Synthesis of [60]Fullerene-Fused Lactones via Carboxylic Acid Group-Directed C-H Bond Activation and Further Retro Baeyer-Villiger Reaction.

An efficient palladium-catalyzed reaction of [60]fullerene with benzoic acids via carboxylic acid group-directed C-H bond activation is achieved. The obtained [60]fullerene-fused lactones can undergo a retro Baeyer-Villiger reaction to provide [60]fullerene-fused ketones via apparent reduction in the presence of triflic acid. A representative ketone product obtained by the reduction reaction can be employed as an overcoating layer for the electron-transporting layer in an n-type perovskite solar cell.

Electrosynthesis of an Improbable Directly Bonded Phosphorene-Fullerene Heterodimensional Hybrid toward Boosted Photocatalytic Hydrogen Evolution.

Phosphorene and fullerene are representative two-dimensional (2D) and zero-dimensional (0D) nanomaterials respectively, constructing their heterodimensional hybrid not only complements their physiochemical properties but also extends their applications via synergistic interactions. This is however challenging because of their diversities in dimension and chemical reactivity, and theoretical studies predicted that it is improbable to directly bond C60 onto the surface of phosphorene due to their strong repulsion. Here, we develop a facile electrosynthesis method to synthesize the first phosphorene-fullerene hybrid featuring fullerene surface bonding via P-C bonds. Few-layer black phosphorus nanosheets (BPNSs) obtained from electrochemical exfoliation react with C602- dianion prepared by electroreduction of C60, fulfilling formation of the "improbable" phosphorene-fullerene hybrid (BPNS-s-C60). Theoretical results reveal that the energy barrier for formation of [BPNS-s-C60]2- intermediate is significantly decreased by 1.88 eV, followed by an oxidization reaction to generate neutral BPNS-s-C60 hybrid. Surface bonding of C60 molecules not only improves significantly the ambient stability of BPNSs, but also boosts dramatically the visible light and near-infrared (NIR) photocatalytic hydrogen evolution rates, reaching 1466 and 1039 µmol h-1 g-1 respectively, which are both the highest values among all reported BP-based metal-free photocatalysts.

Interface Passivation of a Pyridine-Based Bifunctional Molecule for Inverted Perovskite Solar Cells.

Organic-inorganic hybrid perovskite solar cells (PSCs) have recently been demonstrated to be promising renewable harvesters because of their prominent photovoltaic power conversion efficiency (PCE), although their stability and efficiency still have not reached commercial criteria. Trouble-oriented analyses showcase that defect reduction among the grain boundaries and interfaces in the prepared perovskite polycrystalline films is a practical strategy, which has prompted researchers to develop functional molecules for interface passivation. Herein, the pyridine-based bifunctional molecule dimethylpyridine-3,5-dicarboxylate (DPDC) was employed as the interface between the electron-transport layer and perovskite layer, which achieved a champion PCE of 21.37% for an inverted MAPbI3-based PSC, which was greater than 18.64% for the control device. The mechanistic studies indicated that the significantly improved performance was mainly attributed to the remarkably enhanced fill factor with a value greater than 83%, which was primarily due to the nonradiative recombination suppression offered by the passivation effect of DPDC. Moreover, the promoted carrier mobility together with the enlarged crystal size contributed to a higher short-circuit current density. In addition, an increase in the open-circuit voltage was also observed in the DPDC-treated PSC, which benefited from the improved work function for reducing the energy loss during carrier transport. Furthermore, the DPDC-treated PSC showed substantially enhanced stability, with an over 80% retention rate of its initial PCE value over 300 h even at a 60% relative humidity level, which was attributed to the hydrophobic nature of the DPDC molecule and effective defect passivation. This work is expected not only to serve as an effective strategy for using a pyridine-based bifunctional molecule to passivate perovskite interfaces to enhance photovoltaic performance but also to shed light on the interface passivation mechanism.

Silver(I)-catalyzed highly para-selective phosphonation of 2-aryloxazolines.

