Imidazolium salts bearing TEMPO groups react with commercially available copper powder affording Cu-NHC complexes. The in situ generated Cu-NHC-TEMPO complexes are quite efficient catalysts for aerobic oxidation of primary alcohols into aldehydes. The catalyst is easily available, and various primary alcohols were selectively converted to aldehydes in excellent yields.

No abstract

We have prepared a number of phenanthroline-functionalized imidazolium and triazolium salts from 2-iodo-1,10-phenanthroline and imidazole and triazole derivatives. Simple reactions of these imidazolium salts with copper powder at room temperature have afforded a series of dinuclear copper(I)-NHC complexes doubly bridged by N-(1,10-phenanthrolin-2-yl)imidazolylidene ligands in excellent yields. The two phen-NHC ligands are either head-to-head or head-to-tail arranged depending upon the steric repulsion of the substituents. Reactions of imidazolium halides and copper yielded dinuclear complexes [Cu 2 (μ-X)(L6) 2 ]X (X = Cl, Br, I) in nearly quantitative yields. The dinuclear [Cu 2 (L10) 2 (μ-MeCN)] 2+ was similarly obtained through 1,2,4-triazolium salts and copper, and the compound consists of a bridging CH 3 CN molecule, representing the first example of Cu-NHC complexes with a 3c−2e bond. These Cu(I) complexes have been characterized by NMR spectra and elemental analysis and further confirmed by X-ray diffraction analysis. These dinuclear copper-NHC complexes are highly active for cycloaddition reaction of alkynes and azides at room temperature. [Cu 2 (μ-X)(L6) 2 ]X are the most efficient catalysts among these dinuclear complexes in acetonitrile, which are superior to the commonly used copper catalysts for click reaction.

A halogen-free flame retardant containing nitrogen and phosphorus, 2-[anilino-(6-oxobenzo[c][2,1]benzoxaphosphinin-6-yl)methyl]phenol (PDOP), has been synthesized by reaction of benzo[c][2,1]benzoxaphosphinine-6-oxide (DOPO) with 2-( N-phenyliminomethyl)phenol. Halogen-free flame-retardant rigid polyurethane foams (RPUF-PDOP) were prepared using PDOP as a flame retardant. The flammability was investigated using limiting oxygen index, a vertical burning test (UL-94), and a cone calorimeter. When PDOP (10 wt%) as flame retardant was added to RPUF (RPUF-PDOP10%), the limiting oxygen index value was increased from 18% to 27%, and a UL-94 V-0 rating was achieved; meanwhile, the peak heat release rate, total heat release, and the average mass-loss rates of RPUF-PDOP10% were reduced from 246 to 207 kW m−2, from 26.9 to 21.0 MJ/m2, and from 0.043 to 0.033 g/s, respectively. Especially, the initial decomposition temperature of RPUF-PDOP10% was decreased from 228°C to 209°C. The final residual char from decomposition of RPUF-PDOP10% was significantly increased up to 35.6%. The addition of PDOP did not markedly decrease the mechanical properties of the resulting flame-retardant RPUFs.

We describe a new synthetic procedure for transition-metal N-heterocyclic carbene complexes (NHCs). A number of Pd­(II), Pt­(II), Co­(III), and Ru­(II) complexes containing functionalized NHCs have been obtained in good to excellent yields using NiII–NHC complexes as carbene transfer reagents. NiII–NHC complexes are easily prepared from the direct reactions of the corresponding imidazolium salts with commercially available Raney nickel powder. The byproduct of transmetalation reactions, NiCl2, can be easily removed by simple filtration. This study offers a new, economical, and practical synthetic method for metal–NHC complexes.