1
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Agrawal S, Casanova D, Trivedi DJ, Prezhdo OV. Enhanced Charge Separation in Single Atom Cobalt Based Graphitic Carbon Nitride: Time Domain Ab Initio Analysis. J Phys Chem Lett 2024; 15:2202-2208. [PMID: 38373150 PMCID: PMC10910588 DOI: 10.1021/acs.jpclett.3c03621] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2023] [Revised: 02/07/2024] [Accepted: 02/14/2024] [Indexed: 02/21/2024]
Abstract
In recent years, single atom catalysts have been at the forefront of energy conversion research, particularly in the field of catalysis. Carbon nitrides offer great potential as hosts for stabilizing metal atoms due to their unique electronic structure. We use ab initio nonadiabatic molecular dynamics to study photoexcitation dynamics in single atom cobalt based graphitic carbon nitride. The results elucidate the positive effect of the doped cobalt atom on the electronic structure of GCN. Cobalt doping produces filled midgap states that serve as oxidation centers, advantageous for various redox reactions. The presence of midgap states enables the harvesting of longer wavelength photons, thereby extending the absorption range of solar light. Although doping accelerates charge relaxation overall, charge recombination is significantly slower than charge separation, creating beneficial conditions for catalysis applications. The simulations reveal the detailed microscopic mechanism underlying the improved performance of the doped system due to atomic defects and demonstrate an effective charge separation strategy to construct highly efficient and stable photocatalytic two-dimensional materials.
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Affiliation(s)
- Sraddha Agrawal
- Department
of Chemistry, University of Southern California, Los Angeles, California 90007, United States
| | - David Casanova
- Donostia
International Physics Center (DIPC), 20018 Donostia, Euskadi, Spain
- IKERBASQUE,
Basque Foundation for Science, 48009 Bilbao, Euskadi, Spain
| | - Dhara J. Trivedi
- Department
of Physics, Clarkson University, Potsdam, New York 13699, United States
| | - Oleg V. Prezhdo
- Department
of Chemistry, University of Southern California, Los Angeles, California 90007, United States
- Department
of Physics and Astronomy, University of
Southern California, Los Angeles, California 90007, United States
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2
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Filho JBG, Silva IF, Alafandi M, Rabeah J. Aerobic Oxidation of 5-Hydroxymethylfurfural (HMF) in Aqueous Medium over Fe-Doped-Poly(heptazine imide) Photocatalysts: Unveiling the Bad Role of Hydroxyl Radical Generation on the Catalytic Performance. Molecules 2023; 28:8077. [PMID: 38138567 PMCID: PMC10745455 DOI: 10.3390/molecules28248077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2023] [Revised: 12/11/2023] [Accepted: 12/12/2023] [Indexed: 12/24/2023] Open
Abstract
5-hydroxymethylfurfural (HMF) oxidation in aqueous media using visible photocatalysis is a green and sustainable route for the valorization of lignocellulosic biomass derivatives. Several semiconductors have already been applied for this purpose; however, the use of Poly(heptazine imides), which has high crystallinity and a special cation exchange property that allows the replacement of the cation held between the layers of C3N4 structure by transition metal ions (TM), remains scarce. In this study, PHI(Na) was synthesized using a melamine/NaCl method and used as precursor to prepare metal (Fe, Co, Ni, or Cu)-doped PHI catalysts. The catalysts were tested for selective oxidation of HMF to 2,5-diformylfuran (DFF) in water and O2 atmosphere under blue LED radiation. The catalytic results revealed that the 0.1 wt% PHI(Fe) catalyst is the most efficient photocatalyst while higher Fe loading (1 and 2 wt%) favors the formation of Fe3+ clusters, which are responsible for the drop in HMF oxidation. Moreover, the 0.1 wt% PHI(Fe) photocatalyst has strong oxidative power due to its efficiency in H2O2 production, thus boosting the generation of nonselective hydroxyl radicals (●OH) via different pathways that can destroy HMF. We found that using 50 mM, the highest DFF production rate (393 μmol·h-1·g-1) was obtained in an aqueous medium under visible light radiation.
