Attention:The NSF Public Access Repository (PAR) system and access will be unavailable from 11:00 PM ET on Thursday, October 15th until 12:00 AM ET on Friday, October 16th due to maintenance. We apologize for the inconvenience.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Ligand‐to‐Metal Charge Transfer of Ag(II) CF 2 X Carboxylates: Quantum Yield and Electrophotocatalytic Arene Fluoroalkylation Tuned by X
Title: Ligand‐to‐Metal Charge Transfer of Ag(II) CF 2 X Carboxylates: Quantum Yield and Electrophotocatalytic Arene Fluoroalkylation Tuned by X
Abstract Incorporation of CF2X groups beyond CF3into arene scaffolds is underdeveloped despite these groups’ utility as halogen‐bond donors and as precursors to bioisosteres. Herein, we report the synthesis, characterization, and comparative photochemistry of a suite of [Ag(II)(bpy)2O2CCF2X]+and Ag(II)(bpy)(O2CCF2X)2(bpy = 2,2´‐bipyridine, X = F, CF3, Cl, Br, H, CH3) carboxylate complexes. We find a dramatic effect of the X substituent on the efficiency of generating CF2X radicals by ligand‐to‐metal charge transfer (LMCT), with Ag(II) photoreduction rates varying by over an order of magnitude and quantum yields spanning over 20%. We provide insight into how electronic and structural perturbations of the Ag(II)–O2CCF2X core are manifested in the LMCT quantum efficiency. With this information in hand, Ag(II)‐mediated electrophotocatalytic CF2X functionalization is carried out on a range of (hetero)arenes. This work expands the nascent field of Ag(II)‐based photocatalysis by allowing for (hetero)aryl–CF2X functionalization directly from unactivated fluoroalkyl carboxylate precursors.  more » « less
Award ID(s):
2216066
PAR ID:
10659177
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  
Publisher / Repository:
Wiley Publishing
Date Published:
Journal Name:
Angewandte Chemie International Edition
Volume:
64
Issue:
37
ISSN:
1433-7851
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; (, Science)
    Molecular Ag(II) complexes are superoxidizing photoredox catalysts capable of generating radicals from redox-reticent substrates. In this work, we exploited the electrophilicity of Ag(II) centers in [Ag(bpy)2(TFA)][OTf] and Ag(bpy)(TFA)2(bpy, 2,2′-bipyridine; OTf, CF3SO3–) complexes to activate trifluoroacetate (TFA) by visible light–induced homolysis. The resulting trifluoromethyl radicals may react with a variety of arenes to forge C(sp2)–CF3bonds. This methodology is general and extends to other perfluoroalkyl carboxylates of higher chain length (RFCO2–; RF, CF2CF3or CF2CF2CF3). The photoredox reaction may be rendered electrophotocatalytic by regenerating the Ag(II) complexes electrochemically during irradiation. Electrophotocatalytic perfluoroalkylation of arenes at turnover numbers exceeding 20 was accomplished by photoexciting the Ag(II)–TFA ligand-to-metal charge transfer (LMCT) state, followed by electrochemical reoxidation of the Ag(I) photoproduct back to the Ag(II) photoreactant. 
    more » « less
  2. ; ; ; ; ; ; (, International Journal of Chemical Kinetics)
    ABSTRACT 2‐chloro‐3,3,3‐trifluoropropene, CF3C(Cl)═CH2(HCFO‐1233xf), is a volatile hydrochlorofluoroolefin, commonly used in industrial synthesis of other halogenated olefins. Kinetics and reaction mechanisms for the reactions of OH radicals, Cl atoms, and O3with CF3C(Cl)═CH2were investigated using FTIR/smog chamber studies in 700 Torr of air/N2diluent at 295 ± 2 K. The rate constantsk(Cl + CF3C(Cl)═CH2) = (8.3 ± 1.1) × 10−11,k(OH + CF3C(Cl)═CH2) = (3.4 ± 0.8) × 10−12andk(O3+ CF3C(Cl)═CH2) = (2.5 ± 0.1)  × 10−21cm3molecule−1s−1, were measured. An atmospheric lifetime of 3.3 days for CF3C(Cl)═CH2was determined, dominated by reaction with OH radicals. The reaction of OH radicals and Cl atoms with CF3C(Cl)═CH2proceeds by addition to the double bond, and primary and secondary products of the reactions were quantified. Approximately 90% of Cl atoms undergo addition to the terminal carbon. We were unable to establish any preference of reaction site of the OH addition. Reaction of O3with CF3C(Cl)═CH2leads to the formation of Criegee intermediates that decompose yielding CF3C(O)Cl and HC(O)H as major products. An upper limit of < 0.3% for the yield CF3Cl was estimated. The integrated IR absorption cross‐section for CF3C(Cl)═CH2is (1.22 ± 0.06) × 10−16 cm molecule−1(600–1800 cm−1). The effective radiative efficiency was determined as 0.007 W m−2ppb−1leading to a Global Warming Potential (GWP) for the 100‐year time horizon of 0.031. The environmental impact of release of CF3C(Cl)═CH2to the atmosphere is discussed. 
