Hydrogen Bond-Enabled Heterolytic and Homolytic Peroxide Activation within Nonheme Copper(II)-Alkylperoxo Complexes

To explore the reactivity of copper-alkylperoxo species enabled by the heterolytic peroxide activation, room-temperature stable mononuclear nonheme copper­(II)–alkylperoxo complexes bearing a N-(2-ethoxyethanol)-bis(2-picolyl)­amine ligand (HN3O2), [CuII(OOR)­(HN3O2)]+ (R = cumyl or tBu), were synthesized and spectroscopically characterized. A combined experimental and computational investigation on the reactivity and reaction mechanisms in the phosphorus oxidation, C–H bond activation, and aldehyde deformylation reactions by the copper­(II)–alkylperoxo complexes has been conducted. DFT-optimized structures suggested that a hydrogen bonding interaction exists between the ethoxyethanol backbone of the HN3O2 ligand and either the proximal or distal oxygen atom of the alkylperoxide moiety, and this interaction consequently results in the enhanced stability of the copper­(II)–alkylperoxo species. In the phosphorus oxidation reaction, both experimental and computational results indicated that a phosphine-triggered heterolytic O–O bond cleavage occurred to yield phosphine oxide and alcohol products. DFT calculations suggested that (i) the H-bonding between the ethoxyethanol backbone and distal oxygen of the alkylperoxide moiety and (ii) the phosphine binding to the proximal oxygen of the alkylperoxide moiety engendered the heterolytic peroxide activation. In the C–H bond activation reactions, temperature-dependent reactivity of the copper­(II)–alkylperoxo complexes was observed, and a relatively strong activation energy of 95 kcal mol–1 was required to promote the homolytic peroxide activation. A rate-limiting hydrogen atom abstraction reaction of xanthene by the putative copper­(II)-oxyl radical resulted in the formation of the dimeric copper product and the substrate radical that further underwent autocatalytic oxidation reactions to form an oxygen incorporated product. Finally, amphoteric reactivity of copper­(II)–alkylperoxo complexes has been assessed by conducting kinetic studies and product analysis of the aldehyde deformylation reaction

Facile Nitrite Reduction and Conversion Cycle of {Fe(NO)}^6/7 Species: Chemistry of Iron N-Confused Porphyrin Complexes via Protonation/Deprotonation

Facile Nitrite Reduction and Conversion Cycle of {Fe(NO)}6/7 Species: Chemistry of Iron N-Confused Porphyrin Complexes via Protonation/Deprotonatio

Facile Nitrite Reduction and Conversion Cycle of {Fe(NO)}^6/7 Species: Chemistry of Iron N-Confused Porphyrin Complexes via Protonation/Deprotonation

Facile Nitrite Reduction and Conversion Cycle of {Fe(NO)}6/7 Species: Chemistry of Iron N-Confused Porphyrin Complexes via Protonation/Deprotonatio

Facile Nitrite Reduction and Conversion Cycle of {Fe(NO)}^6/7 Species: Chemistry of Iron N-Confused Porphyrin Complexes via Protonation/Deprotonation

Facile Nitrite Reduction and Conversion Cycle of {Fe(NO)}6/7 Species: Chemistry of Iron N-Confused Porphyrin Complexes via Protonation/Deprotonatio

Facile Nitrite Reduction and Conversion Cycle of {Fe(NO)}^6/7 Species: Chemistry of Iron N-Confused Porphyrin Complexes via Protonation/Deprotonation

Facile Nitrite Reduction and Conversion Cycle of {Fe(NO)}6/7 Species: Chemistry of Iron N-Confused Porphyrin Complexes via Protonation/Deprotonatio

Formation of a Sulfur-Atom-Inserted N-Confused Porphyrin Iron Nitrosyl Complex by Denitrosation and C<i>−</i>S Bond Cleavage of an <i>S-</i>Nitrosothiol

