Synthesis of neutral gold(III) pyrimidine-complexes and theoretical studies on the proton affinity of the coordinated ligands

Abstract

The neutral gold(III) complexes AuCl 3(pm) (pm = pyrimidine, 2-methylpyrimidine, 4-methylpyrimidine, 5-methylpyrimidine, 4,6-dimethylpyrimidine, 2-aminopyrimidine) have been synthesised and characterised. The proton affinity (PA) values of the free and coordinated N-heterocycles have been theoretically estimated on the basis of DFT calculations. The coordination to the AuCl 3 metal fragment causes a strong lowering of the basicity of the residual protonation sites, with PA variations around −25 kcal mol −1. The lowering of PA caused by the bonding to the gold centre results related to the presence of space-demanding groups near the coordinating nitrogen atom and to the π-back donation of electron density from the metal to the protonated ligand.