Cesium dimethyltetrachloroplatinate, a complex of dimethylplatinum(IV). Synthesis and some reductive elimination reactions involving the monomethylplatinum(II) complex as an intermediate

Competitive Oxidation and Protonation of Aqueous Monomethylplatinum(II) Complexes: A Comparison of Oxidants

“…Competitive Oxidation and Protonation at Elevated Temperature: Cu-Mediated Oxidation by O 2 . Zamashchikov and co-workers determined the relative rates of protonolysis and oxidation of [Pt II (CH 3 )Cl 3 ] 2-(1) by means of the system shown in Scheme 3 7 Here nucleophilic attack of chloride on the dimethyl complex [Pt IV (CH 3 ) 2 Cl 4 ] 2-(2) generates 1 (along with an equivalent of methyl chloride), which is competitively protonated to generate methane and [Pt II As shown in Scheme 3, there are two side reactions. Nucleophilic attack by [Pt II Cl 4 ] 2on 2 generates 1 and 3; however, this has no net effect on the final product distribution.…”

“…Assuming the reaction is first-order in both oxidant and 1, as is the case for Na 2 [Pt IV Cl 6 ], the ratios of the "observed" rate constants for formation of CH 3 Cl versus methane (k MeCl /k MeH ) and the second-order rate constants for oxidation versus protonation (k ox /k H+ ) are found using eqs 2 and 3, respectively, where n is the number of moles of the corresponding species. 7 The results for several different oxidants are shown in Table 1; that for Na 2 [Pt IV Cl 6 ], 20 ( 4, is within experimental error of the previously reported value. As noted above, the calculation assumes first-order dependence on reagent concentration.…”

“…Under these reaction conditions CH 3 Cl substantially decomposes (to CH 3 OH) and cannot be accurately quantified; nonetheless the extent of competing oxidation (when an oxidant is present) can be calculated from the reduction in methane yield. Assuming the reaction is first-order in both oxidant and 1 , as is the case for Na 2 [Pt IV Cl 6 ], the ratios of the “observed” rate constants for formation of CH 3 Cl versus methane ( k MeCl / k MeH ) and the second-order rate constants for oxidation versus protonation ( k ox / k H + ) are found using eqs 2 and 3, respectively, where n is the number of moles of the corresponding species …”

“…4 Isotopic labeling experiments have placed an upper limit on the rate of the self-exchange reaction between tetrachloroplatinate(II) and hexachloroplatinate(IV) 5 that would be much too slow to compete with protonolysis. Nonetheless, two studies have demonstrated that the rate constant for oxidation of [Pt II -CH 3 ] is comparable to (at room temperature) 6 or much faster than (at 95 °C) 7 the competing protonolysis. The reasons for this great enhancement of reactivity are not entirely clear; possible factors include the lower oxidation potential of methylated Pt(II) complexes and/or the lower energy required for formation of the five-coordinate species as a consequence of the greater cis-and trans-effects of a methyl ligand.…”

Reductive Cross-Electrophile C(sp2)–C(sp3) Coupling Catalyzed by PtI2: In Situ Structural Determination of the Intermediates by X-ray Absorption Spectroscopy and Multinuclear NMR

“…Indeed, as shown earlier, 43,44 the dimethyl platinum(IV) complex [Pt(Me) 2 Cl 5 ] 2− almost fails to give the C−C coupling product, ethane: even upon heating to 95 °C in aqueous solutions, the main decomposition products of the [Pt(Me) 2 Cl 5 ] 2− complex were methane and methyl chloride. 43 Similarly, no C(sp 3 )−C(sp 3 ) coupling was detected from bis-acetonyl and bis-carboxymethyl platinum(IV) com- plexes in acetone solutions of NaI. 20 These experimental data are in line with theoretical predictions for the largest barrier for the C(sp 3 )−C(sp 3 ) reductive elimination elementary step in the series C(sp 3 )−C(sp 3 ) > C(sp 2 )−C(sp 3 ) > C(sp 2 )− C(sp 2 ).…”