Ru(II), Os(II), and Ir(III) complexes with chelating pyridyl-mesoionic carbene ligands: structural characterization and applications in transfer hydrogenation catalysis

Chelating ligands with one pyridine donor and one mesoionic carbene donor are fast establishing themselves as privileged ligands in homogeneous catalysis. The synthesis of several new Ir(III)-Cp*- and Os(II)-Cym complexes (Cp* = pentamethylcyclopentadienyl, Cym = p-cymene=4-isopropyl-toluene) derived from chelating pyridyltriazolylidenes where the additional pyridine donor was incorporated via the azide part of the triazole is presented. Furthermore, different 4-substituted phenylacetylene building blocks have been used to introduce electronic fine-tuning in the ligands. The ligands thus can be generally described as 4-(4-R-phenyl)-3-methyl-1-(pyridin-2-yl)-1H-1,2,3-triazol-5-ylidene (with R being H (L(1)), Me (L(2)), OMe (L(3)), CN (L(4)), CF3 (L(5)), Br (L(6)) or NO2 (L(7))). The corresponding complexes (Ir-1 to Ir-7 and Os-1 to Os-7) were characterized by standard spectroscopic methods, and the expected three-legged, piano-stool type coordination was unambiguously confirmed by X-ray diffraction analysis of selected compounds. Together with Ru(II) analogues previously reported by us, a total of 21 complexes were tested as (pre)catalysts for the transfer hydrogenation of carbonyl groups, showing a remarkable reactivity even at very low catalyst loadings. The electronic effects of the ligands as well as different substrates were investigated. Some mechanistic elucidations are also presented.

E- or Z-Selective synthesis of 4-fluorovinyl-1,2,3-triazoles with fluorinated second-generation Julia-Kocienski reagents

A highly modular approach to N-substituted 4-(1-fluorovinyl)triazoles is described. In situ desilylation and Cu-catalyzed ligation reaction of TMS-protected α-fluoropropargyl benzothiazole sulfone with aryl, alkyl, and metallocenyl azides furnished second-generation Julia-Kocienski reagents in good to excellent yields. Condensation reactions of these reagents with aldehydes can be tuned to yield E or Z-alkenes selectively. Under mild conditions with DBU as the base, reactions of aldehydes furnished E-alkenes as the major isomer. On the other hand, in condensation reactions with LHMDS as the base and in appropriate solvents, both aldehydes and ketones reacted to yield fluoroalkenes with Z-selectivity. Stereochemical assignment of E/Z olefins obtained in the reaction of a ketone with two Julia reagents was performed via X-ray crystallographic analysis and comparisons of NMR data. The method allows efficient and ready diversification of the N1-substituent and substituents at the double bond.

The ligand field of the azido ligand: insights into bonding parameters and magnetic anisotropy in a Co(II)-azido complex

The azido ligand is one of the most investigated ligands in magnetochemistry. Despite its importance, not much is known about the ligand field of the azido ligand and its influence on magnetic anisotropy. Here we present the electronic structure of a novel five-coordinate Co(II)-azido complex (1), which has been characterized experimentally (magnetically and by electronic d-d absorption spectroscopy) and theoretically (by means of multireference electronic structure methods). Static and dynamic magnetic data on 1 have been collected, and the latter demonstrate slow relaxation of the magnetization in an applied external magnetic field of H = 3000 Oe. The zero-field splitting parameters deduced from static susceptibility and magnetizations (D = -10.7 cm(-1), E/D = 0.22) are in excellent agreement with the value of D inferred from an Arrhenius plot of the magnetic relaxation time versus the temperature. Application of the so-called N-electron valence second-order perturbation theory (NEVPT2) resulted in excellent agreement between experimental and computed energies of low-lying d-d transitions. Calculations were performed on 1 and a related four-coordinate Co(II)-azido complex lacking a fifth axial ligand (2). On the basis of these results and contrary to previous suggestions, the N3(-) ligand is shown to behave as a strong σ and π donor. Magnetostructural correlations show a strong increase in the negative D with increasing Lewis basicity (shortening of the Co-N bond distances) of the axial ligand on the N3(-) site. The effect on the change in sign of D in going from four-coordinate Co(II) (positive D) to five-coordinate Co(II) (negative D) is discussed in the light of the bonding scheme derived from ligand field analysis of the ab initio results.

