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

Abstract

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.