Alessandro Bismuto

As perfluoroalkyl‐substituted aluminum compounds are virtually unknown, this work presents a convenient synthesis of a tetrakis(perfluoroalkyl) aluminum species, the tetrakis(pentafluoroethyl)aluminate, [Al(C₂F₅)₄]⁻. Several salts of the [Al(C₂F₅)₄]⁻ ion are accessible by treatment of Li[AlH₄] with Si(C₂F₅)₃CH₃ and subsequent cation exchange.

Abstract

While perfluorinated aryl, aryloxy and alkoxy aluminum species are well‐established as weakly coordinating anions (WCAs), corresponding perfluoroalkyl aluminum derivatives are virtually unknown. Reaction of Si(C₂F₅)₃CH₃ with Li[AlH₄] afforded the tetrakis(pentafluoroethyl)aluminate, [Al(C₂F₅)₄]⁻. Several salts of the [Al(C₂F₅)₄]⁻ ion were synthesized and characterized by NMR spectroscopic methods, mass spectrometry, X‐ray diffraction studies and elemental analysis.

Al finds Y: The reaction between a dialkyl‐Al anion and [Y(CH₂SiMe₃)₂(thf)₃][BPh₄] gave (dialkylalumanyl)yttrium complex 2, possessing the unprecedented 2 center–2 electron Al−Y bond as characterized by the NMR spectra and X‐ray analysis. DFT calculations on 2 revealed its overlapping 3 p‐ and 4 d‐orbitals of the Al and Y atoms to be LUMO. A visible absorption of 2 at 432 nm was assigned to a transition from Al−Y bond to LUMO without any π‐electrons.

Abstract

The reaction between a dialkyl‐substituted alumanyl anion and [Y(CH₂SiMe₃)₂(thf)₃][BPh₄] resulted in the formation of (dialkylalumanyl)yttrium complex 2, which exhibits the first 2‐center–2‐electron (2 c‐2 e) Al−Y bond. The ¹H and ¹³C NMR spectra of 2 together with an X‐ray crystallographic analysis indicated a C _2v symmetrical structure. DFT calculations on 2 revealed that its LUMO consists of overlapping 3 p‐ and 4 d‐orbitals of the Al and Y atoms, respectively, and that the HOMO–LUMO gap is narrow. The UV/Vis spectrum of 2 exhibited a visible absorption at 432 nm, which suggests that the strong σ‐donating and π‐accepting character of the three‐coordinate dialkylalumanyl ligand generates a colored d⁰‐complex that does not contain any π‐electrons.

The nickel⁰‐catalyzed anionic cross‐coupling reaction (ACCR) of lithium sulfonimidoyl alkylidene carbenoids (metalloalkenyl sulfoximines) with organometallic reagents affords substituted alkenylmetals and lithium sulfinamides. The Ni⁰‐catalyzed ACCR of three different types of metalloalkenyl sulfoximines, including acyclic, axially chiral, and exocyclic derivatives, with sp² organolithiums and sp² and sp³ Grignard reagents has been experimentally and theoretically studied.

Abstract

The mechanistic platform for a novel nickel⁰‐catalyzed anionic cross‐coupling reaction (ACCR) of lithium sulfonimidoyl alkylidene carbenoids (metalloalkenyl sulfoximines) with organometallic reagents is reported herein, affording substituted alkenylmetals and lithium sulfinamides. The Ni⁰‐catalyzed ACCR of three different types of metalloalkenyl sulfoximines, including acyclic, axially chiral and exocyclic derivatives, with sp² organolithiums and sp² and sp³ Grignard reagents has been studied. The ACCR of metalloalkenyl sulfoximines with PhLi in the presence of the Ni⁰‐catalyst and precatalyst Ni(PPh₃)₂Cl₂ afforded alkenyllithiums, under inversion of configuration at the C atom and complete retention at the S atom. In a combination of experimental and DFT studies, we propose a catalytic cycle of the Ni⁰‐catalyzed ACCR of lithioalkenyl sulfoximines. Computational studies reveal two distinctive pathways of the ACCR, depending on whether a phosphine or 1,5‐cyclooctadiene (COD) is the ligand of the Ni atom. They rectify the underlying importance of forming the key Ni⁰‐vinylidene intermediate through an indispensable electron‐rich Ni⁰‐center coordinated by phosphine ligands. Fundamentally, we present a mechanistic study in controlling the diastereoselectivity of the alkenyllithium formation via the key lithium sulfinamide coordinated Ni⁰‐vinylidene complex, which consequently avoids an unselective formation of an alkylidene carbene Ni‐complex and ultimately racemic alkenyllithium.

Al in : Reaction of the aluminum dialkynyl with B(C₆F₅)₃ proceeds through an intermediate with Al⋅⋅⋅η²‐C≡C side‐on coordination to form the alumole. Some of the alumoles synthesized in this way exhibit an aggregation‐induced emission (AIE) bright yellow fluorescence.

