Using feedstock methanol as a green methylation reagent, the selective N-monomethylation of anilines is realized under mild reaction conditions by using N-heterocyclic carbene iridium (NHC-Ir) coordination assemblies as highly efficient solid molecular catalysts. Along with a broad substrate scope and good functional group tolerance, up to quantitative yield and 2.0 × 104 turnover numbers (TONs) are obtained even at low catalyst loadings. Notably, the solid NHC-Ir molecular catalyst can be easily recovered and recycled more than 20 times without obvious loss of reactivity and selectivity. Furthermore, this selective practical protocol can be successfully extended to direct methylation of highly functionalized bioactive compounds including 3-aminoestrone, cinacalcet, and their analogues in excellent yields and selectivities, highlighting their potential application in pharmaceuticals.Keywords: Amine synthesis; Catalytic methylation; Coordination assembly; Iridium; Methanol activation;

AbstractUnsymmetrical 3-arylidene-2-oxindoles are useful pharmacophores for many clinical drugs or intermediates in alkaloids synthesis. An IridiumIII-catalyzed sequential C−H oxidative reaction of 2-indolyl enamides has been established. This protocol utilized α,α-dimethyl benzylhydroperoxide as the oxidant and silver fluoride as a key promoter, to provide a wide range of (Z)-3-arylidene-2-oxindole imides in moderate to good yields, together with good regio- and stereoselectivity. The silver fluoride was found to function as a base to facilitate the generation of the active Iridium catalyst species. The resulting (Z)-3-arylidene-2-oxindole imides could be further transformed to various valuable derivatives. Mechanistically, radical-process was excluded from this C−H oxidative transformation, and a 6-membered cationic iridacycle intermediate was proposed to be involved in the catalytic cycle.

AbstractA ligand-free Pd/Cu-catalyzed aminosulfonylation of aryl iodides has been successfully developed. The protocol provides a straightforward approach to access a broad range of structurally intriguing sulfonamides in one pot, at low catalyst loading from the sulfur dioxide surrogate 1,4-diazabicyclo[2.2.2]octane bis(sulfur oxide) (DABSO) and O-benzoyl hydroxylamines under mild conditions. Even without additional ligands, the protocol reveals broad substrate scope for both partners and tolerates all kinds of functional groups. Furthermore, the proposed sulfinate intermediate could be critical for this ligand-free catalytic transformation.

Robust N-heterocyclic carbene palladium complexes are highly efficient catalysts for direct alkylsulfonylation of (hetero)aryl- or alkenyl-boronic acids with potassium metabisulfite and (hetero)alkyl-halides. Among them, acenaphthoimidazolylidene palladium(II) complexes exhibited the highest activities, and up to quantitative yields were obtained for diverse structurally distinct sulfones under very mild reaction conditions.

A robust magnetic nanoparticle-supported N-heterocyclic carbene-palladacycle has been readily synthesized by directly anchoring the structural defined acenaphthoimidazolylidene palladacycle with a long tail on magnetic nanoparticles (MNPs), and functioned as a solid molecular catalyst and exhibited extremely high catalytic activity towards the challenging Suzuki–Miyaura cross-coupling reactions between less-studied heterocyclic 9-chloroacridine and diverse boronic acids. Remarkably, the catalyst could be used 5 times without obvious loss of activity highlighting the efficiency of our strategy of immobilization of previledged catalysts.

A class of robust solid molecular NHC-based catalysts were readily fabricated via self-assembly from a p-phenylene-bridged bis-benzimidazolium salt with selected metal precursors. Among them, the NHC-Ru polymer demonstrated high catalytic activity and excellent stability as a solid molecular catalyst for the solvent-free reductive amination of biomass levulinic acid with inexpensive ammonium formate, furnishing a challenging unprotected 5-methyl-2-pyrrolidone quantitatively at a 0.15 mol% catalyst loading. The solid catalyst was readily recovered and reused for 37 runs without obvious loss of activity. Remarkably, a TON value up to 6.7 × 104 was achieved in a molar-scale reaction with a catalyst loading at 0.001 mol%. Inspired by the results of a preliminary mechanistic study, notably, one-pot tandem reductive reactions of LA with aldehydes or ketones were successfully developed, affording a variety of structurally intriguing and functional N-substituted 5-methyl-2-pyrrolidones in high chemo-selectivity with good to excellent yields.

