Efficient and selective external activator-free cobalt catalyst for hydroboration of terminal alkynes enabled by BiPyPhos.

Herein, a robust catalyst system, composed of a bipyridine-based diphosphine ligand (BiPyPhos) and a cobalt precursor Co(acac)2, is successfully developed and applied in the hydroboration of terminal alkynes, exclusively affording various versatile ß-E-vinylboronates in high yields at room temperature.

Balancing Activity and Stability in Halogen-Bonding Catalysis: Iodopyridinium-Catalyzed One-Pot Synthesis of 2,3-Dihydropyridinones.

A one-pot cascade reaction for 2,3-dihydropyridinone synthesis was accomplished with 3-fluoro-2-iodo-1-methylpyridinium triflate as the halogen bond catalyst. The desired [4+2] cycloaddition products, bearing aryl, heteroaryl, alkyl, and alicyclic substituents, were successfully furnished in 28-99% yields. Mechanistic investigations proved that a strong halogen-bonding interaction forged between the iodopyridinium catalyst and imine intermediate was essential to dynamically masking the vulnerable C-I bond on the catalyst and accelerating the following aza-Diels-Alder reaction.

One-step green synthesis of oil-dispersible carbonized polymer dots as eco-friendly lubricant additives with superior dispersibility, lubricity, and durability.

Chemical functionalization provides effective protocols for inorganic nanomaterials as oil-dispersible lubricant additives. Nevertheless, harsh reaction conditions and arduous post-processing are frequently encountered when adopting this approach. Herein, four types of carbonized polymer dots (CPDs) with admirable dispersibility and long-term stability (more than 6 months without any sediments) in polyethylene glycol (PEG200) were synthesized by a one-step and green solvothermal route using saccharides as the single precursors. The tribological behaviors of CPDs as the lubricant additives of PEG200 were systematically evaluated and compared, confirming that the anti-wear and friction-reducing performances of PEG200 can be effectively enhanced after blended with CPDs. Clarified by the friction evaluations and worn surface detections, the superior lubricity and durability of CPDs-c are mainly attributed to the synergy between the interfacial adsorption of polymeric shells, the nano-lubrication effects of carbon cores, and the establishment of CPDs-inserted tribofilm with a uniform thickness of about 86 nm. This work explores a green and facile strategy for synthesizing the CPDs toward oil lubrication and reveals the lubrication mechanism of CPDs, which facilitates the practical application of CPDs in tribology.

Synthesis of degradable and chemically recyclable polymers using 4,4-disubstituted five-membered cyclic ketene hemiacetal ester (CKHE) monomers.

Novel degradable and chemically recyclable polymers were synthesized using five-membered cyclic ketene hemiacetal ester (CKHE) monomers. The studied monomers were 4,4-dimethyl-2-methylene-1,3-dioxolan-5-one (DMDL) and 5-methyl-2-methylene-5-phenyl-1,3-dioxolan-4-one (PhDL). The two monomers were synthesized in high yields (80-90%), which is an attractive feature. DMDL afforded its homopolymer with a relatively high molecular weight (M n >100 000, where M n is the number-average molecular weight). DMDL and PhDL were copolymerized with various families of vinyl monomers, i.e., methacrylates, acrylates, styrene, acrylonitrile, vinyl pyrrolidinone, and acrylamide, and various functional methacrylates and acrylate. Such a wide scope of the accessible polymers is highly useful for material design. The obtained homopolymers and random copolymers of DMDL degraded in basic conditions (in the presence of a hydroxide or an amine) at relatively mild temperatures (room temperature to 65 °C). The degradation of the DMDL homopolymer generated 2-hydroxyisobutyric acid (HIBA). The generated HIBA was recovered and used as an ingredient to re-synthesize DMDL monomer, and this monomer was further used to re-synthesize the DMDL polymer, demonstrating the chemical recycling of the DMDL polymer. Such degradability and chemical recyclability of the DMDL polymer may contribute to the circular materials economy.

Synthesis of ABC Miktoarm Star Copolymers via Organocatalyzed Living Radical Polymerization.

