230 results on '"Chun-Hsing Chen"'
Search Results
2. Oxidative Addition of a Phosphinite P–O Bond at Nickel
- Author
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Quinton J. Bruch, Noah D. McMillion, Chun-Hsing Chen, and Alexander J. M. Miller
- Subjects
Inorganic Chemistry ,Physical and Theoretical Chemistry - Published
- 2023
3. Isocyanide Ligands Promote Ligand-to-Metal Charge Transfer Excited States in a Rhenium(II) Complex
- Author
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Tayliz M. Rodriguez, Mawuli Deegbey, Chun-Hsing Chen, Elena Jakubikova, and Jillian L. Dempsey
- Subjects
Inorganic Chemistry ,Physical and Theoretical Chemistry - Published
- 2023
4. Visible light induced formation of a tungsten hydride complex
- Author
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Diane P. Isaacs, Cole T. Gruninger, Tao Huang, Aldo M. Jordan, Genique Nicholas, Chun-Hsing Chen, Marc A. ter Horst, and Jillian L. Dempsey
- Subjects
Inorganic Chemistry - Abstract
The bond cleavage of [CpW(CO)3]2 with blue light in the presence of acid leads to disproportionation followed by fast protonation. Quantum yield measurements indicate disproportionation occurs through a radical chain mechanism.
- Published
- 2023
5. Cation-Controlled Olefin Isomerization Catalysis with Palladium Pincer Complexes
- Author
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Alexandra H. Farquhar, Kristen E. Gardner, Sebastian Acosta-Calle, Andrew M. Camp, Chun-Hsing Chen, and Alexander J. M. Miller
- Subjects
Inorganic Chemistry ,Organic Chemistry ,Physical and Theoretical Chemistry - Published
- 2022
6. Accessing and Photo-Accelerating Low-Overpotential Pathways for CO2 Reduction: A Bis-Carbene Ruthenium Terpyridine Catalyst
- Author
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Eric A. Assaf, Sergio Gonell, Chun-Hsing Chen, and Alexander J. M. Miller
- Subjects
General Chemistry ,Catalysis - Published
- 2022
7. Doubly stereoconvergent crystallization enabled by asymmetric catalysis
- Author
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Pedro de Jesús Cruz, William R. Cassels, Chun-Hsing Chen, and Jeffrey S. Johnson
- Subjects
Multidisciplinary ,Article - Abstract
Synthetic methods that enable simultaneous control over multiple stereogenic centers are desirable for the efficient preparation of pharmaceutical compounds. Herein, we report the discovery and development of a catalyst-mediated asymmetric Michael addition/crystallization–induced diastereomer transformation of broad scope. The sequence controls three stereogenic centers, two of which are stereochemically labile. The configurational instability of 1,3-dicarbonyls and nitroalkanes, typically considered a liability in stereoselective synthesis, is productively leveraged by merging enantioselective Brønsted base organocatalysis and thermodynamic stereocontrol using a single convergent crystallization. The synthesis of useful γ-nitro β-keto amides containing three contiguous stereogenic centers is thus achieved from Michael acceptors containing two prochiral centers.
- Published
- 2023
8. A Redox‐Active Tetrazine‐Based Pincer Ligand for the Reduction of N‐Oxyanions Using a Redox‐Inert Metal
- Author
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Chun-Hsing Chen, Ivan J Huerfano, Maren Pink, Kenneth G. Caulton, Nicholas A. Maciulis, Daniel M. Beagan, and Veronica Carta
- Subjects
Hydrogen bond ,Ligand ,Organic Chemistry ,chemistry.chemical_element ,General Chemistry ,Zinc ,Redox ,Catalysis ,chemistry.chemical_compound ,Tetrazine ,chemistry ,Polymer chemistry ,Nitrite ,Pincer ligand ,Deoxygenation - Abstract
The reaction chemistry of the bis-tetrazinyl pyridine ligand (btzp) towards nitrogen oxyanions coordinated to zinc is studied in order to explore the reduction of the NOx- substrates with a redox-active ligand in the absence of redox activity at the metal. Following syntheses and characterization of (btzp)ZnX2 for X=Cl, NO3 and NO2 , featuring O-Zn linkage of both nitrogen oxyanions, it is shown that a silylating agent selectively delivers silyl substituents to tetrazine nitrogens, without reductive deoxygenation of NOx-1 . A new synthesis of the highly hydrogenated H4 btzp, containing two dihydrotetrazine reductants is described as is the synthesis and characterization of (H4 btzp)ZnX2 for X=Cl and NO3 , both of which show considerable hydrogen bonding potential of the dihydrotetrazine ring NH groups. The (H4 btzp)ZnCl2 complex does not bind zinc in the pincer pocket, but instead H4 btzp becomes a bridge between neighboring atoms through tetrazine nitrogen atoms, forming a polymeric chain. The reaction of AgNO2 with (H4 btzp)ZnCl2 is shown to proceed with fast nitrite deoxygenation, yielding water and free NO. Half of the H4 btzp reducing equivalents form Ag0 and thus the chloride ligand remains coordinated to the zinc metal center to yield (btzp)ZnCl2 . To compare with AgNO2 , experiments of (H4 btzp)ZnCl2 with NaNO2 result in salt metathesis between chloride and nitrite, highlighting the importance of a redox-active cation in the reduction of nitrite to NO.
- Published
- 2021
9. Pincers with diverse donors and their interconversion: application to Ni(II)
- Author
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Maren Pink, Alyssa C. Cabelof, Kenneth G. Caulton, Chun-Hsing Chen, and Veronica Carta
- Subjects
Inorganic Chemistry ,Chemistry ,Medicinal chemistry - Published
- 2021
10. Synthesis, photochemical properties, and computational analysis of a pyrene-benzimidazole bipodal molecular scaffold for pH and perchlorate sensing
- Author
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P.U. Ashvin Iresh Fernando, Gilbert K. Kosgei, Timothy Schutt, Glen Jenness, Chun-Hsing Chen, Garrett W. George, Ashley N. Kimble, William M. Nelson, David L. Henderson, and Lee C. Moores
- Subjects
General Chemical Engineering ,General Physics and Astronomy ,General Chemistry - Published
- 2023
11. Cation-Controlled Olefin Isomerization Catalysis with Palladium Pincer Complexes
- Author
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Alexandra Farquhar, Kristen Gardner, Sebastian Acosta-Calle, Andrew Camp, Chun-Hsing Chen, and Alexander Miller
- Abstract
A series of palladium(II) pincer complexes with dif-ferent substituents on the amine donor has been prepared and studied in olefin isomerization cataly-sis. Installing a macrocycle into the pincer ligand enables cation-switchable positional olefin isomer-ization: no reaction is observed with the catalyst alone, while in the presence of Li+ salts isomeriza-tion proceeds cleanly. Mechanistic studies implicate a key role of highly electrophilic Pd centers with accessible olefin binding sites in catalysis.
- Published
- 2022
12. Selecting Double Bond Positions with a Single Cation-Responsive Iridium Olefin Isomerization Catalyst
- Author
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Matthew R. Kita, P Thomas Blackburn, Alexander J. M. Miller, Henry M. Dodge, Andrew M. Camp, and Chun-Hsing Chen
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chemistry.chemical_classification ,Double bond ,Chemistry ,Alkene ,Regioselectivity ,chemistry.chemical_element ,Ether ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Combinatorial chemistry ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Iridium ,Selectivity ,Isomerization - Abstract
The catalytic transposition of double bonds holds promise as an ideal route to alkenes of value as fragrances, commodity chemicals, and pharmaceuticals; yet, selective access to specific isomers is a challenge, normally requiring independent development of different catalysts for different products. In this work, a single cation-responsive iridium catalyst selectively produces either of two different internal alkene isomers. In the absence of salts, a single positional isomerization of 1-butene derivatives furnishes 2-alkenes with exceptional regioselectivity and stereoselectivity. The same catalyst, in the presence of Na+, mediates two positional isomerizations to produce 3-alkenes. The synthesis of new iridium pincer-crown ether catalysts based on an aza-18-crown-6 ether proved instrumental in achieving cation-controlled selectivity. Experimental and computational studies guided the development of a mechanistic model that explains the observed selectivity for various functionalized 1-butenes, providing insight into strategies for catalyst development based on noncovalent modifications.
