14 research outputs found
Copper(II) Activation of Nitrite: Nitrosation of Nucleophiles and Generation of NO by Thiols
Nitrite
(NO<sub>2</sub><sup>ā</sup>) and nitroso compounds
(E-NO, E = RS, RO, and R<sub>2</sub>N) in mammalian plasma and cells
serve important roles in nitric oxide (NO) dependent as well as NO
independent signaling. Employing an electron deficient Ī²-diketiminato
copperĀ(II) nitrito complex [Cl<sub>2</sub>NN<sub>F6</sub>]ĀCuĀ(Īŗ<sup>2</sup>-O<sub>2</sub>N)Ā·THF, thiols mediate reduction of nitrite
to NO. In contrast to NO generation upon reaction of thiols at iron
nitrite species, at copper this conversion proceeds through nucleophilic
attack of thiol RSH on the bound nitrite in [Cu<sup>II</sup>]Ā(Īŗ<sup>2</sup>-O<sub>2</sub>N) that leads to <i>S</i>-nitrosation
to give the <i>S</i>-nitrosothiol RSNO and copperĀ(II) hydroxide
[Cu<sup>II</sup>]-OH. This nitrosation pathway is general and results
in the nitrosation of the amine Ph<sub>2</sub>NH and alcohol <sup>t</sup>BuOH to give Ph<sub>2</sub>NNO and <sup>t</sup>BuONO, respectively.
NO formation from thiols occurs from the reaction of RSNO and a copperĀ(II)
thiolate [Cu<sup>II</sup>]-SR intermediate formed upon reaction of
an additional equiv thiol with [Cu<sup>II</sup>]-OH
Copper(II) Activation of Nitrite: Nitrosation of Nucleophiles and Generation of NO by Thiols
Nitrite
(NO<sub>2</sub><sup>ā</sup>) and nitroso compounds
(E-NO, E = RS, RO, and R<sub>2</sub>N) in mammalian plasma and cells
serve important roles in nitric oxide (NO) dependent as well as NO
independent signaling. Employing an electron deficient Ī²-diketiminato
copperĀ(II) nitrito complex [Cl<sub>2</sub>NN<sub>F6</sub>]ĀCuĀ(Īŗ<sup>2</sup>-O<sub>2</sub>N)Ā·THF, thiols mediate reduction of nitrite
to NO. In contrast to NO generation upon reaction of thiols at iron
nitrite species, at copper this conversion proceeds through nucleophilic
attack of thiol RSH on the bound nitrite in [Cu<sup>II</sup>]Ā(Īŗ<sup>2</sup>-O<sub>2</sub>N) that leads to <i>S</i>-nitrosation
to give the <i>S</i>-nitrosothiol RSNO and copperĀ(II) hydroxide
[Cu<sup>II</sup>]-OH. This nitrosation pathway is general and results
in the nitrosation of the amine Ph<sub>2</sub>NH and alcohol <sup>t</sup>BuOH to give Ph<sub>2</sub>NNO and <sup>t</sup>BuONO, respectively.
NO formation from thiols occurs from the reaction of RSNO and a copperĀ(II)
thiolate [Cu<sup>II</sup>]-SR intermediate formed upon reaction of
an additional equiv thiol with [Cu<sup>II</sup>]-OH
Copper(II) Activation of Nitrite: Nitrosation of Nucleophiles and Generation of NO by Thiols
Nitrite
(NO<sub>2</sub><sup>ā</sup>) and nitroso compounds
(E-NO, E = RS, RO, and R<sub>2</sub>N) in mammalian plasma and cells
serve important roles in nitric oxide (NO) dependent as well as NO
independent signaling. Employing an electron deficient Ī²-diketiminato
copperĀ(II) nitrito complex [Cl<sub>2</sub>NN<sub>F6</sub>]ĀCuĀ(Īŗ<sup>2</sup>-O<sub>2</sub>N)Ā·THF, thiols mediate reduction of nitrite
to NO. In contrast to NO generation upon reaction of thiols at iron
nitrite species, at copper this conversion proceeds through nucleophilic
attack of thiol RSH on the bound nitrite in [Cu<sup>II</sup>]Ā(Īŗ<sup>2</sup>-O<sub>2</sub>N) that leads to <i>S</i>-nitrosation
to give the <i>S</i>-nitrosothiol RSNO and copperĀ(II) hydroxide
[Cu<sup>II</sup>]-OH. This nitrosation pathway is general and results
in the nitrosation of the amine Ph<sub>2</sub>NH and alcohol <sup>t</sup>BuOH to give Ph<sub>2</sub>NNO and <sup>t</sup>BuONO, respectively.
