2 Homometallic Alkoxides

130 Alkoxo and Aryloxo Derivatives of Metals
4.10 Reactions with Thiols
Although the reactions (Eq. 2.248) of thiols are quite facile with alkoxides of germanium,
890 tin, 891 and antimony, 892 the alkoxides of titanium, 893 zirconium, 893 aluminium,
893 and silicon 893 do not undergo such reactions:
M⊲OR⊳x C xR 0 SH ⇀
↽ M⊲SR 0 ⊳x C xROH ⊲2.248⊳
Qualitatively this difference might be understood on the basis of Pearson’s concept of
hard and soft acids and bases.
The convenient preparation of thiolates of titanium 894 and uranium 213 from their
respective dialkylamides, but not from alkoxide analogues, demonstrates the oxophilic
nature of these metals in their higher oxidation states.
4.11 Reactions with Halogens, Hydrogen Halides, Acyl Halides, and
Metal Halides
4.11.1 Reactions with Halogens
The reactions of metal alkoxides with halogens were investigated by Nesmeyanov
et al. 895 who observed that the reaction between titanium tetra-n-butoxide and chlorine
or bromine yielded the dihalide dibutoxide coordinated with one mole of alcohol
as TiX2⊲OBu⊳2.BuOH and n-butyl propionate. The reaction may be represented by
Eqs (2.249)–(2.252):
Ti⊲OCH2R⊳4 C X2 ! TiX2⊲OCH2R⊳2 C 2RCH2O ⊲2.249⊳
2RCH2O ! RCH2OH C RCHO ⊲2.250⊳
TiX2⊲OCH2R⊳2 C RCH2OH ! TiX2⊲OCH2R⊳2.RCH2OH ⊲2.251⊳
2RCHO ! RCH2COOR ⊲2.252⊳
where R D C3H7.
It was observed that the treatment of ferric trimethoxide with excess of chlorine at
ambient temperature yielded FeCl3.2MeOH. However, when the above reaction was
carried out at 72 Ž C, only partial replacement occurred, yielding ferric monochloride
dimethoxide. 210
Jones et al. 379 observed that uranium tetraethoxide reacted with bromine to yield
uranium monobromide tetraethoxide which was then used for the preparation of the
pentaethoxide (Section 2.10.1)
4.11.2 Reactions with Hydrogen Halides
2U⊲OEt⊳4 C Br2 ! 2U⊲OEt⊳4Br ⊲2.253⊳
In view of an interesting gradation observed (Section 2.4) in the reactivity of tetrahalides
of silicon, titanium, zirconium, and thorium with ethyl and isopropyl alcohols,
the reverse reactions of alkoxides of these elements with hydrogen chloride (bromide)
were investigated by Mehrotra 896,897 who demonstrated that the reaction products of