scholarly journals Hydrogen activation using a novel tribenzyltin Lewis acid

2017 ◽  
Vol 375 (2101) ◽  
pp. 20170008 ◽  
Author(s):  
Robert T. Cooper ◽  
Joshua S. Sapsford ◽  
Roland C. Turnell-Ritson ◽  
Dong-Hun Hyon ◽  
Andrew J. P. White ◽  
...  
Keyword(s):  
Low Temperature ◽  
Lewis Acid ◽  
Lewis Acids ◽  
Lewis Acidity ◽  
The Novel ◽  
Hydrogen Activation ◽  
Frustrated Lewis Pair

Over the last decade there has been an explosion in the reactivity and applications of frustrated Lewis pair (FLP) chemistry. Despite this, the Lewis acids (LAs) in these transformations are often boranes, with heavier p -block elements receiving surprisingly little attention. The novel LA Bn 3 SnOTf ( 1 ) has been synthesized from simple, inexpensive starting materials and has been spectroscopically and structurally characterized. Subtle modulation of the electronics at the tin centre has led to an increase in its Lewis acidity in comparison with previously reported R 3 SnOTf LAs, and has facilitated low temperature hydrogen activation and imine hydrogenation. Deactivation pathways of the R 3 Sn + LA core have also been investigated. This article is part of the themed issue ‘Frustrated Lewis pair chemistry’.

Fluorinated 9-borafluorenes vs. conventional perfluoroaryl boranes — Comparative Lewis acidity

2005 ◽  
Vol 83 (12) ◽  
pp. 2098-2105 ◽  
Author(s):  
Preston A Chase ◽  
Patricio E Romero ◽  
Warren E Piers ◽  
Masood Parvez ◽  
Brian O Patrick
Keyword(s):  
Key Words ◽  
Lewis Acid ◽  
Lewis Acids ◽  
Acid Strength ◽  
Lewis Base ◽  
Lewis Acidity ◽  
Electrochemical Studies ◽  
Steric Factors

Perfluorinated 9-phenyl-9-borafluorene, 1, is an antiaromatic analog of the well-known tris(pentafluorophenyl)borane. Spectroscopic, structural, and electrochemical studies have been performed on 1 and its Lewis base adducts with MeCN, THF, and PMe3 with a view to assessing its comparative Lewis acid strength relative to B(C6F5)3. For the sterically undemanding Lewis base MeCN, 1 and B(C6F5)3 have comparable LA strengths, while for more sterically prominent THF, 1 is clearly the stronger Lewis acid (LA) based on competition experiments. We conclude that steric factors, rather than antiaromaticity, are the most important determinants in the LA strength differences between 1 and B(C6F5)3.Key words: boranes, Lewis acids, fluorinated compounds, heterocycles.

Synthesis of heteronuclear bifunctional Lewis acids by transmetalation of 1,8-bis(trimethylstannyl)naphthalene with BCl3

2002 ◽  
Vol 80 (10) ◽  
pp. 1308-1312 ◽  
Author(s):  
Marcus Schulte ◽  
François P Gabbaï
Keyword(s):  
Elevated Temperature ◽  
Nmr Spectroscopy ◽  
Single Crystal ◽  
Acid Derivative ◽  
Lewis Acid ◽  
Lewis Acids ◽  
The Novel ◽  
X Ray ◽  
Boron Center ◽  
Chloride Methyl

Reaction of 1,8-bis(trimethylstannyl)naphthalene (1) with an excess of BCl3 at –78°, followed by warming to 0°C, results in the exclusive formation of the novel bifunctional Lewis acid 1-(chlorodimethylstannyl)-8-(dichloroboryl)naphthalene (2), a compound in which a boryl and a stannyl moiety coexist at the peri-positions of a naphthalene core. At elevated temperature compound 2 undergoes a chloride–methyl exchange, which affords 1-(dichloromethylstannyl)-8-(chloromethylboryl)naphthalene (3). Compounds 2 and 3 have been characterized by multi-nuclear NMR spectroscopy. The single crystal X-ray analysis for compound 3 reveals a sterically crowded structure with an essentially trigonal planar boron center, and a tin center pentacoordinated in a [4+1]-fashion. Upon exposure to traces of water, compound 3 is converted into the borinic acid derivative 1-(dichloromethylstannyl)-8-(hydroxymethylboryl)naphthalene (4), which has been characterized by multi-nuclear NMR spectroscopy and single crystal X-ray analysis.Key words: multidentate Lewis acids, organoboranes, organostannanes.

scholarly journals Recent Advances in Water-Tolerance in Frustrated Lewis Pair Chemistry

