Kong Richard Y, Batuecas Maria, Crimmin Mark R
Department of Chemistry, Molecular Sciences Research Hub, Imperial College London 82 Wood Lane, Shepherds Bush London W12 0BZ UK
Chem Sci. 2021 Oct 25;12(44):14845-14854. doi: 10.1039/d1sc04940b. eCollection 2021 Nov 17.
Over the past few decades, numerous model systems have been discovered that create carbon-carbon bonds from CO. These reactions are of potential relevance to the Fischer-Tropsch process, a technology that converts syngas (H/CO) into mixtures of hydrocarbons. In this paper, a homogeneous model system that constructs carbon chains from CO is reported. The system exploits the cooperative effect of a transition metal complex and main group reductant. An entire reaction sequence from C → C → C → C has been synthetically verified. The scope of reactivity is broad and includes a variety of transition metals (M = Cr, Mo, W, Mn, Re, Co), including those found in industrial heterogeneous Fischer-Tropsch catalysts. Variation of the transition metal fragment impacts the relative rate of the steps of chain growth, allowing isolation and structural characterisation of a rare C intermediate. The selectivity of carbon chain growth is also impacted by this variable; two distinct isomers of the C carbon chain were observed to form in different ratios with different transition metal reagents. Based on a combination of experiments (isotope labelling studies, study of intermediates) and calculations (DFT, NBO, ETS-NOCV) we propose a complete mechanism for chain growth that involves defined reactivity at both transition metal and main group centres.
在过去几十年中，人们发现了许多能从一氧化碳生成碳-碳键的模型体系。这些反应与费托合成工艺潜在相关，费托合成工艺是一种将合成气（H₂/CO）转化为碳氢化合物混合物的技术。本文报道了一种由一氧化碳构建碳链的均相模型体系。该体系利用了过渡金属配合物和主族还原剂的协同效应。从C₁→C₂→C₃→C₄的完整反应序列已通过合成得到验证。反应活性范围广泛，包括多种过渡金属（M = Cr、Mo、W、Mn、Re、Co），其中包括在工业非均相费托合成催化剂中发现的那些金属。过渡金属片段的变化会影响链增长步骤的相对速率，从而能够分离并对一种罕见的C中间体进行结构表征。碳链增长的选择性也受此变量影响；观察到不同过渡金属试剂会以不同比例形成C₄碳链的两种不同异构体。基于实验（同位素标记研究、中间体研究）和计算（密度泛函理论、自然键轨道理论、能量分解分析-自然轨道耦合簇方法）的结合，我们提出了一个完整的链增长机制，该机制涉及过渡金属和主族中心的特定反应活性。
