Alessandro Bismuto

Abstract

The hydroboration of alkynes and styrene with HBpin has been developed using tris(pentaflurophenyl)borane (B(C₆F₅)₃) as the initiator of catalysis. The hydroboration is proposed to be initiated by Lewis acid activation of the alkyne by (B(C₆F₅)₃) to form a highly reactive zwitterionic species which subsequently react with HBpin to give the alkenyl boronic ester. This zwitterion has also showed potential to be a competent catalyst for the hydroboration of styrene. The zwitterionic intermediate is analogous to that proposed in the Piers borane‐catalysed hydroboration and 1,1‐carboboration of alkynes with B(C₆F₅)_3.

The one pot synthesis of a series of sulfonium salts containing transferable diazomethyl groups is described, and the structure of these compounds elucidated by X‐ray crystallography. Under photochemical conditions, reaction of these salts with N,N‐dialkyl hydrazones affords 1‐(dialkylamino)‐1,2,3‐triazoles via diazomethyl radical addition to the azomethine carbon followed by intramolecular ring closure. The straightforward transformation of the structures thus obtained into mesoionic carbene‐metal complexes is also reported and the donor properties of these new ligands characterized.

Planar tetracoordinate silicon: A group of stable tetracoordinate silicon (ptSi) molecules, which are stabilized by π*→p donation, are reported. Interestingly, this donation also brings an unusual carbenoid‐type behavior to Si.

Abstract

Designing and synthesizing a stable compound with a planar tetracoordinate silicon (ptSi) center is a challenging goal for chemists. Here, a series of potential aromatic ptSi compounds composed of four conjugated rings shared by a centrally embedded Si atom are theoretically designed and computationally verified. Both Born–Oppenheimer molecular dynamics (BOMD) simulations and potential energy surface scannings verify the high stability and likely existence of these compounds, particularly Si‐16‐5555 (SiN₄C₈H₈) with 16 π electrons, under standard ambient temperature and pressure. Notably, the Hückel aromaticity rule, which works well for single rings, is inconsistent with the high stability of Si‐16‐5555 where the 16 p electrons are spread over four five‐membered rings fused together. Bonding analyses show that the strong electron donation from the peripheral 12‐membered conjugated ring with 16 π electrons to the vacant central atomic orbital Si 3p _z leads to the stabilization for both the ptSi coordination and planar aromaticity. The partial occupation of Si 3p _z results in the peculiar carbenoid‐type behaviors for the amphoteric center. By modulating the electron density on the ring with substituent groups, we can regulate the nucleophilic and electrophilic properties of the central Si.

Abstract

A convenient and effective method of palladium‐catalyzed C−H selenylation of the 2‐aryl acetamides assisted with removable 8‐aminoquinoline with readily available diselenides and selenyl chlorides has been developed. This selenylation reaction is scalable and tolerates a wide range of functional groups, providing a straightforward way of the preparing unsymmetrical diaryl selenides and dibenzoselene‐pinone. Preliminary mechanistic studies indicated that a single‐electron transfer type mechanism and facile C−H metalation are operative.

Abstract

Solid state structures of five new molecular complexes of SbI₃ with Py have been determined by single crystal X‐ray structural analysis. In all complexes, all antimony atoms adopt a pseudo‐octahedral coordination geometry, which is completed by additional Sb⋅⋅⋅I contacts shorter than sum of van der Waals radii, with I−Sb⋅⋅⋅I angles close to 180°. Analysis of the electrostatic potentials, the orbital interactions and topological analysis indicate that these contacts are due to the presence of Sb⋅⋅⋅I pnictogen bonds. The first example of three pnictogen bonds of SbI₃ is reported.

The Te(II)/Te(III) catalyzed dehydrogenative C─H phenothiazination of challenging phenols featuring electron withdrawing substituents is herein described, under mild aerobic conditions and with high yields. These unexpected Te(II)/Te(III) radical catalytic properties were characterized by cyclic voltammetry, EPR spectroscopy, kinetic experiments and DFT calculations.

