2 Homometallic Alkoxides

128 Alkoxo and Aryloxo Derivatives of Metals
The general reaction of metal alkoxides with monofunctional bidentate (Figs 2.15a–c,
designated as SBH) and bifunctional tri- and tetradentate (Figs 2.15d–f, designated as
SBH2) ligands can be represented by Eqs (2.246) and (2.247).
M⊲OR⊳x C ySBH benzene
! M⊲OR⊳x y⊲SB⊳y C yROH ⊲2.246⊳
M⊲OR⊳x C ySBH2
benzene
! M⊲OR⊳x 2y⊲SB⊳y C 2yROH ⊲2.247⊳
where R is generally Et or Pr i ,andx is the valency of the metal or metalloid.
This synthetic procedure has been employed to prepare a wide variety of Schiff
base and ˇ-ketoamine derivatives of lanthanides: La, 847–851 Pr, 847–851 Nd, 847,849–851
Sm, 852 Er, 847 Yb; 850 transition metals: Ti, 853–863 Zr 853,858,862–867 Hf, 868 Nb, 863,869–874
Ta; 870,872,873,875,876 and main group metal(loid)s: B, 877–879 Al, 859,863,878–886
Ga, 847,862,887,888 As, 879 and Sb. 879,889
It is pertinent to mention the salient features of the reactions represented by Eqs
(2.246) and (2.247) and their products. These reactions offer attractive possibilities
for preparing derivatives with the metal in interesting coordination environments. For
example, reactions of titanium alkoxides with bifunctional tridentate Schiff base ligands
⊲SBH2⊳ 855–858 like o-HOC6H4CHDNCH2⊲CH2⊳nOH (n D 1 or 2) afford dialkoxide
derivatives of the type Ti⊲OR⊳2⊲SB⊳, which exhibit a dimeric octahedral structure
involving bridging when R is stercally compact, but monomeric with sterically bulky
RsuchasBu t : 858
O
N
O
R
O
Ti
R
O
O
R
Ti
O
R
O
N
O
Equimolar reaction of Ti⊲OPr i ⊳4 with a bifunctional tetradentate Schiff base ligand like
salenH2 (N,N 0 -ethylenebis(salicylideneimine)) affords 858 a six-coordinate monomeric
derivative:
O
C
H
OPr i
Ti
N N
OPr i
Similar reactions of Al⊲OPr i ⊳3 with bifunctional tri- and tetradentate ˇ-ketoamines 847
afford dimeric and monomeric species, respectively in which aluminium atoms are in
a five-coordinated environment.
In general, Schiff base and ˇ-ketoamine derivatives of metals and metalloids exhibit
variations in the degree of molecular association depending upon their empirical formulae,
the valency and covalent radius of the metal, as well as the ligand type.
O
C
H