Experimental and Computational Studies of a Multi‐Electron Donor–Acceptor Ligand Containing the Thiazolo[5,4‐d]thiazole Core and its Incorporation into a Metal–Organic Framework

A ligand containing the thiazolo[5,4‐d]thiazole (TzTz) core (acceptor) with terminal triarylamine moieties (donors), N,N′‐(thiazolo[5,4‐d]thiazole‐2,5‐diylbis(4,1‐phenylene))bis(N‐(pyridine‐4‐yl)pyridin‐4‐amine ( 1 ), was designed as a donor–acceptor system for incorporation into electronically active metal–organic frameworks (MOFs). The capacity for the ligand to undergo multiple sequential oxidation and reduction processes was examined using UV/Vis‐near‐infrared spectroelectrochemistry (UV/Vis‐NIR SEC) in combination with DFT calculations. The delocalized nature of the highest occupied molecular orbital (HOMO) was found to inhibit charge‐transfer interactions between the terminal triarylamine moieties upon oxidation, whereas radical species localized on the TzTz core were formed upon reduction. Conversion of 1 to diamagnetic 2+ and 4+ species resulted in marked changes in the emission spectra. Incorporation of this highly delocalized multi‐electron donor–acceptor ligand into a new two‐dimensional MOF, [Zn(NO₃)₂( 1 )] ( 2 ), resulted in an inhibition of the oxidation processes, but retention of the reduction capability of 1 . Changes in the electrochemistry of 1 upon integration into 2 are broadly consistent with the geometric and electronic constraints enforced by ligation.     

Reactivity of Oxygen Radical Anions Bound to Scandia Nanoparticles in the Gas Phase: CH Bond Activation

The activation of C?H bonds in alkanes is currently a hot research topic in chemistry. The atomic oxygen radical anion (O^?.) is an important species in C?H activation. The mechanistic details of C?H activation by O^?. radicals can be well understood by studying the reactions between O^?. containing transition metal oxide clusters and alkanes. Here the reactivity of scandium oxide cluster anions toward n‐butane was studied by using a high‐resolution time‐of‐flight mass spectrometer coupled with a fast flow reactor. Hydrogen atom abstraction (HAA) from n‐butane by (Sc₂O₃)_NO^? (N=1–18) clusters was observed. The reactivity of (Sc₂O₃)_NO^? (N=1–18) clusters is significantly sizedependent and the highest reactivity was observed for N=4 (Sc₈O₁₃^?) and 12 (Sc₂₄O₃₇^?). Larger (Sc₂O₃)_NO^? clusters generally have higher reactivity than the smaller ones. Density functional theory calculations were performed to interpret the reactivity of (Sc₂O₃)_NO^? (N=1–5) clusters, which were found to contain the O^?. radicals as the active sites. The local charge environment around the O^?. radicals was demonstrated to control the experimentally observed size‐dependent reactivity. This work is among the first to report HAA reactivity of cluster anions with dimensions up to nanosize toward alkane molecules. The anionic O^?. containing scandium oxide clusters are found to be more reactive than the corresponding cationic ones in the C?H bond activation.     

A New Class of Tunable Dendritic Diphosphine Ligands: Synthesis and Applications in the Ru‐Catalyzed Asymmetric Hydrogenation of Functionalized Ketones

A series of tunable G₀–G₃ dendritic 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (BINAP) ligands was prepared by attaching polyaryl ether dendrons onto the four phenyl rings on the P atoms. Their ruthenium complexes were employed in the asymmetric hydrogenation of β‐ketoesters, α‐ketoesters, and α‐ketoamides to reveal the effects of dendron size on the catalytic properties. The second‐ and third‐generation catalysts exhibited excellent enantioselectivities, which are remarkably higher than those obtained from the small molecular catalysts and the first‐generation catalyst. Molecular modeling indicates that the incorporation of bulky dendritic wedges can influence the steric environments around the metal center. In addition, the ruthenium catalyst bearing a second‐generation dendritic ligand could be recycled and reused seven times without any obvious decrease in enantioselectivity.     

