Shi-Qiang Bai

Recent advances in C–S bond formation via C–H bond functionalization and decarboxylation

The development of mild and general methods for C-S bond formation has received significant attention because the C-S bond is indispensable in many important biological and pharmaceutical compounds. Early examples for the synthesis of C-S bonds are generally limited to the condensation reaction between a metal thiolate and an organic halide. Recent chemical approaches for C-S bond formation, based upon direct C-H bond functionalization and decarboxylative reactions, not only provide new insights into the mechanistic understanding of C-S coupling reactions but also allow the synthesis of sulfur-containing compounds from more effective synthetic routes with high atom economy. This review intends to explore recent advances in C-S bond formation via C-H functionalization and decarboxylation, and the growing opportunities they present to the construction of complex chemical scaffolds for applications encompassing natural product synthesis, synthetic methodology development, and functional materials as well as nanotechnology.

Structures of copper complexes of the hybrid [SNS] ligand of bis(2-(benzylthio)ethyl)amine and facile catalytic formation of 1-benzyl-4-phenyl-1H-1,2,3-triazole through click reaction

A hybrid ligand, bis(2-(benzylthio)ethyl)amine (SNS), with an amine and two thioether donors reacts with Cu(II) to give mononuclear [CuCl(2)(SNS)] (1), [CuBr(2)(SNS)] (2), [Cu(OTf)(2)(SNS)(OH(2))] (3), and an one-dimensional Cu(I) coordination polymer [Cu(2)I(2)(SNS)](n) (4). All complexes have been characterized by single-crystal X-ray diffraction analysis, and 1-3 were studied by EPR analysis at room temperature. Complexes 1 and 2 are penta-coordinated with a distorted square pyramidal metal supported by a tridentate SNS ligand on the basal plane. Complex 3 shows a tetragonally distorted octahedral sphere with two trans and weakly bonding monodentate triflates. A 12-membered ring in the solid lattice is formed by intermolecular H-bonding among the coordinated triflate and aqua ligands from four neighboring molecules. Complex 4, the only Cu(I) in this series, shows a coordination polymer chain [Cu(4)I(4)](n) comprising tetrahedral Cu(I) centers stitched by the SNS ligand in a unique bridge-chelate mode in the form of a helix. All four complexes are catalytically active at room temperature in a copper-catalyzed azide-alkyne cycloaddition (CuAAA) three-component click reaction of benzyl chloride, sodium azide, and phenylacetylene in an aqueous MeCN mixture to give good isolated yields of 1-benzyl-4-phenyl-1H-1,2,3-triazole, without the use of a base or reducing agent.

Functionalized 1,2,3-Triazoles as Building Blocks for Photoluminescent POLOs (Polymers of Oligomers) of Copper(I)

Two 3-D and one 2-D metal-organic frameworks [Cu(8)I(8)(L1)(4)](n) (1), [Cu(8)I(8)(L2)(4)](n) (2) and [Cu(4)I(4)(L3)(2)](n) ()3 were synthesized using three novel pyridine and pyrazole supported 1,2,3-triazoles, 1-(4-picolyl)-4-butyl-1H-1,2,3-triazole (L1), 1-(4-picolyl)-4-pentyl-1H-1,2,3-triazole (L2) and 1-(4-picolyl)-4-(3,5-dimethylpyrazolylmethyl)-1H-1,2,3-triazole (L3). In both complexes 1 and 2, there co-exist a 1-D Cu(I) oligomer and Cu(4) tetrahedron cluster in the 3-D polymeric structures. Complex 3 shows a 2-D (4, 4) net with the stair-step Cu(4)I(4) as node and L3 as a building block. All three complexes exhibit photoluminescence.

