A series of substituted, pyridyl-functionalized 2,4,6-triarylpyrylium salts were prepared and investigated for their light absorption and emission properties. After reaction with P(SiMe3)3, the corresponding λ3-phosphinines were obtained, which carry on the 4- or 6-aryl ring ±I and ±M substituents. Supported by DFT calculations, a systematic evaluation of the σ-donor and π-donor as well as π-acceptor properties of these low-coordinate P,N-hybrid ligands was performed. The modular synthetic approach allowed us at the same time to synthesize the structurally related bipyridine derivatives for comparison reasons. Reaction of the chelating ligands with [W(CO)6] in THF afforded the corresponding [(P^N)W(CO)4] and [(N^N)W(CO)4] complexes. A crystallographic characterization of selected coordination compounds revealed significant structural differences between the pyridyl-phosphinine- and the bipyridine-based compounds. Their characterization by means of IR-spectroscopy gave experimental insight into the electronic properties of the respective ligands.@en

Bis-N-heterocyclic carbene (NHC) aminopincer ligands were successfully applied for the first time in the catalytic hydrogenation of esters. We have isolated and characterized a well-defined catalyst precursor as a dimeric [Ru2(L)2Cl3]PF6 complex and studied its reactivity and catalytic performance. Remarkable initial activities up to 283 000 h-1 were achieved in the hydrogenation of ethyl hexanoate at only 12.5 ppm Ru loading. A wide range of aliphatic and aromatic esters can be converted with this catalyst to corresponding alcohols in near quantitative yields. The described synthetic protocol makes use of air-stable reagents available in multigram quantities, rendering the bis-NHC ligands an attractive alternative to the conventional phosphine-based systems.@en