Mechanistic Aspects of Isotactic CO/Styrene Copolymerization Catalyzed by Oxazoline Palladium(II) Complexes

详细信息    查看全文

• 作者：Barbara Binotti ; Carla Carfagna ; Giuseppe Gatti ; Domenico Martini ; Luca Mosca ; and Claudio Pettinari
• 刊名：Organometallics
• 出版年：2003
• 出版时间：March 3, 2003
• 年：2003
• 卷：22
• 期：5
• 页码：1115 - 1123
• 全文大小：135K
• 年卷期：v.22,no.5(March 3, 2003)
• ISSN：1520-6041

文摘

Catalytic systems of the type [Pd(CH₃)(NCCH₃)(N-N)]⁺[B{3,5-(CF₃)₂C₆H₃}₄]^-, whereN-N = (4S,4'S)-(-)-4,4',5,5'-tetrahydro-4,4'-bis(1-methylethyl)-2,2'-bioxazole (BIOX) orN-N = (4S,4'S)-(-)-2,2'-(1-methylethylidene)bis[4,5-dihydro-4-(phenylmethyl)oxazole]) (BISOX),afford highly isotactic CO/styrene or p-methylstyrene copolymers. The reactivity of thecatalyst with the BIOX ligand toward carbon monoxide was studied and the correspondingmethyl carbonyl Pd complex was isolated and identified as the real catalytic species. Startingfrom this compound the first steps of the copolymerization process were investigated andparticular attention was paid to the stereochemistry of the intermediates. Specifically, NOEexperiments carried out on the five-membered palladacycle, obtained from the first insertionof p-methylstyrene, indicated that regiochemistry is of the 2,1 type and that one diastereoisomeric species is exclusively generated, with an R configuration of the new -CHAr-stereogenic center. Moreover, the investigation of the intermediate resulting after the secondsequence of p-methylstyrene and CO insertion showed the presence of only one diastereoisomer. This evidence indicates that the stereocontrol of the isospecific catalyst is alreadyvery efficient at the first stages of copolymerization.