Photocatalytic Monofluorination of Benzene by Fluoride via Photoinduced Electron Transfer with 3-Cyano-1-methylquinolinium
Photocatalytic Monofluorination of Benzene by Fluoride via Photoinduced Electron Transfer with 3-Cyano-1-methylquinolinium
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DOI：
10.1021/jp408315a
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发表时间：
2013-10-17
影响因子：
2.9
通讯作者：
Fukuzumi, Shunichi
中科院分区：
文献类型：
--
作者：
Ohkubo, Kei;Fujimoto, Atsushi;Fukuzumi, Shunichi
苯的光催化氟化发生在含苯和四乙基氟化铵四氢氟化物（TEAF.4HF）的3-氰基-1-甲基喹啉离子（QuCN(+)）的氧饱和乙腈（MeCN）光照射下，氙灯（500 W）连接有色玻璃滤光片（λ < 290 nm），产生氟苯和过氧化氢。生成氟苯的量子产率为6%。采用纳秒激光闪光光解实验阐明了光催化氟化的机理。QuCN（+）和苯脱气的MeCN溶液在355nm处被纳秒激光激发后的瞬态吸收光谱显示出由于QuCN（中心点）（λ (max) = 500 nm）和苯二聚体自由基阳离子（λ (max) = 900 nm）的吸收带，这些吸收带是由光诱导电子从苯转移到QuCN（+）的单线态而产生的。TEAF.4HF的加入加速了苯二聚体自由基阳离子引起的瞬态吸收带的衰减速率。观察到的速率常数随着TEAF.4HF浓度的增加而增大。亲电加成的速率常数。测定了氟对苯自由基阳离子的影响为9.4 X 10(9) M-1 s（-1）。因此，光催化反应是由分子间光诱导电子从苯转移到QuCN（+）的单激发态引发的。由光诱导电子转移形成的苯自由基阳离子与氟阴离子反应生成f -加合自由基。而QuCN（中心点）可以将O-2还原为O-2（中心点-），然后将O-2（中心点-）质子化生成HO2中心点。f -加合自由基中HO2中心点的抽氢得到最终产物氟苯和H2O2。
The photocatalytic fluorination of benzene occurs under photoirradiation of an oxygen-saturated acetonitrile (MeCN) of the 3-cyano-1-methylquinolinium ion (QuCN(+)) containing benzene and tetraethylammonium fluoride tetrahydrofluoride (TEAF.4HF) with a xenon lamp (500 W) attached to a colored-glass filter (lambda < 290 nm) to yield fluorobenzene and hydrogen peroxide. The quantum yield of formation of fluorobenzene was 6%. Nanosecond laser flash photolysis measurements were performed to elucidate the mechanistic details for photocatalytic fluorination. Transient absorption spectra taken after the nanosecond laser excitation at 355 nm of a degassed MeCN solution of QuCN(+) and benzene exhibited absorption bands due to QuCN(center dot) (lambda(max) = 500 nm) and the benzene dimer radical cation (lambda(max) = 900 nm), which were generated by photoinduced electron transfer from benzene to the singlet excited state of QuCN(+). The decay rate of the transient absorption band due to the benzene dimer radical cation was accelerated by the addition of TEAF.4HF. The observed rate constant increased with increasing concentration of TEAF.4HF. The rate constant of the electrophilic addition of. fluoride to the benzene radical cation was determined to be 9.4 X 10(9) M-1 s(-1). Thus, the photocatalytic reaction is initiated by intermolecular photoinduced electron transfer from benzene to the single excited state of QuCN(+). The benzene radical cation formed by photoinduced electron transfer reacts with the fluoride anion to yield the F-adducted radical. However, QuCN(center dot) can reduce O-2 to O-2(center dot-), and this is followed by the protonation of O-2(center dot-) to afford HO2 center dot. The hydrogen abstraction of HO2 center dot from the F-adduct radical affords fluorobenzene and H2O2 as the final products.