- Published
- 2021
13. Chemo- and Stereospecific Solid-State Thermal Dimerization of Sodium trans-2-Butenoate and γ-Ray-Induced Single-Crystal-to-Single-Crystal Dimerization of Hexaaquamagnesium trans-2-Butenoate Dihydrate: Both Give rel-(3S,4R)-1-Hexene-3,4-dicarboxylate but by Different Mechanisms. Stereospecific γ-Ray-Induced Trimerization of Sodium trans-2-Butenoate
- Author
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Jingye Zhou, Bruce M. Foxman, Chun-Hsing Chen, Roxana F. Schlam, Barry B. Snider, Magali B. Hickey, Graciela Díaz de Delgado, Kraig A. Wheeler, and Wen Shang
- Subjects
1-Hexene ,chemistry.chemical_compound ,Crystallography ,Stereospecificity ,chemistry ,Sodium ,Solid-state ,chemistry.chemical_element ,General Materials Science ,General Chemistry ,Condensed Matter Physics ,Single crystal - Abstract
γ-Irradiation of crystalline hexaaquamagnesium trans-2-butenoate dihydrate affords rel-(3S,4R)-1-hexene-3,4-dicarboxylate by a single-crystal-to-single-crystal reaction. The reaction proceeds by a ...
- Published
- 2020
14. Identifying and Evading Olefin Isomerization Catalyst Deactivation Pathways Resulting from Ion-Tunable Hemilability
- Author
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Henry M. Dodge, Matthew R. Kita, Chun-Hsing Chen, and Alexander J. M. Miller
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chemistry.chemical_classification ,Olefin fiber ,010405 organic chemistry ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Combinatorial chemistry ,Catalysis ,0104 chemical sciences ,Ion ,Pincer movement ,chemistry ,Hemilability ,Iridium ,Isomerization ,Crown ether - Abstract
Hemilabile ligands are found in many leading organometallic catalysts, but it can be challenging to tune the degree of hemilability in a particular catalyst. This work explores the impact of cation...
- Published
- 2020
15. Synthesis, Photochemical Properties, and Computational Study of a Novel Pyrene-Benzimidazole Based Bipodal Molecular Scaffold Towards pH and Perchlorate Sensing
- Author
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P. U. Ashvin Iresh Fernando, Gilbert Kosgei, Chun-Hsing Chen, Timothy Schutt, Glen Jenness, Garret W. George, Ashley N. Kimble, William M. Nelson, David L. Henderson, and Lee C. Moores
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History ,Polymers and Plastics ,Business and International Management ,Industrial and Manufacturing Engineering - Published
- 2022
16. Visible light induced formation of a tungsten hydride complex.
- Author
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Isaacs, Diane P., Gruninger, Cole T., Tao Huang, Jordan, Aldo M., Nicholas, Genique, Chun-Hsing Chen, ter Horst, Marc A., and Dempsey, Jillian L.
- Subjects
VISIBLE spectra ,NUCLEAR magnetic resonance spectroscopy ,PHOTON flux ,LEWIS bases ,TUNGSTEN ,SCISSION (Chemistry) ,METAL-metal bonds ,HYDRIDES - Abstract
When irradiated with blue light in the presence of a Lewis base (L), [CpW(CO)
3 ]2 undergoes metal-metal bond cleavage followed by a disproportionation reaction to form [CpW(CO)3 L]+ and [CpW(CO)3 ]- . Here, we show that in the presence of pyridinium tetrafluoroborate, [CpW(CO)3 ]- reacts further to form a metal hydride complex CpW(CO)3 H. The rection was monitored through in situ photo ¹H NMR spectroscopy experiments and the mechanism of light-driven hydride formation was investigated by determining quantum yields of formation. Quantum yields of formation of CpW(CO)3 H correlate with I-1/2 (I = photon flux on our sample tube), indicating that the net disproportionation of [CpW(CO)3 ]2 to form the hydride precursor [CpW(CO)3 ]- occurs primarily through a radical chain mechanism. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
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17. Stabilization of the Dinitrogen Analogue, Phosphorus Nitride
- Author
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Veronica Carta, Sean A. Lutz, Pierre Moënne-Loccoz, Jorge L. Martinez, Chun-Hsing Chen, Maren Pink, Daniel M. Beagan, Jeremy M. Smith, and Xinfeng Gao
- Subjects
010405 organic chemistry ,Phosphide ,General Chemical Engineering ,chemistry.chemical_element ,Bridging ligand ,General Chemistry ,Nitride ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Chemistry ,Crystallography ,chemistry.chemical_compound ,chemistry ,Nucleophile ,Molybdenum ,Electrophile ,Linkage isomerism ,QD1-999 ,Isomerization ,Research Article - Abstract
The N2 analogue phosphorus nitride (PN) was the first phosphorus-containing compound to be detected in the interstellar medium; however, this thermodynamically unstable compound has a fleeting existence on Earth. Here, we show that reductive coupling of iron(IV) nitride and molybdenum(VI) phosphide complexes assembles PN as a bridging ligand in a structurally characterized bimetallic complex. Reaction with C≡NtBu releases the mononuclear complex [(N3N)Mo—PN]−, N3N = [(Me3SiNCH2CH2)3N]3–), which undergoes light-induced linkage isomerization to provide [(N3N)Mo—NP]−, as revealed by photocrystallography. While structural and spectroscopic characterization, supported by electronic structure calculations, reveals the PN multiple bond character, coordination to molybdenum induces a nucleophilic character at the terminal atom of the PN/NP ligands. Indeed, the linkage isomers can be trapped in solution by reaction with a Rh(I) electrophile., The highly reactive interstellar gas, phosphorus nitride, is assembled and stabilized as a reactive ligand in transition metal complexes.
- Published
- 2020
18. Electrosynthetic Route to Cyclopentadienyl Rhenium Hydride Complexes Enabled by Electrochemical Investigations of their Redox-Induced Formation
- Author
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Daniel A. Kurtz, Cole T. Gruninger, Aldo M. Jordan, Tayliz M. Rodriguez, Jillian L. Dempsey, Chun-Hsing Chen, and Tao Huang
- Subjects
Reaction mechanism ,010405 organic chemistry ,Hydride ,Organic Chemistry ,chemistry.chemical_element ,Rhenium ,010402 general chemistry ,Electrochemistry ,01 natural sciences ,Chemical reaction ,Combinatorial chemistry ,Redox ,0104 chemical sciences ,Inorganic Chemistry ,chemistry ,Cyclopentadienyl complex ,Electroanalytical method ,Physical and Theoretical Chemistry - Abstract
As the utility of electroanalytical methods to study reaction mechanisms continues to develop, a wider scope of chemical reactions will fall under the scrutiny of electrochemical investigation. We ...
