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

Abstract

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 (CH2CHOR, 2a−c: R = tBu (a), Et (b), Bu (c)) in toluene at 60−100 °C to linear copolymers containing up to 7 mol % of vinyl ether. Addition of CH2CHOR 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/CH2CHOR 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 CH2CHOEt yields the adduct (PO−OMe)PdMe(CH2CHOEt), which undergoes 1,2-insertion to generate (PO−OMe)PdCH2CH(OEt)Me.