PT-195 NMR AND STRUCTURAL STUDIES OF PLATINUM(II) O-TOLYL AND MESITYL COMPLEXES

The syn and anti isomers Of cis-Pt(o-tolyl)2(PEt3)2 have distinguishable Pt-195 NMR spectra and have been separated chromatographically. Pt-195 and H-1 NMR spectra of these and a variety of related platinum complexes are reported, together with X-ray structures of four o-tolyl complexes: trans-Pt(o-tolyl)(PEt3)2Cl monoclinic, Cc, a = 14.412(3) angstrom, b = 11.615(3) angstrom, c = 14.818(3) angstrom, beta = 106.14(2)-degrees, Z = 4, V = 3282.8(8) angstrom3, R = 0.030, R(w) = 0.039 based on 2142 reflections with I > sigma(I); trans-Pt(o-tolyl)(PEt3)2Br, orthorhombic, Pcmn, a = 11.245(4) angstrom, b = 12.862(5) angstrom, c = 16.750(5) angstrom, Z = 4, V = 2422.5 (13) angstrom3, R = 0.052, R(w) = 0.056 based on 2075 reflections with I > sigma(I); cis-syn-Pt(o-tolyl)2(PEt3)2, monoclinic, P2(1)/n, a = 10.403(4) angstrom, b = 15.127(6) angstrom, c = 18.372(6) angstrom, beta = 106.47(3)-degrees, Z = 4, V = 2773(2) angstrom3, R = 0.120, R(w) = 0.134 based on 2075 reflections with I > 3sigma(I); cis-anti-Pt(o-tolyl)2(PEt3)2, monoclinic, P2(1)/c, a = 10.189(4) angstrom, b = 15.425(6) angstrom, c = 18.297(6) angstrom, beta = 104.35(3)-degrees, Z = 4, V = 2786(2) angstrom3, R = 0.043, R(w) = 0.036 based on 3264 reflections with I > sigma(I). All four structures show approximate square planar coordination about platinum but with significant distortions to maintain the Pt-CH3 distance at approximately the sum of the van der Waals radii. Although electrochemical oxidations of the o-tolyl complexes are chemically irreversible, oxidation of trans-Pt(mesityl)(PEt3)2Cl apparently gives a short-lived monomeric Pt(III) species.