Search

Despite the progress made in the field of synthetic organic photocatalysis over the past decade, the use of higher wavelengths, especially those in the deep-red portion of the electromagnetic spectrum, remains comparatively rare. We have previously disclosed that a well-defined N,C,N -pincer bismuthinidene ( 1a ) can undergo formal oxidative addition into a wide range of aryl electrophiles upon absorption of low-energy red light. In this study, we map out the photophysical dynamics of 1a and glean insights into the nature of the excited state responsible for the activation of aryl electrophiles. Transient absorption and emission techniques reveal that, upon irradiation with red light, the complex undergoes a direct S 0 → S 1 metal-to-ligand charge transfer (MLCT) transition, followed by rapid intersystem crossing (ISC) to a highly reducing emissive triplet state (-2.61 V vs Fc +/0 in MeCN). The low dissipative losses incurred during ISC (∼6% of the incident light energy) help rationalize the ability of the bismuthinidene to convert low-energy light into useful chemical energy. Spectroelectrochemical and computational data support a charge-separated excited-state structure with radical-anion character on the ligand and radical-cation character on bismuth. Kinetic studies and competition experiments afford insights into the mechanism of oxidative addition into aryl iodides; concerted and inner-sphere processes from the triplet excited state are ruled out, with the data strongly supporting a pathway that proceeds via outer-sphere dissociative electron transfer.

A series of dibenzobismepinyl (C 14 H 10 Bi) substituted transition metal complexes of the type [(C 14 H 10 Bi)M(CO) x (L)] (M=Mn, Co, Fe) was prepared in salt elimination reactions from a halobismepine and sodium metallates. Irradiation of these complexes with visible light has been investigated, aiming at the elimination of one carbonyl ligand and the concomitant coordination of the bismepine's olefin moiety to the transition metal center. The resulting complexes of the type [{κ 2 C,κ 1 Bi-(C 14 H 10 )Bi}M(CO) x-1 (L)] (M=Co, Fe) have been isolated and fully characterized. When two dibenzobismepinyl units are positioned in the coordination sphere of an iron carbonyl complex fragment, reductive elimination/oxidative addition events of the dibismuthane (C 14 H 10 Bi) 2 have been shown to be relevant. The analytical techniques applied in this work include (heteronuclear) NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction analysis, UV/Vis spectroscopy, IR spectroscopy and (TD)-DFT calculations., (© 2024 The Author(s). Chemistry - A European Journal published by Wiley-VCH GmbH.)

In this study, we report the first example of acyclic (amino)(N-pyridinium)carbenoid gold(III) complexes synthesized via a coupling reaction between 2-pyridylselenyl chloride and Au(I)-bound isonitriles. The reaction involves an initial oxidative addition of the Se–Cl moiety to Au(I), followed by the nucleophilic addition of the pyridine fragment to the isonitrile's C≡N bond, furnishing a metallacycle. Importantly, this is the first example of the pyridine acting as a nucleophile towards metal-bound isonitriles. Arguably, such an addition is due to the chelate effect. The structures of the gold(III) carbenoid complexes were unambiguously established using X-ray diffraction and NMR spectroscopy. Theoretical calculations, including DFT, Natural Resonance Theory (NRT), and Meyer bond order (MBO) analyses, were used to analyze the different resonance forms. The reaction mechanism was further elucidated using DFT calculations, which identified the oxidative addition as the rate-determining step with a barrier of 29.7 kcal/mol. The nucleophilic addition proceeds with a minimal barrier, making the reaction highly favorable. The antiproliferative activity of new compounds 2a–2e was tested against two human cancer cell lines: A2780 ovarian adenocarcinoma and the A278Cis cisplatin-resistant variant. [ABSTRACT FROM AUTHOR]

Zwitterionic π-allenyl palladium species are newly developed intermediates. A substrate-controlled step existed in the cycloaddition of zwitterionic π-allenyl palladium species with tropsulfimides or tropones. With the assistance of previously experimental studies, zwitterionic allenyl/propargyl palladium species was provenly found by HRMS. Further DFT calculation studies show that zwitterionic π-allenyl palladium species are generated through the oxidative addition of Pd(0), which can be promoted by Lewis acid like Yb(OTf)3, and the cycloaddition more likely undergoes through an outer sphere nucleophilic attack. The isomerization is caused by the difference of dissociation energy between the cycloaddition intermediation of tropsulfimides and tropones, forming the substrate-controlled specificity. [ABSTRACT FROM AUTHOR]

