Investigation of the [Cp*Mo(PMe 3 ) 3 H] n + ( n = 0, 1) Redox Pair: Dynamic Processes on Very Different Time Scales - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Inorganic Chemistry Année : 2009

Investigation of the [Cp*Mo(PMe 3 ) 3 H] n + ( n = 0, 1) Redox Pair: Dynamic Processes on Very Different Time Scales

Résumé

The compound [Cp*Mo(PMe3)3H] (1) is reversibly oxidized at E1/2 = −1.40 V vs ferrocene in MeCN. Its oxidation with Cp2FePF6 yields thermally stable [Cp*Mo(PMe3)3H]PF6 (2), which has been isolated and characterized by IR and EPR spectroscopy and by single-crystal X-ray diffraction. The 1H and 31P NMR spectra of 1 show two types of PMe3 ligands in a 1:2 ratio at low temperature, but only one average signal at room temperature, with activation parameters of ΔH⧧ = 11.7(3) kcal mol−1 and ΔS⧧ = −3(1) eu for the exchange process. Although only one species is evidenced by NMR for 1 and by EPR for 2, the solution IR spectra of each complex show two bands in the ν(Mo−H) region (1, major at 1794 cm−1 and minor at ca. 1730 cm−1; 2, ca. 1800 and 1770 cm−1 with approximately equal intensity), the position and relative intensity being little dependent on the solvent. A thorough DFT investigation suggests that these are different rotamers involving different relative orientations of the Cp* ring and the PMe3 ligands in these complexes. This ring rotation process is very rapid on the NMR and EPR time scale but slow on the IR time scale. The X-ray data and the theoretical calculations suggest the presence of weak Mo−H···F interactions in compound 2. The possibility of PMe3 dissociation, as well as other intramolecular rearrangements, for 1 and 2 is excluded by experimental and computational studies. Protonation of 1 yields [Cp*Mo(PMe3)3H2]+ (3), which also reveals a dynamic process interconverting the two inequivalent H ligands and the three PMe3 ligands (two sets in a 1:2 ratio in the frozen structure) on the NMR time scale (activation parameters of ΔH⧧ = 9.3(1) kcal/mol and ΔS⧧ = −4.1(4) eu). A DFT study suggests that this exchange process occurs via a low-energy symmetric dihydride intermediate and not through a dihydrogen complex.
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hal-03184647 , version 1 (29-03-2021)

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Miguel Baya, Pavel Dub, Jennifer Houghton, Jean-Claude Daran, Natalia V Belkova, et al.. Investigation of the [Cp*Mo(PMe 3 ) 3 H] n + ( n = 0, 1) Redox Pair: Dynamic Processes on Very Different Time Scales. Inorganic Chemistry, 2009, 48 (1), pp.209-220. ⟨10.1021/ic801676n⟩. ⟨hal-03184647⟩
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