Why the Chromyl Bond Is Stronger Than the Perchromyl Bond in High-Valent Oxochromium(IV,V) Complexes of Tris(pentafluorophenyl)corrole

Resonance Raman (RR) spectroscopy and density functional theory (DFT) calculations of oxochromium(IV,V) derivatives of 5,10,15-tris(pentafluorophenyl)corrole (tpfpc) are shown to provide useful information about the relative strength of the metal−oxo bond in high-valent CrIV versus CrV corroles. Isotope labeling of the terminal oxo group with 18O revealed that the CrV−oxo (perchromyl) stretch of (tpfpc)CrVO vibrates at a frequency of 986 cm−1 in carbon disulfide, consistent with a triply bonded CrV≡O unit. In contrast, an acetonitrile solution produced RR scattering that rapidly changed with the number of scans collected and eventually became dominated by an 18O-sensitive vibration at a significantly higher frequency of 1002 cm−1. On the basis of DFT calculations and the observed 18/16O isotopic shift, we assigned this new RR band at 1002 cm−1 in acetonitrile as the CrIV−oxo (chromyl) stretch of the autoreduced [(tpfpc)CrIVO]− product, which previously has been shown to form only during the course of the ...