Catalytic Biomimetic Asymmetric Reduction of Alkenes and Imines Enabled by Chiral and Regenerable NAD(P)H Models

The development of biomimetic chemistry based on the NAD(P)H with hydrogen gas as terminal reductant is a long‐standing challenge. Through rational design of the chiral and regenerable NAD(P)H analogues based on planar‐chiral ferrocene, a biomimetic asymmetric reduction has been realized using bench‐stable Lewis acids as transfer catalysts. A broad set of alkenes and imines could be reduced with up to 98 % yield and 98 % ee, likely enabled by enzyme‐like cooperative bifunctional activation. This reaction represents the first general biomimetic asymmetric reduction (BMAR) process enabled by chiral and regenerable NAD(P)H analogues. This concept demonstrates catalytic utility of a chiral coenzyme NAD(P)H in asymmetric catalysis.     

Cooperative Catalysis and Activation with N‐Heterocyclic Carbenes

N‐Heterocyclic carbene (NHC) catalysis has emerged as a powerful stratagem in organic synthesis to construct complex molecules primarily by polarity reversal (umpolung) approaches. These unique Lewis bases have been used to generate acyl anions, enolates, and homoenolates in catalytic fashion. Recently, a new strategy has emerged that dramatically expands the synthetic utility of carbene catalysis by leveraging additional activation modes: cooperative catalysis. The careful selection and balance of cocatalysts have led to enhanced reactivity, increased yields, and improved stereoselectivity. In certain cases, these catalytic additives have changed the regioselectivity or diastereoselectivity. This Minireview highlights new advances in NHC cooperative catalysis and surveys the evolution of this field.     

A Bioinspired Catalytic Aerobic Oxidative CH Functionalization of Primary Aliphatic Amines: Synthesis of 1,2‐Disubstituted Benzimidazoles

Aerobic oxidative C?H functionalization of primary aliphatic amines has been accomplished with a biomimetic cooperative catalytic system to furnish 1,2‐disubstituted benzimidazoles that play an important role as drug discovery targets. This one‐pot atom‐economical multistep process, which proceeds under mild conditions, with ambient air and equimolar amounts of each coupling partner, constitutes a convenient environmentally friendly strategy to functionalize non‐activated aliphatic amines that remain challenging substrates for non‐enzymatic catalytic aerobic systems.     

Neutral Tridentate PNP Ligands and Their Hybrid Analogues: Versatile Non‐Innocent Scaffolds for Homogeneous Catalysis

Ligands in coordination chemistry and homogeneous catalysis are traditionally “static” spectators that do not actively participate in the catalytic cycle. However, such classic systems do not provide additional “handles” that could facilitate or trigger alternative productive reaction pathways. Recent advances in the use of novel nitrogen‐centered pincer systems have unveiled interesting opportunities for cooperative catalysis. The chemistry of pyridine‐derived, neutral ligands is discussed, with a specific focus on their non‐innocent behavior and potential as facilitators for metal‐mediated organic transformations. This overview should provide inspiration and an incentive to incorporate non‐innocent ligands and their metal complexes within old and new homogeneously catalyzed reactions.     

The Mechanism of Gold(I)‐Catalyzed Hydroalkoxylation of Alkynes: An Extensive Experimental Study

An extensive experimental study of the mechanism of gold(I)‐catalyzed hydroalkoxylation of internal alkynes has been conducted by using NMR spectroscopy. This study was focused on the organogold intermediates, observations of actual catalytic intermediates in situ, and the reaction kinetics that are involved in this reaction. Based on the experimental results, a complete mechanistic picture was established, including on‐ and off‐cycle processes that explain the role of diaurated species. We have shown that gold‐catalyzed hydroalkoxylation of internal alkynes is a reaction that requires only one gold atom for the catalytic cycle, disproving a recent hypothesis regarding the involvement of cooperative gold catalysis.     