Abstract

Reaction of the aluminum dialkynyl LAl(CCR)₂ (L=N,N‐chelate ligand and R=organic group) with B(C₆F₅)₃ proceeds through an intermediate with Al⋅⋅⋅η²‐C≡C side‐on coordination to form the alumoles (2 , 4 , 6 ). A distinctive reaction pattern indicates a new facile synthetic route to aluminum‐containing heterocycles. The synthetic process is described, and the characterization of compounds and computational calculations were carried out. Furthermore, alumoles 2 and 4 exhibit an aggregation‐induced emission (AIE) of the bright yellow fluorescence.

An abstract concept: A trigonal planar imido cobalt(III) complex, obtained from reaction of a quasi‐linear cobalt(I) complex with an organo azide, is capable of intermolecular H atom abstraction of C−H bonds. The resulting cobalt(II) amide itself can either deprotonate the substrate, facilitate an H atom abstraction or mediate a stepwise proton/electron transfer. As the latter regenerates the starting cobalt(I) complex, a first catalytic application is presented.

Abstract

The 3d‐metal mediated nitrene transfer is under intense scrutiny due to its potential as an atom economic and ecologically benign way for the directed amination of (un)functionalised C−H bonds. Here we present the isolation and characterisation of a rare, trigonal imido cobalt(III) complex, which bears a rather long cobalt–imido bond. It can cleanly cleave strong C−H bonds with a bond dissociation energy of up to 92 kcal mol⁻¹ in an intermolecular fashion, unprecedented for imido cobalt complexes. This resulted in the amido cobalt(II) complex [Co(hmds)₂(NH ^t Bu)]⁻. Kinetic studies on this reaction revealed an H atom transfer mechanism. Remarkably, the cobalt(II) amide itself is capable of mediating H atom abstraction or stepwise proton/electron transfer depending on the substrate. A cobalt‐mediated catalytic application for substrate dehydrogenation using an organo azide is presented.

The phenomenon of redox activity has remained a pivotal concept underlining various electronic processes. This minireview focuses on the diverse bond activations mediated by redox active ligands that have been documented recently.

Redox active ligands are an integral part of many biological events and significant natural processes. Transformations assisted by such ligands gather the limelight owing to their excellent activity and selectivity towards the transformation of organic functionalities as well as activation of small molecules. The past few decades have seen an increasing demand of the field featuring its significance as the concept derived products find applications in chemical, pharmaceutical and agrochemical industries. Besides, the mechanistic insights allow for a grass root understanding of the underlining chemistry. The present article aims to highlight bond activations platformed on this concept by citing a few recent examples.

Terminal, electrophilic phosphinidene complexes (M=PR) are attractive platforms for PR‐transfer to organic substrates. In contrast to aryl‐ or alkylphosphinidene complexes terminal chlorophosphinidenes (M=PCl) have only been proposed as transient intermediates but isolable example remain elusive. Here we present the transfer of PCl from chloro‐substituted dibenzo‐7λ³‐phosphanorbornadiene to a square‐planar osmium(II) PNP pincer complex to give the first isolable, terminal chlorophosphinidene complex with remarkable thermal stability. Os=P bonding was examined computationally giving rise to highly covalent {Os^II=P^ICl} double bonding.

Heterocycle Cross‐Couplings by Sulfur. Addition of heteroaryl nucleophiles onto a simple, readily‐accessible alkyl sulfinyl(IV) chloride allows formation of a trigonal bipyramidal sulfurane intermediate. Reductive elimination provides bis‐heteroaryl products in a practical and efficient fashion.

Abstract

Despite the tremendous utilities of metal‐mediated cross‐couplings in modern organic chemistry, coupling reactions involving nitrogenous heteroarenes remain a challenging undertaking – coordination of Lewis basic atoms into metal centers often necessitate elevated temperature, high catalyst loading, etc. Herein, we report a sulfur (IV) mediated cross‐coupling amendable for the efficient synthesis of heteroaromatic substrates. Addition of heteroaryl nucleophiles to a simple, readily‐accessible alkyl sulfinyl (IV) chloride allows formation of a trigonal bipyramidal sulfurane intermediate. Reductive elimination therefrom provides bis‐heteroaryl products in a practical and efficient fashion.

The BeOBeC multiple radical features a quartet carbyne moiety, and thus represents the first carbyne radical to have a quartet ground state with three unpaired electrons on the carbon center.

Abstract

Through reaction of beryllium dimers with carbon monoxide, a carbonyl complex BeBeCO is formed in solid neon. Upon visible light excitation, the BeBeCO complex rearranges to a BeCOBe isomer, which further isomerizes to a low‐energy BeOBeC species under UV‐visible light excitation. These species are identified on the basis of infrared absorption spectroscopy with isotopic substitutions and quantum chemical studies. The BeOBeC molecule is characterized to be a multiple radical species having an electronic quintet ground state featuring an unusual quartet carbyne unit with three unpaired electrons on the carbon center. Bonding analysis indicates that the strong Pauli repulsion between carbon 2s lone pair electrons and the σ electrons of the BeOBe fragment significantly weakens the Be−C bonding and destabilizes the triplet state of the BeOBeC radical with a doublet carbyne unit. The three‐center π‐bonding of BeOBe is also found to play a role in stabilizing the quartet carbyne.