    more » « less
  3. ; ; ; ; ; ; (, Angewandte Chemie International Edition)
    Abstract We report copper(II) and copper(III) trifluoromethyl complexes supported by a pyridinedicarboxamide ligand (L) as a platform for investigating the role of electron transfer in C(sp2)−H trifluoromethylation. While the copper(II) trifluoromethyl complex is unreactive towards (hetero)arenes, the formal copper(III) trifluoromethyl complex performs C(sp2)−H trifluoromethylation of a wide range of (hetero)arenes. Mechanistic studies using the copper(III) trifluoromethyl complex suggest that the mechanism of arene trifluoromethylation is substrate‐dependent. When the thermodynamic driving force for electron transfer is high, the reaction proceeds through a previously unidentified single electron transfer (SET) mechanism, where an initial electron transfer occurs between the substrate and oxidant prior to CF3group transfer. Otherwise, a CF3radical release/electrophilic aromatic substitution (SEAr) mechanism is followed. These studies provide valuable insights into the role of strong oxidants and potential mechanistic dichotomy in Cu‐mediated C(sp2)−H trifluoromethylation. 
    more » « less
  4. ; ; ; ; ; ; ; ; (, Angewandte Chemie International Edition)
    Abstract Synthesizing solids in molten fluxes enables the rapid diffusion of soluble species at temperatures lower than in solid‐state reactions, leading to crystal formation of kinetically stable compounds. In this study, we demonstrate the effectiveness of mixed hydroxide and halide fluxes in synthesizing complex Sr/Ag/Se in mixed LiOH/LiCl. We have accessed a series of two‐dimensional Sr(Ag1−xLix)2Se2layered phases. With increased LiOH/LiCl ratio or reaction temperature, Li partially substituted Ag to form solid solutions of Sr(Ag1−xLix)2Se2withxup to 0.45. In addition, a new type of intergrowth compound [Sr3Se2][(Ag1−xLix)2Se2] was synthesized upon further reaction of Sr(Ag1−xLix)2Se2with SrSe. Both Sr(Ag1−xLix)2Se2and [Sr3Se2][(Ag1−xLix)2Se2] exhibit a direct band gap, which increases with increasing Li substitution (x). Therefore, the band gap of Sr(Ag1−xLix)2Se2can be precisely tuned via fine‐tuningxthat is controlled by only the flux ratio and temperature. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, Advanced Functional Materials)
    Abstract Silk nanofibers (SNFs) from abundant sources are low‐cost and environmentally friendly. Combined with other functional materials, SNFs can help create bioelectronics with excellent biocompatibility without environmental concerns. However, it is still challenging to construct an SNF‐based composite with high conductivity, flexibility, and mechanical strength for all SNF‐based electronics. Herein, this work reports the design and fabrication of Ti3C2Tx‐silver@silk nanofibers (Ti3C2Tx‐Ag@SNF) composites with multi‐dimensional heterogeneous conductive networks using combined in situ growth and vacuum filtration methods. The ultrahigh electrical conductivity of Ti3C2Tx‐Ag@SNF composites (142959 S m−1) provides the kirigami‐patterned soft heaters with a rapid heating rate of 87 °C s−1. The multi‐dimensional heterogeneous network further allows the creation of electromagnetic interference shielding devices with an exceptionally high specific shielding effectiveness of 10,088 dB cm−1. Besides working as a triboelectric layer to harvest the mechanical energy and recognize the hand gesture, the Ti3C2Tx‐Ag@SNF composites can also be combined with an ionic layer to result in a capacitive pressure sensor with a high sensitivity of 410 kPa−1in a large range due to electronic‐double layer effect. The applications of the Ti3C2Tx‐Ag@SNF composites in recognizing human gestures and human‐machine interfaces to wirelessly control a trolley demonstrate the future development of all SNF‐based electronics. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Text Encoded Conversion
  • XML
  • Save / Share this Record
  • Send to Email