An Organocopper(III) Fluoride Triggering C-CF3 Bond Formation

Copper(III) fluorides are catalytically competent, yet elusive, intermediates in cross-coupling. The synthesis of [PPh4 ][CuIII (CF3 )3 F] (2), the first stable (isolable) CuIII -F, was accomplished via chloride addition to [CuIII (CF3 )3 (py)] (1) yielding [PPh4 ][CuIII (CF3 )3 Cl(py)] (1⋅Cl), followed by treatment with AgF. The CuIII halides 1⋅Cl and 2 were fully characterized using nuclear magnetic resonance (NMR) spectroscopy, single crystal X-ray diffraction (Sc-XRD) and elemental analysis (EA). Complex 2 proved capable of forging C-CF3 bonds from silyl-capped alkynes. In-depth mechanistic studies combining probes, theoretical calculations, trapping of intermediate 4a ([PPh4 ][CuIII (CF3 )3 (C≡CPh)]) and radical tests unveil the key role of the CuIII acetylides that undergo facile 2e- reductive elimination furnishing the trifluoromethylated alkynes (RC≡CCF3 ), which are industrially relevant synthons in drug discovery, pharma and agrochemistry.

Cross-Coupling Reactions Enabled by Well-Defined Ag(III) Compounds: Main Focus on Aromatic Fluorination and Trifluoromethylation

AgIII compounds are considered strong oxidizers of difficult handling. Accordingly, the involvement of Ag catalysts in cross-coupling via 2e- redox sequences is frequently discarded. Nevertheless, organosilver(III) compounds have been authenticated using tetradentate macrocycles or perfluorinated groups as supporting ligands, and since 2014, first examples of cross-coupling enabled by AgI /AgIII redox cycles saw light. This review collects the most relevant contributions to this field, with main focus on aromatic fluorination/perfluoroalkylation and the identification of AgIII key intermediates. Pertinent comparison between the activity of AgIII RF compounds in aryl-F and aryl-CF3 couplings vs. the one shown by its CuIII RF and AuIII RF congeners is herein disclosed, thus providing a more profound picture on the scope of these transformations and the pathways commonly associated to C-RF bond formations enabled by coinage metals.

Scrutinizing formally NiIV centers through the lenses of core spectroscopy, molecular orbital theory, and valence bond theory

Nickel K- and L_2,3-edge X-ray absorption spectra (XAS) are discussed for 16 complexes and complex ions with nickel centers spanning a range of formal oxidation states from II to IV. K-edge XAS alone is shown to be an ambiguous metric of physical oxidation state for these Ni complexes. Meanwhile, L_2,3-edge XAS reveals that the physical d-counts of the formally Ni^IV compounds measured lie well above the d⁶ count implied by the oxidation state formalism. The generality of this phenomenon is explored computationally by scrutinizing 8 additional complexes. The extreme case of NiF₆^2- is considered using high-level molecular orbital approaches as well as advanced valence bond methods. The emergent electronic structure picture reveals that even highly electronegative F-donors are incapable of supporting a physical d⁶ Ni^IV center. The reactivity of Ni^IV complexes is then discussed, highlighting the dominant role of the ligands in this chemistry over that of the metal centers.

Electrophilicity of neutral square-planar organosilver(III) compounds

Neutral Ag(III) complexes stabilised with just monodentate ligands are here unambiguously established. In a series of square-planar (CF₃)₃Ag(L) compounds with hard and soft Group 15 donor ligands, L, the metal center has been found to exhibit substantial acidity favouring apical coordination of an additional ligand under no coordination constraints.

Cross-Coupling through Ag(I)/Ag(III) Redox Manifold

In ample variety of transformations, the presence of silver as an additive or co-catalyst is believed to be innocuous for the efficiency of the operating metal catalyst. Even though Ag additives are required often as coupling partners, oxidants or halide scavengers, its role as a catalytically competent species is widely neglected in cross-coupling reactions. Most likely, this is due to the erroneously assumed incapacity of Ag to undergo 2e^- redox steps. Definite proof is herein provided for the required elementary steps to accomplish the oxidative trifluoromethylation of arenes through Ag^I /Ag^III redox catalysis (i. e. CEL coupling), namely: i) easy Ag^I /Ag^III 2e^- oxidation mediated by air; ii) bpy/phen ligation to Ag^III ; iii) boron-to-Ag^III aryl transfer; and iv) ulterior reductive elimination of benzotrifluorides from an [aryl-Ag^III -CF₃ ] fragment. More precisely, an ultimate entry and full characterization of organosilver(III) compounds [K]⁺ [Ag^III (CF₃ )₄ ]^- (K-1), [(bpy)Ag^III (CF₃ )₃ ] (2) and [(phen)Ag^III (CF₃ )₃ ] (3), is described. The utility of 3 in cross-coupling has been showcased unambiguously, and a large variety of arylboron compounds was trifluoromethylated via [Ag^III (aryl)(CF₃ )₃ ]^- intermediates. This work breaks with old stereotypes and misconceptions regarding the inability of Ag to undergo cross-coupling by itself.