Palladium (Pd) is a 4d transition metal with electronic configuration [Kr] 4d10 5s0, and it is one of the most widely studied metals in the periodic table due to its versatile catalytic role in organic synthesis. The choice of ligands that can coordinate with Pd sites plays a crucial role in the progress of the reaction. Due to the coexistence of multiple oxidation states (Pd(0)/Pd(II)), the active Pd sites of the catalysts can participate in various stages of the coupling reaction. The Pd-catalyzed C-C coupling reactions proceed through four steps: (1) oxidative addition of the reactant to the catalytic site, (2) transmetallation, (3) rearrangements of ligand centers and (4) reductive elimination to the coupling products. For the heterogeneous Pd nanocatalysts, active Pd sites are often strongly bound (chelated) with the solid catalyst surfaces. In this review, we have highlighted the advancements made in the heterogeneous Pd nanocatalysts with an emphasis on the types of different classes of porous solids, which could ligate with the Pd centers via strong covalent bonds. The high specific surface areas and small Pd sites of these nanocatalysts provide a larger number of catalytic sites and thus facilitate the reaction. Mechanistic aspects of the C-C cross-coupling reactions are discussed in the context of the structure–reactivity relationship. [ABSTRACT FROM AUTHOR]

Transition‐metal‐catalyzed hydroamination of unsaturated hydrocarbons is an appealing synthetic tool for the construction of high value‐added chiral amines. Despite significant progress in the asymmetric hydroamination of alkenes, allenes, and 1,3‐dienes, asymmetric hydroamination of 1,6‐enynes or 1,7‐enynes remains rather limited due to the enormous challenges in controlling the chemoselectivity and stereoselectivity of the reaction. Herein, we report a Ni‐catalyzed chemo‐ and enantioselective reductive cyclization/amidation and amination of 1,6‐enynes and 1,7‐enynes using dioxazolones or anthranils as nitrene‐transfer reagents. This mild, modular, and practical protocol provides rapid access to a variety of enantioenriched 2‐pyrrolidone and 2‐piperidone derivatives bearing an aminomethylene group at the 4‐position in good yields (up to 83 %) with excellent enantioselectivities (46 examples, up to 99 % ee). Mechanistic experiments and density functional theory calculations indicate that the reaction is initiated by hydronickelation of alkynes followed by migratory insertion into alkenes, rather than by a [2+2+1] oxidative addition process of nickel to alkenes and alkynes. [ABSTRACT FROM AUTHOR]

Reactions of the anti-alcohol drug disulfiram (tetraethylthiuram disulphide = Et4TDS) with low valent triosmium complexes are described. Room temperature reaction with [Os3(CO)10(MeCN)2], affords three new open polynuclear clusters, [Os3(CO)10(S2CNEt2)2] (1), [Os4(CO)12{µ3-η1(C),κ2(O,O)-CO2}(S2CNEt2)(µ-S2CNEt2)] (2) and [Os3(CO)9(µ3-SCNEt2){µ-SC(O)NEt2}] (3) together with the known mononuclear complex cis-[Os(CO)2(S2CNEt2)2] (4). All result from oxidative-addition of disulfiram to the triosmium centre, with 2 also capturing CO2, while cluster 3 has undergone further C–S bond scission and partial oxidation of one of the generated thiocarboxamide ligands. With [Os3(CO)10(µ-H)2], complexes 1 and 4 are also formed along with previously reported [Os3(CO)10(µ-S2CNEt2)(µ-H)] (5), [Os3(CO)9(µ3-S2CNEt2)(µ-H)] (6), and the new cluster, [Os3(CO)9(µ-S2CNEt2)(µ-H)] (8), which is an isomer of 6. The product distribution is rationalized by completing pathways following the oxidative-addition of disulfiram. Thus, reductive-elimination of H2 affords 1, which in turn converts to 4, while reductive-elimination of the (unstable) dithiocarbamic acid, Et2NCS2H, leads to the formation of 5, which can further lose CO to afford isomers 6 and 8. Heating disulfiram with [Os3(CO)12] at 110 °C predominantly affords 4, together with smaller amounts of the novel trithiocarbamate complex, cis-[Os(CO)2(S2CNEt2)(S3CNEt2)] (9). All the compounds have been characterized by elemental analysis, IR and 1H NMR spectroscopy, together with single crystal X-ray diffraction analysis of six molecules. [ABSTRACT FROM AUTHOR]

