Complexes of Platinum IV

Platinum(IV) forms complexes with a range of ligands [1, 2, 10, 11]. 

---

Reaction of iodine with Pt(phen)Cl2 gives compounds with the unusual stoichiometries Pt(phen)I (a = 5,6) these contain Pt(phen)I4 molecules and free iodine molecules in the lattice. Pt(bipy)I4 has also been made [172], Macrocyclic complexes of platinum(IV) are readily made by oxidation ... 

The most important of the tertiary phosphine complexes of platinum(IV) are Pt(QR3)2X4, generally prepared by halogen oxidation [174] of cis- or trans-Pt(QR3)2X2 (Q = P, As, R = alkyl Q = Sb, R = Me), since direct reaction of the platinum(IV) halides with the ligands leads to reduction. Once made, the platinum(IV) compounds are stable to reduction ... 

The first reported porphyrin complexes of platinum(IV) date from 1980 and were obtained by hydrogen peroxide oxidation of platinum(II) porphyrin complexes in an acidic medium (HC1).479 Since then oxidation of platinum(II) complexes of other porphyrins has been achieved by the same method,480 and by chlorine,481 or bromine482 oxidation. Reaction with iodine did not lead to oxidation and treatment of platinum(IV) porphyrin complexes with iodide resulted in reduction to platinum(II). 

However, in our experiments the complex of platinum (IV) with KI, K2[PtIg], was not affected by 1 h of sonication, probably because of the low concentration and inert nature of the metal ion involved and the relatively weak power of the ultrasound (20 kHz, 6 W/cm2). 

Section III.C A Hydrido(methyl)carbene Complex of Platinum(IV) (223) and Methyl(hydrido)platinum(IV) Complexes with Flexible Tridentate Nitrogen-Donor Ligands (224) are structurally related to the system shown in Scheme 13 and give additional information on how steric and electronic factors influence the stability of platinum(IV) methyl hydrides. 

PtBrs (arsine) 2, which are octahedral complexes of platinum(IV) in which the olefinic side chains of the ligands have been fully brominated. An alternative and more realistic formulation of these compounds is PtBr4 (arsine Bre) 2- These same compounds are formed by reaction of an excess (> 3 equivalents) of bromine with the original platinum(II) compounds. 

Both hydride cind jr-allyl complexes of these metals are well known in the -f-2 oxidation state (60), but neither hydride nor r-allyl complexes of platinum(IV) are known. 

Carbonyl halide complexes of platinum(IV) are less common. The reaction of [Pt(CO)2]s with chloride ion in an aqueous solution of iron(HI) ions gives Pt(CO)H2Cl2, which adds chloride to give Pt(CO)H2ClJ.313,314 Addition of chlorine to a thionyl chloride solution of Pt(CO)2Cl2 at room temperature results in the rapid formation of Pt(CO)Cl (equation 106), which shows a carbonyl stretch at 2191 cm-1. The yellow-orange compound is stable toward Cl- but reacts with water to form C02.315... 

An unusual tetrazene complex of platinum(IV) is obtained from tra/ts-Pt(C CPh)2(PEt3)2 and 4-nitrophenylazide (equation 371).1209 The structure has been verified by crystallography. The analogous platinum(Il) complexes can be formed by reacting Pt(cod)2 with aryl azides followed by triethylphosphine.1210 The complexes with non-symmetrical RN4R ligands are also known.1211... 

Oxygen-bonded sulfito complexes of platinum(IV) can be prepared by the reaction of aqueous sulfite with [Pt(NH3)5(H20)]4+ to give the O-bonded sulfito complex [Pt(NH3)5(0S02)]2+. This compound rearranges to the S-bonded sulfite complex, or at elevated temperatures in addic solution a single-step two-electron reduction occurs to yield a platinum(II) complex Pt(S03)(NH3)3 (equation 480).1631 The O-bonded sulfite complexes show a series of IR bands in the range 460-960 cm-1.1632... 

In the recent time, a great interest was aroused for platinum IV compounds. The scientists-organochemists of the Institute of Theoretical Problems of Chemical Physics synthesized complexes of platinum IV with aminonitroxyl radicals. These compoimds were tested on the experimental model of P-388 leukemia. In the experiments, the complexes exhibited a strong effect on mice-leukemia-carriers sometimes to complete recovery the toxicity reduced two- to four-fold [70]. 

The most impressive results were obtained for low doses of cisplatinum and complexes of platinum IV with amino nitroxyl radicals applied in combination for treatment of P-388 leukemia. The survival rate for leukemia mice was 100%. As was noted above, nitroxylation of antitnmor componnds was successful. There are some other examples of application of hybrid compounds containing nitroxyl radicals in their molecules. 

The complexes of platinum(IV), less well known than those of platinum(II), can be prepared by oxidation of the latter. Such a conversion often proceeds with retention of configuration. Early workers reported that halogenation of either cis- or irans-dihalobis(dialkyl sulfide)platinum(II) resulted in only one product. The compound obtained by Loir and R y and Bose-R y by treating diethyl sulfide with aqueous or alcoholic H2[Pt(OH)2Cl4] was probably mainly the trans isomer. The preparation given here, based on the work of Angell, Drew, and Wardlaw, involves the chlorination of cis- and benzene solution. In this nonpolar solvent, isomerization is minimized. 

It should be noted that complexes of types VII-5 or VII-7 can be easily prepared by the method initially described in [30a-d], The chloride complex Pt"Cl4 - reacts at room temperature in aqueous solution with alkyl iodide to produce a o-alkyl complex of platinum(IV). Methyl [30a], ethyl [30b,c], and acetonyl [30d] complexes of Pt(IV) have been prepared by this method. An interesting feature of the reaction is that the sixth coordination site in the octahedral molecule of the product is occupied by water, while the T ion is bound to another molecule of the platinum(II) complex (Ptlj and analogous products are formed and precipitate) ... 

The experimental data reported in the previous sections leave no doubt of the intermediate formation of aryl and alkyl platinum derivatives in the reactions of Pt(ll) and Pt(IV) chloride complexes with arenes and alkanes in aqueous solutions. In the 1980s, it was discovered that the reaction of H PtCCwith arenes in aqueous carboxylic acids produces stable a-aryl complexes of platinum(IV) which can be isolated in crystalline form (see, for example, [43]). 

Heating a solution of HjPtCU and an aromatic compound ArH in the CF3COOH-H2O mixture or in CH3COOH leads to the formation of fairly stable CT-aryl complexes of platinum(IV) in yields up to 95%, which can be isolated in the form of anionic adducts with ammonia after chromatography on sihca gel containing ammonia [43, 44] ... 

On prolonged heating, the complexes decompose [43, 44d] to produce biaryls, chlorinated arenes and platinum(II) derivatives. The process of formation of the CT-tolyl complex of platinum(IV) is accompanied by its para-meta isomerization [43, 44e, 47], If in the initial instant the substitution takes place mainly (to extent of 90%) in the />ara-position in toluene, then the statistical distribution metaipara = 2 1 is gradually attained (Figure VII.4). 

The reaction of H2PtCls with anisole in CF5COOH-H2O (9 1) at 85 °C produces the o-mcthoxyphenyl complex of platinum(IV) which decomposes to give 4,4"-dimethoxybiphenyl and, after an induction period, a smaller amount of 2,4 "-dimethoxydiphenyl (Figure VII.6) [48b],... 

---