NO formation from thiols occurs from the reaction of RSNO and a copperĀ(II)
thiolate [Cu<sup>II</sup>]-SR intermediate formed upon reaction of
an additional equiv thiol with [Cu<sup>II</sup>]-OH
Copper(II) Activation of Nitrite: Nitrosation of Nucleophiles and Generation of NO by Thiols
Nitrite
(NO<sub>2</sub><sup>ā</sup>) and nitroso compounds
(E-NO, E = RS, RO, and R<sub>2</sub>N) in mammalian plasma and cells
serve important roles in nitric oxide (NO) dependent as well as NO
independent signaling. Employing an electron deficient Ī²-diketiminato
copperĀ(II) nitrito complex [Cl<sub>2</sub>NN<sub>F6</sub>]ĀCuĀ(Īŗ<sup>2</sup>-O<sub>2</sub>N)Ā·THF, thiols mediate reduction of nitrite
to NO. In contrast to NO generation upon reaction of thiols at iron
nitrite species, at copper this conversion proceeds through nucleophilic
attack of thiol RSH on the bound nitrite in [Cu<sup>II</sup>]Ā(Īŗ<sup>2</sup>-O<sub>2</sub>N) that leads to <i>S</i>-nitrosation
to give the <i>S</i>-nitrosothiol RSNO and copperĀ(II) hydroxide
[Cu<sup>II</sup>]-OH. This nitrosation pathway is general and results
in the nitrosation of the amine Ph<sub>2</sub>NH and alcohol <sup>t</sup>BuOH to give Ph<sub>2</sub>NNO and <sup>t</sup>BuONO, respectively.
NO formation from thiols occurs from the reaction of RSNO and a copperĀ(II)
thiolate [Cu<sup>II</sup>]-SR intermediate formed upon reaction of
an additional equiv thiol with [Cu<sup>II</sup>]-OH
Copper(II) Activation of Nitrite: Nitrosation of Nucleophiles and Generation of NO by Thiols
Nitrite
(NO<sub>2</sub><sup>ā</sup>) and nitroso compounds
(E-NO, E = RS, RO, and R<sub>2</sub>N) in mammalian plasma and cells
serve important roles in nitric oxide (NO) dependent as well as NO
independent signaling. Employing an electron deficient Ī²-diketiminato
copperĀ(II) nitrito complex [Cl<sub>2</sub>NN<sub>F6</sub>]ĀCuĀ(Īŗ<sup>2</sup>-O<sub>2</sub>N)Ā·THF, thiols mediate reduction of nitrite
to NO. In contrast to NO generation upon reaction of thiols at iron
nitrite species, at copper this conversion proceeds through nucleophilic
attack of thiol RSH on the bound nitrite in [Cu<sup>II</sup>]Ā(Īŗ<sup>2</sup>-O<sub>2</sub>N) that leads to <i>S</i>-nitrosation
to give the <i>S</i>-nitrosothiol RSNO and copperĀ(II) hydroxide
[Cu<sup>II</sup>]-OH. This nitrosation pathway is general and results
in the nitrosation of the amine Ph<sub>2</sub>NH and alcohol <sup>t</sup>BuOH to give Ph<sub>2</sub>NNO and <sup>t</sup>BuONO, respectively.
