Metal‐Catalyzed Reductive Coupling Reactions of Organic Halides with Carbonyl‐Type Compounds

Metal‐catalyzed reductive coupling reactions of aryl halides and (pseudo)halides with carbonyl‐type compounds have undergone an impressive development within the last years. These methodologies have shown to be a powerful alternate strategy, practicality aside, to the use of stoichiometric, well‐defined, and, in some cases, air‐sensitive organometallic species. In this Minireview, the recent findings in this field are summarized, with particular emphasis on the mechanistic interpretation of the results and future aspects of this area of expertise.     

Synthesis and Theoretical Investigation of a 1,8‐Bis(bis(diisopropylamino)cyclopropeniminyl)naphthalene Proton Sponge Derivative

We report herein the synthesis and characterization of a new proton sponge derivative, 1,8‐bis(bis(diisopropylamino)cyclopropeniminyl)naphthalene 4 (DACN), as well as its bis‐protonated counterpart 6 . A crystal structure of 6 is presented, along with variable temperature ¹H NMR data on the BF₄^? salt ( 6?BF₄ ). DFT calculations were performed to investigate the structure of the monoprotonated species 7 and to gain insight into the structural and electronic nature of all three species. The proton affinity (PA) of 4 , calculated at the B3LYP/6‐311G++(d,p)//B3LYP/6‐31G(d,p) level, taking into account thermal corrections from the B3LYP/6‐31G(d,p) method, was 282.3 kcal mol^?1, while its pK_a was estimated at 27.0. NICS calculations were performed to examine the changes in aromaticity within these systems upon each successive protonation. Lastly, homodesmotic reaction schemes were used in order to estimate the factors contributing to the strong PA predicted for 4 .     

Combining Experimental and Computational Studies to Understand and Predict Reactivities of Relevance to Homogeneous Catalysis

This article showcases three major uses of computational chemistry in reactivity studies: the application after, in combination with, and before experiment. Following a brief introduction of suitable computational tools, challenges and opportunities in the implementation of computational chemistry in reactivity studies are discussed, exemplified with selected case studies from our and other laboratories.     

Enhanced Thermal Oxidation Stability of Reduced Graphene Oxide by Nitrogen Doping

Nitrogen‐doped reduced graphene oxide (N‐doped RGO) samples with a high level of doping, up to 13 wt. %, have been prepared by annealing graphene oxide under a flow of pure ammonia. The presence of nitrogen within the structure of RGO induces a remarkable increase in the thermal stability against oxidation by air. The thermal stability is closely related with the temperature of synthesis and the nitrogen content. The combustion reaction of nitrogen in different coordination environments (pyridinic, pyrrolic, and graphitic) is analyzed against a graphene fragment (undoped) from a thermodynamic point of view. In agreement with the experimental observations, the combustion of undoped graphene turns out to be more spontaneous than when nitrogen atoms are present.     

Manganese‐Corrole Complexes as Versatile Catalysts for the Ring‐Opening Homo‐ and Co‐Polymerization of Epoxide

Manganese‐corrole complexes in combination with a co‐catalyst [PPN]X ([PPN]⁺=bis(triphenylphosphoranylidene)iminium) were found to be new versatile catalysts for the polymerization of epoxides, copolymerization of epoxides with CO₂, and copolymerization of epoxides with cyclic anhydrides affording a wide range of polymeric materials. This work should allow the synthesis of new types of improved innovative (co)polymers with original properties and would clearly increase the number of applications for polyesters, polycarbonates, and polyethers.     

Urea‐Based Porous Organic Frameworks: Effective Supports for Catalysis in Neat Water

Two urea‐based porous organic frameworks, UOF‐1 and UOF‐2, were synthesized through a urea‐forming condensation of 1,3,5‐benzenetriisocyanate with 1,4‐diaminobenzene and benzidine, respectively. UOF‐1 and UOF‐2 possess good hydrophilic properties and high scavenging ability for palladium. Their palladium polymers, Pd^II/UOF‐1 and Pd^II/UOF‐2, exhibit high catalytic activity and selectivity for Suzuki–Miyaura cross‐coupling reactions and selective reduction of nitroarenes in water. The catalytic reactions can be efficiently performed at room temperature. Palladium nanoparticles with narrow size distribution were formed after the catalytic reaction and were well dispersed in UOF‐1 and UOF‐2. XPS analysis confirmed the coordination of the urea oxygen atom with palladium. SEM and TEM images showed that the original network morphology of UOF‐1 and UOF‐2 was maintained after palladium loading and catalytic reactions.     

Mukaiyama–Michael Reactions with trans‐2,5‐Diarylpyrrolidine Catalysts: Enantioselectivity Arises from Attractive Noncovalent Interactions,Not from Steric Hindrance

The scope of the enantioselective Mukaiyama–Michael reactions catalyzed by trans‐2,5‐diphenylpyrrolidine has been expanded to include both α‐ and β‐substituted enals. However, the rationalization of the observed enantioselectivity is far from obvious since the catalyst is not very sterically hindered. DFT calculations were carried out to rationalize the observed stereoselectivities. Transition states of the C?C bond formation between iminium intermediates and silyloxyfurans were located and their relative energies were used to estimate the stereoselectivity data. We find excellent agreement between the predicted and observed stereoselectivities. The analysis of intermolecular forces reveals that the enantioselectivity is mostly due to stabilizing noncovalent interactions between the reacting partners, not due to steric hindrance. The role of attractive noncovalent interactions in enantioselective catalysis may be underappreciated.     

Synthesis and Antiviral Properties of Spirocyclic [1,2,3]‐Triazolooxazine Nucleosides

An efficient synthesis of spirocyclic triazolooxazine nucleosides is described. This was achieved by the conversion of β‐D ‐psicofuranose to the corresponding azido‐derivative, followed by alkylation of the primary alcohol with a range of propargyl bromides, obtained by Sonogashira chemistry. The products of these reactions underwent 1,3‐dipolar addition smoothly to generate the protected spirocyclic adducts. These were easily deprotected to give the corresponding ribose nucleosides. The library of compounds obtained was investigated for its antiviral activity using MHV (mouse hepatitis virus) as a model wherein derivative 3 f showed the most promising activity and tolerability.     

Solvothermal Transformation of a Calcium Oleate Precursor into Large‐Sized Highly Ordered Arrays of Ultralong Hydroxyapatite Microtubes

Hydroxyapatite (HAP), a well‐known member of the calcium phosphate family, is the major inorganic component of bones and teeth in vertebrates. The highly ordered arrays of HAP structures are of great significance for hard tissue repair and for understanding the formation mechanisms of bones and teeth. However, the synthesis of highly ordered HAP structure arrays remains a great challenge. In this work, inspired by the ordered structure of tooth enamel, we have successfully synthesized three‐dimensional bulk materials with large sizes (millimeter scale) that are made of highly ordered arrays of ultralong HAP microtubes (HOAUHMs) by solvothermal transformation of calcium oleate precursor. The core–shell‐structured oblate sphere consists of a core that is composed of HAP nanorods and a shell that consists of highly ordered HAP microtube arrays. The prepared HOAUHMs are large: 6.0 mm in diameter and up to 1.4 mm in thickness. With increasing solvothermal reaction time, the HOAUHMs grow larger; the microtubes become more uniform and more ordered. This work provides a new synthetic method for synthesizing highly ordered arrays of uniform HAP ultralong microtubes that are promising for biomedical applications.