A series of novel water-soluble AuI complexes using sulfonated N-heterocyclic imidazolylidene carbenes as ligands was prepared by transmetalation from the corresponding bis-carbene AgI complexes. ...Monocarbene AuI complexes were employed as catalysts in the hydration of terminal alkynes in aqueous media. Hydrations proceeded selectively according to Markovnikov’s rule with high rates and turnover numbers (up to TON 935). The highest activity was achieved in hydration of p-ethynylanisole (TOF = 400.2 h−1). Effects of additives (H2SO4, AgOTs, AgBF4, NaOH) were examined. Corresponding bis-carbene AuI complexes were also isolated and characterized. However, these exhibit no catalytic activity in the explored systems.
The bromate–aniline oscillatory reaction was discovered 4 decades ago, but neither the detailed mechanism nor the key products or intermediates of the reaction were described. We report herein a ...detailed study of this reaction, which yielded new insights. We found that oscillatory oxidation of aniline by acidic bromate proceeds, to a significant extent, via a novel reaction pathway with the periodic release of carbon dioxide. Several products were isolated, and their structures, not described so far, were justified on the basis of MS and NMR. One of the main products of the reaction associated with the CO2 release route can be assigned to 2,2-dibromo-5-(phenylimino)cyclopent-3-en-1-one. A number of known compounds produced in the studied reaction, including unexpected brominated 1-phenylpyrroles and 1-phenylmaleimides, were identified by comparison with standards. A mechanism is suggested to explain the appearance of the detected compounds, based on coupling of the anilino radical with the produced 1,4-benzoquinone. We assume that the radical adduct reacts with bromine to form a cyclopropanone intermediate that undergoes a Favorskii-type rearrangement. Further oxidation and bromination steps including decarboxylation lead to the found brominated phenyliminocyclopentenones. The detected derivatives of 1-phenylpyrrole could be produced by a one-electron oxidation of a proposed intermediate 2-phenylamino-5-bromocyclopenta-1,3-dien-1-ol followed by β-scission with the abstraction of carbon monoxide. Such a mechanism is known from the combustion chemistry of cyclopentadiene. The proposed mechanism of this reaction provides a framework for understanding the observed oscillatory kinetics.
Novel oxotriazinoindoles (
OTI
s) were recently reported as highly efficient and selective aldose reductase inhibitors. Here, a series of novel
N(2)
-substituted oxotriazinoindoles was developed with ...the aim to investigate molecular interactions within the aldose reductase (ALR2) inhibitor binding site. About twice increased inhibition efficacy of the most efficient derivative
14
(
N(2)
-CH
2
CH
2
COOH) compared to the unsubstituted lead
OTI
was obtained, yet at the expense of selectivity relative to anti-target aldehyde reductase (ALR1). To explain the major drop in selectivity, observed also in other
N(2)
-substituted derivatives, in silico molecular modeling approach revealed the role of extra interactions with the residues of Arg309, Arg312 and Met302 located in the additional
C
-terminal loop of ALR1 missing in ALR2, which can prevent or enhance binding in ALR1. These key findings will be used for development of the next generation of selective OTI inhibitors.
Fe–Li Interactions in Ferrocenyllithium Compounds Malastová, Andrea; Vallo, Ján; Almássy, Ambroz ...
European journal of inorganic chemistry,
January 10, 2017, Letnik:
2017, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Intermetallic Fe–Li interactions likely occur during some stereoselective lithiation reactions of ferrocene derivatives. The nature of this interaction was assessed for a ferrocene–methyllithium ...complex as a model system by coupled‐cluster methods CCSD(T). The CCSD(T) calculations predicted an interaction energy of –38.0 kJ mol–1 and an Fe–Li distance of 2.75 Å. The abilities of commonly used DFT functionals to describe this interaction were also screened. The best agreement of the structural parameters (energy and Fe–Li distance) with the CCSD(T) results was achieved with the dispersion‐corrected TPSS functional. DFT calculations were also used for natural bond orbital analysis of the intramolecular Fe–Li interactions in benzylferrocene ortho‐lithiated at the phenyl ring. This dimetallic bond can be explained as a donor–acceptor orbital interaction between the Fe lone pair or the C–Fe bonding electrons with the empty Li orbitals.
Bonding interactions between the iron and lithium atoms in ferrocenyl organolithium compounds are described by quantum‐chemical computational methods DFT, MP2, and CCSD(T).
We present an experiment which was designed to assess the separation technique skills of the gifted high school students who attended the 50th International Chemistry Olympiad 2018. The procedure ...consists of two synthetic tasks and is also applicable for teaching undergraduates. The haloform reaction of 2-acetonaphthone with sodium hypochlorite in commercial bleach gave the corresponding carboxylate salt and some unreacted 2-acetonaphthone. This unreacted material is separated and then treated with in situ prepared Brady’s reagent to give a near-quantitative yield of the hydrazone, while acidification of the carboxylate salt affords the corresponding carboxylic acid. The procedure includes several separation techniques: acid–base extraction, TLC analysis, and suction filtration. The grading of the student’s work based on the combined yield of both products avoids having to account for the effects of temperature, reaction time, and reagent quality on the efficiency of the haloform reaction. The duration of the experiment is 3–4 h of working time, depending on the student’s time management skills.
