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

The known ligands HC(pz)(3), HC(3,5-Me(2)pz)(3), HC(3-Phpz)(3), and HC(3-(t)Bupz)(3) and the new ligand HC(3-'Prpz)(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)(2)py (py = pyridyl ring) is prepared in the CoCl2 catalyzed condensation reaction of (pz)(2)S=O and Ph(py)C=O. The reaction of HC(pz)(3), (KOBu)-Bu-t and para-formaldehyde followed by quenching with water yields HOCH2C(pz)(3). All of these ligands, except HC(3-(t)Bupz)(3), react with [Mn(CO)(5)]SO3CF3, prepared in situ from Mn(CO)(5)Br and Ag(SO3CF3), to yield the respective [(ligand)Mn(CO)(3)]SO3CF3 complex. The carbonyl stretching frequencies and C-13-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-'Prpz)(3)]Mn(CO)(3)}(+) shows the HC(3-'Prpz)(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. (C) 2000 Elsevier Science S.A. All rights reserved.