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Affiliation(s)
- José B. G. Filho
- Leibniz Institute for Catalysis (LIKAT Rostock), D-18059 Rostock, Germany; (J.B.G.F.); (M.A.)
- Department of Chemistry, Federal University of Minas Gerais (UFMG), Belo Horizonte 31270-901, MG, Brazil
| | - Ingrid F. Silva
- Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, Potsdam Science Park, Am Mühlenberg 1, D-14476 Potsdam, Germany;
| | - Mamdouh Alafandi
- Leibniz Institute for Catalysis (LIKAT Rostock), D-18059 Rostock, Germany; (J.B.G.F.); (M.A.)
| | - Jabor Rabeah
- Leibniz Institute for Catalysis (LIKAT Rostock), D-18059 Rostock, Germany; (J.B.G.F.); (M.A.)
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3
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da Silva MAR, Tarakina NV, Filho JBG, Cunha CS, Rocha GFSR, Diab GAA, Ando RA, Savateev O, Agirrezabal-Telleria I, Silva IF, Stolfi S, Ghigna P, Fagnoni M, Ravelli D, Torelli P, Braglia L, Teixeira IF. Single-Atoms on Crystalline Carbon Nitrides for Selective C─H Photooxidation: A Bridge to Achieve Homogeneous Pathways in Heterogeneous Materials. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2304152. [PMID: 37986204 DOI: 10.1002/adma.202304152] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Revised: 09/15/2023] [Indexed: 11/22/2023]
Abstract
Single-atom catalysis is a field of paramount importance in contemporary science due to its exceptional ability to combine the domains of homogeneous and heterogeneous catalysis. Iron and manganese metalloenzymes are known to be effective in C─H oxidation reactions in nature, inspiring scientists to mimic their active sites in artificial catalytic systems. Herein, a simple and versatile cation exchange method is successfully employed to stabilize low-cost iron and manganese single-atoms in poly(heptazine imides) (PHI). The resulting materials are employed as photocatalysts for toluene oxidation, demonstrating remarkable selectivity toward benzaldehyde. The protocol is then extended to the selective oxidation of different substrates, including (substituted) alkylaromatics, benzyl alcohols, and sulfides. Detailed mechanistic investigations revealed that iron- and manganese-containing photocatalysts work through a similar mechanism via the formation of high-valent M═O species. Operando X-ray absorption spectroscopy (XAS) is employed to confirm the formation of high-valent iron- and manganese-oxo species, typically found in metalloenzymes involved in highly selective C─H oxidations.
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Affiliation(s)
- Marcos A R da Silva
- Department of Chemistry, Federal University of São Carlos, São Carlos, São Paulo, 13565-905, Brazil
| | - Nadezda V Tarakina
- Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, Am Mühlenberg 1, D-14476, Potsdam, Germany
| | - José B G Filho
- Department of Chemistry, ICEx, Federal University of Minas Gerais, Belo Horizonte, MG, 31270-901, Brazil
| | - Carla S Cunha
- Department of Chemistry, Federal University of São Carlos, São Carlos, São Paulo, 13565-905, Brazil
| | - Guilherme F S R Rocha
- Department of Chemistry, Federal University of São Carlos, São Carlos, São Paulo, 13565-905, Brazil
| | - Gabriel A A Diab
- Department of Chemistry, Federal University of São Carlos, São Carlos, São Paulo, 13565-905, Brazil
| | - Rômulo Augusto Ando
- Department of Fundamental Chemistry, Institute of Chemistry, University of São Paulo, Av. Prof. Lineu Prestes, 748, São Paulo, 05508-000, Brazil
| | - Oleksandr Savateev
- Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, Am Mühlenberg 1, D-14476, Potsdam, Germany
| | - Iker Agirrezabal-Telleria
- Department of Chemical and Environmental Engineering of the Bilbao Engineering School, University of Basque Country (UPV/EHU), Plaza Torres Quevedo 1, Bilbao, 48013, Spain
| | - Ingrid F Silva
- Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, Am Mühlenberg 1, D-14476, Potsdam, Germany
| | - Sara Stolfi
- Department of Chemistry, University of Pavia, viale Taramelli 12, Pavia, 27100, Italy
| | - Paolo Ghigna
- Department of Chemistry, University of Pavia, viale Taramelli 12, Pavia, 27100, Italy
| | - Maurizio Fagnoni
- Department of Chemistry, University of Pavia, viale Taramelli 12, Pavia, 27100, Italy
| | - Davide Ravelli
