Platinum complexes base hydrolysis

Any detailed description of the mechanism of an octahedral substitution must also account for the stereochemical changes that accompany reaction. Werner recognized this and made use of it in his discussions of the stereochemistry of reactions of cobalt(III) complexes. The available experimental results can be explained on the basis of possible molecular rearrangements and some cautious predictions can even be made. The base hydrolysis of cobalt III)ammines appears to be unique in that it often occurs with rearrangement it also affords the few known examples of optical inversion. These results can be explained by formation of a 5-coordinated species with a trigonal bipyramidal structure. Optically active metal complexes racemize by either an intramolecular or an in-termolecular process. Substitution reactions of platinum metal complexes often occur with retention of configuration. 

Urea hydrolyzes about 3 x 10 times faster coordinated to [Rh(NH3)5] than in the uncoordinated state. This is a marked acceleration, but still very much less than the promotion of base hydrolysis of acetonitrile by [Ru(NH3)5] (cf. Section 8.3.2). Formation and aquation reactions of carbonato complexes are often coordinated ligand reactions, involving C-0 rather than Rh-0 bond formation and breaking. "" " Inversion at coordinated sulfur has an activation barrier (AG ) of 87.3 and 85.5 kJ moP in d(,-DMSO (at 383 and 378 K, respectively) in the dithiahexane complexes [Rh(dth)Cl4] and [Rh(dth)Br4) . As one might well expect, these barriers, though high, are less than that for the platinum(IV) analogue [Pt(dth)Cl4] " (cf. Section 8.7.2, and see Sections 8.3.1 and 8.6). 

Several methods are employed for the purification of the single platinum metal salts, for instance re-crystallization of Na2[Pt(Cl)6] with oxidative hydrolysis of the impurities of Pd, Rh, Ir, etc. which together with base-heavy metals are removed as insoluble hydroxides. Generally the metals are obtained, initially as sponge or powder, by conversion of their salts through thermal decomposition or by reduction of aqueous solutions of the ammonium-chloro complexes. Os which has been oxidized to the volatile 0s04 and Ru have to be reduced by H2. 

Lock, C. J. L. (1980). Structural studies of the hydrolysis products of platinum anticancer drugs, and their complexes with DNA base. In A. E. Martell (ed.), ACS Symposium Series, Vol. 140 Inorganic Chemistry in Biology and Medicine, pp. 209-24. 

The molecular derivatives of platinum group metals are usually rather well soluble in organic solvents and volatile in vacuum. At normal pressure they demonstrate very low thermal stability and easily decompose producing fine metal powders. This decomposition occurs more easily for the derivatives of branched radicals as it is based on a P-hydrogen elimination process. An important feature of the chemical behavior of these alkoxide complexes is their rather high stability to hydrolysis. Some derivatives can even form outer sphere hydrates when reacted with water in organic solvents. This stability to hydrolysis can at least partially be due to the kinetic inertness of the complexes of this group. 

The sesquioxide, Cr Oa, containing trivalent chromium, is an amphoteric oxide. It yields chromic salts, such as chromic chloride, CrCla, and sulphate, Cr2(S04)a, which are very stable and show great similarity to the ferric salts and to salts of aluminium as, for example, in the formation of alums. Since, however, chromic oxide functions as a weaker base than chromous oxide, the latter having a lower oxygen content, the chromic salts are more liable to hydrolysis than the chromous salts. This is well marked in the case of the chlorides. Again, in spite of the stability of chromic salts, only a slight tendency to form simple Cr " ions is exhibited, whilst complex ions are formed much more readily, not only complex anions, as in the case of iron and aluminium, but also complex cations, as in the extensive chromammine series. In this respect chromium resembles cobalt and platinum. 

Structural Studies of the Hydrolysis Products of Platinum Anticancer Drugs, and Their Complexes with DNA Bases... 

The increase in electrophilicity of coordinated ligands commonly leads to more favorable hydrolysis reactions. There are many reports on hydrolysis reactions of coordinated carboxamides, halogenated alkylamines, Schiff bases, thioamides, nitriles, etc. For example, thiourea and thioacetamide complexes of platinum metals decompose on heating in basic solution with formation of the corresponding metal sulfides, Eq. 1.26 and 1.27 ... 

---