Enantioselective [3+2] Annulation of Aldimines with Alkynes by Scandium-Catalyzed C-H Activation.

The enantioselective [3+2] annulation of readily accessible aldimines with alkynes via C-H activation is, in principle, a straightforward and atom-efficient route for synthesizing chiral 1-aminoindenes, which are important components in a wide array of natural products, bioactive molecules, and functional materials. However, such asymmetric transformation has remained undeveloped to date due to the lack of suitable chiral catalysts. Here, we report for the first time the enantioselective [3+2] annulation of aldimines with alkynes via C-H activation using chiral half-sandwich scandium catalysts.

Denitrogenative Ring-Contraction of Pyridines to a Cyclopentadienyl Skeleton at a Dititanium Hydride Framework.

Selective removal of the nitrogen atom from an aromatic -heterocycle, such as pyridine, is of significant interest and importance, yet it remains highly challenging. Here, we report an unprecedented denitrogenative ring-contraction reaction of pyridines at a dititanium hydride framework, yielding cyclopentadienyl and nitride species under mild conditions. The reaction of pyridine with a dititanium tetrahydride complex () bearing rigid acridane-based PNP-pincer ligands at room temperature produced a cyclopentadienyl/nitride complex (), in which the two Ti atoms are bridged by a nitride atom and one Ti atom is bonded to a cyclopentadienyl group formed by pyridine denitrogenation and ring-contraction.

()-Selective Isomerization of 1,1-Disubstituted Alkenes by Scandium-Catalyzed Allylic C-H Activation.

The isomerization of 1,1-disubstituted alkenes through 1,3-hydrogen shift is an atom-efficient route for synthesizing trisubstituted alkenes, which are important moieties in many natural products, pharmaceuticals, and organic materials. However, this reaction often encounters regio- and stereoselectivity challenges, typically yielding /-mixtures of the alkene products or thermodynamically favored ()-alkenes. Herein, we report the ()-selective isomerization of 1,1-disubstituted alkenes to trisubstituted ()-alkenes via the regio- and stereospecific activation of an allylic C-H bond.

Hydroamination of alkenes with dinitrogen and titanium polyhydrides.

An ideal synthesis of alkyl amines would involve the direct use of abundant and easily accessible molecules such as dinitrogen (N) and feedstock alkenes. However, this ambition remains a great challenge as it is usually difficult to simultaneously activate both N and a simple alkene and combine them together through carbon-nitrogen (C-N) bond formation. Currently, the synthesis of alkyl amines relies on the use of ammonia produced through the Haber-Bosch process and prefunctionalized electrophilic carbon sources.

Dinitrogen Cleavage and Multicoupling with Isocyanides in a Dititanium Dihydride Framework.

Dinitrogen (N) activation and functionalization through N-N bond cleavage and N-C bond formation are of great interest and importance but remain highly challenging. We report here for the first time N cleavage and selective multicoupling with isocyanides in a dititanium dihydride framework. The reaction of a dinitrogen dititanium dihydride complex [{(PNP)Ti}(μ-η:η-N)(μ-H)] () with an excess (four or more equivalents) of -methoxyphenyl isocyanide at room temperature gave a novel amidoamidinatoguanidinate complex [(PNP)Ti{NC(═NR)NC(═NR)CHNR}Ti(PNP)(CNR)] (, PNP = 4,5-bis(diisopropylphosphino)-2,7,9,9-tetramethyl-9-acridin-10-ide; R = -MeOCH) through N splitting and coupling with three isocyanide molecules.

Regio- and Diastereoselective Annulation of α,β-Unsaturated Aldimines with Alkenes via Allylic C(sp)-H Activation by Rare-Earth Catalysts.

The [3 + 2] or [4 + 2] annulation of α,β-unsaturated aldimines with alkenes via β'- or γ-allylic C(sp)-H activation is, in principle, an atom-efficient route for the synthesis of five- or six-membered-ring cycloalkylamines, which are important structural motifs in numerous natural products, bioactive molecules, and pharmaceuticals. However, such a transformation has remained undeveloped to date probably due to the lack of suitable catalysts. We report herein for the first time the regio- and diastereoselective [3 + 2] and [4 + 2] annulations of α,β-unsaturated imines with alkenes via allylic C(sp)-H activation by half-sandwich rare-earth catalysts having different metal ion sizes.

