537708-89-7Relevant academic research and scientific papers
Substituent control of hydrogen bonding in palladium(II)-pyrazole complexes
Grotjahn, Douglas B.,Van, Sang,Combs, David,Lev, Daniel A.,Schneider, Christian,Incarvito, Christopher D.,Lam, Kim-Chung,Rossi, Gene,Rheingold, Arnold L.,Rideout, Marc,Meyer, Christoph,Hernandez, Genaro,Mejorado, Lupe
, p. 3347 - 3355 (2008/10/08)
Inter- and intramolecular hydrogen bonding of an N-H group in pyrazole complexes was studied using ligands with two different groups at pyrazole C-3 and C-5. At C-5, groups such as methyl, i-propyl, phenyl, or tert-butyl were present. At C-3, side chains L-CH2- and L-CH2CH2- (L = thioether or phosphine) ensured formation of chelates to a cis-dichloropalladium(II) fragment through side-chain atom L and the pyrazole nitrogen closest to the side chain. The significance of the ligands is that by placing a ligating side chain on a ring carbon (C-3), rather than on a ring nitrogen, the ring nitrogen not bound to the metal and its attached proton are available for hydrogen bonding. As desired, seven chelate complexes examined by X-ray diffraction all showed intramolecular hydrogen bonding between the pyrazole N-H and a chloride ligand in the cis position. In addition, however, intermolecular hydrogen bonding could be controlled by the substituent at C-5: complexes with either a methyl at C-5 or no substituent there showed significant intermolecular hydrogen bonding interactions, which were completely avoided by placing a tert-butyl group at C-5. The acidity of two complexes in acetonitrile solutions was estimated to be closer to that of pyridinium ion than those of imidazolium or triethylammonium ions.
