51301-55-4Relevant articles and documents
Mechanism of CO2hydrogenation to formates by homogeneous Ru-PNP pincer catalyst: From a theoretical description to performance optimization
Filonenko, Georgy A.,Hensen, Emiel J. M.,Pidko, Evgeny A.
, p. 3474 - 3485 (2014)
The reaction mechanism of CO2hydrogenation by pyridine-based Ru-PNP catalyst in the presence of DBU base promoter was studied by means of density functional theory calculations. Three alternative reaction channels promoted by the complexes potentially present under the reaction conditions, namely the dearomatized complex 2 and the products of cooperative CO2(3) and H2(4) addition, were analysed. It is shown that the bis-hydrido Ru-PNP complex 4 provides the unique lowest-energy reaction path involving a direct effectively barrierless hydrogenolysis of the polarized complex 5?. The reaction rate in this case is controlled by the CO2activation by Ru-H that proceeds with a very low barrier of ca. 20 kJ mol-1. The catalytic reaction can be hampered by the formation of a stable formato-complex 5. In this case, the rate is controlled by the H2insertion into the Ru-OCHO coordination bond, for which a barrier of 65 kJ mol-1is predicted. The DFT calculations suggest that the preference for the particular route can be controlled by varying the partial pressure of H2in the reaction mixture. Under H2-rich conditions, the former more facile catalytic path should be preferred. Dedicated kinetic experiments verify these theoretical predictions. The apparent activation energies measured at different H2/CO2molar ratios are in a perfect agreement with the calculated values. Ru-PNP is a highly active CO2hydrogenation catalyst allowing reaching turnover frequencies in the order of 106h-1at elevated temperatures. Moreover, a minor temperature dependency of the reaction rate attainable in excess H2points to the possibility of efficient CO2hydrogenation at near-ambient temperatures. This journal is
Aperture-Opening Encapsulation of a Transition Metal Catalyst in a Metal-Organic Framework for CO2 Hydrogenation
Li, Zhehui,Rayder, Thomas M.,Luo, Lianshun,Byers, Jeffery A.,Tsung, Chia-Kuang
, p. 8082 - 8085 (2018)
The aperture-opening process resulting from dissociative linker exchange in zirconium-based metal-organic framework (MOF) UiO-66 was used to encapsulate the ruthenium complex (tBuPNP)Ru(CO)HCl in the framework (tBuPNP = 2,6-bis((di-tert-butyl-phosphino)methyl)pyridine). The resulting encapsulated complex, [Ru]@UiO-66, was a very active catalyst for the hydrogenation of CO2 to formate. Unlike the analogous homogeneous catalyst, [Ru]@UiO-66 could be recycled five times, showed no evidence for bimolecular catalyst decomposition, and was less prone to catalyst poisoning. These results demonstrated for the first time how the aperture-opening process in MOFs can be used to synthesize host-guest materials useful for chemical catalysis.
Amidines as effective ancillary ligands in copper-catalyzed hydrogenation of carbon dioxide
Kayaki, Yoshihito,Kuwata, Shigeki,Watari, Ryo
, p. 252 - 254 (2020)
Mononuclear Cu(II) complexes bearing a bidentate bisamidine ligand were newly synthesized and characterized. The catalytic activity was evaluated in the hydrogenation of carbon dioxide to formate salts. A substantial enhancement of the catalyst turnover number was achieved by the imidazoline-based complex, indicating that amidines serve as effective ancillary ligands for homogeneous copper catalysis.
Catalytic Formic Acid Dehydrogenation and CO2 Hydrogenation Using Iron PNRP Pincer Complexes with Isonitrile Ligands
Curley, Julia B.,Smith, Nicholas E.,Bernskoetter, Wesley H.,Hazari, Nilay,Mercado, Brandon Q.
, p. 3846 - 3853 (2018)
It has previously been demonstrated that complexes of the form (iPrPNP)Fe(H)(C≡NR) (iPrPNP = N(CH2CH2P(iPr)2)2-, R = 2,6-dimethylphenyl or 4-methoxyphenyl), which contain a pincer ligand capable of metal-ligand cooperation (MLC), are active for CO2 hydrogenation. Herein, the synthesis and catalytic activity of a second-generation of precatalysts containing a tertiary amine ligand, which cannot participate in MLC, are presented. Specifically, the complexes (iPrPNMeP)Fe(H)(HBH3)(C≡NR) (iPrPNMeP = MeN(CH2CH2P(iPr)2)2, R = 2,6-dimethylphenyl (2a), tert-butyl (2b), or adamantyl (2c)) have been prepared and crystallographically characterized. These complexes are precatalysts for both formic acid dehydrogenation and CO2 hydrogenation to formate, and give improved activity compared to first-generation systems with isonitrile ligands. The second-generation systems 2a-c, however, give inferior activity compared to the related carbonyl complexes (iPrPNP)Fe(H)(CO) and (iPrPNMeP)Fe(H)(HBH3)(CO), which have been previously reported. This study demonstrates that a ligand which can participate in MLC is not universally advantageous for promoting the hydrogenation and dehydrogenation reactions studied in this work and provides guidance for the rational design of improved catalysts for reactions relevant to energy storage.
