Alcohol Interchange Reaction

The most important feature of metal alkoxides is their facile ligand exchange reactivity originating from predominantly electrostatic nature of the M—O bonding. This leads to quick achievement of coordination equilibria. When alkoxides - derivatives of one alcohol - are dissolved in a different alcohol, they transform instantaneously into, most often, more thermodynamically stable mixed ligand species in solutions. The latter often possesses increased solubility in organic solvents  

To achieve complete exchange of the ligands, it is necessary to shift the equilibrium, applying huge excess of the new alcohol and removing at the same time the original alcohol by (vacuum) distillation. 

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Soluble and volatile alkoxides of copper are precursors in sol-gel-like routes to cuprate-oxide superconductors1 and in the CVD of copper and copper oxides,2 respectively. Copper(II) alkoxides are typically prepared by alcohol-interchange reactions with dimethoxycopper(II) however, most are insoluble... 

Application of the alcohol interchange reaction (method 6) is limited by certain phenols and also di and trisubstituted glyoxides (while the reaction of metals with glycols gives only monosubstituted derivatives) [745, 621, 575, 1584,1369]. As redox processes (method 7) can be considered the Grignard-type reactions — the interaction of metal alkyls with carbonyl compounds,... 

The greatest number of Ti(OR)4homologs was obtained using the alcohol interchange reaction (method 6), the isopropoxide being usually applied as reactant [225, 224, 235]. This reaction has also been reported to lead to numerous T OR OR )., . Application of esters as alkoxylating agents has also been reported Mehrotra [1111, 1800],... 

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... 

MC15 with alcohols in the presence of ammonia (method 5) and the alcohol interchange of M(OPr )5 (method 6). Mehrotra proposed later the application of esters in the alcohol interchange reaction for Nb(OEt)5 [223],... 

Of great interest are the data on numerous M[Mv(OPri) ]n—derivatives of the 3 -elements Cr1", Fe", Co,Ni, Cu" [12, 501, 618, 818,1109,1462,1561], prepared by interchange reactions of MCI, with KMv(OPr )6. The other M[Ta(OR)6] (R = Me, Et, Pr", Bu ) homologs were prepared from the isopropoxides by alcohol interchange reactions. The data on formation of bi- and trimetallic alkoxoniobates and tantalates underthe conditions described in [12, 14, 501, 618, 818, 1109, 1462] was questioned. The products described could be obtained only in the presence of traces of water and were undoubtedly oxoalkoxides by nature. The mass-spectra of trimetallic BeAlMv(OPri)10 (considered as the major proof of their individuality [14]) have discovered only the presence of the fragments of [M(OR)5]2 and [AIM(OR) ] [1622, 1561]. 

The choice of solvents in sol-gel processes is very important because alcohol interchange reactions are possible. As an example, when silica gel was prepared from Si(OMe)4 and heated to 600 °C the surface area was 300 m g" with a mean pore diameter of 29 A when ethanol was used as a solvent. However, when methanol was used, the surface area dropped to 170m g and the mean pore diameter increased to 36A [32]. The rate of hydrolysis also becomes slower as the coordination number around the metal center in the alkoxide increases. Therefore, alkoxides that tend to form oligomers usually show slower rates of hydrolysis and. 

Substitution of other branched R groups with the lower straight-chain alcohols has been carried out in an alcohol interchange reaction [10] ... 

Alcohol interchange reactions are known to occur when alkoxides are dissolved in alcohols other than the parent one. Alcoholysis is rather slow for silicon alkoxides. It is much faster in the case of transition metal alkoxides. 47,49ji jvjmR experiments show that alcoholysis of Ti(OPr )4 occurs as soon as the alkoxide is dissolved into tertio-amyl alcohol (Fig.2). Five different species corresponding to x ranging from 0 to 4 are formed as follows ... 

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