Mechanistic aspects of samarium-mediated σ-bond activations of arene C-H and arylsilane Si-C bonds
Mechanistic aspects of samarium-mediated σ-bond activations of arene C-H and arylsilane Si-C bonds
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DOI：
10.1021/ja011472w
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发表时间：
2001-10-31
影响因子：
15
通讯作者：
Tilley, TD
中科院分区：
文献类型：
--
作者：
Castillo, I;Tilley, TD
为了研究Sm-Ph作为中间体在钐催化PhSiH3重分配到Ph2SiH2和SiH4中的潜在作用，用HgPh2氧化Cp*Sm-2(2)制备了samarin -苯基配合物[Cp*2SmPh](2)(1)。化合物1热分解生成苯和苯桥式钐配合物CP*Sm-2(mu -1,4- c6h4)SmCp*(2)(3)。这种分解反应似乎是通过1解离成单体CP*2SmPh，然后通过单分子和双分子途径进行反应，分别涉及限速CP*金属化和直接C-H活化。观察到的这一过程的速率规律为：速率= k(1)[1] + k(2)[1](2)配合物I有效地转移它的苯基。生成Ph2SiH2和[Cp*Sm-2(mu -H)](2)(4)。C6F5SiH3的定量Si-C键断裂受氢化钐配合物4的影响，生成硅烷和[Cp*Sm-2(mu -C6F5)](2)(5)。相反，Si-H在4与o-MeOC6H4SiH3反应时发生活化，产生钐。硅基物质Cp*2SmSiH2(o-MeOC6H4)(7)。配合物7迅速分解为[Cp*Sm-2(mu -0-MeOC6H4)](2)(6)和其他含钐产物。化合物5和6分别由Hg(C6F5)(2)和Hg(o-MeOC6H4)(2)氧化得到。讨论了钐在硅上的重分布机理和sigma键转化反应的化学选择性。
To investigate the potential role of Sm-Ph species as intermediates in the samarium-catalyzed redistribution of PhSiH3 to Ph2SiH2 and SiH4, the samariurn phenyl complex [Cp*2SmPh](2) (1) was prepared by oxidation of Cp*Sm-2 (2) with HgPh2. Compound 1 thermally decomposes to yield benzene and the phenylene-bridged disamarium complex CP*Sm-2(mu -1,4-C6H4)SmCp*(2) (3). This decomposition reaction appears to proceed through dissociation of 1 into monomeric CP*2SmPh species which then react via unimolecular and bimolecular pathways, involving rate-limiting Cp* metalation and direct C-H activation, respectively. The observed rate law for this process is of the form: rate = k(1)[1] + k(2)[1](2) Complex I efficiently transfers its phenyl. group to PhSiH3, with formation of Ph2SiH2 and [Cp*Sm-2(mu -H)](2) (4). Quantitative Si-C bond cleavage Of C6F5SiH3 is effected by the samarium hydride complex 4, yielding silane and [Cp*Sm-2(mu -C6F5)](2) (5). In contrast, Si-H activation takes place upon reaction of 4 with o-MeOC6H4SiH3, affording the samarium. silyl species Cp*2SmSiH2(o-MeOC6H4) (7). Complex 7 rapidly decomposes to [Cp*Sm-2(mu -0-MeOC6H4)](2) (6) and other samarium-containing products. Compounds 5 and 6 were prepared independently by oxidation of 2 with Hg(C6F5)(2), and Hg(o-MeOC6H4)(2), respectively. The mechanism of samarium-mediated redistribution at silicon, and chemoselectivity in sigma -bond metathesis reactions, are discussed.