Platinum iv

Reductive elimination followed by oxidative addition has been found for the anation of the /ra 5 -[Pt(CN)4(H20)Cl] ion by bromide ion.  

Miscellaneous Metal Ions.— The rate of reaction of the [UOa] + ion with the metal ion indicator PAR has been measured at pH 1.0—3,9, and the reaction rate varies inversely with [H+]. In this pH range, the dominant pathway is the reaction of [UOa] with unionized PAR. A low pH (2.3— 2,9) has also been used to investigate the rate of the reactions between (M = Eu, Am, or Cu) and cydta by an 

Platinum(iv).— The kinetics of the oxidation of hydroxylamine have been studied in acetate buffers over the range 25—40 °C. The rate increases with decreasing acidity. The stoicheiometry varies with oxidant to reductant ratio but under the conditions used the reaction may be represented by the equation 

The fact that hydrogen ion inhibits the reaction suggests that the unprotonated form of the reductant is probably the active one. A reaction scheme consistent with the data may be expressed as 

The corresponding reaction with hydrazinium ion has been studied under similar conditions. Whereas [H+] has no effect on the rate, sodium perchlorate acts as an accelerator and NaCl as an inhibitor. At pH 4.7, the reductant is in the undissociated form and the rate expression, 

The observation that both Ng and NH4+ are formed is indicative of the platinium(iv) acting as a one-electron oxidant. 

Two papers give information relating to solvent effects in photochemistry of iridium(III) diimine complexes mechanisms of photosubstitution at iridium(III) feature in two review articles. 

There is a brief discussion of kinetics of complex formation of nickel(III) complexes of tetraazamacrocyclic ligands such as cyclam with chloride, bromide, thiocyanate, and sulfate in a review of the synthesis and reactions of nickel(III) complexes.Such reactions are really rather fast—it is at nickel(IV) that slow substitution may be expected, if not obscured by rapid oxidation of ligands. 

There is some discussion of interconversion mechanisms in complexes of the type [Pt(IV)(amino acid)L2XY] , where L2 = en or (NH3)2 and X and Y are taken variously from CF, Br , OH , and OH2, in an article on ring formation and alkaline hydrolysis. 

Substitution Reactions—Nos. 6 and Above Other Inert Centers 

The first example of pseudobase formation with coordinated pyridine, as opposed to 2,2 -bipyridyl or 1,10-phenanthroline and their derivatives, has been suggested for the reaction in equation (6). This claim has been 

The rate constant for aquation of [Pt(NH3)5(0S02CF3)] is 2.1 x 10 s at 298 [Pt(NH3)5(OS02)] reacts slowly with sulfite to give 

In continuation of recent studies on conjugate bases of ammine and amine complexes of metal(III) ions, the dinuclear species (52) has been fully characterized in the solid state (X-ray diffraction), and almost proved ( N NMR) to exist in solution. A speculative mechanism for its formation in solution has been proposed. The photoreactivity of [Pt(NCS)6f has been ascribed to its lowest ligand field excited state. Quantum eflBciency and intersystem crossing probability have been discussed.  

Complex Formation Involving Unsubstituted Metal Ions Unidentate Ligands and Solvent Exchange 

Both inversion at sulfur and 1,3-metal shifts can be monitored by NMR in the related metal(O) carbonyl complexes [M(CO)5(MeSCH2SMe)] and [M(CO)5(MeSCH SMe SMe)], as can inversion at sulfur in dihydrothiophen derivatives such as [W(CO)5(dht)], [Re(CO)5(dht)], and [PdCl2(dht)2]. a somewhat different form of intramoleculat motion is provided by the so-called 

8 Inert-Metal Complexes Other Inert Centers 

The vast majority of fast ligand substitutions studied to date are in the s, ms, and fjLS time scales, which encompass a vast range of reactions, and for which fast reaction techniques have become both refined and readily commercially available. Not surprisingly the majority of reactions reported in this chapter fall into these time scales, and have been studied predominantly by stopped-flow, temperature-jump, or nuclear magnetic resonance fast reaction techniques, which are referred to by the initials SF, TJ, and NMR hereafter. However, substantial rewards await those who venture into the ns and ps time scale as shown by a study of the recombination kinetics of small ligands at the Fe(II) center of sperm whale and elephant myoglobins in which laser pulses of 1 ps and 4 ns facilitated the determination of rate constants in the range 3 x 10 to 5 x s and 10 to 10  

