Chromium,molybdenum and ruthenium complexes of chloranilic acid

Chloranilic acid (H₂CA) reacts with Cr(CO)₆ and CrCl₃ to give the tris derivatives Cr(H₂CA)₃ and Cr(HCA)₃. Spectroscopic measurements on the two complexes reveal that the ligand–metal bond is of the semiquinone type. Susceptibility determinations showed effective magnetic moments of 1.82 and 1.07_B. Examination of Cr(H₂CA)₃ by cyclic voltammetry revealed two redox reactions due to tautomeric interconversion through electron transfer. Boiling Mo(CO)₆ with H₂CA in air gave MoO₃(HCA) in which the molybdenum atom is in the +5 oxidation state. The i.r. spectrum of the MoO₃(HCA) displayed bands due to terminal M=O bonds. The cluster compound Ru₃(CO)₁₂ reacted with H₂CA to give Ru₃(CO)₁₀(-H)(HCA), the i.r. spectrum of which revealed that the ligand is bound to the metal as a catechol moiety. The spectroscopic and magnetic studies of the molybdenum and ruthenium complexes confirmed the proposed structures.