Catalytic stereodivergent functionalization of H2@C60

Impact of confining hydrogen molecule inside fullerenes: A glance through DFT study

CONTEXT

In this work, we have studied different properties of a series of fullerenes, from C24 to C50 by confining hydrogen molecule inside their cavity. The compression of the hydrogen molecule upon encapsulation is evidenced by its altered bond length, while a slight expansion of the fullerene cages due to H2 confinement is also noted. The chemical reactivity parameters of both the empty and H2 confined fullerenes are computed, alongside an examination of the energy components through energy decomposition analysis. Analysis of the absorption spectra indicated that both H2 encapsulated and empty fullerenes exhibited absorption in the UV region. Nevertheless, the inclusion of H2 within the fullerene cages appeared to have minimal influence on the reactivity parameters and absorption spectra, as evidenced by the comparison between the sets of empty and H2-confined fullerenes.

METHODS

The computational work including the geometry optimization, followed by the frequency analysis and other parameters has been achieved using Gaussian09 software. For doing these calculations, B3LYP and CAM-B3LYP functionals along with 6-311 + G(d,p) basis set is used. In addition, MULTIWFN software has been considered for studying bonding analysis and energy decomposition analysis for the systems.

Diastereodivergence in catalytic asymmetric conjugate addition of carbon nucleophiles

Catalytic asymmetric conjugate additions of carbon nucleophiles have emerged as a potent tool for constructing multi-stereogenic molecules with precise stereochemical control. This review explores the concept of diastereodivergence in such reactions, focusing on strategies to achieve selective access to diverse diastereomeric products upon carbon-carbon bond formation. Drawing from a rich array of examples, we delve into key approaches for controlling the stereochemical outcome of these transformations, including alteration of alkene geometry, fine-tuning of reaction parameters, synergistic catalysis, and isomerization of conjugate adducts. Additionally, we highlight the iterative strategies for conjugate additions, showcasing their potential for diastereodivergent synthesis of methyl-branched stereocenters in 1,3-relationships. By presenting a concentrated overview of this significant topic, this review aims to provide valuable insights into the design and execution of stereodivergent catalytic conjugate additions, offering new avenues for advancing stereoselective synthesis and structural diversity in organic synthesis.

Chiral bisphosphine Ph-BPE ligand: a rising star in asymmetric synthesis

Chiral 1,2-bis(2,5-diphenylphospholano)ethane (Ph-BPE) is a class of optimal organic bisphosphine ligands with C2-symmetry. Ph-BPE with its excellent catalytic performance in asymmetric synthesis has attracted much attention of chemists with increasing popularity and is growing into one of the most commonly used organophosphorus ligands, especially in asymmetric catalysis. Over two hundred examples have been reported since 2012. This review presents how Ph-BPE is utilized in asymmetric synthesis and how powerful it is as a chiral ligand or even a catalyst in a wide range of reactions including applications in the total synthesis of bioactive molecules.

Unveiling the regioselectivity of rhodium(I)-catalyzed [2 + 2 + 2] cycloaddition reactions for open-cage C70 production

The regioselective functionalization of fullerenes holds significant promise for applications in the fields of medicinal chemistry, materials science, and photovoltaics. In this study, we investigate the regioselectivity of the rhodium(I)-catalyzed [2 + 2 + 2] cycloaddition reactions between diynes and C70 as a novel procedure for generating C70 bis(fulleroid) derivatives. The aim is to shed light on the regioselectivity of the process through both experimental and computational approaches. In addition, the photooxidation of one of the C-C double bonds in the synthesized bis(fulleroids) affords open-cage C70 derivatives having a 12-membered ring opening.

Chiral Open-[60]Fullerene Ligands with Giant Dissymmetry Factors

The optical resolution of open-[60]fullerenes has been limited to only one example since 1998, while the recent advances revealed the excellence of fullerenes as revisited chiral functional materials. Different from conventional chiral induction on [60]fullerene by a multiple-functionalization, a random disruption of the spherical π-conjugation is avoidable for open-[60]fullerenes. Moreover, the macrocyclic orifices enable a metal coordination which endows modulated electronic structures on chiral chromophores. Herein, we showcase Li⁺-coordination behavior and optical resolution of three chiral open-[60]fullerene ligands, showing a giant dissymmetry factor up to 0.20 owing to a congenital topology of the spherical π-conjugation.

An Androsterone-H2 @C60 hybrid: Synthesis, Properties and Molecular Docking Simulations with SARS-Cov-2

We report the synthesis and characterization of a fullerene-steroid hybrid that contains H2 @C60 and a dehydroepiandrosterone moiety synthesized by a cyclopropanation reaction with 76 % yield. Theoretical calculations at the DFT-D3(BJ)/PBE 6-311G(d,p) level predict the most stable conformation and that the saturation of a double bond is the main factor causing the upfield shielding of the signal appearing at -3.13 ppm, which corresponds to the H2 located inside the fullerene cage. Relevant stereoelectronic parameters were also investigated and reinforce the idea that electronic interactions must be considered to develop studies on chemical-biological interactions. A molecular docking simulation predicted that the binding energy values for the protease-hybrid complexes were -9.9 kcal/mol and -13.5 kcal/mol for PLpro and 3CLpro respectively, indicating the potential use of the synthesized steroid-H2 @C60 as anti-SARS-Cov-2 agent.

