Hydroxo-alkoxide formation

Alkoxides and aryloxides demonstrate similar chemistry to that of hydroxides in that it is possible to prepare mixed metal or double metal derivatives similar to hydroxo salts such as Na2[Sn(OH)6]. The formation of mixed metal alkoxides, e.g. Na2[Zr(OEt)6] and Ln[Al(OPri)4]3, is typically a result of the electron deficiency (Lewis acidity) of the metal centers in units of the type M(OR)x or M(OAr)JC (x < 5). This then leads either to oligomerization via alkoxide bridges or, in the presence of other alkoxides, to the formation of mixed metal compounds. 

Shin gta/. " have shown that Fe complexes of tetraphenylporphyrins and etioporphyrin undergo autoreduction in DMSO solution by addition of hydroxide or alkoxide ions or solid sodium hydride. The autoreduction leads to the formation of the corresponding five-coordinate hydroxo-iron(II) (S = 2) complexes. This reduction can be followed easily by NMR spectroscopy. 

Presence of small nonalkoxide ligands such as oxo, hydroxo, hydrido, halo, and chalcogenido groups is commonly observed in lanthanide alkoxide clusters. These small anionic species are important in facilitating the formation and maintaining the structural integrity of the cluster structures. 

The basic chemical principle behind sol-gel processing of metal alkoxides is the transformation of M—OR groups to M—O—M units via M—OH species. The direct formation of M—O—M units from metal alkoxides by ether cleavage is possible, but is only rarely observed under sol-gel conditions (see Section 7.10.3.3.1). Thus, the alkoxo ligands first have to be converted into hydroxo ligands (hydrolysis reaction), which can then undergo condensation reactions. 

It is presumed that the first stage in the hydrolysis of a metal alkoxide is the formation of a hydroxo derivative which then condenses to form the 0x0 ligand (Eqs 5.2 and 5.3). 

An interesting feature of the chemistry of monomeric organoplatinum(II) hydroxides and alkoxides is that CO inserts into the Pt—O bond more readily than into the Pt—C bond. Thus in 1993, Bennett and coworkers in an effort to examine the structures and properties of Pt(II)-hydroxycarbonyls with trans-arranged phosphines explored the reaction of the monomeric pincer Pt(II)-hydroxo species (14) with CO [9]. Hence, treating the (PCP)Pt(OH) pincer complex (14) with CO in benzene under ambient conditions caused the formation of the hydroxycarbonyl complex (15) as a... 

---