Mechanistic study of the photo‐generation of hydrogen by decamethylruthenocene

Hydrogen evolution by decamethylruthenocene (Cp*2RuII) was studied in detail highlighting that metallocenes are capable of photo‐reducing hydrogen without the need of an additional sensitizer. Electrochemical, gas chromatographic and spectroscopic (UV/vis, 1H and 13C NMR) measurements corroborated by density functional theory (DFT) calculations indicate that the production of hydrogen occurs by a two‐step process. First, the decamethylruthenocene hydride ([Cp*2RuIV(H)]+) is formed in the presence of an organic acid. Subsequently, [Cp*2RuIV(H)]+ is reversibly reduced via a heterolytic reaction with one‐photon excitation leading to a first release of hydrogen. Thereafter, the resultant decamethylruthenocenium ion ([Cp*2RuIII]+) is further reduced leading to a second release of hydrogen by deprotonation of a methyl group of [Cp*2RuIII]+. Experimental and computational data show the spontaneous conversion of [Cp*2RuII] to [Cp*2RuIV(H)]+ in the presence of protons. Calculations highlight that the first reduction is endergonic (ΔG0 = 108 kJ·mol−1) and needs an input of energy by light for the reaction to occur. The hydricity of the methyl protons of [Cp*2RuII] was also considered.


Published in:
Chemistry – A European Journal
Year:
2019
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 Record created 2019-07-15, last modified 2019-07-15


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