•Ferrocenyl phosphinites isomerizes to phosphane-oxides•DFT calculations suggest that the isomerization proceeds via cyclic transition state•Carbanion-initiated phospha-Brook rearrangement affords ...ferrocene arylphosphane•Brook rearrangement proceed from BH3 complexed as well as unprotected phosphinite
Ferrocene-containing phosphorus derivatives are important as ligands in transition-metal catalysis. We have investigated the synthesis of ferrocene-based phosphanes from corresponding phosphinites via retro-phospha-Brook rearrangement. Ferrocenyl phosphinites isomerize to thermodynamically more stable phosphine oxides. Interestingly, retro-phospha-Brook rearrangement proceeds on the adjacent phenyl ring with the assistance of the ferrocenyl moiety. DFT calculations provided insight into the reaction mechanisms of these transformations. Isomerization probably proceeds intramolecularly with the participation of developing charge stabilization with iron´s d-orbitals. BH3 complexation seems to favor the phosphinite structure as was evidenced by 31P-11B scalar coupling. Retro-phospha-Brook rearrangement also likely proceeds as intramolecular migration of the phosphanyl group from oxygen to carbon, from both BH3 complexes and the uncomplexed starting material.
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Diastereoselective ortho‐lithiation of ferrocenes is a principal strategy for the synthesis of chiral ferrocene ligands. Dilithiation of (R)‐1‐(2‐bromophenyl)‐1‐ferrocenyl‐N,N‐dimethylmethanamine ...leads to a dilithium intermediate, which can be transformed to a Taniaphos ligand with (R,Rp)‐configuration. On the other hand, lithiation of (R)‐1‐phenyl‐1‐ferrocenyl‐N,N‐dimethylmethanamine affords a lithiated product with opposite configuration of the stereogenic plane. Presumably, the second lithium atom attached at the ortho‐position of the phenyl ring is responsible for this difference through the intramolecular multicenter arrangement involving both lithium atoms and their adjacent carbon atoms, the iron atom of the ferrocenyl moiety, and the nitrogen atom of the amino group. This hypothesis has been supported also by quantum chemical calculations.
Diastereoselective ortho‐lithiation of ferrocenyl(phenyl)methanamines was studied by 7Li NMR spectroscopy and DFT calculations. The configurations of the phosphane products were confirmed by X‐ray crystallography. The different facial selectivities of the lithiation can be explained by the multicenter arrangement of the dilithium transition state, which features also Fe–Li interactions.
An intramolecular Li–Si exchange was observed on various lithiated ferrocenylbenzyl silyl ethers. The thermodynamically more stable C‐silylated isomers were isolated in good yields and fully ...characterized. The reaction mechanism of the 1,4 retro‐Brook rearrangement was investigated by DFT calculations. Two distinct reaction routes were proposed and a possible stabilization effect of the ferrocenyl fragment on the C‐silylated isomers was described. The diastereoselective rearrangement of the trimethylsilyl group to the ortho position of the ferrocenyl cyclopentadienyl ring was also accomplished and the absolute configuration of the product was determined.
Rearrange it: The lithiation of 2‐bromophenyl‐substituted ferrocenyl silyl ethers initiates an effective 1,4‐retro‐Brook rearrangement (see scheme, R=methyl, tBu, or iPr). This rearrangement proceeds also if a carbanionic intermediate is generated by diastereoselective ortho‐lithiation of the ferrocene moiety.
Chiral ferrocene phosphane–carbenes are good ligands for the copper-catalyzed 1,4-addition of Grignard reagents to various Michael acceptors. The products were obtained in high enantiomeric purity ...(up to e.r. = 95:5) and excellent regioselectivity (r.r. = 99:1). These ligands are also useful for domino conjugate addition followed by enolate trapping with imine and aldehyde.
Chiral ferrocene phosphane–carbenes are useful in the copper-catalyzed 1,4-addition of Grignard reagents to cyclic α,β-unsaturated carbonyl compounds. The products were obtained in high enantiomeric purity (up to e.r. = 95:5) and excellent regioselectivity. These ligands are applicable also for domino conjugate addition followed by reaction with imine or aldehyde. Display omitted
•Ferrocenyl phosphane–carbene ligands are useful for Cu-catalyzed conjugate addition of Grignard reagents.•Best Michael acceptors are 5,6-dihydro-2H-pyran-2-one and cyclohex-2-enone.•The ligands are applicable also to domino conjugate addition followed by aldol or Mannich reaction.•NMR shows coordination of copper with carbene and weak coordination with phosphorus.
Synthesis of epimer of Taniaphos ligand Almássy, Ambroz; Rakovský, Erik; Malastová, Andrea ...
Journal of organometallic chemistry,
03/2016, Letnik:
805
Journal Article
Recenzirano
The spatial arrangement of groups within a chiral ligand is essential for its catalytic performance. This work describes convenient synthesis of ...(R,Sp)-1-(2-(diphenylphosphano)ferrocenyl)-1-(2-diphenylphosphanophenyl)-N,N-dimethylmethanamine, a diastereomer of the well known (R,Rp)-Taniaphos ligand. The compound was prepared from the same homochiral amine as Taniaphos by sequential twofold lithiation followed by trapping with diphenyphosphane chloride. Sequential twofold lithiation, in contrast to simultaneous dilithiation, leads to the opposite configuration of the stereogenic plane. The structure and configuration of the (R,Sp)-diastereomer along with its CuBr-complex were confirmed by X-ray structural analysis. DFT calculations elucidated underlying effects controlling the stereochemical outcome of the lithiation.
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•Epimer of Taniaphos ligand was synthesized by step-wise lithiation.•The structure of the ligands was unambiguously determined by X-ray crystallography.•Diastereoselectivity of lithiation was elucidated by quantum-chemical calculations.
