Platinum solvation

Several hydrido(phenoxo) complexes of nickel, trans-[NiH(OPh)L2] (6) (a L= P Prs b L = PCys c L = PBnj), have been prepared by the metathesis reaction of NaOPh with trans-[NiHClL2] (Eq. 6.6). The complex 6c was obtained as the phenol-solvated complex whose structure was determined by X-ray analysis [9]. An analogous platinum complex trans-[PtH(OPh)(PEt3)2] (7) was prepared by the reaction of trans-[PtH(N03)(PEt3)2] with NaOPh (Eq. 6.7). The complex 7 is air-stable but thermally sensitive and decomposes at room temperature. The structure was elucidated by X-ray analysis [10]. 

Benkeser and Tincher 128>, on the other hand, reduced acetylenes preferentially to trans olefins using solvated electrons generated at a platinum cathode by electrolytic reduction of lithium chloride in methylamine [lithium metal is formed from lithium ion at the cathode in this electrolysis its dissolution in methylamine generates the solvated electron and regenerates lithium... 

Complex C (Scheme 21) seems to shows stable penta-coordination for apparently very different reasons. The compound is cationic, but the counterion is a non-coordinating tetraarylborate. Interestingly, neither the dichloromethane solvent nor the diethylether present in the reaction mixture seem to coordinate to the open site in solution. The compound was crystallized from a tetrahydrofuran/pentane mixture as the tetrahy-drofuran (THF) solvate, but in the crystal structure, the THF is remote from the open site at platinum. The open site is shielded somewhat by the methyl groups of the protonated TpMe2 ligand, but it does not appear completely inaccessible. A reasonable explanation for the... 

In this flow sheet, the aqueous raffinate from extraction is acidified to 5-6 mol dm with hydrochloric acid to optimize platinum extraction by the solvating extractant TBP. The coextraction of iridium is prevented by reduction with sulfur dioxide, which converts the iridium(IV) to the (III) species, which is not extractable. Once again, kinetics are a factor in this reduction step because, although the redox potentials are quite similar, [Ir(IV)/(III) —0.87 V Pt(IV)/(II) —0.77 V], iridium(IV) has a relatively labile configuration, whereas platinum(IV) has the inert arrangement. The species H2PtCl6 is extracted by TBP, from which platinum can be stripped by water and recovered by precipitation as (NH3)2PtCl2. 

First of all, the important role of platinum as the metal part of the standard hydrogen electrode (SHE), which is the primary standard in electrochemistry should be mentioned. The standard potential of an electrode reaction (standard electrode potential) is defined as the value of the standard potential of a cell reaction when that involves the oxidation of molecular hydrogen to solvated (hydrated) protons (hydrogen ions) ... 

Don S. Martin I want to make some modifications in the data presented by Dr. Basolo. These results were originally reported by me and my group of students. It is the Table I that is quoted in the paper which indicates quite strikingly and correctly, I think, that charge on the ion does not affect the rate of solvation, the replacement of a chloride ligand with platinum (I I) with water. 

Corresponding platinum-containing ions show no shifts in their solution spectra, even when dissolved in strong hydrochloric acid (118) thus the solvation here has a minimal effect on the ligand field. 

When the apparently penta-coordinated diarsine complexes just described are dissolved in solvents more polar than nitrobenzene, they tend to dissociate into halide ions and bivalent cations, thus becoming 2 1 electrolytes (119). The effect is most marked with the platinum compounds. It has been shown that solvation effects might be less with platinum than with palladium, and so, other things in the equilibria being equal, it can also be concluded that the bonding of further ligands by a square-planar complex is much weaker with platinum than with palladium. Square-planar nickel complexes are of course the most ready to take up further ligands. 

C,Hj, Acetic acid palladium complex, 26 208 tungsten complex, 26 224 02CiH(, 2-Propenoic acid, methyl ester platinum ester, 26 138 02C4Hu, Ethane, 1,2-dimethoxy-solvates of chromium, molybdenum, and tungsten carbonyl cyclopentadienyl complexes, 26 343 tungsten complex, 26 50 ytterbium complex, 26 22 02C4Hi, -NaCsHs, Ethane, 1,2-dimethoxy-compd with cyclopentadienylsodium(l l), 26 341... 

In strongly basic solvents like HMPA, amines and liquid ammonia, solvated electrons are relatively stable. In these solvents, if the supporting electrolyte is the salt of Li+ or Na+, blue solvated electrons, esm are generated from the surface of the platinum electrode polarized at a very negative potential ... 

A useful method to probe whether the reaction mechanism involves an associative or dissociative pathway is to measure AV (the volume of activation) for the reaction. High pressure kinetics in methanol give AV 1 —12 cm3 mol-1 for an associative first step, and +7.7 cm3 mol"1 for the isomerization reaction. It is proposed that the faster reaction is a solvolytic replacement of Cl" followed by a dissociative isomerization step with [PtR(MeOH)(PEt3)2]+ (R = alkyl, aryl equation 210).580 Since isomerization and substitution reactions are mechanistically intertwined, it is useful to note here that for the rates of substitution of both cis- and frara,-PtBr(2,4,6-Me3C6H2)(PEt3)2 by I" and thiourea, the volumes of activation are negative, in support of associative processes.581 Further support for associative solvation as the first step in the isomerization of aryl platinum(II) complexes has been presented,582 and the arguments in favor summarized.583... 

W-(2-Aminoethyl)-l,2-diaminoethane (dien) yields complexes [PdX(dien)]X (X = Cl or I) 204,20s a range of solvated complexes may be obtained by reaction of [Pdl(dien)] with AgC104 in the appropriate solvent. As for the platinum analogue, the aqua complex [Pd(dien)(H20)](C104)2 reacts with tetraphenylborate to yield [PdPh(dien)](BPh4). Reaction of the hydroxo complex with carbon monoxide yields C02 and palladium metal is deposited.206... 

The use of solvating extractants in the recovery of gold and platinum-group metals (PGM) was described in the previous section. These extractants have also found some specialized applications in the extractive metallurgy of base metals. For example, they have been used in the recovery of uranium, the separation of zirconium and hafnium, the separation of niobium and tantalum, the removal of iron from solutions of cobalt and nickel chlorides, and in the separation of the rare-earth metals from one another. 

The complex /rara-PtH(02CH)[PEt3]2 catalyzes the decomposition of formic acid in the presence of sodium formate. A mechanism based on the equilibria described in Scheme 2 has been proposed by Paonessa and Trogler (60). The role of formate ion is to promote catalysis by reaction with the platinum dimer (10) or the solvated complex [frans-PtH(S)L2]+, where S = acetone, to reform the catalytically active monomeric species 11 and 12. 

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