Unveiling the Takai Olefination Reagent via Tris( tert-butoxy)siloxy Variants.
Unveiling the Takai Olefination Reagent via Tris( tert-butoxy)siloxy Variants.
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DOI：
10.1021/jacs.8b08739
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发表时间：
2018-09
影响因子：
15
通讯作者：
Daniel Werner;R. Anwander
中科院分区：
文献类型：
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作者：
Daniel Werner;R. Anwander
在-35℃下，CrCl2与CHI3在四氢呋喃中发生反应，在-35℃的温度下，通过处理CrCl2与CHI3的反应，分离出了难以捉摸的Takai烯化试剂，即碘-亚甲基铬(III)配合物[Cr2Cl4(CHI)(THF)4]。或者，用CHI3处理[Cr(OSI(OtBu)3)2]得到混价二卤代甲烷配合物[CrII/III2I2(OSI(OTBu)3)2(CHI2)]。在TMEDA存在下，CHI2发生亲核攻击，生成两性离子物种[CrIII(OSI(O TBu)3)2(tmeda-chi)][I]。考察了配合物[Cr2Cl4(CHI)(THF)4]和[CrII/III2I2(OSI(O TBU)3)2(CHI2)]对苯甲醛一卤代烯化反应的诱导作用。值得注意的是，两种配合物都促进了烯化反应，其中[Cr2Cl4(CHI)(THf)4]达到了与高井S原混合物相同的E选择性，而配合物[CrII/III2I2(OSI(OTbu)3)2(CHI2)]则优先产生Z异构体，证实了原生Takai试剂混合物的活性组份为一碘亚甲基类铬(III)-铬(III)。
The elusive Takai olefination reagent, namely, the iodo-methylidene Cr(III) complex [Cr2Cl4(CHI)(thf)4], has been isolated by careful handling of the reaction between CrCl2 and CHI3 in THF at -35 °C. Alternatively, treatment of [Cr(OSi(O tBu)3)2] with CHI3 gave the mixed-valent dihalido-methanide complex [CrII/III2I2(OSi(O tBu)3)2(CHI2)], featuring a Cr(III)-CHI2 moiety. In the presence of TMEDA nucleophilic attack at CHI2 occurred generating the zwitterionic species [CrIII(OSi(O tBu)3)2(tmeda-CHI)][I]. Complexes [Cr2Cl4(CHI)(thf)4] and [CrII/III2I2(OSi(O tBu)3)2(CHI2)] were screened for their ability to induce monohalido olefination of benzaldehyde. Remarkably, both complexes promote olefination, with [Cr2Cl4(CHI)(thf)4] accomplishing the same E selectivity as Takai 's original mixture. Complex [CrII/III2I2(OSi(O tBu)3)2(CHI2)], however, appeared to give preferentially Z isomer, corroborating the monoiodo-methylidene species Cr(III)-CHI-Cr(III) as the active olefination component of the original in situ generated Takai reagent mixture.