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.