Tricolor Emission of a Fluorescent Heteroditopic Ligand over a Concentration Gradient of Zinc(II) Ions

The internal charge transfer (ICT) type fluoroionophore arylvinyl-bipy (bipy = 2,2′-bipyridyl) is covalently tethered to the spirolactam form of rhodamine to afford fluorescent heteroditopic ligand 4. Compound 4 can be excited in the visible region, the emission of which undergoes sequential bathochromic shifts over an increasing concentration gradient of Zn­(ClO4)2 in acetonitrile. Coordination of Zn2+ stabilizes the ICT excited state of the arylvinyl-bipy component of 4, leading to the first emission color shift from blue to green. At sufficiently high concentrations of Zn­(ClO4)2, the nonfluorescent spirolactam component of 4 is transformed to the fluorescent rhodamine, which turns the emission color from green to orange via intramolecular fluorescence resonance energy transfer (FRET) from the Zn2+-bound arylvinyl-bipy fluorophore to rhodamine. While this work offers a new design of ratiometric chemosensors, in which sequential analyte-induced emission band shifts result in the sampling of multiple colors at different concentration ranges (i.e., from blue to green to orange as [Zn2+] increases in the current case), it also reveals the nuances of rhodamine spirolactam chemistry that have not been sufficiently addressed in the published literature. These issues include the ability of rhodamine spirolactam as a fluorescence quencher via electron transfer, and the slow kinetics of spirolactam ring-opening effected by Zn2+ coordination under pH neutral aqueous conditions

Highly Sensitive Fluorescent Probes for Zinc Ion Based on Triazolyl-Containing Tetradentate Coordination Motifs

Two new 1,2,3-triazolyl-containing N4-tetradentate ligands show nanomolar affinity for Zn2+ under physiological conditions. Furthermore, they are easily derivatizable to afford fluorescent probes suitable for sensitive Zn2+ detection. Structural characterizations in both solid and solution states suggest that N3 and N2 in the 1,2,3-triazolyl moiety coordinate with Zn2+ in A and B to afford five-membered and six-membered coordination rings, respectively. The probes show sensitive fluorescence enhancement and ratiometric responses to Zn2+

Synthesis of 1‑Cyanoalkynes and Their Ruthenium(II)-Catalyzed Cycloaddition with Organic Azides to Afford 4‑Cyano-1,2,3-triazoles

A new method to convert terminal alkynes under relatively mild conditions to 1-cyanoalkynes using in situ formed cyanogen is described. 1-Cyanoalkynes have a higher reactivity than terminal alkynes in the ruthenium­(II)-catalyzed regiospecific azide–alkyne cycloaddition to afford 4-cyano-1,2,3-triazoles. A mechanistic proposal different from the one that terminal alkynes adopt under the same reaction conditions is proposed. This work provides a new and convenient two-step sequence to prepare 4-cyano-1,2,3-triazoles from terminal alkynes and organic azides

Synthesis of 5-Iodo-1,4-disubstituted-1,2,3-triazoles Mediated by in Situ Generated Copper(I) Catalyst and Electrophilic Triiodide Ion

Mixing copper­(II) perchlorate and sodium iodide solutions results in copper­(I) species and the electrophilic triiodide ions, which collectively mediate the cycloaddition reaction of organic azide and terminal alkyne to afford 5-iodo-1,4-disubstituted-1,2,3-triazoles. One molar equivalent of an amine additive is required for achieving a full conversion. Excessive addition of the amine compromises the selectivity for 5-iodo-1,2,3-triazole by promoting the formation of 5-proto-1,2,3-triazole. Based on preliminary kinetic and structural evidence, a mechanistic model is formulated in which a 5-iodo-1,2,3-triazole is formed via iodination of a copper­(I) triazolide intermediate by the electrophilic triiodide ions (and possibly triethyliodoammonium ions). The experimental evidence explains the higher reactivity of the in situ generated copper­(I) species and triiodide ion in the formation of 5-iodo-1,2,3-triazoles than that of the pure forms of copper­(I) iodide and iodine

Synthesis of 1‑Cyanoalkynes and Their Ruthenium(II)-Catalyzed Cycloaddition with Organic Azides to Afford 4‑Cyano-1,2,3-triazoles

A new method to convert terminal alkynes under relatively mild conditions to 1-cyanoalkynes using in situ formed cyanogen is described. 1-Cyanoalkynes have a higher reactivity than terminal alkynes in the ruthenium­(II)-catalyzed regiospecific azide–alkyne cycloaddition to afford 4-cyano-1,2,3-triazoles. A mechanistic proposal different from the one that terminal alkynes adopt under the same reaction conditions is proposed. This work provides a new and convenient two-step sequence to prepare 4-cyano-1,2,3-triazoles from terminal alkynes and organic azides

