Simple Zinc Complexes of Pyridyl-Substituted Tris(pyrazolyl)borate Ligands

Treatment of the potassium salts of the Tpx ligands
hydrotris(5-methyl-3-py*-pyrazolyl)borate
Tp3Py,Me (py* =
3-pyridyl) and TpPic,Me (py* = 5-α-picolyl) with zinc
halides or with Zn(ClO4)2 and KOH yields
the halide
complexes Tp3Py,MeZn−Hal (Hal = F, Cl, Br, I) and
the hydroxide complexes Tp3Py,MeZn−OH and
TpPic,MeZn−OH, as well as the bis(ligand) complex
(Tp3Py,Me)2Zn. All
Tp3Py,MeZn−X complexes show a tendency
for
dimerization, using one pyridyl group each of the two
Tp3Py,Me units to coordinate to the zinc ion of the
opposite
Tp3Py,MeZn fragment, as evidenced by the solid state
structures of Tp3Py,MeZn−F (strong interaction) and
Tp3Py,MeZn−I (weak interaction) and by a variable-temperature NMR study of
Tp3Py,MeZn−OH. Despite the steric
bulk
of the Tp3Py,Me ligands, the bis(ligand) complex
(Tp3Py,Me)2Zn contains zinc bound to all
pyrazole nitrogen donor
atoms in an octahedral fashion. Tp3Py,MeZn−F
crystallizes in the triclinic space group P1̄ with
a = 11.123(5) Å,
b = 11.638(7) Å, c = 13.793(4) Å,
α = 72.34(3)°, β = 75.32(3)°, γ =
73.09(5)°, and Z = 2.
Tp3Py,MeZn−I
crystallizes in the monoclinic space group C2/c
with a = 18.922(1) Å, b =
10.476(4) Å, c = 31.444(1) Å, β
=
101.99(4)°, and Z = 8.
(Tp3Py,Me)2Zn crystallizes in the
monoclinic space group C2/c with a =
18.330(2) Å, b
= 13.876(1) Å, c = 21.616(1) Å, β =
115.96(7)°, and Z = 4.