Potassium tetrachloroplatinate reaction

Heretofore, the most common method for the preparation of the useful platinum(II) complexes of the type [PtCl2L3], where L is a tertiary phosphine, consisted of the reaction between potassium tetrachloroplatinate(II) and tertiary phosphines.1 When trialkylphosphines are used, the reaction usually leads to a mixture of cis- and trans isomers,2 3 and when triaiylphosphines are employed4 only the cis isomers are obtained. The preparation of pure trans complexes by a simple, convenient procedure is highly desirable. 

A 150-mL beaker or Erlenmeyer flask is filled with a solution of 0.566 g (1.36 mmol) of potassium tetrachloroplatinate(II), K.2[PtCl4] (purchased from Aldrich), in 60 mL of water and placed on a magnetic stirrer. A solution of 1.878 g (3.27 mmol) of [ (CeHs P NJCl (purchased from Aldrich) dissolved in 10 mL of ethanol is added dropwise from a 25-mL dropping funnel over a period of 10 min. A pink precipitate appears immediately after addition of the first few drops. After complete mixing, the reaction mixture is stirred at 20-25°C for 15 min. The fine-grained pink precipitate is collected on a Millipore filter (type HV, 0.45 pm other small-pore glass or paper filters can be used as well) or separated by centrifugation, washed three times with 3-mL portions of water, and dried in air at 80-90°C. 

Cisplatin, an anticancer agent used for the treatment of solid tumors, is prepared by the reaction of ammonia with potassium tetrachloroplatinate ... 

The original method1 of preparation of Zeise s salt, K[Pt(C2 H4 )C13 ]-H20, and subsequent modifications thereof2-4 all require either prolonged reaction times (7-14 days) or the use of high pressures. Furthermore, these procedures tend to yield products contaminated with potassium chloride and unreacted potassium tetrachloroplatinate(II). The improved procedure described below, which utilizes tin(II) chloride to catalyze the reaction between ethylene and the tetrachloroplatinate(II),5,6 results in the formation of Zeise s salt of high purity and in high yield within a few hours at atmospheric pressure. 

Similar reactions occurred with potassium tetrachloroplatinate(II) and with bis[triphenylphosphane] dichloroplatinum5. 

The cyclization of methyl-substituted 4-alkenylamines 2, 4, and 6 catalyzed by potassium tetrachloroplatinate(II) gave diastereomeric mixtures of the corresponding pyrrolidines 3, 5 and 7. The diastereoselectivity was satisfactory for 7 (1,2-asymmetric induction), but the reaction is too slow to be synthetically useful48. 

Fig. 18. Apparatus for the reaction of potassium tetrachloroplatinate(II) with ethylene.

The preparations given here for the cis and trans isomers are modifications of the methods of Ramberg and Peyrone, respectively, and involve a minimum of side reactions. Both methods involve the preliminary preparation of potassium tetrachloroplatinate(II), which need not be isolated. 

Reaction conditions Potassium tetrachloroplatinate (2.00 mmoles) dissolved in 10 mis of doubly distilled-deionized water added to a solution containing the nitrogen-containing reactant (2.00 mmoles) coatained in 10 mis of water at 25 C with stirring for 3 days. 

Carbene complex 138 has been isolated under considerably less extreme conditions/" The air and water stable complex 138 is isolated from the reaction of potassium tetrachloroplatinate with a free pyridine in ethanoic acid, even though a cyclometallated complex coordinated to the platinum through a nitrogen might have been anticipated. In principle, the carbene structure of 138 could be redrawn as the ionic structure 139 (Scheme 34) however, a short Pt-G distance of 1.952(7) A in the X-ray structure and a solution G chemical shift of 324 ppm for the carbon bonded to platinum confirms that carbene form 138 more accurately represents the molecular form present. 

Some reductants are rarely used in preparative coordination chemistry and others have only limited application. Such reductants are discussed here. Hydrazine and its salts are strong reductants capable of generating noble metals from their coiriplexes. However, if the amount of reductant is carefully controlled, the metal center in a noble metal complex can be reduced to a lower oxidation state. For example, the synthesis of potassium tetrachloroplatinate(II) by reduction of K2[PtCl6l with hydrazine sulfate, N2HfH2S04, is well known. Grinberg has shown, 63 in his classic experiments, that the reaction mechanism involves the formation of platinum black which reacts with potassium hexachloroplatinate(IV), Eq. 9.46 ... 

The treatment of many metal salts either in solution or in the solid state may give smooth addition of the olefin to the complex. The famous Zeise s salt, first isolated in 1827 [16], is prepared by bubbling ethylene through an aqueous solution of potassium tetrachloroplatinate(Il) from which the yellow crystals of the complex, K+[C2H4PtCh]".H20, are precipitated. The reaction is catalysed by tin(Il) chloride [17], The bis-ethylene rhodium complex, 1.1, is similarly prepared [18]. 

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