Copolymerization of Ethylene and Alkyl Vinyl Ethers by a (Phosphine- sulfonate)PdMe Catalyst

The neutral complex (PO−OMe)PdMe(py) (1, PO−OMe = 2-[bis(2-OMe−Ph)phosphino]-4-methylbenzenesulfonate) polymerizes ethylene to a linear polymer with 1−10 branches/103 carbons (mostly methyl) and vinyl and 2-olefin unsaturated end groups. Complex 1 copolymerizes ethylene and alkyl vinyl ethers (CH2CHOR, 2a−c: R = t Bu (a), Et (b), Bu (c)) in toluene at 60−100 °C to linear copolymers containing up to 7 mol % of vinyl ether. Addition of CH2CHOR lowers the polymerization rate and the polymer molecular weight. The copolymer structures are similar to that of homopolyethylene generated under the same conditions. The major comonomer units are −CH2CH(OR)CH2− (I) and CH3CH(OR)CH2− (II). The ethylene/CH2CHOR copolymers can be converted to hydroxy- and bromo-polyethylene. The results of control experiments argue against cationic and radical mechanisms for the copolymerization, and an insertion mechanism is proposed. The reaction of base-free (PO−OMe)PdMe with CH2CHOEt yields the adduct (PO−OMe)PdMe(CH2CHOEt), which undergoes 1,2-insertion to generate (PO−OMe)PdCH2CH(OEt)Me.