Comparison of inverse and regular 2-pyridyl-1,2,3-triazole "click" complexes: structures, stability, electrochemical, and photophysical properties

Two inverse 2-pyridyl-1,2,3-triazole "click" ligands, 2-(4-phenyl-1H-1,2,3-triazol-1-yl)pyridine and 2-(4-benzyl-1H-1,2,3-triazol-1-yl)pyridine, and their palladium(II), platinum(II), rhenium(I), and ruthenium(II) complexes have been synthesized in good to excellent yields. The properties of these inverse "click" complexes have been compared to the isomeric regular compounds using a variety of techniques. X-ray crystallographic analysis shows that the regular and inverse complexes are structurally very similar. However, the chemical and physical properties of the isomers are quite different. Ligand exchange studies and density functional theory (DFT) calculations indicate that metal complexes of the regular 2-(1-R-1H-1,2,3-triazol-4-yl)pyridine (R = phenyl, benzyl) ligands are more stable than those formed with the inverse 2-(4-R-1H-1,2,3-triazol-1-yl)pyridine (R = phenyl, benzyl) "click" chelators. Additionally, the bis-2,2'-bipyridine (bpy) ruthenium(II) complexes of the "click" chelators have been shown to have short excited state lifetimes, which in the inverse triazole case, resulted in ejection of the 2-pyridyl-1,2,3-triazole ligand from the complex. Under identical conditions, the isomeric regular 2-pyridyl-1,2,3-triazole ruthenium(II) bpy complexes are photochemically inert. The absorption spectra of the inverse rhenium(I) and platinum(II) complexes are red-shifted compared to the regular compounds. It is shown that conjugation between the substituent group R and triazolyl unit has a negligible effect on the photophysical properties of the complexes. The inverse rhenium(I) complexes have large Stokes shifts, long metal-to-ligand charge transfer (MLCT) excited state lifetimes, and respectable quantum yields which are relatively solvent insensitive.

Versatile O- and S-functionalized 1,2,3-triazoliums: ionic liquids for the Baylis–Hillman reaction and ligand precursors for stable MIC-transition metal complexes

A series of O- and S-functionalized triazolium salts display high performance in the Baylis–Hillman addition and allow the one-pot formation of MIC-transition metal complexes.

A simple and effective 1,2,3-triazole based “turn-on” fluorescence sensor for the detection of anions

1,2,3-Triazole based chemosensor is synthesized using “Click chemistry” approach. Addition of fluoride ion “turn-on” the fluorescence response of probe.

Halogen bonding assisted selective removal of bromide

The selective removal of bromide from a mixture of competing anions through an XB donor receptor via halogen bonding interactions.

Luminescent [Cu4I4] aggregates and [Cu3I3]-cyclic coordination polymers supported by quinolyl-triazoles

A series of quinolyl-1,2,3-triazole supported luminescent [Cu₄I₄] aggregates and six-membered [Cu₃I₃]-cyclic coordination polymers.

Self-assembly formation of a healable lanthanide luminescent supramolecular metallogel from 2,6-bis(1,2,3-triazol-4-yl)pyridine (btp) ligands

The self-assembly and rheological studies of self-healing Eu(iii) luminescent metallogels from a btp (2,6-bis(1,2,3-triazol-4-yl)pyridine) ligand is described.

C–H activation in IrIII and N-demethylation in PtII complexes with mesoionic carbene ligands: examples of monometallic, homobimetallic and heterobimetallic complexes

Mononuclear Pt^II and the first dinuclear Pt^II complexes along with a cyclometalated heterobimetallic Ir^III/Pd^II complex bearing mesoionic carbene donor ligands are presented starting from the same bis-triazolium salt.

