Steric Control in the Synthesis of Phosphinous Acid-Coordinated Mono- and Binuclear Platinum(II) Complexes

Several phosphinous acid-coordinated platinum complexes were prepared and characterized. In the presence of secondary phosphine oxide (2 equiv), PtCl₂(cod) was converted to a series of cis/trans platinum complexes PtCl₂[R¹R²POH]₂ featuring phosphinous acids (PAs) as ligands (20−29). A balance between the steric and electronic effects of ligands governs their coordination mode. NMR experiments and density functional theory calculations show that the anti conformer for trans complexes is favored by intramolecular H···Cl bonding. PtCl₂[R¹R²POH]₂ treated with NEt₃ (1 equiv) gave bimetallic platinum complexes cis-[Pt₂(μ-Cl)₂{(R¹R²PO)₂H}₂] characterized by ³¹P NMR and X-ray diffraction. An unusual monometallic platinum complex, cis-[PtCl₂{(i-Bu)₂PO}₂H]⁻[HNEt₃]⁺ (30), was isolated and characterized as a possible intermediate in the formation of dinuclear species. Silver acetate and triethylamine both reacted with PtCl₂[(t-Bu)₂POH]₂ to yield new bulky Pt(κ²-acetato){[(t-Bu)₂PO]₂H} platinum complex 31. The structure of complexes 20d (R¹ = Ph, R² = Cy), 21 (R¹ = Ph, R² = t-Bu), 21d (R¹ = Ph, R² = t-Bu), 24 (R¹ = R² = t-Bu), 25 (R¹ = R² = Cy), 30 (R¹ = R² = i-Bu), and 31 (R¹ = R² = t-Bu) were determined by X-ray diffraction.