Crystal structures and magnetic behaviour of three new azido-bridged dinuclear cobalt(II) and copper(II) complexes

Three dinuclear cobalt(II) and copper(II) complexes with double end-on (EO) azido bridges, [Co2(DMP)2(N3)4] (1), [Cu2(DMP)2(N3)4] (2) and [Cu2(PAP)2(N3)4] (3) (DMP = 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine; PAP = 1-phenyl-2-(2-pyridyl)-1-azapropylene) have been synthesized and characterized by single-crystal X-ray diffraction and magnetic analyses. The EPR spectra of powder samples for the two copper(II) complexes have also been examined at room temperature and 77 K, respectively. In the isomorphous complexes 1 and 2, the metal ions are penta-coordinated with distorted trigonal bipyramidal geometries, and the EO azido bridges assume an equatorial–axial disposition between metal ions. In contrast, the copper(II) ion in complex 3 adopts a distorted square pyramidal geometry, and the EO azido bridges assume a basal–apical disposition between metal ions. According to magnetic studies, the double end-on azido bridges mediate ferromagnetic coupling with J = 18.1 cm−1 in 1, antiferromagnetic coupling with J = −27.6 cm−1 in 2, and ferromagnetic coupling with J = 35.0 cm−1 in 3.

Composite Metal–Oxide Nanocatalysts

To incorporate new functionalities, various oxide materials can be composited with metal nanoparticles to form metal–oxide nanostructures, which are very promising for a wide range of applications. In this review, we summarize the recent developments in advanced synthesis of structure‐diversified core–shell, yolk–shell, Janus, and their combined metal–oxide nanostructures. We also summarize their representative catalytic applications including organic reduction and oxidation, CO oxidation, CO2 conversion, water–gas shift reaction, and water splitting. We discuss recyclable metal–oxide nanocatalysts with mesoporous, hollow, or multilayered structures. We highlight perspectives for their challenges ahead and opportunities for their widely used applications in plasmon localization enhanced photocatalysis, artificial enzyme catalysis, and catalytic biomass conversion.

click-and-click-hybridised 1,2,3-triazoles supported Cu(i) coordination polymers for azide-alkyne cycloaddition

Two novel pyridyl and thioether hybridised 1,2,3-triazole ligands 1-(2-picolyl)-4-(2-(methylthio)-pyridine)-1H-1,2,3-triazole (L1) and 1-(4-picolyl)-4-(2-(methylthio)-pyridine)-1H-1,2,3-triazole (L2) were prepared from CuAAC click reactions. Reactions of CuI with the ligands L1 and L2 yielded two one-dimensional coordination polymers [Cu6I6(L1)2]n (1) and [Cu2I2(L2)2]n (2). Single-crystal X-ray diffraction reveals that 1 and 2 are polymeric with [Cu6I6] and [Cu2I2] respectively as building blocks. Both ligands (L1 and L2) and complexes (1 and 2) are photoluminescence active. Complexes 1 and 2 are also catalytically active towards azide-alkyne cycloaddition reactions.

Nitrogen-rich azoles as ligand spacers in coordination polymers.

N-heterocycle-based ligands are versatile building-blocks for coordination oligomer and polymer assemblies of first-row transition metals. Herein, we review recent developments in the design and synthesis of some nitrogen-rich azole-based ligands, their assembly modes in coordination oligomers and polymers, and the potential applications of the resulting metallosupramolecules.

Isolation of an [SNS]Pd(II) pincer with a water ladder and its Suzuki coupling activity in water

A water-compatible Pd(ii) pincer with a hybrid [SNS]-donor set, [L(1)PdCl]Cl.2H(2)O [L(1) = bis-(2-(i-butylsulfanyl)-ethyl)-amine] has been isolated and crystallographically characterized; its solid lattice at 223 K contains a ladder-like water polymer of tetramers and extensive H-bonding exists among the cation, anion and water cluster, and this water-soluble complex is active in Suzuki-Miyaura coupling of phenylboronic acid and selected aryl bromides in water at 75 degrees C.

