3378-72-1Relevant articles and documents
Correlating electronic and catalytic properties of frustrated Lewis pairs for imine hydrogenation
Dorkó, éva,Kótai, Bianka,F?ldes, Tamás,Gy?m?re, ádám,Pápai, Imre,Soós, Tibor
, p. 258 - 262 (2017)
Combined computational and experimental work to probe Lewis acidity of some boranes to be used in FLP hydrogenation. Gutmann-Beckett method of estimating Lewis acidity has limited capacity for sterically congested boranes. Calculated hydride affinity is a more appropriate tool for gauging Lewis acidity and correlate their FLP hydrogenation utility.
Synthesis of a diboryl-N-heterocycle and its conversion to a bidentate cationic Lewis acid
Farrell, Jeffrey M.,Stephan, Douglas W.
, p. 14322 - 14325 (2015)
Sequential reaction of 2-lithio-1-methylimidazole with 9-borabicyclo[3.3.1]nonane (9-BBN) dimer and 9-Cl-9-BBN yields diboryl-N-heterocycle C4H5N2(H)(BC8H14)2 (1). Reaction of 1 with I2 results in the net substitution of chelated hydride for a singly boron-bound iodide to produce C4H5N2(I)(BC8H14)2 (2). Conversely, reaction of 1 with [Ph3C][B(C6F5)4] results in the formation of the bidentate cationic Lewis acid [(C4H5N2)(BC8H14)2][B(C6F5)4] (3). Compound 3 catalyzes the hydrogenation of N-benzylidene-tert-butylamine at room-temperature.
Reaction of carbon oxides with an ethylene-bridged PH/B Lewis pair
Sun, Qiu,Daniliuc, Constantin G.,Kehr, Gerald,Erker, Gerhard
, p. 3523 - 3528 (2021)
The reaction of 2,4,6-tri(tert-butyl)phenyl vinyl phosphane with Piers’ borane [HB(C6F5)2] gave the ethylene-bridged PH/B frustrated Lewis pair (FLP) system. It is a monomer at high temperature (>323 K), but exists as an associated 12-membered macrocyclic trimer below 273 K. The PH/B FLP splits dihydrogen and serves as a metal-free hydrogenation catalyst. It adds carbon dioxide. It serves as a PH/B template for the reduction of carbon monoxide by the HB(C6F5)2borane to the formyl stage. The resulting six membered P/B/O containing heterocycle is opened upon treatment with pyridine and it reacts with benzaldehyde in a boron mediated Claisen-Tishchenko reaction.
Iridium(III) Complexes Bearing Chelating Bis-NHC Ligands and Their Application in the Catalytic Reduction of Imines
Aznarez, Francisco,Iglesias, Manuel,Hepp, Alexander,Veit, Benjamin,Sanz Miguel, Pablo J.,Oro, Luis A.,Jin, Guo-Xin,Hahn, F. Ekkehardt
, p. 4598 - 4603 (2016)
The IrIIIcomplexes 4 and 5 bearing bis-NHC ligands (NHC = N-heterocyclic carbene) composed of one classical NR,NR NHC and one N,NR NHC donor were prepared by the reaction of the azolium/azole compounds 2I and 3Br, respectively, with [{Cp*IrCl(μ-Cl)}2] (Cp=η5-C5Me5) in the presence of NaOAc as base. Most likely, the salts 2I and 3Br were first selectively deprotonated at the C2 position of the disubstituted (NR,NR) diazaheterocycle to generate an NHC donor, which then coordinated to the IrIIIcenter. Subsequently, NaOAc promoted C–H bond activation at the pendant imidazole moiety of the intermediate IrIIImono-NHC complexes led to the formation of the six-membered iridacycles 4 and 5, which bear a chelating, doubly C-metalated C(NHC)^C(NHC′) bis-NHC ligand. The IrIIIcomplexes 4 and 5 were tested as precatalysts for the reduction of imines with molecular hydrogen. Moderate to good activity was observed at a catalyst loading of 5 mol-% and an H2pressure of 3 bar in MeOH.
Influence of the lewis acidity of gallium atoms on the reactivity of a frustrated lewis pair: Experimental and theoretical studies
Possart, Josephine,Uhl, Werner
, p. 1314 - 1323 (2018)
The reactivity of the Ga/P-based frustrated Lewis pair (FLP) Mes2P-C[=C(H)-Ph]-GatBu2 (3) is influenced by the relatively weak Lewis acidity of its Ga atom and differs significantly from that of the analogous Al compound 1. The adduct of 3 with CO2 was only detectable at low temperature by NMR spectroscopy. Benzaldehyde was coordinated only via a Ga-O bond; the P atom was not involved. In contrast, a relatively persistent adduct was formed with soft CS2 to yield a five-membered GaCPCS heterocycle. Dehydrocoupling with H3B←NHMe2 afforded the dimeric amidoborane (H2B-NMe2)2, while an adduct with a GaCPBN heterocycle was isolated with the sterically less shielded ammonia-borane H3B←NH3. The latter product was unstable in solution and decomposed by H2 elimination and formation of oligomeric BN compounds. Small quantities of 3 catalyzed hydrogen transfer from H3B←NH3 to an imine. The Lewis acidities of the Al/P- and Ga/P-based FLPs were examined by experiments (Gutmann-Beckett method) and by calculation of the fluoride ion affinity (including the B and In analogues). The Al compound is the strongest Lewis acid; the Ga FLP is significantly weaker but is a stronger F- acceptor in comparison to the unknown analogues of B and In. These results reflect the different reactivities of these FLPs and may help to develop FLPs with finely adjusted properties.
Imine reduction with me2s-bh3
Kamal, Mohammad M.,Liu, Zhizhou,Vidovi?, Dragoslav,Zhai, Siyuan
, (2021/09/13)
Although there exists a variety of different catalysts for hydroboration of organic substrates such as aldehydes, ketones, imines, nitriles etc., recent evidence suggests that tetra-coordinate borohydride species, formed by activation, redistribution, or decomposition of boron reagents, are the true hydride donors. We then proposed that Me2S-BH3 could also act as a hydride donor for the reduction of various imines, as similar compounds have been observed to reduce carbonyl substrates. This boron reagent was shown to be an effective and chemoselective hydroboration reagent for a wide variety of imines.
Metallic Barium: A Versatile and Efficient Hydrogenation Catalyst
Stegner, Philipp,F?rber, Christian,Zenneck, Ulrich,Knüpfer, Christian,Eyselein, Jonathan,Wiesinger, Michael,Harder, Sjoerd
supporting information, p. 4252 - 4258 (2020/12/22)
Ba metal was activated by evaporation and cocondensation with heptane. This black powder is a highly active hydrogenation catalyst for the reduction of a variety of unactivated (non-conjugated) mono-, di- and tri-substituted alkenes, tetraphenylethylene, benzene, a number of polycyclic aromatic hydrocarbons, aldimines, ketimines and various pyridines. The performance of metallic Ba in hydrogenation catalysis tops that of the hitherto most active molecular group 2 metal catalysts. Depending on the substrate, two different catalytic cycles are proposed. A: a classical metal hydride cycle and B: the Ba metal cycle. The latter is proposed for substrates that are easily reduced by Ba0, that is, conjugated alkenes, alkynes, annulated rings, imines and pyridines. In addition, a mechanism in which Ba0 and BaH2 are both essential is discussed. DFT calculations on benzene hydrogenation with a simple model system (Ba/BaH2) confirm that the presence of metallic Ba has an accelerating effect.
