Homogeneous reduction of CO2 by photogenerated pyridinyl radicals.
Homogeneous reduction of CO2 by photogenerated pyridinyl radicals.
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DOI：
10.1021/jp509735z
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发表时间：
2015-05
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影响因子：
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通讯作者：
F. Riboni;E. Selli;Michael R. Hoffmann;A. Colussi
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文献类型：
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作者：
F. Riboni;E. Selli;Michael R. Hoffmann;A. Colussi
我们报道了在溶液中光生成的1-氢吡啶基自由基（1-PyH（•））在其2e（-）还原成羧酸的过程中与溶解的CO2发生反应。吡啶（Py）在1 atm CO2饱和的脱氧2- proh /H2O混合物中经254 nm激发得到一系列产物，其中电喷雾质谱法鉴定出Na(HCOO)2(-) （m/z(-) = 113）、C5H6NCOO(-) （m/z(-) = 124）和C5H10O2NCOO(-) （m/z(-) = 160）。这些产品明显含有羧酸官能，通过碰撞诱导解离分裂二氧化碳中性。我们推断1- pyh（•）[从(1)(3)Py* + 2-PrOH→1- pyh（•）+（•）PrOH]与自由基-自由基反应竞争，增加CO2，导致中间体反过来被（•）PrOH还原成观察到的物种。在该体系中羧酸盐的形成需要CO2、Py、2-PrOH和光化辐射，相当于由Py*引发的2-PrOH对CO2的均匀2e（-）还原。我们评估了速率常数(2)k2(1-PyH（•）+ CO2→（•）Py-1-COOH)≈O (10) M(-1) s（-1）和活化能E2≥9 kcal mol(-1)，与热化学估计相一致。
We report that 1-hydropyridinyl radicals (1-PyH(•)) photogenerated in solution react with dissolved CO2 en route to its 2e(-) reduction into carboxylic acids. The 254 nm excitation of pyridine (Py) in deaerated 2-PrOH/H2O mixtures saturated with 1 atm of CO2 yields a suite of products, among which we identified Na(HCOO)2(-) (m/z(-) = 113), C5H6NCOO(-) (m/z(-) = 124), and C5H10O2NCOO(-) (m/z(-) = 160) species by electrospray ionization mass spectrometry. These products demonstrably contain carboxylate functionalities that split CO2 neutrals via collisionally induced dissociation. We infer that 1-PyH(•) [from (1) (3)Py* + 2-PrOH → 1-PyH(•) + (•)PrOH] adds to CO2, in competition with radical-radical reactions, leading to intermediates that are in turn reduced by (•)PrOH into the observed species. The formation of carboxylates in this system, which is shown to require CO2, Py, 2-PrOH, and actinic radiation, amounts to the homogeneous 2e(-) reduction of CO2 by 2-PrOH initiated by Py*. We evaluate a rate constant (2) k2(1-PyH(•) + CO2 → (•)Py-1-COOH) ≈ O (10) M(-1) s(-1) and an activation energy E2 ≥ 9 kcal mol(-1) that are compatible with thermochemical estimates for this reaction.