Lithium Amide Protected against Hydrolysis by Aggregated Lithium Halides: An MS + DFT Investigation

Addition of allyl Grignard to nitriles in air and at room temperature: experimental and computational mechanistic insights in pH-switchable synthesis

A straightforward and selective conversion of nitriles into highly substituted tetrahydropyridines, aminoketones or enamines by using allylmagnesium bromide as an addition partner (under neat conditions) and subsequent treatment with different aqueous-based hydrolysis protocols is reported. Refuting the conventional wisdom of the incompatibility of Grignard reagents with air and moisture, we herein report that the presence of water allows us to promote the chemoselective formation of the target tetrahydropyridines over other competing products (even in the case of highly challenging aliphatic nitriles). Moreover, the careful tuning of both the reaction media employed (acid or basic aqueous solutions for the hydrolysis protocol) and the electronic properties of the starting nitriles allowed us to design a multi-task system capable of producing either β-aminoketones or enamines in a totally selective manner. Importantly, and for the first time in the chemistry of main-group polar organometallic reagents in non-conventional protic solvents (e.g., water), both experimental and computational studies showed that the excellent efficiency and selectivity observed in aqueous media cannot be replicated by using standard dry volatile organic solvents (VOCs) under inert atmosphere conditions.

Insight into the Bonding and Aggregation of Alkyllithiums by Experimental Charge Density Studies and Energy Decomposition Analyses

In this Article, the organolithiums [((-)-sparteine)Li^tBu] (1), [(ABCO)Li^tBu]₂ (2), and [(ABCO)₂(LiⁱPr)₄] (3) are investigated by means of experimental and theoretical charge density determination to elucidate the nature of the Li-C and Li-N bonds. Furthermore, the valence shell charge concentrations (VSCCs) in the nonbonding region of the deprotonated C_α-atom will provide some insight on the localization of the carbanionic lone pair. Analysis of the electron density (ρ(r_BCP)), Laplacian (∇²ρ(r_BCP)), and the energy decomposition (EDA) confirmed that the Li-C/N bond exhibits astonishingly similar characteristics, to reveal an increasingly polar contact with decreasing aggregate size. This explains former observations on the incorporation of halide salts in organolithium reagents. Furthermore, it could be shown that the bonding properties of the ⁱPr group are similar to those of the ^tBu substituent. The accuracy of fit to all previously determined properties in organolithiums is remarkable.

Complexation behaviour of LiCl and LiPF6– model studies in the solid-state and in solution using a bidentate picolyl-based ligand

Using a new bulky bidentate ligand and combining various structure elucidation methods, coordination modes of [ligand·LiX] (X = Cl, PF₆) complexes both in solid-state and in solution have been revealed.

Combination of organocatalytic oxidation of alcohols and organolithium chemistry (RLi) in aqueous media, at room temperature and under aerobic conditions

Organocatalysis and highly-polar s-block organometallic chemistry (RLi) work together in water, under air and at room temperature for the selective and ultrafast synthesis of tertiary alcohols.

Organolithium-Initiated Polymerization of Olefins in Deep Eutectic Solvents under Aerobic Conditions

Despite their ubiquitous presence in synthesis, the use of polar organolithium reagents under environmentally benign conditions constitutes one of the greatest challenges in sustainable chemistry. Their high reactivity imposes the use of severely restrictive protocols (e.g., moisture- and oxygen-free, toxic organic solvents, inert atmospheres, low temperatures, etc.). Making inroads towards meeting this challenge, a new air- and moisture-compatible organolithium-mediated methodology for the anionic polymerization of different olefins (e.g., styrenes and vinylpyridines) was established by pioneering the use of deep eutectic solvents (DESs) as an eco-friendly reaction medium in this type of transformation. Fine-tuning of the conditions (sonication of the reaction mixture at 40 °C in the absence of protecting atmosphere) along with careful choice of components of the DES [choline chloride (ChCl) and glycerol (Gly) in a 1:2 ratio] furnished the desired organic polymers (homopolymers and random copolymers) in excellent yields (up to 90 %) and low polydispersities (IPD 1.1-1.3). Remarkably, the in situ-formed polystyril lithium intermediates exhibited a great resistance to hydrolysis in the eutectic mixture 1ChCl/2Gly (up to 1.5 h), hinting at an unexpected high stability of these otherwise highly reactive organolithium species in these unconventional reaction media. This unique stability can be exploited to create well defined block-copolymers.

