Displacement of Neutral Nitrogen Donors by Chloride in AuCl3(am) (am = Pyridines and Amines): Kinetics and DFT Calculations Show the Effects of Basicity and π-Acceptor Ability

The reactions of an aluminium(I) reagent with a series of 1,2-, 1,3- and 1,5-dienes are reported. In the case of 1,3-dienes the reaction occurs by a pericyclic reaction mechanism, specifically a cheletropic cycloaddition, to form aluminocyclopentene containing products. This mechanism has been interrogated by stereochemical experiments and DFT calculations. The stereochemical experiments show that the (4+1) cycloaddition follows a suprafacial topology, while calculations support a concerted albeit asynchronous pathway in which the transition state demonstrates aromatic character. Remarkably, the substrate scope of the (4+1) cycloaddition includes dienes that are either in part, or entirely, contained within aromatic rings. In these cases, reactions occur with dearomatisation of the substrate and can be reversible. In the case of 1,2- or 1,5-dienes complementary reactivity is observed; the orthogonal nature of the C=C π-bonds (1,2-diene) and the homoconjugated system (1,5-diene) both disfavour a (4+1) cycloaddition. Rather, reaction pathways are determined by an initial (2+1) cycloaddition to form an aluminocyclopropane intermediate which can in turn undergo insertion of a further C=C π-bond leading to complex organometallic products that incorporate fused hydrocarbon rings.

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Reversible Oxidative-Addition and Reductive-Elimination of Thiophene from a Titanium Complex and Its Thermally-Induced Hydrodesulfurization Chemistry

10.26434/chemrxiv.10321946.v1 ◽

2019 ◽

Author(s):

Alejandra Gomez-Torres ◽

J. Rolando Aguilar-Calderón ◽

Carlos Saucedo ◽

Aldo Jordan ◽

Alejandro J. Metta-Magaña ◽

...

Keyword(s):

Dft Calculations ◽

Ring Opening ◽

Thiophene Ring ◽

Oxidative Addition ◽

Reductive Elimination ◽

Thermally Induced ◽

Titanium Complex

The masked Ti(II) synthon (Ketguan)(η6-ImDippN)Ti (1) oxidatively adds across thiophene to give ring-opened (Ketguan)(ImDippN)Ti[κ2-S(CH)3CH] (2). Complex 2 is photosensitive, and upon exposure to light, reductively eliminates thiophene to regenerate 1 – a rare example of early-metal mediated oxidative-addition/reductive-elimination chemistry. DFT calculations indicate strong titanium π-backdonation to the thiophene π*-orbitals leads to the observed thiophene ring opening across titanium, while a proposed photoinduced LMCT promotes the reverse thiophene elimination from 2. Finally, pressurizing solutions of 2 with H2 (150 psi) at 80 °C leads to the hydrodesulfurization of thiophene to give the Ti(IV) sulfide (Ketguan)(ImDippN)Ti(S) (3) and butane.

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Solvent Dependence of Structural Dynamics and Spin-flip Processes in 3,4,5-tri(9H-carbazole-9-yl)benzonitrile (ortho-3CzBN)

10.26434/chemrxiv.11798568.v2 ◽

2020 ◽

Author(s):

Masaki Saigo ◽

Kiyoshi Miyata ◽

Hajime Nakanotani ◽

Chihaya Adachi ◽

Ken Onda

Keyword(s):

Dft Calculations ◽

Excited States ◽

Structural Changes ◽

Photophysical Properties ◽

Delayed Fluorescence ◽

Time Resolved ◽

Thermally Activated Delayed Fluorescence ◽

Thermally Activated ◽

Solvent Dependence ◽

Acetonitrile Solutions

We have investigated the solvent-dependence of structural changes along with intersystem crossing of a thermally activated delayed fluorescence (TADF) molecule, 3,4,5-tri(9H-carbazole-9-yl)benzonitrile (o-3CzBN), in toluene, tetrahydrofuran, and acetonitrile solutions using time-resolved infrared (TR-IR) spectroscopy and DFT calculations. We found that the geometries of the S1 and T1 states are very similar in all solvents though the photophysical properties mostly depend on the solvent. In addition, the time-dependent DFT calculations based on these geometries suggested that the thermally activated delayed fluorescence process of o-3CzBN is governed more by the higher-lying excited states than by the structural changes in the excited states.

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Pt-Pd Nanoalloy for the Unprecedented Activation of Carbon-Fluorine Bond at Low Temperature

10.26434/chemrxiv.11145098 ◽

2019 ◽

Author(s):

Raghu Nath Dhital ◽

keigo nomura ◽

Yoshinori Sato ◽

Setsiri Haesuwannakij ◽

Masahiro Ehara ◽

...

Keyword(s):

Activation Energy ◽

Low Temperature ◽

Dft Calculations ◽

Bond Activation ◽

Mild Conditions ◽

Selective Transformation ◽

Rate Determining Step ◽

Highly Active ◽

Harsh Conditions ◽

Reaction Profile

Carbon-Fluorine (C-F) bonds are considered the most inert organic functionality and their selective transformation under mild conditions remains challenging. Herein, we report a highly active Pt-Pd nanoalloy as a robust catalyst for the transformation of C-F bonds into C-H bonds at low temperature, a reaction that often required harsh conditions. The alloying of Pt with Pd is crucial to activate C-F bond. The reaction profile kinetics revealed that the major source of hydrogen in the defluorinated product is the alcoholic proton of 2-propanol, and the rate-determining step is the reduction of the metal upon transfer of the beta-H from 2-propanol. DFT calculations elucidated that the key step is the selective oxidative addition of the O-H bond of 2-propanol to a Pd center prior to C-F bond activation at a Pt site, which crucially reduces the activation energy of the C-F bond. Therefore, both Pt and Pd work independently but synergistically to promote the overall reaction

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Computationally Assisted Design of High Signal-to-Noise Photoinduced Electron Transfer-Based Voltage-Sensitive Dyes

10.26434/chemrxiv.12401753 ◽

2020 ◽

Author(s):

Rishikesh Kulkarni ◽

Anneliese Gest ◽

Chun Kei Lam ◽

Benjamin Raliski ◽

Feroz James ◽

...

Keyword(s):

Electron Transfer ◽

Dft Calculations ◽

Photoinduced Electron Transfer ◽

Density Functional ◽

Embryonic Stem ◽

High Sensitivity ◽

Md Simulations ◽

High Signal ◽

Signal To Noise ◽

Green Fluorescent

High signal-to-noise optical voltage indicators will enable simultaneous interrogation of membrane potential in large ensembles of neurons. However, design principles for voltage sensors with high sensitivity and brightness remain elusive, limiting the applicability of voltage imaging. In this paper, we use molecular dynamics (MD) simulations and density functional theory (DFT) calculations to guide the design of a bright and sensitive green-fluorescent voltage-sensitive fluorophore, or VoltageFluor (VF dye), that uses photoinduced electron transfer (PeT) as a voltage-sensing mechanism. MD simulations predict an 11% increase in sensitivity due to membrane orientation, while DFT calculations predict an increase in fluorescence quantum yield, but a decrease in sensitivity due to a decrease in rate of PeT. We confirm these predictions by synthesizing a new VF dye and demonstrating that it displays the expected improvements by doubling the brightness and retaining similar sensitivity to prior VF dyes. Combining theoretical predictions and experimental validation has resulted in the synthesis of the highest signal-to-noise green VF dye to date. We use this new voltage indicator to monitor the electrophysiological maturation of human embryonic stem cell-derived medium spiny neurons.

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