With use of simple terpyridine zinc nitrate complexes, intriguing visual recognition of adenosine triphosphate (ATP) via selective coordination assembly leading to two-component metallo-hydrogel formation has been realized. With intensive fluorescent study and density functional theory calculations, it may be inferred, besides the selective metal–ligand interaction between Zn center and phosphate groups, the intramolecular π-stacking between the planar nucleobases of ATP and the metal-hybrid aromatic ring of pincer complex strongly affected the geometry of the coordinated adducts and possible molecular self-assembly process, which constitute a completely new sensing strategy in comparison with the conventional approaches. Furthermore, in light of extreme sensitivity of pincer zinc complexes toward ATP at micromolar scale (1.85 μM) and remarkable fluorescent enhancement (ca. 44-fold) upon ATP addition, the feasibility of the low cytotoxicity pincer zinc complexes in monitoring ATP in HeLa cells has been fulfilled with confocal fluorescence microscopy.Keywords: adenosine triphosphate; celluar imaging; fluorescence enhancement; metallo-hydrogel; visual recognition

Along with the rapid expansion of the biodiesel industry to deal with the world energy crisis, inexpensive glycerol is also produced in large scale as the main byproduct in biodiesel production via transesterification. Much attention has been paid to the development of environmentally benign technologies for the transformation of glycerol to valuable DL-lactic acid and its derivatives. Herein, a series of NHC-Ir coordination polymers were readily synthesized via reaction of some structurally rigid bis-benzimidazolium salts with iridium precursors under alkaline conditions and were successfully applied as robust self-supported catalysts in the oxidative dehydrogenation of glycerol to potassium lactate with dihydrogen liberation. Extremely high activity and selectivity were attained in open air under the mild reaction conditions even with ppm-level loadings of the catalysts, which were readily recovered after reaction by simple filtration and reused for up to 31 runs without obvious loss of activity or selectivity. Probably owing to the effective suppression of inactive binuclear iridium species in a homogeneously catalyzed reaction, the catalysts assembled via self-supported strategy exhibited high selectivity and productivity for potassium lactate, with up to 1.24 × 105 turnover numbers (TON) being attained even in large-scale reactions of neat glycerol at an elevated temperature. The high catalytic activity, recyclability, and scalability of the robust self-supported catalysts highlight their potential toward the development of practical technologies for transformation of glycerol to value-added chemicals.Keywords: coordination assembly; iridium; lactate; oxidative dehydrogenation; self-support catalyst

Due to its special coordination ability to Cu(II)–terpyridine complexes, a simple and straightforward visual recognition of p-DMAP out of its analogues has been realized via selective metallogel collapse. In combination with the selective gel collapse and the self-healing properties of metallohydrogel 1a, its potential application towards chemo-switch is also demonstrated.

By using O-benzoyl hydroxylamines as amine sources, the first convenient copper-catalyzed electrophilic amination of sodium sulfinates has been realized. Even with 2 mol% catalyst loading, the protocol provided an efficient and straightforward synthesis of a broad range of functional sulfonamides under ambient reaction conditions without an additional base and ligand. Based on the control experiments, a plausible mechanism was proposed.

Incorporating the visual discrimination of 2,2′-bipyridine and self-healing properties, a novel photo-switchable metallo-hydrogel system is fabricated using a pincer-type Cu(II) complex and 2,2′-azopyridine.

A series of fluorescent (hetero)-aryl substituted anthracene derivatives were readily accessible from the corresponding bulky anthracen-9-yl carboxylates via Suzuki–Miyaura cross-coupling reactions by using pincer nickel N-heterocyclic carbene complex 1 even at the catalyst loading as low as 0.1 mol% in the presence of catalytic amounts of PCy3.