A silver-catalyzed phosphonation of 2-aryloxazolines has been accomplished. This protocol provides highly regioselective access to para-phosphonation products with good functional group tolerance and moderate to good yields via cross-dehydrogenation coupling. Mechanistic studies have shown that para-phosphonation products are obtained via a radical pathway. Furthermore, the directing oxazoline group in the para-phosphonation products is removable and can be converted to benzoic esters.

Visible-Light-Mediated Bimetal-Catalyzed meta-Alkylation of Arenes.

A mild approach to the visible-light-mediated bimetal-catalyzed meta-alkylation of arenes has been accomplished. The regioselective meta-alkylation is realized by a bimetallic ruthenium-palladium system. Ruthenium acts as a catalyst for the directing effect and as a photosensitizer, while the cocatalyst palladium behaves as a catalyst for the generation of fluoroalkyl radicals. This reaction not only is suitable for two-component meta-fluoroalkylation of arenes but can also be extended to three-component reactions to achieve bifunctionalization of olefins.

Electrosynthesis of buckyballs with fused-ring systems from PCBM and its analogue.

[6,6]-Phenyl-C61-butyric acid methyl ester (PCBM), a star molecule in the fullerene field, has found wide applications in materials science. Herein, electrosynthesis of buckyballs with fused-ring systems has been achieved through radical α-C-H functionalization of the side-chain ester for both PCBM and its analogue, [6,6]-phenyl-C61-propionic acid methyl ester (PCPM), in the presence of a trace amount of oxygen. Two classes of buckyballs with fused bi- and tricyclic carbocycles have been electrochemically synthesized. Furthermore, an unknown type of a bisfulleroid with two tethered [6,6]-open orifices can also be efficiently generated from PCPM. All three types of products have been confirmed by single-crystal X-ray crystallography. A representative intramolecularly annulated isomer of PCBM has been applied as an additive to inverted planar perovskite solar cells and boosted a significant enhancement of power conversion efficiency from 15.83% to 17.67%.

Dearomative Ring-Fused Azafulleroids and Carbazole-Derived Metallofullerenes: Reactivity Dictated by Encapsulation in a Fullerene Cage.

Herein, we report divergent additions of 2,2'-diazidobiphenyls to C60 and Sc3 N@Ih -C80 . In stark contrast to that of the previously reported bis-azide additions, the unexpected cascade reaction leads to the dearomative formation of azafulleroids 2 fused with a 7-6-5-membered ring system in the case of C60 . In contrast, the corresponding reaction with Sc3 N@Ih -C80 switches to the C-H insertion pathway, thereby resulting in multiple isomers, including a carbazole-derived [6,6]-azametallofulleroid 3 and a [5,6]-azametallofulleroid 4 and an unusual 1,2,3,6-tetrahydropyrrolo[3,2-c]carbazole-derived metallofullerene 5, whose molecular structures have been unambiguously determined by single-crystal X-ray diffraction analyses. Among them, the addition type of 5 is observed for the first time in all reported additions of azides to fullerenes. Furthermore, unexpected isomerizations from 3 to 5 and from 4 to 5 have been discovered, providing the first examples of the isomerization of an azafulleroid to a carbazole-derived fullerene rather than an aziridinofullerene. In particular, the isomerism of the [5,6]-isomer 4 to the [5,6]-isomer 5 is unprecedented in fullerene chemistry, contradicting the present understanding that isomerization generally occurs between [5,6]- and [6,6]-isomers. Control experiments have been carried out to rationalize the reaction mechanism. Furthermore, representative azafulleroids have been applied in organic solar cells, thereby resulting in improved power conversion efficiencies.

Simultaneous Ring Contraction and Expansion Reaction: Electrosynthesis of Heterocycle-Fused Fulleroids and Photovoltaic Application.

