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Chaudhri N, Guberman-Pfeffer MJ, Zeller M, Brückner C. Oxochlorin frameworks confining a β-hydroxyketone moiety. Dalton Trans 2024; 53:13142-13150. [PMID: 39041824 DOI: 10.1039/d4dt01386g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/24/2024]
Abstract
Nominally, meso-hydroxyoxochlorins, like known 5-hydroxy-7-oxo-octaethylchlorin (9), its nickel complex [5-hydroxy-7-oxo-octaethylchlorinato]nickel(II) (9Ni), or the novel 5-hydroxy-7,17-dioxo-octaethylbacteriochlorin (10), incorporate an acetylacetonate (acac)-moiety in the enol form in their chromophore structures. X-Ray diffraction studies of the compounds show the presence of a strong H-bond between the enol and flanking β-ketone. Like acac, the functionality can be deprotonated. However, unlike regular acac-like moieties, we did not find any indication that this functionality is competent in chelating any of the 3d or 4d transition metal ions tested. Evidently, the conjugation that contributes to the stability of acac as a ligand cannot be expressed in the meso-hydroxyoxochlorins since it would perturb the aromaticity of the porphyrinic chromophores; in other words, the metal binding energies do not offset the loss in aromaticity. The halochromic properties of the molecules provide some more insight into the location of the protonation/deprotonation sites. The interpretation of the findings is supported by computations.
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Affiliation(s)
- Nivedita Chaudhri
- Department of Chemistry, University of Connecticut, Storrs, CT 06269-3060, USA.
- Department of Chemistry, Guru Nanak Dev University Amritsar, Punjab-143005, India
| | - Matthew J Guberman-Pfeffer
- Department of Chemistry and Biochemistry, Baylor University, One Bear Place #97348, Waco, Texas 76706, USA
| | - Matthias Zeller
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907-2084, USA
| | - Christian Brückner
- Department of Chemistry, University of Connecticut, Storrs, CT 06269-3060, USA.
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2
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Bhattacharya S, Nevonen DE, Auty AJ, Graf A, Appleby M, Chaudhri N, Chekulaev D, Brückner C, Chauvet AAP, Nemykin VN. Photophysical Exploration of Two Isomers of Octaethyltrioxopyrrocorphin. J Phys Chem A 2023; 127:7694-7706. [PMID: 37690121 DOI: 10.1021/acs.jpca.3c03184] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/12/2023]
Abstract
The introduction of three β-oxosubstituents to octaethylporphyrin by means of an oxidation/rearrangement reaction generates the trioxopyrrocorphin chromophore. Pyrrocorphins (hexahydroporphyrins) are generally nonaromatic, but we recently demonstrated trioxopyrrocorphins to possess considerable aromatic character. This contribution explores the photophysical characteristics of these unusual chromophores. In agreement with density functional theory modeling, the UV-vis and magnetic circular dichroism spectra of the two─out of the four possible─triketone regioisomers investigated conform to the Gouterman model of porphyrinoid optical spectra, in alignment with their aromaticity. Their excited-state dynamics shed further light on the degree to which β-oxo substitutions tune the photophysical properties of porphyrinoids. Introduction of β-oxo functionalities increases the rate and yield of intersystem crossing and shortens the triplet state lifetime. Unexpectedly, the singlet oxygen generation yield of both pyrrocorphins remains relatively high, with modes of distortion from planarity likely enhancing triplet energy transfer. This work thus expands our understanding of a rare class of porphyrinoids and further characterizes them as sustaining aromatic porphyrinic π-systems. Our findings suggest triple β-oxo substitution as a viable route toward the development of novel, high-singlet oxygen yield porphyrinic photosensitizers.