Recent Progress of Cu-Catalyzed Azide-Alkyne Cycloaddition Reactions (CuAAC) in Sustainable Solvents: Glycerol, Deep Eutectic Solvents, and Aqueous Media

This mini-review presents a general overview of the progress achieved during the last decade on the amalgamation of CuAAC processes (copper-catalyzed azide-alkyne cycloaddition) with the employment of sustainable solvents as reaction media. In most of the presented examples, the use of water, glycerol (Gly), or deep eutectic solvents (DESs) as non-conventional reaction media allowed not only to recycle the catalytic system (thus reducing the amount of the copper catalyst needed per mole of substrate), but also to achieve higher conversions and selectivities when compared with the reaction promoted in hazardous and volatile organic solvents (VOCs). Moreover, the use of the aforementioned green solvents also permits the improvement of the overall sustainability of the Cu-catalyzed 1,3-dipolar cycloaddition process, thus fulfilling several important principles of green chemistry.

High-Valent NiIII and NiIV Species Relevant to C-C and C-Heteroatom Cross-Coupling Reactions: State of the Art

Ni catalysis constitutes an active research arena with notable applications in diverse fields. By analogy with its parent element palladium, Ni catalysts provide an appealing entry to build molecular complexity via cross-coupling reactions. While Pd catalysts typically involve a M⁰/M^II redox scenario, in the case of Ni congeners the mechanistic elucidation becomes more challenging due to their innate properties (like enhanced reactivity, propensity to undergo single electron transformations vs. 2e⁻ redox sequences or weaker M–Ligand interaction). In recent years, mechanistic studies have demonstrated the participation of high-valent Ni^III and Ni^IV species in a plethora of cross-coupling events, thus accessing novel synthetic schemes and unprecedented transformations. This comprehensive review collects the main contributions effected within this topic, and focuses on the key role of isolated and/or spectroscopically identified Ni^III and Ni^IV complexes. Amongst other transformations, the resulting Ni^III and Ni^IV compounds have efficiently accomplished: i) C–C and C–heteroatom bond formation; ii) C–H bond functionalization; and iii) N–N and C–N cyclizative couplings to forge heterocycles.

Geminal Dianions Stabilized by Main Group Elements

This review is dedicated to the chemistry of stable and isolable species that bear two lone pairs at the same C center, i.e., geminal dianions, stabilized by main group elements. Three cases can thus be considered: the geminal-dilithio derivative, for which the two substituents at C are neutral, the yldiide derivatives, for which one substituent is neutral while the other is charged, and finally the geminal bisylides, for which the two substituents are positively charged. In this review, the syntheses and electronic structures of the geminal dianions are presented, followed by the studies dedicated to their reactivity toward organic substrates and finally to their coordination chemistry and applications.

Synthesis and Reactivity of an End-Deck cyclo-P4 Iron Complex

Reduction of the Fe^II complex [(^Ph PP₂^Cy )FeCl₂ ] (2) generated an electron-rich and unsaturated Fe⁰ species, which was reacted with white phosphorus. The resulting new complex, [(^Ph PP₂^Cy )Fe(η⁴ -P₄ )] (3), is the first iron cyclo-P₄ complex and the only known stable end-deck cyclo-P₄ complex outside Group V. Complex 3 features an Fe^II center, as shown by Mössbauer spectroscopy, associated to a P₄^2- fragment. The distinct reactivity of complex 3 was rationalized by analysis of the molecular orbitals. Reaction of complex 3 with H⁺ afforded the unstable complex [(^Ph PP₂^Cy )Fe(η⁴ -P₄ )(H)]⁺ (4), whereas with CuCl and BCF, the complexes [(^Ph PP₂^Cy )Fe(η⁴ :η¹ -P₄ )(μ-CuCl)]₂ (5) and [(^Ph PP₂^Cy )Fe(η⁴ :η¹ -P₄ )B(C₆ F₅ )₃ ] (6) were formed.

Triphos–Fe dinitrogen and dinitrogen–hydride complexes: relevance to catalytic N2 reductions

Mechanistic investigations of the catalyzed reduction of N₂ with a rare (tridentate phosphine)Fe(0) bis dinitrogen complex.

C-H Bond Trifluoromethylation of Arenes Enabled by a Robust, High-Valent Nickel(IV) Complex

The robust, high-valent Ni^IV complex [(Py)₂ Ni^IV F₂ (CF₃ )₂ ] (Py=pyridine) was synthesized and fully characterized by NMR spectroscopy, X-ray diffraction, and elemental analysis. It reacts with aromatic compounds at 25 °C to form the corresponding benzotrifluorides in nearly quantitative yield. The monomeric and dimeric Ni^III CF₃ complexes 2⋅Py and 2 were identified as key intermediates, and their structures were unambiguously determined by EPR spectroscopy and X-ray diffraction. Preliminary kinetic studies in combination with the isolation of reaction intermediates confirmed that the C-H bond-breaking/C-CF₃ bond-forming sequence can occur both at Ni^IV CF₃ and Ni^III CF₃ centers.

