Fachbereich Chemie and Forschungszentrum OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany.
J Phys Chem A. 2013 Feb 14;117(6):1197-203. doi: 10.1021/jp305281m. Epub 2013 Jan 23.
Reactions under single collision conditions with benzene C(6)H(6) and with benzene-d(6) C(6)D(6) of size selected cationic cobalt clusters Co(n)(+) and of anionic cobalt clusters Co(n)(-) in the cluster size range n = 3-28 revealed that dehydrogenation by cationic clusters is sparse, whereas it is ubiquitous in reactions by anionic clusters. Kinetic isotope effects (KIE) in total reaction rates are inverse and, in part, large. Dehydrogenation isotope effects (DIE) are normal. A multistep model of adsorption and stepwise dehydrogenation from the precursor adsorbate unravels a possible origin of the inverse KIE: Single step C-H bond activation is swift (no KIE in forward direction) and largely reversible (normal KIE backward) whereas H/D tunneling is likely to contribute (backward). DFT calculations of the structures and energetics along the reaction path in Co(13)C(6)H(6) lend support to the proposed multistep model. The observed effects on rates and KIEs of cluster charges and of cluster sizes are noted to elucidate further.
在单个碰撞条件下，用苯 C(6)H(6) 和苯-d(6) C(6)D(6) 与尺寸选择的阳离子钴团簇 Co(n)(+) 和阴离子钴团簇 Co(n)(-) 反应，揭示了阳离子团簇的脱氢反应很少，而阴离子团簇的脱氢反应则普遍存在。总反应速率的动力学同位素效应 (KIE) 是相反的，部分 KIE 很大。脱氢同位素效应 (DIE) 是正常的。吸附和解离逐步脱氢的多步模型揭示了反 KIE 的可能起源：单步 C-H 键活化迅速（正向无 KIE）且大部分可逆（反向正常 KIE），而 H/D 隧道效应可能起作用（反向）。Co(13)C(6)H(6) 沿反应路径的结构和能态的 DFT 计算为所提出的多步模型提供了支持。注意观察到团簇电荷和团簇大小对速率和 KIE 的影响，以进一步阐明。