- Published
- 2020
19. Unusual Dinitrogen Binding and Electron Storage in Dinuclear Iron Complexes
- Author
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Keith Searles, Guillaume Gouget, Chun-Hsing Chen, Christopher B. Murray, Kenneth G. Caulton, Marat M. Khusniyarov, Eva M. Zolnhofer, Dieter Sorsche, Daniel J. Mindiola, Matthias E. Miehlich, Patrick J. Carroll, Skye Fortier, Karsten Meyer, Michael R. Gau, Department of Chemistry, University of Pennsylvania, and University of Pennsylvania [Philadelphia]
- Subjects
Chemistry ,Dimer ,Nanoparticle ,General Chemistry ,Electronic structure ,[CHIM.INOR]Chemical Sciences/Inorganic chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,3. Good health ,Crystallography ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Octahedron ,Mössbauer spectroscopy ,Pyridine ,Moiety ,ComputingMilieux_MISCELLANEOUS ,Coordination geometry - Abstract
A rare example of a dinuclear iron core with a non-linearly bridged dinitrogen ligand is reported in this work. One-electron reduction of [(tBupyrr2py)Fe(OEt2)] (1) (tBupyrr2py2- = 2,6-bis((3,5-di-tert-butyl)pyrrol-2-yl)pyridine) with KC8 yields the complex [K]2[(tBupyrr2py)Fe]2(μ2-η1:η1-N2) (2), where the unusual cis-divacant octahedral coordination geometry about each iron and the η5-cation-π coordination of two potassium ions with four pyrrolyl units of the ligand cause distortion of the bridging end-on μ-N2 about the FeN2Fe core. Attempts to generate a Et2O-free version of 1 resulted instead in a dinuclear helical dimer, [(tBupyrr2py)Fe]2 (3), via bridging of the pyridine moieties of the ligand. Reduction of 3 by two electrons under N2 does not break up the dimer, nor does it result in formation of 2 but instead formation of the ate-complex [K(OEt2)]2[(tBupyrr2py)Fe]2 (4). Reduction of 1 by two electrons and in the presence of crown-ether forms the tetraanionic N2 complex [K2][K(18-crown-6)]2(tBupyrr2py)Fe]2(μ2-η1:η1-N2) (5), also having a distorted FeN2Fe moiety akin to 2. Complex 2 is thermally unstable and loses N2, disproportionating to Fe nanoparticles among other products. A combination of single-crystal X-ray diffraction studies, solution and solid-state magnetic studies, and 57Fe Mossbauer spectroscopy has been applied to characterize complexes 2-5, whereas DFT studies have been used to help explain the bonding and electronic structure in these unique diiron-N2 complexes 2 and 5.
- Published
- 2020
20. Designing Synergistic Nanocatalysts for Multiple Substrate Activation: Interlattice Ag–Fe3O4 Hybrid Materials for CO2-Inserted Lactones
- Author
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U. Chinna Rajesh, Jeffrey M. Zaleski, Yaroslav Losovyj, and Chun-Hsing Chen
- Subjects
Scaffold ,Materials science ,Tandem ,010405 organic chemistry ,Substrate (chemistry) ,Nanotechnology ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Catalysis ,Nanomaterial-based catalyst ,0104 chemical sciences ,Hybrid material ,human activities - Abstract
Multimetallic architectures that combine chemically diverse materials to affect tandem reactions within a single scaffold drive future nanocatalyst development. Here, we show the unique, interlatti...
- Published
- 2020
21. Hydrosilylation of an Iron(IV) Nitride Complex
- Author
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Veronica Carta, Jeremy M. Smith, Xinfeng Gao, Sean P. Millikan, Chun-Hsing Chen, and Juan A. Valdez-Moreira
- Subjects
Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Ligand ,Hydrosilylation ,Hydride ,Polymer chemistry ,Physical and Theoretical Chemistry ,Nitride ,Silane - Abstract
The nitride ligand in iron(IV) complex PhB(MesIm)3Fe≡N reacts with excess H3SiPh to afford PhB(MesIm)3Fe(μ-H)3(SiHPh) as the major product, which has been structurally and spectroscopically characterized. Bulkier silane HaSiPh2 provides iron(II) amido complex PhB(MesIm)3FeN(H)(SiHPh2) as the initial product of the reaction, with excess H2SiPh2 affording diamagnetic PhB(MesIm)3Fe(μ-H)3(SiPh2) as the major product. Unobserved iron(II) hydride PhB(MesIm)3Fe–H is implicated as an intermediate in this reaction, as suggested by the results of the reaction between iron(II) amido PhB(MesIm)3FeN(H)tBu and H3SiPh, which provides PhB(MesIm)3Fe(H)(μ-H)2(Si(NHtBu)Ph) as the sole product.
- Published
- 2019
22. Dinitrogen Reduction to Ammonium at Rhenium Utilizing Light and Proton-Coupled Electron Transfer
- Author
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Alexander J. M. Miller, James M. Mayer, Faraj Hasanayn, Quinton J. Bruch, Chun-Hsing Chen, Patrick L. Holland, and Gannon P. Connor
- Subjects
chemistry.chemical_element ,Quantum yield ,General Chemistry ,Rhenium ,010402 general chemistry ,Triple bond ,Photochemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Electron transfer ,Colloid and Surface Chemistry ,chemistry ,Yield (chemistry) ,Pyridine ,Proton-coupled electron transfer ,Bond cleavage - Abstract
The direct scission of the triple bond of dinitrogen (N2) by a metal complex is an alluring entry point into the transformation of N2 to ammonia (NH3) in molecular catalysis. Reported herein is a pincer-ligated rhenium system that reduces N2 to NH3 via a well-defined reaction sequence involving reductive formation of a bridging N2 complex, photolytic N2 splitting, and proton-coupled electron transfer (PCET) reduction of the metal-nitride bond. The new complex (PONOP)ReCl3 (PONOP = 2,6- bis(diisopropylphosphinito)pyridine) is reduced under N2 to afford the trans,trans-isomer of the bimetallic complex [(PONOP)ReCl2]2(μ-N2) as an isolable kinetic product that isomerizes sequentially upon heating into the trans,cis and cis,cis isomers. All isomers are inert to thermal N2 scission, and thetrans,trans-isomer is also inert to photolytic N2 cleavage. In striking contrast, illumination of the trans,cisand cis,cis-isomers with blue light affords the octahedral nitride complex cis-(PONOP)Re(N)Cl2 in 47% spectroscopic yield and 11% quantum efficiency. The photon energy drives an N2 splitting reaction that is thermodynamically unfavorable under standard conditions, producing a nitrido complex that reacts with SmI2/H2O to produce a rhenium tetrahydride complex and furnish ammonia in 74% yield.
- Published
- 2019
23. Organometallic Elaboration as a Strategy for Tuning the Supramolecular Characteristics of Aza-Crown Ethers
- Author
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Chun-Hsing Chen, Stewart H. Kerr, Jacob B. Smith, Alexandra H. Farquhar, Andrew M. Camp, and Alexander J. M. Miller
- Subjects
Inorganic Chemistry ,chemistry.chemical_compound ,010405 organic chemistry ,Chemistry ,Organic Chemistry ,Supramolecular chemistry ,Ether ,Physical and Theoretical Chemistry ,010402 general chemistry ,01 natural sciences ,Combinatorial chemistry ,Elaboration ,0104 chemical sciences - Abstract
Outfitting an aza-crown ether with an organotransition-metal pendant provides a mechanism for tuning its supramolecular properties. The binding affinity can be tuned by more than 2 orders of magnit...
