1
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Gao S, Cao CQ, Liu ZJ, Yao ZJ. Half-Sandwich Iridium Complexes: A Recyclable and Stable Catalyst for Dehydrogenation of Alcohols to Carboxylic Acids. Inorg Chem 2024; 63:13311-13320. [PMID: 38977684 DOI: 10.1021/acs.inorgchem.4c01066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/10/2024]
Abstract
A series of acylhydrazone-based N,N-chelate half-sandwich iridium complexes have been synthesized through a facile route in good yields. The dehydrogenation of a series of aromatic and aliphatic primary alcohols to corresponding carboxylic acids has been accomplished catalyzed by the prepared air stable iridium complexes under mild reaction conditions. Carboxylic acids were obtained in high yields under open flask condition with broad substrates and good tolerance to sensitive functional groups. Such a half-sandwich iridium catalyst system exhibited high catalytic activity and stability, and a high TOF of 316.7 h-1 could be achieved with a catalyst loading as low as 0.05 mol %. Furthermore, the sustainable catalyst could be reused at least five times without obviously losing its activity, highlighting its potential application in industry. Molecular structure of iridium complex 1 was confirmed by single-crystal X-ray analysis.
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Affiliation(s)
- Song Gao
- School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Shanghai 201418, China
| | - Chuan-Qi Cao
- School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Shanghai 201418, China
| | - Zhen-Jiang Liu
- School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Shanghai 201418, China
| | - Zi-Jian Yao
- School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Shanghai 201418, China
- State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China
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2
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Mondal S, Chakraborty S, Khanra S, Chakraborty S, Pal S, Brandão P, Paul ND. A Phosphine-Free Air-Stable Mn(II)-Catalyst for Sustainable Synthesis of Quinazolin-4(3 H)-ones, Quinolines, and Quinoxalines in Water. J Org Chem 2024; 89:5250-5265. [PMID: 38554095 DOI: 10.1021/acs.joc.3c02579] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/01/2024]
Abstract
The synthesis, characterization, and catalytic application of a new phosphine-free, well-defined, water-soluble, and air-stable Mn(II)-catalyst [Mn(L)(H2O)2Cl](Cl) ([1]Cl) featuring a 1,10-phenanthroline based tridentate pincer ligand, 2-(1H-pyrazol-1-yl)-1,10-phenanthroline (L), in dehydrogenative functionalization of alcohols to various N-heterocycles such as quinazolin-4(3H)-ones, quinolines, and quinoxalines are reported here. A wide array of multisubstituted quinazolin-4(3H)-ones were prepared in water under air following two pathways via the dehydrogenative coupling of alcohols with 2-aminobenzamides and 2-aminobenzonitriles, respectively. 2-Aminobenzyl alcohol and ketones bearing active methylene group were used as coupling partners for synthesizing quinoline derivatives, and various quinoxaline derivatives were prepared by coupling vicinal diols and 1,2-diamines. In all cases, the reaction proceeded smoothly using our Mn(II)-catalyst [1]Cl in water under air, affording the desired N-heterocycles in satisfactory yields starting from cheap and readily accessible precursors. Gram-scale synthesis of the compounds indicates the industrial relevance of our synthetic strategy. Control experiments were performed to understand and unveil the plausible reaction mechanism.
