Luo Shuji, Jordan Richard F
Department of Chemistry, The University of Chicago, Illinois 60637, USA.
J Am Chem Soc. 2006 Sep 20;128(37):12072-3. doi: 10.1021/ja064398w.
This paper reports that (alpha-diimine)PdMe+ catalyzes the copolymerization of olefins and silyl vinyl ethers. The reactions of (alpha-diimine)PdMe+ (alpha-diimine = (2,6-iPr2-C6H3)N=CMe-CMe=N(2,6-iPr2-C6H3)) with excess vinyl ethers CH2=CHOR (1a-d: R = tBu (a), SiMe3 (b), SiPh3 (c), Ph (d)) in CH2Cl2 at 20 degrees C afford polymers for 1a (rapidly) and 1b (slowly) but not for 1c or 1d. The structures of poly(1a,b) indicate a cationic polymerization mechanism. The reaction of (alpha-diimine)PdMe+ with 1-2 equiv of 1a-d proceeds by sequential C=C pi-complexation to form (alpha-diimine)PdMe(CH2=CHOR)+ (2a-d), 1,2 insertion to form (alpha-diimine)Pd(CH2CHMeOR)+ (3a-d), reversible isomerization to (alpha-diimine)Pd(CMe2OR)+ (4a-d), beta-OR elimination to generate (alpha-diimine)Pd(OR)(CH2=CHMe)+ (not observed), and allylic C-H activation to yield (alpha-diimine)Pd(eta3-C3H5)+ (5) and ROH. The reaction of (alpha-diimine)PdMe+ with 1-hexene/1b and 1-hexene/1c mixtures in CH2Cl2 at 20 degrees C affords copolymers containing up to 20 mol % silyl vinyl ether. The copolymers were purified to be free of any -[CH2CHOSiR3]n- homopolymer. The copolymer structures are similar to that of homopoly(1-hexene) generated under the same conditions. The major comonomer units are CH3CH(OSiR3)CH2-, CH2(OSiR3)CH2- and -CH2CH(OSiR3)CH2-. The 1-hexene/CH2=CHOSiR3 copolymers can be desilylated to give 1-hexene/CH2=CHOH copolymers. The results of control experiments argue against cationic and radical mechanisms for the copolymerization, and an insertion/chain-walking mechanism is proposed.
本文报道(α-二亚胺)PdMe⁺催化烯烃与甲硅烷基乙烯基醚的共聚反应。(α-二亚胺)PdMe⁺(α-二亚胺=(2,6-二异丙基-C₆H₃)N=CMe-CMe=N(2,6-二异丙基-C₆H₃))与过量的乙烯基醚CH₂=CHOR(1a - d：R = tBu(a)、SiMe₃(b)、SiPh₃(c)、Ph(d))在二氯甲烷中于20℃反应，对于1a能快速生成聚合物，对于1b能缓慢生成聚合物，但对于1c或1d则不能。聚(1a,b)的结构表明其为阳离子聚合机理。(α-二亚胺)PdMe⁺与1 - 2当量的1a - d反应，通过连续的C=C π-络合形成(α-二亚胺)PdMe(CH₂=CHOR)⁺(2a - d)，1,2插入形成(α-二亚胺)Pd(CH₂CHMeOR)⁺(3a - d)，可逆异构化为(α-二亚胺)Pd(CMe₂OR)⁺(4a - d)，β-OR消除生成(α-二亚胺)Pd(OR)(CH₂=CHMe)⁺(未观察到)，以及烯丙基C-H活化生成(α-二亚胺)Pd(η³-C₃H₅)⁺(5)和ROH。(α-二亚胺)PdMe⁺与1-己烯/1b以及1-己烯/1c的混合物在二氯甲烷中于20℃反应，得到含有高达20 mol%甲硅烷基乙烯基醚的共聚物。将共聚物纯化以不含任何-[CH₂CHOSiR₃]ₙ-均聚物。共聚物结构与在相同条件下生成的聚(1-己烯)相似。主要的共聚单体单元为CH₃CH(OSiR₃)CH₂-、CH₂(OSiR₃)CH₂-和-CH₂CH(OSiR₃)CH₂-。1-己烯/CH₂=CHOSiR₃共聚物可以脱硅烷基化得到1-己烯/CH₂=CHOH共聚物。对照实验结果排除了共聚反应的阳离子和自由基机理，并提出了一种插入/链行走机理。