- Published
- 2019
24. Gauging the Redox Non‐Innocence of a Highly Pi‐Acidic Bis‐Tetrazine Pincer Ligand
- Author
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Brian J. Cook, Kenneth G. Caulton, Chun-Hsing Chen, and Richard L. Lord
- Subjects
Inorganic Chemistry ,Tetrazine ,chemistry.chemical_compound ,chemistry ,Polymer chemistry ,chemistry.chemical_element ,Pincer ligand ,Redox ,Ruthenium ,Pi backbonding - Published
- 2019
25. A bis ‐Pyrazolate Pincer on Reduced Cr Deoxygenates CO 2 : Selective Capture of the Derived Oxide by Cr II
- Author
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Kenneth G. Caulton, Nicholas S. Labrum, and Chun-Hsing Chen
- Subjects
010405 organic chemistry ,Chemistry ,Ligand ,Organic Chemistry ,Oxide ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Catalysis ,Square pyramidal molecular geometry ,0104 chemical sciences ,Pincer movement ,Crystallography ,chemistry.chemical_compound ,Chromium ,Pyridine ,Selectivity ,Stoichiometry - Abstract
Reduction of the bis-(pyrazolyl)pyridine complex [LCr]2 with stoichiometric KC8 in THF produces a species that is reactive with CO2 to produce an aggregate composed of paramagnetic K2 L2 Cr2 (CO3 ) linked by KCl into a product of formula [K2 L2 Cr2 (CO3 )]4 ⋅2KCl. X-ray diffraction reveals a pincer hydrocarbon exterior and an inorganic interior composed of K+ , Cl- and carbonate oxygens. Every Cr is five coordinate and square pyramidal, with the axial N donor weakly bonded to Cr due to the Jahn-Teller effect of a high spin d4 configuration. Reaction with 13 CO2 confirms that carbonate here is derived from CO2 , that oxide is derived from CO2 , and that CO is indeed released, since it is not a competent ligand to CrII . Guiding principles for selectivity in CO2 reduction are deduced from the diverse successful molecular constructs to date.
- Published
- 2019
26. Reactivity of an Unusual Divalent Chromium Aggregate Supported by a Multifunctional Bis(pyrazolate) Pincer Ligand
- Author
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Kenneth G. Caulton, Chun-Hsing Chen, Nicholas S. Labrum, and Maren Pink
- Subjects
Inorganic Chemistry ,chemistry.chemical_classification ,Chromium ,Aggregate (composite) ,chemistry ,Jahn–Teller effect ,Polymer chemistry ,chemistry.chemical_element ,Reactivity (chemistry) ,Pincer ligand ,Divalent - Published
- 2019
27. Di- and trivalent chromium bis(pyrazol-3-yl)pyridine pincer complexes with good leaving groups
- Author
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Kenneth G. Caulton, Nicholas S. Labrum, Daniel M. Beagan, Junghee Seo, Chun-Hsing Chen, and Maren Pink
- Subjects
Ligand ,Chemistry ,Hydrogen bond ,Pyrazole ,Medicinal chemistry ,Square pyramidal molecular geometry ,Pincer movement ,Inorganic Chemistry ,chemistry.chemical_compound ,Pyridine ,Materials Chemistry ,Physical and Theoretical Chemistry ,Pincer ligand ,Trifluoromethanesulfonate - Abstract
The consequences of installing two versions of a potentially redox active pincer ligand on Cr(III) and Cr(II) are described, and reveal influence of the Jahn-Teller effect. The ligand involves two pyrazole rings attached by pyrazole carbons to the ortho positions of pyridine, thus creating two 1,4-diazabutadiene moieties. In one version, each pyrazole carries an NH proton (H2L), while a comparison version (LMe) involves methyl in place of the two weakly acidic protons, to identify the impact of hydrogen bonding. Complexes synthesized include (H2L)CrX3, where X Cl, triflate and nitrate, (LMe)CrCl3 and (LMe)Cr(OTf)3, together with the divalent metal complexes (H2L)CrCl2, (LMe)CrCl2 and (LMe)Cr(OTf)2. Cyclic voltammetry establishes the relationship between the tri- and divalent triflate complexes of LMe, and DFT calculations indicate further reduction of the latter occurs at the LMe ligand. Nitrate is shown to be a stronger ligand than triflate to Cr(III) here. NaBArF24 in THF removes only one chloride from (H2L)CrCl2, to give square pyramidal [(H2L)CrCl(THF)]+.
- Published
- 2019
28. A new face for bis(pyrazol-3-yl)pyridine: Incompatible geometric preferences dictates unprecedented pincer ligand connectivity
- Author
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Kenneth G. Caulton, Chun-Hsing Chen, and Nicholas S. Labrum
- Subjects
chemistry.chemical_classification ,010405 organic chemistry ,Iodide ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,Copper ,0104 chemical sciences ,Inorganic Chemistry ,Crystallography ,chemistry.chemical_compound ,chemistry ,Pyridine ,Materials Chemistry ,Physical and Theoretical Chemistry ,Pincer ligand ,Single crystal - Abstract
The planar pincer ligand bis(pyrazol-3-yl)pyridine, H2L, binds to copper(I) iodide to give a product of formula (H2L)2(CuI)3 which single crystal X-ray diffraction reveals to have two unprecedented features for this ligand: κ2 binding of one H2L and bridging of the second H2L across two copper centers. The broader implications of this finding are discussed.
- Published
- 2019
29. Electrochemical C–H bond activation via cationic iridium hydride pincer complexes
- Author
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Andrew G. Walden, Nicholas Lease, Andrea Casuras, Brian M. Lindley, Chun-Hsing Chen, Ann Marie Brasacchio, Alexander J. M. Miller, and Alan S. Goldman
- Subjects
chemistry.chemical_classification ,010405 organic chemistry ,Hydride ,Alkene ,Cationic polymerization ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Phosphorane ,Medicinal chemistry ,0104 chemical sciences ,Catalysis ,chemistry.chemical_compound ,Deprotonation ,chemistry ,Pyridine ,Phosphazene - Abstract
A C–H bond activation strategy based on electrochemical activation of a metal hydride is introduced. Electrochemical oxidation of (tBu4PCP)IrH4 (tBu4PCP is [1,3-(tBu2PCH2)-C6H3]−) in the presence of pyridine derivatives generates cationic Ir hydride complexes of the type [(tBu4PCP)IrH(L)]+ (where L = pyridine, 2,6-lutidine, or 2-phenylpyridine). Facile deprotonation of [(tBu4PCP)IrH(2,6-lutidine)]+ with the phosphazene base tert-butylimino-tris(pyrrolidino)phosphorane, tBuP1(pyrr), results in selective C–H activation of 1,2-difluorobenzene (1,2-DFB) solvent to generate (tBu4PCP)Ir(H)(2,3-C6F2H3). The overall electrochemical C–H activation reaction proceeds at room temperature without need for chemical activation by a sacrificial alkene hydrogen acceptor. This rare example of undirected electrochemical C–H activation holds promise for the development of future catalytic processes.
- Published
- 2019
30. Electrophile Recruitment as a Structural Element in Bis‐Pyrazolate Pyridine Complex Aggregation
- Author
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Chun-Hsing Chen, Kenneth G. Caulton, Brian J. Cook, and Maren Pink
- Subjects
Inorganic Chemistry ,chemistry.chemical_compound ,010405 organic chemistry ,Chemistry ,Polymer chemistry ,Pyridine ,Electrophile ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,Cobalt ,0104 chemical sciences ,Structural element - Published
- 2018
31. Heteroleptic nickel complexes of a bulky bis(carbene)borate ligand
- Author
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Chun-Hsing Chen, Jeremy M. Smith, Jorge L. Martinez, Wei-Tsung Lee, and Maren Pink
- Subjects
010405 organic chemistry ,Ligand ,Synthon ,chemistry.chemical_element ,Trigonal pyramidal molecular geometry ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Inorganic Chemistry ,Benzaldehyde ,chemistry.chemical_compound ,Crystallography ,Nickel ,chemistry ,Materials Chemistry ,Hydroxide ,Physical and Theoretical Chemistry ,Homoleptic ,Carbene - Abstract
Bis(carbene)borate ligand transfer to the nickel nitrosyl synthon Ni(NO)(PPh3)2Br provides the new nickel nitrosyl complex Ph2B(tBuIm)2Ni(NO)(PPh3). The solid state structure reveals a trigonal pyramidal nickel ion with a very long bond to the apical PPh3 ligand. The complex reversibly dissociates PPh3 in solution to afford three-coordinate Ph2B(tBuIm)2Ni(NO), with NMR data providing evidence for PPh3 binding at low temperatures. Ligand transfer to Ni(PMe3)2Cl2 provides the square planar complex, Ph2B(tBuIm)2Ni(PMe3)Cl, which shows no evidence for rearranging to the form a homoleptic complex with two bis(carbene)borate ligands. This complex is a suitable synthon for the [Ph2B(tBuIm)2Ni]+ fragment, as demonstrated by the synthesis of the π-allyl complex Ph2B(tBuIm)2Ni(η3-C7H7). The π-allyl complex reacts with O2 to provide benzaldehyde and an unstable complex that is tentatively identified as the nickel(II) hydroxide [Ph2B(tBuIm)2Ni(μ-OH)]2.
