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Electrochemical and Theoretical Investigations of the Role of the Appended Base on the Reduction of Protons by [Fe 2 (CO) 4 (κ 2 ‐PNP R )(μ‐S(CH 2 ) 3 S] (PNP R ={Ph 2 PCH 2 } 2 NR, R=Me, Ph)
Author(s) -
Lounissi Sondes,
Zampella Giuseppe,
Capon JeanFrançois,
De Gioia Luca,
Matoussi Fatma,
Mahfoudhi Sélim,
Pétillon François Y.,
Schollhammer Philippe,
Talarmin Jean
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201201087
Subject(s) - protonation , chemistry , hydride , amine gas treating , redox , substituent , metal , electrochemistry , ligand (biochemistry) , proton affinity , medicinal chemistry , proton , crystallography , stereochemistry , inorganic chemistry , ion , organic chemistry , biochemistry , physics , receptor , electrode , quantum mechanics
The behavior of [Fe 2 (CO) 4 (κ 2 ‐PNP R )(μ‐pdt)] (PNP R =(Ph 2 PCH 2 ) 2 NR, R=Me ( 1 ), Ph ( 2 ); pdt=S(CH 2 ) 3 S) in the presence of acids is investigated experimentally and theoretically (using density functional theory) in order to determine the mechanisms of the proton reduction steps supported by these complexes, and to assess the role of the PNP R appended base in these processes for different redox states of the metal centers. The nature of the R substituent of the nitrogen base does not substantially affect the course of the protonation of the neutral complex by CF 3 SO 3 H or CH 3 SO 3 H; the cation with a bridging hydride ligand, 1 μH + (R=Me) or 2 μH + (R=Ph) is obtained rapidly. Only 1 μH + can be protonated at the nitrogen atom of the PNP chelate by HBF 4 ⋅Et 2 O or CF 3 SO 3 H, which results in a positive shift of the proton reduction by approximately 0.15 V. The theoretical study demonstrates that in this process, dihydrogen can be released from a η 2 ‐H 2 species in the Fe I Fe II state. When R=Ph, the bridging hydride cation 2 μH + cannot be protonated at the amine function by HBF 4 ⋅Et 2 O or CF 3 SO 3 H, and protonation at the N atom of the one‐electron reduced analogue is also less favored than that of a S atom of the partially de‐coordinated dithiolate bridge. In this situation, proton reduction occurs at the potential of the bridging hydride cation, 2 μH + . The rate constants of the overall proton reduction processes are small for both complexes 1 and 2 ( k obs ≈4–7 s −1 ) because of the slow intramolecular proton migration and H 2 release steps identified by the theoretical study.