Trans-dioxo Manganese(V) Porphyrins

Abstract

Transition metal oxo-species have been the focus of extensive studies because of their relevance to the redox biochemistry of dioxygen as well as myriads of oxidative catalytic processes. High valent oxo-manganese complexes have been described for porphyrin, 1 salen, 2 corrole, 3 corrolazine, 4 and non-heme systems. 5 The O=Mn V moiety has been suggested in the photosynthetic water oxidation process, 6 and a bridged Mn V porphyrin dimer has recently been demonstrated to oxidize water into dioxygen. 7 We have previously described low-spin d 2 oxomanganese(V) porphyrin complexes that display an extraordinary range of reactivity toward oxo-transfer as a function of prototropic equilibria involving the axial ligand. 8 A prediction of that work was that oxo-aqua and oxo-hydroxomanganese(V) intermediates are reactive oxidants while the stable species observed at high pH are trans-dioxo complexes. Here we provide the first definitive spectroscopic evidence for trans-dioxomanganese(V) porphyrins [O=Mn V =O]. Further, we show that protonation of these species affords the reactive intermediates usually associated with these catalytic systems (Scheme 1).

The Effect of the Equatorial Environment on Oxo‐Group Silylation of the Uranyl Dication: A Computational Study

“…Thus, the silylation of uranyl in a water environment could occur if an appropriate water-stable aminosilane could be identified. It is interesting to note that Berthet and co-workers [41] observed the formation of UI 4 (MeCN) 4 from UO 2 I 2 (THF) 3 or UO 2 I 2 (OTf) 2 and excess Me 3 SiI, although the presence of intermediates was not discussed.…”

“…It is chemically robust [1] and shows little propensity to participate in the myriad reactions that are characteristic of its Group 6 transition-metal analogues, [MO 2 ] 2+ . [2][3][4][5][6] Furthermore, this stability coupled with its mobility in the aqueous phase means that it is a problematic environmental contaminant. [7][8][9] A better understanding of the reduction of the mobile uranyl ion to insoluble U IV phases, through the pentavalent [UO 2 ] + ion, is important in the context of environmental immobilization and the treatment of mixed waste.…”

Oxygen‐Atom Transfer by a Naked Manganese(V)–Oxo–Porphyrin Complex Reveals Axial Ligand Effect

“…[5] At lower pH the prototropic equilibria shift in favour of oxo-hydroxo, Mn V O(OH) and oxo-aqua, Mn…”

The Groves–Spiro Dioxomanganese(V) Story

“…[8] The uniqueness of the most recent contribution by Groves, Spiro, and co-workers is that they have now obtained physical (spectroscopic) data for species 1 (Scheme 1) and demonstrated the relationship of the structural and electronic features with chemical reactivity. [5] In doing so, they turned their attention to the manganese complexes of the non watersoluble 5,10,15,20-tetramesitylporphyrinato dianion (TMP), and worked in acetonitrile/water solutions. This approach allowed for selective labeling of the oxygen atoms involved in binding to the two available axial coordination sites of the metal ion.…”