Selective recognition and extraction of iodide from pure water by a tripodal selenoimidazol(ium)-based chalcogen bonding receptor.

A selenium-based tripodal chalcogen bond (ChB) donor TPI-3Se is demonstrated for the recognition and extraction of I- from 100% water medium. NMR and ITC studies with the halides reveal that the ChB donor selectively binds with the large, weakly hydrated I-. Interestingly, I- crystallizes out selectively in the presence of other halides supporting the superiority of the selective recognition of I-. The X-ray structure of the ChB-iodide complex manifests both the µ1 and µ2 coordinated interactions, which is rare in the C-Se···I chalcogen bonding. Furthermore, to validate the selective I- binding potency of TPI-3Se in pure water, comparisons are made with its hydrogen and halogen bond donor analogs. The computational analysis also provides the mode of I- recognition by TPI-3Se. Importantly, this receptor is capable of extracting I- from pure water through selenium sigma-hole and I- interaction with a high degree of efficiency (∼70%).

Development and Application of Ruthenium(II) and Iridium(III) Based Complexes for Anion Sensing.

Improvements in the design of receptors for the detection and quantification of anions are desirable and ongoing in the field of anion chemistry, and remarkable progress has been made in this direction. In this regard, the development of luminescent chemosensors for sensing anions is an imperative and demanding sub-area in supramolecular chemistry. This decade, in particular, witnessed advancements in chemosensors based on ruthenium and iridium complexes for anion sensing by virtue of their modular synthesis and rich chemical and photophysical properties, such as visible excitation wavelength, high quantum efficiency, high luminescence intensity, long lifetimes of phosphorescence, and large Stokes shifts, etc. Thus, this review aims to summarize the recent advances in the development of ruthenium(II) and iridium(III)-based complexes for their application as luminescent chemosensors for anion sensing. In addition, the focus was devoted to designing aspects of polypyridyl complexes of these two transition metals with different recognition motifs, which upon interacting with different inorganic anions, produces desirable quantifiable outputs.

Merging Photocatalytic C-O Cross-Coupling for α-Oxycarbonyl-ß-ketones: Esterification of Carboxylic Acids via a Decarboxylative Pathway.

Herein, the first merged photocatalytic pathway for the C-O cross-coupled esterification of carboxylic acids to α-oxycarbonyl-ß-ketones has been demonstrated. Decarboxylation of α,ß-unsaturated acids promotes the formation of the ß-ketone fragment of the desired product. Water as the source of oxygen for the ketone segment and aerial oxygen as an oxidant make the present synthetic methodology green and sustainable. This new C═O and C-O bond-forming methodology takes place in a cascade manner under a dual Ir/Pd-catalytic pathway, with the liberation of H2O and CO2 as the only byproducts.

Room-Temperature Synthesis of 1,3,5-Tri(het)aryl Benzene from Nitroalkenes Using Pd(OAc)2: Complete Mechanistic and Theoretical Studies.

Herein, a room-temperature catalytic pathway for 1,3,5-tri(het)aryl derivatives from nitroalkenes using simple Pd(OAc)2 is presented. This newly developed C-C bond-forming methodology takes place in a cascade manner with the initial pallado-Morita-Baylis-Hillman (MBH) type adduct. The broad substrate scopes, functional group tolerance, and different aryl-substituted benzene derivatives make this methodology more attractive. Furthermore, the mechanistic understanding through isolation of intermediates and DFT studies of the catalytic cycle provide requisite insight into the methodology.

A Bis-heteroleptic Imidazolium-bipyridine Functionalized Iridium(III) Complex for Fluorescence Lifetime-based Recognition and Sensing of Phosphates.

A new IrIII based 3,3'-([2,2'-bipyridine]-5,5'-diylbis(methylene))bis(1-ethyl-1H-imidazol-3-ium) functionalized receptor Ir-1 has been synthesized for selective recognition, sensing and as a lifetime based sensor for H2 PO4 - and HP2 O7 3- in acetonitrile. An increase in the lifetime (τ) from 0.03543 µs to 0.2736 µs and 0.1323 µs in the presence of H2 PO4 - and HP2 O7 3- , respectively, among all other competitive anions establishes Ir-1 as a simple lifetime-based sensor. Furthermore, 13.7- and 8.5-fold enhancement in PL intensities of Ir-1 along with blue-shifting is seen with H2 PO4 - and HP2 O7 3- , respectively. High selectivity of Ir-1 for these two ions even in the presence of a large excess of other anions also displayed sensitive detection (LOD=0.035 µM for HP2 O7 3- and 0.040 µM for H2 PO4 - ). NMR data further suggest that the recognition of phosphates by Ir-1 is occurring through C-H⋅⋅⋅phosphate hydrogen bond (HB) interaction.

Influence of Triazole Substituents of Bis-Heteroleptic Ru(II) Probes toward Selective Sensing of Dihydrogen Phosphate.

