A Mononuclear Non-heme Manganese(III)-Aqua Complex as a New Active Oxidant in Hydrogen Atom Transfer Reactions

Sankaralingam, Muniyandi,Lee, Yong-Min,Karmalkar, Deepika G.,Nam, Wonwoo,Fukuzumi, Shunichi American Chemical Society 2018 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.140 No.40

<P>A mononuclear non-heme Mn(III)-aqua complex, [(dpaq)Mn<SUP>III</SUP>(OH<SUB>2</SUB>)]<SUP>2+</SUP> (<B>1</B>, dpaq = 2-[bis(pyridin-2-ylmethyl)]amino-<I>N</I>-quinolin-8-yl-acetamidate), is capable of conducting hydrogen atom transfer (HAT) reactions much more efficiently than the corresponding Mn(III)-hydroxo complex, [(dpaq)Mn<SUP>III</SUP>(OH)]<SUP>+</SUP> (<B>2</B>); the high reactivity of <B>1</B> results from the positive one-electron reduction potential of <B>1</B> (<I>E</I><SUB>red</SUB> vs SCE = 1.03 V), compared to that of <B>2</B> (<I>E</I><SUB>red</SUB> vs SCE = −0.1 V). The HAT mechanism of <B>1</B> varies between electron transfer followed by proton transfer and one-step concerted proton-coupled electron transfer, depending on the one-electron oxidation potentials of substrates. To the best of our knowledge, this is the first example showing that metal(III)-aqua complex can be an effective H-atom abstraction reagent.</P> [FIG OMISSION]</BR>

Compositional variations of chromian spinels from peridotites of the Spontang ophiolite complex, Ladakh, NW Himalayas, India: petrogenetic implications

Mallika K. Jonnalagadda,Nitin R. Karmalkar,Mathieu Benoit,Michel Gregoire,Raymond A. Duraiswami,Shivani Harshe,Sagar Kamble 한국지질과학협의회 2019 Geosciences Journal Vol.23 No.6

The Spontang ophiolite complex exposed along the Indus Tsangpo Suture Zone (ITSZ) represents a fragment of oceanic lithosphere emplaced after the closure of the Neo-Tethyan Ocean. The complex lying south of the ITSZ forms the highest tectonic thrust slice above the Mesozoic–Early Tertiary continental margin in the Ladakh-Zanskar Himalaya. The complex consists of a well-preserved ophiolite sequence dominated by peridotites, gabbros and ultramafic cumulates along with highly tectonized sheeted dykes and pillow lavas. The mantle suite of rocks is represented by minor lherzolites, harzburgites and dunites. Chromian spinel is brown to reddish, and its morphology and textural relationship with coexisting silicates varies with strain. Spinel occurs as blebs and vermicular exsolutions within orthopyroxene to spherical inclusions within olivine, characteristic of which is the elongate holly leaf shape. Chrome spinels are characterized by low TiO2 and high Cr2O3 indicative of their depleted nature. Cr# [= atomic ratio Cr/(Cr + Al)] in the studied spinels are characterized by a small decrease in TiO2 for a larger increase in Cr# consistent with observations for spinels aligned along the Luobusa trend of the Yarlung Zangpo Suture Zone (YZSZ) ophiolites. Variations in Cr-spinel Cr# and Mg# observed in the investigated peridotites may have resulted from a wide range of degrees of mantle melting during their evolution. Mineral and whole-rock chemistry of the Spontang peridotites is characterized by interaction between depleted magma and pre-existing oceanic lithosphere, typical of supra-subduction zone settings. The Spontang peridotites have olivine, clinopyroxene and orthopyroxene compositions similar to those from both abyssal and fore-arc peridotites and display spoon shaped REE profiles characteristic of interaction between LREE-enriched melt, derived from the subducting slab and LREE depleted mantle residues. Equilibration temperatures calculated for the above rocks indicate that the studied samples represent typical mantle peridotites formed within the spinel stability field.

A mononuclear nonheme {FeNO} ⁶ complex: synthesis and structural and spectroscopic characterization

Hong, Seungwoo,Yan, James J.,Karmalkar, Deepika G.,Sutherlin, Kyle D.,Kim, Jin,Lee, Yong-Min,Goo, Yire,Mascharak, Pradip K.,Hedman, Britt,Hodgson, Keith O.,Karlin, Kenneth D.,Solomon, Edward I.,Nam, W Royal Society of Chemistry 2018 Chemical science Vol.9 No.34