Squeezing in CO: Ni^I complexes can promote the carbonylative coupling of Ni^II‐acyl complexes with primary and secondary iodides to provide a general method for the accessing aliphatic ketones directly from carbon monoxide. The methodology is ideal for carbon isotope labeling and illustrated with examples for accessing carbon 13 and carbon 14 bioactive molecules.

Abstract

An extensive range of functionalized aliphatic ketones with good functional‐group tolerance has been prepared by a Ni^I‐promoted coupling of either primary or secondary alkyl iodides with NN₂ pincer Ni^II‐acyl complexes. The latter were easily accessed from the corresponding Ni^II‐alkyl complexes with stoichiometric CO. This Ni‐mediated carbonylative coupling is adaptable to late‐stage carbon isotope labeling, as illustrated by the preparation of isotopically labelled pharmaceuticals. Preliminary investigations suggest the intermediacy of carbon‐centered radicals.

Dynamic dimers: Chlorin cyclophane dimers with distinct syn‐ and anti‐conformational structures were synthesized for the first time. The unusual dynamic behaviours of both the chlorin cyclophane dimers were established by using variable temperature (VT)‐NMR, VT‐UV, and VT‐EPR spectroscopy and X‐ray diffraction analysis.

Abstract

2,18‐Bis(dicyanomethyl)‐substituted Ni^II porphyrin 8 and Zn^II porphyrin 11 were prepared and subjected to oxidation with PbO₂ in CH₂Cl₂ at 298 K to give cyclophane‐type chlorin dimers (9)₂ and (12)₂ as a consequence of double recombination of biradicals 9 and 12, respectively. Dimer (9)₂ takes a syn‐conformation of two distorted Ni^II chlorins but (12)₂ takes an anti‐conformation of relatively planar Zn^II chlorins. At 298 K, dimer (9)₂ is stable and its ¹H NMR spectrum is sharp but becomes broad at high temperature, while the ¹H NMR spectrum of (12)₂ is considerably broad even at 298 K but becomes sharper at low temperature. These results indicate that the chlorin dimers dissociate to radical species, but the activation barrier of the dissociation of (12)₂ is much less than that of (9)₂. The involvement of diradicals in dynamic covalent chemistry has been suggested by thermal scrambling of hetero dimer (16)₂ to give homo dimers (9)₂ and (15)₂.

The first example of an isolable bent μ‐carbido complex, that behaves in a manner reminiscent of a heterocyclic carbene is described.

Abstract

The linear μ‐carbido complex [Rh₂(μ‐C)Cl₂(dppm)₂] (dppm=bis(diphenylphosphino)methane) reacts with dimethylacetylene dicarboxylate (DMAD) to afford [Rh₂(μ‐C)(μ‐DMAD)Cl₂(dppm)₂], which features a bent RhCRh linkage (124.7°) that might be described as a dirhoda‐heterocyclic carbene, as demonstrated by coordination to further metal centers.

Hype in science is commonplace, compounded by the hypocrisy of those who engage in or tolerate it while disapproving of the consequences. These are first steps along a slippery slope of hype, hypocrisy, data falsification, and dissemination of fake science, encouraged by systemic drivers in the contemporary structure of the science establishment. Collective, concerted intervention is required to discourage entry to this dangerous pathway; chemists must play an active role.

Abstract

In chemistry and other sciences, hype has become commonplace, compounded by the hypocrisy of those who tolerate or encourage it while disapproving of the consequences. This reduces the credibility and trust upon which all science depends for support. Hype and hypocrisy are but first steps down a slippery slope towards falsification of results and dissemination of fake science. Systemic drivers in the contemporary structure of the science establishment encourage exaggeration and may lure the individual into further steps along the hype‐hypocrisy‐falsification‐fakery continuum. Collective, concerted intervention is required to effectively discourage entry to this dangerous pathway and to restore and protect the probity and reputation of the science system. Chemists must play and active role in this effort.

Synthesis and characterization of the new cyclometalated complex salts [Rh(ptpy)₂(5.6‐dimethyl‐1,10‐phenanthroline)]PF₆ (1a ) [Rh(ptpy)₂(2.9‐dimethyl‐4.7‐diphenyl‐1,10‐ phenanthroline)]PF₆ (2a ), [Rh(ptpy)₂(5‐amino‐1,10‐phenanthroline)] PF₆ (3a ), and [M(ptpy)₂ (pyrazino‐[2.3‐f]‐1,10‐phenanthroline)]PF₆ (M = Rh, 4a ; M = Ir, 4b ), (ptpy = 2‐(p‐tolyl)pyridinato) are described. The molecular structures of compounds 1b and 4a in the solid state were determined by single‐crystal X‐ray diffraction. All these compounds and their already known Iridium counterparts 1b – 3b display significant cytotoxicity against human cancer cell lines MCF‐7 (human breast adenocarcinoma) and HT‐29 (colon adenocarcinoma) with IC₅₀ values in the low micromolar range.