Alessandro Bismuto

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.

Methods for the selective chlorination of organogermylhydrides are given by the selective functionalization of organogermylhydrides of types R₃GeH, R₂GeH₂ and RGeH₃ (R = alkyl, aryl). The use of trichloroisocyanuric acid (TCCA) allows the direct conversion of Ge‐H functions into their monochlorinated derivatives R₂Ge(Cl)H and RGe(Cl)H₂.

The valence‐isolectronic three‐atomic molecules CS₂ and CO₂ react in a series of consecutive reactions with the hydride‐bridged silylium cation [Et₃Si−H−SiEt₃]⁺ to give a number of new silyl‐substituted sulfonium or oxonium ions, respectively. Crystal structure determinations and quantum‐chemical calculations give detailed insight into the reaction cascade (see scheme).

Abstract

The hydride‐bridged silylium cation [Et₃Si−H−SiEt₃]⁺, stabilized by the weakly coordinating [Me₃NB₁₂Cl₁₁]⁻ anion, undergoes, in the presence of excess silane, a series of unexpected consecutive reactions with the valence‐isoelectronic molecules CS₂ and CO₂. The final products of the reaction with CS₂ are methane and the previously unknown [(Et₃Si)₃S]⁺ cation. To gain insight into the entire reaction cascade, numerous experiments with varying conditions were performed, intermediate products were intercepted, and their structures were determined by X‐ray crystallography. Besides the [(Et₃Si)₃S]⁺ cation as the final product, crystal structures of [(Et₃Si)₂SMe]⁺, [Et₃SiS(H)Me]⁺, and [Et₃SiOC(H)OSiEt₃]⁺ were obtained. Experimental results combined with supporting quantum‐chemical calculations in the gas phase and solution allow a detailed understanding of the reaction cascade.

A Rh(III)‐catalyzed C‐H arylation reaction of N‐nitrosoanilines was developed in which arylboronic acids were used as arylation reagents. N‐nitroso was used as a transformable directing group. The product N‐nitroso‐[1,1′‐biphenyl]‐2‐amine can be used for the synthesis of diverse N‐hetero biaryl compounds, such as [1,1′‐biphenyl]‐2‐amine, carbazole, phenanthridone.

Abstract

A Rh(III)‐catalyzed C−H arylation reaction of N‐nitrosoanilines has been developed in which arylboronic acids were used as arylation reagents. It provides an efficient strategy for the synthesis of N‐nitroso‐[1,1′‐biphenyl]‐2‐amine, which is an important starting material for the synthesis of N‐hetero biaryl compounds, such as 2‐amine‐1,1′‐biphenyl, carbazole, phenanthridone. This protocol can be applied to various N‐alkyl substituted N‐nitrosoanilines and N‐nitrosoanilines with substituents on the phenyl ring. Arylboronic acids with both electron‐donating and electron‐withdrawing groups are tolerated.

The metal‐catalyzed cross‐coupling of organozinc reagents has been studied since its discovery in 1977, but the dramatic dependence on salt additives was only realized some 30 years later. LiCl and LiBr have been found not only to improve coupling outcomes, but their absence can shut down the reaction completely. This Review summarizes all reports outlining the ways that salt additives impact the formation of organozinc reagents and their use in Negishi cross‐coupling.

Abstract

The first cross‐coupling of organozinc nucleophiles with aryl halides was reported in 1977 by Negishi. Unknown to all at the time was the importance of salt additives that were often present as a byproduct from the organozinc preparation. For decades, these salt additives were overlooked until 2006 when it was discovered that two different, yet effective methods for preparing organozinc solutions (i.e. one with salt and one without) provided drastically different results. Since this finding, the exact role of salt additives in cross‐coupling has been debated in the catalysis community. In this Review we highlight all the major discoveries regarding the influence of salt additives on the formation of organozinc reagents and their use in the Negishi reaction. These effects include solubilizing key intermediates, the formation of higher‐order zincates, product inhibition, catalyst protection, and solvent effects.

Ni _x (N _y H _z ) complexes are synthesized and characterized as intermediates in a homogenous nickel‐mediated ammonia oxidation cycle. Data on the key N−N bond formation step are consistent with the homocoupling of a Ni^III–NH₂ species to yield a nickel(II)‐bound hydrazine adduct.

Abstract

M(NH _x ) intermediates involved in N−N bond formation are central to ammonia oxidation (AO) catalysis, an enabling technology to ultimately exploit ammonia (NH₃) as an alternative fuel source. While homocoupling of a terminal amide species (M‐NH₂) to form hydrazine (N₂H₄) has been proposed, well‐defined examples are without precedent. Herein, we discuss the generation and electronic structure of a Ni^III‐NH₂ species that undergoes bimolecular coupling to generate a Ni^II ₂(N₂H₄) complex. This hydrazine adduct can be further oxidized to a structurally unusual Ni₂(N₂H₂) species; this releases N₂ in the presence of NH₃, thus establishing a synthetic cycle for Ni‐mediated AO. Distribution of the redox load for H₂N‐NH₂ formation via NH₂ coupling between two metal centers presents an attractive strategy for AO catalysis using Earth‐abundant, late first‐row metals.

The rising of the photoluminescence quantum yield: This work describes a new design for blue‐phosphorescent platinum acetylide complexes, using strong σ‐donor acyclic diaminocarbene (ADC) auxiliary ligands. Conversion of one isocyanide in the precursor complex to and ADC, by nucleophilic addition of a secondary amine, engenders up to a 16‐fold increase in photoluminescence quantum yield.