Cu(i) complex bearing a PNP-pincer-Type phosphaalkene ligand with a bulky fused-ring Eind group: Properties and applications to FLP-Type bond activation and catalytic CO2 reduction
Choi, Jun-Chul,Ozawa, Fumiyuki,Takeuchi, Katsuhiko,Tanaka, Yuto,Tanigawa, Ippei
, p. 3630 - 3637 (2020)
Herein, we report the synthesis of [Cu(Eind2-BPEP)][PF6] (2) (Eind2-BPEP = 2,6-bis(2-Eind-2-phosphaethenyl)pyridine, Eind = 1,1,3,3,5,5,7,7-octaethyl-1,2,3,5,6,7-hexahydro-s-indacen-4-yl), a three-coordinated Cu(i) complex bearing a PNP-pincer-Type phosphaalkene ligand with bulky fused-ring Eind groups. The Gutmann-Beckett test revealed that complex 2 is highly Lewis acidic and comparable in strength to B(C6F5)3, which is a relatively strong Lewis acid. In addition, 2 is more Lewis acidic than [Cu(Mes?2-BPEP)][PF6] (3), the analogous complex with less-bulky Mes? instead of Eind groups. DFT calculations using model compounds revealed that the higher Lewis acidity of 2 compared to 3 is not due to the electronic effects of the ligand, but due to a reduction in the LUMO energy caused by the steric effect of the bulky Eind groups. When combined with a tertiary amine, the highly Lewis acidic and bulky 2 exhibits the reactivity of a frustrated Lewis pair (FLP) and can activate hydrogen and phenylacetylene. Complexes 2 and 3 were found to catalyze the hydrogenation and hydrosilylation of CO2 in the presence of DBU under relatively mild conditions.
Understanding the efficiency of ionic liquids-DMSO as solvents for carbohydrates: use of solvatochromic- And related physicochemical properties
Bioni, Thaís A.,de Oliveira, Mayara L.,Dignani, Marcella T.,El Seoud, Omar A.
, p. 14906 - 14914 (2020/09/23)
The physical dissolution of carbohydrates (cellulose, chitin, and starch),i.e., without the formation of covalent bonds requires the solvent to possess certain physicochemical properties. Concentrating on cellulose, the solvent should act both as a Lewis acid and a Lewis base, and disrupt the present hydrophobic interactions, as the biopolymer exhibits amphiphilic characteristics. The quantification of the relative importance of these physicochemical properties helps in predicting the solvent structures, which are expected to be efficient as cellulose solvents. Ionic liquids (ILs) are extensively used as carbohydrate solvents because they disrupt the intramolecular-, intermolecular-, and hydrophobic interactions within the biopolymer structure, leading to its dissolution. Solvatochromic substances (probes) are especially sensitive to one or more of the above-mentioned biopolymer-solvent interactions. Consequently, they are used to predict and rationalize the solvent efficiency. The solvent parameters (descriptors) most widely employed are empirical polarity,ET(probe), Lewis acidity (SA); Lewis basicity (SB), dipolarity (SD), and polarizability (SP); S refers to the solvent. We synthesized 18 ILs, including derivatives of imidazole, 1,8-diazabicyclo[5.4.0]undec-7-ene, and tetramethylguanidine; the corresponding anions are carboxylates, chloride and dimethylphosphate. We used solvatochromic probes to calculate the descriptors of IL-DMSO (at fixed DMSO mole fraction of 0.6; 40 °C), and correlatedET(probe) with the other descriptors. We also tested the correlations by using a molar volume of the IL (VM) instead of SD, and the Lorentz-Lorenz refractive index functionf(n) of the IL-DMSO mixture instead of SP. The quality of the regression analysis increased noticeably when we limited the ILs correlated with those based on imidazole (13 ILs), and used (VM) andf(n). The regression coefficients showed that SA is the most important descriptor; the solvent empirical polarity is inversely dependent onVM. The value off(n) shows the importance of hydrophobic interactions. By using different probes, we showed that the observed small contribution of SB reflects the steric crowding around the positive nitrogen atoms in some probes. The results obtained help in selecting ILs as solvents for cellulose and other carbohydrates, based on the expected strength of their interactions with the biopolymers. Therefore, using solvatochromism for solvent efficiency screening saves labor and cost.
