Highly Selective and Catalytic Oxygenations of C−H and C=C Bonds by a Mononuclear Nonheme High‐Spin Iron(III)‐Alkylperoxo Species

Abstract

The reactivity of a mononuclear high‐spin iron(III)‐alkylperoxo intermediate [FeIII(t‐BuLUrea)(OOCm)(OH2)]2+(2), generated from [FeII(t‐BuLUrea)(H2O)(OTf)](OTf) (1) [t‐BuLUrea=1,1′‐(((pyridin‐2‐ylmethyl)azanediyl)bis(ethane‐2,1‐diyl))bis(3‐(tert‐butyl)urea), OTf=trifluoromethanesulfonate] with cumyl hydroperoxide (CmOOH), toward the C−H and C=C bonds of hydrocarbons is reported. 2 oxygenates the strong C−H bonds of aliphatic substrates with high chemo‐ and stereoselectivity in the presence of 2,6‐lutidine. While 2 itself is a sluggish oxidant, 2,6‐lutidine assists the heterolytic O−O bond cleavage of the metal‐bound alkylperoxo, giving rise to a reactive metal‐based oxidant. The roles of the urea groups on the supporting ligand, and of the base, in directing the selective and catalytic oxygenation of hydrocarbon substrates by 2 are discussed.

Characterization and chemical reactivity of room-temperature-stable MnIII–alkylperoxo complexes

“…In contrast, there are examples of Cu II -alkylperoxo 54 adducts that decay exclusively by heterolytic cleavage of the O-O bond, and there are a handful of examples where the decay of a metal-alkylperoxo adduct yields a mixture of products characteristic of both pathways. 2,5,11,13,55 Analysis of the organic decay products of [Mn III (OOCm)( 6-Me dpaq)] + reveal both 2-phenyl-2-propanol and acetophenone (61 and 26% yield relative to the [Mn III (OOCm)( 6Me dpaq)] + adduct). Electronic absorption, 1 H NMR, and ESI-MS data identify [Mn III (OH)( 6Me dpaq)] + as a dominant decay product (Fig.…”

“…Recent reports show that Brønsted and Lewis acids, or the introduction of secondary coordination interaction through pendant amines which act as hydrogen-bond acceptor in an Fe III -OOR (R ¼ H, acyl) adduct could direct heterolytic cleavage. 11,[59][60][61] This interaction between [Mn III (OOR)( 6Me dpaq)] + and PPh 3 may also be able to instigate heterolytic cleavage of the Mn III -alkylperoxo O-O bond. For the [Mn III (OOCm)( 6Me dpaq)] + complex, this decay will lead to the formation of cumyloxy anion, which gives 2-phenyl-2-propanol aer protonation 2,54,55 and a Mn III -species that is reduced to the Mn II product observed by UV-vis and EPR spectroscopy (Scheme 3).…”

“…4 In biological systems, metal-alkylperoxo adducts are common intermediates in a variety of oxygenase enzymes, where they can be directly involved in substrate oxidation or precede the formation of high-valent metal-oxo species. 9,10 Given the importance of metal-alkylperoxo species in such reactions, there are now many examples of synthetic Fe-, 11,12 Co-, 1,4,5 and Cu-alkylperoxo 3,13,14 adducts, and these complexes are capable of oxidizing substrates such as 1,4-cyclohexadiene, 2-phenylpropionaldehyde, and triphenylphosphine.…”

A Combined Spectroscopic and Computational Study on the Mechanism of Iron-Catalyzed Aminofunctionalization of Olefins Using Hydroxylamine Derived N–O Reagent as the “Amino” Source and “Oxidant”

“…Int II subsequently participates in the N -transfer reaction; the detailed mechanism of aminomethoxylation of styrenyl olefin has been delineated in the subsequent section via DFT calculations ( vide infra ). Similar to metal–alkyl/acyl peroxide chemistry, 101 , 160 − 162 product analyses from PivONH 3 OTf may be used as an indirect mechanistic probe, to differentiate between the proposed homolytic and heterolytic N–O bond cleavage pathways. In fact, GC-MS analysis of the headspace of the reaction after decay of Int II reveals formation of CO 2 and isobutene ( Scheme S1 , Figure S15 and S16 , SI).…”

Catalytic Oxidation of Primary C–H Bonds in Alkanes with Bioinspired Catalysts

“…[4][5][6][7][8][9][10][11][12][13][14] Oxidation of secondary and tertiary C-H bonds is well documented for a number of these type of catalysts, and competitive oxidation of these two type of bonds is customarily observed in substrates containing the two types. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] In contrast, oxidation of primary aliphatic C-H bonds of alkanes has been only seldom observed. The reaction is particularly interesting when applied to light alkanes, which stand as one of the most difficult classes of substrates in aliphatic C-H oxidation.…”