A robust allylic palladium–NHC complex was developed and exhibited extremely high catalytic activity toward aminocarbonylation of various (hetero)aryl iodides under atmospheric carbon monoxide pressure, in which a broad range of secondary and primary amines were well tolerated. In addition, the concise synthesis of an anticancer drug tamibarotene was accomplished even in a gram scale, further highlighting the practical applicability of the protocol.

Even without obvious sticky sites, novel supramolecular thixotropic metallohydrogels consisting of rare metal–organic nanoparticles (MNPs) have been readily accessible from simple structured pincer-type terpyridine Cu(II) complexes at the gelator concentration as low as 0.25 wt %. The obtained soft materials have been fully characterized by using a combination of experimental techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS), X-ray diffraction (XRD), high-resolution mass spectrometry (HR-MS), and rheology measurements. Based on these studies, hypothesized molecular assembly mechanisms for distinctly different morphologies observed in different solvents were proposed. Besides general heating–cooling gel preparation procedures, surprisingly, the metallohydrogel was formed by simply stirring the mixture of pincer ligand and Cu salts in water directly, further indicating thixotropic property and self-healing ability of the resulting metallohydrogel under external stress. This stirring approach is highly anion and phase selective with various potential applications. Furthermore, the infrequent observation of the crystal growth from metallogels in situ readily reavealed the self-assembly mechanism that π-stacking and metal–metal interactions along with hydrogen-bonding interactions between gelator and guest molecules are responsible for the gel formation, which is further confirmed by the control gel collapse experiment via external ligand substitution. All these results indicated that pincer organometallic complexes not only can function as a new type of hydrogelators but also are readily to fabricate useful thixotropic materials with various applicability based on their morphologies and assembly mechanism studies.

Considering that the strong σ-donor property of ylidenes derived from π-extended imidazolium salts is conducive to increasing the catalytic activity of the resulting palladium N-heterocyclic carbene complexes, robust acenaphthoimidazol-ylidene palladium complexes 3a–c with varying bulky substituted groups were prepared from the corresponding acenaphthoimidazolium chlorides by heating with PdCl2 and K2CO3 in neat 3-chloropyridine in satisfactory yields. Even at a catalyst loading as low as 0.25 mol %, complex 3a exhibited extremely high catalytic activity toward Negishi cross-coupling of alkylzinc reagents with a wide range of (hetero)aryl halides under mild reaction conditions within 30 min. Besides a great number of bromoarenes, various less expensive and inactive (hetero)aryl chlorides were coupled successfully with the alkyl- and arylzinc reagents, in which active functional groups (such as -NH2) were well tolerated even in one-pot dicoupling transformations without protection. In addition, in the case of coupling with secondary alkylzinc reagents, undesired β-hydride elimination leading to isomerized linear products was efficaciously suppressed. The catalyst system also displayed superiority in the construction of heterobiaryls through the coupling of heteroarylzinc reagents and heterocylic chloroarenes which were hardly accessible from the corresponding organoboron reagents by Suzuki-coupling reactions. Therefore, the protocol described in this paper represents a mild, general, and scalable approach to access various structurally intriguing and functionalized (hetero)aryls.

K2CO3 can act as an efficient catalyst for the hydration of organonitriles in aqueous conditions assisted by microwave irradiation, which represents an inexpensive, practical, atom-economical, and straightforward transition metal-free protocol to various amides.

Robust acenaphthoimidazolylidene palladium complexes have been demonstrated as highly efficient and general catalysts for the sterically hindered Suzuki–Miyaura cross-coupling reactions in excellent yields even with low catalyst loadings under mild reaction conditions. The high catalytic activity of these complexes highlights that, besides the “flexible steric bulky” concept, σ-donor properties of the NHC ligands are also crucial to accelerate the transformations.

A robust palladium NHC complex was synthesized and exhibits exceptional activity and selectivity as a precatalyst in the amination of aryl chlorides and tolerates a wide range of substrates at low catalyst loadings.

