Kinetic data are reported for the reaction of either tetrachloroplatinate(II) ion or Zeise’s salt with SnCl3-. Data support a bimolecular attack of SnCl3- upon the substrate. Data for the reaction of tetrachloroplatinate(II) with ethylene in the presence of chlorostannate(II) ion (at various Pt:Sn ratios) in acidic aqueous solution are also reported. The ethylene absorption by the metal complex affording PtC2H4Cl3- appears to involve both the cis and trans isomers, the cis-Pt(SnCl3)2Cl22- being the more active absorbing intermediate. No ethylene absorption is detectable at high Sn:Pt ratios, at which the predominant species is the five-coordinated Pt(SnCl3)53-. Results are discussed in terms of the high trans effect and of the pronounced -acceptor character of SnCl3- bonded to platinum(II). © 1969, American Chemical Society. All rights reserved.