfer initiation. Insertion of vinyl ether into the Pd−Me bond in [( P ∼ N )PdMe(H 2 O)]BF 4 does not proceed, but the single insertion of the same substrate into the Pd−acetal bond of [( P ∼ N )PdCOCH 3 (L)]BF 4 provides the stable inserted product [( P ∼ N )PdCH(OEt)CH 2 COCH 3 ]BF 4, which has been characterized by an X-ray structural determination. However, these palladium complexes do not catalyze the polymerization or copolymerization of vinyl ether and carbon monoxide.