N,N′-Bis(aryl)pyridine-2,6-dicarboxamide complexes of ruthenium: Synthesis,structure and redox properties

Reaction of five N,N′-bis(aryl)pyridine-2,6-dicarboxamides (H₂L-R, where H₂ denotes the two acidic protons and R (R = OCH₃, CH₃, H, Cl and NO₂) the para substituent in the aryl fragment) with [Ru(trpy)Cl₃](trpy = 2,2′,2″-terpyridine) in refluxing ethanol in the presence of a base (NEt₃) affords a group of complexes of the type [Ru^II(trpy)(L-R)], each of which contains an amide ligand coordinated to the metal center as a dianionic tridentate N,N,N-donor along with a terpyridine ligand. Structure of the [Ru^II(trpy)(L-Cl)] complex has been determined by X-ray crystallography. All the Ru(II) complexes are diamagnetic, and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on the [Ru^II(trpy)(L-R)] complexes shows a Ru(II)–Ru(III) oxidation within 0.16–0.33 V versus SCE. An oxidation of the coordinated amide ligand is also observed within 0.94–1.33 V versus SCE and a reduction of coordinated terpyridine ligand within −1.10 to −1.15 V versus SCE. Constant potential coulometric oxidation of the [Ru^II(trpy)(L-R)] complexes produces the corresponding [Ru^III(trpy)(L-R)]⁺ complexes, which have been isolated as the perchlorate salts. Structure of the [Ru^III(trpy)(L-CH₃)]ClO₄ complex has been determined by X-ray crystallography. All the Ru(III) complexes are one-electron paramagnetic, and show anisotropic ESR spectra at 77 K and intense LMCT transitions in the visible region. A weak ligand-field band has also been shown by all the [Ru^III(trpy)(L-R)]ClO₄ complexes near 1600 nm.     

Copper(II) complexes with pyridine-2,6-dicarboxylic acid from the oxidation of copper(I) iodide

Via an oxidation reaction of Cu(I) iodide with pyridine-2,6-dicarboxylic acid (H₂L) in DMF three copper(II) complexes, [(CH₃)₂NH₂]₂[CuL₂] (1), K₂[CuL₂]?H₂L?H₂O (2) and [Cu(L)(H₂O)]_n (3), were synthesized and characterized. The structures of 1–3 were determined by single crystal X-ray diffraction studies. In-situ DMF decomposition produces dimethylamine base under solvothermal conditions and a proton transfer reaction takes place for the complex formation of 1. 3-D networks are stabilized in 1 and 2 via hydrogen bonds. Complex 3 is a 1-D coordination polymer with Cu-O semi-coordination bonds. Thermal decomposition of the complexes results in the corresponding metal oxides. Also, the electrochemical behavior of 1 was determined to be a metal-centered and diffusion-controlled, one-electron reduction process.     

First use of a palladium complex with a thiosemicarbazone ligand as catalyst precursor for the Heck reaction

A novel palladium complex with salicylaldehyde N(4)-ethylthiosemicarbazone has been synthesized and according to its crystal structure the ligand is bound to the metal in an O, N, S-terdentate coordination mode. This phosphorus-free system efficiently catalyzes the Heck reaction of aryl bromides (from electron-rich to electron-poor) with styrene under argon, with turnover numbers of up to 43,000, at 150 °C after 24 h, and with a selectivity toward trans-stilbenes ranging from 92 to 96%. In air, for activated aryl bromides and for a palladium concentration of 1 mM, the yields are essentially the same as those obtained when the reaction was performed under argon.     

Poly(propylene carbonate)/poly(3‐hydroxybutyrate)‐based bionanocomposites reinforced with cellulose nanocrystal for potential application as a packaging material

Poly(propylene carbonate) (PPC) is an aliphatic polycarbonate synthesized from carbon dioxide and propylene oxide. Poly(3‐hydroxybutyrate) (PHB) is a type of thermoplastic polyester produced by biological fermentation. The blending of PHB with PPC can effectively enhance the mechanical properties and barrier properties of PPC. Bionanocomposites of PPC/PHB enhanced by cellulose nanocrystal (CNC) are prepared via a two‐step process using polyethylene glycol as a carrier. Results show that the oxygen barrier properties of the composites increased with the increase of the CNC content. When the CNC content is 1 wt%, the oxygen barrier performance increases nearly 18 times. The assumed model can predict the barrier performance of composites with the combined influence of morphology and CNC distribution. This will make PPC/PHB/CNC nanocomposites a very promising degradable material for food packaging application.