Slower processes occurring in the /as time scale were also studied by flash photolysis. Interpretation of the kinetic data requires a four-state model shown in equation (4) where MbL represents myoglobin with the small ligand bound at six-coordinated Fe(II), Mb L (generated by photodissociation) represents the short-lived 

At lower temperatures, these cis and trans complexes exhibit inversion at the coordinated sulfur atoms, as do the complexes [MX2 MeS(CH2) CH=CH2 ] where M = Pt or Pd, and n = 2 or Inversion at sulfur in thioether complexes of platinum(II) has been documented, and an example of such inversion at rhodium(III) was mentioned in Section The whole area of fluxional 

Ligand Substitution on Complexes of Uni- and Bivalent Metal Ions 

Vanadium(v) ( / ).—Reaction of (HVO.,) with the metal ion indicator l-(2-pyridylazo)-2-naphthol (pan) has been studied by a stopped-flow method in the presence of charged micelle-forming compounds such as tetradecyldimethyl-benzylammonium chloride (A) and hexadecylpyridinium chloride (B). In a solution of pan in (A), it is believed that pan is in the neighbourhood of the charged micelle surface and aligns its chelating group with that surface. The reaction in the presence of (B) is faster than in the presence of (A).  

A novel high-pressure stopped-flow study of the reaction of [V02(nta)] ion with H2O2 has been reported. From studies between pH 2.2 and 4.2, = 

Jones and M. V. Twigg, Inorg. Chem., 1969, 8, 2120 Inorg. Nuclear Chem. 

Dimerisation.—The mechanisms of dimerisation of iron(m), vana-dium(iv), and uranium(vi) in aqueous solution have been deduced from stopped-flow studies of the kinetics of dissociation of [FeOH]2 +, [VO(OH)]a +, and [U02(0H)]a +. In each case, formation takes place through reactions of the type UOa + UOa(OH)+ - U0a(0H)U02 .  

Rates of formation, and of dissociation, of dimeric iron(m) complexes of cydta, edta, and hedta have been determined as a function of pH. This represents a contribution to the knowledge of the kinetic behaviour associated with M-O-M and M-OH-M systems, to complement the long-known thermodynamic properties of such complexes. T-Jump studies of the dimerisation of iron(m)-edta show one relaxation, ascribed to the equilibrium 

The left to right direction appears to be dissociative in nature.  

Borghi, F. Monacelli, and T. Prosper , Inorg. Nuclear Chem. Letters, 1970, 6, 667  

Aquation rates increase in the order chloride bromide iodide, which is the opposite order of reactivity to that observed for the platinum(u) complexes [Pt(NH8)2Xa]. The order of reactivity of the platinum(iv) complexes reflects a connection between lability and reducing power of the halide ligand. A polarographic study of the reaction of [PtClgCOHa)] with nioxime indicates rate-determining loss of water followed by reduction to platinum(n) the product is [Pt(nioxH)2Cl2]. The activation parameters are = 19.3 kcal mol and AS = —19.2 cal mol deg. Irradiation of aqueous solutions of [Pt(NHs)4(NH2)(N02)] + results in photoisomerization to the nitrito-complex and redox reactions, as well as photoaquation with replacement of the nitro-ligand. Quantum yields are reported, but no kinetic results.  

Langford and V. S. Sastri, in Reaction Mechanisms in Inorganic Chemistry , cd. M. L. Tobe, M.T.P. International Review of Science, Butterworths, London, 1971, Series 1, Vol. 9, p. 240. 

This mechanism parallels that proposed earlier for the aquation of nitrito-cobalt(m), -rhodium(ra), and -iridium(ni) complexes in acid media.  

The rate constant for, and extent of, chloride anation at [Pt(bipy) (tach)(OH2)], tach = (79), have been determined in 0.2 mol dm DCl 

It is customary to include references to inversion at sulfur coordinated 

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For more selective hydrogenations, supported 5—10 wt % palladium on activated carbon is preferred for reductions in which ring hydrogenation is not wanted. Mild conditions, a neutral solvent, and a stoichiometric amount of hydrogen are used to avoid ring hydrogenation. There are also appHcations for 35—40 wt % cobalt on kieselguhr, copper chromite (nonpromoted or promoted with barium), 5—10 wt % platinum on activated carbon, platinum (IV) oxide (Adams catalyst), and rhenium heptasulfide. Alcohol yields can sometimes be increased by the use of nonpolar (nonacidic) solvents and small amounts of bases, such as tertiary amines, which act as catalyst inhibitors. 