The electron motion mechanism of the metal-catalyzed Kumada cross-coupling reaction, which synthesizes biphenyl from chlorobenzene and phenylmagnesium chloride (a Grignard reagent) using a palladium (Pd) complex with an auxiliary phosphine ligand, is elucidated. This analysis is grounded in reactive orbital energy theory (ROET), enabling the examination of electron motions in comprehensive chemical reactions. We first calculated the intrinsic reaction coordinates (IRCs) for the four key processes of this reaction: oxidative addition, transmetalation steps 1 and 2, and reductive elimination. Using automatic orbital tracing in the ROET analysis, we identified the reactive orbitals for these IRCs. Consequently, we revealed the sequential electron motions driving these processes through animations, clarifying the electronic roles of the Pd center, the auxiliary ligand, and the Grignard reagent. These electron motions are consistent with experimental observations, indicating that the electron motions driving metal complex reactions can be effectively represented by changes in a single molecular orbital. [ABSTRACT FROM AUTHOR]

A detailed theoretical study delving into the molecular mechanisms of the Ullmann-type O-arylation reactions catalyzed by manganese and zinc metal ions has been investigated with the aid of the density functional theory (DFT) method. In contrast to the redox-active mechanisms proposed for classical Ullmann-type condensation reaction, a redox-neutral mechanism involving σ-bond metathesis emerged as the most appealing pathway for the investigated high-valent Mn(II) and Zn(II)-catalyzed O-arylation reactions. The mechanism remains invariant with respect to the nature of the central metal, ligand, base, etc. This unusuality in the mechanism has been dissected by considering three cases: ligand-free and ligand-assisted Mn(II)-catalyzed O-arylation reaction and ligand-assisted Zn(II)-catalyzed O-arylation reactions. In each class, a metal phenoxide species was identified as the active catalyst. The unusual mechanistic trends observed in these C–O cross-coupling reactions could be attributed to the stable electronic configurations (d5, d10) combined with the higher oxidation states of the catalytic metal centers (Mn(II), Zn(II)). The exploration into the electronic effects of functional groups in controlling the reaction feasibility within each metal variant disclosed a consistent trend irrespective of the transition metal catalyst involved in the reaction. It was found that the introduction of electron-withdrawing groups at the para-position of organic halide lowers the energy of their lowest unoccupied molecular orbitals (LUMO), thereby lowering the HOMO–LUMO gap between the coupling partners. This study thereby revealed a comprehensive understanding of the fundamental mechanisms exhibited by high-valent first-row transition metal catalysts that could foster the development of eco-friendly protocols for preparing biaryl ether moieties. [ABSTRACT FROM AUTHOR]

A cationic N-heterocyclic phosphenium (NHP) iron tetracarbonyl complex was synthesised from the free cation and its behaviour towards various anionic reactants studied. Reactions with fluoride, chloride, and hydride sources proceeded under attachment of the anion at phosphorus to yield Fe(CO)4-complexes of neutral diazaphospholenes, while bromide and iodide reacted under addition of the anion at the metal and decarbonylation to yield NHP iron halides. Reactions with amides and organometallics were unselective. At room temperature, predominantly reduction of the cationic complex to yield a spectroscopically detectable Fe-centred radical and its deactivation products was observable. At −78 °C, CH-metalation at the heterocycle was preferred, as evidenced by the structural characterisation of a neutral borane-adduct of the metalation product of a modified NHP complex. The dimer of the Fe-centred radical formed also in reactions of chloro- and bromo-diazaphospholenes with Fe2(CO)9, which proceed not only by complexation of the P-donors as expected, but involve also oxidative addition steps and single electron transfer processes in which excess iron complex acts as the reductant. The title complex and the products isolated in the reaction studies were characterised by spectroscopic data and in many cases by XRD studies. Computational studies were employed to analyse the differing reactivity of the cationic NHP complex towards light and heavy halide ions, and to help in the assignment of the radical intermediate observed. The more diverse reactivity of the cationic NHP complexes compared to their neutral analogues is attributed to their higher electrophilicity. [ABSTRACT FROM AUTHOR]

