Dinuclear gold(I)-N-heterocyclic carbene complexes: Synthesis,characterization, and catalytic application for hydrohydrazidation of terminal alkynes

Dinuclear gold(I)-N-heterocyclic carbene complexes were developed for the hydrohydrazidation of terminal alkynes. The gold(I)-N-heterocyclic carbene complexes 2a-2b were synthesized in good yields from silver complexes synthesized in situ, which in turn were obtained from the corresponding imidazolium salts with Ag₂O in dichloromethane as a solvent. The new air-stable gold(I)-NHC complexes, 2a - 2b, were characterized using NMR spectroscopy, elemental analysis, infrared, and mass spectroscopy studies. The gold(I) complex 2a was characterized using X-ray crystallography. Bis-N-heterocyclic carbene–based gold(I) complexes 2a - 2b exhibited excellent catalytic activities for hydrohydrazidation of terminal alkynes yielding acylhydrazone derivatives. The working catalytic system can be used in gram-scale synthesis. In addition, the catalytic reaction mechanism of the hydrohydrazidation of terminal alkynes by gold(I)-NHC complex was studied in detail using density functional theory.     

Correction to: Macrocycles in dual role: ancillary ligands in metal complexes and organocatalysts for the ring‑opening polymerization of lactide

Journal of Inclusion Phenomena and Macrocyclic Chemistry - A correction to this paper has been published: https://doi.org/10.1007/s10847-021-01060-y     

A Theoretical Account of the Coupling between Metal- and Ligand-centred Spins

This study addresses the magnetic interaction between paramagnetic metal ions and the radical ligands taking the [Cu^II(hfac)₂(imVDZ)] and [M^II(hfac)₂(pyDTDA)] (imVDZ=1,5-dimethyl-3-(1-methyl-2-imidazolyl)-6-oxoverdazyl; hfac=(1,1,1,5,5,5)hexafluroacetylacetonate; pyDTDA=4-(2′-pyridyl)-1,2,3,5-dithiadiazolyl), (M=Cu, Ni, Co, Fe, Mn) compounds as reference systems. The coupling between the metal and ligand spins is quantified in terms of the exchange coupling constant (J) in the platform of density functional theory (DFT) and the wave function-based complete active space self-consistent field (CASSCF) method. Application of DFT and broken symmetry (BS) formalism results ferromagnetic coupling for all the transition metal complexes except the Mn(II) complex. This DFT-BS prediction of magnetic nature matches with the experimental finding for all the complexes other than the Fe(II)-pyDTDA complex, for which an antiferromagnetic coupling between high spin iron and the thiazyl ligand has been reported. However, evaluation of spin state energetics through the multiconfigurational wave function-based method produces the S=3/2 ground spin state for the iron-thiazyl in parity with experiment. Electronic structure analyses find the overlap between the metal- and ligand-based singly occupied molecular orbitals (SOMOs) to be one of the major reasons attributing to different extent of exchange coupling in the systems under investigation.     

Radioanalytical separation and size-dependent ion exchange property of micelle-directed titanium phosphate nanocomposites

Nanocomposite titanium-phosphate (TiP) of different sizes was synthesized using Triton X-100 (polyethylene glycol-p-isooctylphenyl ether) surfactant. The materials were characterized by FTIR and powdered X-ray diffraction (XRD). The structural and morphological details of the material were obtained by scanning electron microscopy (SEM) and transmission electron microscopy. The SEM study was followed by energy dispersive spectroscopic analysis for elemental analysis of the sample. The important peaks of the XRD spectra were analyzed to determine the probable composition of the material. The average size distribution of the particles was determined by dynamic light scattering method. Ion exchange capacity was measured for different metal ions with sizes of the TiP nanocomposite and size-dependent ion exchange property of the material was investigated thoroughly. The nanomaterial of the smallest size of around 43 nm was employed to separate carrier-free ^137mBa from ¹³⁷Cs in column chromatographic technique using 1.0 M HNO₃ as eluting agent at pH 5.     