Procedure To an aliquot of the sample solution containing 12.5 - 305 p.g of platinum(IV) were added 5 ml of hydrochloric acid - sodium acetate buffer of pH 2.1, 1 ml of O.IM Cu(II) sulphate solution, and 3.0 ml of 0.5% propericiazine solution. The solution was diluted to 25 ml with distilled water, mixed thoroughly, and the absorbance measured at 520 nm against a reagent blank solution after 10 min. The platinum concentration of the sample solution was determined using a standar d calibration curve. 

Consequent potentiometric titration of osmium(IV) and laithenium (IV) in their mixtures has been canied out in broad range of concentrations from 1 mkg to 200 mkg in samples of 20 ml. It has been shown the possibility of amperemetric determination of osmium(VI) in binary and triple systems with silver(I), platinum(IV), palladium(II), gold(III), founded on formation of corresponding compounds with dimerkaptotiopiron, having a different solubility. The deteriuination of Os(VI) is possible under tenfold - hundredfold excess of above mentioned metals. 

COMPARATIVE SORPTION OF GOLD(III), PLATINUM(IV) AND PALLADIUM(II) ON VARIOUS ORGANOPOLYMERIC... 

We have conducted the comparative study of gold (III), platinum (IV) and palladium (II) acidocomplexes solution on macroporous granular sorbents on the basis of polystyrene with functional groups of methyleneamine, 3-methylpyrasolyl, N,N-dimethylaminomethylene, dimethylmethylene-P-oxyethylamine and with functional 6-(3-methylpyridine) groups on polyvinylpyridine basis as well as fibrous polystyrene sorbent with pyrazolyl groups. 

Gold (III) and palladium (II) are sorbed quantitatively on all studied sorbents, except for methyleneamine, from solutions 0,2-2 M HCI. The degree of platinum (IV) complex extraction substantially depends not only on the nature of sorbent functional groups, but also on geometrical parameters of the matrix. This factor influences gold (III) and palladium (II) soi ption to a lesser extent. 

MEMBRANE EXTRACTION AND SEPARATION OF COPPER(II) FROM PLATINUM(IV) BY DI(2-ETHYLHEXYL)PHOSPHORIC ACID DURING ELECTRODIALYSIS... 

The copper(II) flux is directly proportional to the cuiTent density up to 10 mPJcrcf. The extraction degree of platinum(IV) into the strip solution is less than 0.1 % per hour of electrodialysis. About 55% of copper(II) is removed from the feed solution under optimal conditions. The copper(II) extraction process is characterized by high selectivity. Maximum separation factor exceeds 900 in the studied system. 

The copper(II) transport rate increases, as a rule, as Cu + initial concentration in the feed solution increases. The increase of the caiiier s concentration from 10 to 30 vol.% results in a decrease of both metal fluxes and in an increase of Cu transport selectivity. The increase of TOA concentration in the liquid membrane up to 0.1 M leads to a reduction of the copper(II) flux, and the platinum(IV) flux increases at > 0.2 M. Composition of the strip solution (HCl, H,SO, HNO, HCIO, H,0)does not exert significant influence on the transport of extracted components through the liquid membranes at electrodialysis. 

Differences are also observed in the reactivity of platinum(II) complexes of [82X2] and [802X2] towards halogens. In the former case oxidative addition to give platinum(IV) complexes occurs, with retention... 

Also in the divalent state, Pd and Pt show the class-b characteristic of preferring CN and ligands with nitrogen or heavy donor atoms rather than oxygen or fluorine. Platinum(IV) by contrast is more nearly class-a in character and is frequently reduced to Pt by P- and Aj-donor ligands. The organometallic chemistry of these metals is rich and varied and that involving unsaturated hydrocarbons is the most familiar of its type. 

Platin-hydroxyd, n. platinum hydroxide, specif, platinic hydroxide, platinum(IV) hydroxide, -hydroxydul, n. platinous hydroxide, plati-num(II) hydroxide. 

