Platinum—chlorine bonds reactions with

Alkanes appear to react with platinum(IV) in an identical manner to benzene (34, 84) chloromethane and chloroethane can be detected as the reaction products from methane and ethane, respectively. When propane, butane, or hexane is the reactant, the terminal chloro isomers predominate over the internal isomers. This was interpreted to mean that primary C—H bonds are the most reactive (34), but a more detailed study has shown that this conclusion does not necessarily follow from the experimental results (84). When cyclohexane is the reactant, dehydrogenation (or chlorination and then dehydrohalogenation) occurs to give benzene as one of the reaction products (29, 34, 84). 

The reaction of PtX and liquid ammonia gives mixtures of haloammine complexes [PtX (NH3)6 ]X4 n (X = Cl, Br, I n = 3, 2, 1, 0). The salts Pt(NH3)6]X, may be isolated as the main product only after several weeks of reaction. Interactions at room temperature of PtCl -and PtBr salts with liquid ammonia yield the dinuclear p-amido ammine complex [(NH3)4Pt(/i-NH2)2Pt(NH3)4]X6 quantitatively.1033 The structure shows a Pt-Pt separation of 3.16(1) A. 34 Interaction of PtXg with liquid or gaseous ammonia followed by addition of excess KNH2 yields the hexakis(amido) complex K2[Pt(NH2)6] (equation 333).1033 Complexes of the anionic ligand NC12 bonded to platinum(IV) have also been prepared. One method is by treatment of [PtCl(NH3)s]CI3 with chlorine (equation 334).1035... 

Chloromethane is an important industrial chemical. Olah et al. [56] have reported the selective catalytic monochlorination of methane to chloromethane over superacidic sulfated zirconia solid catalysts, for example 804 /Zr02, Pt/ S04 7Zr02, and Fe/Mn/S04 7Zr02- The reactions were conducted in a continuous-flow reactor under atmospheric pressure. At 200 °C with 30 % chlorine the selectivity to chloromethane was > 90 %.The selectivity could be enhanced by adding platinum. The only by-product was CH2CI2. The latter is formed by the subsequent chlorination of chloromethane. No chloroform or carbon tetrachloride was formed. The authors postulated that chlorination occurs by an electrophilic insertion of an electron-deficient, metal coordinated, chlorine molecule into the C-H bond of methane. One drawback of the process was that above 225 °C, part of the metal was removed as the metal chloride [56]. Formation and subsequent loss of volatile metal chlorides is a major pitfall that should be avoided during vapor-phase chlorination over solid catalysts. 

A proposed mechanism [9] for the hydrosilylation of olefins catalyzed by platinum(II) complexes (chloroplatinic acid is thought to be reduced to a plati-num(II) species in the early stages of the catalytic reaction) is similar to that for the rhodium(I) complex-catalyzed hydrogenation of olefins, which was advanced mostly by Wilkinson and his co-workers [10]. Besides the Speier s catalyst, it has been shown that tertiary phosphine complexes of nickel [11], palladium [12], platinum [13], and rhodium [14] are also effective as catalysts, and homogeneous catalysis by these Group VIII transition metal complexes is our present concern. In addition, as we will see later, hydrosilanes with chlorine, alkyl or aryl substituents on silicon show their characteristic reactivities in the metal complex-catalyzed hydrosilylation. Therefore, it seems appropriate to summarize here briefly recent advances in elucidation of the catalysis by metal complexes, including activation of silicon-hydrogen bonds. 

Reaction of [Pt Au (dppm)2(Ph)Cl]PFg [178] with the chlorine source PhIClj yields [Pt "Au" (dppm)2(Ph)Cl3]PFg, the first Pt(III)-Au(II) heterobimetallic [179]. The reduced complex lacks a metal-metal o-bond, with a platinum-gold distance of 2.9646(3) A. The oxidized complex has a 2.6457(3) A Pt-Au bond. In the presence of an olefin trap, photolysis of [Pt Au (dppmljfPhlClj ] PFg affords reduced [Pt Au (dppm)2(Ph)Cl] (PFg) along with chlorination products of the olefin. Scheme 11.7. 

---