2 Homometallic Alkoxides

Homometallic Alkoxides 131
metal alkoxides and hydrogen halides were essentially the same as those obtained in
the reactions involving the metal chloride and an alcohol:
M⊲OR⊳x C yHX benzene
! M⊲OR⊳x y⊲X⊳y C yROH ⊲2.254⊳
Ti⊲OR⊳4 C 2HX ! Ti⊲OR⊳2X2.ROH C ROH ⊲2.255⊳
where R D Et, Pri ;XD Cl, Br.
2Zr⊲OR⊳4 C 5HX ! Zr⊲OR⊳X3.2ROH C Zr⊲OR⊳2X2.2ROH C ROH ⊲2.256⊳
Th⊲OR⊳4 C 4HX ! ThX4.4ROH ⊲2.257⊳
where R D Et, Prn ,Pri ;XD Cl, Br.
Gilman and co-workers898 have also shown that interaction of uranium pentaethoxide
and hydrogen chloride in appropriate molar ratios of reactants in ether afforded the
products: UCl⊲OEt⊳4, UCl2⊲OEt⊳3, andUCl3⊲OEt⊳2.
In contrast to the non-reactivity of Si⊲OR⊳4 towards hydrogen halides, germanium295 and tin tetra-alkoxides899 show high reactivity on interaction with HCl as shown by
Eqs (2.258) and (2.259):
Ge⊲OR⊳4 C 4HCl
benzene
! GeCl4 C 4ROH ⊲2.258⊳
2Sn⊲OR⊳4 C 7HCl ! SnCl3⊲OR⊳.ROH C SnCl4.2ROH C 4ROH ⊲2.259⊳
An equimolar reaction of As⊲OMe⊳5 and HCl or HF gives AsX⊲OMe⊳4 (X D F,
Cl); 900 the fluoro derivative was stable in vacuo below 30 Ž C whereas the chloro
analogue appeared to be unstable and decomposed ⊲AsCl⊲OMe⊳4 ! AsO⊲OMe⊳3 C
MeCl⊳ to give arsenyl trimethoxide and methyl chloride.
In contrast to the partial reactions illustrated by Eq. (2.254), complete substitution
has been shown to occur to give metal halides that are known to form only alcohol
adducts when treated with alcohols:
where Ln D a lanthanide. 102
Th⊲OPr i ⊳4 C 4HCl
Ln⊲OPr i ⊳3 C 3HCl
benzene
! ThCl4.4Pr i OH ⊲2.260⊳
benzene
! LnCl3.3Pr i OH ⊲2.261⊳
Fe⊲OPr i ⊳3 C 3HCl ! FeCl3.2Pr i OH C Pr i OH 210
Te⊲OEt⊳4 C 4HCl ! TeCl4.3EtOH C EtOH 901
⊲2.262⊳
⊲2.263⊳
4.11.3 Reactions with Acyl Halides
The reactions of metal alkoxides with acyl halides may be illustrated by Eq. (2.264):
M⊲OR⊳x C yCH3COX benzene
! M⊲OR⊳x yXy.zCH3COOR C ⊲y z⊳CH3COOR
⊲2.264⊳
where R D Et, Pri ;XD Cl, Br; y D 1, 2, 3, 4 ...x; z D 0, 0.5, 1.
This type of facile reactivity was first observed in 1936 by Jennings et al. 902 who
synthesized titanium monochloride triethoxide and dichloride diethoxide by the reactions
of titanium tetraethoxide and acetyl chloride in the appropriate molar ratios.