Amino-λ3 -iodane-Enabled Electrophilic Amination of Arylboronic Acid Derivatives.

In this report, we describe the use of amino-λ3 -iodanes in the electrophilic amination of arylboronic acids and boronates. Iodine(III) reagents with transferable amino groups, including one with an NH2 group, were synthesized and used in the amination, allowing the synthesis of a wide range of primary and secondary (hetero)arylamines. Mechanistic studies by DFT calculations indicate that the reaction proceeds through an electrophilic amination process from a tetravalent borate complex with a B-N dative bond.

Anion-Responsive Colorimetric and Fluorometric Red-Shift in Triarylborane Derivatives: Dual Role of Phenazaborine as Lewis Acid and Electron Donor.

Photophysical modulation of triarylboranes (TABs) through Lewis acid-base interactions is a fundamental approach for sensing anions. Yet, design principles for anion-responsive TABs displaying significant red-shift in absorption and photoluminescence (PL) have remained elusive. Herein, a new strategy for modulating the photophysical properties of TABs in a red-shift mode has been presented, by using a nitrogen-bridged triarylborane (1,4-phenazaborine: PAzB) with a contradictory dual role as a Lewis acid and an electron donor. Following the strategy, PAzB derivatives connected with an electron-deficient azaaromatic have been developed, and these compounds display a distinct red-shift in their absorption and PL in response to an anion. Spectroscopic analyses and quantum chemical calculations have revealed the formation of a tetracoordinate borate upon the addition of fluoride, narrowing the HOMO-LUMO gap and enhancing the charge-transfer character in the excited state. This approach has also been demonstrated in modulating the photophysical properties of solid-state films.

α-Amination of Carbonyl Compounds by Using Hypervalent Iodine-Based Aminating Reagents Containing a Transferable (Diarylmethylene)amino Group.

Hypervalent iodine-based aminating reagents containing a transferable (diarylmethylene)amino group can be used for the α-amination of simple carbonyl compounds such as esters, amides, and ketones in the presence of a lithium base. The (diarylmethylene)amino groups of the products can be readily modified, thus providing access to primary amines and diarylmethylamines. The developed method features transition-metal-free conditions and a simple one-pot procedure without the need to prepare enolate equivalents separately, thus offering a general and practical approach to the synthesis of a wide variety of α-amino carbonyl compounds. Experimental mechanistic investigations indicate that this amination proceeds through a unique radical coupling of an α-carbonyl radical with an iminyl radical; they are generated through a single-electron transfer between a lithium enolate and the hypervalent iodine reagent.

3,11-Diaminodibenzo[a,j]phenazine: Synthesis, Properties, and Applications to Tröger's Base-Forming Ladder Polymerization.

A new class of diamino-substituted π-extended phenazine compound was synthesized, and its photophysical properties were investigated. The U-shaped diaminophenazine displayed photoluminescence in solution with moderate quantum yield. The diamino aromatic compound was found applicable to the poly-condensation with formaldehyde to form Tröger's base ladder polymer. The obtained microporous ladder polymer features high CO2 adsorption selectivity against N2 , most likely due to the presence of basic nitrogen atoms in the phenazine rings.

Stereospecific Oxycyanation of Alkenes with Sulfonyl Cyanide.

Oxycyanation of alkenes would allow the direct construction of useful ß-hydroxy nitrile scaffolds. However, only limited examples of such reactions have been reported, and some problems including limited substrate scope and the lack of diastereocontrol in the case of the oxycyanation of internal alkenes have arisen. We herein report on the intermolecular oxycyanation of alkenes using p-toluenesulfonyl cyanide (TsCN) in the presence of tris(pentafluorophenyl)borane (B(C6 F5 )3 ) as a catalyst, affording products that contain a sulfinyloxy group and a cyano group at the vicinal position. The reaction features a stereospecific syn-addition. The reaction also shows a broad substrate scope with good functional group tolerance. Mechanistic investigations by experimental studies and density functional theory (DFT) calculations revealed that the reaction proceeds via an unprecedented stereospecific mechanism through the electrophilic cyanation of alkenes, in which B(C6 F5 )3 efficiently activates TsCN through the coordination of the cyano group to the boron center.

Dibenzophenazine-Based TADF Emitters as Dual Electrochromic and Electroluminescence Materials.

Previous work has reported the synthesis of donor-acceptor-donor molecules based on dibenzophenazine acceptor group, presenting thermally activated delayed fluorescent (TADF) properties and their application in the assembly of highly efficient electroluminescent devices. Herein, we focus on the characterisation of charge carrier species through UV-Vis-NIR spectroelectrochemical and potentiostatic EPR techniques, in addition to the investigation of electropolymerisation properties of some compounds depicted in this study. The promising electrochromic features of both small molecules and conjugated polymers led to the assembly and investigation of electrochromic devices, evidencing the materials' versatility, applied in such different approaches as electrochromic windows and electroluminescent devices. Furthermore, the assembled OLEDs provided high efficiencies, with small roll-off, EQEs up to 20.5 % and luminance values up to 85 000 cd/m2 .