Catalytic ammonia synthesis on HY-zeolite-supported angstrom-size molybdenum cluster.

The development of new catalysts with high N activation ability is an effective approach for low-temperature ammonia synthesis. Herein, we report a novel angstrom-size molybdenum metal cluster catalyst for efficient ammonia synthesis. This catalyst is prepared by the impregnation of a molybdenum halide cluster complex with an octahedral Mo metal core on HY zeolite, followed by the removal of all the halide ligands by activation with hydrogen.

Synthesis of Tough and Fluorescent Self-Healing Elastomers by Scandium-Catalyzed Terpolymerization of Pyrenylethenylstyrene, Ethylene, and Anisylpropylene.

The synthesis of fluorescent self-healing polymers by the incorporation of a fluorophore-containing olefin into a polyolefin backbone through catalyst-controlled multicomponent copolymerization is of fundamental interest and practical importance, but such an approach has remained unexplored to date. Herein, we report for the first time the synthesis of tough and fluorescent self-healing polymers by sequence-controlled terpolymerization of 4-[2-(1-pyrenyl)ethenyl]styrene (), ethylene (), and anisylpropylene () using a sterically demanding half-sandwich scandium catalyst. The resulting terpolymers consisted of relatively long alternating -- sequences, isolated units, and short - blocks, which exhibited excellent tensile strength, remarkable self-healability, and high fluorescence quantum yield.

Divergent Synthesis of Multi-Substituted Aminotetralins via [4+2] Annulation of Aldimines with Alkenes by Rare-Earth-Catalyzed Benzylic C(sp )-H Activation.

The search for efficient and selective methods for the divergent synthesis of multi-substituted aminotetralins is of much interest and importance. We report herein for the first time the diastereoselective [4+2] annulation of 2-methyl aromatic aldimines with alkenes via benzylic C(sp )-H activation by half-sandwich rare-earth catalysts, which constitutes an efficient route for the divergent synthesis of both trans and cis diastereoisomers of multi-substituted 1-aminotetralin derivatives from readily accessible aldimines and alkenes. The use of a scandium catalyst bearing a sterically demanding cyclopentadienyl ligand such as C Me SiMe or C Me exclusively afforded the trans-selective annulation products in the reaction of aldimines with styrenes and aliphatic alkenes.

Aza-Michael Addition of Dinitrogen to α,β-Unsaturated Carbonyl Compounds in a Dititanium Framework.

The direct use of dinitrogen (N) as a building block for the synthesis of NN-containing organic compounds is of fundamental interest and practical importance but has remained a formidable challenge to date. Here, we report an unprecedented 1,4-conjugate (aza-Michael) addition of N to α,β-unsaturated carbonyl compounds in a dititanium framework. The resulting hydrazinopropenolate products could be easily converted to diverse NN-containing organic compounds such as β-hydrazine-functionalized esters and amides, pyrazolidinones, and pyrazolines depending on the types of Michael acceptors through protonation with MeOH.

Enantioselective Synthesis of 1-Aminoindanes via [3 + 2] Annulation of Aldimines with Alkenes by Scandium-Catalyzed C-H Activation.

Multisubstituted chiral 1-aminoindanes are important components in many pharmaceuticals and bioactive molecules. Therefore, the development of efficient and selective methods for the synthesis of chiral 1-aminoindanes is of great interest and importance. In principle, the asymmetric [3 + 2] annulation of aldimines with alkenes through C-H activation is the most atom-efficient and straightforward route for the construction of chiral 1-aminoindanes, but such a transformation has remained undeveloped to date probably due to the lack of suitable catalysts.

Hydrodeoxygenative Coupling and Transformation of Aldehydes at a N-Derived Tetranuclear Titanium Imide/Hydride Framework.

Carbon-carbon bond formation via coupling of two organic components is among the most important chemical transformations in organic synthesis. Herein, we report an unprecedented hydrodeoxygenative coupling of aromatic aldehydes to form bibenzyls by a N-derived tetranuclear titanium imide/hydride complex [(Cp'Ti)(μ-NH)(μ-H)] (; Cp' = CMeSiMe). Further reactions with the corresponding aldehydes under air afford hydrobenzamides together with a titanium oxo complex.

