Selective Methylation of Amines with Carbon Dioxide and H2
Selective Methylation of Amines with Carbon Dioxide and H2
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DOI：
10.1002/anie.201306850
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发表时间：
2013-11-11
影响因子：
16.6
通讯作者：
Beller, Matthias
中科院分区：
文献类型：
--
作者：
Li, Yuehui;Sorribes, Ivan;Beller, Matthias
二氧化碳是自然界中最丰富的碳源，负责构建所有有机化合物。由于CO2的人为排放不断增加，其作为廉价且可再生的C1原料的用途对于生产增值的大宗化学品如甲醇、聚碳酸酯以及精细化学品越来越感兴趣。[1-3]近年来，已经报道了使用不同还原剂将热稳定的CO2分子转化为甲酸盐、甲醇和甲烷的重要进展。[4-15]除了这些方法，Cantat等人最近报道了使用CO2的有趣甲基化。[16]还有我们[17]不幸的是，在这两种情况下，在Zn/NHC或Ru/BuPAd 2催化剂存在下，氢硅烷必须用作生产甲基化胺产物的还原剂。由于甲基取代胺作为生物活性化合物广泛存在，并作为关键中间体和重要化学品得到广泛应用，因此在过去的几十年中，开发更有效的甲基化方法一直吸引着化学家的注意力。[18]尽管如此，在工业中最常见的胺的甲基化使用有毒的甲醛，而在有机合成中，不太温和的甲基化试剂，例如碘甲烷和硫酸二甲酯，占主导地位。[19因此，高度期望应用具有良好选择性（例如官能团耐受性和单甲基化）的更可持续的试剂。显然，使用CO2和H2的催化甲基化是一种优雅而可行的方法，H2O是唯一的副产物（图1）。[21]本文描述了一种通用的和选择性的碳二亚胺催化的芳香胺和脂肪胺的CO2/H2甲基化反应，本工作的动机是碳二亚胺催化的CO2和羧酸衍生物的氢化以及醇的N-烷基化反应的效率。[14最初，我们研究了二氧化碳、H2和苯胺（1a）在作为模型系统的原位形成的钌络合物存在下的反应（支持信息中的表1和表S1-S4）。活性最高的催化剂由乙酰丙酮钌[Ru（acac）3]和1，1，1-三（二苯基膦基甲基）乙烷（triphos; 4f）形成，并得到完全的
Carbon dioxide is the most abundant carbon source responsible for the construction of all organic compounds in nature. Because of the rising anthropogenic emission of CO2, its use as a cheap and renewable C1 feedstock is of increasing interest for the production of value-added bulk chemicals such as methanol, polycarbonates, as well as fine chemicals.[1–3] In recent years, important developments to convert the thermodynamically stable CO2 molecule into formates, methanol, and methane have been reported using different reductants.[4–15] In addition to these methods, very recently interesting methylations using CO2 were reported by Cantat et al.[16] and us.[17] Unfortunately, in both cases hydrosilanes had to be used as the reductant for the production of methylated amine products in the presence of either a Zn/NHC or Ru/BuPAd2 catalyst. Since methyl-substituted amines exist frequently as bioactive compounds and have been widely utilized as key intermediates and important chemicals, the development of more efficient methylation methods continuously attracted the attention of chemists in the last decades.[18] Still, the most common methylation of amines in industry makes use of toxic formaldehyde, whereas in organic synthesis less benign methylation reagents, for example, methyl iodide, and dimethyl sulfate, prevail.[19, 20] Thus, the application of more sustainable reagents with good selectivity (eg functionalgroup tolerance and monomethylation) is highly desired. Obviously, catalytic methylations using CO2 and H2 represent an elegant and viable method with H2O as the only byproduct (Figure 1).[21] Herein we describe a general and selective ruthenium-catalyzed methylation of both aromatic and aliphatic amines using carbon dioxide/hydrogen to N-methylated products.The present work was motivated by the efficiency of ruthenium-catalyzed hydrogenation of CO2 and carboxylic acid derivatives as well as N-alkylation from alcohols previously reported by us and other groups.[14, 22–28] Initially, we investigated the reaction of carbon dioxide, H2, and aniline (1a) in the presence of in situ formed ruthenium complexes as a model system (Table 1 and Tables S1–S4 in the Supporting Information). The most active catalyst was formed from ruthenium acetylacetonate [Ru (acac) 3] and 1, 1, 1-tris (diphenylphosphinomethyl) ethane (triphos; 4 f), and afforded full