Kinetic data for the reactions of trans-[Pt( P(CzHs)3]2(CH~)X] (X = C1 or I) with hydrogen chloride in methanol to give trans-[Pt(P(C2Hs)3]zClX] are reported. The reactions obey the following rate law: rate = (kz[H+] + ks[H+][Cl-])[complex]. A two-step mechanism is proposed involving the formation of labile platinum-(IV) intermediates of the type [Pt(P(C2H5)3)2(CH3)(H)XY] (X = C1 or I; Y = C1 or solvent) followed by slow elimination of methane and rearrangement to trans-[Pt( P(CzH5)3)2ClX] in the rate-controlling step. A comparison of electrophilic reaction mechanisms of post-transition and transition metal-carbon compounds is presented. t is known that d8 transition metal ion complexes 1 (e.&!., of Rh(I),' Ir(I),2 and Pt(II)394) are active catalysts in the homogeneous hydrogenation of unsaturated compounds containing olefinic and acetylenic linkage~,5-~ and labile species with metal-to-hydrogen (1)

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The preparation of new hydrido-cationic species of the general formula [Pt(PEt,),LH]X is reported (L = As Ph, SbPh,. thiourea, isopropylamine, 3-chloropyridine, 3-methylpyridine, 2,6-dimethylpyridine, and 4-cyanopyridine), together with the reaction of trans-[Pt( PEt,),(H) CI] with 1.2-diarsinoethane. Equilibrium indices for the reactions trans-[Pt(PEt,),HCI] f L + trans-[Pt(PEt,),LH]+ + CIin ethanol (L = PPh,, AsPh,, SbPh,, pyridine, 4-cyanopyridine, isopropylamine, and thiourea) have been also measured. The greater the equilibrium index of the cationic hydrido-species the lower is the stretching frequency of the Pt-H bond.THE homogeneous hydrogenation of unsaturated hydrocarbons catalysed by transition-metal complexes implies the formation of species containing metal-hydrogen bond(s) acting as labile intermediate(s).l-, It is therefore interesting to study the factors influencing the strength of the metal-hydrogen bond in hydridocomplexes. This work deals with cationic hydridocomplexes of platinum(I1). Such complexes having the hydrogen tram to phosphines, pyridines, CO, and RNC groups have been d e ~c r i b e d . ~~~We report the preparation, i.r. spectra, and formation equilibria of some new cationic hydrides of the type tram-[Pt (PEt,),HL]+ where L = AsPh,, SbPh,, thiourea, isopropylamine, and substituted pyridines.

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