Baya Miguel, Dub Pavel A, Houghton Jennifer, Daran Jean-Claude, Belkova Natalia V, Shubina Elena S, Epstein Lina M, Lledós Agustí, Poli Rinaldo
LCC (Laboratoire de Chimie de Coordination), CNRS, 205 route de Narbonne, F-31077 Toulouse, France.
Inorg Chem. 2009 Jan 5;48(1):209-20. doi: 10.1021/ic801676n.
The compound [CpMo(PMe3)3H] (1) is reversibly oxidized at E1/2 = -1.40 V vs ferrocene in MeCN. Its oxidation with Cp2FePF6 yields thermally stable [CpMo(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 DeltaH++ = 11.7(3) kcal mol-1 and DeltaS++ = -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 v(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 DeltaH++ = 9.3(1) kcal/mol and DeltaS++ = -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.
化合物[CpMo(PMe₃)₃H]（1）在乙腈中相对于二茂铁在E₁/₂ = -1.40 V处可被可逆氧化。它与Cp₂FePF₆发生氧化反应生成热稳定的[CpMo(PMe₃)₃H]PF₆（2），该产物已通过红外光谱、电子顺磁共振光谱和单晶X射线衍射进行了分离和表征。1的¹H和³¹P核磁共振谱在低温下显示两种类型的PMe₃配体，比例为1:2，但在室温下只有一个平均信号，该交换过程的活化参数为ΔH⁺⁺ = 11.7(3) kcal/mol和ΔS⁺⁺ = -3(1) eu。尽管通过核磁共振（NMR）对1和通过电子顺磁共振（EPR）对2仅证明有一种物质，但每个配合物的溶液红外光谱在v(Mo - H)区域显示出两个谱带（1，主要在1794 cm⁻¹，次要在约1730 cm⁻¹；2，约1800和1770 cm⁻¹，强度大致相等），其位置和相对强度几乎不依赖于溶剂。一项全面的密度泛函理论（DFT）研究表明，这些是不同的旋转异构体，涉及这些配合物中Cp环和PMe₃配体的不同相对取向。这种环旋转过程在核磁共振和电子顺磁共振时间尺度上非常快，但在红外时间尺度上很慢。X射线数据和理论计算表明化合物2中存在弱的Mo - H...F相互作用。实验和计算研究排除了1和2中PMe₃解离以及其他分子内重排的可能性。1的质子化产生[CpMo(PMe₃)₃H₂]⁺（3），这也揭示了在核磁共振时间尺度上两种不等价的H配体和三个PMe₃配体（在冷冻结构中两组比例为1:2）相互转化的动态过程（活化参数为ΔH⁺⁺ = 9.3(1) kcal/mol和ΔS⁺⁺ = -4.1(4) eu）。一项DFT研究表明，这种交换过程通过低能量对称二氢化物中间体发生，而不是通过二氢配合物。
