SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF THE FIRST ISOLATED HOMOLEPTIC ORGANOPLATINUM(IV) COMPOUND - [PT(C6CL5)(4)]

The neutral member of the triad [Pt(C6Cl5)(4)](n-) (n = 0, 1, or 2) has been synthesized and characterized. Treatment of [NBu(4)(n)][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, C-13 and Pt-195 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 P2(1)/c, with a = 11.5972(18) Angstrom, b = 21.213(4) Angstrom, c = 16.838(3) Angstrom, beta = 102.04(2)degrees, V = 4051.22 Angstrom(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 a-bonded ligands, while the other two act as chelating ligands bonded through the ipso-C atom and one of the ortho-C1 atoms. Crystals of 3 contain the enantiomeric couple (OC-6-32-A)- and (OC-6-32-C)-bis(pentachlorophenyl-kappa C)bis(pentachloro-kappa Cl-2-phenyl-kappa-C)platinum(IV). Complex 3 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 [NBu(4)(n)](2)[Pt-II(C6Cl5)(4)] (1) yielding 2.