NO formation from thiols occurs from the reaction of RSNO and a copperĀ(II)
thiolate [Cu<sup>II</sup>]-SR intermediate formed upon reaction of
an additional equiv thiol with [Cu<sup>II</sup>]-OH
Facile CāH, CāF, CāCl, and CāC Activation by Oxatitanacyclobutene Complexes
Aryl
ketones react readily with oxatitanacyclobutenes bearing pentamethylcyclopentadienyl
ligands to form unique titanocene complexes resulting from Cp* modification
and CāH activation. An intermediate in this reaction is intercepted
with various functional groups to form carbonyl insertion, CāF
activation, and cyclopropane ring-opening products
El Diario de Pontevedra : periĆ³dico liberal: Ano XXVII NĆŗmero 7742 - 1910 marzo 1
CopperĀ(II) aryl species are proposed
key intermediates in Cu-catalyzed
cross-coupling reactions. Novel three-coordinate copperĀ(II) aryls
[Cu<sup>II</sup>]-C<sub>6</sub>F<sub>5</sub> supported by ancillary
Ī²-diketiminate ligands form in reactions between copperĀ(II)
alkoxides [Cu<sup>II</sup>]-O<sup><i>t</i></sup>Bu and BĀ(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>. Crystallographic, spectroscopic,
and DFT studies reveal geometric and electronic structures of these
CuĀ(II) organometallic complexes. Reaction of [Cu<sup>II</sup>]-C<sub>6</sub>F<sub>5</sub> with the free radical NO<sub>(g)</sub> results
in C-N bond formation to give [Cu]Ā(Ī·<sup>2</sup>-ONC<sub>6</sub>F<sub>5</sub>). Remarkably, addition of the phenolate anion
PhO<sup>ā</sup> to [Cu<sup>II</sup>]-C<sub>6</sub>F<sub>5</sub> directly affords diaryl ether PhO-C<sub>6</sub>F<sub>5</sub> with
concomitant generation of the copperĀ(I) species [Cu<sup>I</sup>]Ā(solvent)
and {[Cu<sup>I</sup>]-C<sub>6</sub>F<sub>5</sub>}<sup>ā</sup>. Experimental and computational analysis supports redox disproportionation
between [Cu<sup>II</sup>]-C<sub>6</sub>F<sub>5</sub> and {[Cu<sup>II</sup>]Ā(C<sub>6</sub>F<sub>5</sub>)Ā(OPh)}<sup>ā</sup> to give {[Cu<sup>I</sup>]-C<sub>6</sub>F<sub>5</sub>}<sup>ā</sup> and [Cu<sup>III</sup>]Ā(C<sub>6</sub>F<sub>5</sub>)Ā(OPh) unstable
toward reductive elimination to [Cu<sup>I</sup>]Ā(solvent) and
PhO-C<sub>6</sub>F<sub>5</sub>
Quantitative Analysis of Different Formation Modes of Platinum Nanocrystals Controlled by Ligand Chemistry
Well-defined
metal nanocrystals play important roles in various
fields, such as catalysis, medicine, and nanotechnology. They are
often synthesized through kinetically controlled process in colloidal
systems that contain metal precursors and surfactant molecules. The
chemical functionality of surfactants as coordinating ligands to metal
ions however remains a largely unsolved problem in this process. Understanding
the metalāligand complexation and its effect on formation kinetics
at the molecular level is challenging but essential to the synthesis
design of colloidal nanocrystals. Herein we report that spontaneous
ligand replacement and anion exchange control the form of coordinated
Ptāligand intermediates in the system of platinum acetylacetonate
[PtĀ(acac)<sub>2</sub>], primary aliphatic amine, and carboxylic acid
ligands. The formed intermediates govern the formation mode of Pt
nanocrystals, leading to either a pseudo two-step or a one-step mechanism
by switching on or off an autocatalytic surface growth. This finding
shows the importance of metalāligand complexation at the prenucleation
stage and represents a critical step forward for the designed synthesis
of nanocrystal-based materials
Uranium(IV) Chloride Complexes: UCl<sub>6</sub><sup>2ā</sup> and an Unprecedented U(H<sub>2</sub>O)<sub>4</sub>Cl<sub>4</sub> Structural Unit
The room temperature
synthesis and structural characterization of two UĀ(IV) compounds isolated
from acidic aqueous solution is reported. Evaporation of a UĀ(IV)/HCl
solution containing pyridinium (HPy) yielded (HPy)<sub>2</sub>UCl<sub>6</sub> (<b>1</b>), yet in the presence of an organic carboxylate
UĀ(H<sub>2</sub>O)<sub>4</sub>Cl<sub>4</sub>ĀĀ·(HPyĀ·Cl)<sub>2</sub> (<b>2</b>) is obtained. The structures have been determined
by single crystal X-ray diffraction and characterized by Raman, IR,
and optical spectroscopies. The magnetism of both compounds was also
investigated. The structure of <b>1</b> is built from UCl<sub>6</sub><sup>2ā</sup> anionic units, pervasive in descriptions
of the aqueous chemistry of tetravalent uranium, and is found to undergo
a phase transition from <i>C</i>2/<i>m</i> to <i>P</i>1Ģ
upon cooling. By comparison, the structure of <b>2</b> contains a neutral UĀ(IV)-aquo-chloro complex, UĀ(H<sub>2</sub>O)<sub>4</sub>Cl<sub>4</sub>, for which there is no literature precedence.