Synthesis ◽  
2018 ◽  
Vol 50 (09) ◽  
pp. 1783-1795 ◽  
Author(s):  
Michael Ingleson ◽  
Valerio Fasano
Keyword(s):  
Small Molecules ◽  
Lewis Acid ◽  
Lewis Acids ◽  
Short Review ◽  
Lewis Base ◽  
Small Molecule Activation ◽  
Significant Progress ◽  
Water Tolerance ◽  
Frustrated Lewis Pair ◽  
Main Challenge

A water-tolerant frustrated Lewis pair (FLP) combines a sterically encumbered Lewis acid and Lewis base that in synergy are able to activate small molecules even in the presence of water. The main challenge introduced by water comes from its reversible coordination to the Lewis acid which causes a marked increase in the Brønsted acidity of water. Indeed, the oxophilic Lewis acids typically used in FLP chemistry form water adducts whose acidity can be comparable to that of strong Brønsted acids such as HCl, thus they can protonate the Lewis base component of the FLP. Irreversible proton transfer quenches the reactivity of both the Lewis acid and the Lewis base, precluding small molecule activation. This short review discusses the efforts to overcome water-intolerance in FLP systems, a topic that in less than five years has seen significant progress.1 Introduction2 Water-Tolerance (or Alcohol-Tolerance) in Carbonyl Reductions3 Water-Tolerance with Stronger Bases4 Water-Tolerant Non-Boron-Based Lewis Acids in FLP Chemistry5 Conclusions

scholarly journals Halogenated triphenylgallium and -indium in frustrated Lewis pair activations and hydrogenation catalysis

2017 ◽  
Vol 375 (2101) ◽  
pp. 20170014 ◽  
Author(s):  
Maotong Xu ◽  
Josephine Possart ◽  
Alexander E. Waked ◽  
Julie Roy ◽  
Werner Uhl ◽  
...  
Keyword(s):  
Lewis Acids ◽  
Lewis Acidity ◽  
Frustrated Lewis Pairs ◽  
Frustrated Lewis Pair ◽  
Hydrogenation Catalysis ◽  
Lewis Pairs

The Lewis acids Ga(C 6 F 5 ) 3 , In(C 6 F 5 ) 3 and Ga(C 6 Cl 5 ) 3 are prepared and their Lewis acidity has been probed experimentally and computationally. The species Ga(C 6 F 5 ) 3 and In(C 6 F 5 ) 3 in conjunction with phosphine donors are shown to heterolytically split H 2 and catalyse the hydrogenation of an imine. In addition, frustrated Lewis pairs (FLPs) derived from Ga(C 6 F 5 ) 3 and In(C 6 F 5 ) 3 and phosphines react with diphenyldisulfide to phosphoniumgallates or indates of the form [ t Bu 3 PSPh][PhSE(C 6 F 5 ) 3 ] and [ t Bu 3 PSPh][(μ-SPh)(E(C 6 F 5 ) 3 ) 2 ] (E = Ga, In). The potential of the FLPs based on Ga(C 6 F 5 ) 3 , In(C 6 F 5 ) 3 and Ga(C 6 Cl 5 ) 3 and phosphines is also shown in reactions with phenylacetylene to give pure or mixtures of the products [ t Bu 3 PH][PhCCE(C 6 X 5 ) 3 ] and R 3 P(Ph)C=C(H)E(C 6 X 5 ) 3 . A number of these species are crystallographically characterized. The implications for the use of these species in FLP chemistry are considered. This article is part of the themed issue ‘Frustrated Lewis pair chemistry’.

Lewis Acid Assisted C–CN Cleavage of Benzonitrile Using [(dippe)NiH]2

Synlett ◽  
2017 ◽  
Vol 29 (06) ◽  
pp. 747-753 ◽  
Author(s):  
William Jones ◽  
Brett Swartz ◽  
William Brennessel
Keyword(s):  
Low Temperature ◽  
Lewis Acid ◽  
Lewis Acids ◽  
Reaction Rate ◽  
Acid Dissociation ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Dramatic Variation

Reactions of [(dippe)NiH]2 with benzonitrile and varying concentrations of Lewis acids (primarily BPh3 and BF3) have shown a dramatic variation of reaction rate compared to the same reaction without Lewis acids. When less than one equivalent of Lewis acid is used, the reaction rate is as much as 100 times greater than without Lewis acid. Boron exchange was observed with less than one equivalent of Lewis acid allowing the formation of a Ni(0)–η2-aryl complex (observed by low-temperature NMR and calculations) to which the Lewis acid is postulated to re-coordinate as the rate-limiting step allowing the formation of a stable Ni(II) product. When one equivalent or greater of Lewis acid is used, the reaction shows dramatic inhibition even compared to the reaction without Lewis acid. Lewis acid dissociation can be considered as the rate-limiting step under these conditions. The overall work detailed herein has shown the importance of Lewis acids in the activation of benzonitriles due to the strengthening of the C–N bond allowing for increased stabilization of the products.

