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 (2029). 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.