Precise control of the number and position of the catalytic metal ions in heterogeneous catalysts remains a big challenge. Here we synthesized a series of two-dimensional (2D) covalent organic frameworks (COFs) containing two different types of nitrogen ligands, namely imine and bipyridine, with controllable contents. For the first time, the selective coordination of the two nitrogen ligands of the 2D COFs to two different metal complexes, chloro(1,5-cyclooctadiene)rhodium(I) (Rh(COD)Cl) and palladium(II) acetate (Pd(OAc)2 ), has been realized using a programmed synthetic procedure. The bimetallically docked COFs showed excellent catalytic activity in a one-pot addition-oxidation cascade reaction. The high surface area, controllable metal-loading content, and predesigned active sites make them ideal candidates for their use as heterogeneous catalysts in a wide range of chemical reactions.

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Chemoselective hydrogenation of substrates with more than one functional group that could be hydrogenated is quite challenging and is of fundamental importance. Here, the enhanced chemoselectivity of ultrasmall (<1 nm) platinum nanoparticles (NPs) stabilized on silica modified with triphenylphosphine (PSiO ) in hydrogenation reactions is reported. Platinum NPs on PSiO exhibit much higher selectivity than those on SiO in the hydrogenation of acetophenone to 1-phenylethanol (99.9 versus 36 %) and hydrogenation of phenylacetylene to styrene (85 versus 52 %). The results of NMR spectroscopy, X-ray photoelectron spectroscopy, and in situ CO adsorption FTIR spectroscopy indicate the existence of strong interactions between triphenylphosphine and Pt NPs. Consequently, Pt NPs on PSiO have smaller particle sizes and more positive Pt 4 f binding energy than those of Pt/SiO ; these are the main contributors to the superior chemoselectivity of Pt NPs. The organically modified silica could act as an efficient solid ligand for tuning the catalytic performance of metal NPs.

A new Cu-catalyzed asymmetric [3 + 3] cycloaddition of propargyl esters with cyclic enamines is reported. With a combination of Cu(OAc)(2)·H(2)O and a chiral tridentate ferrocenyl-P,N,N ligand as the catalyst, perfect endo selectivities (endo/exo > 98/2) and excellent enantioselectivities (up to 98% ee) for endo cycloadducts were achieved under mild conditions. This method provides a simple and efficient approach for the synthesis of optically active bicyclo[n.3.1] frameworks.

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An enantioselective synthesis of highly functionalized dihydrofurans through a copper-catalyzed asymmetric [3+2] cycloaddition of β-ketoesters with propargylic esters has been developed. With a combination of Cu(OTf)2 and a chiral tridentate P,N,N ligand as the catalyst, a variety of 2,3-dihydrofurans bearing an exocyclic double bond at the 2 position were obtained in good chemical yields and with good to high enantioselectivities. The exocyclic double bond can be hydrogenated in a highly diastereoselective fashion to give unusual cis-2,3-dihydrofuran derivatives, thus further enhancing the scope of this transformation.

A multifunctional copolymer (PyPPh2 -SO3 H@porous organic polymers, POPs) was prepared by combining acidic groups and heterogeneous P,N ligands through the copolymerization of vinyl-functionalized 2-pyridyldiphenylphosphine (2-PyPPh2 ) and p-styrene sulfonic acid under solvothermal conditions. The morphology and chemical structure of the copolymer were evaluated using a series of characterization techniques. Compared with traditional homogeneous Pd(OAc)2 /2-PyPPh2 / p-toluenesulfonic acid catalyst, the copolymer supported palladium catalyst (Pd-PyPPh2 -SO3 H@POPs) exhibited higher activity for alkoxycarbonylation of terminal alkynes under the same conditions. This phenomenon could be attributed to the synergistic effect between the single-site Pd centers, 2-PyPPh2 ligands, and SO3 H groups, the outstanding swelling properties as well as the high enrichment of the reactant concentration by the porous catalyst. In addition, the catalyst could be reused at least 4 times without any apparent loss of activity. The excellent catalytic reactivity and good recycling properties make it an attractive catalyst for industrial applications. This work paves the way for advanced multifunctional porous organic polymers as a new type of platform for heterogeneous catalysis in the future.

A catalytic asymmetric [3 + 2] cycloaddition of hydrazines to bis-electrophilic C3 synthons generated from propargylic acetates, followed by an intramolecular 1,3-H migration, for the regio-and enantioselective construction of chiral 2-pyrazolines has been reported. By employment of copper catalysis in combination with a structurally rigid tridentate P,N,Nligand, a variety of chiral 2-pyrazolines were obtained in good yields and with high enantioselectivities (up to 96% ee). A possible transition state has been proposed to explain the origin of the regio-and enantioselectivities. P yrazolines are privileged and valuable five-membered azaheterocycles, which are found in many bioactive compounds with antidepressant, anti-inflammatory, anticancer, antibacterial, and antiviral activities, 1 and also serve as important intermediates for organic synthesis. 2 The development of new chemical reactions for the synthesis of these azaheterocycles, in particular in catalytic asymmetric versions, has therefore become an important issue. However, the number of available synthetic methodologies for the stereoselective construction of optically active pyrazolines is still very limited, and the methods mostly rely on two prominent strategies: (1) catalytic asymmetric 1,3-dipolar cycloadditions of diazoalkanes, 3 nitrile imine dipole precursors, 4 and azomethine imines 5 with alkenes or alkynes; (2) catalytic asymmetric Fischer's pyrazoline synthesis via a sequential aza-Michael addition/cyclocondensation process. 6,7 Despite these achievements, the development of novel strategies for the enantioselective construction of optically active pyrazolines with functional diversity remains a challenging and highly desirable task.Recently, Nishibayashi's 8 and our 9 groups have demonstrated that propargylic derivatives can be used as bis-electrophilic C3 synthons via metal-allenylidene intermediates for the catalytic [3 + 3] cycloaddition, affording six-membered hetero-and carbocyclic motifs. However, the use of this new type of biselectrophilic C 3 synthons in other cycloadditions remains unexploited. 10 In particular, no catalytic asymmetric [3 + 2] cycloaddition has yet been realized, thus severely narrowing their synthetic utility. To this end, we wondered about the possibility of a catalytic [3 + 2] cycloaddition of propargylic esters with hydrazines, possessing two adjacent nucleophilic nitrogen atoms, which should represent a novel strategy for stereoselectively producing optically active pyrazolines. However, the initial screening of the catalytic reaction of propargylic acetates with N,N′-diphenylhydrazine did not lead to any cycloadducts (Table 1, entry 1), clearly expressing the methodological difficulties. We envisioned that monosubstituted hydrazines should be more suitable bis-nucleophiles for realizing this transformation due to the clearly different steric properties of two nitrogen atoms toward the cycloaddition, which may be crucial to initiate the reaction in a chemo-and regioselective form. As a result, herein we dis...