Titanium oxo-alkoxides

Both homometallic and heterometallic oxo-alkoxides can be produced by partial hydrolysis of metal alkoxide precursors via dehydroxylation and dealkoxolation of metal hydroxo alkoxides. The crystal structures of a number of polynuclear titanium oxo alkoxides have been elucidated, these structures having evolved during the slow addition of small amounts of water to Ti(OEt)4 47,48,76-79... 

Klemperer and co-workers "have shown that with increasing 0x0 content titanium oxo-alkoxides become increasingly resistant to hydrolysis in alcoholic solutions, although gel formation occurs readily by hydrolysis in nonalcoholic solvents."... 

Of considerable interest is the selective alkoxo exchange shown by the more hydrolysed titanium oxo-alkoxides. The two isomeric forms of [Tii20i6(0Pr )i6] both reacted with ethanol (Eq. 5.31) to form isomers of [Tii20i6(OEt)6(OPr )io] by exchange of terminal isopropoxo groups bonded to the 6 five-coordinated Ti atoms in each molecule."... 

Single metal and mixed metal oxo alkoxides can also be prepared by reaction between metal halides, oxy halides, and alkali metal alkoxides.47,48 One of the first to be structurally characterized was a series of mixed Cd or Sn containing zirconium, tin, and titanium alkoxides.84,85 These and other examples are shown in skeletal form in Figure 3. 

Figure 35 (a) Molecular structure of Ba-Ti oxo-alkoxide, reproduced with permission from the Royal Society of Chemistry, (b) Comparison of the core structure of monoclinic barium-titanium oxo-isopropoxide with the BaTiOs structure viewed along the [111] direction, reproduced with permission from Wiley. ... 

Pure titanium alkoxides Ti(OR)4 are highly reactive toward hydrolysis and lead to the uncontrolled precipitation of Ti02 when water is added. However, for very low hydrolysis ratio (halkoxide bridges. Solute molecular oxo-alkoxides such as Ti7O4(OEt)20 (h=0.6), Tiio08(OEt)24 (h=0.8) and even Tii60i6(0Et)32 (h=l) are then obtained. 

A.H. Senouci, M. Ycicikoub, C. Huguencird cuid M. Henry, Moleculcir tem-plating using titanium (IV) (oxo)alkoxides and titanium(IV) (oxo)arylox-ides, /. Mater. Chem., vol. 14, pp. 3215-3230,2004. 

As an alternative to adding water to a metal alkoxide it has been shown that acetone will undergo aldol-type condensation in the presence of a metal alkoxide leading to the formation of an oxo-alkoxide. For example the zinc alkoxide [Zn(OCEt3)2] was converted to a gel whilst titanium tetraisopropoxide gave a trinuclear species... 

Heterometallic oxo-alkoxides may also be formed by conversion from heterometallic alkoxides. Thus the insoluble [Pb(OPr)2]j reacted with Ti(OPr% to form [Pb4Ti403PPr g] and [Pb2Ti2(Ai4-0)(/u,3-0Pr )2(/Li-0Pr )4(0Pr )4] presumably by ether elimination. Similarly, from reactions of barium alkoxides and titanium alkoxides the heterometallic oxo-alkoxides [Ba4Ti404(OPr )i6(Pr OH)4][Ba4Ti404(OPr )io(Pr OH)3] and [Ba2Ti40(0Me)ig(Me0H)7]2° were obtained as a result of ether elimination, although similar complexes are readily prepared when the barium alkoxide solution is aerobically oxidized. ... 

Titanium Sub-group Metal-containing Oxo-alkoxides (Including Heterometallic Compounds) (Table 5.4)... 

Table 5.4 Titanium and zirconium-containing oxo-alkoxides (including heterometallic compounds) ...

The structure of the hexanuclear mixed ligand oxo-alkoxide [Ti6(/z3-0)2(Ai-0)2(M-01 )2(/r-0Ac)8(0Pr )6] showed the presence of exclusively octahedral titanium. Similarly the centrosymmetric hexanuclear [Ti6(/Z3-0)2(M-0)2(/r-0Bu )2(/z-OAc)8(OBu")g] also contained octahedral titanium and the /T3-oxo atoms were in trigonal planar configurations. ... 

A vanadium(v)-molybdenum(vi) heterometallic oxo-alkoxide [V2Mo2(0)g (0Me)2 (0CH2)3C(CH20H) 2] has also been characterized. The V2M02O16 core involving octahedral metals is reminiscent of the Ti40ie core of titanium tetraUcoxides. ... 

In the case of the reaction between titanium and zirconium alkoxides and excess carboxylic acids, however, ester elimination could not be avoided at the later stages and the final product was oxo-acetate (AcO)3TiOTi(OAc)3 or (AcO)3Zr—0-Zr(0Ac)3. 

We previously reported the preparation and quantitative characterization of well-defined, uniform titanium alkoxide complexes on a sihca surface, via the grafting of Ti(0 Pr)4. We demonstrated, via the mass balance, that the reaction on Aerosil-200 silica pretreated at 200°C results exclusively in the formation of dinuclear oxo-bridged complexes regardless of Ti loading (13), eq 1. 

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