Metal oxoalkoxides

The steps involved in formation of the metal oxoalkoxide are hydrolysis, dehydration, and dealkoxylation ... 

Besides direct hydrolysis, heterometaHic oxoalkoxides may be produced by ester elimination from a mixture of a metal alkoxide and the acetate of another metal. In addition to their use in the preparation of ceramic materials, bimetallic oxoalkoxides having the general formula (RO) MOM OM(OR) where M is Ti or Al, is a bivalent metal (such as Mn, Co, Ni, and Zn), is 3 or 4, and R is Pr or Bu, are being evaluated as catalysts for polymerization of heterocychc monomers, such as lactones, oxiranes, and epoxides. An excellent review of metal oxoalkoxides has been pubUshed (571). 

Polymeric metal oxoalkoxides — the products of partial hydrolysis or thermolysis ofM(OR) — have long been applied as refractory and isolating protection coatings. It has been supposed that these amorphous products contain metal-oxygen chains surrounded by OR-groups [199,48]. 

Table 4 Transition Metal Oxoalkoxides Derived from Hydrolysis Reactions... 

Efforts to prepare new alkoxides continue and many complex metal alkoxides have been prepared. For example, several metal oxoalkoxide clusters have been prepared by Bradley et al. [14]. Aluminium oxoalkoxides such as OBu)j(OBUgOH and Aljg(0Et)2j04 have been reported in the literature [15]. 

The fragmentation pattern for tantalum penta-alkoxides Ta(OR)5 (R = Me, Ft, Pr, CH2CH20Me), in their mass spectra is similar to that for alkoxides of zirconium and hafnium, niobium, molybdenum, and tungsten. For example, at first the loss of OR groups occurs, followed by elimination of the molecules of unsaturated hydrocarbons (usually, with the same number of carbon atoms as R). However, the decomposition of Ta(OMe)s differs from that of other homologues by the loss of HCHO molecules and H atoms. Elimination of ethers, R2O, which is accompanied by the formation of the metal oxoalkoxide ions of the above mentioned alkoxides is typical. In the absence of X-ray crystallographic data, considerable effort had been directed earlier to throw light on the molecular complexities of aluminium trialkoxides in different (solid, liquid, or vapour) states. 

The oxoalkoxides U3O(OBu)1065b and U3O(OCMe3)10 c are structurally similar to the molybdenum analogue, Mo3O(OCH2CMe3)i0, but the U—U bond distances, 3.576(1) A and 3.574(1) A, show that metal-metal bonding does not occur. 

This process is a common one in the fragmentation of the majority of metal alkoxide molecules in the mass-spectra. A typical example of the latter is the fragmentation pattern of zirconium and hafnium oxoalkoxides [1612] (Fig. 5.1). 

The controlled oxidation of the low-valent metal alkoxides has in fact been used for the preparation of oxocomplexes. Thus on action of 02 onMo2(OBu )6 or the red-colored solutions obtained by anodic dissolution of molybdenum metal in alcohols (containing the derivatives of Mo(V)) were obtained the di-oxoalkoxides, Mo02(OR)2 [356,908],... 

Herrmann and Streck recently reported polyethylene and polypropylene MWD variations by varying the type of metal M, in catalytic systems such as (TiM ljClyOJ —AIR3 obtained from the reaction of A CjHjl C with bimetallic p-oxoalkoxides. 

Heterometallic alkoxides and oxoalkoxides as intermediates in chemical routes to mixed-metal oxides (23). 

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