The reaction of nitrosothiol, Ph3CSNO, with a divalent iron N-confused porphyrin complex, Fe(HCTPPH)Br, yields a {Fe(NO)}6 iron nitrosyl complex with a sulfur atom inserted in the Fe−C bond. The crystal structure reveals a bent Fe−N−O geometry and an η2-(C,S) bonding mode between iron and the C−S bond. A reaction mechanism involving a transnitrosation and a nitrosothiol C−S bond cleavage is proposed

Characterization of the Fleeting Hydroxoiron(III) Complex of the Pentadentate TMC-py Ligand

Nonheme mononuclear hydroxoiron­(III) species are important intermediates in biological oxidations, but well-characterized examples of synthetic complexes are scarce due to their instability or tendency to form μ-oxodiiron­(III) complexes, which are the thermodynamic sink for such chemistry. Herein, we report the successful stabilization and characterization of a mononuclear hydroxoiron­(III) complex, [Fe^III(OH)­(TMC-py)]²⁺ (<b>3</b>; TMC-py = 1<i>-</i>(pyridyl-2′-methyl)-4,8,11-trimethyl-1,4,8,11-tetrazacyclotetradecane), which is directly generated from the reaction of [Fe^IV(O)­(TMC-py)]²⁺ (<b>2</b>) with 1,4-cyclohexadiene at −40 °C by H-atom abstraction. Complex <b>3</b> exhibits a UV spectrum with a λ_max at 335 nm (ε ≈ 3500 M^–1 cm^–1) and a molecular ion in its electrospray ionization mass spectrum at <i>m</i>/<i>z</i> 555 with an isotope distribution pattern consistent with its formulation. Electron paramagnetic resonance and Mössbauer spectroscopy show <b>3</b> to be a high-spin Fe­(III) center that is formed in 85% yield. Extended X-ray absorption fine structure analysis reveals an Fe–OH bond distance of 1.84 Å, which is also found in [(TMC-py)­Fe^III–O–Cr^III(OTf)₃]⁺ (<b>4</b>) obtained from the reaction of <b>2</b> with Cr­(OTf)₂. The <i>S</i> = 5/2 spin ground state and the 1.84 Å Fe–OH bond distance are supported computationally. Complex <b>3</b> reacts with 1-hydroxy-2,2,6,6-tetramethylpiperidine (TEMPOH) at −40 °C with a second-order rate constant of 7.1 M^–1 s^–1 and an OH/OD kinetic isotope effect value of 6. On the basis of density functional theory calculations, the reaction between <b>3</b> and TEMPOH is classified as a proton-coupled electron transfer as opposed to a hydrogen-atom transfer

