Structural Characterization and Unique Catalytic Performance of Silyl-Group-Substituted Geminal Dichromiomethane Complexes Stabilized with a Diamine Ligand

Stabilization by a silyl group on the methylene carbon and a diamine ligand led to the isolation of gem-dichromio­methane species. X-ray crystallography confirmed the identity of the structure of this rare example of reactive gem-dimetallo­alkane species. The isolated gem-dichromio­methane complex acted as a storable silyl­methylidene carbene equivalent, with reactivity that could be changed dramatically upon addition of a Lewis acid (ZnCl₂) and a base (TMEDA) to promote both silyl­alkyl­iden­ation of polar aldehydes and silyl­cyclo­propan­ation of nonpolar alkenes. Identification of a key reactive species also identified the catalytic version of these transformations and provided insights into the reaction mechanism. In contrast to Simmons–Smith cyclo­propan­ation, the real reactive species for the current cyclo­propan­ation was a chromio­carbene species, not a chromium carbenoid species.