Motivated by the inherent benefits of synergistically combining electrochemical methodologies with nickel catalysis, we present here a Ni-catalyzed enantioselective electroreductive cross-coupling of benzyl chlorides with aryl halides, yielding chiral 1,1-diaryl compounds with good to excellent enantioselectivity. This catalytic reaction can not only be applied to aryl chlorides/bromides, which are challenging to access by other means, but also to benzyl chlorides containing silicon groups. Additionally, the absence of a sacrificial anode lays a foundation for scalability. The combination of cyclic voltammetry analysis with electrode potential studies suggests that NiI species activate aryl halides via oxidative addition and alkyl chlorides via single electron transfer. Reductive cross-coupling of aryl chlorides or electron-rich aryl bromides with benzyl chlorides remains a significant challenge, presumably due to the lower reactivity of aryl chlorides or electron-rich aryl bromides with the nickel catalyst compared with aryl iodides. Here, the authors present Ni-catalyzed enantioselective electroreductive cross-coupling of benzyl chlorides with aryl halides, yielding chiral 1,1-diaryl compounds with good to excellent enantioselectivity, without resorting to heterogeneous metal reductants or sacrificial anodes. [ABSTRACT FROM AUTHOR]

In recent years, there has been growing interest in the development of greener alternatives to traditional reagents used in carbon–carbon coupling reactions, particularly in response to environmental concerns. The commonly used aryl halides, despite being highly reactive in the Suzuki–Miyaura coupling (SMC), pose significant environmental risks. As a result, research has shifted towards exploring the use of phenols, which are widely accessible and environmentally benign. However, phenols are considerably less reactive due to the poor leaving group properties of the hydroxyl group, necessitating prior activation to facilitate their use in coupling reactions. This work aims to review the recent investigations on the activation strategies for phenols, focusing on their application in the Suzuki–Miyaura and related C-C couplings. In addition, the exploration of the potential of conducting the activation step "in situ" will also be discussed. We hope that this article will pave the way for the development of more sustainable and efficient coupling methodologies, addressing both ecological and practical challenges in organic synthesis. [ABSTRACT FROM AUTHOR]

C7H4IrNO4, triclinic, P 1 ‾ (no. 2), a = 3.5665(2) Å, b = 10.8307(5) Å, c = 10.8865(5) Å, α = 72.9610(10)°, β = 83.631(2)°, γ = 89.189(2)°, V = 399.51(3) Å3, Z = 2, Rgt(F) = 0.0484, wRref(F2) = 0.0201, T = 100 K. [ABSTRACT FROM AUTHOR]

The chemistry of platinum(II) and platinum(IV) with the ligands 3,4,5-tris(2-pyridyl)-4-H-1,2,4-triazole, L1, and 3,5-di(2-pyridyl)-4-(4-pyridyl)-4-H-1,2,4-triazole, L2, is described. The ligand L1 forms platinum(II) complexes [PtXY(κ2-N, N′-L1)] (X, Y = Cl, Cl; Cl, Me; Me, Me) by chelation while ligand L2 forms either analogous chelate complexes [PtXY(κ2-N, N′-L2)] (X, Y = Cl, Me; Me, Me) or acts as a monodentate ligand in forming trans-[PtCl2(SMe2)(κ1-N-L2)], in which only the 4-pyridyl group is coordinated. The electron-rich dimethylplatinum(II) complexes undergo oxidative addition reactions with methyl iodide to give [PtIMe3(κ2-N, N′-L1)], or with dichloromethane to give [PtClMe2(CH2Cl)(κ2-N, N′-L1)] or [PtClMe2(CH2Cl)(κ2-N, N′-L2)], each of which is formed as a mixture of three isomers. Structure determinations of several of these complexes are reported. [ABSTRACT FROM AUTHOR]

