Monometallic alkoxides

Certainly, most of the ideas concerning the rates of hydrolysis and their impact on the forms and morphologies of the hydrolysis products comply with those discussed earlier for monometallic alkoxides (Chapter 9). 

Novel types of heterometallic alkoxymethoxide complexes are accessible by the reactions of two monometallic alkoxide derivatives. 

Preparation of Monometallic Alkoxides and Its Conversion into Corresponding Metal Oxides... 

The same reason was given in the literature for the formation of a number of other bimetallic oxocomplexes such as Cd4Sn4(p4-O)(OCH2Bu,)10(OAc)10 [325] and [PbTi2(p4-0)(0Et)7(0Ac)]2 [320]. When the alkoxides of zirconium, hafnium, or cerium are used for this reaction, the formation of the oxocomplexes can be due to the elimination of an unsaturated hydrocarbon from the initial alkoxide [1565], leading to the formation of monometallic oxoalkox-ides as intermediates (the latter are formed already on desolvation of [M(OR)4(ROH)]2 and are always present as admixtures in the samples of des-olvated M(OR)4, where R is a primary or secondary radical [1612] (see also Section 12.12). In this case the possible sequence of transformations (taking place usually on reflux in toluene) can look as follows ... 

In this way, alkoxides, glycolates, catecholates, carboxylates, or Schiff base complexes have been obtained.37,38 Other metal chelates have been synthesized by electro-oxidation of the bare metal electrode phosphido, azolates, phthalocyanines, semicarbazides, Schiff bases, etc.37 In addition to the syntheses of monometallic complexes, electrochemistry has been proven to yield polynuclear complexes by using assembling or multidentate ligands.37... 

Shibasaki et al. first reported a chiral barium catalyst prepared from BINOL monomethyl ether and barium alkoxide, which was a good catalyst for asymmetric direct-type aldol reactions (Table 1) [21]. In the presence of a barium catalyst, several aliphatic aldehydes were tested, and the desired cross aldol products were obtained in good yields with moderate to good enantioselectivities. For the substrate BnOC(CH3)2CHO, the best enantioselectivity was observed (Table 1, entry 6). Although there is no definitive experimented proof, the barium catalyst was assumed to be monometallic and could be stored for several months under argon atmosphere. 

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