Oxide-alkoxides

Metal oxide alkoxide (trialkylsilyloxide) polymers. D. C. Bradley, Coord. Chem. Rev., 1967, 2, 299-318 (25). 

In 1967, Bradley (8) wrote further about metal oxide -alkoxide (trialkylsiloxide) polymers. He noted that these com-... 

X-ray studies confirm Bi2(ju,-OR)2 centrosymmetric dimers 4 in the solid state (24). Terminal alkoxides are generally bound more tightly than bridging units [terminal Bi-0 2.064(7) A bridging Bi-0 2.188(7) and 2.688(7) A], The bismuth oxide alkoxide cluster compounds [Bi6(p,3-07)(p,3-OC6F5) Bi(OC6F6)4 3(sol)2] [sol]2 (sol = thf or toluene) were also isolated as minor products (25). Both structures contain the unusual octahedral I Bi, (/x3-07 X/x3-OCeF.-) I" cores 5, which... 

A single example has been reported of a bis(aluminium) oxide-alkoxide based on an Al(/x-0)2Al motif where one oxygen centre represents the oxide while the other one is part of the organooxide moiety [47]. [(i-Pr)OH]3 ClAl(/x-0) [fi-0 (f-Pr)]AlCl2 reveals a 4-membered metallocycle with the sterically-available bridging oxide centre also coordinating to a molecule of AICI3. 

Whereas a mononuclear alkoxide complex of aluminium which incorporates azaindole ligands has been noted [116], so azaindoles have been reported to bridge Al-centres in oxides [23, 41, 42]. This is also true of an oxide-alkoxide which incorporates the bis(trifluoromethyl)isopropoxide ligand [42]. In the case of dinuclear aggregate [[(F3C)2C(H)]0 2Al[/r-0C(H)(CF3)2]-... 

In the stoichiometric oxidation of secondary alcohols to ketones by tetraoxoferr-ate(VI), the second-order rate constant depends on pH. Rate acceleration at high [HO-] is attributed to formation of HOFeO -, proposed to be more susceptible to attack by nucleophiles (alcohols, R2CHOH) than FeO itself, to generate a ferrate ester, H0Fe(0-)4-0CHR2. A second effect accounting for the steep dependence on [HO-] is attributed to ionization of alcohols to generate the more readily oxidized alkoxide ions.88... 

Treatment of [OsH2(CO)4] with tin oxides, alkoxides, or amines has yielded organotin complexes of the type trun.s-[Os(SnR3)2(CO)4] (R3 = Ph3, Bu3, or... 

Ca, Sr, and Ba Aryl Oxide, Alkoxide, and Siloxidf. Compounds and Their Physical Properties ... 

Evans, W.J. and Sollberger, M.S. (1988) Synthetic and structural studies on the formation of a tetradecametallic yttrium oxide alkoxide chloride complex an example of how molecular yttrirrm oxygen frameworks form extended arrays. Inorganic Chemistry, 27, 4417 423. 

All mentioned polymeric oxides, alkoxides, aroxides and carboxylates are intensely coloured and insoluble in organic solvents. The structures were estimated by elementary analysis, IR spectra and model reactions. The mechanism of the reactions with alcohols and phenols is described as nucleophilic substitution at the metal atom for alonium and gennonhun ions ... 

FIGURE 12.10 Schematic of the oxide (alkoxides) or nonoxide (polymers) matrix precursors infiltration for fabricating three-dimensional reinforced composites. (After Reference 87.)... 

As mentioned in the above introduction, the formation of a number of hy-droxo- and oxo-alkoxide products of different metals was reported (till 1978) (1,6) during the extensive hydrolytic studies carried out on metal alkoxides and even crystal structures of a few oxide-alkoxides of Ti (475a), Nb (476a), Zr (477a), and Sn(II) (477b). 

This early work is summarised in Krause and von Grosse s Organometallische Che-mie which was published first in 1937,11 and which described examples of tetraalkyl-and tetraaryl-stannanes, and of the organotin halides, hydrides, carboxylates, hydroxides, oxides, alkoxides, phenoxides, R2Sn(II) compounds (incorrectly), distannanes (R3SnSnR3), and oligostannanes (RiSn) . 

In this type of reaction, the intermediate, an alkyl oxide (alkoxide) is the major product, but as seen above lithium aluminum hydride is oxidized to LiAl02 The intermediate is then protonated through hydrolysis to yield an alcohol. 

Campion, J, F., Payne, D. A., Choe, H. K., Maurin, J. K., and Wilson, S. R., Synthesis of bimetallic barium titanium alkoxides as precursors for electrical ceramics. Molecular structure of the new barium titanium oxide alkoxide Ba4Tii30i2(OC2H40Me)24, Inorg. Chem., 30, 3245 (1991). 

Early alkoxide work was certainly done without modem materials in mind rather the early sol-gel chemistry was with absorbents and catalyst supports in view. Much synthetic work has been done on alkoxides, but a peculiar theoretical schizophrenia exists about them and their relation to oxides. Studies show that bond lengths and angles are very similar in alkoxide clusters to those found in oxides and polyoxyanions. This is mentioned several times in the book (e.g.. Chapters 1, 2, and 21). If it looks like a duck, etc., it probably is a duck, which is to say that the bonding in alkoxides is very similar to that in oxides. Alkoxides are not covalent and oxides ionic they are similar. Modem X-ray methods to determine actual charges on ions in oxides show them to be very small. While modeling Madelung potential methods, etc., often work, they are as ballet or opera is to love, merely an artistic (and often useful) imaginative representation. This will become more apparent as workers are attracted to this field and as old shibboleths fade. 

Isothiocyanatostannanes. A mixture of bis(tri- -butyltin) oxide and NH4-thio-cyanate in methylcyclohexane stirred and refluxed 4 hrs. -> tri- -butyltin isothiocyanate. Y 88%. - NH4-salts are excellent reagents for similar conversions of organometallic oxides, - alkoxides, and metal alkoxides. F. e., also halogeno-stannanes, s. K. C. Pande, J. Organometal. Chem. 13, 187 (1968). 

Bradley D C, Carter D G (1961) Metal oxide alkoxide polymers part 1. the hydrolysis of smne primary alkoxides of zirconium. Can J Chem 39 1434-1443... 

A most remarkable mixed ligand heterometallic oxide-alkoxide anion [Ag2Moio(0)g(Ai5-0)2(Ar-0)i6(fr-OMe)g(NO)2f has been characterized. The centrosymmetrical anions consist of two Mo5(0)4(/i5-0)(/i-0)g(/x-OMe)4(NO) units connected by four Mo(/x-0)Ag(/r-0)Mo bridges involving square planar Ag04 with a... 

Similar products are formed in the reactions with anhydrides of carbon acids. It is interesting that the oxide/alkoxide of yttrium Y5(0C3H7-i)i30 in the reaction with Ph3SiOH gives the oxide-free product Y(OSiPh3)3(THF)3 [37]. 

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