Silagermylenation of C=O bonds and radical fragmentation of CO2-expanded bis(germylene) by a cyclic (alkyl)(amino)carbene

The transformation of the greenhouse gas CO₂ into value-added products represents a major contemporary challenge. Low-valent p-block compounds typically react at the oxygen termini of CO₂ due to the oxophilicity of the metal centers. We now report on the selective activation of CO₂ and ethyl isocyanate at the central carbon atom by an N-heterocyclic carbene (NHC)-stabilized para-silylenephenylene-bridged bis(germylene). During the net silagermylenation, the C=X (X = O, NEt) bonds are inserted into the Ge–Si bonds through cooperativity of the low-valent metal center and the electrophilic silyl backbone. The germanium(II) centers are retained in the products, as is confirmed by multinuclear NMR data, IR spectroscopy and X-ray analysis and supported by DFT calculations. Attempts to substitute the NHCs by cyclic (alkyl)(amino)carbenes (CAACs) resulted in a germylene-CAAC radical by homolytic cleavage of the Si–O bonds as evidenced by single crystal X-ray diffraction and continuous-wave EPR spectroscopy.