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Affiliation(s)
- Sucheta Mondal
- Department of Chemistry, Indian Institute of Engineering Science and Technology, Botanic Garden, Howrah, Shibpur 711103, India
| | - Subhajit Chakraborty
- Department of Chemistry, Indian Institute of Engineering Science and Technology, Botanic Garden, Howrah, Shibpur 711103, India
| | - Subhankar Khanra
- Department of Chemistry, Indian Institute of Engineering Science and Technology, Botanic Garden, Howrah, Shibpur 711103, India
| | - Santana Chakraborty
- Department of Chemistry, Indian Institute of Engineering Science and Technology, Botanic Garden, Howrah, Shibpur 711103, India
| | - Shrestha Pal
- Department of Chemistry, Indian Institute of Engineering Science and Technology, Botanic Garden, Howrah, Shibpur 711103, India
| | - Paula Brandão
- Departamento de Química/CICECO, Instituto de Materiais de Aveiro, Universidade de Aveiro, Aveiro 3810-193, Portugal
| | - Nanda D Paul
- Department of Chemistry, Indian Institute of Engineering Science and Technology, Botanic Garden, Howrah, Shibpur 711103, India
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3
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Wang Y, Luo YZ, Liu ZJ, Yao ZJ. Cationic N,S-chelate half-sandwich iridium complexes: synthesis, characterization, anticancer and antiplasmodial activity. Biomater Sci 2023; 11:7090-7098. [PMID: 37667825 DOI: 10.1039/d3bm01027a] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/06/2023]
Abstract
A series of pyrazole-based ligands and their corresponding cationic N,S-chelate half-sandwich iridium complexes were successfully synthesized. All iridium complexes exhibited good anticancer activity against the MCF-7 and MDA-MB-231 human breast cancer cells. The cytotoxic activity of unsubstituted iridium complex 1 is greater than that of cisplatin against MCF-7 cells. In addition, the cationic half-sandwich iridium complexes are also efficient in antiplasmodial study and complex 1 displayed the best activity as its IC50 was observed to be approximately 0.11 μM against the CQS-NF54 strain. These iridium complexes generally exhibited enhanced activity against the CQS-NF54 strain in comparison with that against the CQR-K1 strain. An "IC50 speed assay" investigation against the CQS-NF54 strain indicated complexes 1-3 to be fast-acting complexes that reach their lowest IC50 values within 16 hours. All complexes were fully characterized by IR spectroscopy, NMR spectroscopy, and elemental analysis, and the structure of the iridium complex was confirmed by single-crystal X-ray diffraction.
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Affiliation(s)
- Yang Wang
- School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Shanghai, 201418, China.
| | - Yu-Zhou Luo
- Scientific Research Office, Guangzhou College of Commerce, Guangzhou, 511363, China.
| | - Zhen-Jiang Liu
- School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Shanghai, 201418, China.
| | - Zi-Jian Yao
- School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Shanghai, 201418, China.
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4
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Paul T, Saikia PP, Borah D, Mahanta N, Baruah A, Borah JM, Saikia BJ, Raidongia K, Gogoi RK, Gogoi R. Ni(OH)
2
nanoparticles as a recyclable catalyst in acceptorless dehydrogenation of alcohols to acids/acid salts under aerobic conditions. ChemistrySelect 2023. [DOI: 10.1002/slct.202204713] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/07/2023]
Affiliation(s)
- Tumpa Paul
- Department of Chemistry Darrang College 784001 Tezpur India
| | | | | | | | - Arabinda Baruah
- Department of Chemistry Gauhati University 781014 Guwahati India
| | | | | | | | | | - Raktim Gogoi
- Department of Chemistry IIT Guwahati 781039 Guwahati India
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5
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Zeolitic Imidazolate Framework-8 as an Efficient and Facile Heterogeneous Catalyst for the Acceptorless Alcohol Dehydrogenation to Carboxylates. J Catal 2022. [DOI: 10.1016/j.jcat.2022.12.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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6
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Carmona M, Pérez R, Ferrer J, Rodríguez R, Passarelli V, Lahoz FJ, García-Orduña P, Carmona D. Activation of H-H, HO-H, C(sp 2)-H, C(sp 3)-H, and RO-H Bonds by Transition-Metal Frustrated Lewis Pairs Based on M/N (M = Rh, Ir) Couples. Inorg Chem 2022; 61:13149-13164. [PMID: 35948430 PMCID: PMC9406284 DOI: 10.1021/acs.inorgchem.2c01902] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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Reaction of the dimers [(Cp*MCl)2(μ-Cl)2] (Cp* = η5-C5Me5)
with Ph2PCH2CH2NC(NH(p-Tolyl))2 (H2L) in the presence
of NaSbF6 affords the chlorido complexes [Cp*MCl(κ2N,P-H2L)][SbF6] (M = Rh, 1; Ir, 2).
