Phosphane-free rhodium catalyst in an anionic micellar system for [4+2] annulation of dienynes.-猫眼课题宝

DOI：

10.1002/anie.200353123

发表时间：

2004-03

期刊：

Angewandte Chemie

影响因子：

通讯作者：

中科院分区：

文献类型：

作者：

Dai Motoda;H. Kinoshita;H. Shinokubo;K. Oshima

阳离子配合物在许多过渡金属催化的反应中表现出显著的催化活性，因为它们比相应的中性配合物具有更多的可用于底物配位的空位。特别地，阳离子铑催化剂经常用作氢化、不对称氢化、氢化硅烷化、氢化物转移、环加成等的均相催化剂。[1]阳离子铑催化剂通常通过用银盐处理相应的氯络合物与外层抗衡阴离子（例如BF 4+或PF 6+）来制备。[2]本文报道了一种不含膦的阳离子铑催化剂，该催化剂在阴离子胶束水溶液体系中对二烯炔的[4+ 2]成环反应具有高活性。[3]We研究了在水介质中铑催化的1，3-二烯-8-炔1a的分子内[4+ 2]成环（表1）。[4，5]该方法通常使用阳离子铑络合物作为催化剂。膦配体的存在也是至关重要的，据报道，1，4-二苯基膦基丁烷提供了高效的催化剂。[5g]以[{RhCl（cod）} 2]和三（间磺酸基苯基）膦的三钠盐（tppts）为原料，原位合成了水溶性铑催化剂。在50 ℃下将二烯炔1a加入到催化剂溶液中，搅拌12小时后得到环加成产物2a，产率为51%（表1，条目1）。还获得芳香化产物3a。反应体系为非均相体系，考察了表面活性剂的加入量。[8]阴离子表面活性剂十二烷基硫酸钠（SDS）提高了反应效率，2a的产率提高到91%（表1，条目4）。阳离子和中性表面活性剂的作用不如SDS有效（表1，条目2和3）。然后我们尝试将反应温度降低至室温（表1，条目5-12）。在258 ℃下，用[{RhCl（cod）} 2]-tppts的催化剂组合没有观察到环加成产物（表1，条目5）。使用二苯基膦基丁烷（dppb）产生少量的2a（表1，条目6）。在几个实验之后，我们发现没有任何膦配体的氯化铑二聚体导致定量转化（表1，条目7）。将氯化铑二聚体和SDS在水中混合得到澄清的黄色均匀溶液，尽管[{RhCl（cod）} 2]本身不溶于水。在20分钟反应中测试了几种铑络合物（表1，条目8-12）。威尔金森络合物和[{RhOH（cod）} 2]未表现出催化活性（表1，分别为条目9和10）。降冰片二烯（nbd）络合物证明是比相应的环辛烯络合物更有效的催化剂前体（表1，条目11）。在室温下，在20分钟内观察到几乎定量的转化。相反，乙烯络合物根本不起作用（表1，条目12）。根据这些铑配合物之间的差异，我们推测，烯烃配体仍然与铑原子在水中。在一个有效的反应方案在手的铑催化的[4+ 2]成环在水中，与几个二烯炔1的反应进行了检查。表2总结了结果。亲水性二烯炔1b的反应性很强，在10分钟内定量转化。值得注意的是，该反应可以在空气气氛下进行（表2，条目5）。氮栓系的二烯炔1 e也以优异的产率提供成环产物（表2，条目6）。似乎

Cationic complexes often exhibit marked catalytic activity in a number of transition-metal-catalyzed reactions because they have more available vacant sites for coordination of substrates than the corresponding neutral complexes. In particular, cationic rhodium catalysts are frequently employed as homogeneous catalysts for hydrogenation, asymmetric hydrogenation, hydrosilylation, hydride transfer, cycloaddition, and so forth.[1] Cationic rhodium catalysts are usually prepared by treatment of the corresponding chloro complex with silver salts with outer-sphere counteranions, such as BF4 À or PF6 À.[2] Herein we report a phosphane-free cationic rhodium species that forms a highly active catalyst in an aqueous anionic micellar system for the [4+ 2] annulation of dienynes.[3]We investigated the rhodium-catalyzed intramolecular [4+ 2] annulation of 1, 3-dien-8-ynes 1a in aqueous media (Table 1).[4, 5] This process often employs cationic rhodium complexes as the catalyst. The presence of phosphane ligands is also crucial, and it was reported that 1, 4-diphenylphosphanylbutane provides a highly efficient catalyst.[5g] A water-soluble rhodium catalyst was prepared in situ from [{RhCl (cod)} 2] and the trisodium salt of tris (m-sulfonatophenyl) phosphane (tppts).[6, 7] The addition of dienyne 1a to a solution of the catalyst at 508C provided the cycloaddition product 2a in 51% yield after stirring for 12h (Table1, entry 1). The aromatized product 3a was also obtained. The reaction system was heterogeneous, and the addition of surfactants was examined.[8] An anionic surfactant, sodium dodecyl sulfate (SDS), enhanced the efficiency of the reaction, and the yield of 2a was improved to 91%(Table 1, entry 4). Cationic and neutral surfactants did not work as effectively as SDS (Table 1, entries 2 and 3). We then tried to lower the reaction temperature to room temperature (Table 1, entries 5–12). None of the cycloaddition product was observed at 258C with the catalyst combination of [{RhCl (cod)} 2]–tppts (Table 1, entry 5). The use of diphenylphosphanylbutane (dppb) yielded a small amount of 2a (Table 1, entry 6). After several experiments, we found that the rhodium chloride dimer without any phosphane ligands led to quantitative conversion (Table1, entry7). Mixing the rhodium chloride dimer and SDS in water afforded a clear yellow homogeneous solution, although [{RhCl (cod)} 2] itself is insoluble in water. Several rhodium complexes were tested in 20-min reactions (Table 1, entries 8–12). The Wilkinson complex and [{RhOH (cod)} 2] did not exhibit catalytic activity (Table 1, entries 9 and 10, respectively). The norbornadiene (nbd) complex proved to be a more efficient catalyst precursor than the corresponding cyclooctadiene complex (Table 1, entry 11). Almost quantitative conversion within 20 min at room temperature was observed. In contrast, the ethylene complex did not work at all (Table 1, entry 12). On the basis of the difference between these rhodium complexes we speculate that the alkene ligand is still associated with the rhodium atom in water. With an efficient reaction protocol in hand for the rhodium-catalyzed [4+ 2] annulation in water, the reaction with several dienynes 1 was examined. Table 2 summarizes the results. Hydrophilic dienyne 1b was very reactive and was converted quantitatively within 10 min. Notably, the reaction can be conducted under an air atmosphere (Table 2, entry 5). Nitrogen-tethered dienyne 1e also afforded the annulation product in excellent yield (Table 2, entry 6). It seems that

Phosphane-free rhodium catalyst in an anionic micellar system for [4+2] annulation of dienynes.

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