Pyrazolylcyclohexanol complexes of vanadium - A temperature- and solvent-dependent monomer-dimer equilibrium

The reaction Of VOCl3 with tridentate rac-trans-[1-pyrazolyl-3-(2-pyridyl)] cyclohexanol in the presence of K2CO3 generates a mononuclear six-coordinat e V-V complex. With the bidentate ligand rac-trans-2-(pyrazol-1-yl)cyclohex an-1-ol, reduction of V-V to V-IV takes place to give a dinuclear complex w ith bridging alkoxo units; this compound is also accessible starting direct ly from the V-IV precursor VOSO4 and LiCl. Both complexes were characterize d spectroscopically and by X-ray diffraction. The dimeric V-IV complex is i n equilibrium with its monomeric counterpart; this temperature- and solvent -dependent equilibrium was followed by EPR spectroscopy.