New Rh2(II,II) Architecture for the Catalytic Reduction of H+

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• 作者：Travis A. White ; Suzanne E. Witt ; Zhanyong Li ; Kim R. Dunbar ; Claudia Turro
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：October 19, 2015
• 年：2015
• 卷：54
• 期：20
• 页码：10042-10048
• 全文大小：475K
• ISSN：1520-510X

文摘

Formamidinate-bridged Rh₂^II,II complexes containing diimine ligands of the formula cis-[Rh₂^II,II(渭-DTolF)₂(NN)₂]²⁺ (Rh₂-NN₂), where DTolF = p-ditolylformamidinate and NN = dppn (benzo[i]dipyrido[3,2-a:2鈥?3鈥?h]quinoxaline), dppz (dipyrido[3,2-a:2鈥?3鈥?c]phenazine), and phen (1,10-phenanthroline), electrocatalytically reduce H⁺ to H₂ in DMF solutions containing CH₃COOH at a glassy carbon electrode. Cathodic scans in the absence of acid display a Rh^III,II/II,II reduction at 鈭?.90 V vs Fc⁺/Fc followed by NN^{0/鈥?/sup> reduction at 鈭?.13, 鈭?.36, and 鈭?.65 V for Rh₂-dppn₂, Rh₂-dppz₂, and Rh₂-phen₂, respectively. Upon the addition of acid, Rh₂-dppn₂ and Rh₂-dppz₂ undergo reduction鈥損rotonation鈥搑eduction at each pyrazine-containing NN ligand prior to the Rh₂II,II/II,I reduction. The Rh₂II,I species is then protonated at one of the metal centers, resulting in the formation of the corresponding Rh₂II,III-hydride. In the case of Rh₂-phen₂, the reduction of the phen ligand is followed by intramolecular electron transfer to the Rh₂II,II core in the presence of protons to form a Rh₂II,III-hydride species. Further reduction and protonation at the Rh₂ core for all three complexes rapidly catalyzes H₂ formation with varied calculated turnover frequencies (TOF) and overpotential values (畏): 2.6 脳 104 s鈥? and 0.56 V for Rh₂-dppn, 2.8 脳 104 s鈥? and 0.50 V for Rh₂-dppz₂, and 5.9 脳 104 s鈥? and 0.64 V for Rh₂-phen₂. Bulk electrolysis confirmed H₂ formation, and further CH₃COOH addition regenerates H₂ production, attesting to the robust nature of the architecture. The cis-[Rh₂II,II(渭-DTolF)₂(NN)₂]2+ architecture benefits by combining electron-rich formamidinate bridges, a redox-active Rh₂II,II core, and electron-accepting NN diimine ligands to allow for the electrocatalysis of H+ substrate to H₂ fuel.}