Electronic properties and reactivity patterns of high‐valent metal‐oxo species of Mn, Fe, Co, and Ni

Abstract

Density functional theory (DFT) calculations were performed for a series of significant terminal high‐valent metal‐oxo complexes, where the metals are Mn, Fe, Co, and Ni, to reveal their electronic property and reactivity patterns toward the inert CH bond activation. We found that as the metal center changes from Mn to Ni, the bond strength of metal‐oxo decreases while the oxyl character of the oxygen increases, which suggests an increase in the hydrogen‐abstraction reactivity. This prediction was further strengthened by theoretical reactivity studies, that is, the reactivities of these four metal‐oxo species toward inert CH bond followed an order of MnO ≈ FeO ≪ CoO < NiO. At the orbital level, it was found that three different electron transfer mechanisms were active among these four species. Thus, this study would provide an explanation and intuitive clues for chemists to understand the nature of the high‐valent late transition metal‐oxo species.

Heme compound II models in chemoselectivity and disproportionation reactions

“…The formation of 2-cyclohexen-1-ol with the large KIE value of 41 demonstrates that the allylic C–H bond oxidation pathway is preferred over the CC bond epoxidation pathway in the oxidation of cyclohexene by 1a (Scheme 1C, pathway a); the preference for C–H bond hydroxylation in cyclohexene oxidation was observed in nonheme iron( iv )-oxo and other nonheme metal( iv )-oxo complexes. 10 In addition, the decay product of 1a was found to be [Fe III (TPFPP)] + by UV-vis and EPR spectroscopies (Fig. 3a and S9†); it is noted that nonheme iron( iv )-oxo species are converted to iron( iii ) species in C–H bond hydroxylation reactions.…”

“…3a and S9†); it is noted that nonheme iron( iv )-oxo species are converted to iron( iii ) species in C–H bond hydroxylation reactions. 9,10…”

“…Further, it is notable that the reaction of 1a resembles the mononuclear nonheme iron( iv )-oxo reaction ( i.e. , C–H bond hydroxylation; Scheme 1B, pathway a), 10 whereas the reaction of 2a follows the Cpd I reaction ( i.e. , CC bond epoxidation; Scheme 1B, pathway b).…”

“…10 a The distinct chemoselectivity shown by nonheme metal( iv )-oxo complexes was interpreted with density functional theory (DFT) calculations. 10…”

“…We now report that the chemoselectivity of Cpd II models in the oxidation of cyclohexene varies depending on the electron-richness of the porphyrin ligands (see Scheme 1A for structures); that is, a Cpd II model with an electron-deficient porphyrin ligand, [Fe IV (O)(TPFPP)(Cl)] − ( 1a , TPFPP = meso -tetrakis(pentafluorophenyl)porphyrinato dianion), affords the allylic oxidation product, as observed in the reactions of nonheme iron( iv )-oxo complexes (see Scheme 1B and C, reaction pathway a), 10 whereas a Cpd II model with an electron-rich porphyrin ligand, [Fe IV (O)(TMP)(Cl)] − ( 2a , TMP = meso -tetrakis(2,4,6-trimethylphenyl)porphyrinato dianion), yields the cyclohexene oxide product, as observed in the Cpd I model reactions (see Scheme 1B and C, reaction pathway b). 11 We also report that the preference for CC bond epoxidation by 2a results from the disproportionation of 2a that forms Cpd I, [Fe IV (O)(TMP + ˙)] + ( 2b ), as the active oxidant that effects the epoxidation of cyclohexene to give the corresponding epoxide product selectively (see Scheme 1D, reaction pathway b).…”