MONOMERIC AND DIMERIC PYRAZOLE AND PYRAZOLYL COMPLEXES OF RUTHENIUM

The first examples of well-characterized, monomeric ruthenium-pyrazole complexes have been obtained. The complexes include [(bpy)2Ru(pzH)2]2+, [(bpy)2Ru(pz)(pzH)]+, and (bpy)2Ru(pz)2-H20 (bpy = 2, 2'-bipyridine, pzH = pyrazole, pz = pyrazolyl anion). From the results of cyclic voltammetry and electronic spectral measurements it is concluded that, in the complexes, the pzH ligand is a poorer π acceptor than pyridine while in its deprotonated form (pz), it is a better π donor than Cl- ion. The pyrazole complexes can be deprotonated in solution giving the complex (bpy)2Ru(pz)2 which is itself capable of reacting as a chelating ligand. It undergoes a reaction with the labile solvent complex [(bpy)2Ru-((CH3)2CO)2]2+ giving the doubly bridged dimer [(bpy)2RuII(pz)2RuII(bpy)2]2+. The reactivity of the mixed-valence form of this ion, [(bpy)2RuII(pz)2RuIII(bpy)2]3+, is similar to that reported for the previously characterized chloro-bridged dimers [(bpy)2RuCl2Ru(bpy)2]3+, in that it undergoes an asymmetrical cleavage reaction in CH3CN solution. © 1979, American Chemical Society. All rights reserved.