Enantioselective α-C(sp)-H Borylation of Masked Primary Alcohols Enabled by Iridium Catalysis.

Functional group-directed site- and enantioselective C(sp)-H functionalization of alcohols or masked alcohols represents a formidable challenge. We herein report the first example of iridium-catalyzed asymmetric α-C(sp)-H borylation of primary alcohol-derived carbamates by the judicious choice of directing groups. A variety of chiral borylated carbamates were obtained with good to high enantioselectivities.

Evidence of boride-borylene ligand-tautomerism leading to a remote C-C-bond and concomitant boryl ligand formation.

The formation of a rhodium pincer-type complex with a boron-based donor ligand and its reactivity are reported. The starting complex contains a formal borylene moiety, stabilised by two pyridine substituents. Quantum chemical investigations indicate the possibility of deprotonation of the central donor group of the type pyBH in this complex.

Catalyst-Free Activation and Fixation of Nitrogen by Laser-Induced Conversion.

Ultrafast N fixation reactions are quite challenging. Currently used methods for N fixation are limited, and strong dinitrogen bonds usually need to be activated via extreme temperature or pressure or by the use of an energy-consuming process with sophisticated catalysts. Herein, we report a novel laser-based chemical method for N fixation under ambient conditions without catalysts, this method is called laser bubbling in liquids (LBL), and it directly activates N in water (HO) and efficiently converts N into valuable NH (max: 4.

Sequential radical and cationic reactivity at separated sites within one molecule in solution.

Distonic radical cations (DRCs) with spatially separated charge and radical sites are expected to show both radical and cationic reactivity at different sites within one molecule. However, such "dual" reactivity has rarely been observed in the condensed phase. Herein we report the isolation of crystalline 1λ,3λ-1-phosphonia-3-phosphinyl-cyclohex-4-enes 2a,b˙, which can be considered delocalized DRCs and were completely characterized by crystallographic, spectroscopic, and computational methods.

Laser direct overall water splitting for H and HO production.

Hydrogen (H) and hydrogen peroxide (HO) play crucial roles as energy carriers and raw materials for industrial production. However, the current techniques for H and HO production rely on complex catalysts and involve multiple intermediate steps. In this study, we present a straightforward, environmentally friendly, and highly efficient laser-induced conversion method for overall water splitting to simultaneously generate H and HO at ambient conditions without any catalysts.

Efficient and Rapid Hydrogen Extraction from Ammonia-Water Laser Under Ambient Conditions without Catalyst.

As a good carrier of hydrogen, ammonia-water has been employed to extract hydrogen in many ways. Here, we demonstrate a simple, green, ultrafast, and highly efficient method for hydrogen extraction from ammonia-water by laser bubbling in liquids (LBL) at room temperature and ambient pressure without catalyst. A maximum apparent yield of 33.

Laser-Induced Methanol Decomposition for Ultrafast Hydrogen Production.

Methanol (CHOH) is a liquid hydrogen (H) source that effectively releases H and is convenient for transportation. Traditional thermocatalytic CHOH reforming reaction is used to produce H, but this process needs to undergo high reaction temperature (e.g.

Feature Analysis in High-Dimensional Data: Structure-Activity Relationships of Lewis Acid-Transition-Metal Complex-Catalyzed H Activation.

Lewis acid-transition metal (LA-TM) catalysts have been proven to have an advantage in catalyzing hydrogen activation. Herein, a high-dimensional structure-activity relationship study is performed for LA-TM-catalyzed hydrogen activation by density functional theory calculations. The DPB-Ni complex is taken as the representative catalyst, and the explored Lewis acid sites and transition-metal centers include B, Al, Ga and Ni, Pd, Pt, respectively.

Mechanism-Dependent Selectivity: Fluorocyclization of Unsaturated Carboxylic Acids or Alcohols by Hypervalent Iodine.

To understand the unprecedented difference between and selectivity in hypervalent iodine (III) promoted fluorocyclization of unsaturated carboxylic acids or alcohols by difluoroiodotoluene, density functional theory (DFT) studies have been performed to systematically compare both the previous proposed "fluorination first and cyclization later" mechanism and the alternative "cyclization first and fluorination later" mechanism. Our results revealed that the selectivity is mechanism-dependent. The unsaturated alcohol prefers the fluorination first and the cyclization later pathway, leading to the experimentally observed ether product.

Selective C-alkylation Between Alcohols Catalyzed by N-Heterocyclic Carbene Molybdenum.

