- Hydroboration of aldehydes, ketones and CO2under mild conditions mediated by iron(iii) salen complexes
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The hydroboration of aldehydes, ketones and CO2is demonstrated using a cheap and air stable [Fe(salen)]2-μ-oxo pre-catalyst with pinacolborane (HBpin) as the reductant under mild conditions. This catalyst system chemoselectively hydroborates aldehydes over ketones and ketones over alkenes. In addition, the [Fe(salen)2]-μ-oxo pre-catalyst shows good efficacy at reducing “wet” CO2with HBpin at room temperature.
- James, Alexander P.,Lau, Samantha,Provis-Evans, Cei B.,Webster, Ruth L.
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- Dialumenes-aryl: Vs. silyl stabilisation for small molecule activation and catalysis
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Main group multiple bonds have proven their ability to act as transition metal mimics in the last few decades. However, catalytic application of these species is still in its infancy. Herein we report the second neutral NHC-stabilised dialumene species by use of a supporting aryl ligand (3). Different to the trans-planar silyl-substituted dialumene (3Si), compound 3 features a trans-bent and twisted geometry. The differences between the two dialumenes are explored computationally (using B3LYP-D3/6-311G(d)) as well as experimentally. A high influence of the ligand's steric demand on the structural motif is revealed, giving rise to enhanced reactivity of 3 enabled by a higher flexibility in addition to different polarisation of the aluminium centres. As such, facile activation of dihydrogen is now achievable. The influence of ligand choice is further implicated in two different catalytic reactions; not only is the aryl-stabilised dialumene more catalytically active but the resulting product distributions also differ, thus indicating the likelihood of alternate mechanisms simply through a change of supporting ligand.
- Bag, Prasenjit,Hanusch, Franziska,Inoue, Shigeyoshi,Porzelt, Amelie,Weetman, Catherine
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p. 4817 - 4827
(2020/06/17)
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- Ph2PCH2CH2B(C8H14) and Its Formaldehyde Adduct as Catalysts for the Reduction of CO2with Hydroboranes
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We study two metal-free catalysts for the reduction of CO2 with four different hydroboranes and try to identify mechanistically relevant intermediate species. The catalysts are the phosphinoborane Ph2P(CH2)2BBN (1), easily accessible in a one-step synthesis from diphenyl(vinyl)phosphine and 9-borabicyclo[3.3.1]nonane (H-BBN), and its formaldehyde adduct Ph2P(CH2)2BBN(CH2O) (2), detected in the catalytic reduction of CO2 with 1 as the catalyst but properly prepared from compound 1 and p-formaldehyde. Reduction of CO2 with H-BBN gave mixtures of CH2(OBBN)2 (A) and CH3OBBN (B) using both catalysts. Stoichiometric and kinetic studies allowed us to unveil the key role played in this reaction by the formaldehyde adduct 2 and other formaldehyde-formate species, such as the polymeric BBN(CH2)2(Ph2P)(CH2O)BBN(HCO2) (3) and the bisformate macrocycle BBN(CH2)2(Ph2P)(CH2O)BBN(HCO2)BBN(HCO2) (4), whose structures were confirmed by diffractometric analysis. Reduction of CO2 with catecholborane (HBcat) led to MeOBcat (C) exclusively. Another key intermediate was identified in the reaction of 2 with the borane and CO2, this being the bisformaldehyde-formate macrocycle (HCO2){BBN(CH2)2(Ph2P)(CH2O)}2Bcat (5), which was also structurally characterized by X-ray analysis. In contrast, using pinacolborane (HBpin) as the reductant with catalysts 1 and 2 usually led to mixtures of mono-, di-, and trihydroboration products HCO2Bpin (D), CH2(OBpin)2 (E), and CH3OBpin (F). Stoichiometric studies allowed us to detect another formaldehyde-formate species, (HCO2)BBN(CH2)2(Ph2P)(CH2O)Bpin (6), which may play an important role in the catalytic reaction. Finally, only the formaldehyde adduct 2 turned out to be active in the catalytic hydroboration of CO2 using BH3·SMe2 as the reductant, yielding a mixture of two methanol-level products, [(OMe)BO]3 (G, major product) and B(OMe)3 (H, minor product). In this transformation, the Lewis adduct (BH3)Ph2P(CH2)2BBN was identified as the resting state of the catalyst, whereas an intermediate tentatively formulated as the Lewis adduct of compound 2 and BH3 was detected in solution in a stoichiometric experiment and is likely to be mechanistically relevant for the catalytic reaction.