Substrate‐Selective Catalysis

Substrate selectivity is an important output function for the validation of different enzyme models, catalytic cavity compounds, and reaction mechanisms as demonstrated in this review. In contrast to stereo‐, regio‐, and chemoselective catalysis, the field of substrate‐selective catalysis is under‐researched and has to date generated only a few, but important, industrial applications. This review points out the broad spectrum of different reaction types that have been investigated in substrate‐selective catalysis. The present review is the first one covering substrate‐selective catalysis and deals with reactions in which the substrates involved have the same reacting functionality and the catalysts is used in catalytic or in stoichiometric amounts. The review covers real substrate‐selective catalysis, thus only including cases in which substrate‐selective catalysis has been observed in competition between substrates.     

Metal–Support Cooperative Catalysts for Environmentally Benign Molecular Transformations

Metal–support cooperative catalysts have been developed for sustainable and environmentally benign molecular transformations. The active metal centers and supports in these catalysts could cooperatively activate substrates, resulting in high catalytic performance for liquid‐phase reactions under mild conditions. These catalysts involved hydrotalcite‐supported gold and silver nanoparticles with high catalytic activity for organic reactions such as aerobic oxidation, oxidative carbonylation, and chemoselective reduction of epoxides to alkenes and nitrostyrenes to aminostyrenes using alcohols and CO/H₂O as reducing reagents. This high catalytic performance was due to cooperative catalysis between the metal nanoparticles and basic sites of the hydrotalcite support. To increase the metal–support cooperative effect, core–shell nanostructured catalysts consisting of gold or silver nanoparticles in the core and ceria supports in the shell were designed. These core–shell nanocomposite catalysts were effective for the chemoselective hydrogenation of nitrostyrenes to aminostyrenes, unsaturated aldehydes to allyl alcohols, and alkynes to alkenes using H₂ as a clean reductant. In addition, these solid catalysts could be recovered easily from the reaction mixture by simple filtration, and were reusable with high catalytic activity.     

Direct Carbohydroxylation of Arylalkenes with Allylic Alcohols: Cooperative Catalysis of Copper,Silver, and a Brønsted Acid

The cooperative catalysis of copper, silver, and Brønsted acid is presented as a new strategy for olefin functionalization. The catalytic direct carbohydroxylation of arylalkenes with allylic alcohols provided a straightforward and efficient approach for preparing 4,5‐unsaturated alcohols. Synthetically useful functional groups, such as Cl, Br, carbonyl, and chloromethyl, remained intact during the functionalization reaction.     

Asymmetric Catalysis with Bis(hydroxyphenyl)diamides/Rare‐Earth Metal Complexes

A series of asymmetric catalysts composed of conformationally flexible amide‐based chiral ligands and rare‐earth metals was developed for proton‐transfer catalysis. These ligands derived from amino acids provide an intriguing chiral platform for the formation of asymmetric catalysts upon complexation with rare‐earth metals. The scope of this arsenal of catalysts was further broadened by the development of heterobimetallic catalytic systems. The cooperative function of hydrogen bonding and metal coordination resulted in intriguing substrate specificity and stereocontrol, and the dynamic nature of the catalysts led to a switch of their function. Herein, we summarize our recent exploration of this class of catalysts.     

Methandiide as a Non‐Innocent Ligand in Carbene Complexes: From the Electronic Structure to Bond Activation Reactions and Cooperative Catalysis

The synthesis of a ruthenium carbene complex based on a sulfonyl‐substituted methandiide and its application in bond activation reactions and cooperative catalysis is reported. In the complex, the metal–carbon interaction can be tuned between a Ru?C single bond with additional electrostatic interactions and a Ru?C double bond, thus allowing the control of the stability and reactivity of the complex. Hence, activation of polar and non‐polar bonds (O?H, H?H) as well as dehydrogenation reactions become possible. In these reactions the carbene acts as a non‐innocent ligand supporting the bond activation as nucleophilic center in the 1,2‐addition across the metal–carbon double bond. This metal–ligand cooperativity can be applied in the catalytic transfer hydrogenation for the reduction of ketones. This concept opens new ways for the application of carbene complexes in catalysis.     

