Chemistry Reference
In-Depth Information
(11) Reactions with unsaturated substrates (Section 4.12)
(12) Reactions with coordinating ligands (Section 4.13)
(13) Reactions with main group organometallic compounds (Section 4.14)
(14) Tischtchenko, Meerwein - Ponndorf - Verley, and Oppenauer oxidation reactions
(Section 4.15)
(15) Interactions between two different metal alkoxides (Section 4.16)
(16) Special reactions of metal - metal bonded alkoxides (Section 4.17).
The main aim of this section is to highlight the potential of metal alkoxides as unique
synthons for a variety of novel metallo-organic compounds with interesting properties,
structures, and applications.
4.2
Hydrolysis Reactions
The high reactivity of metal alkoxides towards water leads to a complex hydrolysis and
polymerization chemistry.
3
,
21
,
617 - 619
,
645
During hydrolysis, the alkoxo (
OR) groups
are replaced either by hydroxo (OH
)oroxo(O
2
) ligands. This reaction is influenced
by a number of factors such as: (i) the nature of the alkyl (R) group, (ii) the nature
of the solvent, (iii) the concentration of the species present in solution, (iv) the water
to alkoxide molar ratio, and (v) the temperature. It appears reasonable to suggest that
the initial step should involve the coordination of a water molecule through its oxygen
to the metal in a facile nucleophilic process as represented by Eq. (2.190), which
represents the initial stage of a continued hydrolysis process:
Hydrolysis
H
H
δ+
+
O
M(OR)
x
•
(RO)
x
−1
MO
Lewis acid
H
H
O
R
Lewis base
(2.190)
Leaving group
(RO)
x
−1
M-OH
+
ROH
(A)
The hydroxo-metal alkoxides (A) tend to react further in two ways (Eqs 2.191 and
2.192) to form the metal oxo-alkoxide derivatives.
Dealcoholation
RO
x
1
MO
H C RO
M
OR
x
1
!
RO
x
1
MOM
OR
x
1
C ROH
2
.
191
Dehydration
RO
x
1
MO H C HO M
OR
x
1
!
RO
x
1
MOM
OR
x
1
C H
2
O
2
.
192
The above reactions generally proceed further to yield finally the hydroxides (hydrated
oxides) and sometimes hydroxy-alkoxides.
