8 research outputs found
C–S Bond Cleavage, Redox Reactions, and Dioxygen Activation by Nonheme Dicobalt(II) Complexes
Synthesis
and reactivity of a series of thiolate/thiocarboxylate bridged dicobaltÂ(II)
complexes were investigated in comparison with their carboxylate bridged
analogues bearing free thiol/hydroxyl groups. Upon one-electron oxidation,
complexes [Co<sub>2</sub>(<i>N-</i>Et-HPTB)Â(μ-SR<sup>1</sup>)]Â(BF<sub>4</sub>)<sub>2</sub> (R<sup>1</sup> = Ph, <b>1a</b>; Et, <b>1b</b>; Py, <b>1c</b>) and [Co<sub>2</sub>(<i>N-</i>Et-HPTB)Â(μ-SCOR<sup>2</sup>)]Â(BF<sub>4</sub>)<sub>2</sub> (R<sup>2</sup> = Ph, <b>2a</b>; Me, <b>2b</b>) yielded [Co<sub>2</sub>(<i>N-</i>Et-HPTB)Â(DMF)<sub>2</sub>]Â(BF<sub>4</sub>)<sub>3</sub> (<b>6</b>) (DMF = dimethylformamide) along with the corresponding
disulfides (where <i>N</i>-Et-HPTB is the anion of <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetrakisÂ[2-(1-ethylbenzimidazolyl)]-2-hydroxy-1,3-diaminopropane).
Unlike the inertness of carboxylate bridged complexes [Co<sub>2</sub>(<i>N-</i>Et-HPTB)Â(μ-O<sub>2</sub>C-R<sup>3</sup>-SH)]Â(BF<sub>4</sub>)<sub>2</sub> (R<sup>3</sup> = Ph, <b>3a</b>; CH<sub>2</sub>CH<sub>2</sub>, <b>3b</b>) and [Co<sub>2</sub>(<i>N-</i>Et-HPTB)Â(μ-O<sub>2</sub>CR<sup>4</sup>)]Â(BF<sub>4</sub>)<sub>2</sub> (R<sup>4</sup> = Ph, <b>4a</b>; Me, <b>4b</b>; CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>OH, <b>5</b>) toward O<sub>2</sub>, the bridging ethanethiolate
in <b>1b</b> was oxidized to yield a sulfinate bridged complex,
[Co<sub>2</sub>(<i>N-</i>Et-HPTB)Â(μ-O<sub>2</sub>SEt)]Â(BF<sub>4</sub>)<sub>2</sub> (<b>10</b>). Detailed investigation
of the synthetic aspects of <b>1a</b>–<b>1c</b> led to the discovery of a C–S bond cleavage reaction and
yielded the dicobaltÂ(II) complexes [Co<sub>2</sub>(<i>N-</i>Et-HPTB)Â(SH)Â(H<sub>2</sub>O)]Â(BF<sub>4</sub>)<sub>2</sub> (<b>8a</b>), [Co<sub>2</sub>(<i>N-</i>CH<sub>2</sub>Py-HPTB)Â(SH)Â(H<sub>2</sub>O)]Â(BF<sub>4</sub>)<sub>2</sub> (<b>8b</b>) (where <i>N</i>-CH<sub>2</sub>Py-HPTB is the anion of <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetrakisÂ[2-(1-picolylbenzimidazolyl)]-2-hydroxy-1,3-diaminopropane)),
and [Co<sub>2</sub>(<i>N-</i>Et-HPTB)Â(μ-S)]Â(BF<sub>4</sub>) (<b>9</b>). Both <b>8a</b> and <b>8b</b> feature nonheme dinuclear CoÂ(II) units containing a terminal hydrosulfide.