Template-based fabrication of Ag–ZnO core–shell nanorod arrays

We report a simple, versatile, two-step fabrication technique for synthesizing a core–shell nanorod array whose architecture is specifically suited for use as an electrode in a dye sensitized solar cell (DSSC). The particular structure fabricated by us consists of a parallel array of 5 μm long and 150–200 nm wide Ag nanorod cores, each coated with a 15–20 nm thick ZnO shell. Importantly, the shell thickness is roughly uniform throughout the length of the rods, which are free standing but distinctly separated from each other. This would allow the dye to penetrate freely and cover the ZnO surface completely in a DSSC.     

Macrocycles in dual role: ancillary ligands in metal complexes and organocatalysts for the ring-opening polymerization of lactide

Journal of Inclusion Phenomena and Macrocyclic Chemistry - In the twenty-first century, one of the central focus of polymer research in academia and industries is directed towards the design of...     

Bimetallic Al(III) Compounds as Catalysts for the Synthesis of Biodegradable Polyesters and Polycarbonates

Ethylenediamine bridged benzoxazine proligands were synthesized by a modified Mannich condensation reaction. The reaction of the proligands with two equivalents of AlMe₃ resulted in the formation of dinuclear Al(III) compounds in high yield and purity. When the ligand binds to the Al(III) center, it forms two separate six-membered N,O-chelates with the two Al atoms that resembles the N-alkylated salan moiety. Each aluminum atom adopts a distorted tetrahedral geometry as revealed from the single-crystal X-ray diffraction studies of 1 . The catalytic activity of these aluminum compounds was investigated towards the ROP of rac-LA and ROCOP of epoxides (PO, CHO, tBuGE) and phthalic anhydride and ROCOP of CHO with CO₂. These aluminum compounds showed notable catalytic activity towards the ROP and ROCOP reactions in the absence of cocatalyst.     

Well‐Defined N‐Heterocyclic Carbene‐Palladium Complexes as Efficient Catalysts for Domino Sonogashira Coupling/Cyclization Reaction and C‐H bond Arylation of Benzothiazole

Well‐defined and air‐stable PEPPSI (Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) themed palladium bis‐N‐heterocyclic carbene complexes have been developed for the domino Sonogashira coupling/cyclization reaction of 2‐iodophenol with a variety of terminal alkynes and C‐H bond arylation of benzothiazole with aryl iodides. The PEPPSI themed palladium complexes, 2a and 2b were synthesized in good yields from the reaction of corresponding imidazolium salts with PdCl₂ and K₂CO₃ in pyridine. The new air‐stable palladium‐NHC complexes were characterized by NMR spectroscopy, X‐ray crystallography, elemental analysis, and mass spectroscopy studies. The PEPPSI themed palladium(II) bis‐N‐heterocyclic carbene complexes 2a and 2b exhibited excellent catalytic activities for domino Sonogashira coupling/cyclization reaction of 2‐iodophenol with terminal alkynes yielding benzofuran derivatives. In addition, the palladium complexes, 2a and 2b successfully catalyzed the direct C‐H bond arylation of benzothiazole with aryl iodides as coupling partners in presence of CuI as co‐catalyst.     

Design of nickel chelates of tetradentate N-heterocyclic carbenes with subdued cytotoxicity

A series of nickel complexes, 1b-3b, exhibiting subdued cytotoxicity have been designed with the intent of their use as agents for developing resistance to nickel toxicity. Indeed, the nickel complexes, 1b-3b, display less cytotoxic activity towards two commonly occurring human cancer cell lines namely, HeLa cells (16-64%) and MCF-7 cells (70-90%) in culture as compared to the maximum inhibition by NiCl₂ · 6H₂O under analogous conditions at three different concentrations (1 μM, 5 μM and 20 μM). Similarly, the suppression of cytotoxicity through chelation of the metal ion can also be seen in normal cells as was evident from a significant reduction in cytotoxicity (9-41%) for a non-tumorigenic CHO cell line in case of a representative complex 3b. The reduction in carcinogenic activity in the complexes relative to nickel(II) ion from NiCl₂ · 6H₂O is brought about by successful chelation of the metal center by a class of specially designed new tetradentate N/O-functionalized N-heterocyclic carbene ligands. The two strongly σ-donating carbene moieties coupled with two negatively charged amido moieties present in the N-heterocyclic carbene ligands facilitate complete chelation of the metal center and thereby significantly reduce the cytotoxic effects of the metal.