29 research outputs found
identification of a reversible EC-mechanism
Bu4N[Fe(CO)3(NO)] displays unique catalytic properties in electron-transfer
catalysis such as in allylic substitutions, hydrosilylation,
transesterifications, or carbene transfer chemistry. Herein we present a
detailed spectroelectrochemical investigation of this complex that unravels an
interesting electrochemical–chemical transformation in which two parts of
[Fe(CO)3(NO)]− are oxidized and undergo a disproportionation in the presence
of CO to [Fe(CO)5] and [Fe(CO)2(NO)2]. Upon re-reduction the former two
complexes regenerate [Fe(CO)3(NO)]− to about 85
Valence and spin situations in isomeric [(bpy)Ru(Q′)2]n (Q′ = 3,5-di-tert- butyl-N-aryl-1,2-benzoquinonemonoimine). An experimental and DFT analysis
The article deals with the ruthenium complexes, [(bpy)Ru(Q′)2] (1–3)
incorporating two unsymmetrical redox-noninnocent iminoquinone moieties [bpy =
2,2′-bipyridine; Q′ = 3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine, aryl
= C6H5 (Q′1), 1; m-Cl2C6H3 (Q′2), 2; m-(OCH3)2C6H3 (Q′3), 3]. 1 and 3 have
been preferentially stabilised in the cc-isomeric form while both the ct- and
cc-isomeric forms of 2 are isolated [ct: cis and trans and cc: cis and cis
with respect to the mutual orientations of O and N donors of two Q′]. The
isomeric identities of 1–3 have been authenticated by their single-crystal
X-ray structures. The collective consideration of crystallographic and DFT
data along with other analytical events reveals that 1–3 exhibit the valence
configuration of [(bpy)RuII(Q′Sq)2]. The magnetization studies reveal a
ferromagnetic response at 300 K and virtual diamagnetic behaviour at 2 K. DFT
calculations on representative 2a and 2b predict that the excited triplet (S =
1) state is lying close to the singlet (S = 0) ground state with
singlet–triplet separation of 0.038 eV and 0.075 eV, respectively. In
corroboration with the paramagnetic features the complexes exhibit free
radical EPR signals with g [similar]2 and 1HNMR spectra with broad aromatic
proton signals associated with the Q′ at 300 K. Experimental results in
conjunction with the DFT (for representative 2a and 2b) reveal iminoquinone
based preferential electron-transfer processes leaving the ruthenium(II) ion
mostly as a redox insensitive entity: [(bpy)RuII(Q′Q)2]2+ (12+–32+)
[leftrightharpoons] [(bpy)RuII(Q′Sq)(Q′Q)]+ (1+–3+) [leftrightharpoons]
[(bpy)RuII(Q′Sq)2] (1–3) [leftrightharpoons]
[(bpy)RuII(Q′Sq)(Q′Cat)]−/[(bpy)RuIII(Q′Cat)2]− (1−–3−). The diamagnetic
doubly oxidised state, [(bpy)RuII(Q′Q)2]2+ in 12+–32+ has been authenticated
further by the crystal structure determination of the representative
[(bpy)RuII(Q′3)2](ClO4)2 [3](ClO4)2 as well as by its sharp 1H NMR spectrum.
The key electronic transitions in each redox state of 1n–3n have been assigned
by TD–DFT calculations on representative 2a and 2b
Expanding the diversity of mycobacteriophages: insights into genome architecture and evolution.
Mycobacteriophages are viruses that infect mycobacterial hosts such as Mycobacterium smegmatis and Mycobacterium tuberculosis. All mycobacteriophages characterized to date are dsDNA tailed phages, and have either siphoviral or myoviral morphotypes. However, their genetic diversity is considerable, and although sixty-two genomes have been sequenced and comparatively analyzed, these likely represent only a small portion of the diversity of the mycobacteriophage population at large. Here we report the isolation, sequencing and comparative genomic analysis of 18 new mycobacteriophages isolated from geographically distinct locations within the United States. Although no clear correlation between location and genome type can be discerned, these genomes expand our knowledge of mycobacteriophage diversity and enhance our understanding of the roles of mobile elements in viral evolution. Expansion of the number of mycobacteriophages grouped within Cluster A provides insights into the basis of immune specificity in these temperate phages, and we also describe a novel example of apparent immunity theft. The isolation and genomic analysis of bacteriophages by freshman college students provides an example of an authentic research experience for novice scientists
