Pocket Semiquinonate Complexes of Cobalt(II), Copper(II), and Zinc(II) Prepared with the Hydrotris(cumenylmethylpyrazolyl)borate Ligand

3,5-Di-tert-butyl-1,2-semiquinonate
(3,5-DBSQ) complexes of Co(II), Cu(II), and Zn(II) have
been prepared that
contain the hydrotris(cumenylmethyl-pyrazolyl)borate
(TpCum,Me) coligand.
TpCum,MeZn(3,5-DBSQ) and
TpCum,MeCu(3,5-DBSQ) were prepared by treating the parent hydroxide,
TpCum,MeM(OH), M = Cu and Zn, with 3,5-di-tert-butylcatechol.
TpCum,MeCo(3,5-DBSQ) was prepared by a
reaction between (TpCum,Me)2Co and
3,5-DBCat.
The identity of (TpCum,Me)2Co in this
reaction was confirmed by a structure determination
[(TpCum,Me)2Co: 
orthorhombic, Pbcn, a = 17.7189(4) Å,
b = 17.4806(3) Å, c = 25.7123(6)
Å, V = 7964.1(3) Å3, Z =
4, R(F)
= 0.054]. Intersecting cumenyl substituents of the
pyrazolylborate ligand encapsulate the Co(II) ion.
Structural
characterization on all three members of the
TpCum,MeM(3,5-DBSQ) series has been carried out.
The complexes
of Co(II) and Zn(II) are isomorphous and isostructural
[TpCum,MeCo(3,5-DBSQ):  triclinic,
P1̄, a = 14.4631(2) Å,
b = 18.5438(3) Å, c = 21.6142(2)
Å, α = 79.8430(10)°, β = 90.0900(10)°, γ =
84.9900(10)°, V = 5683.45(13)
Å3, Z = 4, R(F) =
0.072; TpCum,MeZn(3,5-DBSQ), triclinic,
P1̄, a = 14.261(3) Å, b
= 18.760(7) Å, c = 21.710(4) Å, α = 80.049(12)°, β = 89.853(8)°, γ =
85.542(12)°, V = 5703(3) Å3,
Z = 4, R(F) = 0.064].
TpCum,MeCu(3,5-DBSQ) [monoclinic, P21/c,
a = 19.3081(3) Å, b = 13.0291(2)
Å, c = 21.4783(4) Å, β =
102.8420(10)°,
V = 5268.1(2) Å3, Z = 4,
R(F) = 0.071] has a distorted square pyramidal
structure, the complexes of Zn and Co
have structures that are closer to a trigonal bipyramid. Parent
catecholate complexes of all three metals are
unusually stable in air but undergo slow oxidation in solution to give
the semiquinonate products characterized
structurally. Copper(II) and SQ spins of
TpCum,MeCu(3,5-DBSQ) are located in orthogonal
orbitals, and the complex
has a S = 1 spin state. The charge distribution in
TpCum,MeCo(3,5-DBSQ) is Co(II)−SQ, rather
than the more
common Co(III)−Cat, due to surprisingly weak donation by the
TpCum,Me nitrogens.