Simultaneous electrochemical ring contraction and expansion reactions remain unexplored to date. Herein, the reductive electrosynthesis of heterocycle-fused fulleroids from fullerotetrahydropyridazines and electrophiles in the presence of a trace amount of oxygen has been achieved with concurrent ring contraction and ring expansion. When trifluoroacetic acid and alkyl bromides are employed as electrophiles, heterocycle-fused fulleroids with a 1,1,2,6-configuration are regioselectively formed. In contrast, heterocycle-fused fulleroids with a 1,1,4,6-configuration are regioselectively produced as two separable stereoisomers if phthaloyl chloride is used as the electrophile. The reaction proceeds through multiple steps of electroreduction, heterocycle ring-opening, oxygen oxidation, heterocycle contraction, fullerene cage expansion, and nucleophilic addition. The structures of these fulleroids have been determined by spectroscopic data and single-crystal X-ray diffraction analyses. The observed high regioselectivities have been rationalized by theoretical calculations. Representative fulleroids have been applied in organic solar cells as the third component and exhibit good performance.

Visible-Light-Promoted C4-Selective Phosphorylation of Pyridine and Quinoline Derivatives.

The visible-light-promoted C4-selective phosphorylation of unprefunctionalized pyridine and quinoline derivatives has been accomplished. This Minisci-type protocol provides highly regioselective access to C4-phosphorylation products with good functional group tolerance and moderate to good yields via cross-dehydrogenation coupling under mild conditions. Mechanistic studies have shown that the C4-phosphorylation products are obtained via a radical pathway.

[60]Fullerene-Fused Cyclopentanes: Mechanosynthesis and Photovoltaic Application.

The mechanochemical cascade reaction of [60]fullerene with 3-benzylidene succinimides, diethyl 2-benzylidene succinate, or 2-benzylidene succinonitrile in the presence of an inorganic base has been investigated under solvent-free and ball-milling conditions. This protocol provides an expedient method to afford various [60]fullerene-fused cyclopentanes, showing advantages of good substrate scope, short reaction time, and solvent-free and ambient reaction conditions. Furthermore, representative fullerene products have been applied in inverted planar perovskite solar cells as efficient cathode interlayers.

I2/FeCl3-Catalyzed Domino Reaction of Aurones with Enamino Esters for the Synthesis of Highly Functionalized Pyrroles.

A novel and efficient I2/FeCl3-catalyzed domino reaction of aurones with enamino esters via Michael addition, iodination, intramolecular nucleophilic substitution, and spiro ring opening processes has been developed, affording a vast variety of polysubstituted pyrroles in moderate to excellent yields. This protocol features mild reaction conditions, broad substrate scope, high atom economy and efficiency, and feasibility for large-scale synthesis. A plausible mechanism for the pyrrole synthesis is proposed.

Palladium-Catalyzed C-H Activation/Cyclization for the Synthesis of [60]Fullerene-Fused Phosphinolactones.

A novel and efficient palladium-catalyzed C-H activation reaction of [60]fullerene with arylphosphinic acids has been developed for the synthesis of [60]fullerene-fused phosphinolactones. A possible reaction mechanism is proposed to explain the generation of the obtained products. A representative product can be further electrochemically transformed into bis-benzylated 1,2- and 1,4-adducts of [60]fullerene. In addition, a [60]fullerene-fused phosphinolactone with a 12-membered ring can also be synthesized from the electrochemical ring expansion of the employed phosphinolactone with a 6-memebered ring with 1,2-bis(bromomethyl)benzene.

A 4-Arm Small Molecule Acceptor with High Photovoltaic Performance.

Manipulating the backbone of small molecule acceptors (SMAs) is of particular importance in developing efficient organic solar cells (OSCs). The common design is constructing 2-arm SMAs with linear or curved backbones. Herein, we report an acceptor 4A-DFIC with a 4-arm backbone unexpectedly generated in the reaction of an electron-rich aromatic diamine and hexaketocyclohexane. Single-crystal X-ray diffraction analysis indicates the rigid and twisted molecular plane and the effective molecular stacking of 4A-DFIC in solid state. 4A-DFIC shows a low band gap of 1.40 eV and excellent light-harvesting capability from visible to near-infrared region. Binary and ternary OSCs based on 4A-DFIC gave power conversion efficiencies (PCEs) of 15.76 % and 18.60 % (certified 18.1 %), respectively, which are the highest PCEs for multi-arm SMA-based OSCs to date.