A fluorescent light-up platform with “AIE + ESIPT” characteristics for multi-target detection both in solution and on paper strip

We report a fluorescent light-up platform for multi-target detection in aqueous solution and on paper strip. The platform is based on a salicylaldazine fluorogen with aggregation-induced emission (AIE) and excited state intramolecular proton transfer (ESIPT) characteristics, which shows distinct advantages including ease of chemical modifications, free of self-quenching effect, excellent light-up ratio and large Stokes shift. To demonstrate the versatility of the platform, palladium cation and perborate anion, as well as UV light, were selected as the targets. The three representative probes, AIE-Pd, AIE-perborate and AIE-UV, light up specifically in the presence of the target both in aqueous solution and on paper strip. The immediate naked-eye response makes the probes ideal for instrument-free and power-free detection.

Zinc, cobalt and copper coordination polymers with different structural motifs from picolyl-triazole hybrid ligands

A series of one-dimensional coordination polymers, viz. [ZnCl2L1]n (1a: 1a-I and 1a-II), [ZnCl2L2]n (1b), [ZnCl2L3]n (1c), {[Co(L1)2(OH2)2]·(ClO4)2·(H2O)2}n (2a), {[Co(L2)2(OH2)2]·(ClO4)2·(H2O)2}n (2b), {[Cu(L1)2(OH2)2]·(ClO4)2·(H2O)2}n (3a), {[Cu(L2)2(OH2)]·(ClO4)2·(H2O)·(MeOH)}n (3b), and {[Cu(L3)2(OH2)]·(ClO4)2·(H2O)2}n (3c), and a three-dimensional coordination polymer [Cu2I2L3]n (4c) have been synthesized by self-assembly of 4-picolyl substituted 1,2,3-triazoles, viz.1-(4-picolyl)-4-butyl-1H-1,2,3-triazole (L1), 1-(4-picolyl)-4-pentyl-1H-1,2,3-triazole (L2) and 1-(4-picolyl)-4-hexyl-1H-1,2,3-triazole (L3), with appropriate metal salts. These coordination polymers have been characterized by single-crystal and powder X-ray diffraction (XRD) and thermogravimetric analyses (TGA). Complexes 3a–c have been subject to EPR analysis. Complexes 1a–c are 1D coordination polymers formed by singly bridging L1–L3 using their picolyl and 3-positioned nitrogen. Their modes of propagation (zig-zag, helical and wave-like) vary with the length of the alkyl pendant at the 4-position on the triazole moiety. Centro-symmetric polymers 2a and 2b are formed by doubly bridging spacers as 1D chains of 18-membered metallocycles fused at octahedral Co(II) centers with coordinated aqua ligands with extensive water–ClO4− H-bonding. Cu(II) complex 3a (space groupP21/n) is isostructural with 2a, but 3b and 3c crystallize with a chiral space group (P21) with square pyramidal Cu(II) doubly bridged by L2 and L3 to give 1D macrocyclic chiral chains. The spacer in 4c shows uniquely high coordination ability by engaging the donor functions of the nitrogen, not only at the picolyl and 3-position but also at the 2-position of the triazole. The resultant 3D polymer network is neutral and solvate free and has higher symmetry (space groupI41/a) than 4a and 4b. The spontaneous resolution of 3b and 3c is traced to the configurational characteristics of the four ligands and its transfer to the crystal network through space chiral packing. The 1D coordination polymers 1 are thermally most stable, whereas the MeOH-solvated and hydrated perchlorate salt 3b decomposes violently upon heating. Variable temperature photoluminescence (VT-PL) measurements revealed strong low energy (LE) rt emissions for 4a and 4b but not for 4c. The high energy (HE) emissions of 4a–c however increase significantly as temperature decreases. The remarkable variety of structural motifs in these coordination polymers is the result of (a) flexible bonding modes of the picolyl–triazole hybrid ligands, (b) different metal geometry options, (c) halide participation as bridging or capping ligands, (d) possibility of hydrate or solvate coordination and (e) extensive H-bonding involving anionic perchlorate methanol solvate as well as hydrates that are coordinated directly (viz. primary) and indirectly (viz. secondary) to the metal.