Experimental and Computational Characterization of the Transition State for C–X Bimetallic Oxidative Addition at a Cu–Fe Reaction Center
Experimental and Computational Characterization of the Transition State for C–X Bimetallic Oxidative Addition at a Cu–Fe Reaction Center
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DOI：
10.1021/acs.organomet.5b00476
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发表时间：
2015-07
期刊：
影响因子：
2.8
通讯作者：
Malkanthi K. Karunananda;S. Parmelee;Greyson W. Waldhart;Neal P. Mankad
中科院分区：
文献类型：
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作者：
Malkanthi K. Karunananda;S. Parmelee;Greyson W. Waldhart;Neal P. Mankad
异丙基咪唑亚基配合物（IPr）Cu-Fp（IPr = N，N′-bis（2，6-diisopropylimidazole-2-ylidene，Fp = FeCp（CO）2）是一种非贵金属C-H硼化催化剂。为了更好地理解在这个系统中的反应途径的性质，我们已经进行了彻底的机械研究的卤代烷活化的铜-铁heterocyclic反应中心。使用环丙基甲基卤化物基板作为自由基时钟建立，烷基卤化物活化发生的两个电子机制的烷基溴和氯化物，但不是碘化物。对氯化苄活化的艾林分析允许实验测定活化参数，包括大的负活化熵（ΔS = −36 eu）。对对位取代的苄基氯的Hammett研究显示反应常数ρ = 1.6，表明在卤代烷碳上的过渡态中负电荷的积累。发现了Ru的类似物（IPr）Cu-Rp（Rp = RuCp（CO）2）。
The heterobimetallic complex (IPr)Cu-Fp (IPr = N,N′-bis(2,6-diisopropylimidazol-2-ylidene, Fp = FeCp(CO)2) was identified previously as a nonprecious metal catalyst for C–H borylation. To better understand the nature of the bimetallic reaction pathways operative in this system, we have conducted a thorough mechanistic study of alkyl halide activation by the Cu–Fe heterobimetallic reaction center. Use of cyclopropylmethyl halide substrates as radical clocks established that alkyl halide activation occurs by a two-electron mechanism for alkyl bromides and chlorides but not iodides. Eyring analysis of the activation of benzyl chloride allowed for experimental determination of activation parameters, including a large and negative entropy of activation (ΔS⧧ = −36 eu). A Hammett study with para-substituted benzyl chlorides revealed a reaction constant of ρ = 1.6, indicating accumulation of negative charge in the transition state on the alkyl halide carbon. The Ru analogue, (IPr)Cu-Rp (Rp = RuCp(CO)2), was found...