Alkoxides metal alcoholysis

Synthesis of more sterically hindered divalent metal alkoxides by alcoholysis of metal... 

From Alcoholysis and Transesteriflcation. Metal alkoxides of higher, unsaturated, or branched alcohols are difficult to prepare directiy and are usually made from lower metal alkoxides by means of alcoholysis ... 

The reaction is driven to completion by distilling the lower boiling alcohol. Metal methoxides are frequentiy insoluble and caimot be employed as starting materials in this reaction by the same token, they can be convenientiy prepared from solutions of higher alkoxides by precipitation with methanol. Alcoholysis also gives mixed metal alkoxides ... 

Reaction of trialkoxyboranes with metal alcoholates, alcoholysis or hydride transfer reactions of tetrahydroborates with aldehydes or ketones all result in the formation of tetraalkoxobor-ates. Steric factors play an important role in these reactions. As a consequence, sec-alcohols react very slowly and tetra-r-alkoxoborates in general cannot be obtained by any of the reactions above. At elevated temperatures the tetraalkoxoborates revert to the trialkoxyborane and metal alkoxide.75 Thioalcoholysis of tetrahydroborates can also be effected but, in contrast to the situation in alcoholysis, the last hydrogen atom is more difficult to substitute, probably for steric reasons.119 Tetraalkoxoborates and tetramercaptoborates are readily hydrolyzed by water or moist air. 

Te tram eric alkyl beryllium, zinc and cadmium alkoxides are formed by controlled alcoholysis of the metal dialkyls,16U62 while cubanoid thallium alkoxides are obtained by reaction of the metal with refluxing ethanol, and alcohol metathesis.163 Reaction (4) affords a tin phosphide cubane in low yield 164... 

Indeed the alcoholysis of metal amides is an excellent method for the synthesis of alkoxides. However, some synthetic utility to this reaction has been found for the synthesis of aminoboranes where the equilibrium can be forced to the right by using either an involatile or a chelating amine.59,60 Hydrocarbon solutions of Mo2Me2(OBu )4 also react with MeNHCH2CH2NHMe (>6 equiv.) to give Mo2(MeNCH2CH2NMe)3 with the liberation of methane (2 equiv.) and /-butyl alcohol.61... 

Similarly, alcoholysis of Mo(NMe2)4 allows a ready entry into Molv alkoxide chemistry,75 although reactions with silanols76 and phenols77 typically produce adducts in which the liberated dimethyl-amine remains coordinated to the metal center (equation 12). 

Alcoholysis of metal oxides may also be used for the synthesis of multivalent metal alkoxides nevertheless, application of this method is restricted to covalent oxides with low values of lattice activation energies. Usually these are derivatives of M in the higher oxidation states, and their interaction with alcohols is complicated by oxidation-reduction processes — for example,... 

On the other hand, to accelerate alcoholysis of NaH and KH in solutions of benzene or THF [22.1] - [2.22] - ctyptands are used (which bind alkaline metal into a rather stable chelate complex) [1004], Quite stable, volatile per-fluorotert-butoxides were first obtained in reactions of LiH or NaH with (CF3)3COH they distill at atmospheric pressure at 218 and 232°C, respectively [467] (the application of metals would presumably lead in this case to condensation of Wurtz type). Li and Na hydrides are used as cheaper than metal raw materials for production of the corresponding metal alkoxides. In particular it has been suggested that the equipment used in production of MH could be cleaned from its residue by the mixture ofEtOH and the aromatic hydrocarbon (40 to 60% by volume). After hydrogen evolution is completed the solvent is eliminated under vacuum at < 90°C the residue is MOEt with the content of the main product > 98% [342],... 

We would like to mention alcoholysis of MR (accompanied by evolution of hydrocarbons). However, metal alkyls are practically unavailable therefore, they are used for the synthesis of metal alkoxides very rarely. Only a few examples arc known CuOMe [413], Mn(OPri)2 [1306], V(OBu )4 [1338], Cr(OR)2 [350], On the other hand, alcoholysis of metal alkyls is frequently performed... 

The most important ways to prepare heteroleptic complexes are (1) the reaction of chemical modification, (2) the interaction of an alkoxide with a carboxylate, p-diketonate, or other derivative of the same or the other metal, and (3) reactions of alcoholysis of derivatives initially not containing alkoxoli-gands. 

The alcoholysis of oxides or hydroxides of alkaline or alkaline earth metals (method 3) is used mainly in the industrial preparation of the alkoxides [1644, 1499]. This method has become the major route to the hydrolysis-insensitive phenoxides, even in laboratory practice. The alcohols, benzene, and water have been used as reaction medias. 

That was in fact for zirconium alkoxides that Bradley developed all the major synthetic approaches to the alkoxides ofhigh-valent metals—metathesis of ZrCl4or (more preferably [PyH]2ZrCl6)with ammonia [201] (method 5), alcoholysis of Zr(NR2)4 [1579] (method 4), alcohol interchange reactions... 

The metathesis reaction of metal chloride with alkali alkoxides (method 5) was historically the first approach applied, and it remains the main route to both mono- and bimetallic derivatives of Mn(H). The most efficient approach to Mn(II) derivatives is, however, provided by the alcoholysis of the corresponding silylamide (method 4). The derivatives of Mn(IH) and mixed-valence Mn(H,IH) were obtained by alcoholysis ofMn(III) acetate by polyatomic phenols in the presence of 2,2 -dipyridil accompanied by reduction in the latter case (methods 4 and 4+7). 

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). 

---