The Future of Polar Organometallic Chemistry Written in Bio-Based Solvents and Water

There is a strong imperative to reduce the release of volatile organic compounds (VOCs) into the environment, and many efforts are currently being made to replace conventional hazardous VOCs in favour of safe, green and bio-renewable reaction media that are not based on crude petroleum. Recent ground-breaking studies from a few laboratories worldwide have shown that both Grignard and (functionalised) organolithium reagents, traditionally handled under strict exclusion of air and humidity and in anhydrous VOCs, can smoothly promote both nucleophilic additions to unsaturated substrates and nucleophilic substitutions in water and other bio-based solvents (glycerol, deep eutectic solvents), competitively with protonolysis, at room temperature and under air. The chemistry of polar organometallics in the above protic media is a complex phenomenon influenced by several factors, and understanding its foundational character is stimulating in the perspective of the development of a sustainable organometallic chemistry.

Alkali metal complexes based on bisheterocyclomethanide ligands

A series of new alkali metal complexes containing deprotonated bisheterocyclomethanide were synthesised and structurally as well as spectroscopically characterised. Starting from the neutral bis-(benzoxazol-2-yl)methane ({NCOC6H4}2CH2), the complexes were obtained by facile deprotonation of the methylene bridge with nbutyllithium (nBuLi) or potassium hydride. Each of the resulting complexes [({NCOC6H4}2CH)Li(OEt2)2] (1), [({NCOC6H4}2CH)K(thf)]n (2) and [({NCOC6H4}2CH)K(18-crown-6)]n (3) (n → ∞) was analysed in the solid state by single crystal X-ray diffraction and in solution by various NMR techniques. All the compounds show a nearly planar ligand with the alkali metal ion chelated by the two ring nitrogen atoms of the conjugated C3N2 moiety. Furthermore, water NMR titration experiments revealed that both compounds 2 and 3 are examples of water-stable reactive organo potassium compounds. Due to their hydrolysis stability, these complexes are under further investigations in deep eutectic solvents.

Reactivity of Lithium β-Ketocarboxylates: The Role of Lithium Salts

Lithium β-ketocarboxylates 1(COOLi), prepared by the reaction of lithium enolates 2(Li⁺) with carbon dioxide, readily undergo decarboxylative disproportionation in THF solution unless in the presence of lithium salts, in which case they are indefinitely stable at room temperature in inert atmosphere. The availability of stable THF solutions of lithium β-ketocarboxylates 1(COOLi) in the absence of carbon dioxide allowed reactions to take place with nitrogen bases and alkyl halides 3 to give α-alkyl ketones 1(R) after acidic hydrolysis. The sequence thus represents the use of carbon dioxide as a removable directing group for the selective monoalkylation of lithium enolates 2(Li⁺). The roles of lithium salts in preventing the disproportionation of lithium β-ketocarboxylates 1(COOLi) and in determining the course of the reaction with bases and alkyl halides 3 are discussed.

A Water-Containing Organopotassium Compound Based on Bis(4,6-tBu-benzoxazol-2-yl)methanide and Its Unexpected Stability to Hydrolysis

The bulky bis(4,6-tBu-benzoxazol-2-yl)methane ligand system enabled the synthesis of the water-containing organometallic potassium complex [(18-crown-6)K{(4,6-tBu-OCNC₆ H₂ )₂ CH}⋅H₂ O] (2), which is an unprecedented example of a water-stable reactive organopotassium compound. Furthermore, 2 is a rare example of a bis(benzoxazol-2-yl)methanide ligand displaying solely O-coordination to a metal ion. Compound 2 was fully characterized through its solid-state structure. Furthermore, its behavior in solution was investigated by NMR titration DOSY experiments. These revealed full protonation of the complex only after seven days and the addition of 114 equivalents of water.