Isolation and Study of Ruthenium–Cobalt Oxo Cubanes Bearing a High-Valent, Terminal RuV–Oxo with Significant Oxyl Radical Character

High-valent RuV–oxo intermediates have
long been
proposed in catalytic oxidation chemistry, but investigations into
their electronic and chemical properties have been limited due to
their reactive nature and rarity. The incorporation of Ru into the
[Co3O4] subcluster via the single-step assembly
reaction of CoII(OAc)2(H2O)4 (OAc = acetate), perruthenate (RuO4–), and pyridine (py) yielded an unprecedented Ru­(O)­Co3(μ3-O)4(OAc)4(py)3 cubane featuring an isolable, yet reactive, RuV–oxo
moiety. EPR, ENDOR, and DFT studies reveal a valence-localized [RuV(S = 1/2)CoIII3(S = 0)O4] configuration
and non-negligible covalency in the cubane core. Significant oxyl
radical character in the RuV–oxo unit is experimentally
demonstrated by radical coupling reactions between the oxo cubane
and both 2,4,6-tri-tert-butylphenoxyl and trityl
radicals. The oxo cubane oxidizes organic substrates and, notably,
reacts with water to form an isolable μ-oxo bis-cubane complex
[(py)3(OAc)4Co3(μ3-O)4Ru]–O–[RuCo3(μ3-O)4(OAc)4(py)3]. Redox activity
of the RuV–oxo fragment is easily tuned by the electron-donating
ability of the distal pyridyl ligand set at the Co sites demonstrating
strong electronic communication throughout the entire cubane cluster.
Natural bond orbital calculations reveal cooperative orbital interactions
of the [Co3O4] unit in supporting the RuV–oxo moiety via a strong π-electron donation.

高氧化态的RuV-oxo中间体在催化氧化化学中早已被提出，然而，由于它们的反应活性和稀有性，对其电子和化学性质的探究一直受限。通过一步法将Ru整合至[Co3O4]亚簇中，即使用CoII(OAc)2(H2O)4（OAc代表乙酸根）、过钌酸盐（RuO4–）和吡啶（py）的组装反应，获得了一种前所未有的Ru(O)Co3(μ3-O)4(OAc)4(py)3立方烷，其中包含一个可分离但仍具有反应活性的RuV-oxo基团。电子顺磁共振（EPR）、电子核双共振（ENDOR）和密度泛函理论（DFT）研究表明，立方烷核心中存在一个价态局域的[RuV(S = 1/2)CoIII3(S = 0)O4]配置以及不可忽视的共价性。通过实验证明，RuV-oxo单元中存在显著的氧自由基特征，这是通过氧化立方烷与2,4,6-三叔丁基苯氧基自由基和三苯甲基自由基之间的自由基偶合反应所证实。氧化立方烷可以氧化有机底物，并且特别地，与水反应生成一个可分离的μ-oxo双立方烷复合物[(py)3(OAc)4Co3(μ3-O)4Ru]–O–[RuCo3(μ3-O)4(OAc)4(py)3]。通过调节远端吡啶配体在Co位点的电子给予能力，可以轻松地调节RuV-oxo片段的氧化还原活性，这在整个立方烷簇中表现出强烈的电子通信。自然键轨道计算揭示了[Co3O4]单元通过强烈的π电子捐赠，协同支持RuV-oxo基团。