Mechanistic insights into the reactions of hydride transfer <i>versus</i> hydrogen atom transfer by a <i>trans</i>-dioxoruthenium(<small>VI</small>) complex

Dhuri, Sunder N.,Lee, Yong-Min,Seo, Mi Sook,Cho, Jaeheung,Narulkar, Dattaprasad D.,Fukuzumi, Shunichi,Nam, Wonwoo The Royal Society of Chemistry 2015 Dalton Transactions Vol.44 No.16

<P>A mononuclear high-valent <I>trans</I>-dioxoruthenium(<SMALL>VI</SMALL>) complex, <I>trans</I>-[Ru<SUP>VI</SUP>(TMC)(O)<SUB>2</SUB>]<SUP>2+</SUP> (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), was synthesized and characterized by various spectroscopic techniques and X-ray crystallography. The reactivity of the <I>trans</I>-[Ru<SUP>VI</SUP>(TMC)(O)<SUB>2</SUB>]<SUP>2+</SUP> complex was investigated in hydride transfer and hydrogen atom transfer reactions. The mechanism of hydride transfer from dihydronicotinamide adenine dinucleotide (NADH) analogues to <I>trans</I>-[Ru<SUP>VI</SUP>(TMC)(O)<SUB>2</SUB>]<SUP>2+</SUP>, which proceeds <I>via</I> a proton-coupled electron transfer (PCET), followed by a rapid electron transfer (ET), has been proposed by the observation of a good linear correlation between the log rate constants of <I>trans</I>-[Ru<SUP>VI</SUP>(TMC)(O)<SUB>2</SUB>]<SUP>2+</SUP> and <I>p</I>-chloranil (Cl<SUB>4</SUB>Q) and a large kinetic isotope effect (KIE) value of 13(1). In the case of the oxidation of alkyl hydrocarbons by the <I>trans</I>-[Ru<SUP>VI</SUP>(TMC)(O)<SUB>2</SUB>]<SUP>2+</SUP> complex, the second-order rate constants were dependent on the C–H bond dissociation energy (BDE) of the substrates, and a large KIE value of 26(2) was obtained in the oxidation of xanthene and deuterated xanthene-<I>d</I><SUB>2</SUB> by the <I>trans</I>-[Ru<SUP>VI</SUP>(TMC)(O)<SUB>2</SUB>]<SUP>2+</SUP> complex, indicating that the C–H bond activation of alkyl hydrocarbons proceeds <I>via</I> an H-atom abstraction in the rate-determining step.</P> <P>Graphic Abstract</P><P>Valuable insights into the hydride-transfer mechanism and C–H bond activation reactions by high-valent <I>trans</I>-dioxoruthenium(<SMALL>VI</SMALL>) species is provided. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5dt00809c'> </P>

Interplay of Experiment and Theory in Elucidating Mechanisms of Oxidation Reactions by a Nonheme Ru^IVO Complex

Dhuri, Sunder N.,Cho, Kyung-Bin,Lee, Yong-Min,Shin, Sun Young,Kim, Jin Hwa,Mandal, Debasish,Shaik, Sason,Nam, Wonwoo American Chemical Society 2015 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.137 No.26

<P>A comprehensive experimental and theoretical study of the reactivity patterns and reaction mechanisms in alkane hydroxylation, olefin epoxidation, cyclohexene oxidation, and sulfoxidation reactions by a mononuclear nonheme ruthenium(IV)-oxo complex, [Ru-IV(O)(terpy)-(bpm)](2+) (1), has been conducted. In alkane hydroxylation (i.e., oxygen rebound vs oxygen non-rebound mechanisms), both the experimental and theoretical results show that the substrate radical formed via a rate-determining H atom abstraction of alkanes by 1 prefers dissociation over oxygen rebound and desaturation processes. In the oxidation of olefins by 1, the observations of a kinetic isotope effect (KIE) value of 1 and styrene oxide formation lead us to conclude that an epoxidation reaction via oxygen atom transfer (OAT) from the (RuO)-O-IV complex to the C=C double bond is the dominant pathway. Density functional theory (DFT) calculations show that the epoxidation reaction is a two-step, two-spin-state process. In contrast, the oxidation of cyclohexene by 1 affords products derived from allylic C-H bond oxidation, with a high KIE value of 38(3). The preference for H atom abstraction over C=C double bond epoxidation in the oxidation of cyclohexene by 1 is elucidated by DFT calculations, which show that the energy barrier for C-H activation is 4.5 kcal mol(-1) lower than the energy barrier for epoxidation. In the oxidation of sulfides, sulfoxidation by the electrophilic Ru-oxo group of 1 occurs via a direct OAT mechanism, and DFT calculations show that this is a two-spin-state reaction in which the transition state is the lowest in the S = 0 state.</P>

Experiment and Theory Reveal the Fundamental Difference between Two-State and Single-State Reactivity Patterns in Nonheme Fe^IV&n.dbond;O versus Ru^IV&n.dbond;O Oxidants

Dhuri, Sunder N.,Seo, Mi Sook,Lee, Yong-Min,Hirao, Hajime,Wang, Yong,Nam, Wonwoo,Shaik, Sason WILEY-VCH Verlag 2008 Angewandte Chemie. international edition Vol.47 No.18