Access to unusual polycyclic spiro-enones from 2,2'-bis(allyloxy)-1,1'-binaphthyls using Grubbs' catalysts: an unprecedented one-pot RCM/Claisen sequence

Treatment of 2,2'-bis(allyloxy)-1,1'-binaphthyls with the first-generation Grubbs' carbene under MW-irradiation results in the formation of new polycyclic spiro-enones through an unprecedented RCM/Claisen sequence.

One-pot three-component catalytic synthesis of fully substituted pyrroles from readily available propargylic alcohols, 1,3-dicarbonyl compounds and primary amines

A simple and highly efficient method for the preparation of fully substituted pyrroles, from readily accessible secondary propargylic alcohols, 1,3-dicarbonyl compounds and primary amines, has been developed. The one-pot multicomponent reaction, which is catalysed by the system [Ru(eta(3)-2-C(3)H(4)Me)(CO)(dppf)][SbF(6)]/CF(3)CO(2)H (dppf: 1,1'-bis(diphenylphosphanyl)ferrocene), involves initial propargylation of the 1,3-dicarbonyl compound promoted by CF(3)CO(2)H and subsequent condensation between the resulting gamma-keto alkyne and the primary amine to afford a propargylated beta-enamino ester or ketone, which undergoes a ruthenium-catalysed 5-exo-dig annulation to form the final pyrrole.

Efficient Tandem Process for the Catalytic Deprotection of N-Allyl Amides and Lactams in Aqueous Media: A Novel Application of the Bis(allyl)–Ruthenium(IV) Catalysts [Ru(η3:η2:η3-C12H18)Cl2] and [{Ru(η3:η3-C10H16)(μ-Cl)Cl}2]

An operationally simple and highly efficient methodology for the removal of the allyl protecting group in amides and lactams has been developed by using the commercially available bis(allyl)-ruthenium(IV) catalysts [Ru(eta(3):eta(2):eta(3)-C(12)H(18))Cl(2)] (C(12)H(18)=dodeca-2,6,10-triene-1,12-diyl) and [{Ru(eta(3):eta(3)-C(10)H(16))(micro-Cl)Cl}(2)] (C(10)H(16)=2,7-dimethylocta-2,6-diene-1,8-diyl). The tandem process, which takes place in aqueous media and proceeds in a one-pot manner, involves the initial isomerization of the C=C bond of the allyl unit and subsequent oxidative cleavage of the resulting enamide.

Ruthenium-catalyzed reduction of allylic alcohols: An efficient isomerization/transfer hydrogenation tandem process

A simple and highly efficient method for the selective reduction of the C=C bond in allylic alcohols has been developed using the ruthenium(II) catalyst [{RuCl(mu-Cl)(eta(6)-C(6)Me(6)}2].

Synthesis and reactivity studies of palladium(ii) complexes containing the N-phosphorylated iminophosphorane-phosphine ligands Ph2PCH2P{NP(O)(OR)2}Ph2(R = Et, Ph): application to the catalytic synthesis of 2,3-dimethylfuran

Reactions of [PdCl2(COD)] with 1 equiv. of the iminophosphorane-phosphine ligands Ph2PCH2P{=NP(=O)(OR)2}Ph2 (R=Et, Ph) lead to the novel Pd(II) derivatives cis-[PdCl2(kappa2-(P,N)-Ph2PCH2P{=NP(=O)(OR)2}Ph2)] (R=Et, Ph). Pd-N bond cleavage readily takes place upon treatment of these species with a variety of two-electron donor ligands. By this way, complexes cis-[PdCl2(kappa1-(P)-Ph2PCH2P{=NP(=O)(OR)2}Ph2)(L)] (R=Et, L=CNtBu, CN-2,6-C6H3Me2, py, P(OMe)3, P(OEt)3; R=Ph, L=CNtBu, CN-2,6-C6H3Me2, py, P(OMe)3, P(OEt)3) have been synthesized in high yields. The addition of two equivalents of ligands to dichloromethane solutions of [PdCl2(COD)] results in the formation of complexes trans-[PdCl2(kappa1-(P)-Ph2PCH2P{=NP(=O)(OR)2}Ph2)2] (R=Et, Ph), which can be converted into the dicationic species [Pd(Ph2PCH2P{=NP(=O)(OR)2}Ph2)2][SbF6]2 (R=Et, Ph) by treatment with AgSbF6. Complex also reacts with CNtBu to afford trans-[Pd(kappa1(P)-Ph2PCH2P{=NP(=O)(OPh)2}Ph2)2(CNtBu)2][SbF6]2. The structures of and have been determined by single-crystal X-ray diffraction methods. In addition, the ability of these Pd(II) complexes to promote the catalytic cycloisomerization of (Z)-3-methylpent-2-en-4-yn-1-ol into 2,3-dimethylfuran has also been studied.

Ru(iv)-catalyzed isomerization of allylamines in water: A highly efficient procedure for the deprotection of N-allylic amines

A general and efficient method for the deprotection of N-allylic substrates in aqueous media, using catalytic amounts of the bis(allyl)-ruthenium(IV) complexes [Ru(eta3:eta2:eta3-C12H18)Cl2] and [{Ru(eta3:eta3-C10H16)(micro-Cl)Cl}2], has been developed.