The application of novel boron complexes in asymmetric transfer hydrogenation of aromatic ketones (original) (raw)

Developments in transfer hydrogenations of aromatic ketones catalyzed by boron compounds

Journal of Coordination Chemistry, 2017

Boron complexes BL1 and BL2 were prepared from O-donor ligands, 2,2′-(1E,1′E)-(ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(methane-1yl-1-ylidene)diphenol (L1) and 2,2′-(propane-1,3-diylbis(azan-1-yl-1ylidene))bis(methane-1-yl-1-ylidene)diphenol (L2). The complexes were fully characterized by 1 H and 13 C NMR, LC-MS/MS, TGA/DTA, UV-Vis, elemental analysis, SEM, and FTIR. The transfer hydrogenation of acetophenone derivatives was investigated by the boron complexes in the presence of isoPrOH, as the hydrogen source, under basic condition with NaOH. The results showed that the boron complexes were promising catalytic precursors for transfer hydrogenation of aromatic ketones in 0.1 M isoPrOH solution (up to 99%). Both steric and electronic factors of this class of molecules had a significant impact on the catalytic properties.

Boron containing chiral schiff bases: Synthesis and catalytic activity in asymmetric transfer hydrogenation (ATH) of ketones

Journal of Molecular Structure, 2019

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Fluorine/phenyl chelated boron complexes: Synthesis, fluorescence properties and catalyst for transfer hydrogenation of aromatic ketones

Journal of Fluorine Chemistry, 2014

The fluorine/phenyl chelated boron complexes, one of the most important types of fluorescent dyes, have been extensively studied. In recent years, fluorescent materials of organic fluorine or phenyl boron complexes continue to be developed because of their utilities in many various fields of current research, and the many important applications in science and technology. Among boron compounds, as the most well-known and having excellent fluorescent properties is borondipyrromethenes (BODIPYs) with N,N-bidentate ligands [1-8]. These types of compounds are widely used as chemosensors [9,10], organic light-emitting diodes (OLEDs) [11,12], electron-transport materials [13,14], sensitizers in solar cells [15,16], nonlinear optics [17,18] as well as antibacterial properties [19] and hydrogentransfer catalysts [20-22]. Therefore, in recent years, design and synthesis of novel boron compounds to explore their broad applications have attracted much attention. Among boron compounds, three main types of BF 2 /BPh 2 chelated boron complexes are classified as N,N-bidentate, N,O-bidentate and O,O-bidentate compounds. Compared with three-coordinated boron complexes, which require bulky substituents (such as mesityl or other groups) to stabilize four-coordinated boron complexes are in general stable and can be obtained readily [23]. Also, it is known that boron is strongly electrophilic by virtue of its tendency to fill the vacant orbital and complete the octet, so in contrast to organometallic compounds, organoboron compounds are in general more stable due to the increased covalency of B-O and B N bonds [24]

Asymmetric transfer hydrogenation of ketones in aqueous solution catalyzed by rhodium(III) complexes with C2-symmetric fluorene-ligands containing chiral (1R,2R)-cyclohexane-1,2-diamine

Journal of the Brazilian Chemical Society, 2010

Dois ligantes C 2-simétricos bis(sulfonamide) contendo o fluoreno-quiral (1R,2R)-ciclohexano-1,2-diamina foram complexados com Rh III (Cp*) e usados como catalizador para redução aromática de cetonas. Os alcoois secundários correspondentes foram obtidos com ee 87-100% e rendimento de 85-99%, sob condições de transferência de hidrogenio assimétrica (THA), usando formato de sodio aquoso como fonte de hidretos. Usando acetofenona, obteve-se ee de 94% e rendimento de 86-97%, com uma razão substrato/catalizador de 10.000. Two C 2-symmetric bis(sulfonamide) ligands containing fluorene-chiral (1R,2R)-cyclohexane-1,2-diamine were complexed to Rh III (Cp*) and used as catalyst to reduce aromatic ketones. The corresponding chiral secondary alcohols were obtained in 87-100% ee and 85-99% yield, under asymmetric transfer hydrogenation (ATH) conditions using aqueous sodium formate as the hydride source. With acetophenone, 94% ee and 86-97% yield was achieved with substrate/catalyst (S/C) ratio of 10,000.