The first implementation of a molybdenum complex with an easily accessible bis-N-heterocyclic carbene ligand to catalyze β-alkylation of secondary alcohols via borrowing-hydrogen (BH) strategy using alcohols as alkylating agents is reported. Remarkably high activity, excellent selectivity, and broad substrate scope compatibility with advantages of catalyst usage low to 0.5 mol%, a catalytic amount of NaOH as the base, and H O as the by-product are demonstrated in this green and step-economical protocol.

Enantioselective Oxidative Multi-Functionalization of Terminal Alkynes with Nitrones and Alcohols for Expeditious Assembly of Chiral α-Alkoxy-β-amino-ketones.

Catalytic oxidative functionalization of alkynes has emerged as an effective method in synthetic chemistry in recent decades. However, enantioselective transformations via metal carbene intermediates are quite rare due to the lack of robust chiral catalysts, especially in the intermolecular versions. Herein, we report the first asymmetric three-component reaction of commercially available alkynes with nitrones and alcohols, which affords α-alkoxy-β-amino-ketones in good yields with high to excellent enantioselectivity using combined catalysis by an achiral gold complex and a chiral spiro phosphoric acid (CPA).

Metal Effect Meets Volcano Plots: A DFT Study on Tris(phosphino)borane-Transition Metal Complexes Catalyzed H Activation.

Bifunctional transition metal complexes are of particular interest in metal-ligand cooperative activation of small molecules. As a novel type of bifunctional catalyst, Lewis acid transition metal (LA-TM) complexes have attracted increasing interest in hydrogen activation and storage. To advance the catalyst design, herein the metal effect of LA-TM complexes on the hydrogen activation has been systematically studied with a series of tris(phosphino)borane (TPB) complexes with V, Cr, Mn, Fe, Co, and Ni as metal centers.

Ruthenium(II) complexes with N-heterocyclic carbene-phosphine ligands for the -alkylation of amines with alcohols.

Metal hydride complexes are key intermediates for N-alkylation of amines with alcohols by the borrowing hydrogen/hydrogen autotransfer (BH/HA) strategy. Reactivity tuning of metal hydride complexes could adjust the dehydrogenation of alcohols and the hydrogenation of imines. Herein we report ruthenium(ii) complexes with hetero-bidentate N-heterocyclic carbene (NHC)-phosphine ligands, which realize smart pathway selection in the N-alkylated reaction via reactivity tuning of [Ru-H] species by hetero-bidentate ligands.

Design, synthesis, and physicochemical study of a biomass-derived CO sorbent 2,5-furan-bis(iminoguanidine).

In this study, the concept of biomass-based direct air capture is proposed, and the aminoguanidine CO chemical sorbent 2,5-furan-bis(iminoguanidine) (FuBIG) was designed, synthesized, and elucidated for the physicochemical properties in the process of CO capture and release. Results showed that the aqueous solution of FuBIG could readily capture CO from ambient air and provided an insoluble tetrahydrated carbonate salt FuBIGH(CO) (HO) with a second order kinetics. Hydrogen binding modes of iminoguanidine cations with carbonate ions and water were identified by single-crystal X-ray diffraction analysis.

Visible-Light-Induced Amination of Quinoline at the C8 Position via a Postcoordinated Interligand-Coupling Strategy under Mild Conditions.

The postcoordinated interligand-coupling strategy provides a useful and complementary protocol for synthesizing polydentate ligands. Herein, diastereoselective photoreactions of Λ-[Ir(pq)(d-AA)] () and Λ-[Ir(pq)(l-AA)] (, where pq is 2-phenylquinoline and AA is an amino acid) are reported in the presence of O under mild conditions. Diastereomer is dehydrogenatively oxidized into an imino acid complex, while diastereomer mainly occurs via interligand C-N cross-dehydrogenative coupling between quinoline at the C8 position and AA ligands at room temperature, affording Λ-[Ir(pq)(l-pq-AA)].

From carbones to carbenes and ylides in the coordination sphere of iridium.

The carbodiphosphorane-based iridium pincer complex (2) is demonstrated to rearrange in chlorinated organic solvents under cleavage of a P-C-bond to give a chelating phosphine ylide ligand. A detailed mechanistic investigation reveals that these types of donor groups are prone for P-C-bond cleavage in the coordination sphere of transition metal hydrido complexes. Finally, complex 2 is demonstrated to be an efficient hydrogen-borrowing catalyst.