Ruthenium Complexes of Thiaporphyrin and Dithiaporphyrin

Successful synthesis and characterization of the six-coordinated complex [Ru­(STTP)­(CO)­Cl] (<b>1</b>; STTP = 5,10,15,20-tetratolyl-21-thiaporphyrinato) allowed the development of the coordination chemistry of ruthenium–thiaporphyrin through dechlorination and metathesis reactions. Accordingly, [Ru^II(STTP)­(CO)­X] (X = NO₃^<b>–</b> (<b>2</b>), NO₂^<b>–</b> (<b>3</b>), and N₃^<b>–</b> (<b>4</b>)) was synthesized and analyzed by single-crystal X-ray structural determination and NMR, UV–vis, and FT-IR spectroscopic methods. An independent reaction of STPPH and [Ru­(COD)­Cl₂] led to [Ru^III(STTP)­Cl₂] (<b>5</b>), which possessed a higher-valent Ru­(III) center and exhibited good stability in the solution state. This stability allowed reversible redox processes in a cyclic voltammetric study. Reactions of [Ru­(S₂TTP)­Cl₂] (S₂TTP = 5,10,15,20-tetratolyl-21,23-dithiaporphyrinato) with AgNO₃ and NaSePh, also via the metathesis strategy, resulted in novel dithiaporphyrin complexes [Ru^II(S₂TTP)­(NO₃)₂] (<b>6</b>) and [Ru⁰(S₂TTP)­(PhSeCH₂SePh)₂] (<b>7</b>), respectively. The structures of <b>6</b> and <b>7</b> were corroborated by X-ray crystallographic analyses. Complex <b>7</b> is an unprecedented ruthenium(0)–dithiaporphyrin with two <i>bis</i>(phenylseleno)­methanes as axial ligands. A comparison of the analyses of the crude products from reactions of NaSePh and CH₂Cl₂ with or without [Ru­(S₂TTP)­Cl₂], further supported by UV–vis spectral changes under stoichiometric reactions between [Ru­(S₂TTP)­Cl₂] and NaSePh, suggested a reaction sequence in the order of (1) formation of a putative [Ru^II(S₂TTP)­(SePh)₂] intermediate, followed by (2) the concerted formation of PhSe–CH₂Cl and simultaneously a reduction of Ru­(II) to Ru(0) and finally (3) nucleophilic substitution of PhSeCH₂Cl by excess PhSe^–, resulting in PhSeCH₂SePh, which readily coordinated to the Ru(0) and completed the formation of <i>bis</i>(phenylseleno)­methane complex <b>7</b>

Ruthenium Complexes of Thiaporphyrin and Dithiaporphyrin

Successful synthesis and characterization of the six-coordinated complex [Ru­(STTP)­(CO)­Cl] (<b>1</b>; STTP = 5,10,15,20-tetratolyl-21-thiaporphyrinato) allowed the development of the coordination chemistry of ruthenium–thiaporphyrin through dechlorination and metathesis reactions. Accordingly, [Ru^II(STTP)­(CO)­X] (X = NO₃^<b>–</b> (<b>2</b>), NO₂^<b>–</b> (<b>3</b>), and N₃^<b>–</b> (<b>4</b>)) was synthesized and analyzed by single-crystal X-ray structural determination and NMR, UV–vis, and FT-IR spectroscopic methods. An independent reaction of STPPH and [Ru­(COD)­Cl₂] led to [Ru^III(STTP)­Cl₂] (<b>5</b>), which possessed a higher-valent Ru­(III) center and exhibited good stability in the solution state. This stability allowed reversible redox processes in a cyclic voltammetric study. Reactions of [Ru­(S₂TTP)­Cl₂] (S₂TTP = 5,10,15,20-tetratolyl-21,23-dithiaporphyrinato) with AgNO₃ and NaSePh, also via the metathesis strategy, resulted in novel dithiaporphyrin complexes [Ru^II(S₂TTP)­(NO₃)₂] (<b>6</b>) and [Ru⁰(S₂TTP)­(PhSeCH₂SePh)₂] (<b>7</b>), respectively. The structures of <b>6</b> and <b>7</b> were corroborated by X-ray crystallographic analyses. Complex <b>7</b> is an unprecedented ruthenium(0)–dithiaporphyrin with two <i>bis</i>(phenylseleno)­methanes as axial ligands. A comparison of the analyses of the crude products from reactions of NaSePh and CH₂Cl₂ with or without [Ru­(S₂TTP)­Cl₂], further supported by UV–vis spectral changes under stoichiometric reactions between [Ru­(S₂TTP)­Cl₂] and NaSePh, suggested a reaction sequence in the order of (1) formation of a putative [Ru^II(S₂TTP)­(SePh)₂] intermediate, followed by (2) the concerted formation of PhSe–CH₂Cl and simultaneously a reduction of Ru­(II) to Ru(0) and finally (3) nucleophilic substitution of PhSeCH₂Cl by excess PhSe^–, resulting in PhSeCH₂SePh, which readily coordinated to the Ru(0) and completed the formation of <i>bis</i>(phenylseleno)­methane complex <b>7</b>