Sources of Error for Single-shot PMT-Based Phosphor Thermometry in Harsh Conditions

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 <i>beta</i>-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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A Mild and Simple Method for Making MIDA Boronates

10.26434/chemrxiv.12054036.v1 ◽

2020 ◽

Author(s):

Aidan Kelly ◽

Peng-Jui (Ruby) Chen ◽

Jenna Klubnick ◽

Daniel J. Blair ◽

Martin D. Burke

Keyword(s):

Organic Synthesis ◽

Boronic Acids ◽

Simple Method ◽

Direct Preparation ◽

Synthesis Procedure ◽

Harsh Conditions

<div> <div> <div> <p>Existing methods for making MIDA boronates require harsh conditions and complex procedures to achieve dehydration. Here we disclose that a pre-dried form of MIDA, MIDA anhydride, acts as both a source of the MIDA ligand and an in situ desiccant to enable a mild and simple MIDA boronate synthesis procedure. This method expands the range of sensitive boronic acids that can be converted into their MIDA boronate counterparts. Further utilizing unique properties of MIDA boronates, we have developed a MIDA Boronate Maker Kit which enables the direct preparation and purification of MIDA boronates from boronic acids using only heating and centrifuge equipment that is widely available in labs that do not specialize in organic synthesis. </p> </div> </div> </div>

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Visible Light-Mediated Oxidative Debenzylation

10.26434/chemrxiv.13135814 ◽

2020 ◽

Author(s):

Cristian Cavedon ◽

Eric T. Sletten ◽

Amiera Madani ◽

Olaf Niemeyer ◽

Peter H. Seeberger ◽

...

Keyword(s):

Reaction Time ◽

Visible Light ◽

Functional Groups ◽

Continuous Flow ◽

Protecting Groups ◽

Benzyl Ether ◽

Complex Molecules ◽

Protective Groups ◽

Benzyl Ethers ◽

Harsh Conditions

Protecting groups are key in the synthesis of complex molecules such as carbohydrates to distinguish functional groups of similar reactivity. The harsh conditions required to cleave stable benzyl ether protective groups are not compatible with many other protective and functional groups. The mild, visible light-mediated debenzylation disclosed here renders benzyl ethers orthogonal protective groups. Key to success is the use of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as stoichiometric or catalytic photooxidant such that benzyl ethers can be cleaved in the presence of azides, alkenes, and alkynes. The reaction time for this transformation can be reduced from hours to minutes in continuous flow. <br>

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Cooperative Self-Assembly of Pyridine-2,6-Diimine-Linked Macrocycles into Mechanically Robust Nanotubes

10.26434/chemrxiv.8080043 ◽

2019 ◽

Author(s):

Michael J. Strauss ◽

Darya Asheghali ◽

Austin Evans ◽

Rebecca Li ◽

Anton Chavez ◽

...

Keyword(s):

Aspect Ratio ◽

High Aspect Ratio ◽

Self Assembly ◽

Gel Permeation Chromatography ◽

Synthetic Polymers ◽

Young’S Moduli ◽

Structural Rigidity ◽

Assembly Mechanism ◽

Low Dimensionality ◽

Harsh Conditions

<p>Nanotubes assembled from macrocyclic precursors offer a unique combination of low dimensionality, structural rigidity, and distinct interior and exterior microenvironments. Usually the weak stacking energies of macrocycles limit the length or strength of the resultant nanotubes. Imine-linked macrocycles were recently found to assemble into high-aspect ratio (>10<sup>3</sup>), lyotropic nanotubes in the presence of excess acid. Yet these harsh conditions are incompatible with many functional groups and processing methods, and lower acid loadings instead catalyze macrocycle degradation. Here we report pyridine-2,6-diimine-linked macrocycles that assemble into high-aspect ratio nanotubes in the presence of less than 1 equiv of CF<sub>3</sub>CO<sub>2</sub>H per macrocycle. Analysis by gel permeation chromatography and fluorescence spectroscopy revealed a cooperative self-assembly mechanism. Nanofibers obtained by touch-spinning the pyridinium-based nanotubes exhibit Young’s moduli of 1.48 GPa, which exceeds that of many synthetic polymers and biological filaments. These findings will enable the design of structurally diverse nanotubes from synthetically accessible macrocycles. </p>

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