The redox series [Ru(bpy)2(L)]n, n = +3, +2, +1, 0, with L = bipyridine, “click” derived pyridyl-triazole or bis-triazole: a combined structural, electrochemical, spectroelectrochemical and DFT investigation
The compounds [Ru(bpy)2(L1)](ClO4)2 (1(ClO4)2), [Ru(bpy)2(L2)](ClO4)2
(2(ClO4)2), [Ru(bpy)2(L3)](ClO4)2 (3(ClO4)2), [Ru(bpy)2(L4)](ClO4)2
(4(ClO4)2), [Ru(bpy)2(L5)](ClO4)2 (5(ClO4)2), and
[Ru(bpy)2(L6)](ClO4)26(ClO4)2 (bpy = 2,2′-bipyridine, L1 = 1-(4-isopropyl-
phenyl)-4-(2-pyridyl)-1,2,3-triazole, L2 = 1-(4-butoxy-
phenyl)-4-(2-pyridyl)-1,2,3-triazole, L3 = 1-(2-trifluoromethyl-
phenyl)-4-(2-pyridyl)-1,2,3-triazole, L4 = 4,4′-bis-{1-(2,6-diisopropyl-
phenyl)}-1,2,3-triazole, L5 = 4,4′-bis-{(1-phenyl)}-1,2,3-triazole, L6 =
4,4′-bis-{1-(2-trifluoromethyl-phenyl)}-1,2,3-triazole) were synthesized from
[Ru(bpy)2(EtOH)2](ClO4)2 and the corresponding “click”-derived pyridyl-
triazole or bis-triazole ligands, and characterized by 1H-NMR spectroscopy,
elemental analysis, mass spectrometry and X-ray crystallography. Structural
analysis showed a distorted octahedral coordination environment about the
Ru(II) centers, and shorter Ru–N(triazole) bond distances compared to
Ru–N(pyridine) distances in complexes of mixed-donor ligands. All the
complexes were subjected to cyclic voltammetric studies, and the results were
compared to the well-known [Ru(bpy)3]2+ compound. The oxidation and reduction
potentials were found to be largely uninfluenced by ligand changes, with all
the investigated complexes showing their oxidation and reduction steps at
rather similar potentials. A combined UV-vis-NIR and EPR
spectroelectrochemical investigation, together with DFT calculations, was used
to determine the site of electron transfer in these complexes. These results
provided insights into their electronic structures in the various investigated
redox states, showed subtle differences in the spectroscopic signatures of
these complexes despite their similar electrochemical properties, and provided
clues to the unperturbed redox potentials in these complexes with respect to
ligand substitutions. The reduced forms of the complexes display structured
absorption bands in the NIR region. Additionally, we also present new
synthetic routes for the ligands presented here using Cu-abnormal carbene
catalysts
Structural Effects on Distinct Spectroelectrochemical Properties of Rhenium-based Metalloprisms
Substituent-Induced Reactivity in Quinonoid-Bridged Dinuclear Complexes: Comparison between the Ruthenium and Osmium Systems
The ligand 2,5-bis[2-(methylthio)anilino]-1,4-benzoquinone
(<b>L</b>) was used in its doubly deprotonated form to synthesize
the complex [{Cl(η<sup>6</sup>-Cym)Os}<sub>2</sub>(μ<i>-</i>η<sup>2</sup>:η<sup>2</sup>-<b>L</b><sub><b>‑2H</b></sub>)] (<b>1</b>; Cym = <i>p</i>-cymene = 1-isopropyl-4-methylbenzene). Spectroscopic characterization
and elemental analysis confirms the presence of the chloride ligands
in <b>1</b>, which indirectly shows that the bridging ligand <b>L</b><sub><b>‑2H</b></sub> acts in a bis-bidentate
fashion in <b>1</b>, with the thioether substituents on the
bridge remaining uncoordinated. Abstraction of the chloride ligands
in <b>1</b> by AgBF<sub>4</sub> in CH<sub>3</sub>CN leads not
only to the release of those chloride ligands but also to a simultaneous
substituent-induced release of Cym with the bridging ligand changing
its coordination mode to bis-tridentate. In the resulting complex
[{(CH<sub>3</sub>CN)<sub>3</sub>Os}<sub>2</sub>(μ-η<sup>3</sup>:η<sup>3</sup>-<b>L</b><sub><b>‑2H</b></sub>)]<sup>2+</sup> (<b>2</b><sup><b>2+</b></sup>),
the thioether groups of <b>L</b><sub><b>‑2H</b></sub> are now coordinated to the osmium centers with the bridging
ligand coordinating to the metal center in a bis-meridional form.