The present study thus reports comparative redox reactions for a rare
class of 16 dicobaltÂ(II) complexes and introduces a selective synthetic
strategy for the synthesis of unprecedented dicobaltÂ(II) complexes
featuring only one terminal hydrosulfide
Controlling the Reactivity of Bifunctional Ligands: Carboxylate-Bridged Nonheme Diiron(II) Complexes Bearing Free Thiol Groups
Carboxylate-bridged
nonheme diironÂ(II) complexes, bearing free functional groups in general,
and free thiol groups in particular, were sought. While the addition
of sodium γ-hydroxybutyrate into a mixture of FeÂ(BF<sub>4</sub>)<sub>2</sub>·6H<sub>2</sub>O, H<i>N</i>-Et-HPTB,
and Et<sub>3</sub>N afforded the complex [Fe<sub>2</sub>(<i>N</i>-Et-HPTB)Â(μ-O<sub>2</sub>C–(CH<sub>2</sub>)<sub>3</sub>–OH)]Â(BF<sub>4</sub>)<sub>2</sub> (<b>2</b>) (where <i>N</i>-Et-HPTB is the anion of <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetrakisÂ(2-(1-ethylbenzimidazolyl))-2-hydroxy-1,3-diaminopropane),
a similar, straightforward process could not be used for the synthesis
of diironÂ(II) complexes with free thiol groups. In order to circumvent
this problem, a new class of thiolate bridged diironÂ(II) complexes,
[Fe<sub>2</sub>(<i>N</i>-Et-HPTB)Â(μ-SR<sup>1</sup>)]Â(BF<sub>4</sub>)<sub>2</sub> (R<sup>1</sup> = Me (<b>1a</b>), Et (<b>1b</b>), <sup><i>t</i></sup>Bu (<b>1c</b>), Ph (<b>1d</b>)) was synthesized. Selective proton exchange
reactions of one representative compound, <b>1b</b>, with reagents
of the type HS–R<sup>2</sup>–COOH yielded the target
compounds, [Fe<sub>2</sub>(<i>N</i>-Et-HPTB)Â(μ-O<sub>2</sub>C–R<sup>2</sup>–SH)]Â(BF<sub>4</sub>)<sub>2</sub> (R<sup>2</sup> = C<sub>6</sub>H<sub>4</sub> (<b>3a</b>), CH<sub>2</sub>CH<sub>2</sub> (<b>3b</b>), CH<sub>2</sub>(CH<sub>2</sub>)<sub>5</sub>CH<sub>2</sub> (<b>3c</b>)). Redox properties
of the complexes <b>3a</b>–<b>3c</b> were studied
in comparison with the complex, [Fe<sub>2</sub>(<i>N</i>-Et-HPTB)Â(μ-O<sub>2</sub>CMe)]Â(BF<sub>4</sub>)<sub>2</sub> (<b>5</b>). Reaction of (Cp<sub>2</sub>Fe)Â(BF<sub>4</sub>) with <b>1b</b> yielded [Fe<sup>II</sup><sub>2</sub>(<i>N</i>-Et-HPTB)Â(DMF)<sub>3</sub>]Â(BF<sub>4</sub>)<sub>3</sub>·DMF
(<b>4</b>) (when crystallized from DMF/diethyl ether), which
might indicate the formation of a transient ethanethiolate bridged
{Fe<sup>II</sup>Fe<sup>III</sup>} species, followed by a rapid internal
redox reaction to generate diethyldisulfide and the solvent coordinated
diironÂ(II) complex, <b>4</b>. This possibility was supported
by a comparative cyclic voltammetric study of <b>1a</b>–<b>1c</b> and <b>4</b>. Prospects of the complexes of the type <b>3a</b>–<b>3c</b> as potential building blocks for
the synthesis of nonheme diironÂ(II) complexes covalently attached
with other redox active metals has been substantiated by the synthesis
of the complexes, [Fe<sub>2</sub>(<i>N</i>-EtHPTB)Â(μ-O<sub>2</sub>C–R<sup>2</sup>–S)ÂCuÂ(Me<sub>3</sub>TACN)]Â(BF<sub>4</sub>)<sub>2</sub> (R = <i>p</i>-C<sub>6</sub>H<sub>4</sub> (<b>7a</b>), CH<sub>2</sub>CH<sub>2</sub> (<b>7b</b>)). All the compounds were characterized by a combination of single-crystal