Study of enzyme models and imitation of enzyme action

This paper deals with some of the research activities in our group in recent years in the areas of artificial enzyme models with porphyrin, steroids and calixarenes as building units. Wherein two kinds of novel enzyme models of steroids-metalloporphvrin and calixarene-metalloporphyrin have been synthesized and employed as cytochrome P450 modeling. These biomimetic systems exhibited high catalytic selectivity and efficiency in oxidation of olefins (styrene, cyclohexene) and hydrocarbonds (isopropylbenzene) as well as phenol ( p-benzenedi-ol). The excellent catalytic property stems mainly from hydrophobic effect and multiple recognition sites that lead to cooperative catalysis.     

Redox‐Active Ligands in Catalysis

Nature’s use of redox‐active moieties combined with 3d transition‐metal ions is a powerful strategy to promote multi‐electron catalytic reactions. The ability of these moieties to store redox equivalents aids metalloenzymes in promoting multi‐electron reactions, avoiding high‐energy intermediates. In a biomimetic spirit, chemists have recently developed approaches relying on redox‐active moieties in the vicinity of metal centers to catalyze challenging transformations. This approach enables chemists to impart noble‐metal character to less toxic, and cost effective 3d transitional metals, such as Fe or Cu, in multi‐electron catalytic reactions.     

Phosphoramidites: Privileged Ligands in Asymmetric Catalysis

Asymmetric catalysis with transition‐metal complexes is the basis for a vast array of stereoselective transformations and has changed the face of modern synthetic chemistry. Key to this success has been the design of chiral ligands to control the regio‐, diastereo‐, and enantioselectivity. Phosphoramidites have emerged as a highly versatile and readily accessible class of chiral ligands. Their modular structure enables the formation of ligand libraries and easy fine‐tuning for a specific catalytic reaction. Phosphoramidites frequently show exceptional levels of stereocontrol, and their monodentate nature is essential in combinatorial catalysis, where a ligand‐mixture approach is used. In this Review, recent developments in asymmetric catalysis with phosphoramidites used as ligands are discussed, with a focus on the formation of carbon–carbon and carbon–heteroatom bonds.     

Stereoconvergent,Redox‐Neutral Access to Tetrahydroquinoxalines through Relay Epoxide Opening/Amination of Alcohols

We present an economical catalytic procedure to convert readily available 1,2‐diaminobenzenes and terminal epoxides into valuable 1,2,3,4‐tetrahydroquinoxalines in a highly enantioselective fashion. This procedure operates through relay zinc and iridium catalysis, and achieves redox‐neutral and stereoconvergent production of valuable chiral heterocycles from racemic starting materials with water as the only side product. The use of commercially available reagents and catalysts and a convenient procedure also make this catalytic method attractive for practical application.     

Exploiting the Multidentate Nature of Chiral Disulfonimides in a Multicomponent Reaction for the Asymmetric Synthesis of Pyrrolo[1,2‐a]indoles: A Remarkable Case of Enantioinversion

A new multicomponent coupling reaction for the enantioselective synthesis of pyrrolo[1,2‐a]indoles under the catalysis of a chiral disulfonimide is described. The high specificity of the reaction is a consequence of the multidentate character of the Brønsted acid catalyst. Insights from DFT calculations helped explain the unexpected high enantioselectivity observed with the simplest 3,3′‐unsubstituted binaphthyl catalyst as a result of transition‐state stabilization by a network of cooperative noncovalent interactions. The remarkable enantioinversion resulting from the simple introduction of substituents at 3‐ and 3′‐positions, the first reported example of this phenomenon in the context of binaphthalene‐derived Brønsted acid catalysis, was instead attributed to destabilizing steric interactions.     