- Department of Chemistry, University of Pavia, viale Taramelli 12, Pavia, 27100, Italy
| | - Piero Torelli
- TASC Laboratory, CNR-IOM, Istituto Officina dei Materiali, Trieste, 34149, Italy
| | - Luca Braglia
- TASC Laboratory, CNR-IOM, Istituto Officina dei Materiali, Trieste, 34149, Italy
| | - Ivo F Teixeira
- Department of Chemistry, Federal University of São Carlos, São Carlos, São Paulo, 13565-905, Brazil
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4
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Poly(heptazine imide) ligand exchange enables remarkable low catalyst loadings in heterogeneous metallaphotocatalysis. Nat Commun 2023; 14:1501. [PMID: 36932064 PMCID: PMC10023668 DOI: 10.1038/s41467-023-37113-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2022] [Accepted: 03/02/2023] [Indexed: 03/19/2023] Open
Abstract
The development of heterogeneous metallaphotocatalysis is of great interest for sustainable organic synthesis. The rational design and controllable preparation of well-defined (site-isolated) metal/photo bifunctional solid catalysts to meet such goal remains a critical challenge. Herein, we demonstrate the incorporation of privileged homogeneous bipyridyl-based Ni-catalysts into highly ordered and crystalline potassium poly(heptazine imide) (K-PHI). A variety of PHI-supported cationic bipyridyl-based Ni-catalysts (LnNi-PHI) have been prepared and fully characterized by various techniques including NMR, ICP-OES, XPS, HAADF-STEM and XAS. The LnNi-PHI catalysts exhibit exceptional chemical stability and recyclability in diverse C-P, C-S, C-O and C-N cross-coupling reactions. The proximity and cooperativity effects in LnNi-PHI significantly enhances the photo/Ni dual catalytic activity, thus resulting in low catalyst loadings and high turnover numbers.
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5
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Lin X, Ng SF, Ong WJ. Coordinating single-atom catalysts on two-dimensional nanomaterials: A paradigm towards bolstered photocatalytic energy conversion. Coord Chem Rev 2022. [DOI: 10.1016/j.ccr.2022.214743] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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6
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Rogolino A, Silva IF, Tarakina NV, da Silva MAR, Rocha GFSR, Antonietti M, Teixeira IF. Modified Poly(Heptazine Imides): Minimizing H 2O 2 Decomposition to Maximize Oxygen Reduction. ACS APPLIED MATERIALS & INTERFACES 2022; 14:49820-49829. [PMID: 36315872 PMCID: PMC9650642 DOI: 10.1021/acsami.2c14872] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/18/2022] [Accepted: 10/20/2022] [Indexed: 06/16/2023]
Abstract
Photocatalysis provides a sustainable pathway to produce the consumer chemical H2O2 from atmospheric O2 via an oxygen reduction reaction (ORR). Such an alternative is attractive to replace the cumbersome traditional anthraquinone method for H2O2 synthesis on a large scale. Carbon nitrides have shown very interesting results as heterogeneous photocatalysts in ORR because their covalent two-dimensional (2D) structure is believed to increase selectivity toward the two-electron process. However, an efficient and scalable application of carbon nitrides for this reaction is far from being achieved. Poly(heptazine imides) (PHIs) are a more powerful subgroup of carbon nitrides whose structure provides high crystallinity and a scaffold to host transition-metal single atoms. Herein, we show that PHIs functionalized with sodium and the recently reported fully protonated PHI exhibit high activity in two-electron ORR under visible light. The latter converted O2 to up to 1556 mmol L-1 h-1 g-1 H2O2 under 410 nm irradiation using inexpensive but otherwise chemically demanding glycerin as a sacrificial electron donor. We also prove that functionalization with transition metals is not beneficial for H2O2 synthesis, as the metal also catalyzes its decomposition. Transient photoluminescence spectroscopy suggests that H-PHIs exhibit higher activity due to their longer excited-state lifetime. Overall, this work highlights the high photocatalytic activity of the rarely examined fully protonated PHI and represents a step forward in the application of inexpensive covalent materials for photocatalytic H2O2 synthesis.
