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%).