Lewis Acid Transition-Metal-Catalyzed Hydrogen Activation: Structures, Mechanisms, and Reactivities.

As a new type of bifunctional catalyst, the Lewis acid transition-metal (LA-TM) catalysts have been widely applied for hydrogen activation. This study presents a mechanistic framework to understand the LA-TM-catalyzed H activation through DFT studies. The mer(trans)-homolytic cleavage, the fac(cis)-homolytic cleavage, the synergetic heterolytic cleavage, and the dissociative heterolytic cleavage should be taken as general mechanisms for the field of LA-TM catalysis.

Room temperature N-heterocyclic carbene manganese catalyzed selective N-alkylation of anilines with alcohols.

The first example of room temperature non-noble metal homogeneous system catalyzed selective N-alkylation of anilines with alcohols by a bis-NHC manganese complex is presented. This system was applied to a large range of alcohols and anilines, including biologically relevant motifs and challenging methanol. Experimental and computational studies suggest an outer-sphere mechanism for this NHC-Mn system.

Chiral Bidentate Boryl Ligand Enabled Iridium-Catalyzed Asymmetric C(sp)-H Borylation of Diarylmethylamines.

Optically active organoboronic acids and their derivatives are an important family of target compounds in organic chemistry, catalysis, and medicinal chemistry. Yet there are rare asymmetric catalytic examples reported for the synthesis of these compounds via atom and step economic ways. Herein, we report a chelate-directed iridium-catalyzed asymmetric C(sp)-H borylation of aromatic C-H bonds directed by free amine groups.

Mechanism of Hypervalent Iodine Promoted Fluorocyclization of Unsaturated Alcohols: Metathesis via Double Acids Activation.

Lewis/Bronsted acid activation plays a key role in hypervalent iodine reagent-mediated reactions. In addition to generally accepted cis-activation or trans-activation, this study reveals another important Lewis/Bronsted acid activation mode, the double-activation. Different from the generally proposed iodine(III)iranium S2 mechanism, the hypervalent difluoro-iodoarene-promoted fluorocyclization of unsaturated alcohol prefers to undergo the metathesis mechanism via an iodine(III)-π intermediate.

Frustrated Lewis Pair Catalyzed C-H Activation of Heteroarenes: A Stepwise Carbene Mechanism Due to Distance Effect.

This study presents new mechanistic insights into the frustrated Lewis pairs (FLPs) catalyzed C-H activation of heteroarenes. Besides the generally accepted concerted C-H activation, a novel stepwise carbene type pathway is proposed as an alternative mechanism. The reaction mechanisms can be varied by tuning the distance between Lewis acid and Lewis base due to catalyst-substrate match.

Flexible Steric Bulky Bis(Imino)acenaphthene (BIAN)-Supported N-Heterocyclic Carbene Palladium Precatalysts: Catalytic Application in Buchwald-Hartwig Amination in Air.

To achieve efficient palladium-catalyzed cross-coupling reaction under mild reaction conditions with the flexible steric bulk strategy, a series of Pd-PEPPSI (PEPPSI: pyridine-enhanced precatalyst preparation, stabilization, and initiation) complexes C1-C6 were synthesized and characterized, in which unsymmetric flexible steric bulk was introduced on the N-aryl of ancenaphthyl skeleton. These well-defined palladium complexes were found to be excellent precatalysts for Buchwald-Hartwig amination of aryl chlorides with amines in air. The electronic effect of the Pd-PEPPSI complexes and the effect of ancillary pyridine ligands were evaluated, among which complex C3 exhibited the most efficiency.

Rationalization of the selectivity between 1,3- and 1,2-migration: a DFT study on gold(i)-catalyzed propargylic ester rearrangement.

Gold catalyzed rearrangement of propargylic esters can undergo 1,3-acyloxy migration to form allenes, or undergo 1,2-acyloxy migration to access gold-carbenoids. The variation in migration leads to different reactivities and diverse cascade transformations. The effect of terminal substituents is very important for the rearrangement.

Unusual non-bifunctional mechanism for Co-PNP complex catalyzed transfer hydrogenation governed by the electronic configuration of metal center.

The mimic of hydrogenases has unleashed a myriad of bifunctional catalysts, which are widely used in the catalytic hydrogenation of polar multiple bonds. With respect to ancillary ligands, the bifunctional mechanism is generally considered to proceed via the metal-ligand cooperation transition state. Inspired by the interesting study conducted by Hanson et al.