The coordination mode of <b>L</b><sub><b>‑2H</b></sub> in <b>2</b><sup><b>2+</b></sup> was confirmed
by single-crystal X-ray diffraction data. A structural analysis of <b>2</b><sup><b>2+</b></sup> reveals localization of double
bonds within the “upper” and “lower” parts
of the bridging ligand in comparison to bond distances in the free
ligand. Additionally, the binding of the bridge to the osmium centers
is seen to occur through O<sup>–</sup> and neutral imine-type
N donors. The complexes <b>1</b> and <b>2</b><sup><b>2+</b></sup> were investigated by cyclic voltammetry and UV–vis–near-IR
and EPR spectroelectrochemistry. This combined approach was used to
unravel the redox-active nature of the ligand <b>L</b><sub><b>‑2H</b></sub>, to determine the sites of electron transfer
(ligand radical versus mixed valency), and to compare the present
systems with their ruthenium analogues <b>3</b> and <b>4</b><sup><b>2+</b></sup> (Schweinfurth, D. Inorg. Chem. 2011, 50, 1150). The effect of replacing ruthenium by its
higher homologue osmium on the reactivity and the electrochemical
and spectroscopic properties were explored, and the differences were
deciphered by taking into account the intrinsic dissimilarities between
the two homologues. The usefulness of incorporating additional donor
substituents on potentially bridging quinonoid ligands was probed
in this work
Tuning Ligand Effects and Probing the Inner-Workings of Bond Activation Steps: Generation of Ruthenium Complexes with Tailor-Made Properties
Activating chemical bonds through
external triggers and understanding
the underlying mechanism are at the heart of developing molecules
with catalytic and switchable functions. Thermal, photochemical, and
electrochemical bond activation pathways are useful for many chemical
reactions. In this Article, a series of Ru<sup>II</sup> complexes
containing a bidentate and a tripodal ligand were synthesized. Starting
from all-pyridine complex <b>1</b><sup>2+</sup>, the pyridines
were stepwise substituted with “click” triazoles (<b>2</b><sup>2+</sup>–<b>7</b><sup>2+</sup>). Whereas
the thermo- and photoreactivity of <b>1</b><sup>2+</sup> are
due to steric repulsion within the equatorial plane of the complex, <b>3</b><sup>2+</sup>–<b>6</b><sup>2+</sup> are reactive
because of triazoles in axial positions, and <b>4</b><sup>2+</sup> shows unprecedented photoreactivity. Complexes that feature neither
steric interactions nor axial triazoles (<b>2</b><sup>2+</sup> and <b>7</b><sup>2+</sup>) do not show any reactivity. Furthermore,
a redox-triggered conversion mechanism was discovered in <b>1</b><sup>2+</sup>, <b>3</b><sup>2+</sup>, and <b>4</b><sup>2+</sup>. We show here ligand design principles required to convert
a completely inert molecule to a reactive one and vice versa, and
provide mechanistic insights into their functioning. The results presented
here will likely have consequences for developing a future generation
of catalysts, sensors, and molecular switches
Tuning Ligand Effects and Probing the Inner-Workings of Bond Activation Steps: Generation of Ruthenium Complexes with Tailor-Made Properties
Activating chemical bonds through
external triggers and understanding
the underlying mechanism are at the heart of developing molecules
with catalytic and switchable functions. Thermal, photochemical, and
electrochemical bond activation pathways are useful for many chemical
reactions. In this Article, a series of Ru<sup>II</sup> complexes
containing a bidentate and a tripodal ligand were synthesized. Starting
from all-pyridine complex <b>1</b><sup>2+</sup>, the pyridines
were stepwise substituted with “click” triazoles (<b>2</b><sup>2+</sup>–<b>7</b><sup>2+</sup>). Whereas
the thermo- and photoreactivity of <b>1</b><sup>2+</sup> are
due to steric repulsion within the equatorial plane of the complex, <b>3</b><sup>2+</sup>–<b>6</b><sup>2+</sup> are reactive
because of triazoles in axial positions, and <b>4</b><sup>2+</sup> shows unprecedented photoreactivity. Complexes that feature neither
steric interactions nor axial triazoles (<b>2</b><sup>2+</sup> and <b>7</b><sup>2+</sup>) do not show any reactivity. Furthermore,
a redox-triggered conversion mechanism was discovered in <b>1</b><sup>2+</sup>, <b>3</b><sup>2+</sup>, and <b>4</b><sup>2+</sup>. We show here ligand design principles required to convert
a completely inert molecule to a reactive one and vice versa, and
provide mechanistic insights into their functioning. The results presented
here will likely have consequences for developing a future generation
of catalysts, sensors, and molecular switches
Tuning Ligand Effects and Probing the Inner-Workings of Bond Activation Steps: Generation of Ruthenium Complexes with Tailor-Made Properties
Activating chemical bonds through
external triggers and understanding
the underlying mechanism are at the heart of developing molecules
with catalytic and switchable functions. Thermal, photochemical, and
electrochemical bond activation pathways are useful for many chemical
reactions. In this Article, a series of Ru<sup>II</sup> complexes
containing a bidentate and a tripodal ligand were synthesized. Starting
from all-pyridine complex <b>1</b><sup>2+</sup>, the pyridines
were stepwise substituted with “click” triazoles (<b>2</b><sup>2+</sup>–<b>7</b><sup>2+</sup>). Whereas
the thermo- and photoreactivity of <b>1</b><sup>2+</sup> are
due to steric repulsion within the equatorial plane of the complex, <b>3</b><sup>2+</sup>–<b>6</b><sup>2+</sup> are reactive
because of triazoles in axial positions, and <b>4</b><sup>2+</sup> shows unprecedented photoreactivity. Complexes that feature neither
steric interactions nor axial triazoles (<b>2</b><sup>2+</sup> and <b>7</b><sup>2+</sup>) do not show any reactivity. Furthermore,
a redox-triggered conversion mechanism was discovered in <b>1</b><sup>2+</sup>, <b>3</b><sup>2+</sup>, and <b>4</b><sup>2+</sup>. We show here ligand design principles required to convert
a completely inert molecule to a reactive one and vice versa, and
provide mechanistic insights into their functioning. The results presented
here will likely have consequences for developing a future generation
of catalysts, sensors, and molecular switches