112440-06-9Relevant academic research and scientific papers
Proton-deuteron exchange reactions of methyltrioxorhenium(VII) in organic solvents
Matsumoto, Mitsuru,Espenson, James H.
, p. 2780 - 2788 (2005)
Rate constants for the proton/deuteron (H/D) exchange of methyltrioxorhenium(VII) (MTO) were determined in four organic solvents by means of time course 1H NMR measurements. Exchange between MTO and a deuterium donor proceeds only in the presence of a Lewis base; the reaction does not take place in neutral or acidified solutions. The kinetics depends on the bases, deuterium donors, and solvents. The observed pseudo-first-order rate constants (kψ) are negligibly small when coordinating bases are used but increase with noncoordinating bases. A direct relationship was found between kψ and the pKa values of the conjugate acids of the bases. With phenol-d6 as a deuterium donor (D) and 2,6-lutidine as a base (B), the rate law varies with solvents: kψ = ka[D] [B] in benzene-d6 (ka = 1.95 × 10-3 kg2 mol-2 s-1); k ψ = kaκ[D][B]/(1 + κ[D]) in chloroform-d (kψ = 1.41 × 10-2 kg mol-1 s -1, κ = 0.79 kg mol-1); kψ = k a[B] in acetone-d6 and acetonitrile-d3 (k a = 1.22 × 10-2 and 3.87 × 10-2 kg mol-1 s-1, respectively) at 24.8°C. The same treatment applies to the methanol-d4/lutidine system in benzene-d6, once allowance is made for formation of an MTO-methanol adduct. Reasonably rapid exchange under mild conditions reflects the acidic character of MTO, which may arise from its base-promoted keto/enol tautomerization. Three consecutive steps are suggested for the reaction mechanism: attack of a base on an MTO methyl proton, isomerization to the enol intermediate (I2), and H/D exchange between I2 and a deuterium donor.