Density functional theory calculations were performed to predict the
geometries, vibrational frequencies, and relative energetics of the
UCl<sub>6</sub><sup>2ā</sup> and UĀ(H<sub>2</sub>O)<sub>4</sub>Cl<sub>4</sub> units. The energetics of the reaction of UĀ(H<sub>2</sub>O)<sub>4</sub>Cl<sub>4</sub> to form the dianion are predicted to
be exothermic in the gas phase and in aqueous solution. The predicted
energetics coupled with no previous solid state reports of a UĀ(IV)-aquo-chloro
complex may point toward the importance of hydrogen bonding and other
supramolecular interactions, prevalent in the structures of <b>1</b> and <b>2</b>, on the stabilization and/or crystallization
of the UĀ(H<sub>2</sub>O)<sub>4</sub>Cl<sub>4</sub> structural unit
Mechanism of H<sub>2</sub> Production by Models for the [NiFe]-Hydrogenases: Role of Reduced Hydrides
The
intermediacy of a reduced nickelāiron hydride in hydrogen
evolution catalyzed by NiāFe complexes was verified experimentally
and computationally. In addition to catalyzing hydrogen evolution,
the highly basic and bulky (dppv)ĀNiĀ(Ī¼-pdt)ĀFeĀ(CO)Ā(dppv)
([<b>1</b>]<sup>0</sup>; dppv = <i>cis</i>-C<sub>2</sub>H<sub>2</sub>Ā(PPh<sub>2</sub>)<sub>2</sub>) and its hydride
derivatives have yielded to detailed characterization in terms of
spectroscopy, bonding, and reactivity. The protonation of [<b>1</b>]<sup>0</sup> initially produces <i>unsym</i>-[H<b>1</b>]<sup>+</sup>, which converts by a first-order pathway to <i>sym</i>-[H<b>1</b>]<sup>+</sup>. These species have <i>C</i><sub>1</sub> (unsym) and <i>C</i><sub><i>s</i></sub> (sym) symmetries, respectively, depending on the
stereochemistry of the octahedral Fe site. Both experimental and computational
studies show that [H<b>1</b>]<sup>+</sup> protonates at sulfur.
The <i>S</i> = 1/2 hydride [H<b>1</b>]<sup>0</sup> was generated by reduction of [H<b>1</b>]<sup>+</sup> with
Cp*<sub>2</sub>Co. Density functional theory (DFT) calculations indicate
that [H<b>1</b>]<sup>0</sup> is best described as a NiĀ(I)āFeĀ(II)
derivative with significant spin density on Ni and some delocalization
on S and Fe. EPR spectroscopy reveals both kinetic and thermodynamic
isomers of [H<b>1</b>]<sup>0</sup>. Whereas [H<b>1</b>]<sup>+</sup> does not evolve H<sub>2</sub> upon protonation, treatment
of [H<b>1</b>]<sup>0</sup> with acids gives H<sub>2</sub>. The
redox state of the āremoteā metal (Ni) modulates the
hydridic character of the FeĀ(II)āH center. As supported by
DFT calculations, H<sub>2</sub> evolution proceeds either directly
from [H<b>1</b>]<sup>0</sup> and external acid or from protonation
of the FeāH bond in [H<b>1</b>]<sup>0</sup> to give a
labile dihydrogen complex. Stoichiometric tests indicate that protonation-induced
hydrogen evolution from [H<b>1</b>]<sup>0</sup> initially produces
[<b>1</b>]<sup>+</sup>, which is reduced by [H<b>1</b>]<sup>0</sup>. Our results reconcile the required reductive activation
of a metal hydride and the resistance of metal hydrides toward reduction.
This dichotomy is resolved by reduction of the remote (non-hydride)
metal of the bimetallic unit