TAMOF‐1, a homochiral metal‐organic framework (MOF) constructed from an amino acid derivative and Cu(II), was investigated as a heterogeneous catalyst in kinetic resolutions involving the ring ...opening of styrene oxide with a set of anilines. The branched products generated from the ring opening of styrene oxide with anilines and the unreacted epoxide were obtained with moderately high enantiomeric excesses. The linear product arising from the attack on the non‐benzylic position of styrene oxide underwent a second kinetic resolution by reacting with the epoxide, resulting in an amplification of its final enantiomeric excess and a concomitant formation of an array of isomeric aminodiols. Computational studies confirmed the experimental results, providing a deep understanding of the whole process involving the two successive kinetic resolutions. Furthermore, TAMOF‐1 activity was conserved after several catalytic cycles. The ring opening of a meso‐epoxide with aniline catalyzed by TAMOF‐1 was also studied and moderate enantioselectivities were obtained.
The homochiral metal‐organic framework TAMOF‐1 was used as a heterogeneous catalyst in the kinetic resolution of styrene oxide by ring opening reactions with anilines. The linear products underwent a second KR resulting in an amplification of the final stereoselectivity (subtractive Horeau amplification effect). Computational studies rationalized the two successive KR while providing a deep understanding of the process.
The use of supramolecular interactions in catalysis has undergone major growth in the last decade and has contributed to the major advances achieved in the field of enantioselective catalysis. Of the ...various approaches that use supramolecular interactions in enantioselective catalysis, this article highlights different supramolecular strategies to generate a set of enantiopure ligands (or enantioselective catalysts) that retain the majority of the backbone's structural features, yet at the same time incorporate subtle changes at its active site that depend on the structural characteristics of the regulation agent (RA) employed.
The use of supramolecular interactions in catalysis has undergone major growth in the last decade and has contributed to the major advances achieved in the field of enantioselective catalysis.
Carrier mobility in organic thin films is a key parameter for devices that use molecules as selective contacts such as organic and perovskite solar cells. Herein, we describe the synthesis of a free ...base porphyrin symmetrically substituted with four meso‐4‐aminophenyl‐N,N‐bis(2′,4′‐dimethoxy1,1′‐biphenyl‐4‐yl) units and its metalloporphyrin. The electrochemical and photophysical properties for both porphyrins have been measured. The results show that the HOMO and LUMO energy levels are appropriate for use as hole transport materials (HTM) in solar cells. Moreover, measurements of the carrier mobility by using the space charge limited current (SCLC) method in organic thin films leads to a hole mobility value of 2.4 ± 0.5 × 10–5 cm2/V s and 8.0 ± 0.5 × 10–6 cm2/V s for the zinc porphyrin and the free base, respectively. Upon addition of chemical dopants, the mobility values increased to 8.8 ± 0.5 × 10–4 cm2/V s, for the zinc porphyrin, and 5.2 ± 0.5 × 10–4 cm2/V s for the free base porphyrin. These values are close to the reference molecule spiro‐OMeTAD, which has a mobility value of 2.5 ± 0.5 × 10–4 cm2/V s measured under identical conditions.
Two o,p‐dimethoxybiphenyl arylamine substituted derivatives of symmetric free base porphyrin and its Zn derivative have been synthesized and characterized. These molecules can be used as electron‐donor moieties to common materials such as fullerenes. Significant differences were identified between the two porphyrins although their structures differ only in a single atom.
During the last few decades, rhodium-catalysed asymmetric hydrogenation of diverse alkene classes has emerged as a powerful synthetic tool in the pharmaceutical industry, contributing to the ...manufacturing of chiral drugs, recent drug candidates for clinical trials, and major synthetic precursors of drugs. Numerous efficient chiral rhodium complexes, most of which are derived from enantiopure phosphorus ligands, have been employed for the preparation of chiral drugs and intermediates thereof. This
review article
is intended to provide an updated overview of the most striking contributions in this field, organised according to substrate class: acrylate derivatives, itaconate derivatives, α-substituted enamides, α-arylenol acetates, and minimally functionalised olefins.
This
review article
summarises research on rhodium-catalysed asymmetric hydrogenation of diverse alkene classes for the preparation of chiral drugs.
Herein is reported the preparation of a set of narrow bite‐angle P–OP ligands the backbone of which contains a stereogenic carbon atom. The synthesis was based on a Corey–Bakshi–Shibata ...(CBS)‐catalyzed asymmetric reduction of phosphomides. The structure of the resulting 1,1‐P–OP ligands, which was selectively tuned through adequate combination of the configuration of the stereogenic carbon atom, its substituent, and the phosphite fragment, proved crucial for providing a rigid environment around the metal center, as evidenced by X‐ray crystallography. These new ligands enabled very good catalytic properties in the Rh‐mediated enantioselective hydrogenation and hydroformylation of challenging and model substrates (up to 99 % ee). Whereas for asymmetric hydrogenation the optimal P–OP ligand depended on the substrate, for hydroformylation, a single ligand was the highest‐performing one for almost all studied substrates: it contains an R‐configured stereogenic carbon atom between the two phosphorus ligating groups, and an S‐configured 3,3′‐diphenyl‐substituted biaryl unit.
