Highly reactive porphyrin-iron-oxo derivatives produced by photolyses of metastable porphyrin-iron(IV) diperchlorates.
Highly reactive porphyrin-iron-oxo derivatives produced by photolyses of metastable porphyrin-iron(IV) diperchlorates.
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DOI：
10.1021/ja807847q
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发表时间：
2009-02-25
影响因子：
15
通讯作者：
Newcomb M
中科院分区：
文献类型：
--
作者：
Pan Z;Wang Q;Sheng X;Horner JH;Newcomb M
亚稳态卟啉铁（IV）二高氯酸盐在激光闪光光解反应的光解得到了高度反应性的瞬态。所研究的体系为5，10，15，20-四苯基卟啉（TPP）、5，10，15，20-四均三甲苯基卟啉（TMP）和2，3，7，8，12，13，17，18-八乙基卟啉（OEP）。新的物种，在乙腈溶液中在几毫秒内衰减，被证明与有机底物反应的氧代转移反应，涉及插入到烯烃和苯乙烯的碳碳双键或芳烃的苄基碳-氢键。反应活性顺序为OEP > TPP > TMP。在22°C下，测定了与几种底物反应的二级速率常数; TPP衍生物的速率常数的代表性值为k = 8.6 × 105 M−1 s−1（苯乙烯），k = 2.5 × 106 M−1 s−1（环己烯），k = 7.7 × 104 M−1 s−1（环己烯）。这些卟啉-铁-氧代瞬变反应比相应的铁（IV）-氧代卟啉自由基阳离子快4至5个数量级，其速率常数与卟啉-锰（V）-氧代衍生物的速率常数相似。芳烃的苄基C-H位置氧化的速率常数与C-H键离解能相关，与取代苯乙烯反应的Hammett相关性的ρ+值范围为−0.5至−0.7，反映了氧化剂的亲电特性和高反应活性。基于其独特的紫外-可见光谱、高反应活性和氧代转移性质，新的瞬变产物被初步鉴定为卟啉-铁（V）-氧代高氯酸盐，众所周知的铁（IV）-氧代卟啉自由基阳离子的电子异构体（或价互变异构体）。
Photolyses of metastable porphyrin-iron(IV) diperchlorates in laser flash photolysis reactions gave highly reactive transients. The systems studied were 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetramesitylporphyrin (TMP), and 2,3,7,8,12,13,17,18-octaethylporphyrin (OEP). The new species, which decayed within milliseconds in acetonitrile solutions, were shown to react with organic substrates by oxo-transfer reactions involving insertions into carbon-carbon double bonds of alkenes and styrenes or benzylic carbon-hydrogen bonds of arenes. The order of reactivity was OEP > TPP > TMP. Second-order rate constants for reactions with several substrates at 22°C were determined; representative values of rate constants for the TPP derivative were k = 8.6 × 105 M−1 s−1 for styrene, k = 2.5 × 106 M−1 s−1 for cyclohexene, and k = 7.7 × 104 M−1 s−1 for ethylbenzene. These porphyrin-iron-oxo transients reacted 4 to 5 orders of magnitude faster than the corresponding iron(IV)-oxo porphyrin radical cations with rate constants similar to those of porphyrin-manganese(V)-oxo derivatives. Rate constants for oxidations of benzylic C-H positions of arenes correlated with the C-H bond dissociation energies, and Hammett correlations for reactions with substituted styrenes had ρ+ values ranging from −0.5 to −0.7 reflecting electrophilic character of the oxidants and their high reactivity. On the basis of their unique UV-visible spectra, high reactivities, and oxo-transfer properties, the new transients are tentatively identified as porphyrin-iron(V)-oxo perchlorates, electronic isomers (or valence tautomers) of well known iron(IV)-oxo porphyrin radical cations.
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影响因子：
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作者：
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作者：
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