Carbon–hydrogen bond activation

**Carbon–hydrogen bond activation** or **C-H activation** is a reaction that breaks a carbon–hydrogen bond.  Most times, the reaction involves organometallic complexes. The reaction path has coordination of a hydrocarbon to the inner-sphere of the metal atom (“M”). The reaction path includes either an intermediate “alkane or arene complex” or as a transition state leading to a "M-C" intermediate. The reaction path makes C-H activation different from other reactions. During the C-H breaking event the hydrocarbyl group remains linked in the inner-sphere and under the influence of the metal atom.

Chemists study C-H activation because for many years chemists believed that C-H bonds were unreactive.  Theoretical studies and experiments now show that C-H bonds can be broken. This is done by a nearby metal atom changing the electron distribution of the C-H bond (coordination).  Much chemical research looks at the design and synthesis of new reagents and catalysts that can affect C-H activation.  The goal of this research is the conversion of cheap and abundant alkanes into valuable functionalized organic compounds.

Otto Dimroth discovered the first C-H activation reaction. In 1902, he reported that benzene reacted with mercury(II) acetate, but some scholars do not view this reaction as being a C-H activation.  Goldman & Goldberg later wrote, C-H activation looks like H-H activation: both can be achieved by electrophilic or oxidative addition. The first true C-H activation reaction was reported by Joseph Chatt in 1965 with insertion of a ruthenium atom ligated to dmpe in the C-H bond of naphthalene.

## Further reading

- “Activation of C-H Bonds by Metal Complexes”, A. E. Shilov, G. B. Shul’pin, Chem. Rev. 1997, 97, 2879–2932.
- “Activation and Catalytic Reactions of Saturated Hydrocarbons in the Presence of Metal Complexes”, A. E. Shilov, G. B. Shul’pin, Kluwer Academic Publishers, Dordrecht/Boston/London, 2000 (552 p) (Springer, ). https://www.springer.com/chemistry/physical+chemistry/book/978-0-7923-6101-5
- “Alkane C-H activation and functionalization with homogeneous transition metal catalysts: a century of progress – a new millennium in prospect”, R. H. Crabtree, J. Chem. Soc., Dalton Trans. 2001, 17, 2437–2450.
- “Organometallic alkane CH activation”, R. H. Crabtree, J. Organometal. Chem. 2004, 689, 4083–4091.
- “Mechanistic Aspects of C−H Activation by Pt Complexes”, M. Lersch, M.Tilset, Chem. Rev. 2005, 105, 2471−2526.
- “Recent Advances in the Platinum-mediated CH Bond Functionalization”, A. N. Vedernikov, Curr. Org. Chem. 2007, 11, 1401−1416.
- “Catalytic C-H functionalization by metalcarbenoid and nitrenoid insertion”, H. M. L. Davies, J. R. Manning, Nature, 2008, 451, 417−424,
- "Mechanisms of C-H bond activation: rich synergy between computation and experiment”, Y. Boutadla, D. L. Davies, S. A. Macgregor, A. I. Poblador-Bahamonde, Dalton Trans. 2009, 5820−5831.
- “C-H Bond Activation in Transition Metal Species from a Computational Perspective”, D. Balcells, E. Clot, O. Eisenstein, Chem. Rev. 2010, 110, 749–823.
- “Palladium-Catalyzed Ligand-Directed C-H Functionalization Reactions”, T. W. Lyons, M. S. Sanford, Chem. Rev. 2010, 110, 1147–1169.
- “Selectivity enhancement in functionalization of C-H bonds: A review”, G. B. Shul’pin, Org. Biomol. Chem. 2010, 8, 4217–4228.