Solution processable polyamines via click chemistry for water purification

Highly stable amine functionalized polystyrenes were prepared and used for the removal of dissolved pollutants from water.

Cucurbiturils: from synthesis to high-affinity binding and catalysis

Major developments in the synthesis of cucurbiturils and applications related to their high-affinity binding and catalysis have recently taken place.

Copper-catalyzed aerobic carboxygenation and N-arylation of [1,2,3]triazolo[1,5-a]pyridines towards pyridinium triazolinone ylides

Copper-catalyzed aerobic oxyarylation of [1,2,3]triazolo[1,5-a]pyridines is developed.

Hybrid Pyrazolyl-1,2,3-Triazolyl Tripodal Tetraamine Ligands: Click Synthesis and Cobalt(III) Complexes

A family of tripodal tetraamine ligands incorporating two pyrazolyl and one 1,2,3-triazolyl donor arm have been synthesized in modest-to-excellent yields (42–90 %) using the copper(i)-catalyzed azide–alkyne cycloaddition (CuAAC) reaction. Mono-, bis-, and tris-tripodal ligand scaffolds were readily generated using this method. The coordination chemistry of the ligands with cobalt(iii) ions has been studied, and cobalt(iii) carbonato complexes of the ligands have been isolated and characterized spectroscopically and crystallographically. X-ray crystallography and NMR spectroscopy of the mono-metallic complexes showed that racemic mixtures of the cis-isomer are formed selectively. The di- and tri-metallic systems could not be crystallized, but NMR spectroscopy indicates that these compounds were isolated as mixtures of stereoisomers.

Synthesis and characterization of N-2-aryl-1,2,3-triazole based iridium complexes as photocatalysts with tunable photoredox potential

N-2-Aryl chelated 1,2,3-triazole-Ir(iii) complexes with various substituents were prepared for the first time.

Multifaceted glycodendrimers with programmable bioactivity through convergent, divergent, and accelerated approaches using polyfunctional cyclotriphosphazenes

The cyclotriphosphazene-based platform facilitates versatile synthesis of glycodendrimers active as inhibitors of two biomedically relevant lectins.

Design, synthesis and metal sensing studies of ether-linked bis-triazole derivatives

Ether-linked-bis-triazole derivatives have been synthesized by (CuAAC) “Click” reaction. Interaction of the compound with Hg²⁺has been demonstrated by various spectroscopic techniques which was further confirmed with computational studies.

Five Cu(i) and Zn(ii) clusters and coordination polymers of 2-pyridyl-1,2,3-triazoles: synthesis, structures and luminescence properties

2-Pyridyl-1,2,3-triazoles with flexible substituents demonstrate rare coordination modes and support new luminescent clusters and coordination polymers.

A new paradigm of copper oxide nanoparticles catalyzed reactions: synthesis of 1,2,3-triazoles through oxidative azide-olefin cycloaddition

Oxidative [3 + 2] cycloaddition of activated olefins and azides is reported with readily available CuO nanoparticles. 1,4-Disubsitituted and 1,4,5-trisubstituted 1,2,3-triazoles have been achieved without use of base or additives in a shorter time.

Tris(triazole) tripodal receptors as selective probes for citrate anion recognition and multichannel transition and heavy metal cation sensing

The preparation and binding properties towards citrate anions and cations of two three-armed triazole based receptors are described.

2-(1,2,3-Triazol-4-yl)pyridine-containing ethynylarenes as selective 'turn-on' fluorescent chemosensors for Ni(II)

A series of ethynylarene compounds containing 2-(1,2,3-triazol-4-yl)pyridine chelating units were studied as fluorescent chemosensors for metal cations in aqueous solution. Analogs possessing two chelating units bridged by either 1,4-diethynylphenyl or 2,7-diethynylnaphthyl subunits displayed large hypsochromic shifts coupled with signal intensification when exposed to increasing concentrations of Ni(II), a unique response among 22 metal cation analytes. This response was shown to be reversible, and is proposed to derive from disruption of aggregate formation upon Ni(II) binding at the peripheral chelating units.