A novel robust pyridine-bridged bis-benzimidazolylidene nickel pincer complex 3 accessible from inexpensive, commercially available precursors efficiently catalyzes the first practical Suzuki–Miyaura cross-coupling reactions with various less-reactive electrophiles ArX (X = Br, Cl, OTs and OMs) and even tolerates electron-rich, sterically demanding and heterocyclic arenes in the presence of catalytic amounts of PPh3.

A novel hydrophilic pyridine-bridged bis-benzimidazolylidene palladium pincer complex (3) acted as a highly efficient robust recyclable molecular catalyst towards Suzuki–Miyaura coupling reactions in aqueous media and tolerated various functional groups (even heterocycles) with extremely low catalyst loading.

A robust catalyst derived from NiCl2·(DME) and acenaphthoimidazolium chloride exhibited high activity towards the challenging amination of bulky and heterocyclic aryl tosylates with secondary amines under mild reaction conditions at 2 mol% catalyst loading within 3 hours. Further, a wide range of primary amines were also successfully mono-aminated by our newly developed protocol.

By using a robust acenaphthoimidazolylidene palladium complex (Pd-NHC 1), a scalable approach to access a variety of chiral, pharmaceutical and structurally intriguing N-substituted phthalimides via double aminocarbonylations has been established under atmospheric carbon monoxide pressure at catalyst loadings as low as 0.05 mol%. In addition, the fluorescent properties of the selected N-substituted phthalimide products were also characterized. In comparison with well-known fluorescent molecules, some of them exhibited enhanced violet emission, especially for the ester analogue of Alrestatin, which further confirmed the applicability of the protocol.

Due to its special coordination ability to Cu(II)–terpyridine complexes, a simple and straightforward visual recognition of p-DMAP out of its analogues has been realized via selective metallogel collapse. In combination with the selective gel collapse and the self-healing properties of metallohydrogel 1a, its potential application towards chemo-switch is also demonstrated.

By using O-benzoyl hydroxylamines as amine sources, the first convenient copper-catalyzed electrophilic amination of sodium sulfinates has been realized. Even with 2 mol% catalyst loading, the protocol provided an efficient and straightforward synthesis of a broad range of functional sulfonamides under ambient reaction conditions without an additional base and ligand. Based on the control experiments, a plausible mechanism was proposed.

Incorporating the visual discrimination of 2,2′-bipyridine and self-healing properties, a novel photo-switchable metallo-hydrogel system is fabricated using a pincer-type Cu(II) complex and 2,2′-azopyridine.

A series of fluorescent (hetero)-aryl substituted anthracene derivatives were readily accessible from the corresponding bulky anthracen-9-yl carboxylates via Suzuki–Miyaura cross-coupling reactions by using pincer nickel N-heterocyclic carbene complex 1 even at the catalyst loading as low as 0.1 mol% in the presence of catalytic amounts of PCy3.

A robust palladium NHC complex was synthesized and exhibits exceptional activity and selectivity as a precatalyst in the amination of aryl chlorides and tolerates a wide range of substrates at low catalyst loadings.

A novel robust pyridine-bridged bis-benzimidazolylidene nickel pincer complex 3 accessible from inexpensive, commercially available precursors efficiently catalyzes the first practical Suzuki–Miyaura cross-coupling reactions with various less-reactive electrophiles ArX (X = Br, Cl, OTs and OMs) and even tolerates electron-rich, sterically demanding and heterocyclic arenes in the presence of catalytic amounts of PPh3.

A novel hydrophilic pyridine-bridged bis-benzimidazolylidene palladium pincer complex (3) acted as a highly efficient robust recyclable molecular catalyst towards Suzuki–Miyaura coupling reactions in aqueous media and tolerated various functional groups (even heterocycles) with extremely low catalyst loading.

By using metallo-hydrogel as a new platform, a simple and straightforward selective visual discrimination of cysteine, homocysteine and glutathione from each other as well as from other amino acids has been realized.