Combining a Low Valent Molybdenum(0) Center with a Strongly σ-Donating Mesoionic Carbene Chelate Ligand—Synthesis and Structural Characterization

Triazolylidene ligands belong to a class of N-heterocyclic carbenes of growing chemical interest. Their precursors are readily available using Click chemistry and, therefore, highly modular for tuning their electronic characteristics. Due to their notable donor properties, these ligands are particularly suitable for modulating the electronic properties of the central ions of their complexes. Here, a bidentate bistriazolylidene which is a particularly strong donor ligand is combined with a low valent molybdenum(0) center and four carbon monoxide molecules as co-ligands. The novel complex exhibits characteristic electrochemical and IR-spectroscopic behavior. An X-ray structural analysis provides metrical details which are not entirely in agreement with spectroscopic data, likely going back to crystal packing effects. In comparison with precursor and ligand SCXRD data, notable geometrical changes induced by the coordination of the ligand to the metal can be observed. The analyses strongly support the bistriazolylidene ligand as being a particularly good donor of electron density towards the central metal. Potentially, these findings may support, in the future, the design of potent catalysts for the reductive activation of small molecules.

Palladium supported on triazolyl-functionalized hypercrosslinked polymers as a recyclable catalyst for Suzuki-Miyaura coupling reactions

A novel hypercrosslinked polymers-palladium (HCPs-Pd) catalyst was successfully prepared via the external cross-linking reactions of substituted 1,2,3-triazoles with benzene and formaldehyde dimethyl acetal. The preparation of HCPs-Pd has the advantages of low cost, mild conditions, simple procedure, easy separation and high yield. The catalyst structure and composition were characterized by N2 sorption, TGA, FT-IR, SEM, EDX, TEM, XPS and ICP-AES. The HCPs were found to possess high specific surface area, large micropore volume, chemical and thermal stability, low skeletal bone density and good dispersion for palladium chloride. The catalytic performance of HCPs-Pd was evaluated in Suzuki-Miyaura coupling reactions. The results show that HCPs-Pd is a highly active catalyst for the Suzuki-Miyaura coupling reaction in H2O/EtOH solvent with TON numbers up to 1.66 × 104. The yield of biaryls reached 99%. In this reaction, the catalyst was easily recovered and reused six times without a significant decrease in activity.

New 1,2,3-triazole based bis- and trisphosphine ligands: synthesis, transition metal chemistry and catalytic studies

This paper describes a novel synthetic methodology for the preparation of 1,2,3-triazole based phosphines and their transition metal chemistry and preliminary catalytic studies.

Facile synthesis of 1,5-disubstituted 1,2,3-triazoles by the regiospecific alkylation of a ruthenium triazolato complex

The alkylation of the N(2)-bound ruthenium triazolate [Ru]N3C2HCO2Et (2, [Ru] = (η5-C5H5)(dppe)Ru, dppe = Ph2PCH2CH2PPh2) with benzylbromides is reported. The regiospecific alkylation of 2, which results from the [3 + 2] cycloaddition of ethyl propiolate with [Ru]-N3 (1), gives a series of cationic N(1)-bound N(3)-alkylated-4-ethoxycarbonyl triazolato complexes {[Ru]N3(CH2R)C2HCO2Et}[Br] (3a, R = 4-CH2Br-C6H4; 3b, R = 3,5-(CH2Br)2-C6H3; 3c, R = 2,6-F2-C6H3; 3d, R = 4-CN-C6H4) and the subsequent cleavage of the Ru-N bond of 3a-3d gives N(1)-alkylated-5-ethoxycarbonyl triazoles N3(CH2R)C2HCO2Et (4a-4d) and [Ru]-Br, which, on reacting with sodium azide, would afford [Ru]-N3 (1) thus forming a reaction cycle. The treatment of {[Ru]N3(CH2C6F5)C2HCO2Et}[Br] (3e) with sodium azide in refluxing ethanol gives the free triazole N3(CH2C6F5)C2HCO2Et (4e) and 1. The treatment of 2 with an equivalent of 3a affords a dinuclear bis(triazolato) complex {α,α'-bis([Ru]N3C2HCO2Et)-p-xylene}[Br]2 (5) and an organic bis(triazole) complex α,α'-bis(N3C2HCO2Et)-p-xylene (6). The treatment of 2 with CF3COOH in CHCl3 at room temperature affords a mixture of N(2)-bound 1H- and 3H-4-ethoxycarbonyl triazolato complexes {[Ru]N3HC2HCO2Et}[CF3COO] (1H-7) and (3H-7) in a ratio of 5 : 2. The structures of 4e, 5 and 1H-7 were confirmed by single-crystal X-ray diffraction analysis.

Au(III) and Pt(II) Complexes of a Novel and Versatile 1,4-Disubstituted 1,2,3-Triazole-Based Ligand Possessing Diverse Secondary and Tertiary Coordinating Groups

A novel 1,4-disubstituted 1,2,3-triazole-based ligand, 2-(4-(pyridin-2-yl)-1 H-1,2,3-triazol-1-yl)propane-1,3-diamine (ptpd), which possesses pyridyl and diamino secondary and tertiary coordinating groups was synthesized in excellent yield. The reactivity of 2-(1-phenyl-1 H-1,2,3-triazol-4-yl)pyridine (ptp), di- tert-butyl (2-azidopropane-1,3-diyl)dicarbamate (Boc₂-ptpd), and ptpd·3HCl was investigated with Au(III) and Pt(II) precursors. Analysis including X-ray crystal structures of [Au(III)Cl₃(ptp)] (1), [Au(III)Cl₂(ptpd)][Au(I)Cl₂][OH]{[NaAuCl₄·2H₂O]} n (3), and [Pt(II)Cl₂(ptpdH₂)][PtCl₄] (4) revealed that ptpd (i) serves as a monodentate ligand for Au(III) coordinating to the metal center via the pyridine nitrogen only, (ii) preferentially coordinates Au(III) via the bidentate diamino group over the monodentate pyridine group, (iii) can coordinate Pt(II) in a bidentate fashion via the pyridyl nitrogen and the triazole N-3, and (iv) can bridge two Pt(II) centers through bidentate chelation at the diamino group and bidentate chelation via the pyridyl nitrogen and the triazole N-3. ptpd represents a versatile ligand template for the development of mixed metal complexes.