Rh Methylidenes from Redox Cascade Activation of Chloroalkanes

Oxidative addition of carbon-halogen bonds at transition metals typically follow either a two-electron pathway (concerted M-R/M-X formation) or a radical chain pathway (stepwise M-R/M-X formation). When the reactive metal species is generated slowly, however, both mechanisms can compete to yield unexpected reactivity paths. The present report highlights the synthesis of rhodium methylidenes from chloroalkanes (e.g. CH2Cl2 and CHCl3) at POP-pincer frameworks (e.g. POP = 4,6-bis(di-tert- butylphosphino)dibenzo[b,d]furan) via a cascade of halide abstraction and electron transfer steps. Experimental and computational studies are reported that support the proposed mechanism, including characterization of important reaction intermediates. The overall transformation represents a route towards reactive metal alkylidenes using milder and less-reactive carbenoid precursors than what is presently used.