Platinum group metal alkoxides

We have demonstrated (a) the diversity of mechanistic pathways that exists for the thermal decompositon of metal alkoxides, and (b) how the preferred pathway is a function of the nature of the alkoxide ligand. A perhaps surprising conclusion that emerges from the study is that neither M-OR nor MO-R bond homolysis plays a direct role in these decompositions. It should be noted, however, that we have only examined the alkoxides of oxophilic metal ions that are not easily reduced. It is conceivable that for the later transition metal ions that are both less oxophilic and more reducible, decompositon pathways that lead to the reduction of the metal ion may become more important. These include -hydrogen abstraction followed by reductive elimination (cf., eq. 6), as well as M-OR bond cleavage. Note that P-hy(6ogen abstraction has been demonstrated to be quite facile for the platinum-group metal alkoxides. 

The most usual synthetic routes to the derivatives of platinum group metals are the exchange reactions of the complexes containing halide ligands with alkali metal alkoxides (method 5), alcoholysis of the same kind derivatives (usually by phenols, method 4), alcoholysis of hydroxide complexes (method 3), and redox reactions — reduction of chlorides or 0s04 in alcohol media (method 7) (Table 12.25). 

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. 

It is noteworthy that the homoleptic platinum group metal (Ru, Rh, Pd, Os, Ir, Pt) alkoxides are kinetically more labile possibly owing to j6-hydrogen elimination ... 

Under alkaline conditions, sixteen Pb(II) ions link the secondary hydroxyl side of y-CyD to form a metal-ion-mediated head-to-head dimer [217]. All the secondary hydroxyl groups are deprotonated and coordinated to bind Pb(II) ions forming a hexadecanuclear lead(II) alkoxide. Introduction of ionic substituents on CyDs enhances their metal-binding ability. Two amino groups introduced on the primary hydroxyl side of jS-CyD can chelate a platinum ion [64]. Imidazole-appended yS-CyD forms a ternary complex with a Cu(II) ion and L-tryptophanate [61]. The 6-amino and imidazolyl groups of the host molecule and the carboxyl and amino groups of L-tryptophanate are coordinated to the Cu(II) ion. 

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