Efficient and stereoselective syntheses of isomeric trifluoromethyl-platinum(iv) chlorides

Abstract

The homoleptic, square-planar trifluoromethylplatinate(II) compound [NBu₄]₂[Pt(CF₃)₄] (1) reacts with SOCl₂ undergoing oxidative addition of a S–Cl bond to give the octahedral species [NBu₄]₂[trans-Pt(CF₃)₄Cl(SOCl)] (4), that contains the unusual chlorosulfinyl ligand. Compound 4 readily evolves into the dichloro-derivative [NBu₄]₂[cis-Pt(CF₃)₄Cl₂] (2), whereby the “Pt(CF₃)₄” unit undergoes a stereochemical rearrangement from an initial square-planar (equatorial) geometry to a final sawhorse disposition within the global Pt octahedral environment. Compound 2 is more reactive than the corresponding [NBu₄]₂[trans-Pt(CF₃)₄Cl₂] (3) stereoisomer and thus affords the trichloro-derivative [NBu₄]₂[fac-Pt(CF₃)₃Cl₃] (5) by treatment with the stoichiometrically required amount of HCl(aq). Stereoisomer [NBu₄]₂[mer-Pt(CF₃)₃Cl₃] (6) has been obtained by oxidative addition of Cl₂ to the organoplatinum(II) precursor [NBu₄]₂[Pt(CF₃)₃Cl]. All the synthetic procedures described here proceed in high yields and in a stereoselective manner. The optical properties of the cis-/trans-[Pt(CF₃)₄Cl₂]²⁻ and fac-/mer-[Pt(CF₃)₃Cl₃]²⁻ diastereomeric couples (diffuse reflectance) as well as the solid-state geometries of the latter couple (single-crystal X-ray diffraction methods) are conveniently compared.