Since most chemicals and fuels employed nowadays come from oil, it seems obvious that on the basis of their reserves being reduced year after year, an alternative must be developed. The most convenient one is methane,1 given the vast reserves of this gas that exist in the Earth crust. However, it is quite surprising that one of the remaining challenges deals with one of the simplest molecules in Earth, methane, a consequence of the high inertness of its C-H bonds.
In the last decades there has been a number of systems described for the conversion of methane into valuable products using soluble catalysts, leading to the formation of C-O, C-C or C-B bonds.1 Many of them employ harsh conditions, particularly in terms of corrosive media or high temperatures. As part of our research program focused in the development of catalytic functionalization of non-activated alkanes of formula CnH2n+2, we have targeted methane as the substrate toward that end.2 However, since methane displays the highest bond dissociation energy of the alkane series, its functionalization must be performed in the absence of any other more reactive C-H bond.
For decades we have studied the reaction of diazoacetates with alkanes toward the insertion of a carbene group into the C-H bonds of the hydrocarbon. Extension of this methodology to methane have led us to the use of non-conventional reaction media to avoid competitive reactions. In this contribution, the results obtained employing supercritical carbon dioxide or water as the solvents will be presented.
1. Caballero, A.; Pérez, P. J. Chem. Soc. Rev. 2013, 42, 8809-8820
2. (a) Caballero, A.; Despagnet-Ayoub, E.; Díaz-Requejo, M. M.; Díaz-Rodríguez, A.; González-Núñez, M. E.; Mello, R.; Muñoz, B. K.; Solo Ojo, W.; Asensio, G.; Etienne, M.; Pérez, P. J., Science 2011, 332, 835-838. (b) Gava, R.; Olmos, A.; Noverges, B.; Varea, T.; Álvarez, E.; Belderrain, T. R.; Caballero, A.; Asensio, G.; Pérez, P. J., ACS Catal. 2015, 5,3726–3730.