C O M M U N I C A T I O N S
lowers the reaction barrier by 3.0 kcal/mol, most likely due to a
stabilization of the partial negative charge built up at the oxygen
atoms. We calculated the reaction to have an enthalpic barrier of
7.6 kcal/mol, giving an overall barrier of 13.2 kcal/mol relative to
selenious acid and (CO)5ReCH3. This is consistent with our
experimental ∆H‡ value of 8.0 ( 1.7 kcal/mol.16 For the overall
reaction from H2SeO3 and (CO)5ReCH3 we calculated an entropic
barrier of ∼4.4 kcal/mol (T∆S‡ ) -14.8 eu) (298 K), yielding a
∆G‡ of 17.6 kcal/mol at rt. This relatively large negative entropy
is consistent with the associative nature of the transition state.
In conclusion, we have identified a facile, catalytic OF route for
ReI-CH3 bonds with SeIV and iodine based O-atom donors. We
are exploring strategies to incorporate this reaction sequence into
catalytic cycles for the overall conversion of hydrocarbons to
alcohols utilizing low-valent, weakly electrophilic transition metals
for C-H bond activation.17
Acknowledgment. We thank Chevron Company and Scripps
Florida for financial support, Prof. William C. Kaska for helpful
suggestions, and Ariana Nussdorf for work on kinetic analysis. M.A.
acknowledges The Knut and Alice Wallenberg Foundation. This work
was supported by a fellowship within the Postdoc-Programme of the
German Academic Exchange Service (DAAD) supporting C.H.H.
Supporting Information Available: Synthetic procedures, experi-
mental and computational details. This material is available free of
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Figure 1. Proposed mechanism for methyl transfer to H2SeO3.
A scan of the intrinsic reaction coordinate (IRC) shows that the
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kcal/mol. Interestingly, we found that rearrangement to the S-methyl-
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Figure 2. Transition state (top left) and snapshot views from the IRC of
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(15) (a) All calculations were performed using the B3LYP hybrid density
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(16) We believe that part of the discrepancy between the experimental and
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contributions from solvent rearrangement.
Figure 3. Solvent (MeCN) optimized transition states for O-atom transfer
and H2O attack.
(17) There have been several recent examples of Re mediated C-H activation.
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Organometallics 2007, 26, 1505.
The direct O-atom transfer between CH3SeIV(O)OH and IO4- to
generate CH3SeVI(O)2OH has an activation free energy of 24 kcal/
mol, relative to the methyl SeIV intermediate, which is consistent with
the need to heat the reaction to 100 °C for several hours to give
methanol (Figure 3). Selenium oxidation is most likely followed by
SN2 attack of the CH3SeVI bond by water (∆G‡ ) 18 kcal/mol). An
alternative pathway without Se oxidation via a Baeyer-Villiger type
mechanism has a large activation barrier (∆G‡ ) 53 kcal/mol).
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