2 Homometallic Alkoxides

126 Alkoxo and Aryloxo Derivatives of Metals
Terminal (O-bonded)
M O NR∗ (a)
M
R
N
∗
O
O
N
R∗ M
O,O-bridging
(b)
Chelating
O
M NR ∗
O,N-bidentate
(d)
Bridging ( m 2)
M
O
R
N ∗
N O
R∗ O,N-bridging
(c)
M
O M
N
R∗ R
N
∗
O
M
Chelating and bridging
(e)
R* = CRR′ (R = alkyl, aryl; R′ = H or alkyl/aryl in oximes)
and Et2 (in diethylhydroxylamine)
Figure 2.14 Ligating modes of simple oximes and
N,N-diethylhydroxylamines.
Reactions of N,N-diethylhydroxylamine with alkoxides of metals and metalloids as
shown in Eq. (2.245) have also been cleaner and quite general.
M⊲OR⊳x C yEt2NOH benzene
! M⊲OR⊳x y⊲ONEt2⊳y C yROH ⊲2.245⊳
where R D Et or Pr i .
This reaction (Eq. 2.245) has been employed to prepare binary and mixed alkoxide-
N,N-diethylaminooxide derivatives of titanium, 823 niobium, 829 tantalum, 829 boron, 834
aluminium, 834 arsenic, 832 and antimony. 833
The molecular complexity of ketoximate derivatives (similar to the alkoxide analogues)
is influenced by the chain length and ramification of the alkyl groups attached
to the imino carbon atom. 635 It may be pointed out that generally the same alkyl groups
when attached to the imino carbon atom appear to offer more steric hindrance than
when attached to the carbinol carbon atom. By contrast, the aldoximate derivatives
show a tendency towards higher molecular association depending upon the nature of
the alkyl or aryl group attached to the imino carbon atom.
Homo- and heteroleptic N,N-diethylaminooxides of aluminium and titanium exhibit
molecular complexities of the order of 2.0–2.5 and 1–1.5, respectively. Similar derivatives
of niobium, tantalum, boron, arsenic, and antimony are monomeric in boiling
benzene.