Upon treatment with aqueous NaOH, solutions of 1 and 2 yield the corresponding complexes [Cp*M(κ3N,N′,P-HL)][SbF6] (M = Rh, 3; Ir, 4) in which the ligand HL presents a fac κ3N,N′,P coordination mode. Treatment of THF solutions
of complexes 3 and 4 with hydrogen gas,
at room temperature, results in the formation of the metal hydrido-complexes
[Cp*MH(κ2N,P-H2L)][SbF6] (M = Rh, 5;
Ir, 6) in which the N(p-Tolyl) group
has been protonated. Complexes 3 and 4 react
with deuterated water in a reversible fashion resulting in the gradual
deuteration of the Cp* group. Heating at 383 K THF/H2O
solutions of the complexes 3 and 4 affords
the orthometalated complexes [Cp*M(κ3C,N,P-H2L-H)][SbF6] [M = Rh, 7; Ir, 8, H2L-H = Ph2PCH2CH2NC(NH(p-Tolyl))(NH(4-C6H3Me))], respectively. At 333 K, complexes 3 and 4 react in THF with methanol, primary alcohols,
or 2-propanol giving the metal-hydrido complexes 5 and 6, respectively. The reaction involves the acceptorless dehydrogenation
of the alcohols at a relatively low temperature, without the assistance
of an external base. The new complexes have been characterized by
the usual analytical and spectroscopic methods including the X-ray
diffraction determination of the crystal structures of complexes 1–5, 7, and 8. Notably, the chlorido complexes 1 and 2 crystallize both as enantiopure conglomerates and as racemates.
Reaction mechanisms are proposed based on stoichiometric reactions,
nuclear magnetic resonance studies, and X-ray crystallography as well
as density functional theory calculations. In solution, masked transition-metal
frustrated Lewis pairs
(TMFLPs) give rise to the corresponding TMFLP species which activate
dihydrogen, water, and alcohols following FLP reaction pathways. When
D2O or alcohols with deuterated OH groups were employed,
H/D exchange at the Cp* ligand (involving C(sp3)−H
activation) was observed. C(sp2)−H bond activation
involving orthometalation of the p-Tolyl ring was
also observed.
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Affiliation(s)
- María Carmona
- Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC - Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain
| | - Roberto Pérez
- Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC - Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain
| | - Joaquina Ferrer
- Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC - Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain
| | - Ricardo Rodríguez
- Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC - Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain
| | - Vincenzo Passarelli
- Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC - Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain
| | - Fernando J Lahoz
- Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC - Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain
| | - Pilar García-Orduña
- Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC - Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain
| | - Daniel Carmona
- Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC - Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain
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7
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Tabasi NS, Genç S, Gülcemal D. Tuning the selectivity in iridium-catalyzed acceptorless dehydrogenative coupling of primary alcohols. Org Biomol Chem 2022; 20:6582-6592. [PMID: 35913502 DOI: 10.1039/d2ob01142e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
An acceptorless dehydrogenative coupling of primary alcohols to carboxylic acids/carboxylates, esters, and Guerbet alcohols (via both homo- and cross-β-alkylation of the alcohols) in the presence of an N-heterocyclic carbene iridium(I) catalyst was developed under aerobic conditions. The product selectivity can be easily tuned among the products with a single catalyst through simple modification of the reaction conditions, such as the catalyst and base amounts, the choice of base, and the reaction temperature.
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Affiliation(s)
- Nihal S Tabasi
- Ege University, Chemistry Department, 35100 Bornova, Izmir, Turkey.
| | - Sertaç Genç
- Ege University, Chemistry Department, 35100 Bornova, Izmir, Turkey.
| | - Derya Gülcemal
- Ege University, Chemistry Department, 35100 Bornova, Izmir, Turkey.
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8
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Fe2+ activating persulfate selectively oxidized alcohols by biphasic/homogeneous reaction switch strategy. CHEMICAL PAPERS 2022. [DOI: 10.1007/s11696-022-02366-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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9
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Navale G, Singh S, Agrawal S, Ghosh C, Roy Choudhury A, Roy P, Sarkar D, Ghosh K. DNA binding, antitubercular, antibacterial and anticancer studies of newly designed piano-stool ruthenium( ii) complexes. Dalton Trans 2022; 51:16371-16382. [DOI: 10.1039/d2dt02577a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The chemotherapeutic potential of ruthenium(ii) complexes as DNA binding, antitubercular, antibacterial, and anticancer agents.
