Platinum, halide complex salts

The halide complex salts of platinum, chloroplatinites and chloroplatinates, are highly reactive with proteins, with particular affinity for sulphydryl bonds. They can also be histamine liberators (Parrot et al. 1967,1969). These salts thus represent a polar example of a chemical molecule with most of the features which complicate study as allergens. Many of the problems have been resolved and the findings will be given in extenso . Examples of the relevant platinum salts (molecular weight 444 daltons) are ammonium hexachloroplatinate (NH4)2 [Pt Cl ] and te-trachloroplatinate (NH4)2 [PtCm. 

Many of the synthetic routes parallel those used to prepare alkene complexes c platinum(II). Replacement of chloride ion in PtClJ- by a water soluble alkyne is a frequentl used method (equation 266), 809 812 or the reaction can be assisted by the use of a silver salt t facilitate halide displacement (equation 267).813 With hexafluorobutyne-2 the five-coordinat adduct can be isolated before it converts into the vinyl complex (89 equation 268).814 Alkyne displace alkenes from platinum(ll) complexes. 

Platinum(II) halides react with cyanate salts to give cyanato complexes. Reacting the compounds Pt(NCO)4 with triphenylphosphine gives Pt(NCO)2(PPh3)2.1628 These platinum(II) complexes are N-bonded. Treatment with carbon monoxide and alcohol yields the complex (172 equation 476).1629... 

Divalent and tetravalent Pt probably form as many complexes as any other metal. The platinum(II) complexes are numerous with IV. S, halogens, and C. The letranitritoplatinum complexes are soluble in basic solution. Tetranitntoplatinum(II) ion is formed when a solution of plat-inum(II) chloride is boiled, at about neutral pH, with an excess of NaNO f. The ammonium salt may explode when heated. Generally, platinum-metal nitrites should be destroyed in solution. They never should be heated in the dry form. Pladnum(II) complexes most often have a coordination number of 4. Many compounds have been prepared with olefins, cyanides, nitriles, halides, isonitnles, amines, phosphines, arsines, and nitro compounds. 

Vacating a coordination position by halide abstraction with silverfl) salts triggers the decarbonylation of platinum(II) complexes e.g. ... 

By far the most frequently used method is the deprotonation with potassium tert-butoxide, which gives the potassium salts in nearly quantitative yields. The method seems to be usable for any bis(chalcogenophosphinyl and -phosphoryl)imide and has been employed for a broad diversity of derivatives, regardless of the nature of the chalcogen.2,26,30,33,36-38,49,89,91,99 If the salts are needed for further use in reactions with metal halides to form complexes, the potassium salt can be used in situ, without isolation, e.g., with zinc(II) chloride or palladium and platinum chloro complexes.41,43 Potassium metal in THF also forms the salt K[SPh2PNPPh2S] in 82% yield, 38 but the method is not practical for preparative purposes. Potassium-crown ether complexes, [K(18-crown-6)][Q1Ph2PNPPh2Q1] with Q1 = O,92 Q1 = S,93 and Q1 = Se,98 have been prepared by direct complexation of the potassium salt with the macrocyclic ligand. 

The possible role, in allergenic potency for eliciting reactions, of the leaving chlorine ligands needs to be examined here, as has been done with the halide complex platinum salts (see Sect. B.I) and as also seems indicated for amprolium hydrochloride (see Sect. C.I). 

In order to determine the most favorable reaction conditions, the following parameters were studied (a) the influence of reaction time upon the product (b) the influence of added halide upon the product and (c) the influence of the molar ratio of platinum(II) complex to IBr salt upon the product. 

Among the second- and third-row transition metal halide complexes, those of platinum have received considerable study. Both the octahedral platinum(IV) complex PtCli and the square planar platinum(II) complex PtCl have been investigated. Both complexes are substitution inert under thermal conditions, and kinetic studies of their substitution chemistry have been important in the development of a general understanding of the mechanisms of substitution reactions in transition metal chemistry. The photochemistry of PtCli" was one of the earliest such studies to be made, and the early discoveries of the photosensitive nature of platinum halides led to these salts being used in photographic processes. The subsequent decision to use a silver-based process was based more on economical rather than on technical reasons. 

Iridium(IV) complexes are less common when compared to Ir111 or Ir1. There are examples of N, P, As, Sb, O, S, Se, Te, and halide ligands, often prepared by oxidation from an Ir111 salt. Recent developments (in 1991) in the chemistry of the platinum metals in high oxidation states were addressed by Levason, including complexes of IrIV and Irv.25... 

Dithiophosphato metal complexes are usually prepared by metathesis of metal halides with alkali metal or ammonium salts. A convenient method uses the redox reaction of his th iophosphory 1 )d is ulfanes (RO)2(S)PSSP(S)(OR)2, with metal species in low oxidation states resulting in the insertion of the metal into the sulfur-sulfur bond.24 Recently it was used for the synthesis of long alkyl chain, liquid platinum(II) dithiophosphates25 and for the synthesis of Ru (CO)2[S2P(OPr%]2 from Ru3(CO)i2 with (Pr 0)2(S)PSSP(S)(0Pr,)2.26... 

Synthetic organic chemistry applications employing alkane C-H functionalizations are now well established. For example, alkanes can be oxidized to alkyl halides and alcohols by the Shilov system employing electrophilic platinum salts. Much of the Pt(ll)/Pt(rv) alkane activation chemistry discussed earlier has been based on Shilov chemistry. The mechanism has been investigated and is thought to involve the formation of a platinum(ll) alkyl complex, possibly via a (T-complex. The Pt(ll) complex is oxidized to Pt(iv) by electron transfer, and nucleophilic attack on the Pt(iv) intermediate yields the alkyl chloride or alcohol as well as regenerates the Pt(n) catalyst. This process is catalytic in Pt(ll), although a stoichiometric Pt(rv) oxidant is often required (Scheme 6).27,27l 2711... 

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