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

Abstract

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 Cr(IV) versus Cr(V) corroles. Isotope labeling of the terminal oxo group with (18)O revealed that the Cr(V)-oxo (perchromyl) stretch of (tpfpc)Cr(V)O vibrates at a frequency of 986 cm(-1) in carbon disulfide, consistent with a triply bonded Cr(V)[triple bond]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 (18)O-sensitive vibration at a significantly higher frequency of 1002 cm(-1). On the basis of DFT calculations and the observed (18/16)O isotopic shift, we assigned this new RR band at 1002 cm(-1) in acetonitrile as the Cr(IV)-oxo (chromyl) stretch of the autoreduced [(tpfpc)Cr(IV)O](-) product, which previously has been shown to form only during the course of the oxygen atom transfer (OAT) reaction with triphenylphosphine in acetonitrile or in the presence of a reducing chemical (cobaltocene) and electrochemical agents in other solvents. Consequently, RR observations indicate that the pi-bonding character of the chromyl bond is actually increased relative to that of the perchromyl bond, which is of interest if the beneficial role of acetonitrile in OAT catalysis by high-valent oxochromium(IV,V) corroles is to be elucidated.

Formation and characterization of a reactive chromium(v)–oxo complex: mechanistic insight into hydrogen-atom transfer reactions

“…3 , Raman scattering due to the Cr( v )–oxo moiety was observed at 951 cm –1 , which was comparable to that observed for a reported Cr( v )–oxo complex with a corrole derivative as a supporting ligand (986 cm –1 ). 37 The peak of 1 - 18 O, which was formed by using PhI 18 O with a small amount of H 2 18 O, shifted to 918 cm –1 ; the isotopic shift (33 cm –1 ) is fairly consistent with the calculated value (Δ ν = 41 cm –1 ) as shown in Fig. 3 .…”

Density Functional Study of Oxygen Insertion into Niobium–Phosphorus Bonds: Novel Mechanism for Liberating P3– Synthons

“…Structural characterization of transition-metal-oxo complexes and analysis of their reactivity and transition states have been well represented in the literature. ,− For example, previous work by Goddard et al explored the involvement of transition-metal-oxo complexes in olefin metathesis and alkene epoxidation, noting that spectator oxo ligands are influential in the thermodynamics of insertion reactions. , In addition, Ziegler has computationally explored C–H and O–H bond activation by transition-metal (TM)-oxo complexes of groups 5–8 and rationalized that the difference in energetic trends of TM-d 0 oxo complexes, in abstraction and addition reactions, is related to the radial extension of the metal d orbital …”

The Influence of Peripheral Substituent Modification on PV, MnIII, and MnV(O) Corrolazines: X-ray Crystallography, Electrochemical and Spectroscopic Properties, and HAT and OAT Reactivities

“…We envisioned that these porphyrinoid ligands would provide access to a variety of new metal complexes and exhibit novel spectroscopic features and reactivity that would be quite distinct from porphyrins, porphyrazines, and corroles. One anticipated property of particular interest to us was the stabilization of high oxidation states at the central metal, which was also seen in the analogous corrole − complexes. This property would allow us to target species that mimic reactive intermediates in both heme enzymes and synthetic catalysts, including high-valent metal-oxo species analogous to Compound-I (Fe IV (O)­(porph •+ )) and Compound-II (Fe IV (O)­(porph)) in the Cytochrome P450s, peroxidases, and catalases. − We hypothesized that the corrolazine ligand would also be useful in new metalloporphyrinoid catalysts, especially for reactions involving the oxidation of organic substrates.…”

“…The BArF counterion is also disordered, as three −CF 3 groups can be found in two different orientations. The occupancy factors of the major components of the disorder refine to 0.723 (10), 0.663 (9), and 0.787 (5). The crystal lattice contains some solvent molecules.…”