Phosphorus cations and bulky cyclopentadienyl ligands

Abstract

The synthesis and characterisation of some ethynylphosphonium salts are described starting from 1-bromo-2-phenylacetylene and tertiary phosphines. Structural information for these molecules has been obtained using X-ray crystallography, and deviant reactivity was observed at elevated temperatures when the electron-rich tris(2,4,6-trimethoxyphenyl)phosphine was employed. A new approach to the corresponding 1,4-bis(ethynylphosphonium) salts was also developed by a similar reaction, and the first bis(ethynylphosphonium) salts were characterised using X-ray crystallography. Exploratory research into the synthesis of m-terphenyl substituted cyclopentadienyl ligands (Ter[superscript Mes]Cp and Ter[superscript Dipp]Cp) is also described. A new synthetic route is presented and is accomplished through the reaction of aryl lithium reagents with cobaltocenium salts, followed by oxidation of the intermediate cobalt(I) species to afford the corresponding cyclopentadiene. The preparation, structural, and spectroscopic properties of the alkali metal salts (Li–Cs) is described, and some preliminary coordination chemistry is presented.