Synthesis and structural characterization of the first isolated homoleptic organoplatinum(IV) compound: [Pt(C6Cl5)4]

Article abstract of DOI:10.1021/ja00120a011

The neutral member of the triad [Pt(C₆Cl₅)₄]^n- (n = 0, 1, or 2) has been synthesized and characterized. Treatment of [NBuⁿ₄][Pt^III(C₆Cl₅) ₄] (2) with an excess of chlorine in CCl₄ in the presence of AlCl₃ gives a high yield (80%) of orange [Pt^IV(C₆Cl₅)₄] (3) which can also be generated by electrochemical oxidation of 2 in CH₂Cl₂ at 1.8 V. Complex 3 has been characterized by elemental analysis and spectroscopy (IR, mass, ¹³C and ¹⁹⁵Pt NMR, and EXAFS) as well as by electrochemistry and an X-ray crystal structure determination of its toluene solvate. Cyclic voltammetry indicates that the oxidation of 2 to 3 is accompanied by a substantial structural change, a change confirmed by the EXAFS analyses which imply the symmetry of the [Pt(C₆Cl₅)₄] moiety is lowered, with two o-chlorine atoms entering the platinum coordination sphere. The X-ray study showed that crystals of 3-C₆H₅CH₃ are monoclinic, space group P2₁/c, with a = 11.5972(18) ?, b = 21.213(4) ?, c = 16.838(3) ?, β = 102.04(2)°, V = 4051.22 ?³, and Z = 4. The structural study of 3 reveals the Pt center in a distorted octahedral environment; two of the C₆Cl₅ groups behave as conventional σ-bonded ligands, while the other two act as chelating ligands bonded through the ipso-C atom and one of the ortho-Cl atoms. Crystals of 3 contain the enantiomeric couple (OC-6-32-A)- and (OC-6-32-C)-bis(pentachlorophenyl-κC)bis(pentachloro-κCl ²-phenyl-κC)platinum(IV). Complex is diamagnetic and air-and moisture-stable but with limited thermal stability; at room temperature it eliminates C₆Cl₅-C₆Cl₅ even in the solid state. It undergoes conproportionation with [NBuⁿ₄]2[Pt^II(C₆Cl₅) ₄] (1) yielding 2.