Cu(I)-Catalyzed asymmetric exo-selective synthesis of substituted pyrrolidines via a 1,3-dipolar cycloaddition reaction

An (R)-DM-BINAP/Cu(CH3CN)4BF4 complex catalyzed exo-selective asymmetric 1,3-dipolar cycloaddition (1,3-DCA) reaction of imino esters with α,β-unsaturated pyrazoleamides has been developed. A series of highly functionalized pyrrolidines with multiple stereogenic centers were obtained with good yields and diastereoselectivities and excellent enantioselectivities (up to 99% ee).

New Horizons in Chemical Functionalization of Endohedral Metallofullerenes

This overview explains some new aspects of chemical functionalization of endohedral metallofullerenes (EMFs) that have been unveiled in recent years. After differences in chemical reactivity between EMFs and the corresponding empty fullerenes are discussed, cage-opening reactions of EMFs are examined. Then, the selective bisfunctionalization of EMFs is explained. Finally, single-bonding derivatization of EMFs is addressed. The diversity and applicability of the chemical functionalization of endohedral metallofullerenes are presented to readers worldwide.

Stereochemical diversity in pyrrolidine synthesis by catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides

The pyrrolidine ring is a privileged structural motif in synthetic and medicinal chemisty. This review aims to highlight the high versatility of the catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides for access to different types of stereochemical patterns in enantioselective pyrrolidine synthesis. Special attention will be paid to stereodivergent procedures giving rise to different stereoisomers from the same starting materials.

Chiral Molecular Carbon Nanostructures

Chirality is a fascinating property present in naturally occurring and artificial molecules and materials, observable as chiroptical behavior. The emerging area of carbon nanostructures has undergone tremendous development, with a wide variety of carbon nanoforms reported over the last two decades. However, despite interest in merging chirality and nanocarbons, this has been successfully achieved only in empty fullerenes, whereas in other kinds of fullerenes or carbon nanostructures such as carbon nanotubes, graphene, and graphene quantum dots (GQDs), to name the most popular systems, it is almost unknown. Therefore, controlling chirality in carbon nanostructures currently represents a major challenge for the chemical community. In this Account, we show our progress in the synthesis of chiral molecular carbon nanostructures, namely, metallofullerenes, endohedral fullerenes, GQDs, and curved molecular nanographenes, by using asymmetric catalysis and both top-down and bottom-up chemical approaches. Furthermore, we bring in a new family of lesser-known molecular chiral bilayer nanographenes, where chirality is introduced from the starting helicene moiety and a single enantiomer of the nanographene is synthesized. Some important landmarks in the development of chiral molecular carbon nanostructures shown in this Account are the application of synthesis-tailored, enantiomerically pure metallofullerenes as catalysts for hydrogen transfer reactions and the use of endohedral fullerenes to determine the effect of the incarcerated molecule in the carbon cage on the cis-trans stereoisomerization of optically active pendent moieties. Furthermore, the first top-down synthesis of chiral GQDs by functionalization with chiral alcohols is also presented. An emerging alternative to GQDs, when the desire for purity and atomistic control outweighs the cost of multistep synthesis, is the bottom-up approach, in which molecular nanographenes are formed in precise sizes and shapes and enantiomeric control is feasible. In this regard, a singular and amazing example is given by our synthesis of a single enantiomer of the first chiral bilayer nanographene, which formally represents a new family of molecular nanographenes with chirality controlled and maintained throughout their syntheses. The aforementioned synthetic chiral nanostructures represent groundbreaking nanocarbon systems where chirality is a further dimension of structural control, paving the way to a new scenario for carbon nanoforms in which chirality selection determines the properties of these novel carbon-based materials. Fine-tuning of such properties is envisioned to impact biomedical and materials science applications.

Stereodivergent Catalysis

This review covers diastereo- and enantiodivergent catalyzed reactions in acyclic and cyclic systems using metal complexes or organocatalysts. Among them, nucleophilic addition to carbon-carbon and carbon-nitrogen double bonds, α-functionalization of carbonyl compounds, allylic substitutions, and ring opening of oxiranes and aziridines are considered. The diastereodivergent synthesis of alkenes from alkynes is also included. Finally, stereodivergent intramolecular and intermolecular cycloadditions and other cyclizations are also reported.

Effect of incarcerated HF on the exohedral chemical reactivity of HF@C60

The first chemical modification on the brand new endohedral HF@C₆₀ is reported. In particular, the isomerization from optically pure (2S,5S)-cis-pyrrolidino[3,4:1,2][60]fullerene 2b to (2S,5R)-trans-pyrrolidino[3,4:1,2][60]fullerene 2b has been studied and compared with empty C₆₀ (2a) and endohedral H₂O@C₆₀ (3). The comparative study shows a kinetic order for the isomerization process of H₂O@C₆₀ > HF@C₆₀ > C₆₀, thus confirming the effect of the incarcerated species on the zwitterionic intermediate stability.