A series of seven new bis-heteroleptic Ru(II) probes (1[PF6]2-7[PF6]2) along with two previously reported probes (8[PF6]2 and 9[PF6]2) containing a similar anion binding triazole unit (hydrogen bond donor) functionalized with various substituents are employed in a detailed comparative investigation for the development of superior selective probes for H2PO4-. Various solution- and solid-state studies, such as 1H-DOSY NMR, dynamic light scattering (DLS), single-crystal X-ray crystallography, and transmission electron microscopy (TEM), have established that the selective sensing of H2PO4- by this series of probes is primarily due to supramolecular aggregation driven enhancement of 3MLCT emission. Intestingly, 1[PF6]2 and 7[PF6]2, having an electron-deficient (π-acidic) aromatic pentafluorophenyl substituent are found to be superior probes for H2PO4- in comparison to the other aryl- and polyaromatic-substituted analogues (2[PF6]2-6[PF6]2, 8[PF6]2, and 9[PF6]2), in terms of a higher enhancement of the 3MLCT emission band, a greater binding constant, and a lower detection limit. The superiority of 1[PF6]2 and 7[PF6]2 could be due to better supramolecular aggregation properties in the cases of pentafluorophenyl analogues via both hydrogen bonding and anion-fluorine/anion-π noncovalent interactions.

Discriminative Behavior of a Donor-Acceptor-Donor Triad toward Cyanide and Fluoride: Insights into the Mechanism of Naphthalene Diimide Reduction by Cyanide and Fluoride.

A new molecular donor-acceptor-donor (D-A-D) triad, comprised of an electron deficient 1,4,5,8-naphthalene tetracarboxylic diimide (NDI) unit covalently connected to two flanking photosensitizers, i.e., a bis-heteroleptic Ru(II) complex of 1,10-phenanthroline and pyridine triazole hybrid ligand, is described. The single crystal X-ray structure of the perchlorate salt of the triad demonstrates that the electron deficient NDI unit can act as a host for anions via anion-π interaction. Detailed solution-state studies indicate that fluoride selectively interacts with the D-A-D triad to form a dianionic NDI, NDI2-, via a radical anion, NDI•-. On the contrary, cyanide reduces the NDI moiety to NDI•-, as confirmed by UV-vis, NMR, and EPR spectroscopy. Further, femtosecond transient absorption spectroscopic studies reveal a low luminescence quantum yield of the D-A-D triad attributable to the photoinduced electron transfer (PET) process from the photoactive Ru(II) center to the NDI unit. Interestingly, the triad displays "OFF-ON" luminescence behavior in the presence of fluoride by restoring the Ru(II) to phenanthroline/pyridine-triazole-based MLCT emission, whereas cyanide fails to show a similar property due to a different redox process operational in the latter. The reduction of NDI in the presence of fluoride and cyanide in different polar solvents indicates that involvement of such deprotonated solvents in the electron transfer mechanism may not be operative in our present system. Low-temperature kinetic studies support the formation of a charge transfer associative transient species, which likely allows overcoming the thermodynamically uphill barrier for the direct electron transfer mechanism.

Supramolecular Self-Assembly Driven Selective Sensing of Phosphates.

A new bis-heteroleptic RuII complex (1[PF6]2) with iodotriazole as the anion binding group along with the attached pyrene moiety is developed to investigate anion sensing properties and the origin of its selectivity toward a particular class of anions. Selective sensing of phosphates over other anions in both the solution and solid states by 1[PF6]2 is clearly evident from the perturbation of the absorption band and a large degree of amplification of 3MLCT emission band in the presence of phosphates. Importantly, macroscopic investigation such as Scanning Electron Microscopy (SEM) and Dynamic Light Scattering (DLS) indicated the formation of supramolecular architecture in the presence of dihydrogen phosphate via halogen bonding interaction and π-π stacking of pyrene moieties. Such macroscopic property is further corroborated by solution and solid state spectroscopic studies, e.g., 1H-DOSY NMR, single crystal X-ray crystallography, and solid state photoluminescence (PL) spectroscopy.

An integrated urea and halogen bond donor based receptor for superior and selective sensing of phosphates.

A new RuII based bis-heteroleptic ditopic receptor, 1[PF6]2 (C44H33F12IN10OP2Ru), having integrated anion binding iodotriazole (halogen bond donor) and urea units (-NH bond donor) is employed for selective sensing of phosphates (e.g., H2PO4- and HP2O73-). 1[PF6]2 showed superiority in phosphate sensing in CH3CN as compared to its hydrogen bond donor analogue, 2[PF6]2 (C44H34F12N10OP2Ru), non-urea halogen bond analogue, 3[PF6]2 (C38H27F12IN8P2Ru) and non-urea hydrogen bond donor analogue, 4[PF6]2 (C38H28F12N8P2Ru) in terms of enhanced binding constant values, longer excited state lifetimes and lower detection limit values. 1H-NMR, Isothermal Titration Calorimetry (ITC) and photophysical studies revealed the implementation of the combined role of both the halogen bond donor iodotriazole unit and the -NH unit of the urea moiety for selective and enhanced binding of phosphates.