Characterization of a Rhodium(I) 
-Methane Complex in Solution
Wesley H. Bernskoetter,1,*
Cynthia K. Schauer,1
Karen I. Goldberg,2
Maurice Brookhart1,
Numerous transition metal–mediated reactions, including
hydrogenations, hydrosilations, and alkane functionalizations,
result in the cleavage of strong
bonds. Key intermediates in
these reactions often involve coordination of the
bond of dihydrogen,
silanes (Si-H), or alkanes (C-H) to the metal center without
full scission of the bond. These
complexes have been characterized
to varying degrees in solid state and solution. However, a
complex of the simplest hydrocarbon, methane, has eluded full
solution characterization. Here, we report nuclear magnetic
resonance spectra of a rhodium(I)
-methane complex obtained
by protonation of a rhodium-methyl precursor in CDCl
2F solvent
at –110°C. The
-methane complex is shown to be more
stable than the corresponding rhodium(III) methyl hydride complex.
Even at –110°C, methane rapidly tumbles in the coordination
sphere of rhodium, exchanging free and bound hydrogens. Kinetic
studies reveal a half-life of about 83 minutes at –87°C
for dissociation of methane (free energy of activation is 14.5
kilocalories per mole).
2 Department of Chemistry Box 351700, University of Washington, Seattle, WA 98195–1700, USA.
* Present address: Department of Chemistry, Brown University, Providence, RI 02912, USA.
To whom correspondence should be addressed. E-mail: mbrookhart{at}unc.edu
