Repurposing a supramolecular iridium catalyst secondary Zn⋯O[double bond, length as m-dash]C weak interactions between the ligand and substrate leads to -selective C(sp)-H borylation of benzamides with unusual kinetics.

The iridium-catalyzed C-H borylation of benzamides typically leads to and selectivities using state-of-the-art iridium-based ,-chelating bipyridine ligands. However, reaching selectivity patterns requires extensive trial-and-error screening molecular design at the ligand first coordination sphere. Herein, we demonstrate that triazolylpyridines are excellent ligands for the selective iridium-catalyzed C-H borylation of tertiary benzamides and, importantly, we demonstrate the almost negligible effect of the first coordination sphere in the selectivity, which is so far unprecedented in iridium C-H bond borylations.

Markovnikov-Selective Cobalt-Catalyzed Wacker-Type Oxidation of Styrenes into Ketones under Ambient Conditions Enabled by Hydrogen Bonding.

The replacement of palladium catalysts for Wacker-type oxidation of olefins into ketones by first-row transition metals is a relevant approach for searching more sustainable protocols. Besides highly sophisticated iron catalysts, all the other first-row transition metal complexes have only led to poor activities and selectivities. Herein, we show that the cobalt-tetraphenylporphyrin complex is a competent catalyst for the aerobic oxidation of styrenes into ketones with silanes as the hydrogen sources.

Boosting the activity of Mizoroki-Heck cross-coupling reactions with a supramolecular palladium catalyst favouring remote Zn⋯pyridine interactions.

Transition metal catalysis benefitting from supramolecular interactions in the secondary coordination sphere in order to pre-organize substrates around the active site and reach a specific selectivity typically occurs under long reaction times and mild reaction temperatures with the aim to maximize such subtle effects. Herein, we demonstrate that the kinetically labile Zn⋯N interaction between a pyridine substrate and a zinc-porphyrin site serving for substrate binding is a unique type of weak interaction that enables identification of supramolecular effects in transition metal catalysis after one hour at a high reaction temperature of 130 °C. Under carefully selected reaction conditions, supramolecularly-regulated palladium-catalyzed Mizoroki-Heck reactions between 3-bromopyridine and terminal olefins (acrylates or styrenes) proceeded in a more efficient manner compared to the non-supramolecular version.

Electronic, steric and catalytic properties of N-heterocyclic carbene rhodium(I) complexes linked to (metallo)porphyrins.

Electronic and steric properties of NHC ligands functionalized with porphyrins were investigated. When porphyrins are used as NHC-wingtips, nickel(II) in the macrocyle significantly improves the catalytic activity of the neighbouring NHC-Rh(I) complex in the conjugate addition of phenylboronic acid to cyclohexen-2-one.

Asymmetric Ruthenium Catalysis Enables Fluorophores with Point Chirality Displaying CPL Properties.

A novel enantiopure π-allylruthenium(IV) precatalyst allowed the enantioselective and stereospecific allylations of indoles and gave access to indolin-3-ones, containing vicinal stereogenic centers. Facile separation of diastereoisomers exhibiting opposite circularly polarized luminescence (CPL) activities in diverse solvents, including water, demonstrated the potential of these sustainable transformations and of the newly prepared molecules.

Sustainable Wacker-Type Oxidations.

The Wacker reaction is the oxidation of olefins to ketones and typically requires expensive and scarce palladium catalysts in the presence of an additional copper co-catalyst under harsh conditions (acidic media, high pressure of air/dioxygen, elevated temperatures). Such a transformation is relevant for industry, as shown by the synthesis of acetaldehyde from ethylene as well as for fine-chemicals, because of the versatility of a carbonyl group placed at specific positions. In this regard, many contributions have focused on controlling the chemo- and regioselectivity of the olefin oxidation by means of well-defined palladium catalysts under different sets of reaction conditions.

Unravelling Enzymatic Features in a Supramolecular Iridium Catalyst by Computational Calculations.

Non-biological catalysts following the governing principles of enzymes are attractive systems to disclose unprecedented reactivities. Most of those existing catalysts feature an adaptable molecular recognition site for substrate binding that are prone to undergo conformational selection pathways. Herein, we present a non-biological catalyst that is able to bind substrates via the induced fit model according to in-depth computational calculations.

Iridium-Catalyzed Direct Reductive Amination of Ketones and Secondary Amines: Breaking the Aliphatic Wall.

Invited for the cover of this issue are Matthieu Jouffroy from Discovery Process Research at Janssen Pharmaceutica N.V. and the group of Rafael Gramage-Doria at the University of Rennes.