Diastereo- and Enantioselective Hydrophosphination of Cyclopropenes under Lanthanocene Catalysis.

The asymmetric hydrophosphination of cyclopropenes with phosphines is of much interest and importance, but has remained hardly explored to date probably because of the lack of suitable catalysts. We report here the diastereo- and enantioselective hydrophosphination of 3,3-disubstituted cyclopropenes with phosphines by a chiral lanthanocene catalyst bearing the C -symmetric 5,6-dioxy-4,7-trans-dialkyl-substituted tetrahydroindenyl ligands. This protocol offers a selective and efficient route for the synthesis of a new family of chiral phosphinocyclopropane derivatives, featuring 100 % atom efficiency, good diastereo- and enantioselectivity, broad substrate scope, and no need for a directing group.

Dinitrogen Activation and Addition to Unsaturated C-E (E=C, N, O, S) Bonds Mediated by Transition Metal Complexes.

Dinitrogen (N ) activation and functionalization is of fundamental interest and practical importance. This review focuses on N activation and addition to unsaturated substrates, including carbon monoxide, carbon dioxide, heteroallenes, aldehydes, ketones, acid halides, nitriles, alkynes, and allenes, mediated by transition metal complexes, which afforded a variety of N-C bond formation products. Emphases are placed on the reaction modes and mechanisms.

Auto-Tandem Copper-Catalyzed Carboxylation of Undirected Alkenyl C-H Bonds with CO by Harnessing β-Hydride Elimination.

The exploration into challenging scenarios of the application of elementary reactions offers excellent opportunities for the development of unique transformations under organometallic catalysis. As a ubiquitous reaction of metal alkyl complexes, β-hydride elimination plays a crucial role in a number of important catalytic transformations. However, its functions in these catalytic cycles are limited to either releasing alkene products or generating isomerized intermediates through further migratory insertion.

Regio- and Diastereoselective Formal [2+2] Cycloaddition of Allenes with Amino-Functionalized Alkenes by Rare-Earth-Catalyzed C(sp )-H Activation.

The [2+2] cycloaddition of allenes with alkenes is of much interest and importance as a straightforward route for the construction of four-membered carbocycles but has remained much underexplored to date. Herein we report for the first time the intermolecular regio- and diastereoselective formal [2+2] cycloaddition of a wide range of allenes with amino-functionalized alkenes by half-sandwich rare-earth catalysts. The reaction proceeded through an allene C(sp )-H activation mechanism initiated by the site-selective deprotonation of the allene unit by a rare-earth metal alkyl species followed by alkene insertion into the resulting metal-allenyl bond and the subsequent intramolecular cycloaddition to an allene C=C bond.

Making Polyisoprene Self-Healable through Microstructure Regulation by Rare-Earth Catalysts.

The creation of self-healing polymers from commodity olefins is of great interest and importance but has remained a challenge to date. We report here for the first time the synthesis of self-healing polymers by catalyst-controlled polymerization of a simple commodity diene, isoprene. We found that polyisoprenes having an appropriate mixture (ca.

Phosphine-Functionalized Syndiotactic Polystyrenes: Synthesis and Application to Immobilization of Transition Metal Nanoparticle Catalysts.

The precise control of monomer sequence and stereochemistry in copolymerization is of much interest and importance for the synthesis of high performance materials, but studies toward this goal have met with only limited success to date. The coordination polymerization of diphenylphosphinostyrene (p-StPPh and o-StPPh ) and its copolymerization with styrene (St) by (C Me SiMe )Sc(CH C H NMe -o) have been achieved for the first time to afford a new series of phosphine functionalized syndiotactic polystyrene. By the design of the polymer structure, the copolymer of o-StPPh and St (poly(o-StPPh -alt-St)-b-sPS) containing o-StPPh and St atactic alternating copolymer block and syndiotactic polystyrene block (sPS) showed excellent thermal stability and chemical resistance.

Synthesis of allylanilines scandium-catalysed benzylic C(sp)-H alkenylation with alkynes.

