SYNTHESIS, STRUCTURE, AND REACTIVITY OF ARYLCHLOROBIS(DIALKYL SULFIDE)PLATINUM(II) COMPLEXES

Complexes trans-[PtRCl(SR'(2))(2)], where R = Ph, mesityl, and p-anisy l and R' = Nle or Et, have been synthesized and their crystal and mole cular structures determined. Crystals of trans-[PtPhCl(SEt2)(2)] (2) a re triclinic (<P(1)over bar>) with a = 10.112(4) Angstrom, b = 13.158( 2) Angstrom, c = 14.714(5) Angstrom, alpha = 102.48(2)degrees, beta = 94.394(4)degrees, gamma = 90.22(3)degrees, and Z = 4. Crystals of tran s-[Bt(mesityl)Cl(SMe2)(2)] (4) are monoclinic (P2(1)/c) with a = 13.15 8(2) Angstrom, b = 9.170(1) Angstrom, c = 16.013(3) Angstrom, beta = 1 20.93(2)degrees, and Z = 4, and crystals of [Pt(p-anisyl)Cl(SMe2)(2)] (5) are monoclinic (P2(1)/n) with a = 9.879(4) Angstrom, b = 8.128(2) Angstrom, c = 19.460(5) Angstrom, beta = 96.56(3)degrees, and Z = 4. A ll complexes are square-planar, featuring Pt-CI distances between 2.40 and 2.42 Angstrom, indicating a large ground-state trans influence of the aryl group. The coordination geometry is maintained in methanol a nd chloroform solution as shown by H-1-NMR spectra. The kinetics of su bstitution of the labile chloride trans to aryl by various nucleophile s has been studied in methanol by variable-temperature and -pressure s topped-flow spectrophotometry. A two-term rate law with a well-develop ed solvolytic pathway is followed. Negative entropies and volumes of a ctivation indicate an associative mode of activation in all cases, ind ependent of steric blocking of the axial sites and a large Pt-CI groun d-state bond-weakening. Comparison of the reaction rates of the presen t series of complexes with their bis(phosphine) analogues and with rel ated cyclometalated compounds shows that the triethylphosphine complex es are 2-3 orders of magnitude less reactive than the thioether comple xes, which in turn are a factor 10-20 less reactive than the cyclometa lated ones. This reactivity increase can be rationalized mainly in ter ms of a decrease in steric hindrance in the series. There seems to be no inherent differences with regard to trans labilizing ability of the aryl ligands in the various types of complexes, including the cyclome talated ones.