Christine A. Little

Syntheses of tris(pyrazolyl)methane ligands and {[tris(pyrazolyl)methane]Mn(CO)3}SO3CF3 complexes: comparison of ligand donor properties

Abstract The known ligands HC(pz)3, HC(3,5-Me2pz)3, HC(3-Phpz)3, and HC(3-tBupz)3 and the new ligand HC(3-iPrpz)3 (pz=pyrazolyl ring) are prepared in CHCl3–H2O using the appropriate pyrazole, an excess of Na2CO3, and tetra-n-butylammonium bromide as the phase transfer catalyst. Using these conditions, good yields of the ligands are consistently obtained. The new ligand PhC(pz)2py (py=pyridyl ring) is prepared in the CoCl2 catalyzed condensation reaction of (pz)2SO and Ph(py)CO. The reaction of HC(pz)3, KOtBu and para-formaldehyde followed by quenching with water yields HOCH2C(pz)3. All of these ligands, except HC(3-tBupz)3, react with [Mn(CO)5]SO3CF3, prepared in situ from Mn(CO)5Br and Ag(SO3CF3), to yield the respective [(ligand)Mn(CO)3]SO3CF3 complex. The carbonyl stretching frequencies and 13C-NMR trends of these complexes indicate that the donor abilities of all of the ligands are fairly similar. The solid state structure of {[HC(3-iPrpz)3]Mn(CO)3}+ shows the HC(3-iPrpz)3 ligand is tridentate with the iso-propyl groups rotated away from the Mn(CO)3 core of the cation relieving any possible steric congestion.

Synthesis, solid-state structure, magnetic properties and Mössbauer spectral studies of {Fe[HC(3,5-Me2pz)3](H2O)3}(BF4)2

Abstract The reaction of Fe(BF4)2·6H2O and one equivalent of HC(3,5-Me2pz)3 in acetonitrile leads to the formation of {Fe[HC(3,5-Me2pz)3](H2O)3}(BF4)2. The solution phase 1H NMR spectrum is broad with chemical shifts ranging from 54 to −42 ppm, a range that is indicative of a paramagnetic high-spin complex. Magnetic moment measurements show that the complex is paramagnetic in the solid-state with μeff=4.89μB. The solid-state structure shows the N3FeO3 central core is a distorted octahedron with N–Fe–N angles averaging 84.4° and O–Fe–O angles averaging 90.0°. The average Fe–N distance is 2.18 A and the average Fe–O bond distance is 2.12 A. Mossbauer spectra, obtained at 78 and 295 K, clearly reveal that this complex is high-spin at these temperatures with hyperfine parameters typical of a pseudooctahedral iron(II) complex.