Barats-Damatov Delina, Shimon Linda J W, Weiner Lev, Schreiber Roy E, Jiménez-Lozano Pablo, Poblet Josep M, de Graaf Coen, Neumann Ronny
Department of Organic Chemistry, Weizmann Institute of Science , Rehovot, Israel , 76100.
Inorg Chem. 2014 Feb 3;53(3):1779-87. doi: 10.1021/ic402962c. Epub 2014 Jan 17.
High-valent oxo compounds of transition metals are often implicated as active species in oxygenation of hydrocarbons through carbon-hydrogen bond activation or oxygen transfer and also in water oxidation. Recently, several examples of cobalt-catalyzed water oxidation have been reported, and cobalt(IV) species have been suggested as active intermediates. A reactive species, formally a dicobalt(IV)-μ-oxo polyoxometalate compound (α2-P2W17O61Co)2O, [(POMCo)2O], has now been isolated and characterized by the oxidation of a monomeric α2-P2W17O61Co(II)(H2O), [POMCo(II)H2O], with ozone in water. The crystal structure shows a nearly linear Co-O-Co moiety with a Co-O bond length of ∼1.77 Å. In aqueous solution [(POMCo)2O] was identified by (31)P NMR, Raman, and UV-vis spectroscopy. Reactivity studies showed that [(POMCo)2O]2O] is an active compound for the oxidation of H2O to O2, direct oxygen transfer to water-soluble sulfoxides and phosphines, indirect epoxidation of alkenes via a Mn porphyrin, and the selective oxidation of alcohols by carbon-hydrogen bond activation. The latter appears to occur via a hydrogen atom transfer mechanism. Density functional and CASSCF calculations strongly indicate that the electronic structure of [(POMCo)2O]2O] is best defined as a compound having two cobalt(III) atoms with two oxidized oxygen atoms.
过渡金属的高价含氧化合物常被认为是通过碳氢键活化或氧转移实现碳氢化合物氧化以及水氧化过程中的活性物种。最近，已有几例钴催化水氧化的报道，并提出钴（IV）物种为活性中间体。现在，一种活性物种，即一种二钴（IV）-μ-氧代多金属氧酸盐化合物(α2-P2W17O61Co)2O，[(POMCo)2O]，已通过在水中用臭氧氧化单体α2-P2W17O61Co(II)(H2O)，[POMCo(II)H2O]而被分离和表征。晶体结构显示出一个近乎线性的Co-O-Co部分，Co-O键长约为1.77 Å。在水溶液中，[(POMCo)2O]通过（31）P NMR、拉曼光谱和紫外可见光谱得以鉴定。反应性研究表明，[(POMCo)2O]是一种活性化合物，可用于将H2O氧化为O2、将氧直接转移至水溶性亚砜和膦、通过锰卟啉间接环氧化烯烃以及通过碳氢键活化选择性氧化醇类。后者似乎是通过氢原子转移机制发生的。密度泛函和CASSCF计算有力地表明，[(POMCo)2O]的电子结构最好定义为一种具有两个钴（III）原子和两个氧化态氧原子的化合物。
