Department of Chemistry, Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, Xiangtan University , Xiangtan, Hunan Province, P. R. China 411105.
J Am Chem Soc. 2013 Dec 4;135(48):18067-79. doi: 10.1021/ja404957t. Epub 2013 Nov 20.
The semiring chemistry of the Au25(SR)18, particularly its fragmentation mechanism and catalytic active site, is explored using density functional theory (DFT) calculations. Our calculations show that the magically stable fragmental cluster, Au21(SR)14(-), as detected in several mass spectrometry (MS) measurements of fragmentation of the Au25(SR)18(-), contains a quasi-icosahedral Au13-core fully protected by four -SR-Au-SR- and two -SR-Au-SR-Au-SR- staple motifs. A stepwise fragmentation mechanism of the semiring staple motifs on the surface of Au25(SR)18(-) is proposed for the first time. Initially, the Au25(SR)18(-) transforms into a metastable structure with all staple motifs binding with two neighboring vertex Au-atoms of the Au-core upon energy uptake. Subsequently, a 'step-by-step' detachment and transfer of [Au(SR)]x (x = 1-4) units occurs, which leads to the formation of highly stable products including Au21(SR)14(-) and a cyclic [Au(SR)]4 unit. The continued fragmentation of Au21(SR)14(-) to Au17(SR)10(-) is observed as well, which shows same stepwise fragmentation mechanism. The proposed mechanism well explains the favorable formation of Au21(SR)14(-) and Au17(SR)10(-) from Au25(SR)18(-) as observed from experimental abundance. Taking the Au21(SR)14 and its parent cluster Au25(SR)18 as the benchmark model systems, the catalytic active site of the thiolate protected gold clusters toward the styrene oxidation and the associated reaction mechanism are further investigated. We show that the Au atom in the staple motifs is the major active site for the styrene oxidation in presence of TBHP as oxidant or initiator. The Au atom in the staple motifs can change from Au(I) (bicoordinated) to Au(III) (tetracoordinated). The O2 activation is achieved during this process.
使用密度泛函理论（DFT）计算研究了 Au25（SR）18 的半环化学，特别是其碎片化机制和催化活性位。我们的计算表明，在 Au25（SR）18（-）碎片化的几次质谱（MS）测量中检测到的神奇稳定的碎片化簇 Au21（SR）14（-）包含一个准二十面体 Au13-核，完全被四个-SR-Au-SR-和两个-SR-Au-SR-Au-SR-订书钉基序保护。首次提出了 Au25（SR）18（-）表面半环订书钉基序的逐步碎片化机制。最初，Au25（SR）18（-）在能量吸收后转变为具有所有订书钉基序与 Au 核的两个相邻顶点 Au 原子结合的亚稳态结构。随后，发生[Au（SR）]x（x = 1-4）单元的逐步脱离和转移，导致形成高度稳定的产物，包括 Au21（SR）14（-）和环状[Au（SR）]4 单元。还观察到 Au21（SR）14（-）向 Au17（SR）10（-）的进一步碎片化，其表现出相同的逐步碎片化机制。所提出的机制很好地解释了实验丰度观察到的 Au21（SR）14（-）和 Au17（SR）10（-）从 Au25（SR）18（-）的有利形成。以 Au21（SR）14 和其母体簇 Au25（SR）18 为基准模型系统，进一步研究了硫醇保护金簇在苯乙烯氧化中的催化活性位及其相关反应机制。我们表明，在 TBHP 作为氧化剂或引发剂存在的情况下，订书钉基序中的 Au 原子是苯乙烯氧化的主要活性位。订书钉基序中的 Au 原子可以从 Au（I）（双配位）变为 Au（III）（四配位）。在此过程中实现了 O2 的活化。