- Published
- 2018
32. A multimetal-ligand cooperative approach to CO2 activation
- Author
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Brian J. Cook, Alexander V. Polezhaev, Chun-Hsing Chen, Kenneth G. Caulton, and Maren Pink
- Subjects
010405 organic chemistry ,Chemistry ,Hydrogen bond ,Ligand ,Dimer ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,0104 chemical sciences ,Inorganic Chemistry ,chemistry.chemical_compound ,Deprotonation ,Nucleophile ,Formula unit ,Materials Chemistry ,Molecule ,Hydroxide ,Physical and Theoretical Chemistry - Abstract
The octahedral, S = 2, bis -pyrazolatopyridyl complex LFe(DMAP) 3 reacts with CO 2 in CH 3 CN to yield (LH)Fe(DMAP) 2 (O 3 C)Fe 2 (L)(HL), which is the product of capture of one CO 2 by one doubly deprotonated water molecule, then binding of one iron to each carbonate oxygen. In order to eliminate DMAP as a participant, [LiClFe 2 L 2 ] is shown to add one water per Fe 2 unit to give [LiClFe 2 (HL)(L)(OH)], with the Fe 2 L 2 unit capturing hydroxide, and this entire formula unit is linked into a dimer by Li/OH interactions, supplemented by hydrogen bonds to OH from nucleophilic pyrazolate nitrogens. This is suggested to be the process where carbonate is formed, promoted by the ability of the LFe unit to increase the nucleophilicity of H 2 O, and then attack CO 2 . Related to that conversion, we establish the structure of the conjugate base [Fe 2 L 2 (O)] 2- . Collectively, this shows the combined action of multiple Fe(II) reactants, together with pyrazolate nucleophile and Bronsted base in the hydration of CO 2 , the conversion effected by carbonic anhydrase.
- Published
- 2018
33. Redox-Induced Structural Reorganization Dictates Kinetics of Cobalt(III) Hydride Formation via Proton-Coupled Electron Transfer
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Sean F. McWilliams, Noémie Elgrishi, Jillian L. Dempsey, Daniel A. Kurtz, Chun-Hsing Chen, Banu Kandemir, William C. Howland, and Debanjan Dhar
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Phosphines ,Protonation ,Electrons ,010402 general chemistry ,Ligands ,01 natural sciences ,Biochemistry ,Redox ,Catalysis ,Electron transfer ,Colloid and Surface Chemistry ,Reaction rate constant ,Coordination Complexes ,Elementary reaction ,Chemistry ,Hydride ,Ligand ,General Chemistry ,Cobalt ,Electrochemical Techniques ,0104 chemical sciences ,Crystallography ,Kinetics ,Proton-coupled electron transfer ,Protons ,Oxidation-Reduction ,Hydrogen - Abstract
Two-electron, one-proton reactions of a family of [CoCp(dxpe)(NCCH3)]2+ complexes (Cp = cyclopentadienyl, dxpe = 1,2-bis(di(aryl/alkyl)phosphino)ethane) form the corresponding hydride species [HCoCp(dxpe)]+ (dxpe = dppe (1,2-bis(diphenylphosphino)ethane), depe (1,2-bis(diethylphosphino)ethane), and dcpe (1,2-bis(dicyclohexylphosphino)ethane)) through a stepwise proton-coupled electron transfer process. For three [CoCp(dxpe)(NCCH3)]2+ complexes, peak shift analysis was employed to quantify apparent proton transfer rate constants from cyclic voltammograms recorded with acids ranging 22 pKa units. The apparent proton transfer rate constants correlate with the strength of the proton source for weak acids, but these apparent proton transfer rate constants curiously plateau (kpl) as the reaction becomes increasingly exergonic. The absolute apparent proton transfer rate constants across both these regions correlate with the steric bulk of the chelating diphosphine ligand, with bulkier ligands leading to slower kinetics (kplateau,depe = 3.5 × 107 M-1 s-1, kplateau,dppe = 1.7 × 107 M-1 s-1, kplateau,dcpe = 7.1 × 104 M-1 s-1). Mechanistic studies were conducted to identify the cause of the aberrant kPTapp-ΔpKa trends. When deuterated acids are employed, deuterium incorporation in the Cp ring is observed, indicating protonation of the CoCp(dxpe) species to form the corresponding hydride proceeds via initial ligand protonation. Digital simulations of cyclic voltammograms show ligand loss accompanying initial reduction gates subsequent PCET activity at higher driving forces. Together, these experiments reveal the details of the reaction mechanism: reduction of the Co(III) species is followed by dissociation of the bound acetonitrile ligand, subsequent reduction of the unligated Co(II) species to form a Co(I) species is followed by protonation, which occurs at the Cp ring, followed by tautomerization to generate the stable Co(III)-hydride product [HCoCp(dxpe)]+. Analysis as a function of chelating disphosphine ligand, solvent, and acid strength reveals that the ligand dissociation equilibrium is directly influenced by the steric bulk of the phosphine ligands and gates protonation, giving rise to the plateau of the apparent proton transfer rate constant with strong acids. The complexity of the reaction mechanism underpinning hydride formation, encompassing dynamic behavior of the entire ligand set, highlights the critical need to understand elementary reaction steps in proton-coupled electron transfer reactions.
- Published
- 2021
34. Polarity-Tolerant Chloride Binding in Foldamer Capsules by Programmed Solvent-Exclusion
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Amar H. Flood, Yun Liu, Edward G. Sheetz, Chun-Hsing Chen, and Fred C. Parks
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Aqueous solution ,Chemistry ,Dimethyl sulfoxide ,Foldamer ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Combinatorial chemistry ,Affinities ,Catalysis ,0104 chemical sciences ,Solvent ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Anion binding ,Acetonitrile ,Dichloromethane - Abstract
Persistent anion binding in a wide range of solution environments is a key challenge that continues to motivate and demand new strategies in synthetic receptor design. Though strong binding in low-polarity solvents has become routine, our ability to maintain high affinities in high-polarity solvents has not yet reached the standard set by nature. Anions are bound and transported regularly in aqueous environments by proteins that use secondary and tertiary structure to isolate anion binding sites from water. Inspired by this principle of solvent exclusion, we created a sequence-defined foldameric capsule whose global minimum conformation displays a helical folded state and is preorganized for 1:1 anion complexation. The high stability of the folded geometry and its ability to exclude solvent were supported by solid-state and solution phase studies. This capsule then withstood a 4-fold increase in solvent dielectric constant (er) from dichloromethane (9) to acetonitrile (36) while maintaining a high and solvent-independent affinity of 105 M-1; ΔG ∼ 28 kJ mol-1. This behavior is unusual. More typical of solvent-dependent behavior, Cl- affinities were seen to plummet in control compounds, such as aryl-triazole macrocycles and pentads, with their solvent-exposed binding cavities susceptible to dielectric screening. Finally, dimethyl sulfoxide denatures the foldamer by putative solvent binding, which then lowers the foldamer's Cl- affinity to normal levels. The design of this capsule demonstrates a new prototype for the development of potent receptors that can operate in polar solvents and has the potential to help manage hydrophilic anions present in the hydrosphere and biosphere.