Near Fermi Superatom State Stabilized by Surface State Resonances in a Multiporous Molecular Network.

Two-dimensional honeycomb molecular networks confine a substrate's surface electrons within their pores, providing an ideal playground to investigate the quantum electron scattering phenomena. Besides surface state confinement, laterally protruding organic states can collectively hybridize at the smallest pores into superatom molecular orbitals. Although both types of pore states could be simultaneously hosted within nanocavities, their coexistence and possible interaction are unexplored. Here, we show that these two types of pore states do coexist within the smallest nanocavities of a two-dimensional halogen-bonding multiporous network grown on Ag(111) studied using a combination of scanning tunneling microscopy and spectroscopy, density functional theory calculations, and electron plane wave expansion simulations. We find that superatom molecular orbitals undergo an important stabilization when hybridizing with the confined surface state, following the significant lowering of its free-standing energy. These findings provide further control over the surface electronic structure exerted by two-dimensional nanoporous systems.

Comparative study of thermally activated delayed fluorescent properties of donor-acceptor and donor-acceptor-donor architectures based on phenoxazine and dibenzo[a,j]phenazine.

A new thermally activated delayed fluorescence (TADF) compound based on a donor-acceptor (D-A) architecture (D = phenoxazine; A = dibenzo[a,j]phenazine) has been developed, and its photophysical properties were characterized. The D-A compound is applicable as an emitting material for efficient organic light-emitting diodes (OLEDs), and its external quantum efficiency (EQE) exceeds the theoretical maximum of those with prompt fluorescent emitters. Most importantly, comparative study of the D-A molecule and its D-A-D counterpart from the viewpoints of the experiments and theoretical calculations revealed the effect of the number of the electron donor on the thermally activated delayed fluorescent behavior.

Diastereodivergent Intermolecular 1,2-Diamination of Unactivated Alkenes Enabled by Iodine Catalysis.

The stereospecific, substrate (nitrogen source)-controlled intermolecular anti- and syn-1,2-diaminations of unactivated alkenes using the same catalysis (an iodine catalyst) is reported. The combined use of the two potential methods provides access to all of the disastereomeric forms of 1,2-diamines in spite of the availability of E- and Z-alkenes, and the resulting products can be readily converted into free vicinal diamines.

Palladium-Catalyzed Regioselective and Stereospecific Ring-Opening Cross-Coupling of Aziridines: Experimental and Computational Studies.

Aziridines, i.e., the smallest saturated N-heterocycles, serve as useful building blocks in synthetic organic chemistry. Because of the release of the large ring strain energy accommodated in the small ring, (ca. 27 kcal/mol), aziridines undergo ring-opening reactions with a variety of nucleophiles. Therefore, among the synthetic reactions utilizing aziridines, regioselective ring-opening substitutions of aziridines with nucleophiles, such as heteroatomic nucleophiles (e.g., amines, alcohols, and thiols) and carbonaceous nucleophiles (e.g., carbanions, organometallic reagents, and electron-rich arenes), constitute a useful synthetic methodology to synthesize biologically relevant ß-functionalized alkylamines. However, the regioselection in such traditional ring-opening substitutions of aziridines is highly dependent on the substrate combination, and stereochemical control is challenging to achieve, especially in the case of Lewis acid-promoted variants. Therefore, the development of robust catalytic ring-opening functionalization methods that enable precise prediction of regioselectivity and stereochemistry is desirable. In this direction, our group focused on the highly regioselective and stereospecific nature of the stoichiometric oxidative addition elementary step of 2-substituted aziridines into Pd(0) complexes in an SN2 fashion. In conjunction with the recent advancements in transition-metal-catalyzed cross-coupling reactions of alkyl pseudohalides containing a C(sp3)-Q (Q = O, N, S, etc.) bond, aziridines can be used as nonclassical alkyl pseudohalides in regioselective and stereospecific cross-couplings.In this Account, starting from the background of transition-metal-catalyzed ring-opening functionalization of aziridines, our contributions to the palladium-catalyzed regioselective and stereoinvertive cross-couplings of aziridines with organoboron reagents to form C(sp3)-C, C(sp3)-B, and C(sp3)-Si bonds have been compiled. The developed methods allow the syntheses of medicinally important amine compounds, e.g., enantioenriched ß-phenethylamines, ß-amino acids, and their boron and silyl surrogates, from readily available enantiopure aziridine substrates. Notably, the regioselectivity of the ring opening can be switched by appropriate selection of the catalyst (i.e., Pd/NHC vs Pd/PR3 systems). Computational studies rationalized the detailed mechanisms of the full catalytic cycle and the regioselectivity and stereospecificity of the reactions. The computational results suggested that the interactions operating between the Pd catalyst and aziridine substrate play important roles in determining the regioselection of the aziridine ring-opening event (i.e., oxidative addition). Also, the computational results rationalized the role of water molecules in promoting the transmetalation step through the formation of a Pd-hydroxide active intermediate. This Account evidences the benefits of synergistic collaborations between experimental and computational methods in developing novel transition-metal-catalyzed cross-coupling reactions.

