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Edited by Robert H. Crabtree, Yale University, New Haven, CT, and approved August 3, 2020 (received for review March 9, 2020)
Significance
Functionalization of unreactive molecules is a significant chemical challenge relevant to the conversion of abundant feedstocks such as alkanes into high-value chemicals. Herein, we demonstrate a new mechanism of alkane functionalization by the substitution of a proton by an anion in an alkyl chain. The reactive anion used for this reaction is generated from a highly stable precursor. The reaction mechanism is established using experimental and computational approaches, and the products are collected in the condensed phase using high-flux mass-selected ion deposition. This paves the way for exploiting the properties of gaseous ions for the generation of complex molecular structures in the condensed phase.
Abstract
Alkanes and [B12X12]2− (X = Cl, Br) are both stable compounds which are difficult to functionalize. Here we demonstrate the formation of a boron−carbon bond between these substances in a two-step process. Fragmentation of [B12X12]2− in the gas phase generates highly reactive [B12X11]− ions which spontaneously react with alkanes. The reaction mechanism was investigated using tandem mass spectrometry and gas-phase vibrational spectroscopy combined with electronic structure calculations. [B12X11]− reacts by an electrophilic substitution of a proton in an alkane resulting in a B−C bond formation. The product is a dianionic [B12X11CnH2n+1]2− species, to which H+ is electrostatically bound. High-flux ion soft landing was performed to codeposit [B12X11]− and complex organic molecules (phthalates) in thin layers on surfaces. Molecular structure analysis of the product films revealed that C−H functionalization by [B12X11]− occurred in the presence of other more reactive functional groups. This observation demonstrates the utility of highly reactive fragment ions for selective bond formation processes and may pave the way for the use of gas-phase ion chemistry for the generation of complex molecular structures in the condensed phase.
- electrophilic anions
- fragment ion deposition
- dodecaborates
- alkane functionalization
- spectroscopy of reactive intermediates
Footnotes
- ↵1To whom correspondence may be addressed. Email: jonas.warneke{at}uni-leipzig.de, knut.asmis{at}uni-leipzig.de, or jlaskin{at}purdue.edu.
↵2M.M., M.R., and X.M. contributed equally to this work.
Author contributions: J.W., G.E.J., H.I.K., K.R.A., and J.L. designed research; J.W., M.M., M.R., X.M., J.K.Y.L., M.G., S.D., E.A., and R.P.Y. performed research; C.J. contributed new reagents/analytic tools; J.W., M.M., M.R., X.M., V.A.A., E.A., R.P.Y., C.J., G.E.J., H.I.K., K.R.A., and J.L. analyzed data; J.W. wrote the paper; and V.A.A. performed important literature research.
The authors declare no competing interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2004432117/-/DCSupplemental.
Data Availability.
All study data are included in the article and SI Appendix.
Published under the PNAS license.
References
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Direct functionalization of C−H bonds by electrophilic anions
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