Iridium-Catalyzed Direct Reductive Amination of Ketones and Secondary Amines: Breaking the Aliphatic Wall.

Direct reductive amination (DRA) is a ubiquitous reaction in organic chemistry. This transformation between a carbonyl group and an amine is most often achieved by using a super stoichiometric amount of hazardous hydride reagents, thus being incompatible with many sensitive functional groups. DRA could also be achieved by means of chemo- or biocatalysis, thereby attracting the interest of industry as well as academic laboratories due to the virtually perfect atom economy.

Ultrashort HH intermolecular distance in a supramolecular system in the solid state.

Herein we report experimental evidence for the shortest intermolecular distance reported for two electronically-different hydrogen atoms in the solid state. The Hδ+Hδ- non-covalent interaction was studied using theoretical calculations indicating that electrostatic and dispersion forces are of paramount importance.

Enzyme-like Supramolecular Iridium Catalysis Enabling C-H Bond Borylation of Pyridines with meta-Selectivity.

The use of secondary interactions between substrates and catalysts is a promising strategy to discover selective transition metal catalysts for atom-economy C-H bond functionalization. The most powerful catalysts are found via trial-and-error screening due to the low association constants between the substrate and the catalyst in which small stereo-electronic modifications within them can lead to very different reactivities. To circumvent these limitations and to increase the level of reactivity prediction in these important reactions, we report herein a supramolecular catalyst harnessing Zn⋅⋅⋅N interactions that binds to pyridine-like substrates as tight as it can be found in some enzymes.

Beyond hydrogen bonding: recent trends of outer sphere interactions in transition metal catalysis.

Homogeneous catalytic reactions are typically controlled by the stereoelectronic nature of the ligand(s) that bind to the metal(s). The advantages of the so-called first coordination sphere effects have been used for the efficient synthesis of fine chemicals relevant for industrial and academic laboratories since more than half a century. Such level of catalyst control has significantly upgraded in the last few decades by mastering additional interactions beyond the first coordination sphere.

Steering Site-Selectivity in Transition Metal-Catalyzed C-H Bond Functionalization: the Challenge of Benzanilides.

Selective C-H bond functionalization catalyzed by metal complexes have completely revolutionized the way in which chemical synthesis is conceived nowadays. Typically, the reactivity of a transition metal catalyst is the key to control the site-, regio- and/or stereo-selectivity of a C-H bond functionalization. Of particular interests are molecules that contain multiple C-H bonds prone to undergo C-H bond activations with very similar bond dissociation energies at different positions.

C-H Bond Alkylation of Cyclic Amides with Maleimides via a Site-Selective-Determining Six-Membered Ruthenacycle.

The first example of a ruthenium-catalyzed C-H bond alkylation via six-membered ruthenacycles is presented. This is disclosed for the C-H bond alkylation of biologically relevant cyclic amides with maleimide derivatives. The cyclic tertiary amide core acted as a directing group (DG) enabling formation of six-membered cycloruthenated species responsible for the control of the regio- and site selectivity of the reaction as well as the excellent functional group tolerance.

Ruthenium(ii)-catalysed selective C(sp)-H bond benzoxylation of biologically appealing N-arylisoindolinones.

Site- and regio-selective aromatic C-H bond benzoxylations were found to take place using biologically appealing N-arylisoindolinones under ruthenium(ii) catalysis in the presence of (hetero)aromatic carboxylic acid derivatives as coupling partners. Besides the presence of two potential C(sp)-H sites available for functionalization in the substrates, exclusive ortho selectivity was achieved in the phenyl ring attached to the nitrogen atom. Notably, the reactions occurred in a selective manner as only mono-functionalized products were formed and they tolerated a large number of functional chemical groups.

Site-Selective Ruthenium-Catalyzed C-H Bond Arylations with Boronic Acids: Exploiting Isoindolinones as a Weak Directing Group.

Biologically relevant -arylisoindolinones efficiently underwent arylation reactions under ruthenium catalysis via C-H bond functionalization. The reactions exclusively led to monoarylated products, and only selectivity was observed in the aromatic ring connected to the nitrogen atom. Interestingly, no C-H bond functionalization was observed in the other benzene ring in the position with respect to the carbonyl group.

Ru-Catalyzed Selective C-H Bond Hydroxylation of Cyclic Imides.