Abstract

Here we report five blue‐phosphorescent platinum bis‐phenylacetylide complexes with an investigation of their photophysical and electrochemical attributes. Three of the complexes (1–3) are of the general formula cis‐Pt(CNR)₂(C≡CPh)₂, in which CNR is a variably substituted isocyanide and C≡CPh is phenylacetylide. These isocyanide complexes serve as precursors for complexes of the general formula cis‐Pt(CNR)(ADC)(C≡CPh)₂ (4 and 5), in which ADC is an acyclic diaminocarbene installed by amine nucleophilic addition to one of the isocyanides. All of the complexes exhibit deep blue phosphorescence with λ _max ∼430 nm in poly(methyl methacrylate) (PMMA) thin films. Whereas isocyanide complexes 1–3 exhibit modest photoluminescence quantum yields (Φ _PL), incorporation of one acyclic diaminocarbene ligand results in a three‐fold to 16‐fold increase in Φ _PL while still maintaining an identical deep blue color profile.

The first bismuth‐catalyzed carbonyl hydrosilylation is presented. The catalytically active electrophilic dicationic bismuth species [(Me₂NC₆H₄)Bi(L)₃]²⁺ (L=aldehyde/ketone) is characterized both in solution and in the solid state. Control experiments and computation studies support a carbonyl activation mechanism at bismuth followed by silane addition.

Abstract

Bismuth compounds are gaining importance as potential alternatives to transition‐metal complexes and electron deficient lighter p‐block compounds in homogeneous catalysis. Computational analysis on the two‐coordinate [(Me₂NC₆H₄)Bi]²⁺ possessing three electrophilic sites is experimentally evidenced by the isolation of [{Me₂NC₆H₄}Bi{OP(NMe₂)₃}₃][B(3,5‐C₆H₃Cl₂)₄]₂. These observations led us to generate dicationic organobismuth catalyst, [(Me₂NC₆H₄)Bi(L)₃]²⁺ (L=aldehyde/ketone), evidenced by NMR spectroscopy in solution and by single‐crystal X‐ray diffraction in the solid state. It efficiently catalyzes hydrosilylation of aldehydes and ketones resulting in silyl ethers as the only products in high yields. Our investigations support a carbonyl activation mechanism at the bismuth center followed by Si−H addition.

Small change, big payoff: A small modification of the parent naphthodiazaborines affords stable diazaboryl‐naphthyl‐ketones (DNKs), unlocking new photophysical properties, including extremely bright fluorescence and aggregation induced emission, with promising applications in optoelectronics and chemical analysis such as the low‐ppm quantitation of trace boronic acid contaminants in pharmaceutical intermediates.

Abstract

This study describes the synthesis, structure, and photophysical properties of a new luminescent polyaromatic boronic acid scaffold, diazaboryl‐naphthyl‐ketones (DNKs). These stable compounds display extremely bright fluorescence, aggregation‐induced emission, positive solvatochromism, and solid‐state fluorescence. DFT calculations and X‐ray crystallographic study revealed notable electronic and structural differences between these compounds and the parent diaminonaphthalene (DAN) adducts. Acylation of the DAN system causes a localization of both HOMO and LUMO onto the DNK unit, which validates the negligible influence of the B‐aryl substituent. The LUMO energy is lowered, and its shape significantly altered. Photophysical data in solution and the solid state revealed blue‐shifted, narrowed, and intense emissions for DNKs (up to 89 % quantum yield). The potential utility of the fluorogenic DNK system was demonstrated with a proof‐of‐concept for the determination of trace boronic acid contaminants in solid samples, down to one‐ppm level, using HPLC with fluorescence detection. This method could be useful in pharmaceutical development for the quantitation of difficult‐to‐detect and potentially mutagenic residual boronic acid from late cross‐coupling reactions in drug syntheses.

A new P^III Lewis superacid with an ancillary molybdenum carbonyl fragment reacts with Et₃SiH to give a P‐H stabilized silylium ion that participates in catalytic hydrosilylation.

Abstract

The Mo=PR₂ π* orbital in a Mo phosphenium complex acts as acceptor in a new P^III‐based Lewis superacid. This Lewis acid (LA) participates in electrophilic Si‐H abstraction from E₃SiH to give a Mo‐bound secondary phosphine ligand, Mo‐PR₂H. The resulting Et₃Si⁺ ion remains associated with the Mo complex, stabilized by η¹‐P‐H donation, yet undergoes rapid exchange with an η¹‐Si‐H adduct of free silane in solution. The equilibrium between these two adducts presents an opportunity to assess the role of this new LA in catalytic reactions of silanes: is the LA acting as a catalyst or as an initiator? Preliminary results suggest that a cycle including the Mo‐bound phosphine‐silylium adduct dominates in the catalytic hydrosilylation of acetophenone, relative to a putative cycle involving the silane‐silylium adduct or “free” silylium.

Organoboron analogues of viologens were synthesized and characterized structurally, photophysically, and electrochemically. Bipyridine‐based N^{^}N chelates demonstrate two reversible reduction events, demonstrating their applicability for use in redox‐flow batteries.

This work presents the use of organoboron compounds as anolytes in redox flow batteries. Through the study of their structural, electrochemical, and photophysical properties, four bipyridyl boronium salts show potential for application in such batteries. The compounds were synthesized in moderate to high yields by previously published methods. We find when using chelating bipyridyl‐based substituents, the complexes undergo two reversible reductions; however, when switching to phenanthroline‐based substituents, the reduction events are no longer reversible. Density‐functional theory calculations indicate that the chelating nitrogen heterocycle is the locus of reduction and fluorescence.