• DFT study on the mechanism of the Rh-catalyzed Pauson-Khand [3+2+1] cycloaddition. • Two kinds of reaction mechanisms with the reverse sequence are performed. • The calculations provide interpretation of the experimental observersed diastereoselectivity. DFT calculations have been carried out to study the mechanism of the Rh-catalyzed Pauson-Khand [3+2+1] cycloaddition reaction of vinylidene cyclopropane with carbon monoxide, as well as the diastereoselectivity of the products. It is found that reaction initializes by oxidative addition involves the distal C−C bond cleavage of cyclopropane groups, which is promoted by Rh(I) complex, to give η 4-TMM Rh(III) intermediate, followed by CO insertion. Continuing with the next process, olefin insertion, determines the formation of the cis -product or trans -product, depending on the orientation of coordinated olefin moiety to the Rh center. The calculations provide a successful interpretation of the experimental observersed diastereoselectivity. [Display omitted] [ABSTRACT FROM AUTHOR]

Redox-active ligands provide alternative reaction pathways by facilitating redox events. Among these, tridentate bis(piridylimino)isoindole (BPI) fragments offer great potential, though their redox-active behaviour remains largely underdeveloped. We describe herein a family of BPI germanium(II) complexes and the study of their redox properties. Amido complexes (RBPI)Ge[N(SiMe3)2] 1-R (R = H, Me, Et) showing a κ2-Npy,Niso coordination to the germanium(II) centre were prepared. In contrast, chloride derivatives (RBPI)GeCl, 2-R, display dynamic κ3-Npy,Niso,Npy coordination to the metal centre. The addition of silver bis(trifluoromethane)sulfonimide to compound 1-H generates a dinuclear complex, 3, where the silver atoms are bound to the germanium and one of the imine nitrogen atoms of another BPI fragment. The reduction of 2-R with KC8 generates dinuclear complexes (4-R) characterized by the formation of new C–C bonds between the isoindoline five-membered rings of two different BPI ligands via a radical mechanism, a transformation that does not take place in the absence of germanium. Interestingly, computational and spectroscopic studies support that the reduction takes place exclusively over the RBPI ligand. Strikingly, the newly formed C–C bond is also readily cleaved. Thus, subsequent reduction of 4-R (R = H, Me) using additional KC8 affords dinuclear species 5-R, with polymeric structures between potassium atoms and the corresponding dinuclear Ge2(RBPI2) fragments. [ABSTRACT FROM AUTHOR]

Methodological studies on the transformations of vinylidene cyclopropanes (VDCPs) have been substantially developed in the past few decades, and significant progress has been achieved in visible light-mediated, non-metal-related, and transition metal-catalyzed processes. In particular, when reactive functional groups are introduced into the backbone of VDCPs, a variety of cascade or sequential transformations can take place to produce more complex cyclic or polycyclic compounds. This review describes the recent advancements in this field. [ABSTRACT FROM AUTHOR]

An efficient heterogeneous copper-catalyzed cascade coupling/condensation/deacylation reaction of 2′-halotrifluoroacetanilides with β-keto esters has been developed. The reaction proceeds smoothly in anhydrous dimethyl sulfoxide at 80–90 °C using Cs 2 CO 3 as base and 10–20 mol% SBA-15-immobilized l -proline–CuI complex [SBA-15– l -Proline–CuI] as catalyst and provides a general and practical method for the assembly of a variety of polysubstituted 2-(trifluoromethyl)indoles in good to high yields. This heterogenized copper catalyst can be easily recovered via a simple centrifugation process and reused more than seven cycles with almost consistent catalytic activity. [ABSTRACT FROM AUTHOR]

As an important complement to the Buchwald–Hartwig–Miura arylation, Pd-catalyzed γ-C–H arylations, including γ-C(sp 3)–H and γ-C(sp 2)–H arylations, provide a more direct route to install an aryl group on the less reactive γ-site of unsaturated carbonyl compounds, and have attracted considerable interest from the chemistry community in recent years. This review summarizes the applications of this method with both cyclic and linear unsaturated carbonyl compounds (aldehydes, ketones, esters, amide, and nitriles), as well as in the total synthesis of natural products (NPs), natural product skeletons, and bioactive analogues. 1 Introduction 2 γ-C–H Arylation of Cyclic Unsaturated Carbonyl Substrates 2.1 Exocyclic γ-Arylation 2.1.1 Unsaturated Ketones and the Corresponding Silyl-Dienol Ethers 2.1.2 Unsaturated Lactones 2.2 Endocyclic γ-C–H Arylation 2.2.1 Unsaturated Ketones and the Corresponding Silyl-Dienol Ethers 2.2.2 Unsaturated Lactones 2.2.3 Unsaturated Nitriles 3 γ-C–H Arylation of Linear Unsaturated Carbonyl Substrates 3.1 Unsaturated Aldehydes 3.2 Unsaturated Ketones 3.3 Unsaturated Amides 3.4 Unsaturated Nitriles 3.5 Silyl Ketene Acetals of α,β-Unsaturated Esters 4 Conclusion [ABSTRACT FROM AUTHOR]