<B>Graphic Abstract</B> <P>Two-state reactivity involving close triplet ground and quintet excited states is responsible for the opposite reactivity trends of Fe<SUP>IV</SUP> oxo complexes in O-transfer and H-abstraction reactions in dependence on the electron richness of the axial ligand X (see picture), as shown by comparison with Ru<SUP>IV</SUP> analogues, in which both reactivities are solely governed by the electrophilicity of the complex because the quintet state is inaccessible. <img src='wiley_img/14337851-2008-47-18-ANIE200705880-content.gif' alt='wiley_img/14337851-2008-47-18-ANIE200705880-content'> </P>

Experiment and Theory Reveal the Fundamental Difference between Two-State and Single-State Reactivity Patterns in Nonheme Fe^IV&n.dbond;O versus Ru^IV&n.dbond;O Oxidants

Dhuri, Sunder N.,Seo, Mi Sook,Lee, Yong-Min,Hirao, Hajime,Wang, Yong,Nam, Wonwoo,Shaik, Sason WILEY-VCH Verlag 2008 Angewandte Chemie Vol.120 No.18

<B>Graphic Abstract</B> <P>Zwei reaktive Zustände, ein Triplett-Grundzustand und ein nur wenig höher liegender angeregter Quintettzustand, führen – je nach den elektronischen Verhältnissen des axialen Liganden X – zu entgegengesetzten Reaktivitäten von Fe<SUP>IV</SUP>-Oxokomplexen in O-Transfer- und H-Abstraktionsreaktionen (siehe Bild). Bei den Ru<SUP>IV</SUP>-Analoga werden beide Reaktivitäten dagegen einzig durch die Elektrophilie des Komplexes bestimmt, da der Quintettzustand nicht verfügbar ist. <img src='wiley_img/00448249-2008-120-18-ANGE200705880-content.gif' alt='wiley_img/00448249-2008-120-18-ANGE200705880-content'> </P>

Water as an Oxygen Source in the Generation of Mononuclear Nonheme Iron(IV) Oxo Complexes

Lee, Yong-Min,Dhuri, Sunder N.,Sawant, Sarvesh C.,Cho, Jaeheung,Kubo, Minoru,Ogura, Takashi,Fukuzumi, Shunichi,Nam, Wonwoo WILEY-VCH Verlag 2009 Angewandte Chemie Vol.48 No.10

<P>Give me an “O”! Mononuclear nonheme iron(IV) oxo complexes have been generated using water as an oxygen source and cerium(IV) as an oxidant. The high-yield oxygenation of organic substrates in this system (see picture, Fe green, O red, N blue, C gray) is catalyzed by iron(II) complexes. The source of oxygen in the iron(IV) oxo complexes and the oxygenated products has been assigned unambiguously by isotopic labeling experiments. <img src='wiley_img/14337851-2009-48-10-ANIE200805670-content.gif' alt='wiley_img/14337851-2009-48-10-ANIE200805670-content'> </P> <B>Graphic Abstract</B> <P>Give me an “O”! Mononuclear nonheme iron(IV) oxo complexes have been generated using water as an oxygen source and cerium(IV) as an oxidant. The high-yield oxygenation of organic substrates in this system (see picture, Fe green, O red, N blue, C gray) is catalyzed by iron(II) complexes. The source of oxygen in the iron(IV) oxo complexes and the oxygenated products has been assigned unambiguously by isotopic labeling experiments. <img src='wiley_img/14337851-2009-48-10-ANIE200805670-content.gif' alt='wiley_img/14337851-2009-48-10-ANIE200805670-content'> </P>

Dioxygen Activation and O-O Bond Formation Reactions by Manganese Corroles

Guo, Mian,Lee, Yong-Min,Gupta, Ranjana,Seo, Mi Sook,Ohta, Takehiro,Wang, Hua-Hua,Liu, Hai-Yang,Dhuri, Sunder N.,Sarangi, Ritimukta,Fukuzumi, Shunichi,Nam, Wonwoo American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.44

<P>Activation of dioxygen (O-2) in enzymatic and biomimetic reactions has been intensively investigated over the past several decades. More recently, O-O bond formation, which is the reverse of the O-2-activation reaction, has been the focus of current research. Herein, we report the O-2-activation and O-O bond formation reactions by manganese corrole complexes. In the O-2-activation reaction, Mn(V)-oxo and Mn(IV)-peroxo intermediates were formed when Mn(III) corroles were exposed to O-2 in the presence of base (e.g., OH-) and hydrogen atom (H atom) donor (e.g., THE or cyclic olefins); the O-2-activation reaction did not occur in the absence of base and H atom donor. Moreover, formation of the Mn(V)-oxo and Mn(IV)-peroxo species was dependent on the amounts of base present in the reaction solution. The role of the base was proposed to lower the oxidation potential of the Mn(III) corroles, thereby facilitating the binding of O-2 and forming a Mn(IV)-superoxo species. The putative Mn(IV)-superoxo species was then converted to the corresponding Mn(IV)-hydroperoxo species by abstracting a H atom from H atom donor, followed by the O-O bond cleavage of the putative Mn(IV)-hydroperoxo species to form a Mn(V)-oxo species. We have also shown that addition of hydroxide ion to the Mn(V)-oxo species afforded the Mn(IV)-peroxo species via O-O bond formation and the resulting Mn(IV)-peroxo species reverted to the Mn(V)-oxo species upon addition of proton, indicating that the O-O bond formation and cleavage reactions between the Mn(V)-oxo and Mn(IV)-peroxo complexes are reversible. The present study reports the first example of using the same manganese complex in both O-2-activation and O-O bond formation reactions.</P>