A series of α‐cationic phosphole ligands has been synthesized and their use as ancillary ligands explored in Au‐catalysis. If compared with non‐heterocyclic α‐cationic phospines, higher reaction rates and better control of the stereoselectivity are obtained.

Abstract

A series of structurally differentiated α‐cationic phospholes containing cyclopropenium, imidazolium, and iminium substituents has been synthesized by reaction of chlorophosphole 1 with the corresponding stable carbenes. Evaluation of the donor properties of these compounds reveals that their strong π‐acceptor character is heavily influenced by the nature of the cationic group. The coordination chemistry of these newly prepared ligands towards Au^I centers is also described and their unique electronic properties exploited in catalysis. Interestingly, α‐cationic phosphole containing catalysts were not only able to accelerate model cycloisomerization reactions, but also to efficiently discriminate between concurrent reaction pathways, avoiding the formation of undesired product mixtures.

While pnictaalkenes are well‐established for the light group 15 elements, they become more reactive and exceptionally rare as the group is descended. Herein, we report a combined experimental and theoretical study on the first examples of carbodicarbene (CDC)‐stabilized bismuth complexes, which feature low‐coordinate cationic bismuth centers with C=Bi multiple bond character. Monocations [(CDC)Bi(Ph)Cl][SbF6] (8) and  [(CDC)BiBr2(THF)2][SbF6] (11), dications [(CDC)Bi(Ph)][SbF6]2 (9) and [(CDC)BiBr(THF)3][NTf2]2 (12), and trication [(CDC)2Bi][NTf2]3 (13) have been synthesized via sequential halide abstractions from (CDC)Bi(Ph)Cl2 (7) and (CDC)BiBr3 (10). Notably, the dications and trication exhibit C⇉Bi double dative bonds, and thus represent unprecedented bismaalkene cations. In addition, the synthesis of these species highlights a unique non‐reductive route to C–Bi π‐bonding character. The CDC‐[Bi] complexes (7‐13) were compared with related NHC‐[Bi] complexes (1, 3‐6) and show substantially different structural properties. Indeed, the CDC ligand has a remarkable influence on the overall stability of the resulting low‐coordinate Bi complexes, suggesting that CDC is a superior ligand to NHC in heavy pnictogen chemistry. All compounds have been characterized by multiple analytical methods including 1H and 13C NMR, X‐ray crystallography, elemental analysis, and UV‐Vis spectroscopy. In addition, the bonding situation was analyzed with modern charge and energy decomposition analysis.

A novel one‐pot synthetic strategy towards a series of boron‐doped polycyclic aromatic hydrocarbons from ortho‐aryl substituted diarylalkynes has been developed. A reaction mechanism is proposed based on the experimental investigation together with the theoretical calculations, which involves an unprecedented 1,4‐boron migration process.

Abstract

Herein, we demonstrate a novel one‐pot synthetic method towards a series of boron‐doped polycyclic aromatic hydrocarbons (B‐PAHs, 1 a–1 o), including hitherto unknown B‐doped zethrene derivatives, from ortho‐aryl substituted diarylalkynes with high atom efficiency and broad substrate scopes. A reaction mechanism is proposed based on the experimental investigation together with the theoretical calculations, which involves a unique 1,4‐boron migration process. The resultant benchtop‐stable B‐PAHs are thoroughly investigated by X‐ray crystallography, cyclic voltammetry, UV/Vis absorption, and fluorescence spectroscopies. The blue and green organic light‐emitting diode (OLED) devices based on 1 f and 1 k are further fabricated, demonstrating the promising application potential of B‐PAHs in organic optoelectronics.

Carbazole‐based DABNA analogues (CzDABNAs) were synthesized from triarylamine by regioselective one‐shot single and double borylation. The facile and scalable method enabled synthesis of CzDABNAs exhibiting narrowband thermally activated delayed fluorescence and the preparation of highly efficient organic light‐emitting diode devices showing deep‐blue, sky‐blue, and green emission.