Efficient Copper‐Catalyzed Direct Intramolecular Aminotrifluoromethylation of Unactivated Alkenes with Diverse Nitrogen‐Based Nucleophiles

A mild, convenient, and step‐economical intramolecular aminotrifluoromethylation of unactivated alkenes with a variety of electronically distinct, nitrogen‐based nucleophiles in the presence of a simple copper salt catalyst, in the absence of extra ligands, is described. Many different nitrogen‐based nucleophiles (e.g., basic primary aliphatic and aromatic amines, sulfonamides, carbamates, and ureas) can be employed in this new aminotrifluoromethylation reaction. The aminotrifluoromethylation process allows straightforward access to diversely substituted CF₃‐containing pyrrolidines or indolines, in good to excellent yields, through a direct difunctionalization strategy from the respective acyclic starting materials. Mechanistic studies were conducted and a plausible mechanism was proposed.     

Metal‐Free Oxidative Radical Addition of Carbonyl Compounds to α,α‐Diaryl Allylic Alcohols: Synthesis of Highly Functionalized Ketones

A metal‐free direct alkylation of simple carbonyl compounds (ketones, esters, and amides) with α,α‐diaryl allylic alcohols is described. The protocol provides facile access to highly functionalized dicarbonyl ketones by a radical addition/1,2‐aryl migration cascade. The regioselectivity of the reaction was precisely controlled by the nature of the carbonyl compound.     

Highly Enantioselective Catalytic System for Asymmetric Copolymerization of Carbon Dioxide and Cyclohexene Oxide

A new ligand can be easily prepared, and its intramolecular dinuclear zinc complexes act as a high performance catalyst for the asymmetric alternating copolymerization of cyclohexene oxide and CO₂ under very mild conditions (1 atm CO₂, room temperature), affording completely alternating polycarbonates with up to 93.8 % enantiomeric excess (ee) and 98 % yield. A high M_n value of 28 600 and a relatively narrow polydispersity (M_w/M_n ratio) of 1.43 were also achieved.     

Performance Enhancement of Bulk Heterojunction Solar Cells with Direct Growth of CdS‐Cluster‐Decorated Graphene Nanosheets

Two‐dimensional graphene–CdS (G–CdS) semiconductor hybrid nanosheets were synthesized in situ by graphene oxide (GO) quantum wells and a metal–xanthate precursor through a one‐step growth process. Incorporation of G–CdS nanosheets into a photoactive film consisting of poly[4,8‐bis‐(2‐ethyl‐hexyl‐thiophene‐5‐yl)‐benzo[1,2‐b:4,5‐b]dithiophene‐2,6‐diyl]‐alt‐[2‐(2‐ethyl‐hexanoyl)‐thieno[3,4‐b]thiophen‐4,6‐diyl] (PBDTTT‐C‐T) and [6,6]‐phenyl C₇₀ butyric acid methyl ester (PC₇₀BM) effectively decreases the exciton lifetime to accelerate exciton dissociation. More importantly, the decreasing energy levels of PBDTTT‐C‐T, PC₇₀BM, and G–CdS produces versatile heterojunction interfaces of PBDTTT‐C‐T:PC₇₀BM, PBDTTT‐C‐T:G–CdS, and PBDTTT‐C‐T:PC₇₀BM:G–CdS; this offers multi‐charge‐transfer channels for more efficient charge separation and transfer. The charge transfer in the blend film also depends on the G–CdS nanosheet loadings. In addition, G–CdS nanosheets improve light utilization and charge mobility in the photoactive layer. As a result, by incorporation of G–CdS nanosheets into the active layer, the power‐conversion efficiency of inverted solar cells based on PBDTTT‐C‐T and PC₇₁BM is improved from 6.0 % for a reference device without G–CdS nanosheets to 7.5 % for the device with 1.5wt % G–CdS nanosheets, due to the dramatically enhanced short‐circuit current. Combined with the advantageous mechanical properties of the PBDTTT‐C‐T:PC₇₀BM:G–CdS active layer, the novel CdS‐cluster‐decorated graphene hybrid nanomaterials provide a promising approach to improve the device performance.     