ABC-type miktoarm star copolymers are synthesized using a single living radical polymerization (organocatalyzed living radical polymerization) via a "combinatorial" approach. The arm A is poly(butyl acrylate), the arm B is poly(methyl methacrylate), and the arm C encompasses hydrophobic and hydrophilic polyacrylates. A poly(butyl acrylate) with a vinyl chain end (macromonomer) is synthesized. A poly(methyl methacrylate) is subsequently connected to the reactive vinyl group to generate diblock copolymer. From the junction of the diblock copolymer, polymer C grew to yield star copolymers. An amphiphilic star copolymer is also synthesized, and its self-assembly structure is studied in an aqueous solution.

Halogen-Bonding-Induced Conjugate Addition of Thiophenes to Enones and Enals.

Herein, we report the conjugate addition of α,ß-unsaturated carbonyl compounds to thiophene derivatives. We used a 2-iodoimidazolinium triflate salt as a halogen-bonding donor, which afforded moderate-to-excellent yields of the corresponding alkylated thiophenes. Insight into the catalytic process was obtained from 1 H NMR spectroscopy studies and DFT calculations, which indicated a halogen-bonding-supported mechanism with limited Brønsted acid catalysis.

Guanidine-Copper Complex Catalyzed Allylic Borylation for the Enantioconvergent Synthesis of Tertiary Cyclic Allylboronates.

An enantioconvergent synthesis of chiral cyclic allylboronates from racemic allylic bromides was achieved by using a guanidine-copper catalyst. The allylboronates were obtained with high γ/α regioselectivities (up to 99:1) and enantioselectivities (up to 99 % ee), and could be further transformed into diverse functionalized allylic compounds without erosion of optical purity. Experimental and DFT mechanistic studies support an SN 2' borylation process catalyzed by a monodentate guanidine-copper(I) complex that proceeds through a special direct enantioconvergent transformation mechanism.

Mechanism of Direct C-H Arylation of Pyridine via a Transient Activator Strategy: A Combined Computational and Experimental Study.

Recently, we realized the highly selective one-pot synthesis of 2,6-diarylpyridines by using a Pd-catalyzed direct C-H arylation approach via a transient activator strategy. Although methylation reagent as a transient activator and Cu(I) salt or oxide were found to be prerequisites, details regarding the mechanism remained unclear. In this paper, DFT calculations combined with experimental investigations were carried out to elucidate the principle features of this transformation. The results reveal (1) the origin of the exquisite diarylating selectivity of the pyridine under the transient strategy; (2) the possible demethylating reagent as the counteranion of the pyridinium salt; (3) the reason why Cu2O is a better Cu(I) resource than others.

(Guanidine)copper Complex-Catalyzed Enantioselective Dynamic Kinetic Allylic Alkynylation under Biphasic Condition.

Highly enantioselective allylic alkynylation of racemic bromides under biphasic condition is furnished in this report. This approach employs functionalized terminal alkynes as pro-nucleophiles and provides 6- and 7-membered cyclic 1,4-enynes with high yields and excellent enantioselectivities (up to 96% ee) under mild conditions. Enantioretentive derivatizations highlight the synthetic utility of this transformation. Cold-spray ionization mass spectrometry (CSI-MS) and X-ray crystallography were used to identify some catalytic intermediates, which include guanidinium cuprate ion pairs and a copper-alkynide complex. A linear correlation between the enantiopurity of the catalyst and reaction product indicates the presence of a copper complex bearing a single guanidine ligand at the enantio-determining step. Further experimental and computational studies supported that the alkynylation of allylic bromide underwent an anti-SN2' pathway catalyzed by nucleophilic cuprate species. Moreover, metal-assisted racemization of allylic bromide allowed the reaction to proceed in a dynamic kinetic fashion to afford the major enantiomer in high yield.

Halogen-bonding-induced hydrogen transfer to C═N bond with Hantzsch ester.

Several bidentate dihydroimidazolines were prepared and investigated as catalysts for hydrogen transfer reduction of C═N bond with Hantzsch ester. Highly efficient reactions were observed for quinolines and imines with low catalyst loading of 2 mol %. The presence of halogen bonding was elucidated using NMR studies and isothermal calorimeric titrations. Binding constants of the XB donors were also measured using isothermal calorimeric titrations (ITC).