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.