The -selective benzylic C(sp)-H alkenylation of 2-methyl tertiary anilines with internal alkynes has been achieved for the first time by using a half-sandwich scandium catalyst. This protocol provides a straightforward route for the synthesis of a new family of 2-allylaniline derivatives, featuring broad substrate scope, 100% atom-efficiency, high yields, and high chemo-, regio-, and stereoselectivity.

Dinitrogen Cleavage and Functionalization with Carbon Dioxide in a Dititanium Dihydride Framework.

The activation and functionalization of dinitrogen (N) with carbon dioxide (CO) are of great interest and importance but highly challenging. We report here for the first time the reaction of N with CO in a dititanium dihydride framework, which leads to N-C bond formation and N-N and C-O bond cleavage. Exposure of a dinitrogen dititanium hydride complex {[(PNP)Ti](-:-N)(-H)} () (PNP = 4,5-bis(diisopropylphosphino)-2,7,9,9-tetramethyl-9H-acridin-10-ide) to a CO atmosphere at room temperature rapidly yielded a nitrido/,-dicarboxylamido complex {[(PNP)Ti](-N)[-N(CO)]} (, 28%) and a diisocyanato/dioxo complex {[(PNP)Ti](NCO)(-O)} (, 52%) with release of H.

Theoretical mechanistic insights into dinitrogen cleavage by a dititanium hydride complex bearing PNP-pincer ligands.

The mechanism of dinitrogen cleavage by a PNP-coordinated dititanium polyhydride complex has been computationally investigated. A "multi-state reactivity" scenario has been disclosed for the whole process of N coordination and activation. Remarkably, the H elimination prior to the N-N cleavage is accomplished by the coupling of two terminal hydrides, and planar PNP-pincer ligand could stabilize the corresponding transition state.

Regio- and Diastereoselective [3+2] Annulation of Aliphatic Aldimines with Alkenes by Scandium-Catalyzed β-C(sp )-H Activation.

Here we report for the first time the regio- and diastereoselective [3+2] annulation of a wide range of aliphatic aldimines with alkenes via the activation of an unactivated β-C(sp )-H bond by half-sandwich scandium catalysts. This protocol offers a straightforward and atom-efficient route for the synthesis of a new family of multi-substituted aminocyclopentane derivatives from easily accessible aliphatic aldimines and alkenes. The annulation of aldimines with styrenes exclusively afforded the 5-aryl-trans-substituted 1-aminocyclopentane derivatives with excellent diastereoselectivity through the 2,1-insertion of a styrene unit.

Modular Access to Spiro-dihydroquinolines via Scandium-Catalyzed Dearomative Annulation of Quinolines with Alkynes.

The catalytic enantioselective construction of three-dimensional molecular architectures from planar aromatics such as quinolines is of great interest and importance from the viewpoint of both organic synthesis and drug discovery, but there still exist many challenges. Here, we report the scandium-catalyzed asymmetric dearomative spiro-annulation of quinolines with alkynes. This protocol offers an efficient and selective route for the synthesis of spiro-dihydroquinoline derivatives containing a quaternary carbon stereocenter with an unprotected N-H group from readily accessible quinolines and diverse alkynes, featuring high yields, high enantioselectivity, 100% atom-efficiency, and broad substrate scope.

Terpolymerization of Ethylene and Two Different Methoxyaryl-Substituted Propylenes by Scandium Catalyst Makes Tough and Fast Self-Healing Elastomers.

The terpolymerization of a non-polar olefin (such as ethylene) and two different polar functional olefins in a controlled fashion is of great interest and importance but has hardly been explored to date. We report for the first time the terpolymerization of ethylene (E) and two different methoxyaryl-substituted propylenes (A P=hexylanisyl propylene; A P=methoxynaphthyl propylene or methoxypyrenyl propylene) by a half-sandwich scandium catalyst. The terpolymerization took place in a sequence-controlled fashion, affording unique multi-block copolymers composed of two different ethylene-alt-methoxyarylpropylene sequences E-alt-A P (soft segments) and E-alt-A P (hard segments) and relatively short ethylene-ethylene (EE) blocks (crystalline segments).