The （COCl）2/Hantzsch ester is found to be an effective system for the metal-free reduction of tertiary phosphine oxides. The reaction proceeds under mild conditions, and is applicable to triarylphosphine oxides and alkyldiarylphosphine oxides to produce the corresponding tertiary phosphines in good to excellent yields. This new finding provides a practical, convenient and metal-free method for the reduction of tertiary phosphine oxides to tertiary phosphines, and shows potential application in organic synthesis.
Novel acyclic Pd（II）-N-heterocyclic carbene （NHC） metallacrown ethers 5a, 5b have been synthesized. Reaction of the imidazolium salts hearing a long polyether chain with Ag2O afforded Ag-NHC complexes, which then reacted as carbene transfer agent with PdCl2（MeCN）2 to give the desired acyelic Pd（Ⅱ）-NHC metallacrown ether complexes 5a and 5b. The 1H NMR and 13C NMR spectra show fia and fib exist as mixtures ofcis and trans isomers in solution. The trans isomer of 5a was characterized by X-ray diffraction, which clearly demonstrated two pseudo-crown ether cavities in trans-5a. Pd（Ⅱ）-NHC complexes 5a and 5b have been shown to be highly effective in the Suzuki-Miyaura reactions of a variety of aryl bromides in neat water without the need of inert gas protection.