- Published
- 2021
35. Electrochemistry-enabled organometallic transformation: A Case Study of the electrosynthesis of cyclopentadienyl rhenium hydride complexes
- Author
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Jillian Dempsey, Tao Huang, Aldo Jordan, Cole Gruninger, Tayliz Rodriguez, Daniel Kurtz, and Chun-Hsing Chen
- Published
- 2020
36. Selecting Double Bond Positions with a Single Cation- Responsive Iridium Olefin Isomerization Catalyst
- Author
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Chun-Hsing Chen, P Thomas Blackburn, Andrew M. Camp, Henry M. Dodge, Matthew R. Kita, and Alexander J. M. Miller
- Subjects
chemistry.chemical_classification ,chemistry.chemical_compound ,Olefin fiber ,chemistry ,Double bond ,Alkene ,chemistry.chemical_element ,Regioselectivity ,Ether ,Iridium ,Isomerization ,Combinatorial chemistry ,Catalysis - Abstract
The catalytic transposition of double bonds holds promise as an ideal route to alkenes with value as fragrances, commodity chemicals, and pharmaceuticals; yet, selective access to specific isomers is a challenge, requiring independent development of different catalysts for different products. In this work, a single cation-responsive iridium catalyst is developed for the selective production of either of two different internal alkene isomers. In the absence of salts, a single positional isomerization of 1-butene derivatives furnishes 2-alkenes with exceptional regioselectivity and stereoselectivity. The same catalyst, in the presence of Na+, mediates two positional isomerizations to produce 3-alkenes. The synthesis of new iridium pincer-crown ether catalysts based on an aza-18-crown-6 ether proved instrumental in achieving cation-controlled selectivity. Experimental and computational studies guided the development of a mechanistic model that explains the observed selectivity for various functionalized 1-butenes, providing insight into strategies for catalyst development based on non-covalent modifications.
- Published
- 2020
37. Doubly stereoconvergent crystallization enabled by asymmetric catalysis.
- Author
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de Jesús Cruz, Pedro, Cassels, William R., Chun-Hsing Chen, and Johnson, Jeffrey S.
- Published
- 2022
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38. Two-State Reactivity in Iron-Catalyzed Alkene Isomerization Confers σ-Base Resistance
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Yafei Gao, Chun-Hsing Chen, Jeremy M. Smith, Anne K. Hickey, and Sean A. Lutz
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chemistry.chemical_classification ,Base (chemistry) ,Alkene ,Iron catalyzed ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Medicinal chemistry ,Catalysis ,0104 chemical sciences ,Colloid and Surface Chemistry ,chemistry ,Reactivity (chemistry) ,Isomerization - Abstract
A low-coordinate, high spin (S = 3/2) organometallic iron(I) complex is a catalyst for the isomerization of alkenes. A combination of experimental and computational mechanistic studies supports a m...
- Published
- 2020
39. Plug-and-Play Optical Materials from Fluorescent Dyes and Macrocycles
- Author
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Krishnan Raghavachari, Tumpa Sadhukhan, Bo Qiao, Yoan C. Simon, Chun-Hsing Chen, Christopher R. Benson, Bo W. Laursen, Wei Zhao, Katherine L. VanDenburgh, Brad J. Davis, Sina Borgi, Maren Pink, Laura Kacenauskaite, Junsheng Chen, and Amar H. Flood
- Subjects
Materials science ,Fluorophore ,General Chemical Engineering ,Supramolecular chemistry ,Ionic bonding ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Biochemistry ,chemistry.chemical_compound ,Materials Chemistry ,OLED ,Environmental Chemistry ,chemistry.chemical_classification ,business.industry ,Biochemistry (medical) ,Wide-bandgap semiconductor ,General Chemistry ,Polymer ,021001 nanoscience & nanotechnology ,Fluorescence ,0104 chemical sciences ,chemistry ,Photonics ,0210 nano-technology ,business - Abstract
Summary Fluorescence is critical to applications in optical materials including OLEDs and photonics. While fluorescent dyes are potential key components of these materials, electronic coupling between them in the solid state quenches their emission, preventing their reliable translation to applications. We report a universal solution to this long-standing problem with the discovery of a class of materials called small-molecule ionic isolation lattices (SMILES). SMILES perfectly transfer the optical properties of dyes to solids, are simple to make by mixing cationic dyes with anion-binding cyanostar macrocycles, and work with major classes of commercial dyes, including xanthenes, oxazines, styryls, cyanines, and trianguleniums. Dyes are decoupled spatially and electronically in the lattice by using cyanostar with its wide band gap. Toward applications, SMILES crystals have the highest known brightness per volume and solve concentration quenching to impart fluorescence to commercial polymers. SMILES materials enable predictable fluorophore crystallization to fulfill the promise of optical materials by design.
- Published
- 2020
40. Terrestrial Trapping of the Interstellar Gas, Phosphorus Nitride
- Author
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Daniel M. Beagan, Jorge L. Martinez, Xinfeng Gao, Jeremy M. Smith, Chun-Hsing Chen, Veronica Carta, Sean A. Lutz, Pierre Moënne-Loccoz, and Maren Pink
- Subjects
Crystallography ,chemistry.chemical_compound ,Nucleophile ,chemistry ,Molybdenum ,Phosphide ,Electrophile ,chemistry.chemical_element ,Bridging ligand ,Nitride ,Linkage isomerism ,Isomerization - Abstract
The N2 analogue phosphorus nitride (PN) was the first phosphorus containing compound to be detected in the interstellar medium, however this thermodynamically unstable compound has a fleeting existence on Earth. Here, we show that reductive coupling of iron(IV) nitride and molybdenum(VI) phosphide complexes assembles PN as a bridging ligand in a structurally-characterized bimetallic complex. Reaction with C≡NtBu releases the mononuclear complex [(N3N)Mo-PN]−, N3N = [(Me3SiNCH2CH2)3N]3−), which undergoes light-induced linkage isomerization to provide [(N3N)Mo-NP]−, as revealed by photocrystallography. While structural and spectroscopic characterization, supported by electronic structure calculations reveal PN multiple bond character, coordination to molybdenum creates nucleophilic character at the terminal atom of the PN/NP ligands. Indeed, the linkage isomers can be trapped in solution by reaction with a Rh(I) electrophile.
- Published
- 2020
41. Nitrogen oxyanion reduction by Co(ii) augmented by a proton responsive ligand: recruiting multiple metals
- Author
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Chun-Hsing Chen, Veronica Carta, Kenneth G. Caulton, and Alyssa C. Cabelof
- Subjects
inorganic chemicals ,Ligand ,chemistry.chemical_element ,Pyrazole ,Medicinal chemistry ,Pincer movement ,Inorganic Chemistry ,chemistry.chemical_compound ,Deprotonation ,chemistry ,Pincer ligand ,Cobalt ,Deoxygenation ,Bond cleavage - Abstract
Deoxygenation of nitrite oxygen with divalent cobalt was achieved using (PNNH)CoCl2, carrying a pyridyl pincer ligand with one P(t-Bu)2 arm and one pyrazole arm. Reaction of (PNNH)CoCl2 with NaNO2 at a 2 : 5 mole ratio promptly forms equimolar (PNNH)Co(NO2)3 and (PNN)Co(NO2)(NO), {CoNO}8 with the lost ligand proton combined with removed oxo as hydroxide. These two CoIII products are characterized, showing a bent CoNO unit as the fate of the reduced nitrogen. DFT calculations are consistent with two one-electron CoII reductants binding to one NO2− bridge, then proton transfer being needed for facile N/O bond scission. A species detected by low temperature execution of this reaction contains cobalt in two oxidation states with an N,O bridging nitro group and pincer ligands that have been deprotonated, showing the active participation of the proton responsive ligand.
