Cheng, Mu-Jeng and Nielsen, Robert J. and Ahlquist, Mårten and Goddard, William A., III (2010) Carbon−Oxygen Bond Forming Mechanisms in Rhenium Oxo-Alkyl Complexes. Organometallics, 29 (9). pp. 2026-2033. ISSN 0276-7333 http://resolver.caltech.edu/CaltechAUTHORS:20100524-150452201
- Published Version
See Usage Policy.
- Supplemental Material
See Usage Policy.
Use this Persistent URL to link to this item: http://resolver.caltech.edu/CaltechAUTHORS:20100524-150452201
Three C−X bond formation mechanisms observed in the oxidation of (HBpz_3)ReO(R)(OTf) [HBpz_3 = hydrotris(1-pyrazolyl)borate; R = Me, Et, and iPr; OTf = OSO_2CF_3] by dimethyl sulfoxide (DMSO) were investigated using quantum mechanics (M06//B3LYP DFT) combined with solvation (using the PBF Poisson−Boltzmann polarizable continuum solvent model). For R = Et we find the alkyl group is activated through α-hydrogen abstraction by external base OTf^− with a free energy barrier of only 12.0 kcal/mol, leading to formation of acetaldehyde. Alternatively, ethyl migration across the M═O bond (leading to the formation of acetaldehyde and ethanol) poses a free energy barrier of 22.1 kcal/mol, and the previously proposed α-hydrogen transfer to oxo (a 2+2 forbidden reaction) poses a barrier of 44.9 kcal/mol. The rate-determining step to formation of the final product acetaldehyde is an oxygen atom transfer from DMSO to the ethylidene, with a free energy barrier of 15.3 kcal/mol. When R = iPr, the alkyl 1,2-migration pathway becomes the more favorable pathway (both kinetically and thermodynamically), with a free energy barrier (ΔG^‡ = 11.8 kcal/mol) lower than α-hydrogen abstraction by OTf^− (ΔG^‡ = 13.5 kcal/mol). This suggests the feasibility of utilizing this type of migration to functionalize M−R to M−OR. We also considered the nucleophilic attack of water and ammonia on the Re-ethylidene α-carbon as a means of recovering two-electron-oxidized products from an alkane oxidation. Nucleophilic attack (with internal deprotonation of the nucleophile) is exothermic. However, the subsequent protonolysis of the Re−alkyl bond (to liberate an alcohol or amine) poses a barrier of 37.0 or 42.4 kcal/mol, respectively. Where comparisons are possible, calculated free energies agree very well with experimental measurements.
|Additional Information:||© 2010 American Chemical Society. Received October 9, 2009. Publication Date (Web): April 7, 2010. This work was supported partially by Chevron Energy Technology Company and by the Center for Catalytic Hydrocarbon Functionalization, an Energy Frontier Research Center (DOE DE-SC000- 1298). Computer resources were funded from grants from ARO-DURIP and ONR-DURIP.|
|Official Citation:||Carbon−Oxygen Bond Forming Mechanisms in Rhenium Oxo-Alkyl Complexes Mu-Jeng Cheng, Robert J. Nielsen, Mrten Ahlquist, William A. Goddard III Organometallics 2010 29 (9), 2026-2033|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||25 May 2010 15:06|
|Last Modified:||26 Dec 2012 12:04|
Repository Staff Only: item control page