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(H2O)]BF4 (P∼N = o-C6H4(PPh2)(NCHAr))
promote the reaction via proton-transfer initiation. Insertion of vinyl ether into the Pd−Me
bond in [(P∼N)PdMe(H2O)]BF4 does not proceed, but the single insertion of the same
substrate into the Pd−acetal bond of [(P∼N)PdCOCH3(L)]BF4 provides the stable inserted
product [(P∼N)PdCH(OEt)CH2COCH3]BF4, 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.