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Affiliation(s)
- Sayantan Bhattacharya
- Department of Chemistry, University of Sheffield, Dainton Building, Sheffield S3 7HF, U.K
| | - Dustin E Nevonen
- Department of Chemistry, University of Tennessee, 1420 Circle Dr., Knoxville, Tennessee 37996-1600, United States
| | - Alexander J Auty
- Department of Chemistry, University of Sheffield, Dainton Building, Sheffield S3 7HF, U.K
| | - Arthur Graf
- Department of Chemistry, University of Sheffield, Dainton Building, Sheffield S3 7HF, U.K
| | - Martin Appleby
- Department of Chemistry, University of Sheffield, Dainton Building, Sheffield S3 7HF, U.K
| | - Nivedita Chaudhri
- Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, United States
| | - Dimitri Chekulaev
- Department of Chemistry, University of Sheffield, Dainton Building, Sheffield S3 7HF, U.K
| | - Christian Brückner
- Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, United States
| | - Adrien A P Chauvet
- Department of Chemistry, University of Sheffield, Dainton Building, Sheffield S3 7HF, U.K
| | - Victor N Nemykin
- Department of Chemistry, University of Tennessee, 1420 Circle Dr., Knoxville, Tennessee 37996-1600, United States
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Hewage N, Guberman-Pfeffer MJ, Chaudhri N, Zeller M, Gascón JA, Brückner C. Syntheses and Aromaticity Parameters of Hexahydroxypyrrocorphin, Porphotrilactones, and Their Oxidation State Intermediates. J Org Chem 2022; 87:12096-12108. [PMID: 36066858 DOI: 10.1021/acs.joc.2c01202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Triple OsO4-mediated dihydroxylation of meso-tetrakis(pentafluorophenyl)porphyrin formed a non-aromatic hexahydroxypyrrocorphin as a single stereo-isomer. A one-step oxidative conversion of all three diol functionalities to lactone moieties generated three out of the four possible porphotrilactone regioisomers that were spectroscopically and structurally characterized. This conversion recovered most of the porphyrinic macrocycle aromatic ring current, as seen in their 1H NMR spectra and modeled using DFT computations. Stepwise OsO4-mediated dihydroxylations of porpho-mono- and -di-lactones generated intermediate oxidation state compounds between the pyrrole-three pyrroline macrocycle of the pyrrocorphin and the pyrrole-three oxazolone chromophore of the trilactones. The aromaticity of these chromophores was reduced with increasing number of oxazolone to pyrroline replacements, showing the importance for the presence of three lactone moieties for the retention of the macrocycle aromaticity in the tris-β,β'-modified macrocycles. This work first describes hexahydoxypyrrocorphins, porphotrislactones, and the oxidation state intermediates between them; furthers the understanding of the roles of β-lactone moieties in the expression of porphyrinic macrocycle aromaticity; and generally broadens access to chemically stable pyrrocorphins and pyrrocorphin analogues.
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Affiliation(s)
- Nisansala Hewage
- Department of Chemistry, University of Connecticut, Unit 3060, Storrs, Connecticut 06269-3060, United States
| | - Matthew J Guberman-Pfeffer
- Department of Chemistry, University of Connecticut, Unit 3060, Storrs, Connecticut 06269-3060, United States
| | - Nivedita Chaudhri
- Department of Chemistry, University of Connecticut, Unit 3060, Storrs, Connecticut 06269-3060, United States
| | - Matthias Zeller
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, United States
| | - José A Gascón
- Department of Chemistry, University of Connecticut, Unit 3060, Storrs, Connecticut 06269-3060, United States
| | - Christian Brückner
- Department of Chemistry, University of Connecticut, Unit 3060, Storrs, Connecticut 06269-3060, United States
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Chaudhri N, Guberman-Pfeffer MJ, Zeller M, Brückner C. Stepwise Reduction of β-Trioxopyrrocorphins: Collapse of the Oxo-Induced Macrocycle Aromaticity. J Org Chem 2022; 87:7179-7192. [PMID: 35605247 DOI: 10.1021/acs.joc.2c00399] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The diatropic ring current that characterizes the unexpectedly aromatic octaethyltrioxopyrrocorphins gets drastically reduced upon chemical reduction of one and particularly two ketone moieties. With increasing reduction, the chromophores containing one pyrrole, one/two pyrrolinone, and one/two pyrrolines become more similar to regular, nonmacrocycle-aromatic pyrrocorphins (hexahydroporphyrins). Single-crystal diffraction analysis shows the reduction products to be idealized planar. With increasing reduction, their UV-vis spectroscopic signatures are those of conjugated but nonaromatic oligopyrroles. Their diatropic ring currents, as assessed by 1H NMR spectroscopy, showed them to possess largely nonaromatic π-systems. Dihydroxylation of select β,β'-dioxobacteriochlorin and β,β'-dioxoisobacteriochlorins also resulted in the formation of equivalent mixed pyrrole/two pyrrolinone/pyrroline chromophores. Computations were able to reproduce the experimental trends of the diatropic ring currents and filled in the data for the regioisomers that could not be experimentally accessed. The work further highlights the electronic influence of the β-oxo-substituents and, more specifically, the origin of the aromaticity of the trioxopyrrocorphins. It also presents a series of chemically robust pyrrocorphins, a chromophore class for which many chemically very sensitive members have been reported.