Metal–Organic Frameworks: Opportunities for Catalysis

The role of metal–organic frameworks (MOFs) in the field of catalysis is discussed, and special focus is placed on their assets and limits in light of current challenges in catalysis and green chemistry. Their structural and dynamic features are presented in terms of catalytic functions along with how MOFs can be designed to bridge the gap between zeolites and enzymes. The contributions of MOFs to the field of catalysis are comprehensively reviewed and a list of catalytic candidates is given. The subject is presented from a multidisciplinary point of view covering solid‐state chemistry, materials science, and catalysis.     

Acceleration by Double Activation Catalysis and its Negation with Rising Temperature in Hydrolysis of Cellobiose with Phthalic and Hydrochloric Acids

Double activation catalysis was experimentally observed in hydrolysis of cellobiose catalyzed simultaneously with phthalic and hydrochloric acids, confirming earlier theoretical prediction known from literature. Both acids can catalyze the reaction individually, and contribution of the double-activation pathway to the total reaction rate declines as temperature increases. In fact, above a certain temperature, the hydrolysis rate in presence of both acids becomes lower than the sum of the rates for the two acids acting individually. A kinetic model is proposed to explain this transition between double-activated catalysis and inhibition. The trend of declining contribution of cooperative catalytic pathway with rising temperature is theorized to be generally applicable for any reaction with a pathway involving simultaneous action of two catalysts when either of them can individually catalyze the reaction.     

Recent Advances in Covalent Organic Frameworks for Catalysis

Covalent organic frameworks (COFs) as an emerging type of crystalline porous materials, have obtained considerable attention recently. They have exhibited diverse structure and attractive performance in various catalytic reactions. It is highly expected to have a systematic and comprehensive review summing up COFs‐derived catalysts in homogeneous and heterogeneous catalysis, which is favorable to the judicious design of an efficient catalyst for targeted reaction. Herein, we focus on summarizing recent and significant developments in COFs materials, with an emphasis on both the synthetic strategies and targeted functionalization, and categorize it in accordance with the different types of catalytic reactions. Their potential catalysis applications are reviewed thoroughly. Moreover, a personal view about the future development of COFs catalysts with respect to the large‐scale production is also discussed.     

Highly Efficient Cooperative Catalysis by CoIII(Porphyrin) Pairs in Interpenetrating Metal–Organic Frameworks

A series of porous twofold interpenetrated In‐Co^III(porphyrin) metal–organic frameworks (MOFs) were constructed by in situ metalation of porphyrin bridging ligands and used as efficient cooperative catalysts for the hydration of terminal alkynes. The twofold interpenetrating structure brings adjacent Co^III(porphyrins) in the two networks parallel to each other with a distance of about 8.8 Å, an ideal distance for the simultaneous activation of both substrates in alkyne hydration reactions. As a result, the In‐Co^III(porphyrin) MOFs exhibit much higher (up to 38 times) catalytic activity than either homogeneous catalysts or MOF controls with isolated Co^III(porphyrin) centers, thus highlighting the potential application of MOFs in cooperative catalysis.     

Chiral Macrocycle‐Enabled Counteranion Trapping for Boosting Highly Efficient and Enantioselective Catalysis

The tight binding enabled by tailor‐made macrocycles can be manipulated for tuning the catalysis process. In parallel to well‐developed crown ether‐based cation‐binding catalysis, a macrocycle‐enabled counteranion trapping strategy is presented for boosting highly efficient and enantioselective catalysis. A set of bis‐diarylthiourea macrocycles containing two BINOL moieties were designed and synthesized. They possess a well‐confined chiral cavity and strong binding affinities towards disulfonate anions. Caused by the tight binding, just 1 mol % macrocycle in combination with 1 mol % ethanedisulfonic acid can promote excellent conversion and up to 99 % ee in the Friedel–Crafts reaction of indoles with imines. The acid or the macrocycle alone do not afford any reactivity. The high catalytic efficiency and excellent stereocontrol was ascribed to large, complexation‐induced acidity enhancement and tight ion‐pairing facilitated by cave‐like macrocyclic cavity.