Interfacial Chiral Selection by Bulk Species

A chiral selection process in a self‐assembled soft monolayer of an achiral amphiphile as a consequence of its interaction with chiral species dissolved in the aqueous subphase, is reported. The extent of the chiral selection is statistically measured in terms of the enantiomorphic excess of self‐assembled submillimeter domains endowed with well‐defined orientational chirality that is unambiguously resolved using optical microscopy. Our results show that the emergence of chirality is mediated by electrostatic interactions and significantly enhanced by hydrophobic effects. This chiral chemical effect can be suppressed and even reversed by opposing a macroscopic physical influence, such as vortical stirring. This result gives evidence for the crucial role of hydrodynamic effects in supramolecular aggregation.     

Well‐Defined Iron Complexes as Efficient Catalysts for “Green” Atom‐Transfer Radical Polymerization of Styrene,Methyl Methacrylate,and Butyl Acrylate with Low Catalyst Loadings and Catalyst Recycling

Environmentally friendly iron(II) catalysts for atom‐transfer radical polymerization (ATRP) were synthesized by careful selection of the nitrogen substituents of N,N,N‐trialkylated‐1,4,9‐triazacyclononane (R₃TACN) ligands. Two types of structures were confirmed by crystallography: “[(R₃TACN)FeX₂]” complexes with relatively small R groups have ionic and dinuclear structures including a [(R₃TACN)Fe(μ‐X)₃Fe(R₃TACN)]⁺ moiety, whereas those with more bulky R groups are neutral and mononuclear. The twelve [(R₃TACN)FeX₂]_n complexes that were synthesized were subjected to bulk ATRP of styrene, methyl methacrylate (MMA), and butyl acrylate (BA). Among the iron complexes examined, [{(cyclopentyl)₃TACN}FeBr₂] ( 4 b ) was the best catalyst for the well‐controlled ATRP of all three monomers. This species allowed easy catalyst separation and recycling, a lowering of the catalyst concentration needed for the reaction, and the absence of additional reducing reagents. The lowest catalyst loading was accomplished in the ATRP of MMA with 4 b (59 ppm of Fe based on the charged monomer). Catalyst recycling in ATRP with low catalyst loadings was also successful. The ATRP of styrene with 4 b (117 ppm Fe atom) was followed by precipitation from methanol to give polystyrene that contained residual iron below the calculated detection limit (0.28 ppm). Mechanisms that involve equilibria between the multinuclear and mononuclear species were also examined.     

Novel hydrothermal carbonization of cellulose catalyzed by montmorillonite to produce kerogen-like hydrochar

The conversion of cellulose to petroleum-like fuel is a very challenging yet attractive route to developing biomass-to-fuel technology. Many attempts have been made in liquefaction, pyrolysis and gasification of cellulose to produce fuels or intermediate chemicals. Previous studies indicate that these processes are tough. Hence, the present work is concerned with the development of new technologies for the conversion of cellulose into materials which are analogies to the precursor of petroleum. Montmorillonite-catalyzed hydrothermal carbonization of microcrystalline cellulose for the production of kerogen-like hydrochar under mild conditions was investigated. It was revealed that the hydrothermal carbonization of microcrystalline cellulose alone resulted in hydrochar with type III kerogen-like structure, whereas in the presence of montmorillonite, the hydrothermal carbonization of microcrystalline cellulose yielded a hydrochar-mineral complex, of which the isolated organic fraction was oil-prone type II kerogen-like structure. Results suggested that further improved montmorillonite-aided biomass conversion to more oil-prone kerogen-like solid products could be an alternative efficient route to obtain biofuel and chemicals.