Nickel-catalyzed Dehydrobrominative Polycondensation for the Practical Preparation of Regioregular Poly(3-substituted thiophene)s
Nickel-catalyzed Dehydrobrominative Polycondensation for the Practical Preparation of Regioregular Poly(3-substituted thiophene)s
复制标题
镍催化脱溴氢缩聚反应实际制备立体规整聚（3-取代噻吩）
DOI：
10.1246/cl.2011.398
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发表时间：
2011
影响因子：
1.6
通讯作者：
A. Mori
中科院分区：
文献类型：
--
作者：
Shunsuke Tamba;Shota Tanaka;Youhei Okubo;H. Meguro;Shu Okamoto;A. Mori
低聚硫吩类和聚噻吩类化合物在材料科学中引起了极大的关注。涉及头到尾(HT)重复单元例如聚(3-己基噻吩基)(HT-P3HT)(1)(图1)的区域规则聚噻吩烯特别令人感兴趣，因为该化合物显示出显著的物理性能材料，例如有机TFT、薄膜有机太阳能电池和导电聚合物1。2，5-二溴-3-己基噻吩烯(2a)与格氏试剂在过渡金属催化剂存在下的脱溴缩聚是制备1.1d的一种选择方法，2卤素金属交换中的区域化学错误导致向聚合物的不完全转化1。虽然使用5-碘化衍生物2b是解决这个问题的方法，3制备2b需要多步步骤以及较低的原子效率。另一方面，脱氢溴化法合成1与2-溴-3-己基噻吩酮(3)是一条潜在的原子经济途径。3用锂酰胺去质子化，然后用zinc1d或镁2a-2f进行金属交换，3也得到1，尽管需要极低的温度。最近研究表明，在碱金属碳酸盐存在下，钯催化的直接缩聚反应可以得到聚合物，然而，要以较高的聚合度获得合理的产率和聚合度，需要较高的温度。因此，开发更温和的脱氢溴化聚合(在室温附近)是非常有趣的，这将是高效制备区域规则聚噻吩类化合物的目标。我们最近在过渡金属催化的杂芳烃化合物5，6的C-H官能化方面所做的努力可以应用于合成HT-P3HT(1)，并在此揭示了使用Knochel-Hauser碱7和镍催化剂是一种在室温下对高区域规则的聚(3取代噻吩基)S进行脱氢溴化缩聚的实用方法，具有高原子效率。我们首先研究了钯催化的3a在叔丁氧基锂存在下的聚合。8聚合在50℃下进行，得到了相应的聚合物1，其分子量为7600。与上述结果不同的是，Knochel开发的(2，2，6，6-四甲基哌啶-1-基)氯化镁和LiCl4用于各种sp2-C-H键的质子提取，7能高效地引发聚合。当该反应在0.5mol%[NiCl2(Dppe)]催化下进行时，得到了相应的HTP3HT(1)的定量产率，而用格氏试剂进行的脱溴聚合由于卤素金属交换的区域化学误差而没有达到完全转化。得到的聚合物1具有极高的羟色胺选择性。DPPP作为镍催化剂的配体也与DPPE一样有效，而DPPB或三环己基膦(PCy3)的效果较差。发现所得聚合物的平均分子量受所用镍催化剂的量控制。高分子链的数目与镍催化剂的用量有较好的对应关系，催化剂负载量越低，聚合产物的锰值越高。使用芳基镍络合物作为催化剂也可以得到平滑的聚合反应，并且具有良好的羟色胺选择性，并且通过1H核磁共振证实苯基末端位于聚合物链的末端。2E这些结果在表1中总结。需要指出的是，该反应是在室温下进行的，从而以定量的产率提供相应的聚合物。将前面的聚合物合成与在高温下或在极低温度下进行的C-H官能化进行比较，以用锂盐抽出质子，然后进行锂镁交换，3本反应条件在整个反应过程中在室温下进行。
Oligothiophenes and polythiophenes attract considerable attention in materials science. Regioregular polythiophene, which involves head-to-tail (HT) repeating unit such as poly(3-hexylthiophene) (HT-P3HT) (1) (Chart 1) is of particular interest since the compound shows remarkable physical properties materials such as organic TFTs, thin-film organic solar cells, and conductive polymers.1 Debrominative polycondensation of 2,5-dibromo-3-hexylthiophene (2a) with a Grignard reagent in the presence of a transition-metal catalyst is a method of choice for the preparation of 1.1d,2 A regiochemical error in the halogenmetal exchange causes incomplete conversion to the polymer 1. Although use of the 5-iodinated derivative 2b is a solution to such problem,3 preparation of 2b requires multistep procedures as well as inferior atom efficiency. On the other hand, the dehydrobrominative method to afford 1 with 2-bromo3-hexylthiophene (3) is a potentially atom-economic pathway. Deprotonation of 3 with lithium amide and following metal exchange with zinc1d or magnesium2a2f,3 also gives 1 although extremely low temperature is necessary. A palladium-catalyzed direct polycondensation in the presence of an alkali metal carbonate has recently been shown to lead to polymer,4 however, high temperature is necessary to afford the polythiophene in a reasonable yield with high degree of polymerization. It is thus highly intriguing to develop milder dehydrobrominative polymerization (around room temperature), which would be a goal for the efficient preparation of regioregular polythiophenes. We envisaged that our recent efforts on the development of transition-metal-catalyzed CH functionalization of heteroaromatic compounds5,6 can be applied to the synthesis of HT-P3HT (1) and herein disclose that the employment of Knochel-Hauser base7 and a nickel-catalyst is a practical dehydrobrominative polycondensation method toward highly regioregular poly(3substituted thiophene)s at room temperature with high atom efficiency. We first examined palladium-catalyzed polymerizaton of 3a in the presence of lithium t-butoxide.8 The polymerization occurred at 50 °C to afford the corresponding polymer 1 with Mn of 7600. In contrast to the above undesired results, it was found that the use of (2,2,6,6-tetramethylpiperidin-1-yl)magnesium chloride¢LiCl (4), which was developed by Knochel for the proton abstraction of various sp2 CH bonds,7 induced polymerization highly efficiently. When the reaction was carried out with 0.5mol% [NiCl2(dppe)] as catalyst, the corresponding HTP3HT (1) was obtained in quantitative yield in contrast to debrominative polymerization with a Grignard reagent which does not reach complete conversion due to regiochemical error in the halogenmetal exchange. The obtained polymer 1 exhibited extremely high HT selectivity. DPPP as a ligand of the nickel catalyst also was as effective as DPPE, while DPPB or tricyclohexylphosphine (PCy3) was found less effective. The average molecular weight of the obtained polymer was found to be controlled by the amount of the employed nickel catalyst. The number of the polymer chain showed relatively good correspondence to the amount of nickel catalyst and the Mn value was found to increase by lowering the catalyst loading. The use of arylnickel complex as a catalyst also resulted in smooth polymerization with excellent HT selectivity and it was confirmed by 1HNMR that the phenyl end group was at the terminal of the polymer chain.2e These results are summarized in Table 1. It should be pointed out that the reaction proceeded at room temperature to afford the corresponding polymer in a quantitative yield. Comparing the preceding polymer syntheses with CH functionalization conducted at elevated temperature4 or at extremely low temperature for proton abstraction with lithium amide followed by lithiummagnesium exchange,3 the present reaction conditions proceed at room temperature throughout the