The selectivity of a catalytic alkane functionalization process can be modified just changing the reaction medium from neat alkane to supercritical carbon dioxide (scCO2). A silica supported copper complex bearing an N-heterocyclic carbene ligand promotes the functionalization of carbon–hydrogen bonds of alkanes by transferring the CHCO2Et group from N2═CHCO2Et (ethyl diazoacetate, EDA). In neat hexane, only 3% of the primary C–H bonds (ethyl heptanoate being the product) are functionalized in that manner, whereas the same reaction carried out in scCO2 provides a 30% yield in this linear ester. Such an effect seems to be induced by an electronic density flux from the NHC ligand to the surrounding carbon dioxide molecules.