Picosecond to millisecond tracking of a photocatalytic decarboxylation reaction provides direct mechanistic insights
Picosecond to millisecond tracking of a photocatalytic decarboxylation reaction provides direct mechanistic insights
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DOI：
10.1038/s41467-019-13154-w
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发表时间：
2019-11-13
影响因子：
16.6
通讯作者：
Orr-Ewing, Andrew J.
中科院分区：
文献类型：
--
作者：
Bhattacherjee, Aditi;Sneha, Mahima;Orr-Ewing, Andrew J.
羧酸的光化学脱羧是化学合成自由基中间体的通用途径。然而，这种多步骤反应的顺序性质使得该机制难以探索。在这里，我们在瞬态吸收光谱实验中使用 100 kHz 中红外探针，使用光氧化剂对（菲和 1,4-二氰基苯）在皮秒至毫秒的时间尺度内跟踪乙腈-d(3) 中环己烷甲酸的脱羧。在 256 nm 处选择性激发菲可实现扩散限制的光诱导电子转移至 1,4-二氰基苯。测量的 CO2 副产物上升的时间偏移报告了溶液中反应性羧基自由基的寿命 (520 +/- 120 ns)，并且对羧基自由基的光谱观察证实了其作为反应中间体的形成。对活化的 C-C 键裂变原位产生的自由基的寿命进行精确计时将为提高光催化选择性和周转率铺平道路。
The photochemical decarboxylation of carboxylic acids is a versatile route to free radical intermediates for chemical synthesis. However, the sequential nature of this multi-step reaction renders the mechanism challenging to probe. Here, we employ a 100 kHz mid-infrared probe in a transient absorption spectroscopy experiment to track the decarboxylation of cyclohexanecarboxylic acid in acetonitrile-d(3) over picosecond to millisecond timescales using a photooxidant pair (phenanthrene and 1,4-dicyanobenzene). Selective excitation of phenanthrene at 256 nm enables a diffusion-limited photoinduced electron transfer to 1,4-dicyanobenzene. A measured time offset in the rise of the CO2 byproduct reports on the lifetime (520 +/- 120 ns) of a reactive carboxyl radical in solution, and spectroscopic observation of the carboxyl radical confirm its formation as a reaction intermediate. Precise clocking of the lifetimes of radicals generated in situ by an activated C-C bond fission will pave the way for improving the photocatalytic selectivity and turnover.