We report on cyclic imides as weak directing groups for selective monohydroxylation reactions using ruthenium catalysis. Whereas acyclic amides are known to promote the hydroxylation of the C(sp)-H bond enabling five-membered ring ruthenacycle intermediates, the cyclic imides studied herein enabled the hydroxylation of the C(sp)-H bond via larger six-membered ruthenacycle intermediates. Furthermore, monohydroxylated products were exclusively obtained (even in the presence of overstoichiometric amounts of reagents), which was rationalized by the difficulty to accommodate coplanar intermediates once the first hydroxyl group was introduced into the substrate.

A Supramolecular Palladium Catalyst Displaying Substrate Selectivity by Remote Control.

Inspired by enzymes such as cytochrome P-450, the study of the reactivity of metalloporphyrins continues to attract major interest in the field of homogeneous catalysis. However, little is known about benefitting from the substrate-recognition properties of porphyrins containing additional, catalytically relevant active sites. Herein, such an approach is introduced by using supramolecular ligands derived from metalloporphyrins customized with rigid, palladium-coordinating nitrile groups.

Ruthenium(II)-Catalyzed C-H (Hetero)Arylation of Alkenylic 1,n-Diazines (n = 2, 3, and 4): Scope, Mechanism, and Application in Tandem Hydrogenations.

A general ruthenium(II)-catalyzed methodology enabling the (hetero)arylation of alkenylic C-H bonds utilizing a series of synthetically appealing diazines as directing groups is presented. Despite the presence of additional nitrogen lone pairs remote from the C-H bond activation site, which could eventually poison the catalyst, the reaction times are short (3 h), thus being suitable for selective double C-H bond arylation. Mixtures of E:Z isomeric products were observed in some cases, which were further hydrogenated in a tandem manner in the presence of the remaining ruthenium catalyst from the first step, representing an alternative approach to more difficult C(sp)-H bond functionalization.

Unmasking Amides: Ruthenium-Catalyzed Protodecarbonylation of N-Substituted Phthalimide Derivatives.

The unprecedented transformation of a wide range of synthetically appealing phthalimides into amides in a single-step operation has been achieved in high yields and short reaction times using a ruthenium catalyst. Mechanistic studies revealed a unique, homogeneous pathway involving five-membered ring opening and CO release with water being the source of protons.

Palladium-Catalysed Cross-Coupling Reactions Controlled by Noncovalent Zn⋅⋅⋅N Interactions.

Non-covalent interactions between halopyridine substrates and catalytically inert building blocks, namely zinc(II)-porphyrins and zinc(II)-salphens, influence the catalytic outcome of Suzuki-Miyaura and Mizoroki-Heck palladium-catalysed cross-coupling reactions. The weak Zn⋅⋅⋅N interactions between halopyridine substrates and zinc(II)-containing porphyrins and salphens, respectively, were studied by a combination of H NMR spectroscopy, UV/Vis studies, Job-Plot analysis and, in some cases, X-ray diffraction studies. Additionally, the former studies revealed unique supramolecular polymeric and dimeric rearrangements in the solid state featuring weak Br⋅⋅⋅N (halogen bonding), C-H⋅⋅⋅π, Br⋅⋅⋅π and π⋅⋅⋅π interactions.

Enantioselective hydroformylation by a Rh-catalyst entrapped in a supramolecular metallocage.

Regio- and enantioselective hydroformylation of styrenes is attained upon embedding a chiral Rh complex in a nonchiral supramolecular cage formed from coordination-driven self-assembly of macrocyclic dipalladium complexes and tetracarboxylate zinc porphyrins. The resulting supramolecular catalyst converts styrene derivatives into aldehyde products with much higher chiral induction in comparison to the nonencapsulated Rh catalyst. Spectroscopic analysis shows that encapsulation does not change the electronic properties of the catalyst nor its first coordination sphere.

Phosphinocyclodextrins as confining units for catalytic metal centres. Applications to carbon-carbon bond forming reactions.

The capacity of two cavity-shaped ligands, HUGPHOS-1 and HUGPHOS-2, to generate exclusively singly phosphorus-ligated complexes, in which the cyclodextrin cavity tightly wraps around the metal centre, was explored with a number of late transition metal cations. Both cyclodextrin-derived ligands were assessed in palladium-catalysed Mizoroki-Heck coupling reactions between aryl bromides and styrene on one hand, and the rhodium-catalysed asymmetric hydroformylation of styrene on the other hand. The inability of both chiral ligands to form standard bis(phosphine) complexes under catalytic conditions was established by high-pressure NMR studies and shown to have a deep impact on the two carbon-carbon bond forming reactions both in terms of activity and selectivity.