X-ray structure determinations and/or elemental analysis
Non-Heme Mononitrosyldiiron Complexes: Importance of Iron Oxidation State in Controlling the Nature of the Nitrosylated Products
Mononitrosyldiiron complexes having
either an [Fe<sup>II</sup>·{FeNO}<sup>7</sup>] or an [Fe<sup>III</sup>·{FeNO}<sup>7</sup>] core formulation have been synthesized
by methods that rely on redox-state-induced differentiation of the
diiron starting materials in an otherwise symmetrical dinucleating
ligand environment. The synthesis, X-ray structures, Mössbauer
spectroscopy, cyclic voltammetry, and dioxygen reactivity of [Fe<sup>III</sup>·{FeNO}<sup>7</sup>] are described
Non-Heme Mononitrosyldiiron Complexes: Importance of Iron Oxidation State in Controlling the Nature of the Nitrosylated Products
Mononitrosyldiiron complexes having
either an [Fe<sup>II</sup>·{FeNO}<sup>7</sup>] or an [Fe<sup>III</sup>·{FeNO}<sup>7</sup>] core formulation have been synthesized
by methods that rely on redox-state-induced differentiation of the
diiron starting materials in an otherwise symmetrical dinucleating
ligand environment. The synthesis, X-ray structures, Mössbauer
spectroscopy, cyclic voltammetry, and dioxygen reactivity of [Fe<sup>III</sup>·{FeNO}<sup>7</sup>] are described
Generation and Reactivity of Polychalcogenide Chains in Binuclear Cobalt(II) Complexes
A series of six binuclear Co(II)–thiolate complexes,
[Co2(BPMP)(S–C6H4-o-X)2]1+ (X = OMe, 2;
NH2, 3), [Co2(BPMP)(μ-S–C6H4-o-O)]1+ (4), and [Co2(BPMP)(μ-Y)]1+ (Y = bdt, 5; tdt, 6; mnt, 7), has been synthesized
from [Co2(BPMP)(MeOH)2(Cl)2]1+ (1a) and [Co2(BPMP)(Cl)2]1+ (1b), where BPMP1– is
the anion of 2,6-bis[[bis(2-pyridylmethyl)amino]methyl]-4-methylphenol.
While 2 and 3 could allow the two-electron
redox reaction of the two coordinated thiolates with elemental sulfur
(S8) to generate [Co2(BPMP)(μ-S5)]1+ (8), the complexes, 4–7, could not undergo a similar reaction. An analogous redox reaction
of 2 with elemental selenium ([Se]) produced [{Co2(BPMP)(μ-Se4)}{Co2(BPMP)(μ-Se3)}]2+ (9a) and [Co2(BPMP)(μ-Se4)]1+ (9b). Further reaction of these
polychalcogenido complexes, 8 and 9a/9b, with PPh3 allowed the isolation of [Co2(BPMP)(μ-S)]1+ (10) and [Co2(BPMP)(μ-Se2)]1+ (11), which, in turn, could be converted back to 8 and 9a upon treatment with S8 and [Se], respectively.
Interestingly, while the redox reaction of the polyselenide chains
in 9a and 11 with S8 produced 8 and [Se], the treatment of 8 with [Se] gave
back only the starting material (8), thus demonstrating
the different redox behavior of sulfur and selenium. Furthermore,
the reaction of 8 and 9a/9b with activated alkynes and cyanide (CN–) allowed
the isolation of the complexes, [Co2(BPMP)(μ-E2C2(CO2R)2)]1+ (E
= S: 12a, R = Me; 12b, R = Et; E = Se: 13a, R = Me; 13b, R = Et) and [Co2(BPMP)(μ-SH)(NCS)2] (14), respectively.
