ABSTRACT
Aryl amination is an essential transformation for medicinal, process, and materials chemistry. In addition to classic Buchwald-Hartwig amination conditions, blue-light-driven metallaphotoredox catalysis has emerged as a valuable tool for C-N cross-coupling. However, blue light suffers from low penetration through reaction media, limiting its scalability for industrial purposes. In addition, blue light enhances unwanted side-product formation in metallaphotoredox catalysis, namely hydrodehalogenation. Low-energy light, such as deep red (DR) or near-infrared (NIR), offers a solution to this problem as it can provide enhanced penetration through reaction media as compared to higher-energy wavelengths. Herein, we show that low-energy light can also enhance the desired reactivity in metallaphotoredox catalysis by suppressing unwanted hydrodehalogenation. We hypothesize that the reduced side product is formed by direct photolysis of the aryl-nickel bond by the high-energy light, leading to the generation of aryl radicals. Using deep-red or near-infrared light and an osmium photocatalyst, we demonstrate an enhanced scope of (hetero)aryl bromides and amine-based nucleophiles with minimal formation of hydrodehalogenation byproducts.
Subject(s)
Light , Nickel , Catalysis , Amination , Nickel/chemistry , Bromides/chemistryABSTRACT
Utilizing quinoline as a mild, catalytic additive, broadly applicable conditions for the Ni/photoredox-catalyzed C(sp2)-C(sp3) cross-coupling of (hetero)aryl bromides and alkyl pinacolboronate esters were developed, which can be applied to both batch and flow reactions. In addition to primary benzylic nucleophiles, both stabilized and nonstabilized secondary alkyl boronic esters are effective coupling partners. Density functional theory calculations suggest that alkyl radical generation occurs from an alkyl-B(pin)-quinoline complex, which may proceed via an energy transfer process.
Subject(s)
Bromides , Quinolines , Catalysis , Esters , NickelABSTRACT
A highly stereoselective synthesis of a cyclic dinucleotide (CDN) STING agonist containing two chiral thiophosphoramidate linkages is described. These rare yet key functional groups were, for the first time, installed efficiently and with high diastereoselectivity using a specially designed P(V) reagent. By utilizing this strategy, the CDN was prepared in greater than 16-fold higher yield than the prior P(III) approach, with fewer hazardous reagents and chromatographic purifications.
Subject(s)
Membrane Proteins , Indicators and Reagents , Membrane Proteins/chemistryABSTRACT
Over the past decade, chemists have embraced visible-light photoredox catalysis due to its remarkable ability to activate small molecules. Broadly, these methods employ metal complexes or organic dyes to convert visible light into chemical energy. Unfortunately, the excitation of widely utilized Ru and Ir chromophores is energetically wasteful as â¼25% of light energy is lost thermally before being quenched productively. Hence, photoredox methodologies require high-energy, intense light to accommodate said catalytic inefficiency. Herein, we report photocatalysts which cleanly convert near-infrared (NIR) and deep red (DR) light into chemical energy with minimal energetic waste. We leverage the strong spin-orbit coupling (SOC) of Os(II) photosensitizers to directly access the excited triplet state (T1) with NIR or DR irradiation from the ground state singlet (S0). Through strategic catalyst design, we access a wide range of photoredox, photopolymerization, and metallaphotoredox reactions which usually require 15-50% higher excitation energy. Finally, we demonstrate superior light penetration and scalability of NIR photoredox catalysis through a mole-scale arene trifluoromethylation in a batch reactor.
ABSTRACT
The piezoresistive response of PEDOT:PSS is sensitive to changes in its morphology when exposed to humidity and in response to different strain rates. The piezoresistive response of as-cast PEDOT:PSS transitions from being in-phase to being out-of-phase with applied strain when the relative humidity is reduced from >50% to near zero. At >50% relative humidity, the PSS matrix swells and interrupts the connectivity of electrically conducting PEDOT domains. Stretching PEDOT:PSS at such conditions leads to an increase in resistance with strain. Under dry conditions, PEDOT domains are connected; stretching PEDOT:PSS instead leads to preferential alignment of the conducting domains and a concomitant decrease in resistance. At intermediate humidity, the piezoresistive response of PEDOT:PSS is phase shifted relative to applied strain, with it being out-of-phase at low strain rates (0.34%/min) and in-phase at high strain rates (1.12%/min). We interpret this peculiar and surprising observation as a competition between strain-induced domain separation and alignment, each having a different response time to applied strain. Postdeposition treatment of PEDOT:PSS with dichloroacetic acid removes excess PSS; PEDOT:PSS's piezoresistive response is then invariant with humidity and strain rate. Stabilizing its piezoresistive response can ensure accuracy of PEDOT:PSS-based flexible resistive sensors whose response to small strains is used to monitor environmental and human-health.
ABSTRACT
Polymer acids are increasingly used as dopants/counterions to access and stabilize the electrically conducting states of conducting polymers. Beyond doping and/or charge balancing, these polymer acids also serve as active components that impact the macroscopic properties of the conducting polymer complexes. Judicious selection of the polymer acid at the onset of synthesis or manipulation of the interactions between the polymer acid and the conducting polymer through processing significantly impacts the electrical conductivity, piezoresistivity, electrochromism, mechanical properties, and thermoelectric efficiency of conducting polymers. As polyelectrolytes, these polymer acids enable conducting polymer complexes to transport ions in addition to electrons/holes. Understanding the role of the polymer acid and its interactions with the conducting polymer generates processing-structure-function relationships for conducting polymer/polymer acid complexes, which can help overcome challenges that were associated with these materials, such as low electrical conductivity and sensitivity to humidity, and enable the design of conducting polymer complexes with desired functionalities.
ABSTRACT
We demonstrate the tunability of both the polarity and the magnitude of the piezoresistive response of polyaniline that is template-synthesized on poly(2-acrylamido-2-methyl-1-propanesulfonic acid), PANI-PAAMPSA, by altering the template molecular weight. Piezoresistivity is quantified by gauge factor, a unitless parameter that relates changes in electrical resistance to applied strain. The gauge factor of PANI-PAAMPSA decreases linearly and becomes negative with decreasing PAAMPSA molecular weight. The polarity of PANI-PAAMPSA's gauge factor is determined by macroscopic connectivity across thin films. PANI-PAAMPSA thin films comprise electrostatically stabilized particles whose size is determined at the onset of synthesis. An increase in the interparticle spacing with applied strain results in a positive gauge factor. The presence of PANI crystallites increases connectivity between particles; these samples instead exhibit a negative gauge factor whereby the resistance decreases with increasing strain. The tunability of the piezoresistive response of these conducting polymers allows their utilization in a broad range of flexible electronics applications, including thermo- and chemoresistive sensors and strain gauges.