Abstract

Carbazole‐based DABNA analogues (CzDABNAs) were synthesized from triarylamine by regioselective one‐shot single and double borylation. The reaction proceeded selectively at the ortho position of the carbazolyl group, where the highest occupied molecular orbital is mainly localized owing to the difference in the electron‐donating abilities of the diarylamino and carbazolyl groups. The facile and scalable method enabled synthesis of CzDABNAs, exhibiting narrowband thermally activated delayed fluorescence with emission spectra ranging from deep blue to green. The organic light‐emitting diode devices employing these products as emitters exhibited deep‐blue, sky‐blue, and green emission with high external quantum efficiencies of 19.5, 21.8, and 26.7 %, respectively.

Treatment of a bilindione with trifluoromethanesulfonic anhydride afforded a free‐base 5‐oxaporphyrinium cation. This compound exhibits unusual NH tautomerism, wherein the cis form is more stable than the trans form due to effective charge delocalization, which manifests in dual emission.

Abstract

Replacement of the meso methine carbon atoms of porphyrins with heteroatoms is a powerful strategy for tuning their optical and electronic properties. In particular, 5‐oxaporphyrin is an attractive target due to its importance as an intermediate in heme catabolism. In this work, we describe the synthesis and properties of a free‐base 5‐oxaporphyrinium cation, which was prepared by the ring‐closure of a bilindione with trifluoromethanesulfonic anhydride. This free‐base 5‐oxaporphyrinium cation exhibits dual fluorescence originating from its unique NH tautomerism. In contrast to normal porphyrins, the cis form of the 5‐oxaporphyrinium cation is more stable than the trans form due to the effective delocalization of its positive charge. We thus demonstrate here that meso‐modified heteroporphyrins enable the manipulation of NH tautomerism in porphyrinic macrocycles.

Driven by light: A mild and facile photoredox approach towards asymmetrically substituted phosphines and phosphonium salts is reported. Blue‐light irradiation of mono‐ and diphenylphosphine with various aryl and alkyl iodides, diisopropylethylamine (DIPEA), and the organic photocatalyst 3DPAFIPN affords the desired products in good‐to‐excellent yields. In addition, the same method transforms white phosphorus (P₄) directly into symmetrical aryl phosphines and phosphonium salts.

Abstract

Asymmetrically substituted tertiary phosphines and quaternary phosphonium salts are used extensively in applications throughout industry and academia. Despite their significance, classical methods to synthesize such compounds often demand either harsh reaction conditions, prefunctionalization of starting materials, highly sensitive organometallic reagents, or expensive transition‐metal catalysts. Mild, practical methods thus remain elusive, despite being of great current interest. Herein, we describe a visible‐light‐driven method to form these products from secondary and primary phosphines. Using an inexpensive organic photocatalyst and blue‐light irradiation, arylphosphines can be both alkylated and arylated using commercially available organohalides. In addition, the same organocatalyst can be used to transform white phosphorus (P₄) directly into symmetrical aryl phosphines and phosphonium salts in a single reaction step, which has previously only been possible using precious metal catalysis.

Chemical probes that covalently modify proteins of interest are powerful tools for the research of biological processes. Important in the design of a probe is the choice of reactive group that forms the covalent bond, as it decides the success of a probe. However, choosing the right reactive group is not a simple feat and methodologies for expedient screening of different groups are needed. We here report a modular approach that allows easy coupling of a reactive group to a ligand. α‐Nucleophile ligands are combined with 2‐formylphenylboronic acid‐derived reactive groups to form iminoboronate probes that selectively label their target proteins. A transimination reaction on the labeled proteins with an α‐amino hydrazide provides further modification, for example to introduce a fluorophore.