Individual (f,t A)- and (f,t C)-Fullerene-Based Nickel(II) Glycinates: Protected Chiral Amino Acids Directly Linked to a Chiral π-Electron System

Stereoselective electrosynthesis of the first individual (^f,t A)- and (^f,t C)-1,4-fullerene derivatives with a non-inherently chiral functionalization pattern is described, as well as the first example of an optically pure protected primary amino acid directly linked to the fullerene through only the chiral α-amino-acid carbon atom. An application of an auxiliary chiral nickel-Schiff base moiety as derivatizing agent allowed separation of (^f,t A)- and (^f,t C)-1,4-fullerene derivatives using an achiral stationary phase, a separation which has never been done before.

Isolation and characterization of [5,6]-pyrrolidino-Sc₃N@I(h)-C₈₀ diastereomers

Reactions of Sc3N@I(h)-C80 with aziridine derivatives were conducted to afford the corresponding mono-adducts. A pair of diastereomers of the mono-adduct [5,6]-pyrrolidino-Sc3N@I(h)-C80 was isolated and characterized by means of mass spectrometry, vis-NIR absorption spectroscopy, and electrochemical measurements. Structural analysis of the mono-adducts was conducted by NMR and single-crystal X-ray structure determinations.

Copper(i)-catalyzed heteroannulation of [60]fullerene with ketoxime acetates: preparation of novel 1-fulleropyrrolines

A cuprous bromide-catalyzed heteroannulation reaction of [60]fullerene with ketoxime acetates has been exploited to prepare novel 1-fulleropyrrolines via N–O bond cleavage and C–C/C–N formation under thermal conditions.

The journey of L-tartaric acid in the world of enantiomerically pure bis- and trisadducts of C60 with the inherently chiral trans-3 and all-trans-3 addition patterns

Inherently chiral multi-adducts of [60]fullerene represent unique chiral molecular tectons featuring fascinating optoelectronic properties. Herein we discuss the most recent progress in the synthesis of enantiomerically pure bis- and trisadducts of C60 with the inherently chiral trans-3 and all-trans-3 addition patterns utilizing cyclo-[n]-malonate tethers derived from (-)-dimethyl-2,3-O-isopropylidene-L-tartrate. Some future perspectives regarding the investigation of these chiral building blocks in modern areas of research are discussed.

Chiral fullerenes from asymmetric catalysis

Fullerenes are among the most studied molecules during the last three decades, and therefore, a huge number of chemical reactions have been tested on these new carbon allotropes. However, the aim of most of the reactions carried out on fullerenes has been to afford chemically modified fullerenes that are soluble in organic solvents or even water in the search for different mechanical, optical, or electronic properties. Therefore, although a lot of effort has been devoted to the chemical functionalization of these molecular allotropes of carbon, important aspects in the chemistry of fullerenes have not been properly addressed. In particular, the synthesis of chiral fullerenes at will in an efficient manner using asymmetric catalysis has not been previously addressed in fullerene science. Thus, despite the fact that the chirality of fullerenes has always been considered a fundamental issue, the lack of a general stereoselective synthetic methodology has restricted the use of enantiopure fullerene derivatives, which have usually been obtained only after highly expensive HPLC isolation on specific chiral columns or prepared from a pool of chiral starting materials. In this Account, we describe the first stereodivergent catalytic enantioselective syntheses in fullerene science, which have allowed the highly efficient synthesis of enantiomerically pure derivatives with total control of the stereochemical result using metallic catalysts and/or organocatalysts under very mild conditions. Density functional theory calculations strongly support the experimental findings for the assignment of the absolute configuration of the new stereocenters, which has also been ascertained by application of the sector rule and single-crystal X-ray diffraction. The use of the curved double bond of fullerene cages as a two-π-electron component in a variety of stereoselective cycloaddition reactions represents a challenging goal considering that, in contrast to most of the substituted olefins used in these reactions, pristine fullerene is a noncoordinating dipolarophile. The aforementioned features make the study of stereoselective 1,3-dipolar cycloadditions onto fullerenes a unique scenario to shed light onto important mechanistic aspects. On the other hand, the availability of achiral starting materials as well as the use of nonexpensive asymmetric catalysts should provide access to chiral fullerenes and their further application in a variety of different fields. In this regard, in addition to biomedical applications, chiral fullerenes are of interest in less-studied areas such as materials science, organic electronics, and nanoscience, where control of the order and morphology at the nanometer scale are critical issues for achieving better device efficiencies.

Recent advances in the catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides

The scope of the catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides has been greatly expanded by the incorporation of novel types of dipolarophiles and dipole precursors. This feature article summarizes the recent development in this area.