Platini-, platinic, platini-, platinum (IV). -chlorid, n. platinic chloride, platinum (IV) chloride, -chlorwasserstoff, m., -chlorwasserstoffsaure, /. chloroplatinic acid, chloroplatinic (IV) acid, -cyanwasserstoffsaure, /. cyanoplatinic acid, cyanoplatinic(IV) acid, platinicyanic acid. 

Platini-rhodanwasserstoffsaure, /. thiocyano-platinic acid, thiocyanoplatinic(IV) acid, -salz, n. platinic salt, specif, platinum (IV) salt, -selencyanwasserstoffsaure, /. selen-ocyanoplatinic acid, selenocyanoplatinic(IV) acid, -verbindung, /. platinic compmmd, specif, platinum (IV) compoimd. 

Platin-oxyd, n. platinum oxide, specif, platinic oxide, platinum(IV) oxide. -oxydul, n. platinous oxide, platinum(II) oxide, -oxy-dulverbindung, /. platinous compoimd, platinum (II) compound, -oxydverbindung, /. platinic compound, specif, platinum (IV) compound. 

Complete reduction of the azepine ring to hexahydroazepine has been effected with hydrogen and palladium,40 or platinum,135 239 catalysts. For example, ethyl 1 f/-azepine-l-carboxylate is reduced quantitatively at room temperature to ethyl hexahydroazepine-l-carboxylate (92% bp 118 —120 3C).134 136 TV-Phenyl-S/Z-azepin -amine (1), however, with platinum(IV) oxide and hydrogen in methanol yields the hexahydroazepine 2 in which the amidine unit is preserved in the final product.34 The same result is obtained using 5% palladium/barium carbonate, or 2 % palladium/Raney nickel, as catalyst. 

Reductions of 5//-dibenz[/j,/]azepines to their 10,11-dihydro derivatives have been accomplished in high yield with sodium in ethanol,29 133 with copper(II) chromite (2CuO Cr203) and barium carbonate,224 with 5 % palladium on charcoal29 or platinum(IV) oxide30 in ethanol, and with magnesium in methanol.225 4//-Thieno[3,2-/)][1]benzazepine is reduced similarly with hydrogen and palladium on charcoal in ethanol.137... 

Dinuclear platinum(IV) complexes have recently been reported ... 

On heating, the neopentyl Pt(PEt3)2(CH2CMe3)2 undergoes an intramolecular metallation elimination [108a] (Figure 3.59), which appears to involve initial phosphine loss affording a platinum(IV) metallacycle. 

The suggested mechanism involves breaking of a platinum-ligand bond, again forming a platinum(IV) hydride that can then eliminate the alkane. 

Since n bonding is believed to be more important in low oxidation states, as d orbitals contract with increasing oxidation state leading to poorer dw-pw overlap, this would not be expected on the basis of a 7r-bonding mechanism. Similarly, one can compare /(Pt-P) for pairs of isomers in the +2 and +4 states in a planar platinum(II) complex, the platinum 6s orbital is shared by four ligands whereas in an octahedral platinum(IV) complex it is shared by six ligands. Therefore, the 6s character is expected to be only 2/3 as much in the platinum(IV) complexes, correlating well with the 7(Pt-P) values, which can be taken to be a measure of the a-character in the bond. 

Support for this view is found in the I95Pt-15N coupling constants for dodecylamine complexes of platinum(II) and platinum(IV), where 7r-bonding cannot of course occur, which exhibit similar trends (Table 3.24) [156]. 

Platinum(IV) forms complexes with a range of ligands [1, 2, 10, 11]. 3.10.1 Complexes of N-donors... 

The full range of platinum(IV) ammines can readily be prepared [162]. 

Platinum(IV) ammines react with diketones to give diimmines, a reaction proceeding via deprotonation of one ammonia [167],... 

The platinum(IV) ammines studied in most detail recently [168] have been hydroxy species (Figure 3.100). 

Figure 3.100 Bond lengths in platinum(IV) ammine hydroxy complexes.

Another platinum(IV) ammine complex studied as a possible anti-tumour compound is shown in Figure 3.101 [171] m-(l,2-diaminocyclohexane)tetra-chloroplatinum has undergone clinical trials but was found to be too neurotoxic. 

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 ... 

Some platinum(IV) hydride complexes have been synthesized in situ (Figure 3.103). 

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