 As such, carbene radicals are perhaps best described as 'one-electron reduced Fischer-type carbenes'.Discrete electron transfer from a sigma-type metal d-orbital (typically the dz2 orbital) occurs, leads the typical radical character of the carbene carbon.This behaviour not only explains the carbon-centered radical-type reactivity of these complexes, but also their reduced electrophilicity (suppressing carbene-carbene dimerisation side reactions) as well as their enhanced reactivity to electron-deficient substrates.