Alternating copolymerizations using a Grubbs-type initiator with an unsymmetrical, chiral N-heterocyclic carbene ligand
Alternating copolymerizations using a Grubbs-type initiator with an unsymmetrical, chiral N-heterocyclic carbene ligand
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DOI：
10.1002/anie.200704822
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Blechert, Siegfried
中科院分区：
文献类型：
--
作者：
Vehlow, Kati;Wang, Dongren;Blechert, Siegfried
由两种不同单体复分解共聚制备交替共聚物的报道相对较少。[1-7]在2005年，Chen等人报道了用于序列选择性共聚的开环易位聚合（ROMP）催化剂的基于机理的设计。[8，9]在这里，我们报道了一种用于合成交替共聚物的替代系统，该交替共聚物基于含有不对称手性N-杂环卡宾（NHC）配体的Grubbs型引发剂。作为我们正在进行的关于具有饱和不对称NHC配体的钌复分解催化剂的研究的一部分[10，以[RuCl_2（PCy_3）_2-（CHPh）]和1-均三甲苯基-3-（（1 ′ R）-1-苯乙基）-4，5-二氢咪唑四氟硼酸盐为原料，以90%的产率制备了引发剂1。使用1/NBE/COE为1：2000：100000的化学计量，将该引发剂用于异戊二烯（NBE）和环辛烯（COE）的共聚。在CH_2Cl_2中记录的共聚反应动力学表明，NBE在不到15分钟内被消耗。事实上，在60分钟后终止共聚提供了NBE和COE的几乎完美的交替共聚物。不幸的是，该聚合物仅部分溶于标准溶剂如CHCl 3中。然而，可溶性馏分显示出单峰的分子量分布（PDI= 2.19），和Mn= 40 400克molecular-1被发现。较长的反应时间导致形成大量的聚（COE）均聚物嵌段连接到交替共聚物。这种均聚物嵌段很容易通过NMR光谱鉴定。交替共聚物（97%交替单元，δ= 128- 136 ppm）的13 CNMR谱示于图1中。几乎不能检测到poly（NBE）或poly（COE）的任何信号。[2，12]在δ= 135.0和128.5 ppm附近观察到交替共聚物的信号。δ= 135.0 ppm附近的第一组信号归属于C= C2CH 2
Reports on alternating copolymers prepared by metathesis copolymerization of two different monomers are relatively rare.[1–7] In 2005, Chen et al. reported on the mechanismbased design of a ROMP (ring-opening metathesis polymerization) catalyst for sequence-selective copolymerization.[8, 9] Here, we report on an alternative system for the synthesis of alternating copolymers based on Grubbs-type initiators containing an unsymmetrical, chiral N-heterocyclic carbene (NHC) ligand.As part of our on ongoing research on ruthenium metathesis catalysts with saturated unsymmetrical NHC ligands [10, 11] initiator 1 was prepared from [RuCl2 (PCy3) 2-(CHPh)] and 1-mesityl-3-((1’R)-1-phenylethyl)-4, 5-dihydroimidazolium tetrafluoroborate in 90% yield. This initiator was used for the copolymerization of norbornene (NBE) and cyclooctene (COE) using a stoichiometry of 1/NBE/COE of 1: 2000: 100000. Reactions kinetics recorded for this copolymerization in CH2Cl2 revealed that NBE was consumed in less than 15min. Terminating the copolymerization after 60min in fact provided an almost perfectly alternating copolymer of NBE and COE. Unfortunately, the polymer was only partially soluble in standard solvents such as CHCl3. However, the soluble fraction showed a unimodal molecular weight distribution (PDI= 2.19), and Mn= 40 400 g molÀ1 was found. Longer reaction times led to the formation of substantial amounts of a poly (COE) homopolymer block attached to the alternating copolymer. This homopolymer block is easily identified by NMR spectroscopy. The 13CNMR spectrum of the alternating copolymer (97% alternating units, δ= 128–136ppm) is shown in Figure 1. Hardly any signals for poly (NBE) or poly (COE) can be detected.[2, 12] The signals for the alternating copolymer are observed around δ= 135.0 and 128.5 ppm. The first set of signals around δ= 135.0 ppm is assigned to the C= CÀCH2