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Affiliation(s)
- Andrea Rogolino
- Galilean
School of Higher Education, University of
Padova, Via Venezia 20, Padova35131, Italy
| | - Ingrid F. Silva
- Department
of Colloid Chemistry, Max Planck Institute
of Colloids and Interfaces, Am Mühlenberg 1, Potsdam14476, Germany
| | - Nadezda V. Tarakina
- Department
of Colloid Chemistry, Max Planck Institute
of Colloids and Interfaces, Am Mühlenberg 1, Potsdam14476, Germany
| | - Marcos A. R. da Silva
- Department
of Chemistry, Federal University of São
Carlos, Washington Luis Highway, s/n Km 235, São
Carlos13565-905, São
Paulo, Brazil
| | - Guilherme F. S. R. Rocha
- Department
of Chemistry, Federal University of São
Carlos, Washington Luis Highway, s/n Km 235, São
Carlos13565-905, São
Paulo, Brazil
| | - Markus Antonietti
- Department
of Colloid Chemistry, Max Planck Institute
of Colloids and Interfaces, Am Mühlenberg 1, Potsdam14476, Germany
| | - Ivo F. Teixeira
- Department
of Chemistry, Federal University of São
Carlos, Washington Luis Highway, s/n Km 235, São
Carlos13565-905, São
Paulo, Brazil
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7
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da Silva MAR, Gil JC, Tarakina NV, Silva GTST, Filho JBG, Krambrock K, Antonietti M, Ribeiro C, Teixeira IF. Selective methane photooxidation into methanol under mild conditions promoted by highly dispersed Cu atoms on crystalline carbon nitrides. Chem Commun (Camb) 2022; 58:7419-7422. [PMID: 35695323 DOI: 10.1039/d2cc01757a] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Here we report a photocatalytic system based on crystalline carbon nitrides (PHI) and highly dispersed transition metals (Fe, Co and Cu) for controlled methane photooxidation to methanol under mild conditions. The Cu-PHI catalyst showed a remarkable methanol production (2900 μmol g-1) in 4 hours, with a turnover number of 51 moles of oxygenated liquid product per mole of Cu. To date, this result is the highest value for methane oxidation under mild conditions (1 bar, 25 °C).
