The bromide anation of tr-PtCl&H,O-has been studied at 25 "Cand the chloride anations of tr-PtCl,-BrH,O-and PtBrSHzO-at 50 "C, These reactions proceed via halide assisted mechanisms, compatible with the experimental rate laws: -d [tr-PtCl&H,O-] /dt = 0.43 [Br-] * [ tr-PtClJBrH20-] s-' M-* -d[tr-PtCl,BrH,O-]/dt = (2.7[Br-] [CT] + 2.95 X 10U3 [CT] *) [trPtC14BrH20-Is-'M-* -d[PtBr,H,O-]/dt = (0.47[Br-] [Ct] + 7.6 X 10e4 [CT] *) [PtBr,H,O-] s-'M-* Y7re bromide anation of trPtBr,ClH20-studied at 50 "C gives PtBrSC12-. vta a bromide assisted path and PtBrivia an REOA-path. The observed rate law is -d[tr-PtBr,ClH,O-]/dt = (4.2 X 10-4s-*M-2 X [Br-] * t5.8 X 10-4s-1M-1 X [Br-1) [tr-PtBr,ClH,O-]
PtBrSC12-reacts subsequently with bromide to form PtBrgvia a rate-determining (bromide assisted or REOA) formation of an intermediate aqua complex according to the mechanism +Br-PtBrsCl*-+ H,O---+ +Br-PtBrSH20----+ fast PtBrilhe observed rate law at 50 "C is --d[PtBr,Cl*-]/dt = 4 X IO-' [Br-] [PtBr&'l'-]
s-1 M-1
All reactions have been studied in a 0.50 M perchloric acid medium. A general survey of reactivity correlations and mechanisms for platinum(W) anation reactions is given. Effects of reductants, bridging and entering ligands, and of the four non-labile ligands in the plane around the platinum atom are quantitatively compared.