Intramolecular C-H Amination of N-Alkylsulfamides by tert-Butyl Hypoiodite or N-Iodosuccinimide.

1,3-Diamines are an important class of compounds that are broadly found in natural products and are also widely used as building blocks in organic synthesis. Although the intramolecular C-H amination of N-alkylsulfamide derivatives is a reliable method for the construction of 1,3-diamine structures, the majority of these methods involve the use of a transition-metal catalyst. We herein report on a new transition-metal-free method using tert-butyl hypoiodite (t-BuOI) or N-iodosuccinimide (NIS), enabling secondary non-benzylic and tertiary C-H amination reactions to proceed. The cyclic sulfamide products can be easily transformed into 1,3-diamines. Mechanistic investigations revealed that amination reactions using t-BuOI or NIS each proceed via different pathways.

The Impact of C2 Insertion into a Carbazole Donor on the Physicochemical Properties of Dibenzo[a,j]phenazine-Cored Donor-Acceptor-Donor Triads.

Novel electron donor-acceptor-donor (D-A-D) compounds comprising dibenzo[a,j]phenazine as the central acceptor core and two 7-membered diarylamines (iminodibenzyl and iminostilbene) as the donors have been designed and synthesized. Investigation of their physicochemical properties revealed the impact of C2 insertion into well-known carbazole electron donors on the properties of previously reported twisted dibenzo[a,j]phenazine-core D-A-D triads. Slight structural modification caused a drastic change in conformational preference, allowing unique photophysical behavior of dual emission derived from room-temperature phosphorescence and triplet-triplet annihilation. Furthermore, electrochemical analysis suggested sigma-dimer formation and electrochemical polymerization on the electrode. Quantum chemical calculations also rationalized the experimental results.

Tris(pentafluorophenyl)borane-Catalyzed Formal Cyanoalkylation of Indoles with Cyanohydrins.

Despite the significant achievements related to the C3 functionalization of indoles, cyanoalkylation reactions continue to remain rather limited. We herein report on the formal C3 cyanoalkylation of indoles with cyanohydrins in the presence of a tris(pentafluorophenyl)borane (B(C6F5)3) catalyst. It is noteworthy that cyanohydrins are used as a cyanoalkylating reagent in the present reaction, even though they are usually used as only a HCN source. Mechanistic investigations revealed the unique reactivity of the B(C6F5)3 catalyst in promoting the decomposition of a cyanohydrin by a Lewis acidic activation through the coordination of the cyano group to the boron center. In addition, a catalytic three-component reaction using indoles, aldehydes as a carbon unit, and acetone cyanohydrin that avoids the discrete preparation of each aldehyde-derived cyanohydrin is also reported. The developed methods provide straightforward, highly efficient, and atom-economic access to various types of synthetically useful indole-3-acetonitrile derivatives containing α-tertiary or quaternary carbon centers.

Thermally Activated Delayed Fluorescent Donor-Acceptor-Donor-Acceptor π-Conjugated Macrocycle for Organic Light-Emitting Diodes.

A new class of thermally activated delayed fluorescent donor-acceptor-donor-acceptor (D-A-D-A) π-conjugated macrocycle comprised of two U-shaped electron-acceptors (dibenzo[a,j]phenazine) and two electron-donors (N,N'-diphenyl-p-phenyelendiamine) has been rationally designed and successfully synthesized. The macrocyclic compound displayed polymorphs-dependent conformations and emission properties. Comparative studies on physicochemical properties of the macrocycle with a linear surrogate have revealed significant effects of the structural cyclization of the D-A-repeating unit, including more efficient thermally activated delayed fluorescence (TADF). Furthermore, an organic light-emitting diode (OLED) device fabricated with the macrocycle compound as the emitter has achieved a high external quantum efficiency (EQE) up to 11.6%, far exceeding the theoretical maximum (5%) of conventional fluorescent emitters and that with linear analogue (6.9%).

Ni(II) 10-Phosphacorrole: A Porphyrin Analogue Containing Phosphorus at the Meso Position.