- Published
- 2020
42. Fundamental Design Rules for Turning on Fluorescence in Ionic Molecular Crystals
- Author
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Chun-Hsing Chen, Krishnan Raghavachari, Wei Zhao, Amar H. Flood, Bo Qiao, Junsheng Chen, Katherine L. VanDenburgh, Laura Kacenauskaite, Sina Borgi, Maren Pink, Christopher R. Benson, Tumpa Sadhukhan, and Bo W. Laursen
- Subjects
Rhodamine ,chemistry.chemical_compound ,Materials science ,Fluorophore ,chemistry ,Band gap ,OLED ,Ionic bonding ,Cyanine ,Photochemistry ,HOMO/LUMO ,Fluorescence - Abstract
Fluorescence is critical to many advanced materials including OLEDs and bioimaging. While molecular fluorophores that show bright emission in solution are potential sources of these materials, their emission is frequently lost in the solid state preventing their direct translation to optical applications. Unpredictable packing and coupling of dyes leads to uncontrolled spectral shifts and quenched emission. No universal solution has been found since Perkin made the first synthetic dye 150 years ago. We report the serendipitous discovery of a new type of material that we call small-molecule ionic isolation lattices(SMILES) tackling this long-standing problem. SMILES are easily prepared by adding two equivalents of the anion receptor cyanostar to cationic dyes binding the counter anions and inducing alternating packing of dyes and cyanostar-anion complexes. SMILES materials reinstate solution-like spectral properties and bright fluorescence to thin films and crystals. These positive outcomes derive from the cyanostar. Its wide 3.45-eV band gap allows the HOMO and LUMO levels of the dye to nest inside those of the complex as verified by electrochemistry. This feature simultaneously enables spatial and electronic isolation to decouple the fluorophores from each other and from the cyanostar-anion lattice. Representative dyes from major families of fluorophores, viz, xanthenes, oxazines, styryls, cyanines, and trianguleniums, all crystalize in the characteristic structure and regain their attractive fluorescence. SMILES crystals of rhodamine and cyanine display unsurpassed brightness per volume pointing to uses in demanding applications such as bioimaging. SMILES materials enable predictable fluorophore crystallization to fulfil the promise of optical materials by design.
- Published
- 2019
43. Strong π-Backbonding Enables Record Magnetic Exchange Coupling Through Cyanide
- Author
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T. David Harris, Agnes E. Thorarinsdottir, Jordan A. DeGayner, Sean A. Lutz, Chun-Hsing Chen, Yaroslav Losovyj, Jeremy M. Smith, Maren Pink, and Juan A. Valdez-Moreira
- Subjects
Cyanide ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Bond order ,Magnetic susceptibility ,Catalysis ,0104 chemical sciences ,Delocalized electron ,Crystallography ,chemistry.chemical_compound ,Paramagnetism ,Colloid and Surface Chemistry ,chemistry ,Unpaired electron ,Antiferromagnetism ,Pi backbonding - Abstract
The paramagnetic cyano-bridged complex PhB(tBuIm)3Fe-NC-Mo(NtBuAr)3 (Ar = 3,5-Me2C6H3) is readily assembled from a new four-coordinate, high-spin (S = 2) iron(II) monocyanide complex and the three-coordinate molybdenum(III) complex Mo(NtBuAr)3. X-ray diffraction and IR spectroscopy reveal that delocalization of unpaired electron density into the cyanide π* orbitals leads to a reduction of the C-N bond order. Direct current (dc) magnetic susceptibility measurements, supported by electronic structure calculations, demonstrate the presence of strong antiferromagnetic exchange between spin centers, with a coupling constant of J = -122(2) cm-1. To our knowledge, this value represents the strongest magnetic exchange coupling ever to be observed through cyanide. These results demonstrate the ability of low-coordinate metal fragments to engender extremely strong magnetic exchange coupling through cyanide by virtue of significant π-backbonding into the cyanide ligand.
- Published
- 2019
44. A Multifunctional Pincer Ligand for Cobalt‐Promoted Oxidation by N 2 O
- Author
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Brian J. Cook, Kenneth G. Caulton, and Chun-Hsing Chen
- Subjects
Phosphine oxide ,chemistry.chemical_classification ,010405 organic chemistry ,Organic Chemistry ,chemistry.chemical_element ,Electron donor ,Homogeneous catalysis ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Catalysis ,Square pyramidal molecular geometry ,0104 chemical sciences ,Divalent ,chemistry.chemical_compound ,Monomer ,chemistry ,Polymer chemistry ,Pincer ligand ,Cobalt - Abstract
The divalent cobalt complex of the diprotic pincer ligand bis-pyrazolylpyridine, (H2 L)CoCl2 , is dehydrohalogenated twice by LiN(SiMe3 )2 in the presence of PEt3 to give monomeric S=1/2 LCo(PEt3 )2 (1), fully characterized in the solid-state and solution as a square pyramidal monomer with a long axial Co-P bond. This 17-electron species reacts in time of mixing with N2 O to form L2 Co2 (μ-OPEt3 ) (2)+3 OPEt3 , the former the first example of phosphine oxide bridging two transition metals. The same products are formed from O2 , and divalent cobalt persists even in the presence of excess oxidant. Species (2) catalyzes oxygen atom transfer (OAT) for generation of O=PEt3 from PEt3 from either N2 O or O2 . Bridging and terminal cobalt oxo intermediates are suggested, and the electron donor power, and potential redox activity of the dianionic pincer ligand is emphasized.
- Published
- 2018
45. Dehydrohalogenation of proton responsive complexes: versatile aggregation via pyrazolate pincer ligand arms
- Author
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Chun-Hsing Chen, Kenneth G. Caulton, Brian J. Cook, and Maren Pink
- Subjects
010405 organic chemistry ,Coordination number ,Dimer ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,0104 chemical sciences ,Inorganic Chemistry ,chemistry.chemical_compound ,Deprotonation ,Monomer ,chemistry ,Nucleophile ,Pyridine ,Dehydrohalogenation ,Pincer ligand - Abstract
The behavior of the complex (H2L)CoCl2, where H2L is a bis-(pyrazol-3-yl)pyridine, towards Bronsted bases is studied, to evaluate peripheral NH deprotonation as a route to a dianionic pincer ligand on a d7 center. Deprotonation is found to also remove chloride from cobalt, and the decreased metal coordination number is then satisfied by bimolecular reaction of the newly formed peripheral deprotonated pyrazolate nitrogen, leading to Co2 units bridged by some of the pyrazolates, in the analogous species [Co2(L)(LH)]2(L) and [Co2(L)(HL)]2[Co(L)2], but also occasionally by chloride retention, in LiCo2L2Cl. Reacting LiCo2L2Cl with tBuNC, yields monomeric LCo(tBuNC)2, shown to be a 17 valence electron species. Use of excess LiN(SiMe3)2 in deprotonation of (H2L)CoCl2 leads to a product containing a Co[N(SiMe3)2]2 substructure, which illustrates opening of the Co2L2 dimer in response to an attacking nucleophile.
- Published
- 2018
46. Cyanide Ligand Assembly by Carbon Atom Transfer to an Iron Nitride
- Author
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Wei-Tsung Lee, Jorge L. Martinez, Jeremy M. Smith, Diane A. Dickie, Maren Pink, Chun-Hsing Chen, Hsiu-Jung Lin, and Xinfeng Gao
- Subjects
chemistry.chemical_classification ,Cyclopropenylidene ,Carbon atom ,010405 organic chemistry ,Chemistry ,Cyanide ,Alkyne ,General Chemistry ,Nitride ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Iron nitride ,Colloid and Surface Chemistry ,Polymer chemistry ,Derivative (chemistry) ,Cyanide ligand - Abstract
The new iron(IV) nitride complex PhB(iPr2Im)3Fe≡N reacts with 2 equiv of bis(diisopropylamino)cyclopropenylidene (BAC) to provide PhB(iPr2Im)3Fe(CN)(N2)(BAC). This unusual example of a four-electron reaction involves carbon atom transfer from BAC to create a cyanide ligand along with the alkyne iPr2N-C≡C-NiPr2. The iron complex is in equilibrium with an N2-free species. Further reaction with CO leads to formation of a CO analogue, which can be independently prepared using NaCN as the cyanide source, while reaction with B(C6F5)3 provides the cyanoborane derivative.