Preformed Ni(0) complexes are rarely used as precatalysts in cross-coupling reactions, although they can incorporate catalytically active nickel directly into the reaction. In this work, we focus on the preparation and the catalytic application of low-coordinate Ni(0) complexes supported by bulky monophosphine ligands in C–S cross-coupling reactions. We have prepared two families of Ni(0) complexes, bis-phosphine aducts of the type [Ni(PR2Ar′)2] (Ar′ = m-terphenyl group) and monophosphine derivatives of the type [Ni(PR2Ar′)(DVDS)] (DVDS = divinyltetramethyldisiloxane). DFT calculations were used to account for the atypical bent structures displayed by the bis-phosphine Ni(0) complexes. Monophosphine-Ni(0) complexes display catalytic activity superior to bis-phosphine Ni(0) adducts, which suggests that the former facilitate the generation of highly reactive monoligated PNi(0) species. Furthermore, the reactivity of monophosphine-Ni(0) precatalysts outperform that observed with Ni(II) precatalysts with the same phosphine ligands, supporting a more facile activation step to the same catalytic species. This enhanced reactivity allows for the use of lower catalyst loadings (1–5 mol%) and for carrying out the challenging coupling between aryl chlorides and alkylthiols. [ABSTRACT FROM AUTHOR]

In this Frontier Article, the work carried out within our research group in Bologna in the field of surface decorated metal carbonyl clusters will be outlined and put in a more general context. After a short Introduction, clusters composed of a metal carbonyl core decorated on the surface by metal–ligand fragments will be analyzed. Both metal–ligand fragments behaving as Lewis acids and Lewis bases will be considered. Then, the focus will be moved to clusters composed of a naked metal core decorated and stabilized on the surface by metal-carbonyl fragments. The structure and bonding (where theoretical studies are available) of such surface decorated metal carbonyl clusters will be presented, and compared to atomically precise ligated nanoclusters. [ABSTRACT FROM AUTHOR]

Recycling of epoxy composites is of importance for achieving circular economy as demand for lightweight materials in the field of sustainable technologies is soaring. Although catalytic hydrogenolysis of epoxy resins provides a promising approach to recover valuable fillers and phenolic compounds from the composites, there is a lack of a reusable solid catalyst for this purpose. Here, we report a robust CeO2-supported Ni–Pd bimetallic catalyst (Ni–Pd/CeO2) for the hydrogenolysis of C–O bonds in epoxy resins under 1 atm of H2. Benefiting from its heterogeneous nature, Ni–Pd/CeO2 can be reused for several times. Furthermore, the catalyst is successfully applied to decomposition of epoxy composites to recover carbon or glass fibers and phenolic compounds, implying the potential application of our catalyst system toward recycling of epoxy composites. Hydrogenolysis of epoxy resins is a promising method for recycling epoxy composites. Here, a CeO2-supported Ni–Pd bimetallic catalyst is developed for facilitating such a transformation benefiting from the synergy between the two metals. [ABSTRACT FROM AUTHOR]

With the rapid advancements in asymmetric catalysis, there is a growing need for the asymmetric selective synthesis of complex and diverse molecules with chiral axes. Axially chiral molecules are not only present in natural products and drugs but also in specialized chiral ligands and catalysts. The catalytic asymmetric synthesis of axially chiral molecules has garnered significant attention within the chemical community. To date, two asymmetric catalytic methods have been established for the synthesis of biaxially chiral molecules: transition-metal catalysis and asymmetric organocatalysis. This feature article presents a summary of the research progress made in the field of asymmetric selective synthesis of biaxially chiral molecules. This review focuses on the reaction range, limitations, and reaction mechanism of the biaxially chiral molecular synthesis method, as well as the contribution and advantages of this method in the preparation of various axially chiral compounds. [ABSTRACT FROM AUTHOR]