Electrochemically Promoted Benzylation of [60]Fullerooxazolidinone.

Benzylation of the electrochemically generated dianion from N-p-tolyl-[60]fullerooxazolidinone with benzyl bromide provides three products with different addition patterns. The product distribution can be dramatically altered by varying the reaction conditions. Based on spectral characterizations, these products have been assigned as mono-benzylated 1,4-adduct and bis-benzylated 1,2,3,16- and 1,4,9,25-adducts, respectively. The assigned 1,2,3,16-adduct has been further established by X-ray diffraction analysis. It is believed that the 1,4-adduct is obtained by decarboxylative benzylation of the dianionic species, while bis-benzylated 1,2,3,16- and 1,4,9,25-adducts are achieved via a rearrangement process. In addition, the electrochemical properties of these products have been studied.

Electrosynthesis of Decorated Basket Molecules: [60]Fullerene-Fused 12-Membered Macrolactones.

The electrosynthesis of decorated basket molecules, that is, [60]fullerene-fused 12-membered macrolactones, has been achieved efficiently for the first time by the electrochemical reduction of [60]fullerene-fused 6-membered lactones and subsequent ring expansion with 1,2-bis(1-bromoalkyl)benzenes. The observed isomeric distributions of the obtained macrolactones are elucidated by theoretical calculations. The product structures have been firmly established by single-crystal X-ray analyses.

Solvent-Free Mechanosynthesis of Polysubstituted 1,2-Dihydroquinolines from Anilines and Alkyne Esters.

A novel one-pot reaction of anilines with acetylenedicarboxylate diesters in the presence of boron trifluoride, iodine, and trifluoroacetic acid or methylsulfonic acid has been developed under solvent-free ball-milling conditions, affording a variety of polysubstituted 1,2-dihydroquinolines bearing multiple ester groups in moderate to excellent yields. The present protocol features mild reaction conditions, short reaction time, and feasibility of large-scale synthesis, providing a facile and practical alternative to 1,2-dihydroquinoline synthesis. Intriguingly, the generated 1,2-dihydroquinolines can be further transformed into quinoline derivatives.

Unexpected Formation of Pyrazoline-Fused Metallofullerenes from the Multicomponent Cascade Reaction of Sc3N@Ih-C80 with Tetrazines, Water, and Oxygen.

The multicomponent cascade reaction of Sc3N@Ih-C80 with 3,6-di(pyridin-2-yl)-1,2,4,5-tetrazines, water, and oxygen unexpectedly affords the pyrazoline-fused Sc3N@Ih-C80 derivatives. The obtained endohedral metallofullerene derivatives have been characterized by various spectral means, and their structures have been unambiguously established by single-crystal X-ray crystallography. A possible reaction mechanism via a complicated sequence of Diels-Alder reaction, retro Diels-Alder reaction, hydration, rearrangement, and dehydrogenation processes is proposed for the formation of pyrazoline-fused metallofullerenes.

Mechanochemical Dimerization of Aldoximes to Furoxans.

Solvent-free mechanical milling is a new, environmentally friendly and cost-effective technology that is now widely used in the field of organic synthesis. The mechanochemical solvent-free synthesis of furoxans from aldoximes was achieved through dimerization of the in situ generated nitrile oxides in the presence of sodium chloride, Oxone and a base. A variety of furoxans was obtained with up to a 92% yield. The present protocol has the advantages of high reaction efficiency and mild reaction conditions.

Copper-mediated synthesis of fullerooxazoles from [60]fullerene and N-hydroxybenzimidoyl cyanides.

A novel and efficient copper-mediated [3 + 2] heteroannulation reaction of [60]fullerene with N-hydroxybenzimidoyl cyanides has been developed for the synthesis of fullerooxazoles. A possible reaction mechanism involving unique C-CN and N-OH bond cleavages and subsequent C-OH bond formation for N-hydroxybenzimidoyl cyanides is proposed to explain the generation of fullerooxazoles. In addition, the formed fullerooxazoles can be further electrochemically transformed into amidated 1,2-hydrofullerenes.