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Affiliation(s)
- Govinda Navale
- Department of Chemistry, Indian Institute of Technology, Roorkee 247667, India
| | - Sain Singh
- Department of Chemistry, Indian Institute of Technology, Roorkee 247667, India
| | - Sonia Agrawal
- Department of Organic Chemistry, CSIR-National Chemical Laboratory, Pune 411 008, India
| | - Chandrachur Ghosh
- Department of Biosciences and Bioengineering, Indian Institute of Technology, Roorkee 247667, India
| | - Angshuman Roy Choudhury
- Department of Chemical Sciences, Indian Institute of Science Education and Research, Mohali, India
| | - Partha Roy
- Department of Biosciences and Bioengineering, Indian Institute of Technology, Roorkee 247667, India
| | - Dhiman Sarkar
- Department of Organic Chemistry, CSIR-National Chemical Laboratory, Pune 411 008, India
| | - Kaushik Ghosh
- Department of Chemistry, Indian Institute of Technology, Roorkee 247667, India
- Department of Biosciences and Bioengineering, Indian Institute of Technology, Roorkee 247667, India
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10
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Pragti, Kundu BK, Sonkar C, Ganguly R, Mukhopadhyay S. Modulation of catalytic and biomolecular binding properties of ruthenium(II)-arene complexes with the variation of coligands for selective toxicity against cancerous cells. Polyhedron 2021. [DOI: 10.1016/j.poly.2021.115379] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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11
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Patra S, Deka H, Singh SK. Bis-Imidazole Methane Ligated Ruthenium(II) Complexes: Synthesis, Characterization, and Catalytic Activity for Hydrogen Production from Formic Acid in Water. Inorg Chem 2021; 60:14275-14285. [PMID: 34461719 DOI: 10.1021/acs.inorgchem.1c01784] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A series of half sandwich arene-ruthenium complexes [(η6-arene)RuCl(κ2-L)]+ ([Ru]-1-[Ru]-10) containing bis-imidazole methane-based ligands {4,4'-(phenylmethylene)bis(2-ethyl-5-methyl-1H-imidazole)} (L1), {4,4'-((4-methoxyphenyl)methylene)bis(2-ethyl-5-methyl-1H-imidazole)} (L2), {4,4'-((2-methoxyphenyl)methylene)bis(2-ethyl-5-methyl-1H-imidazole)} (L3), {4,4'-((4-chlorophenyl)methylene)bis(2-ethyl-5-methyl-1H-imidazole)} (L4), and {4,4'-((2-chlorophenyl)methylene)bis(2-ethyl-5-methyl-1H-imidazole)} (L5) are synthesized. The synthesized and purified complexes ([Ru]-1-[Ru]-10) are further employed for hydrogen production from formic acid in aqueous medium. Among the investigated complexes, [(η6-p-cymene)RuCl(κ2-L2)]+ [Ru]-2, having Ru(II) coordinated 4-methoxy phenyl substituted bis-imidazole methane ligand (L2), outperformed over others, displaying a higher catalytic turnover of 8830 and high efficiency (TOF = 1545 h-1) with appreciably high long-term stability for formic acid dehydrogenation in water.
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Affiliation(s)
- Soumyadip Patra
- Catalysis Group, Department of Chemistry, Indian Institute of Technology Indore, Simrol, Indore 453552, Madhya Pradesh, India
| | - Hemanta Deka
- Catalysis Group, Department of Chemistry, Indian Institute of Technology Indore, Simrol, Indore 453552, Madhya Pradesh, India
| | - Sanjay K Singh
- Catalysis Group, Department of Chemistry, Indian Institute of Technology Indore, Simrol, Indore 453552, Madhya Pradesh, India
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12
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Abstract
AbstractOxidation of primary alcohols to carboxylic acids is a fundamental transformation in organic chemistry, yet despite its simplicity, extensive use, and relationship to pH, it remains a subject of active research for synthetic organic chemists. Since 2013, a great number of new methods have emerged that utilize transition-metal compounds as catalysts for acceptorless dehydrogenation of alcohols to carboxylates. The interest in this reaction is explained by its atom economy, which is in accord with the principles of sustainability and green chemistry. Therefore, the methods for the direct synthesis of carboxylic acids from alcohols is ripe for a modern survey, which we provide in this review.1 Introduction2 Thermodynamics of Primary Alcohol Oxidation3 Oxometalate Oxidation4 Transfer Dehydrogenation5 Acceptorless Dehydrogenation6 Electrochemical Methods7 Outlook
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Abstract
Our planet urgently needs sustainable solutions to alleviate the anthropogenic global warming and climate change. Homogeneous catalysis has the potential to play a fundamental role in this process, providing novel, efficient, and at the same time eco-friendly routes for both chemicals and energy production. In particular, pincer-type ligation shows promising properties in terms of long-term stability and selectivity, as well as allowing for mild reaction conditions and low catalyst loading. Indeed, pincer complexes have been applied to a plethora of sustainable chemical processes, such as hydrogen release, CO2 capture and conversion, N2 fixation, and biomass valorization for the synthesis of high-value chemicals and fuels. In this work, we show the main advances of the last five years in the use of pincer transition metal complexes in key catalytic processes aiming for a more sustainable chemical and energy production.
