Tropolone as Neutral Compound and Ligand in Palladium Complexes

Abstract

Focusing mainly on the solid-state effect of halogenation on compounds of tropolone type in the solid state, we report the character and functionality of these molecules. The behaviour of bromo-functionalised tropolone molecules is discussed relative to the tropolone parent compound. To investigate the large influence of bromination, we extracted structural data from the Cambridge Crystallographic Database covering Br...Br non-bonded interactions. Molecules of tropolone type π -stack in a fashion similar to benzene derivatives, with an interplanar distance ca. 3.72 A. Palladium complexes with tropolonato ligands are presented as examples of the effect of coordination that ligands of these types induce on metal centres. These complexes form highly labile species in the presence of tertiary phosphines; the [Pd(TropBr3)Br(PCy3)] complex is reported as an intermediate of these labile species, in which the initial [Pd(TropBr3)2] complex acts as a bromo source in the presence of the PCy3 ligand. Significant Br ... Br interactions at distance ca. 3.6 A stabilise the [Pd(TropBr3)Br(PCy3)] complex in the solid state. Significant π-stacking is observed for palladium(II) tropolonato derivatives in the solid state