Investigation of the [Cp*Mo(PMe3)3H]n+ (n = 0, 1) Redox Pair: Dynamic Processes on Very Different Time Scales

详细信息    查看全文

• 作者：Miguel Baya ; Pavel A. Dub ; Jennifer Houghton ; Jean-Claude Daran ; Natalia V. Belkova ; Elena S. Shubina ; Lina M. Epstein ; Agustí ; Lledó ; s ; Rinaldo Poli
• 刊名：Inorganic Chemistry
• 出版年：2009
• 出版时间：January 5, 2009
• 年：2009
• 卷：48
• 期：1
• 页码：209-220
• 全文大小：404K
• 年卷期：v.48,no.1(January 5, 2009)
• ISSN：1520-510X

文摘

The compound [Cp*Mo(PMe₃)₃H] (1) is reversibly oxidized at E_1/2 = −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.