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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.^[1]^[2]^[3] 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^[1] 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^[4] with insertion of a ruthenium atom ligated to dmpe in the C-H bond of naphthalene.

References

↑ ^1.0 ^1.1 Organometallic C-H Bond Activation: An Introduction Alan S. Goldman and Karen I. Goldberg ACS Symposium Series 885, Activation and Functionalization of C-H Bonds, 2004, 1–43
↑ Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H. “Selective Intermolecular Carbon–Hydrogen Bond Activation by Synthetic Metal Complexes in Homogeneous Solution.” Accounts of Chemical Research, 1995: 28 (3) 154–162.
↑ Periana, R. A.; Bhalla, G.; Tenn, W. J., III, Young, K. J. H.; Liu, X. Y.; Mironov, O.; Jones, C.; Ziatdinov, V. R. “Perspectives on some challenges and approaches for developing the next generation of selective, low temperature, oxidation catalysts for alkane hydroxylation based on the C-H activation reaction.” Journal of Molecular Catalysis A: Chemical, 2004: 220 (1) 7–25. doi:10.1016/j.molcata.2004.05.036
↑ The tautomerism of arene and ditertiary phosphine complexes of ruthenium(0), and the preparation of new types of hydrido-complexes of ruthenium(II) J. Chatt and J. M. Davidson, J. Chem. Soc. 1965, 843 doi:10.1039/JR9650000843

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