Page 102 - Arrow Pushing in Inorganic Chemistry A Logical Approach to the Chemistry of the Main Group Elements

GROUP 13 ELEMENTS
82
(c)

+
Na

− 4 NaCl −
2 GaCl 2 + 6 Na Ga Ga
−

+
Na

(3.30)
For the last product, we have used the triple-bonded “digallyne” formulation simply to
highlight the low coordination number of the gallium centers. An alternative formulation
would be to have a lone pair on each gallium that is only partially involved in -overlap.
Quantum chemical studies also suggest a bond order closer to two than to three:

−
− Ar Ga
Ar
Ga Ga Ga Ar
− Ar −

Gallium and indium metals react with the metal trihalides (X = Cl, Br, I) to yield the
so-called subhalides:
2E + 4EX → 3E X 4 (3.31)
3
2
Interestingly, these compounds are not structurally analogous to the E R species
2 4
described above. Instead, they are mixed-valent ionic compounds, which are better written
III
I
as E [E X ]. They react, however, with neutral donor ligands (L) such as pyridines and
4
dioxane to yield metal–metal bonded E(II)–E(II) derivatives:
E[EX ]+ 2L → LX E − EX L (3.32)
2
2
4
The donor-coordinated products serve as valuable starting materials for other
low–oxidation-state systems. With sterically hindered organolithiums, for example,
Ga X (dioxane) derivatives, yield neutral tetraorgano-Ga tetrahedra:
2 4 2 4
R

Dioxane X X R Ga
LiR
Ga Ga Ga (3.33)
Pentane Ga Ga
X
X Dioxane R R
X = Cl, Br R = C(SiMe 3 ) 3 , Si(SiMe 3 ) 3