The Bis-Phenyltin-Substituted, Lone-Pair-Containing Tungstoarsenate [(C₆H₅Sn)₂As₂W₁₉O₆₇(H₂O)]^8-

The bis-phenyltin-substituted, lone-pair-containing tungstoarsenate [(C6H5Sn)2As2W19O67(H2O)]8- (1) has been synthesized and characterized by multinuclear NMR, IR, and elemental analysis. Single-crystal X-ray analysis was carried out on (NH4)7Na[(C6H5Sn)2As2W19O67(H2O)]·17.5H2O (NH4−1), which crystallizes in the monoclinic system, space group P21/c, with a = 18.3127(17) Å, b = 24.403(2) Å, c = 22.965(2) Å, β = 106.223(2)°, and Z = 4. Polyanion 1 consists of two B-α-(AsIIIW9O33) Keggin moieties linked via a WO(H2O) fragment and two SnC6H5 groups leading to a sandwich-type structure with nominal C2v symmetry. Polyanion 1 is stable in solution as indicated by the expected 6-line pattern (4:4:4:4:2:1) in 183W NMR and the expected 119Sn, 13C, and 1H NMR spectra. Synthesis of 1 was accomplished by reaction of C6H5SnCl3 and K14[As2W19O67(H2O)] in a 2:1 molar ratio in aqueous acidic medium (pH 2). In the solid-state structure of NH4−1, neighboring polyanions are weakly bound via W−O−Na bonds leading to chains which interact with each other via the phenyl rings resulting in a 2-D assembly

Tricolor Emission of a Fluorescent Heteroditopic Ligand over a Concentration Gradient of Zinc(II) Ions

The internal charge transfer (ICT) type fluoroionophore arylvinyl-bipy (bipy = 2,2′-bipyridyl) is covalently tethered to the spirolactam form of rhodamine to afford fluorescent heteroditopic ligand 4. Compound 4 can be excited in the visible region, the emission of which undergoes sequential bathochromic shifts over an increasing concentration gradient of Zn­(ClO4)2 in acetonitrile. Coordination of Zn2+ stabilizes the ICT excited state of the arylvinyl-bipy component of 4, leading to the first emission color shift from blue to green. At sufficiently high concentrations of Zn­(ClO4)2, the nonfluorescent spirolactam component of 4 is transformed to the fluorescent rhodamine, which turns the emission color from green to orange via intramolecular fluorescence resonance energy transfer (FRET) from the Zn2+-bound arylvinyl-bipy fluorophore to rhodamine. While this work offers a new design of ratiometric chemosensors, in which sequential analyte-induced emission band shifts result in the sampling of multiple colors at different concentration ranges (i.e., from blue to green to orange as [Zn2+] increases in the current case), it also reveals the nuances of rhodamine spirolactam chemistry that have not been sufficiently addressed in the published literature. These issues include the ability of rhodamine spirolactam as a fluorescence quencher via electron transfer, and the slow kinetics of spirolactam ring-opening effected by Zn2+ coordination under pH neutral aqueous conditions

Double michael addition reactions of the nazarov reagent with 2-cyano-2-cycloalkenones: An alternative approach to cis-fused bicyclic systems

[[abstract]]A highly stereoselective annulation reaction of 2-cyano-2-cycloalkenones with the Nazarov reagent catalyzed by 1,8-diaza-bicyclo[5.4.0]undec-7-ene (DBU), leading to densely functionalized bicyclic systems, is developed

Synthesis of 1‑Cyanoalkynes and Their Ruthenium(II)-Catalyzed Cycloaddition with Organic Azides to Afford 4‑Cyano-1,2,3-triazoles

A new method to convert terminal alkynes under relatively mild conditions to 1-cyanoalkynes using in situ formed cyanogen is described. 1-Cyanoalkynes have a higher reactivity than terminal alkynes in the ruthenium­(II)-catalyzed regiospecific azide–alkyne cycloaddition to afford 4-cyano-1,2,3-triazoles. A mechanistic proposal different from the one that terminal alkynes adopt under the same reaction conditions is proposed. This work provides a new and convenient two-step sequence to prepare 4-cyano-1,2,3-triazoles from terminal alkynes and organic azides

Highly Sensitive Fluorescent Probes for Zinc Ion Based on Triazolyl-Containing Tetradentate Coordination Motifs

Two new 1,2,3-triazolyl-containing N4-tetradentate ligands show nanomolar affinity for Zn2+ under physiological conditions. Furthermore, they are easily derivatizable to afford fluorescent probes suitable for sensitive Zn2+ detection. Structural characterizations in both solid and solution states suggest that N3 and N2 in the 1,2,3-triazolyl moiety coordinate with Zn2+ in A and B to afford five-membered and six-membered coordination rings, respectively. The probes show sensitive fluorescence enhancement and ratiometric responses to Zn2+