Bicyclo[2.2.2]octane-derived chiral ligands—synthesis and application of BODOLs in the asymmetric reduction of acetophenone with catecholborane

Tetrahedron-asymmetry, 2008

An improved synthetic route to the bicyclo[2.2.2]octane-2,6-diol ligands (2,6-BODOLs) allowed an increased structural variation of the ligand side-arm. The addition of aromatic or vinylic Grignard reagents to hydroxyketone 1 was highly selective and ligands 3f–3l were isolated in 84–97% yield. The addition of alkyl Grignard reagents containing β-hydrogens resulted in lower yields (13–71%) due to competing ketone reduction. A number of 2,5-BODOLs were synthesized using a similar methodology. The ligands, together with Ti(OiPr)4, were tested in the asymmetric reduction of acetophenone with catecholborane (up to 98% ee). 1-Naphthyl-BODOL 3i was employed as an allylboration reagent to benzaldehyde together with Sc(OTf)3, resulting in (1S)-1-phenyl-3-buten-1-ol in 80% ee.

Facile access to functionalized chiral secondary benzylic boronic esters via catalytic asymmetric hydroboration

Chemical Science, 2019

Allylic and homoallylic phosphonates bearing an aryl or heteroaryl substituent at the g-or d-position undergo rhodium-catalyzed asymmetric hydroboration by pinacolborane to give functionalized chiral secondary benzylic boronic esters in yields up to 86% and enantiomer ratios up to 99 : 1. Compared to minimallyfunctionalized terminal and 1,1-disubstituted vinyl arenes, there are relatively few reports of efficient catalytic asymmetric hydroboration (CAHB) of more highly functionalized internal alkenes. Phosphonate substrates bearing a variety of common heterocyclic ring systems, including furan, indole, pyrrole and thiophene derivatives, as well as those bearing basic nitrogen substituents (e.g., morpholine and pyrazine) are tolerated, although donor substituents positioned in close proximity of the alkene can influence the course of the reaction. Stereoisomeric (E)-and (Z)-substrates afford the same major enantiomer of the borated product. Deuterium-labelling studies reveal that rapid (Z)-to (E)-alkene isomerization accounts for the observed (E/Z)-stereoconvergence during CAHB. The synthetic utility of the chiral boronic ester products is illustrated by stereospecific C-B bond transformations including stereoretentive electrophile promoted 1,2-B-to-C migrations, stereoinvertive S E 2 reactions of boron-ate complexes with electrophiles, and stereoretentive palladium-and rhodium-catalyzed cross-coupling protocols.

Chiral Complexes of RhI Containing Binaphthalene-Core P,S-Heterobidentate Ligands − Synthesis, Characterization, and Catalytic Activity in Asymmetric Hydrogenation of α,β-Unsaturated Acids and Esters

European Journal of Inorganic Chemistry, 2003

The enantiopure complexes 3a and 3b [Rh(NBD)(P,S)] + BF 4 − [P,S = (S)-2-(diphenylphosphanyl)-2Ј-(methylthio)-1,1Ј-binaphthalene (a); (S)-2-(diphenylphosphanyl)-2Ј-(isopropylthio)-1,1Ј-binaphthalene (b)] have been prepared from [Rh(NBD)(THF) 2 ] + BF 4 − by reaction with a stoichiometric amount of the appropriate P,S-heterobidentate ligand. Single-crystal X-ray analysis of the S-methyl derivative shows that the seven-membered chelate ring is locked in a boat-like conformation with the methyl group in the equator-[a