Anti-Markovnikov Olefin Arylation Catalyzed by an Iridium Complex
Anti-Markovnikov Olefin Arylation Catalyzed by an Iridium Complex
复制标题
DOI：
10.1021/ja0009830
复制
发表时间：
2000-07
影响因子：
15
通讯作者：
Takaya Matsumoto;D. Taube;R. Periana;and Henry Taube;H. Yoshida
中科院分区：
文献类型：
--
作者：
Takaya Matsumoto;D. Taube;R. Periana;and Henry Taube;H. Yoshida
通过离散的过渡金属络合物对芳香族化合物的均相CH键的活化已经做了大量的工作。1考虑到通过CH活化反应进行的反应可能具有不寻常的产物选择性，通过该反应开发催化剂引起了人们的极大关注。在氧化剂存在下，钯配合物催化苯与乙烯的氧化乙烯基化生成苯乙烯-2或苯的氧化偶联生成联苯。3 Murai等人。报道了芳香酮与烯烃的烷基化反应。该反应由Ru络合物催化，得到传统合成方法不易获得的产物。在这个体系中，需要一个酰基来激活芳环上的邻位CH键，以便发生烷基化反应。4芳烃的其他需要活化官能团存在的相关CH活化反应是吡啶和芳香腈的烷基化反应。5在这里，我们报道了一种新型的反马尔可夫尼科夫芳基化反应，使烯烃与苯发生芳基化反应，生成比支链烷基苯更高选择性的直链烷基苯。该反应由双核Ir(III)配合物[Ir(µ-acac-O，O，C3)-(acac-O，O)(acac-C3)]2，1，6催化，芳香族CH键被CH活化。相比之下，传统的芳香族化合物与烯烃的Friedel-Craft烷基化反应，在Lewis和Brnsted酸活化烯烃的催化下，遵循Markovnikov规则，生成几乎100%选择性的支链烷基苯。7即使用择形酸性沸石进行Friedel-Craft烷基化反应，也几乎不可能得到直链烷基苯。通常情况下，合成直链烷基芳香族化合物的方法是采用Friedel-Craft酰化和Clemenson还原相结合的方法。使用这里描述的反应，可以使用未活化的烯烃和芳烃在一步中获得直链产品。例如，当苯和1在180C下在乙烯存在下加热3h时，得到乙苯(TOF)0.0421 S-1(TN；表1，条目1)。9苯与丙烯的烷基化反应生成正丙苯和异丙苯，选择性分别为61%和39%(表1，条目3)。与1-己烯和异丁烯的反应(表1，条目5和4)分别得到了1-苯基己烷(69%的选择性)和异丁基苯(82%的选择性)，这表明了反应的一般性和对反Markovnikov加成的偏好。作为比较，使用AlCl3作为典型的Friedel-Craft催化剂，仅观察到Markovnikov加成产物(表1，条目7、8和9)。甲苯与乙烯的烷基化反应中，间、对乙基甲苯的选择性分别为63%和37%，未观察到邻位加成产物。同样，乙苯生成间二乙苯和对二乙苯的比例分别为7：3。这种对间位和对位取代的选择性可能是由空间位元驱动的，在其他CH活化体系中也观察到了这种选择性。例如，甲苯在间位和对位被Osh(新戊基)(PMe3)4以统计2：1的比例活化以产生
Significant efforts have been directed at homogeneous CH bond activation of aromatic compounds by discrete transition metal complexes. 1 In view of the unusual product selectivity possible from reactions proceeding through the CH activation reaction, exploitation of catalysis through this reaction has attracted considerable attention. In the presence of an oxidant, Pd complexes catalyze oxidative vinylation of benzene with ethylene to produce styrene2 or oxidative coupling of benzene to give biphenyl. 3 Murai et al. has reported alkylations of aromatic ketones by olefins. The reaction is catalyzed by Ru complexes to afford products that are not easily obtainable by conventional synthetic methods. In this system an acyl group is required to activate the ortho CH bonds of the aromatic ring for alkylation to occur. 4 Other related CH activation reactions of aromatics that require the presence of activating functional groups are the alkylation of pyridines and aromatic nitriles. 5 Herein we report the novel, anti-Markovnikov, arylation of olefins with benzene to produce straight-chain alkylbenzenes with higher selectivity than the branched alkylbenzene. The reaction, catalyzed by the binuclear Ir (III) complex,[Ir (µ-acac-O, O, C3)-(acac-O, O)(acac-C3)] 2, 1, 6 is assumed to occur by the CH activation of the aromatic CH bonds. In contrast, conventional Friedel-Crafts alkylation of aromatic compounds with olefins, catalyzed by Lewis and Brönsted acid activation of the olefin, follow Markovnikov’s rule, producing branched alkylbenzenes in nearly 100% selectivity. 7Even when shape selective, acidic zeolites are employed for Friedel-Crafts alkylations, it is almost impossible to obtain straight-chain alkylbenzene. 8 Typically, to synthesize straight chain alkyl aromatics, a combination of Friedel-Crafts acylation and Clemenson reduction is employed. Using the reactions described herein, it is possible to obtain the straight chain product in one step using unactivated olefins and aromatics. For example, when benzene and 1 were heated in the presence of ethylene at 180 C for 3 h, ethylbenzene was obtained (TOF) 0.0421 s-1, TN) 455; Table 1, entry 1). 9 Alkylation of benzene with propylene resulted in formation of n-propylbenzene and cumene in 61 and 39% selectivities, respectively (Table 1, entry 3). Showing the generality of the reaction and the preference for anti-Markovnikov additon, reaction with 1-hexene and isobutene (Table 1, entries 5 and 4) resulted in 1-phenylhexane (69% selectivity) and isobutylbenzene (82% selectivity), respectively. As a comparison, using AlCl3 as a typical Friedel-Crafts catalyst, only Markovnikov addition products were observed (Table 1, entries 7, 8, and 9). Alkylation of toluene with ethylene gave only m-and p-ethyl methylbenzene in 63 and 37% selectivity: no ortho addition products were observed. Similarly ethylbenzene gave m-and p-diethylbenzene in a 7: 3 ratio, respectively. This selectivity for meta and para substitution, presumably driven by sterics, has also been observed in other CH activation systems. For example, toluene is activated in the meta and para positions by OsH (Neopentyl)(PMe3) 4 in statistical 2: 1 ratio to produce