Ligand design: Narrow‐bite‐angle P–OP ligands incorporating a stereogenic carbon atom in their backbone have been synthesized by Corey–Bakshi–Shibata (CBS)‐catalyzed asymmetric reduction of the corresponding intermediates followed by O‐phosphorylation. Rhodium complexes of these ligands provided very good catalytic performance in hydroformylations and hydrogenations (see scheme).
In this work, we assess the possible reasons for the differences observed in open circuit voltage ( V OC ) in mixed cation perovskite solar cells when comparing four different hole transport ...materials (HTMs), namely TAE-1 , TAE-3 , TAE-4 and spiro-OMeTAD . All these HTMs present close chemical and physical properties, however, once they are finally deposited onto the perovskite layer, the HTMs provide different performance characteristics. Additional to the evaluation of the HTM influence on recombination, we find that, upon deposition of the organic HTM on top of the perovskite, there is an important change in the energy level position, and the impact on the device V OC is discussed. We consider that this experimental observation could be general for other organic HTMs and would justify the difficulties in finding molecules and materials that could improve the efficiency of perovskite solar cells overcoming the solar-to-energy conversion efficiency of solar cells made using spiro-OMeTAD as a hole selective contact.
MaxPHOS is an active and robust P‐stereogenic ligand for asymmetric catalysis. The presence of an NH bridge between the two phosphine moieties allows the NH/PH tautomerism to take place. The ...neutral ligand, in which the NH form predominates, is an air‐sensitive compound. However, protonation of MaxPHOS leads to the stable PH form of the ligand, in which the overall positive charge is distributed on both P centers. This protonation turns the MaxPHOS⋅HBF4 salt 3 into an air‐stable compound both in the solid state and in solution. The salt 3 is also a convenient precursor for the preparation of rhodium(I) complexes by direct ligand exchange with the complex Rh(acac)(cod). Finally, the corresponding rhodium(I)‐MaxPHOS complex was tested in the asymmetric hydrogenation of a wide range of substrates. The complex proved to be a highly selective and robust system in these reactions.
Small amounts of achiral polyether binders are employed to enhance the enantioselectivity of the hydroformylation of an array of diversely substituted substrates (increase of up to 62 % ee for vinyl ...acetate) mediated by chiral rhodium complexes derived from the α,ω‐bis(phosphite)–polyether ligands 1. To the best of our knowledge, this study represents an unprecedented successful example of the positive regulation of enantioselectivity in hydroformylations.
Adaptive hydroformylators: Small amounts of achiral polyethyleneoxy binders are employed to enhance the enantioselectivity in the hydroformylation of an array of diversely substituted alkenes (see scheme). The enantioselectivity was increased by up to 62 % ee (for vinyl acetate).
Rhodium complexes derived from conformationally transformable α,ω-bisphosphite ligands combined with a suitable alkali metal BArF salt as a regulation agent (RA) provide high regio- and ...enantioselectivities in the asymmetric hydroformylation (AHF) of three heterocyclic olefins. The outcome of the AHF could be exquisitely regulated by choosing the appropriate RA with an increase in the ee, the reversal of the regioselectivity, or the complete suppression of one byproduct.
For the first time, supramolecular helical rods composed of an achiral metal complex and a complementary enantiopure monomer provided a good level of enantioinduction in asymmetric catalysis. ...Mixtures containing an achiral ligand monomer (BTA PPh2 , 2 mol %) and an enantiopure ligand-free comonomer (ester BTA, 2.5 mol %), both possessing a complementary benzene-1,3,5-tricarboxamide (BTA) central unit, were investigated in combination with Rh(cod)2BArF (1 mol %) in the asymmetric hydrogenation of dimethyl itaconate. Notably, efficient chirality transfer occurs within the hydrogen-bonded coassemblies formed by BTA Ile and the intrinsically achiral catalytic rhodium catalyst, providing the hydrogenation product with up to 85% ee. The effect of the relative content of BTA Ile as compared to the ligand was investigated. The amount of chiral comonomer can be decreased down to one-fourth of that of the ligand without deteriorating the enantioselectivity of the reaction, while the enantioselectivity decreases for mixtures containing high amounts of BTA Ile. The nonlinear relationship between the amount of chiral comonomer and the enantioselectivity indicates that chirality amplification effects are at work in this catalytic system. Also, right-handed helical rods are formed upon co-assembly of the achiral rhodium complex of BTAPPh2 and the enantiopure comonomer BTA Ile as confirmed by various spectroscopic and scattering techniques. Remarkably, the major enantiomer and the selectivity of the catalytic reaction are related to the handedness and the net helicity of the coassemblies, respectively. Further development of this class of catalysts built on chirally amplified helical scaffolds should contribute to the design of asymmetric catalysts operating with low amounts of chiral entities.
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