Locked Carbene Complexes

The amphiphilic rhenium carbene complex Cp(CO)₂Re=CDCH₂ CH₂CMe₃ undergoes stereospecific addition of HCl to
produce a single diastereomer of cis-Cp(CO)₂ClReCHDCH₂CH₂CMe₃, but the absolute stereochemistry of the process could not be determined in part because rotation about the Re=C bond is expected to be fast. A rotationally restricted "locked" carbene was synthesized to probe this reaction.