Ni(II) 10-Phosphacorrole, a porphyrinoid containing phosphorus at the meso position, was synthesized from a bis(α,α'-dibromodipyrrin) Ni(II) complex and a phosphine anion via the palladium-catalyzed formation of a C-C and two C-P bonds. The optoelectronic properties of Ni(II) 10-phosphacorrole can be modulated effectively by oxidation or coordination of a metal to the phosphorus center. While Ni(II) 10-phosphacorrole exhibits a distinctly aromatic character due to the cyclic conjugation of 18 π-electrons, its oxide exhibited weak antiaromaticity, which was confirmed experimentally and theoretically.

Asymmetric Synthesis of ß2 -Aryl Amino Acids through Pd-Catalyzed Enantiospecific and Regioselective Ring-Opening Suzuki-Miyaura Arylation of Aziridine-2-carboxylates.

A Pd-catalyzed enantiospecific and regioselective ring-opening Suzuki-Miyaura arylation of aziridine-2-carboxylates was developed. The cross-coupling allows for the asymmetric preparation of enantioenriched ß2 -aryl amino acids, starting from commercially available enantiopure d- and l-serine esters. The mechanism and selectivity of the reaction was rationalized based on computational models.

Aromatic-fused diketophosphanyl-core organic functional materials: phosphorus mimics of imides or beyond?

Recently, missing pieces of organophosphorus compounds, i.e., aromatic-fused diketophosphanyl compounds, have attracted much attention as promising scaffolds of building blocks for functional organic materials. In this review, the brief historical background, synthetic methods, structures, and optoelectronic aspects of aromatic-fused diketophosphanyls are overviewed.

Synthesis of Hypervalent Iodine(III) Reagents Containing a Transferable (Diarylmethylene)amino Group and Their Use in the Oxidative Amination of Silyl Ketene Acetals.

The preparation of some hypervalent iodine reagents containing a transferable amino group derived from benzophenone imine derivatives is reported. The reagents can be readily prepared and stored as a bench-stable solid, and were successfully used in the transition-metal-free oxidative amination of silyl ketene acetals to afford the corresponding α-amino esters, the benzophenone imine moieties of which could be easily hydrolyzed, thereby leading to the formation of primary amines.

Enantioselective Electrophilic Cyanation of Boron Enolates: Scope and Mechanistic Studies.

Chiral ß-ketonitriles bearing a stereogenic carbon center at the α-position are an important class of compounds, many of which serve as useful synthetic intermediates for the preparation of chiral 1,3-aminoalcohols, ß-hydroxy nitriles, and related derivatives. Although the enantioselective electrophilic cyanation of enolate equivalents is one of the most promising approaches for the synthesis of chiral ß-ketonitriles, the available methods are largely limited to reactions of 1,3-dicarbonyl compounds. Herein, we report on enantioselective electrophilic cyanation of boron enolates, which are readily prepared from α,ß-unsaturated ketones and diisopinocampheylborane (Ipc2 BH) to afford chiral ß-ketonitriles with a high level of enantioselectivity. The present method is scalable and provides facile access to both enantiomers of chiral ß-ketonitriles. Analysis of the in situ generated boron enolates by NMR revealed that hydroboration proceeds in a stereospecific manner, providing α,α-disubstituted boron enolates in the form of single isomers. Furthermore, the results of DFT calculations suggest that the cyanation of the boron enolates with p-toluenesulfonyl cyanide (TsCN) proceeds in a highly enantioselective manner through a unique six-membered ring transition state.

Syntheses of Diverse Donor-Substituted Bisbenzofuro[2,3- b:3',2'- e]pyridines (BBZFPys) via Pd Catalysis, and Their Photophysical Properties.

A series of bisbenzofuro[2,3- b:3',2'- e]pyridines (BBZFPys) bearing a chlorine functionality have been efficiently synthesized through a Pd-catalyzed double oxidative intramolecular C-H/C-H coupling of monochlorinated 2,6-diaryloxypyridines. The subsequent Buchwald-Hartwig amination of the chlorinated BBZFPys allowed for the access to a new class of donor-acceptor (D-A) π-conjugated compounds that comprise BBZFPy as an electron acceptor (A) and diarylamines as a donor (D) unit. The investigation of the steady-state photophysical properties of the prepared D-A compounds revealed that they are emissive in both solution and solid states in the blue-to-green color region. The singlet-triplet energy splitting (Δ EST) was found to be much smaller than that of substituent-free BBZFPy (0.70 eV), ranging from 0.01 to 0.56 eV. The time-resolved spectroscopy revealed that the D-A compounds, comprising a bis( tert-butyl)carbazole as the D and CF3-attached BBZFPy as the A, showed delayed fluorescence (DF) in nonpolar matrix host material (Zeonex), while in a polar matrix (DPEPO), room-temperature phosphorescence (RTP) was faintly observed. Furthermore, organic light-emitting diodes (OLEDs) fabricated with the D-A compounds as a blue emitter showed a moderate external quantum efficiencies (EQEs) up to 1.5%.