Syntheses of Cationic, Six-Coordinate Cadmium(II) Complexes Containing Tris(pyrazolyl)methane Ligands. Influence of Charge on Cadmium-113 NMR Chemical Shifts

Abstract
Treating a thf (thf = tetrahydrofuran) suspension of Cd(acac)2 (acac = acetylacetonate) with 2 equiv of HBF4·Et2O results in the immediate formation of [Cd2(thf)5](BF4)4 (1). Crystallization of this complex from thf/CH2Cl2 yields [Cd(thf)4](BF4)2 (2), a complex characterized in the solid state by X-ray crystallography. Crystal data: monoclinic, P21/n, a = 7.784(2) Å, b = 10.408(2) Å, c = 14.632(7) Å, β = 94.64(3)°, V = 1181.5(6) Å3, Z = 2, R = 0.0484. The geometry about the cadmium is octahedral with a square planar arrangement of the thf ligands and a fluorine from each (BF4)- occupying the remaining two octahedral sites. Reactions of [Cd2(thf)5](BF4)4 with either HC(3,5-Me2pz)3 or HC(3-Phpz)3 yield the dicationic, homoleptic compounds {[HC(3,5-Me2pz)3]2Cd}(BF4)2 (3) and {[HC(3-Phpz)3]2Cd}(BF4)2 (4) (pz = 1-pyrazolyl). The solid state structure of 3 has been determined by X-ray crystallography. Crystal data: rhombohedral, R3̄, a = 12.236(8) Å, c = 22.69(3) Å, V = 2924(4) Å3, Z = 3, R = 0.0548. The cadmium is bonded to the six nitrogen donor atoms in a trigonally distorted octahedral arrangement. Four monocationic, mixed ligand tris(pyrazolyl)methane−tris(pyrazolyl)borate complexes {[HC(3,5-Me2pz)3][HB(3,5-Me2pz)3]Cd}(BF4) (5), {[HC(3,5-Me2pz)3][HB(3-Phpz)3]Cd}(BF4) (6), {[HC(3-Phpz)3][HB(3,5-Me2pz)3]Cd}(BF4) (7), and {[HC(3-Phpz)3][HB(3-Phpz)3]Cd}(BF4) (8) are prepared by appropriate conproportionation reactions of 3 or 4 with equimolar amounts of the appropriate homoleptic neutral tris(pyrazolyl)borate complexes [HB(3,5-Me2pz)3]2Cd or [HB(3-Phpz)3]2Cd. Solution 113Cd NMR studies on complexes 3−8 demonstrate that the chemical shifts of the new cationic, tris(pyrazolyl)methane complexes are very similar to the neutral tris(pyrazolyl)borate complexes that contain similar substitution of the pyrazolyl rings.

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