Homologation of Alkyl Acetates, Alkyl Ethers, Acetals and Ketals by Formal Insertion of Diazo Compounds into a Carbon-Carbon Bond

Synthesis ◽  
2021 ◽  
Author(s):  
Fei Wang ◽  
Junyi Yi ◽  
Yoshihiro Nishimoto ◽  
Makoto Yasuda
Keyword(s):  
Lewis Acid ◽  
Lewis Acids ◽  
Diazo Compounds ◽  
Lewis Acidity ◽  
Carbon Carbon Bond ◽  
Leaving Group ◽  
Diazo Esters ◽  
Alkyl Ethers ◽  
Alkyl Acetates ◽  
Leaving Groups

We have accomplished homologation of alkyl acetates, alkyl ethers, acetals, and ketals via formal insertion of diazo esters into carbon-carbon σ-bonds. The combined Lewis acid of InI3 with Me3SiBr catalyzed the homologation of alkyl acetates and alkyl ethers. That of acetals and ketals was catalyzed solely by the use of InBr3. The key point of the homologation mechanism is that the indium-based Lewis acids have the appropriate amount of Lewis acidity to achieve both the abstraction and release of leaving groups. The abstraction of a leaving group by an indium-based Lewis acid, the electrophilic addition of carbocation or oxonium intermediates to diazo esters followed by the rearrangement of carbon substituents provides the corresponding cation intermediates. Finally, the leaving group that is captured by the Lewis acid bonds with cation intermediates to furnish the homologated products.

scholarly journals Glucose Conversion into 5-Hydroxymethylfurfural over Niobium Oxides Supported on Natural Rubber-Derived Carbon/Silica Nanocomposite

Catalysts ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 887
Author(s):  
Rujeeluk Khumho ◽  
Satit Yousatit ◽  
Chawalit Ngamcharussrivichai
Keyword(s):  
Natural Rubber ◽  
Lewis Acid ◽  
Value Added ◽  
Acid Sites ◽  
Superior Performance ◽  
Lewis Acidity ◽  
Lewis Acid Sites ◽  
Niobium Oxides ◽  
Silica Nanocomposite ◽  
Loading Amount

5-Hydroxymethylfurfural (HMF) is one of the most important lignocellulosic biomass-derived platform molecules for production of renewable fuel additives, liquid hydrocarbon fuels, and value-added chemicals. The present work developed niobium oxides (Nb2O5) supported on mesoporous carbon/silica nanocomposite (MCS), as novel solid base catalyst for synthesis of HMF via one-pot glucose conversion in a biphasic solvent. The MCS material was prepared via carbonization using natural rubber dispersed in hexagonal mesoporous silica (HMS) as a precursor. The Nb2O5 supported on MCS (Nb/MCS) catalyst with an niobium (Nb) loading amount of 10 wt.% (10-Nb/MCS) was characterized by high dispersion, and so tiny crystallites of Nb2O5, on the MCS surface, good textural properties, and the presence of Bronsted and Lewis acid sites with weak-to-medium strength. By varying the Nb loading amount, the crystallite size of Nb2O5 and molar ratio of Bronsted/Lewis acidity could be tuned. When compared to the pure silica HMS-supported Nb catalyst, the Nb/MCS material showed a superior glucose conversion and HMF yield. The highest HMF yield of 57.5% was achieved at 93.2% glucose conversion when using 10-Nb/MCS as catalyst (5 wt.% loading with respect to the mass of glucose) at 190 °C for 1 h. Furthermore, 10-Nb/MCS had excellent catalytic stability, being reused in the reaction for five consecutive cycles during which both the glucose conversion and HMF yield were insignificantly changed. Its superior performance was ascribed to the suitable ratio of Brønsted/Lewis acid sites, and the hydrophobic properties generated from the carbon moieties dispersed in the MCS nanocomposite.

Lewis Acid-Promoted Suzuki Reaction using Palladium Chloride Anchored on a Polymer as a Catalyst

2008 ◽  
Vol 61 (8) ◽  
pp. 610 ◽  
Author(s):  
Guozhi Fan ◽  
Hanjun Zhang ◽  
Siqing Cheng ◽  
Zhandong Ren ◽  
Zhijun Hu ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Lewis Acid ◽  
Lewis Acids ◽  
Heterogeneous Catalysts ◽  
Suzuki Reaction ◽  
Cross Coupling ◽  
Palladium Chloride ◽  
Coupling Reactions ◽  
Cross Coupling Reactions ◽  
Recoverable Catalyst

Palladium chloride anchored on polystyrene modified by 5-amino-1,10-phenanthroline was prepared and used as an efficient recoverable catalyst for Suzuki cross-coupling reactions. The heterogeneous catalysts can be easily separated from the reaction mixture and reused for five cycles without significant Pd leaching and loss of catalytic activity. Rate enhancement in the Suzuki reaction by Lewis acids was also studied.

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