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Affiliation(s)
- Marcos A R da Silva
- Department of Chemistry, Federal University of São Carlos, 13565-905, São Carlos, SP, Brazil. .,National Nanotechnology Laboratory for Agriculture, Brazilian Agriculture Research Corporation (Embrapa), XV de Novembro Street - 1452, São Carlos, Brazil
| | - Jéssica C Gil
- Department of Chemistry, Federal University of São Carlos, 13565-905, São Carlos, SP, Brazil. .,National Nanotechnology Laboratory for Agriculture, Brazilian Agriculture Research Corporation (Embrapa), XV de Novembro Street - 1452, São Carlos, Brazil
| | - Nadezda V Tarakina
- Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, Am Mühlenberg 1, D-14476 Potsdam, Germany
| | - Gelson T S T Silva
- Department of Chemistry, Federal University of São Carlos, 13565-905, São Carlos, SP, Brazil. .,National Nanotechnology Laboratory for Agriculture, Brazilian Agriculture Research Corporation (Embrapa), XV de Novembro Street - 1452, São Carlos, Brazil
| | - José B G Filho
- Department of Chemistry, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais 35400-000, Brazil
| | - Klaus Krambrock
- Department of Physics, Federal University of Minas Gerais, 31270-901, Belo Horizonte, Minas Gerais, Brazil
| | - Markus Antonietti
- Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, Am Mühlenberg 1, D-14476 Potsdam, Germany
| | - Caue Ribeiro
- National Nanotechnology Laboratory for Agriculture, Brazilian Agriculture Research Corporation (Embrapa), XV de Novembro Street - 1452, São Carlos, Brazil
| | - Ivo F Teixeira
- Department of Chemistry, Federal University of São Carlos, 13565-905, São Carlos, SP, Brazil. .,Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, Am Mühlenberg 1, D-14476 Potsdam, Germany
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8
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Mallakpour S, Sirous F, Hussain CM. Single-Atoms on Covalent or Metal-Organic Frameworks: Current Findings and Perspectives for Pollutants Abatement, Hydrogen Evolution, and Reduction of CO 2. Top Curr Chem (Cham) 2021; 380:7. [PMID: 34958434 DOI: 10.1007/s41061-021-00363-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2021] [Accepted: 11/30/2021] [Indexed: 02/07/2023]
Abstract
Nowadays, attention to single-atoms and also porous structures like metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) for the preparation of high-performance material is expanding rapidly. These dazzling materials with unprecedented properties have lots of applications, especially as promising catalysts for organic pollutants abatement, hydrogen evolution, reduction of CO2, etc. To provide an in-depth understanding, in this mini-review, we begin with a brief description and a general background about single-atoms, COFs, as well as MOFs. After considering some fundamentals, the synergism effects, advantages, and their applications are discussed.
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Affiliation(s)
- Shadpour Mallakpour
- Organic Polymer Chemistry Research Laboratory, Department of Chemistry, Isfahan University of Technology, Isfahan, 84156-83111, Islamic Republic of Iran.
| | - Fariba Sirous
- Organic Polymer Chemistry Research Laboratory, Department of Chemistry, Isfahan University of Technology, Isfahan, 84156-83111, Islamic Republic of Iran
| | - Chaudhery Mustansar Hussain
- Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, NJ 07102, USA
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9
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Markushyna Y, Antonietti M, Savateev A. Synthesis of Sulfonyl Chlorides from Aryldiazonium Salts Mediated by a Heterogeneous Potassium Poly(heptazine imide) Photocatalyst. ACS ORGANIC & INORGANIC AU 2021; 2:153-158. [PMID: 36855461 PMCID: PMC9955386 DOI: 10.1021/acsorginorgau.1c00038] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Visible light photocatalysis is a tool in synthetic chemistry that allows us to utilize the energy of photons via photoinduced electron transfer to promote diverse organic reactions. Herein, a heterogeneous transition metal-free material, a type of carbon nitride photocatalyst, potassium poly(heptazine imide), is employed to produce sulfonyl chlorides from arenediazonium salts under mild conditions (visible light irradiation, room temperature) with 50-95% yields. The method is suitable for the synthesis of both electron rich and electron deficient compounds, and it shows high tolerance toward different functional groups (halides, ester, nitro, cyano groups). Thus, a sustainable photocatalytic alternative to the Meerwein chlorosulfonylation reaction is offered.
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10
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Rosso C, Filippini G, Criado A, Melchionna M, Fornasiero P, Prato M. Metal-Free Photocatalysis: Two-Dimensional Nanomaterial Connection toward Advanced Organic Synthesis. ACS NANO 2021; 15:3621-3630. [PMID: 33715354 PMCID: PMC8041367 DOI: 10.1021/acsnano.1c00627] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Two-dimensional (2D) nanostructures are a frontier in materials chemistry as a result of their extraordinary properties. Metal-free 2D nanomaterials possess extra appeal due to their improved cost-effectiveness and lower toxicity with respect to many inorganic structures. The outstanding electronic characteristics of some metal-free 2D semiconductors have projected them into the world of organic synthesis, where they can function as high-performance photocatalysts to drive the sustainable synthesis of high-value organic molecules. Recent reports on this topic have inspired a stream of research and opened up a theme that we believe will become one of the most dominant trends in the forthcoming years.