- Ramos, Alberto,Anti?olo, Antonio,Carrillo-Hermosilla, Fernando,Fernández-Galán, Rafael
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supporting information
p. 9998 - 10012
(2020/07/24)
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- Acetate-catalyzed hydroboration of CO2 for the selective formation of methanol-equivalent products
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The present study details the use of the acetate anion, an inexpensive and robust anion, as a CO2 hydroboration catalyst for the selective formation, in most cases, of methanol-equivalent borane products. Thus, upon heating (90 °C, PhBr), tetrabutylammonium, sodium and potassium acetate (1, 2 and 3, respectively) effectively catalyze CO2 hydroboration by pinacolborane (pinB-H) to afford CO2 reduction products HOCOBpin (A), pinBOCH2OBpin (B) and methoxyborane (C). In most cases, high selectivity for product C with higher borane loading and longer reaction time with a TON of up to 970 was observed. The reduction catalysis remains efficient at low catalyst loading (down to 0.1 mol%) and may also be performed under solvent-free conditions using salt 1 as a catalyst, reflecting the excellent robustness and stability of the acetate anion. In control experiments, a 1/1 1/pinB-H mixture was found to react fast with CO2 at room temperature to produce formate species [pinB(O2CH)(OAc)][N(nBu)4] (5) through CO2 insertion into the B-H bond. DFT calculations were also performed to gain insight into the acetate-mediated CO2 hydroboration catalysis, which further supported the crucial role of acetate as a Lewis base in CO2 functionalization catalysis by pinB-H. The DFT-estimated mechanism is in line with experimental data and rationalizes the formation of the most thermodynamically stable reduction product C through acetate catalysis.
- Dagorne, Samuel,Dos Santos, Jo?o H. Z.,Jacques, Béatrice,López, Carlos Silva,Nieto Faza, Olalla,Schrekker, Henri S.,Sokolovicz, Yuri C. A.,Specklin, David
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p. 2407 - 2414
(2020/05/13)
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- CO2 Fixation and Catalytic Reduction by a Neutral Aluminum Double Bond
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CO2 fixation and reduction to value-added products is of utmost importance in the battle against rising CO2 levels in the Earth's atmosphere. An organoaluminum complex containing a formal aluminum double bond (dialumene), and thus an alkene equivalent, was used for the fixation and reduction of CO2. The CO2 fixation complex undergoes further reactivity in either the absence or presence of additional CO2, resulting in the first dialuminum carbonyl and carbonate complexes, respectively. Dialumene (1) can also be used in the catalytic reduction of CO2, providing selective formation of a formic acid equivalent via the dialuminum carbonate complex rather than a conventional aluminum–hydride-based cycle. Not only are the CO2 reduction products of interest for C1 added value products, but the organoaluminum complexes isolated represent a significant step forward in the isolation of reactive intermediates proposed in many industrially relevant catalytic processes.
- Weetman, Catherine,Bag, Prasenjit,Szilvási, Tibor,Jandl, Christian,Inoue, Shigeyoshi
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supporting information
p. 10961 - 10965
(2019/07/08)
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- Insertion of CO2 into the carbon-boron bond of a boronic ester ligand
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New Ru and Zn diazafluorenyl complexes undergo C-H borylation of the diazafluorenyl ligand to form the corresponding diazafluorenylboronic ester complexes, which can insert CO2 into their C-B bonds to form boryl ester functionalities. The relev
- Janes, Trevor,Osten, Kimberly M.,Pantaleo, Adam,Yan, Ellen,Yang, Yanxin,Song, Datong
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supporting information
p. 4148 - 4151
(2016/03/19)
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- Organocatalysts with carbon-centered activity for CO2 reduction with boranes
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We report two organocatalysts for CO2 hydroboration to methylborylethers, which upon hydrolysis can produce methanol. These organocatalysts feature carbon-centered reversible CO2 binding, broad borane scopes, and high catalytic activities.
- Yang, Yanxin,Xu, Maotong,Song, Datong
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supporting information
p. 11293 - 11296
(2015/07/07)
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- Trapping formaldehyde in the homogeneous catalytic reduction of carbon dioxide
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Formaldehyde detectives: Evidence for the production of formaldehyde during a ruthenium-catalyzed CO2 reduction process, and for its involvement in the formation of the resulting C2 compound, is disclosed. Ultimately, formaldehyde can be recovered by methanol trapping. HBPin=pinacolborane. Copyright
- Bontemps, Sebastien,Sabo-Etienne, Sylviane
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supporting information
p. 10253 - 10255
(2013/10/21)
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