Substituent effects in pyridyl-functionalized pyrylium salts, pyridines and λ³,σ²-phosphinines

Abstract

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.