- Published
- 2017
47. High‐Fidelity Multistate Switching with Anion–Anion and Acid–Anion Dimers of Organophosphates in Cyanostar Complexes
- Author
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Wei Zhao, Bo Qiao, Amar H. Flood, and Chun-Hsing Chen
- Subjects
chemistry.chemical_classification ,Base (chemistry) ,010405 organic chemistry ,Stereochemistry ,Hydrogen bond ,Picric acid ,General Medicine ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Ion ,chemistry.chemical_compound ,Molecular recognition ,chemistry ,Acid anion ,Polymer chemistry ,Hydroxide ,Triflic acid - Abstract
The acid-base switching of complexes formed from anti-electrostatic anion-anion homodimers of organophosphates and cyanostar macrocycles was investigated for the first time. High-fidelity 2:2 complexes were selected by using suitably sized organo substituents. Reversible and direct switching occurs with triflic acid and hydroxide base. An unexpected acid⋅⋅⋅anion heterodimer was discovered with weaker picric acid, which helped reveal some of the elementary steps. Switching can also proceed in a cooperative (strong anion then weak acid) or stepwise manner (weak acid then strong anion).
- Published
- 2017
48. Deprotonation, Chloride Abstraction, and Dehydrohalogenation as Synthetic Routes to Bis‐Pyrazolate Pyridyl Iron(II) Complexes
- Author
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Brian J. Cook, Alexander V. Polezhaev, Maren Pink, Kenneth G. Caulton, and Chun-Hsing Chen
- Subjects
010405 organic chemistry ,Stereochemistry ,Dimer ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,0104 chemical sciences ,Pincer movement ,Inorganic Chemistry ,chemistry.chemical_compound ,Deprotonation ,chemistry ,Dehydrohalogenation ,Redistribution (chemistry) ,Lewis acids and bases ,Pincer ligand ,Trifluoromethanesulfonate - Abstract
The process of removal of H+ and of Cl-, dehydrohalogenation, from (H₂L)FeCl₂ is investigated systematically, to understand the reactivity of the implied transient LFe(II). Reaction of (H₂L)FeCl₂ with 2 equivalents of LiN(SiMe₃)₂ yields LiClFe₂L₂, as its dimer with every iron 5-coordinate in an FeN₄Cl environment. To avoid Li+ cation derived from base, reaction of Na₂L with FeCl₂ gives a product Na₂[NaFe(HL)(L)]₂(LFeO) from addition of water, which reveals Na/pyrazolate Nβ interactions and a five coordinate oxo group in the OFe₃Na₂ core. Dehydrohalogenation in the presence of Ph₂PC₂H₄PPh₂ gives diamagnetic [LFe(κ²-dppe)]₂(μ-dppe) and LFe(κ²-dppe)(κ¹-dppe). Dehydrohalogenation in the presence of tBuNC gives diamagnetic LFe(CNtBu)₃. This is selectively methylated at both pyrazolate β-N to give LMeFe(tBuNC)₃²+ which is reduced with KC₈ to diamagnetic LMeFe(tBuNC)². Structure determination of these and IR data on isonitrile bands, show L²- to be a stronger donor than LMe. First installing triflate (to avoid the more persistent Cl-) facilitates access to LFe(Lewis base)₃²+ complexes, but this cation shows relatively weak binding of CO to LFeII, which implicates weak π basicity of that d6 species. Production of bis-pincer complexes (H₂L)₂Fe²+ and (LMe)₂Fe²+ in the presence of abundant Lewis base in polar medium is demonstrated, which illustrates a pincer ligand redistribution challenge to be kept in mind when trying to maintain a 1:1 Fe:pincer ratio, for highest reactivity.
- Published
- 2017
49. Room-Temperature Ring-Opening of Quinoline, Isoquinoline, and Pyridine with Low-Valent Titanium
- Author
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Mu-Hyun Baik, Seung-yeol Baek, Maren Pink, Takashi Kurogi, Seongyeon Kwon, Daniel J. Mindiola, Dahye Kang, Patrick J. Carroll, Masahiro Kamitani, Douglas P. Solowey, and Chun-Hsing Chen
- Subjects
010405 organic chemistry ,Stereochemistry ,Quinoline ,Cyclohexene ,Regioselectivity ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Medicinal chemistry ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,chemistry ,Intramolecular force ,Pyridine ,Structural isomer ,Isoquinoline ,Imide - Abstract
The complex (PNP)Ti═CHtBu(CH2tBu) (PNP = N[2-PiPr2-4-methylphenyl]2–) dehydrogenates cyclohexane to cyclohexene by forming a transient low-valent titanium-alkyl species, [(PNP)Ti(CH2tBu)], which reacts with 2 equiv of quinoline (Q) at room temperature to form H3CtBu and a Ti(IV) species where the less hindered C2═N1 bond of Q is ruptured and coupled to another equivalent of Q. The product isolated from this reaction is an imide with a tethered cycloamide group, (PNP)Ti═N[C18H13N] (1). Under photolytic conditions, intramolecular C—H bond activation across the imide moiety in 1 occurs to form 2, and thermolysis reverses this process. The reaction of 2 equiv of isoquinoline (Iq) with intermediate [(PNP)Ti(CH2tBu)] results in regioselective cleavage of the C1═N2 and C1—H bonds, which eventually couple to form complex 3, a constitutional isomer of 1. Akin to 1, the transient [(PNP)Ti(CH2tBu)] complex can ring-open and couple two pyridine molecules, to produce a close analogue of 1, complex (PNP)Ti═N[C10H9N] (4...
- Published
- 2017
50. Ligand Design toward Multifunctional Substrate Reductive Transformations
- Author
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Chun-Hsing Chen, Adam S. Kinne, Alyssa C. Cabelof, Richard L. Lord, Kenneth G. Caulton, and Alexander V. Polezhaev
- Subjects
Steric effects ,010405 organic chemistry ,Chemistry ,Stereochemistry ,Hydrogen bond ,Ligand ,Substituent ,Pyrazole ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,0104 chemical sciences ,Inorganic Chemistry ,chemistry.chemical_compound ,Pyridine ,Moiety ,Physical and Theoretical Chemistry ,Lone pair - Abstract
The synthesis of bis(N1-phenyl-5-hydroxypyrazol-3-yl)pyridines ("L") is described, and these are silylated to achieve analogues ("Si2L") without the variable of the hydroxyl proton mobility. One hydroxyl example is characterized in its bis-pincer iron(II) complex, which shows every OH proton involved in hydrogen bonding. The steric bulk of the silylated N-phenyl-substituted ligands allows the synthesis and characterization of paramagnetic (Si2L)FeCl2 complexes, and one of these is reduced, under CO, to give the diamagnetic (Si2L)Fe(CO)2 species. Structural comparison and density functional theory calculations of the dichloride and dicarbonyl species show that much, but not all, of the reduction occurs at both the ligand pyridine and pyrazole rings, and thus this ligand type is more resistant to reduction than the simpler bis(iminopyridines). The OSiR3 substituent offers a useful diagnostic of reduction at pyrazole via the degree of π-donation to pyrazole by the oxygen lone pairs, and the stereoelectronic features of the NPh moiety are analyzed. The X-ray photoelectron spectroscopy binding energies of both iron and nitrogen are analyzed to show details of the locus of reduction.
- Published
- 2017
Catalog
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