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Affiliation(s)
- Nivedita Chaudhri
- Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269, United States
| | | | - Matthias Zeller
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
| | - Christian Brückner
- Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269, United States
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Chaudhri N, Guberman-Pfeffer MJ, Li R, Zeller M, Brückner C. β-Trioxopyrrocorphins: pyrrocorphins of graded aromaticity. Chem Sci 2021; 12:12292-12301. [PMID: 34603659 PMCID: PMC8480330 DOI: 10.1039/d1sc03403k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Accepted: 08/19/2021] [Indexed: 11/21/2022] Open
Abstract
Octaethyltrioxopyrrocorphins unexpectedly show macrocycle-aromatic properties, even though they contain the macrocyclic π-system of the non-aromatic pyrrocorphins (hexahydroporphyrins). Two of the four possible triketone regioisomers were first reported in 1969 by one-pot oxidation of octaethylporphyrin but remained essentially unexplored since. We detail here the targeted preparation of the remaining two triketone isomers and the optical and NMR spectroscopic properties of all isomers. All four regioisomers possess unique electronic properties, including broadly varying degrees of diatropicity that were experimentally determined using 1H NMR spectroscopy and computationally verified. Structural patterns modulating the aromaticity were recognized. These differences highlight the regioisomerically differentiated influences of the three β-oxo-functionalities. We also present the solid state structure of the two most common isomers (in their free base form or as zinc complexes), allowing further conclusions to be made about the resonance structures present in these triketones. Remarkably, also, the halochromic properties of the triketones differ sharply from those of regular (hydro)porphyrins, providing further support for the proposed 16-membered, 18 π-electron aromatic ring-current. The work conceptually expands the understanding of tris-modified hydroporphyrinoid analogues and the factors that enable and control porphyrinoid aromaticity.
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Affiliation(s)
- Nivedita Chaudhri
- Department of Chemistry, University of Connecticut Storrs CT 06269-3060 USA
| | | | - Ruoshi Li
- Department of Chemistry, University of Connecticut Storrs CT 06269-3060 USA
| | - Matthias Zeller
- Department of Chemistry, Purdue University 560 Oval Drive West Lafayette IN 47907-2084 USA
| | - Christian Brückner
- Department of Chemistry, University of Connecticut Storrs CT 06269-3060 USA
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6
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Brückner C, Chaudhri N, Nevonen DE, Bhattacharya S, Graf A, Kaesmann E, Li R, Guberman-Pfeffer MJ, Mani T, Nimthong-Roldán A, Zeller M, Chauvet AAP, Nemykin V. Structural and Photophysical Characterization of All Five Constitutional Isomers of the Octaethyl-β,β'-dioxo-bacterio- and -isobacteriochlorin Series. Chemistry 2021; 27:16189-16203. [PMID: 34535932 DOI: 10.1002/chem.202103014] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2021] [Indexed: 11/11/2022]
Abstract
It is well-known that treatment of β-octaethylporphyrin with H2 O2 /conc. H2 SO4 converts it to a β-oxochlorin as well as all five constitutional isomers of the corresponding β,β'-dioxo-derivatives: two bacteriochlorin-type isomers (β-oxo groups at opposite pyrrolic building blocks) and three isobacteriochlorin-type isomers (β-oxo-groups at adjacent pyrrolic building blocks). By virtue of the presence of the strongly electronically coupled β-oxo auxochromes, none of the chromophores are archetypical chlorins, bacteriochlorins, or isobacteriochlorins. Here the authors present, inter alia, the single crystal X-ray structures of all free-base diketone isomers and a comparative description of their UV-vis absorption spectra in neutral and acidic solutions, and fluorescence emission and singlet oxygen photosensitization properties, Magnetic Circular Dichroism (MCD) spectra, and singlet excited state lifetimes. DFT computations uncover underlying tautomeric equilibria and electronic interactions controlling their electronic properties, adding to the understanding of porphyrinoids carrying β-oxo functionalities. This comparative study lays the basis for their further study and utilization.
