2 Homometallic Alkoxides

124 Alkoxo and Aryloxo Derivatives of Metals
the context of the above possibilities, a study of the glycolate (particularly the mixed
alkoxide-glycolate) derivatives assumes special interest. Out of the different types of
derivatives those with chelated hydroxyl group(s) (Figs 2.13b, d, h, i, m, n) offer the
possibility of functioning as precursors for heterometallic alkoxides by their reactivity
towards alkoxides of other metals (Section 2.4).
Reeves and Mazzeno 793 as early as 1954 studied cryoscopically the reactions of
Ti(OBu t )4 with various glycols in tertiary butyl alcohol and observed that the products
were not simple monomers but were associated species having the titanium to glycol
ratio 2:3, 4:6, 2:2, and 3:6 (Ti2(OBu t )2(glycolate)6). Yamamoto and Kambara 794 carried
out the reactions of titanium tetra-alkoxides with excess of 2-methylpentane-2,4-diol
and isolated a product of the type Ti⊲OCHMeCH2CMe2O⊳2.⊲HOCHMeCH2CMe2OH⊳.
Extensive work on the reactions of alkoxides of different metals and metalloids
such as alkaline earth metals, 706 lanthanides, 148–156 titanium, 61,708,793–802 zirconium,
61,708,796–802 uranium, 803 vanadium, 804 niobium 805,819 tantalum, 806 iron, 807
boron, 808 aluminium, 809 silicon, 810–813 germanium, 814 tin, 815 antimony, 301 selenium, 816
and tellurium 817 with a wide variety of glycols has been carried out by Mehrotra et al.
Bivalent metals
Trivalent metals
Tetravalent metals
[M(O−G−O)] n [M(O−G−OH) 2 ] n
(a) (b)
[(O−G−O)M(OR)] n [(O−G−O)M(O−G−OH)]n
(c)
(d)
(O−G−O)MO−G−OM(O−G−O)
(e)
[(O−G−O)M(OR) 2] n [M(O−G−O) 2] n [(O−G−O)M(O−G−OH) 2]n or
(f) (g) (h)
(O−G−O) 2 M(O−G−OH) (O−G−O)M(O−G−O) 2 M(O−G−O)
(i) (j)
Pentavalent metals
(RO) 2 (O−G−O)M(m-OR) 2 M(O−G−O)(OR) 2 [(O−G−O) 2 M(m-OR)] 2 ;
(k) (l)
(O−G−O) 2M(O−G−OH) or M 2(O−G−OH) 2(O−G−O) 4 (O−G−O) 2MO−G−OM(O−G−O) 2
(m)
Hexavalent metals
(n) (o)
(O−G−O)M(OR) 4 (O−G−O) 2 M(OR) 2 M(O−G−O) 3
(p) (q) (r)
(where O−G−O = a diolate group such as OC 2H 4O, OCHMeCHMeO,
OCMe 2CMe 2O, OCHMeCH 2CMe 2O, OCMe 2(CH 2 ) 2CMe 2O)
Figure 2.13 Structural variety in binary and mixed alkoxide-glycolate
derivatives of metals.