Aliphatic and Aromatic C–H Bond Oxidation by High-Valent Manganese(IV)-Hydroxo Species

Abstract

The strong C−H bond activation of hydrocarbons is a difficult reaction in environmental and biological chemistry. Herein, a high-valent manganese(IV)-hydroxo complex, [Mn IV (CHDAP-O)(OH)] 2+ (2), was synthesized and characterized by various physicochemical measurements, such as ultraviolet−visible (UV−vis), electrospray ionization-mass spectrometry (ESI-MS), electron paramagnetic resonance (EPR), and helium-tagging infrared photodissociation (IRPD) methods. The one-electron reduction potential (E red ) of 2 was determined to be 0.93 V vs SCE by redox titration. 2 is formed via a transient green species assigned to a manganese(IV)-bis(hydroxo) complex, [Mn IV (CHDAP)(OH) 2 ] 2+ (2′), which performs intramolecular aliphatic C−H bond activation. The kinetic isotope effect (KIE) value of 4.8 in the intramolecular oxidation was observed, which indicates that the C−H bond activation occurs via rate-determining hydrogen atom abstraction. Further, complex 2 can activate the C−H bonds of aromatic compounds, anthracene and its derivatives, under mild conditions. The KIE value of 1.0 was obtained in the oxidation of anthracene. The rate constant (k et ) of electron transfer (ET) from N,N′-dimethylaniline derivatives to 2 is fitted by Marcus theory of electron transfer to afford the reorganization energy of ET (λ = 1.59 eV). The driving force dependence of log k et for oxidation of anthracene derivatives by 2 is well evaluated by Marcus theory of electron transfer. Detailed kinetic studies, including the KIE value and Marcus theory of outer-sphere electron transfer, imply that the mechanism of aromatic C−H bond hydroxylation by 2 proceeds via the rate-determining electron-transfer pathway.

Oxidative addition of an alkyl halide to form a stable Cu(III) product

“…To define the mechanism of the reaction of haloacetonitrile with the ionic or neutral Cu(I) species further, we performed density functional theory (DFT) calculations with the PBE0-D3(BJ) functional. On the basis of previous proposals for the mechanism of copper-mediated cross-coupling reactions (18)(19)(20)(21)(22) and the experimental results reported in this work, we proposed five different pathways that could account for the oxidative addition of haloacetonitrile to ionic and neutral Cu(I) complexes (Fig. 4).…”

“…Previously, two distinct cycles were proposed for copper-catalyzed cross-coupling reactions of alkyl electrophiles. One cycle comprises a two-electron Cu(I)/Cu(III) manifold, and one comprises a stepwise Cu(I)/Cu(II) manifold involving initial single-electron transfer (SET) between the Cu(I) center and the alkyl electrophile to generate a Cu(II) intermediate and an alkyl radical, followed by transfer of the functional group from the resulting Cu(II) species to the alkyl radical (18)(19)(20)(21)(22) (Fig. 1A).…”

Enzyme-Inspired Coordination Polymers for Selective Oxidization of C(sp3)–H Bonds via Multiphoton Excitation

“…Under the same conditions, the initial oxidation rate of 3,5-DTBC by Cu-Cl-bpyc was the fastest. For a direct comparison, the aromatic C−H bond oxidation of anthracene to anthracene-9,10-dione was chosen as the model reaction, 68 as the aromatic oxidation does not occur via a hydrogen atom abstraction, but involves an initial electrophilic attack on the πsystem of the aromatic ring to produce a radical or cationic σcomplex. As shown in Figure 5c, our catalytic results showed that the three catalysts oxidized anthracene to anthracene-9,10dione with good yields, but Cu-Cl-bpyc gave the highest yield.…”

Octahedral Iron‐Acyl‐Nitrenoid Intermediates in Sulphur −Nitrogen Coupling and Hydrogen Atom Transfer Reactions

“…As demonstrated previously, an effective way to detect and study reactive metal complexes is to generate them in a flow reactor with a direct connection to a mass spectrometer with an electrospray ionization interphase (ESI-MS). [39][40][41] Reaction of (TPA)Fe(OTf) 2 with phenyl dioxazolone (A) in a flow reactor (Figure 1a) leads to the detection of a dominant ESI-MS signal with a mass corresponding to the iron-acyl-nitrenoid complex with additional acetonitrile ligand ([(TPA)Fe(NCOPh)(MeCN)] 2 + (2), m/z 253.07, Figure 1b, top). In addition, we detected less abundant signals of the triflato analog ([(TPA)Fe(NCOPh)(OTf)] + , m/z 614.07, Figure S2A) and the complex without the additional ligand ([(TPA)Fe(NCOPh)] 2 + , m/z 232.56, Figure 1b, top).…”