<▼1><P>X-ray structures of nonheme {FeNO}<SUP>6</SUP> and iron(<SMALL>III</SMALL>)-nitrito complexes bearing a tetraamido macrocyclic ligand are reported along with three different generation pathways.</P></▼1><▼2><P>While the synthesis and characterization of {FeNO}<SUP>7,8,9</SUP> complexes have been well documented in heme and nonheme iron models, {FeNO}<SUP>6</SUP> complexes have been less clearly understood. Herein, we report the synthesis and structural and spectroscopic characterization of mononuclear nonheme {FeNO}<SUP>6</SUP> and iron(<SMALL>III</SMALL>)–nitrito complexes bearing a tetraamido macrocyclic ligand (TAML), such as [(TAML)Fe<SUP>III</SUP>(NO)]<SUP>–</SUP> and [(TAML)Fe<SUP>III</SUP>(NO<SUB>2</SUB>)]<SUP>2–</SUP>, respectively. First, direct addition of NO<SUB>(g)</SUB> to [Fe<SUP>III</SUP>(TAML)]<SUP>–</SUP> results in the formation of [(TAML)Fe<SUP>III</SUP>(NO)]<SUP>–</SUP>, which is sensitive to moisture and air. The spectroscopic data of [(TAML)Fe<SUP>III</SUP>(NO)]<SUP>–</SUP>, such as <SUP>1</SUP>H nuclear magnetic resonance and X-ray absorption spectroscopies, combined with computational study suggest the neutral nature of nitric oxide with a diamagnetic Fe center (<I>S</I> = 0). We also provide alternative pathways for the generation of [(TAML)Fe<SUP>III</SUP>(NO)]<SUP>–</SUP>, such as the iron–nitrite reduction triggered by protonation in the presence of ferrocene, which acts as an electron donor, and the photochemical iron–nitrite reduction. To the best of our knowledge, the present study reports the first photochemical nitrite reduction in nonheme iron models.</P></▼2>

Redox Reactivity of a Mononuclear Manganese-Oxo Complex Binding Calcium Ion and Other Redox-Inactive Metal Ions

Sankaralingam, Muniyandi,Lee, Yong-Min,Pineda-Galvan, Yuliana,Karmalkar, Deepika G.,Seo, Mi Sook,Jeon, So Hyun,Pushkar, Yulia,Fukuzumi, Shunichi,Nam, Wonwoo American Chemical Society 2019 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.141 No.3

<P>Mononuclear nonheme manganese(IV)-oxo complexes binding calcium ion and other redox-inactive metal ions, [(dpaq)Mn<SUP>IV</SUP>(O)]<SUP>+</SUP>-M<SUP><I>n</I>+</SUP> (<B>1</B>-M<SUP>n+</SUP>, M<SUP><I>n</I>+</SUP> = Ca<SUP>2+</SUP>, Mg<SUP>2+</SUP>, Zn<SUP>2+</SUP>, Lu<SUP>3+</SUP>, Y<SUP>3+</SUP>, Al<SUP>3+</SUP>, and Sc<SUP>3+</SUP>) (dpaq = 2-[bis(pyridin-2-ylmethyl)]amino-<I>N</I>-quinolin-8-yl-acetamidate), were synthesized by reacting a hydroxomanganese(III) complex, [(dpaq)Mn<SUP>III</SUP>(OH)]<SUP>+</SUP>, with iodosylbenzene (PhIO) in the presence of redox-inactive metal ions (M<SUP><I>n</I>+</SUP>). The Mn(IV)-oxo complexes were characterized using various spectroscopic techniques. In reactivity studies, we observed contrasting effects of M<SUP><I>n</I>+</SUP> on the reactivity of <B>1</B>-M<SUP><I>n</I>+</SUP> in redox reactions such as electron-transfer (ET), oxygen atom transfer (OAT), and hydrogen atom transfer (HAT) reactions. In the OAT and ET reactions, the reactivity order of <B>1</B>-M<SUP><I>n</I>+</SUP>, such as <B>1</B>-Sc<SUP>3+</SUP> ≈ <B>1</B>-Al<SUP>3+</SUP> > <B>1</B>-Y<SUP>3+</SUP> > <B>1</B>-Lu<SUP>3+</SUP> > <B>1</B>-Zn<SUP>2+</SUP> > <B>1</B>-Mg<SUP>2+</SUP> > <B>1</B>-Ca<SUP>2+</SUP>, follows the Lewis acidity of M<SUP><I>n</I>+</SUP> bound to the Mn-O moiety; that is, the stronger the Lewis acidity of M<SUP><I>n</I>+</SUP>, the higher the reactivity of <B>1</B>-M<SUP><I>n</I>+</SUP> becomes. In sharp contrast, the reactivity of <B>1</B>-M<SUP><I>n</I>+</SUP> in the HAT reaction was reversed, giving the reactivity order <B>1</B>-Ca<SUP>2+</SUP> > <B>1</B>-Mg<SUP>2+</SUP> > <B>1</B>-Zn<SUP>2+</SUP> > <B>1</B>-Lu<SUP>3+</SUP>> <B>1</B>-Y<SUP>3+</SUP>> <B>1</B>-Al<SUP>3+</SUP> ≈ <B>1</B>-Sc<SUP>3+</SUP>; that is, the higher is Lewis acidity of M<SUP><I>n</I>+</SUP>, the lower the reactivity of <B>1</B>-M<SUP><I>n</I>+</SUP> in the HAT reaction. The latter result implies that the Lewis acidity of M<SUP><I>n</I>+</SUP> bound to the Mn-O moiety can modulate the basicity of the metal-oxo moiety, thus influencing the HAT reactivity of <B>1</B>-M<SUP><I>n</I>+</SUP>; cytochrome P450 utilizes the axial thiolate ligand to increase the basicity of the iron-oxo moiety, which enhances the reactivity of compound I in C-H bond activation reactions.</P> [FIG OMISSION]</BR>