An improved route to d‐block and main group NSO complexes is presented including the synthesis of the first antimony(V) complexes, (Ar₃Sb(NSO)₂), and copper examples [CuBipy(PPh₃)NSO]. The structures of eight complexes are reported. The observed variation in M–N–S bond angles is due to the combination of orbital overlap (ligand‐to‐metal bonding) and the degree of ionicity of the bonding.

The chemoselective cleavage of an arene ring in biphenylene is reported using an aluminum(I) complex. The reaction proceeds with complete integrity of the central four‐membered ring despite this ring containing the weakest C−C σ‐bond in the hydrocarbon scaffold.

Abstract

The chemoselective cleavage of a six‐membered aromatic ring in biphenylene is reported using an aluminum(I) complex. This type of selectivity is unprecedented. In every example of transition metal mediated C−C σ‐bond activation reported to date, the reaction occurs at the central four‐membered ring of biphenylene. Insight into the origin of chemoselectivity was obtained through a detailed mechanistic analysis (isolation of an intermediate, DFT studies, activation strain analysis). In conclusion, the divergent reactivity can be attributed to differences in both the symmetry and radial extension of the frontier molecular orbitals of the aluminum(I) fragment compared to that of common transition metal fragments.

A new donor‐acceptor‐donor‐acceptor macrocyclic π‐conjugated compound comprising of two electron‐donors (N,N’‐diphenyl‐m‐phenylenediamine) and two electron‐acceptors (dibenzo[a,j]phenazine) has been synthesized, and its structure and physicochemical properties have been investigated. In comparison with para‐linked macrocyclic analogue, the influence of topology of the phenylenediamine donors on properties has been revealed.

Abstract

A new thermally activated delayed fluorescence (TADF)‐displaying macrocyclic compound m‐1 comprising of two electron‐donors (N,N’‐diphenyl‐m‐phenylenediamine) and two electron‐acceptors (dibenzo[a,j]phenazine) has been synthesized. The macrocycle developed herein is regarded as a regioisomer of the previously reported TADF macrocycle p‐1, which has two N,N’‐diphenyl‐p‐phenylenediamines as the donors. To understand the influence of the topology of the phenylenediamine donors on physicochemical properties of TADF‐active macrocycles, herein the molecular structure in the single crystals, photophysical properties, electrochemical behavior, and TADF properties of m‐1 have been investigated compared with those of p‐1. The substitution of p‐phenylene donor with m‐phenylene donor led to distinct positive solvatoluminochromism over the full visible‐color range, unique oxidative electropolymerization, and slightly lower contribution of TADF, due to the lower CT character in the excited states.

Ferroelectric materials, equipping a striking bulk photovoltaic effect (BPVE), have shown great potential for the next generation photovoltaic non‐volatile memories. However, further applications of conventional ferroelectric materials are hindered by their poor performance. The family of hybrid perovskite ferroelectrics combining fascinating polarization and striking semiconducting properties presents significant possibilities. Herein, through a functional unit‐transmutation strategy, a fatigue‐free layered hybrid perovskite ferroelectric (C 6 H 5 CH 2 NH 3 ) 2 CsPb 2 Br 7  ( BCPB ) has been developed, which demonstrates stable spontaneous polarization ( P s ) of 6.5 μC/cm 2 and high Curie temperature up to 425 K. Meanwhile, BCPB shows splendid BPVE properties with noticeable zero‐bias photocurrent density (5 μA/cm 2 ), and high on/off switching ratio of current (over 3×10 5 ); these merits even overmatch the most known ferroelectric semiconductor BiFeO 3 . Particularly, the unique structure with self‐regulated net electrical charged layers gives rise to the fatigue‐free feature of P s and BPVE (no significant fatigue after 10 8 polarity switching cycles), promoting the potential applications of BCPB in photovoltaic non‐volatile memories. As a pioneering work, it offers an efficient approach for exploring fatigue‐free semiconducting ferroelectrics as well as excavates their further applications in next‐generation electronic devices.