The present work, thus, provides an interesting synthetic strategy,
interconversions, and detailed comparative reactivity of binuclear
Co(II)–polychalcogenido complexes
Neuroscience Gateway – An Overview
The Neuroscience Gateway (NSG http://www.nsgportal.org), a NSF funded project, catalyzes computational neuroscience research by lowering or eliminating the <br>administrative and technical barriers that can make it difficult for <br>neuroscience researchers to access supercomputer resources for large <br>scale simulations and brain image data processing. It provides free and <br>open access to supercomputers using time acquired via the peer reviewed allocation process managed by the Extreme Science and Engineering Discovery Environment (XSEDE). <br><br>It has about 400 registered users. Total core hours used, per-user rate of usage, and the number of users have all been growing at a rapid rate. Given current annual usage and the rate at which it has risen over the past 4 years, we expect NSG users to need about 10,000,000 core hours in 2017. <br><br>NSG is enabling participation by the wider neuroscience community in <br>research that would otherwise involve too great a computational burden, <br>such as large scale and detailed models of cells and networks, parameter <br>optimization, brain image processing, connectome pipelines etc., <br>resulting in over 50 publications and posters to date. <br><br>Many neuroscientists who are developing new network modeling tools, data <br>driven parameter optimization pipelines (such as the BluePyOpt from the <br>Human Brain Project) etc. are using the NSG to disseminate their results <br>to the neuroscience community. <br><br>NSG's scope has been expanded to offer programmatic access to <br>supercomputing resources in addition to access via the web portal. <br>Developing and operating the NSG has given us a unique opportunity to <br>understand and analyze how a very diverse range of neuroscientists are <br>using an environment like the NSG, and examine their growing need for <br>supercomputer power, as well as associated issues and needs for <br>collaboration, data sharing/management and various forms of computing
Functional Mononitrosyl Diiron(II) Complex Mediates the Reduction of NO to N<sub>2</sub>O with Relevance for Flavodiiron NO Reductases
Reaction of [Fe<sub>2</sub>(<i>N</i>-Et-HPTB)Â(CH<sub>3</sub>COS)]Â(BF<sub>4</sub>)<sub>2</sub> (<b>1</b>) with (NO)Â(BF<sub>4</sub>) produces
a nonheme mononitrosyl diironÂ(II) complex, [Fe<sub>2</sub>(<i>N</i>-Et-HPTB)Â(NO)Â(DMF)<sub>3</sub>]Â(BF<sub>4</sub>)<sub>3</sub> (<b>2</b>). Complex <b>2</b> is
the first example of a [Fe<sup>II</sup>{FeÂ(NO)}<sup>7</sup>] species
and is also the first example of a mononitrosyl diironÂ(II) complex
that mediates the reduction of NO to N<sub>2</sub>O. This work describes
the selective synthesis, detailed characterization and NO reduction
activity of <b>2</b> and thus provides new insights regarding
the mechanism of flavodiiron nitric oxide reductases
Light-Induced N<sub>2</sub>O Production from a Non-heme Iron–Nitrosyl Dimer
Two
non-heme iron–nitrosyl species, [Fe<sub>2</sub>(<i>N</i>‑Et‑HPTB)Â(O<sub>2</sub>CPh)Â(NO)<sub>2</sub>]Â(BF<sub>4</sub>)<sub>2</sub> (<b>1a</b>) and [Fe<sub>2</sub>(<i>N</i>‑Et‑HPTB)Â(DMF)<sub>2</sub>(NO)Â(OH)]Â(BF<sub>4</sub>)<sub>3</sub> (<b>2a</b>), are characterized by FTIR
and resonance Raman spectroscopy. Binding of NO is reversible in both
complexes, which are prone to NO photolysis under visible light illumination.
Photoproduction of N<sub>2</sub>O occurs in high yield for <b>1a</b> but not <b>2a</b>. Low-temperature FTIR photolysis experiments
with <b>1a</b> in acetonitrile do not reveal any intermediate
species, but in THF at room temperature, a new {FeNO}<sup>7</sup> species
quickly forms under illumination and exhibits a νÂ(NO) vibration
indicative of nitroxyl-like character. This metastable species reacts
further under illumination to produce N<sub>2</sub>O. A reaction mechanism
is proposed, and implications for NO reduction in flavoÂdiiron
proteins are discussed