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Affiliation(s)
- Cristian Rosso
- Department
of Chemical and Pharmaceutical Sciences, CENMAT, Center of Excellence
for Nanostructured Materials, INSTM, UdR Trieste, University of Trieste, Via Licio Giorgieri 1, Trieste 34127, Italy
| | - Giacomo Filippini
- Department
of Chemical and Pharmaceutical Sciences, CENMAT, Center of Excellence
for Nanostructured Materials, INSTM, UdR Trieste, University of Trieste, Via Licio Giorgieri 1, Trieste 34127, Italy
| | - Alejandro Criado
- Center
for Cooperative Research in Biomaterials (CIC biomaGUNE), Basque Research and Technology Alliance (BRTA), Paseo de Miramón 182, 20014 Donostia San Sebastián, Spain
| | - Michele Melchionna
- Department
of Chemical and Pharmaceutical Sciences, CENMAT, Center of Excellence
for Nanostructured Materials, INSTM, UdR Trieste, University of Trieste, Via Licio Giorgieri 1, Trieste 34127, Italy
| | - Paolo Fornasiero
- Department
of Chemical and Pharmaceutical Sciences, CENMAT, Center of Excellence
for Nanostructured Materials, INSTM, UdR Trieste, University of Trieste, Via Licio Giorgieri 1, Trieste 34127, Italy
- ICCOM-CNR
Trieste Research Unit, University of Trieste, Trieste 34127, Italy
| | - Maurizio Prato
- Department
of Chemical and Pharmaceutical Sciences, CENMAT, Center of Excellence
for Nanostructured Materials, INSTM, UdR Trieste, University of Trieste, Via Licio Giorgieri 1, Trieste 34127, Italy
- Center
for Cooperative Research in Biomaterials (CIC biomaGUNE), Basque Research and Technology Alliance (BRTA), Paseo de Miramón 182, 20014 Donostia San Sebastián, Spain
- Basque
Foundation for Science, Ikerbasque, Bilbao 48013, Spain
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11
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Abstract
Abiotic allosterism is most commonly observed in hetero-bimetallic supramolecular complexes and less frequently in homo-bimetallic complexes. The use of hemilabile ligands with high synthetic complexity enables the catalytic center by the addition or removal of allosteric effectors and simplicity is unusually seen in these systems. Here we describe a simpler approach to achieve kinetic regulation by the use of dimeric Schiff base copper complexes connected by a chlorido ligand bridge. The chlorido ligand acts as a weak link between monomers, generating homo-bimetallic self-aggregating supramolecular complexes that generate monomeric species in different reaction rates depending on the solvent and on the radical moiety of the ligand. The ligand exchange was observed by electron paramagnetic resonance (EPR) and conductivity measurements, indicating that complexes with ligands bearing methoxyl (CuIIL2) and ethoxyl (CuIIL5) radicals were more prone to form dimeric complexes in comparison to ligands bearing hydrogen (CuIIL1), methyl (CuIIL3), or t-butyl (CuIIL4) radicals. The equilibrium between dimer and monomer afforded different reactivities of the complexes in acetonitrile/water and methanol/water mixtures toward urea hydrolysis as a model reaction. It was evident that the dimeric species were inactive and that by increasing the water concentration in the reaction medium, the dimeric structures dissociated to form the active monomeric structures. This behavior was more pronounced when methanol/water mixtures were employed due to a slower displacement of the chlorido bridge in this medium than in the acetonitrile/water mixtures, enabling the reaction kinetics to be evaluated. This effect was attributed to the preferential solvation shell by the organic solvents and in essence, an upregulation behavior was observed due to the intrinsic nature of the complexes to form dimeric structures in solution that could be dismantled in the presence of water, indicating their possible use as water-sensors in organic solvents.
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