Coulombic inter-ligand repulsion effects on the Pt(II) coordination chemistry of oligocationic, ammonium-functionalized triarylphosphines

The Pt(II) coordination chemistry of oligocationic ammoniomethyl- and neutral aminomethyl-substituted triarylphosphines (L) is described. Complexes of the type PtX2(L)2 (X = Cl, I) have been isolated and characterized. For the hexa-meta-ammoniomethyl-substituted ligands [1]6+ and [2]6+, two ligands always occupy a trans-configuration with respect to each other in complexes of the type PtX2(L)2, while for the tri-para-ammoniomethyl-substituted ligand [7]3+, the trans/cis ratio is dependent on the ionic strength of the solution. This behaviour was not observed for the neutral aminomethyl-substituted ligands. In the crystal structure of trans-[PtI2(1)2]I12, the geometrical parameters of the phosphine ligand [1]6+ are very similar to those found in the analogous complex of the benchmark ligand PPh3, i.e. trans-PtI2(PPh3)2, indicating that no significant increase in the steric congestion is present in the complex. Instead, the coordination chemistry of this class of phosphine ligands is dominated by repulsive Coulombic inter-ligand interactions.