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Title: Conjugation-Driven “Reverse Mars–van Krevelen”-Type Radical Mechanism for Low-Temperature C–O Bond Activation

 [1];  [1]
  1. Department of Chemical and Biomolecular Engineering, Catalysis Center for Energy Innovation, University of Delaware, Newark, Delaware 19716, United States
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Catalysis Center for Energy Innovation (CCEI)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of the American Chemical Society; Journal Volume: 138; Journal Issue: 26; Related Information: CCEI partners with the University of Delaware (lead); Brookhaven National Laboratory; California Institute of Technology; Columbia University; University of Delaware; Lehigh University; University of Massachusetts, Amherst; Massachusetts Institute of Technology; University of Minnesota; Pacific Northwest National Laboratory; University of Pennsylvania; Princeton University; Rutgers University
Country of Publication:
United States
catalysis (homogeneous), catalysis (heterogeneous), biofuels (including algae and biomass), bio-inspired, hydrogen and fuel cells, materials and chemistry by design, synthesis (novel materials), synthesis (self-assembly), synthesis (scalable processing)

Citation Formats

Mironenko, Alexander V., and Vlachos, Dionisios G. Conjugation-Driven “Reverse Mars–van Krevelen”-Type Radical Mechanism for Low-Temperature C–O Bond Activation. United States: N. p., 2016. Web. doi:10.1021/jacs.6b02871.
Mironenko, Alexander V., & Vlachos, Dionisios G. Conjugation-Driven “Reverse Mars–van Krevelen”-Type Radical Mechanism for Low-Temperature C–O Bond Activation. United States. doi:10.1021/jacs.6b02871.
Mironenko, Alexander V., and Vlachos, Dionisios G. 2016. "Conjugation-Driven “Reverse Mars–van Krevelen”-Type Radical Mechanism for Low-Temperature C–O Bond Activation". United States. doi:10.1021/jacs.6b02871.
title = {Conjugation-Driven “Reverse Mars–van Krevelen”-Type Radical Mechanism for Low-Temperature C–O Bond Activation},
author = {Mironenko, Alexander V. and Vlachos, Dionisios G.},
abstractNote = {},
doi = {10.1021/jacs.6b02871},
journal = {Journal of the American Chemical Society},
number = 26,
volume = 138,
place = {United States},
year = 2016,
month = 6
  • Chemical reactions that break alkane carbon-hydrogen (C-H) bonds are normally carried out under conditions of high temperature and pressure because these bonds are extremely strong ({approx} 100 kilocalories per mole), but certain metal complexes can activate C-H bonds in alkane solution under the mild conditions of room temperature and pressure. Time-resolved infrared experiments probing the initial femtosecond dynamics through the nano- and microsecond kinetics to the final stable products have been used to generate a detailed picture of the C-H activation reaction. Structures of all of the intermediates involved in the reaction of Tp*Rh(CO){sub 2} (Tp* = HB-Pz{sub 3}*, Pz*more » = 3,5-di-methylpyrazolyl) in alkane solution have been identified and assigned, and energy barriers for each reaction step from solvation to formation of the final alkyl hydride product have been estimated from transient lifetimes. 27 refs., 6 figs.« less
  • Resonance Raman spectra have been analyzed for vanadyl porphyrin cation radicals of octaethylporphyrin (OEP), meso-tetra-phenylporphyrin (TPP), and meso-tetrametisylporphyrin (TMP). The strength of the metal-oxo bond in these cation radicals is demonstrated to be a function of radical type, a{sub 1u} or a{sub 2u}. Porphyrin ring mode {nu}{sub 2}, which has previously been shown to be a marker for the radical type was used to identify the radicals. The a{sub 1u} OV(OEP) radical exhibited an upshift in the V{double bond}O stretching frequency resulting from the increased positive charge on the porphyrin, which reduces the porphyrin {yields} vanadium electron donation and increasesmore » the O {yields} vanadium donation. {nu}(V{double bond}O) frequency decreases were observed for the a{sub 2u} OV(TPP) and OV(TMP) radicals. These can be explained on the basis of mixing of the porphyrin {pi} a{sub 2u} orbital with the vanadium d{sub z{sup 2}} and oxygen p{sub z} orbitals, which is allowed in C{sub 4v} symmetry. This interaction decreases the bond strength in a {sub 2u} cation radicals, since an electron is removed from an orbital with partial V-O {sigma}-bonding character. Mixing of the porphyrin a{sub 1u} {pi} orbital with metal or oxygen orbitals is forbidden. These results imply that porphyrin radical type is an important determinant of the Fe{double bond}O bond strength in heme protein cation-radical intermediates. 34 refs., 5 figs.« less
  • The importance of taking into account reverse activation energy and isotope effects in calculating heats of formation from appearance energy measurements is demonstrated in the particular case of HCOH{sup {sm bullet}+} produced from CH{sub 3}OH. New heats of formation for HCOH{sup {sm bullet}+} of 971 kJ mol{sup {minus}1} ({Delta}H{sub f}{sup 0}{sub 0}) and 968 kJ mol{sup {minus}1} ({Delta}H{sub f}{sup 0}{sub 298}) are obtained on this basis. The discrepancy between theoretical and experimental estimates of the energy difference between HCOH{sup {sm bullet}+} and H{sub 2}CO{sup {sm bullet}+} is resolved.
  • The complexes Cp*(PMe{sub 3})Ir(Me)OTf (Me = CH{sub 3}, OTf = OSO{sub 2}CF{sub 3}) (1) and Cp*(PMe{sub 3})Ir(Me)(CH{sub 2}Cl{sub 2})[BAr{sub f}] (BAr{sub f}{sup {minus}} = [(3,5-(CF{sub 3}){sub 2}C{sub 6}H{sub 3}){sub 4}B]{sup {minus}}) (2), which contain iridium in oxidation state +3, were recently shown to undergo C-H activation reactions with alkanes under mild thermal conditions. The authors report a series of observations, including the first conversion of Ir(III) precursors to an isolable, structurally characterized Ir(V) aryl-hydride and a spectroscopically observable Ir(V) alkyl-hydride, that lends convincing experimental support to the Ir(III) {r{underscore}arrow} Ir(V) {r{underscore}arrow} Ir(III) mechanism. The complex Cp*(PMe{sub 3})Ir(Me)OTf (1) reacts rapidlymore » with alkanes (H-CR{sub 3}) to produce 1 equiv of methane (CH{sub 4}) and rearranged products derived from Cp*(PMe{sub 3})Ir(CR{sub 3})OTf, which form as a consequence of the {beta}-hydride elimination pathway. When 1 is added to silanes (H-SiR{sub 3}, R = Me, Ph), products of a structural rearrangement type unobserved in C-H activation reactions are isolated along with 1 equiv of methane. These products, Cp*(PMe{sub 3})Ir(SiR{sub 2}OTf)(R), are presumably derived from a 1,2-migration in Cp*(PMe{sub 3})Ir(SiR{sub 3})OTf, wherein one of the groups initially bound to silicon migrates to iridium (eq 1).« less