188550-32-5

Upstream product

• 204858-71-9 [Cp*Mo(H)3(dppe)](+) 
• 75-05-8 acetonitrile 
• 177342-86-8 [Cp*Mo(H)3(dppe)] 

Relevant academic research and scientific papers

Electrochemical and DFT studies of the oxidative decomposition of the trihydride complexes Cp*M(dppe)H3 (M = Mo, W) in acetonitrile

A detailed electrochemical study of the oxidative decomposition of the trihydride complexes Cp*M(dppe)H3 (M = Mo, W) in acetonitrile is presented. For the Mo complex, the decomposition occurs by four different pathways involving classical and non-classical tautomers, whereas only the classical form is accessible for the W derivative. Each of the decomposition pathways has been quantitatively assessed by analyses of the linear sweep voltammograms. In addition to the previously established (B. Pleune, D. Morales, R. Meunier-Prest, P. Richard, E. Collange, J. C. Fettinger and R. Poli, J. Am. Chem. Soc., 1999, 121, 2209-2225) deprotonation, disproportionation, and H 2 reductive elimination occurring via the non-classical tautomer of the 17-electron complex [Cp*Mo(dppe)H3]+ (obtained by oxidation at E1/2 = -0.33 V vs. Ag/AgCl), a new decomposition pathway from the more stable classical tautomer has been identified following a second oxidation process. In addition, the oxidatively induced H2 reductive elimination, previously evidenced only in THF or CH2Cl 2, has been quantitatively assessed in MeCN. This process occurs preferentially by an associative mechanism (k = 0.020(4) M-1s -1) via the 19-electron [Cp*Mo(dppe)H(H2)(MeCN)] + intermediate and is therefore in direct competition with the disproportionation mechanism. The resulting 17-electron [Cp*Mo(dppe) H(MeCN)]+ product is further oxidized at ca. 0.2 V. The oxidation of [Cp*Mo(dppe)H3]+ occurs at ca. 1.0 V and the resulting 16-electron [Cp*Mo(dppe)H3]2+ complex immediately delivers a proton to the starting material, giving [Cp*Mo(dppe)H4]+ and [Cp*Mo(dppe)H 2]+. The latter coordinates MeCN in a rate determining step to afford [Cp*Mo(dppe)H2(MeCN)]+. The mechanistic details are consistent with studies at different scan rates and different MeCN concentrations, and are backed up by DFT calculations. the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006.

Stable paramagnetic half-sandwich Mo(V) and W(V) polyhydride complexes. Structural, spectroscopic, electrochemical, theoretical, and decomposition mechanism studies of [CP*MH3(dppe)]+ (M = Mo, W)

Compounds Cp*MH3(dppe) (M = Mo, 1; W, 2) are oxidized chemically and electrochemically to the corresponding 17-electron cations 1+ and 2+. Analogous oxidations of 1-d3 and 2-d3 provide 1+-d3 and 2+-d3, respectively. Complex 2+ is stable in CH2Cl2, THF, and MeCN at room temperature. A single-crystal X-ray analysis of the PF6- salt of 2+ shows a geometry for the cation which is intermediate between octahedral and trigonal prismatic, which is reproduced by geometry optimization of the [CpWH3(PH2CH2CH2PH 2)]+ model at the B3LYP/LANL2DZ level. Identical calculations on the neutral analogue also reproduce the previously reported trigonal prismatic structure for 1. A blue shift in the M-H stretching vibrations upon oxidation for both Mo and W compounds indicates that a M-H bond strengthening accompanies the oxidation process. The DFT calculations (M-H bond lengths, BDE, and stretching frequencies) are in good agreement with the experimental results. Complex 1+ decomposes in solution at room temperature by one or more of three different mechanisms depending on conditions: H2 reductive elimination, solvent-assisted disproportionation, or deprotonation. In THF or CH2Cl2, a reductive elimination of H2 affords the stable paramagnetic monohydride Cp*MoH(dppe)PF6 (3), which adds a molecule of solvent in CH2Cl2, THF, and MeCN. EPR studies show that the CH2Cl2 molecule coordinates in a bidentate mode to afford a 19-electron configuration. A solvent dependence of the decomposition rate [A(CH2Cl2) ≈ 7.8k(THF) at 0 °C] and an inverse isotope effect [kH/kD = 0.50(3) in CH2Cl2 at O °C] indicate the nature of 1+ as a classical trihydride and suggest a decomposition mechanism which involves equilibrium conversion to a nonclassical intermediate followed by a rate-determining associative exchange of H2 with a solvent molecule. In MeCN at 20 °C, a solvent-assisted disproportionation (rate = Kdisp[1+]2, kdisp = 3.98(9) × 103 s-1 M-1) and a deprotonation by residual unoxidized 1 (rate = kdeprot[1+][1], kdeprot = 2.8(2) × 102 s-1 M-1) take place competitively, as shown by detailed cyclic voltammetric and thin-layer cyclic voltammetric studies. The stoichiometric chemical oxidation of 1 in MeCN leads to a mixture of [Cp*MoH2(dppe)(MeCN)]+ and [Cp*MoH(dppe)(MeCN)2]2+ by the disproportionation mechanism.