The Mechanism of the Catalytic Functionalization of Haloalkanes by Carbene Insertion: An Experimental and Theoretical Study

Carbon−halogen (C−X) bonds (X = Cl, Br) can be easily functionalized with ethyl diazoacetate (N2CHCO2Et) in the presence of silver-based catalysts containing the TpxAg core (Tpx = hydrotrispyrazolylborate ligand). Polyhalomethanes are converted into products derived from the formal insertion of the carbene CHCO2Et units into the C−X bond. In the case of monohaloalkanes (C4−C6), cleavage of the C−X bond is observed, with formation of XCH2CO2Et and the corresponding olefin. Experimental evidence and theoretical calculations have led to the proposal of a novel mechanism to account for these transformations, in which the metal participates along the pathway in all the reaction steps. Among the experimental data, the first example of a metal-induced, asymmetric functionalization of a C−Cl bond by carbene insertion is included (ee = 14 ± 2%).