181707-48-2Relevant articles and documents
Cationic polymerization and insertion chemistry in the reactions of vinyl ethers with (α-Diimine)PdMe+ species
Chen, Changle,Luo, Shuji,Jordan, Richard F.
, p. 5273 - 5284 (2010/06/15)
The reactions of (α-diimine)PdMe+ species (1, α-diimine = (2,6-iPr2-C6H3)N - CMeCMei - N(2,6-iPr2-C6H3)) with vinyl ethers CH2 - CHOR (2a-g: R = tBu (a), Et (b), SiMe3 (c), SiMe2Ph (d), SiMePh2 (e), SiPh 3 (f), Ph (g); 2a-g: R = tBu (a), Et (b), SiMe3 (c), SiMe2Ph (d), SiMePh2 (e), SiPh3 (f), Ph (g)) were investigated. Two pathways were observed. First, 1 initiates the cationic polymerization of 2a-c with concomitant decomposition of 1 to Pd 0. This reaction proceeds by formation of (α-diimine) PdRAε(CH2i - CHOR)+ Iε complexes (RAε = Me or CH2CHMeOR from insertion), in which the vinyl ether Ci - C bond is polarized with carbocation character at the substituted carbon (Cint). Electrophilic attack of C int on monomer initiates polymerization. Second, 1 reacts with stoichiometric quantities of 2a-g by formation of (α-diimine)PdMe(CH 2i - CHOR)+ (3a-g), insertion to form (α-diimine)Pd(CH2CHMeOR)+ (4a-g), reversible isomerization to (α-diimine)Pd(CMe2OR)+ (5a-g), β-OR elimination of 4a-g to generate (α-diimine)Pd(OR)(CH 2i - CHMe)+ (not observed), and allylic C-H activation to yield (α-diimine)Pd(I3-C3H 5)+ (6) and ROH. Binding strengths vary in the order 2a > 2b ～ 2c > 2d ～ 2g > 2e > 2f. Strongly electron-donating OR groups increase the binding strength, while steric crowding has the opposite effect. The insertion rates vary in the order 3a tBu 3 6- salts than B(C6F5) 4- salts. The implications of these results for olefin/vinyl ether copolymerization are discussed.
