Recent Advances in Transition-Metal-Catalyzed C-H Functionalization of Ferrocene Amides

During the past decades, in synthetic organic chemistry, directing-group-assisted C-H functionalization is found to be a key tool for the expedient and site-selective construction of C-C and hybrid bonds. Among C-H functionalization of ferrocene derivatives, the directed group strategy is undoubtedly the most commonly used method. Compared to the other directing groups, ferrocene amides can be synthesized easily and are now recognized as one of the most efficient devices for the selective functionalization of certain positions because its metal centre permits fine, tuneable and reversible coordination. The family of amide directing groups mainly comprises monodentate and bidentate directing groups, which are categorized on the basis of coordination sites. In this review, various C-H bond functionalization reactions of ferrocene using amide directing groups are broadly discussed.

Efficient synthesis of cyclic carbonates from CO2 under ambient conditions over Zn(betaine)2Br2: experimental and theoretical studies

It is very interesting to synthesize high value-added chemicals from CO₂ under mild conditions with low energy consumption. Here, we report that a novel catalyst, Zn(betaine)₂Br₂, can efficiently promote the cycloaddition of CO₂ with epoxides to synthesize cyclic carbonates under ambient conditions (30 °C, 1 atm). DFT calculations provide important insights into the mechanism, particularly the unusual synergistic catalytic action of Zn²⁺, Br^- and NR⁴⁺, which is the critical factor for the outstanding performance of Zn(betaine)₂Br₂. The unique features of the catalyst are that it is cheap, green and very easy to prepare.

Copper-Catalyzed Single C-H Amination of 8-Aminoquinoline-Directed Ferrocenes

An unprecedented copper-catalyzed C-H monoamination of ferrocenes directed by an 8-aminoquinoline amide directing group is described. This reaction proceeds in the presence of a catalytic amount of copper catalyst with both cyclic and acyclic amines to afford the various aminoferrocenes. The C-H amination of ortho-substituted ferroceneamides was also achieved, enabling rapid access to multisubstituted ferrocenes that are useful for developing new functional molecules.

Highly Active CO2 Fixation into Cyclic Carbonates Catalyzed by Tetranuclear Aluminum Benzodiimidazole-Diylidene Adducts

A set of tetranuclear alkyl aluminum adducts 1 and 2 supported by benzodiimidazole-diylidene ligands L1, N,N’-(1,5-diisopropylbenzodiimidazole-2,6-diylidene)bis(propan-2-amine), and L2, N,N’-(1,5-dicyclohexyl-benzodiimidazole-2,6-diylidene)dicyclohexanamine were synthetized in exceptional yields and characterized by spectroscopic methods. These compounds were studied as catalysts for cyclic carbonate formation (3a–o) from their corresponding terminal epoxides (2a–o) and carbon dioxide utilizing tetrabutylammonium iodide as a nucleophile in the absence of a solvent. The experiments were carried out at 70 °C and 1 bar CO2 pressure for 24 h and adduct 1 was the most efficient catalyst for the synthesis of a large variety of monosubstituted cyclic carbonates with excellent conversions and yields.

Production of Amidinyl Radicals via UV-Vis-Light Promoted Reduction of N-Arylthiophene-2-carboxamidoximes and Application to the Preparation of Some New N-Arylthiophene-2-carboxamidines

A modern method for the preparation of some new N-arylthiophene-2-carboxamidines via amidinyl radicals generated using UV-vis-light promoting the reduction of N-arylthiophene-2-carboxamidoximes without any catalyst in a short amount of time, highly straight forward, and in an efficient manner is described. This method defeats the flaws of the conventional methods for the reduction of amidoxime derivatives to amidine derivatives, which require harsh conditions such as using a strong acid, high temperature, and expensive catalysts. Benzo[d]imidazoles, benzo[d]oxazoles, and amides can also be synthesized by applying this method. The photoproducts were analyzed by various spectroscopic and analytical techniques, including thin-layer chromatography, column chromatography, high-performance liquid chromatography, gas chromatography/mass spectrometry, IR, ¹H NMR, ¹³C NMR, and MS. Notably, the chromatographic analyses proved that the best time for the production of N-arylthiophene-2-carboxamidines is 20 min. The reaction mechanism comprising pathways and intermediates was also suggested via the homolysis of N-O and C-N bonds.

An Aminopyridinium Ionic Liquid: A Simple and Effective Bifunctional Organocatalyst for Carbonate Synthesis from Carbon Dioxide and Epoxides

An aminopyridinium ionic liquid is presented as a green, tunable, and active metal-free one-component catalytic system for the atom-efficient transformation of oxiranes and CO₂ to cyclic carbonates. Inclusion of a positively charged moiety into aminopyridines, through a simple single-step synthesis, provides a one-component ionic liquid catalytic system with superior activity; effective in ring opening of epoxide, CO₂ inclusion, and stabilization of oxoanionic intermediates. An efficiency assessment of a variety of positively charged aminopyridines was pursued, and the impact of temperature, catalyst loading, and the kind of nucleophile on the catalytic performance was also investigated. Under solvent-free conditions, this bifunctional organocatalytic system was used for the preparation of 18 examples of cyclic carbonates from a broad range of alkyl- and aryl-substituted oxiranes and CO₂ , where up to 98 % yield and high selectivity were achieved. DFT calculations validated a mechanism in which nucleophilic ring-opening and CO₂ inclusion occur simultaneously towards cyclic carbonate formation.