Synthesis and study of new cyclometallated complexes

Abstract

Twenty-nine heteroaromatic ligands, which are potentially capable of forming cyclometallated complexes, have been reacted with palladium and rhodium salts. In addition to a number of mono-cyclometallated complexes, two doubly cyclopalladated complexes have been prepared, as have a number of coordination complexes. Specifically, a number of phenoxy- and phenylthio-substituted pyridines and diazines, four of which could potentially be doubly cyclometallated, have been synthesised, and their coordination and cyclopalladation chemistry investigated. The previously reported reactions of 2-benzoylpyridine with rhodium trichloride trihydrate have been revisited, and are discussed in relation to the formation and characterisation of a novel cyclorhodated complex of the ligand. The syntheses-via homo-coupling reactions of aryl halide precursors - and cyclopalladations of two structural analogues of 2,2':4',4":2",2"'-quaterpyridine are also described. All of the soluble complexes and ligands have been fully characterised by ¹H and ¹³C NMR, using combinations of various one- and two-dimensional NMR techniques. The trends in the coordination induced shifts, observed for the NMR spectra of a series of cyclopalladated acetylacetonate complexes and the corresponding free ligands, are discussed, as are those for a related series of octahedral cyclorhodated complexes. Other methods, including IR spectroscopy, mass spectrometry and elemental analysis, have been used to characterise the prepared complexes. In addition, the characterisation of three cyclometallated complexes and four coordination complexes, by single crystal X-ray structure determination, is described.