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Affiliation(s)
- Christian Brückner
- Department of Chemistry, University of Connecticut, Storrs, CT 06269-3060, United States
| | - Nivedita Chaudhri
- Department of Chemistry, University of Connecticut, Storrs, CT 06269-3060, United States
| | - Dustin E Nevonen
- Department of Chemistry, University of Manitoba Winnipeg, Manitoba, R3T 2 N2, Canada
| | - Sayantan Bhattacharya
- Department of Chemistry, University of Sheffield Dainton Building, Sheffield, S3 7HF, United Kingdom
| | - Arthur Graf
- Department of Chemistry, University of Sheffield Dainton Building, Sheffield, S3 7HF, United Kingdom
| | - Elizabeth Kaesmann
- Department of Chemistry, University of Connecticut, Storrs, CT 06269-3060, United States
| | - Ruoshi Li
- Department of Chemistry, University of Connecticut, Storrs, CT 06269-3060, United States
| | | | - Tomoyasu Mani
- Department of Chemistry, University of Connecticut, Storrs, CT 06269-3060, United States
| | - Arunpatcha Nimthong-Roldán
- Department of Chemistry, Youngstown State University One University Plaza, Youngstown, OH 44555-3663, United States
| | - Matthias Zeller
- Department of Chemistry, Youngstown State University One University Plaza, Youngstown, OH 44555-3663, United States.,Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907-2084, United States
| | - Adrien A P Chauvet
- Department of Chemistry, University of Sheffield Dainton Building, Sheffield, S3 7HF, United Kingdom
| | - Victor Nemykin
- Department of Chemistry, University of Manitoba Winnipeg, Manitoba, R3T 2 N2, Canada.,Department of Chemistry, University of Tennessee, 552 Buehler Hall, 1420 Circle Dr., Knoxville, TN, 37996-1600, United States
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Nganga J, Chaudhri N, Brückner C, Angeles-Boza AM. β-Oxochlorin cobalt(II) complexes catalyze the electrochemical reduction of CO 2. Chem Commun (Camb) 2021; 57:4396-4399. [PMID: 33949479 DOI: 10.1039/d1cc00573a] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Inspired by the architecture of the macrocycle of heme d1, a series of synthetic mono-, di- and tri-β-oxo-substituted porphyrinoid cobalt(ii) complexes were evaluated as electrocatalytic CO2 reducers, identifying complexes of unusually high efficiencies in generating multi-electron reduction products, including CH4.
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Affiliation(s)
- John Nganga
- Department of Chemistry, University of Connecticut, 55 N. Eagleville Road, Storrs, CT 06269, USA.
| | - Nivedita Chaudhri
- Department of Chemistry, University of Connecticut, 55 N. Eagleville Road, Storrs, CT 06269, USA.
| | - Christian Brückner
- Department of Chemistry, University of Connecticut, 55 N. Eagleville Road, Storrs, CT 06269, USA.
| | - Alfredo M Angeles-Boza
- Department of Chemistry, University of Connecticut, 55 N. Eagleville Road, Storrs, CT 06269, USA. and Institute of Materials Science, University of Connecticut, 97 N. Eagleville Road, Storrs, CT 06269, USA.
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Chaudhri N, Zeller M, Brückner C. Stepwise Reduction of Octaethyl-β,β'-dioxochlorin Isomers: Access to Structurally and Electronically Diverse Hydroporphyrins. J Org Chem 2020; 85:13951-13964. [PMID: 33085480 DOI: 10.1021/acs.joc.0c01989] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Di- and tetrahydroporphyrins (chlorins, bacteriochlorins and isobacteriochlorins, respectively) are key "pigments of life." They have been a major focus of attention in synthetic tetrapyrrole chemistry. A long-known one-pot epoxidation/epoxide ring-opening/pinacol-pinacolone rearrangement of octaethylporphyrin (OEP) generates a β-ketochlorin and all five β,β'-diketone isomers. We present herein the single and double reductions of all isomers of the β,β'-diketones, generating hydroxychlorin and β-hydroxy-β-ketodihydroporphyrin isomers, generally in regioselective manner, and sets of separable stereoisomeric dihydroxytetrahydroporphyrin regioisomers. The connectivity of the regio- and stereoisomers were determined spectroscopically and, in many cases, using single-crystal X-ray crystallography. The optical properties of the chlorin-, bacteriochlorin-, and isobacteriochlorin-type chromophores are described. They highlight general observations on the regiochemical effects of the β-oxo-auxochrome. This contribution thus delineates the formation of a range of regio- and stereoisomers of a family of chromophores with broadly varying optical properties from a single and readily available starting material (OEP) in two straightforward steps, albeit requiring extensive chromatography.
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Affiliation(s)
- Nivedita Chaudhri
- Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, United States
| | - Matthias Zeller
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, United States
| | - Christian Brückner
- Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, United States
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