2 Homometallic Alkoxides

454 Alkoxo and Aryloxo Derivatives of Metals
3.1 From the Metal
The reaction of the most electropositive metals with phenols can sometimes lead to
direct formation of aryloxide derivatives along with evolved hydrogen (Eq. 6.4 84 ).
where HOAr = HO CH3. Na C HOAr THF
! [NaOAr]n C 1
2 H2
⊲6.4⊳
Although it is possible to carry out the reaction with the metal in neat liquid or molten
phenol, refluxing in a suitable solvent is normally desirable. This method typically
produces adducts, coordinated phenol and/or solvent, of the aryloxide complex (e.g.
Eqs 6.5–6.7). 85,86
6Ba⊲s⊳ C 12PhOH HMPA
! [Ba6⊲OPh⊳12⊲HMPA⊳4] C 6H2
3Sr⊲s⊳ C 6PhOH HMPA
! [Sr3⊲OPh⊳6⊲HMPA⊳5] C 3H2
4Sr⊲s⊳ C 10PhOH THF
! [Sr4⊲OPh⊳8⊲HOPh⊳2⊲THF⊳6] C 4H2
⊲6.5⊳
⊲6.6⊳
⊲6.7⊳
An innovative method involves the use of metal atom vapour procedures to generate a
highly activated dispersion of metal in a hydrocarbon solvent for reaction with phenolic
or other reagents (Eq. 6.8 87 ).
M C 2HOAr THF
! [M⊲OAr⊳2⊲THF⊳n] C H2
Me3C
where M = Ca, n = 3; Ba, n = 4; HOAr = HO .
⊲6.8⊳
Me3C In the case of the reaction of metallic barium with phenol in either THF or HMPA
the products isolated were shown to contain both hydride and oxo ligands (Eqs 6.988 and 6.1089 ).
Ba⊲s⊳ PhOH/THF
! [HBa5⊲O⊳⊲OPh⊳9⊲THF⊳8] ⊲6.9⊳
reflux
Ba⊲s⊳ PhOH
! [H2Ba8⊲ 5-O⊳2⊲OPh⊳14⊲HMPA⊳6] ⊲6.10⊳
HMPA
In some instances the reaction is accelerated by either amalgamation or the addition
of a catalyst (e.g. iodine or a mercury(II) halide, Eq. 6.1190 ) while the stoichiometric
reaction of mercury and thallium compounds with lanthanide metals has been shown
to be a viable route to aryloxide derivatives (Eqs 6.1291 and 6.1392 ).
Y⊲s⊳ C 3HOPh HgCl2⊲cat⊳
! [Y⊲OPh⊳3]n C 3
2 H2
⊲6.11⊳