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14
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Genç S, Gülcemal S, Günnaz S, Çetinkaya B, Gülcemal D. Iridium-Catalyzed Alkylation of Secondary Alcohols with Primary Alcohols: A Route to Access Branched Ketones and Alcohols. J Org Chem 2020; 85:9139-9152. [DOI: 10.1021/acs.joc.0c01099] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Sertaç Genç
- Ege University, Chemistry Department, 35100 Bornova, Izmir, Turkey
| | | | - Salih Günnaz
- Ege University, Chemistry Department, 35100 Bornova, Izmir, Turkey
| | - Bekir Çetinkaya
- Ege University, Chemistry Department, 35100 Bornova, Izmir, Turkey
| | - Derya Gülcemal
- Ege University, Chemistry Department, 35100 Bornova, Izmir, Turkey
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15
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Hazra S, Malik E, Nair A, Tiwari V, Dolui P, Elias AJ. Catalytic Oxidation of Alcohols and Amines to Value‐Added Chemicals using Water as the Solvent. Chem Asian J 2020; 15:1916-1936. [DOI: 10.1002/asia.202000299] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2020] [Revised: 04/20/2020] [Indexed: 01/12/2023]
Affiliation(s)
- Susanta Hazra
- Department of ChemistryIndian Institute of Technology, Delhi Hauz Khas New Delhi 110016 India
| | - Ekta Malik
- Department of ChemistryIndian Institute of Technology, Delhi Hauz Khas New Delhi 110016 India
| | - Abhishek Nair
- Department of ChemistryIndian Institute of Technology, Delhi Hauz Khas New Delhi 110016 India
| | - Vikas Tiwari
- Department of ChemistryIndian Institute of Technology, Delhi Hauz Khas New Delhi 110016 India
| | - Pritam Dolui
- Department of ChemistryIndian Institute of Technology, Delhi Hauz Khas New Delhi 110016 India
| | - Anil J. Elias
- Department of ChemistryIndian Institute of Technology, Delhi Hauz Khas New Delhi 110016 India
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16
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Borah D, Saha B, Sarma B, Das P. A cyclometalated Ir(III)-NHC complex as a recyclable catalyst for acceptorless dehydrogenation of alcohols to carboxylic acids. Dalton Trans 2020; 49:16866-16876. [PMID: 33179681 DOI: 10.1039/d0dt02341h] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
In this work, we have synthesized two new [C, C] cyclometalated Ir(iii)-NHC complexes, [IrCp*(C∧C:NHC)Br](1a,b), [Cp* = pentamethylcyclopentadienyl; NHC = (2-flurobenzyl)-1-(4-methoxyphenyl)-1H-imidazoline-2-ylidene (a); (2-flurobenzyl)-1-(4-formylphenyl)-1H-imidazoline-2-ylidene (b)] via intramolecular C-H bond activation. The molecular structure of complex 1a was determined by X-ray single crystal analysis. The catalytic potentials of the complexes were explored for acceptorless dehydrogenation of alcohols to carboxylic acids with concomitant hydrogen gas evolution. Under similar experimental conditions, complex 1a was found to be slightly more efficient than complex 1b. Using 0.1 mol% of complex 1a, good-to-excellent yields of carboxylic acids/carboxylates have been obtained for a wide range of alcohols, both aliphatic and aromatic, including those involving heterocycles, in a short reaction time with a low loading of catalyst. Remarkably, our method can produce benzoic acid from benzyl alcohol on a gram scale with a catalyst-to-substrate ratio as low as 1 : 5000 and exhibit a TON of 4550. Furthermore, the catalyst could be recycled at least three times without losing its activity. A mechanism has been proposed based on controlled experiments and in situ NMR study.
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Affiliation(s)
- Dhrubajit Borah
- Department of Chemistry, Dibrugarh University, Dibrugarh, Assam 786004, India.
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