X-ray crystallography data, DFT calculations and cyclic voltammograms in synergy shed light on the
mer4fac isomerization process of Cr carbenes of the type [(CO)3(dppe)Cr]C(X)R] with R ¼ 2-thienyl or
2-furyl and X ¼ OEt or NHCy, both in the neutral and oxidized states. Cyclohexylamino-containing
complexes are easier oxidized and reduced than ethoxy-containing complexes. Dppe-containing complexes
are considerably easier oxidized and reduced than non-phosphine containing CreFischer carbene
complexes of the type [(CO)5Cr]C(X)R] with X ¼ OEt, NHBu, NMe2 or N(CH2Ph)2 and R ¼ phenyl, thienyl,
furyl, NMe-pyrrole, H or Me. The oxidation and reduction potential of the [(CO)3(dppe)Cr]C(X)R]
complexes are not very sensitive to the influence of the heteroarene rings 2-thienyl or 2-furyl.