Chromium, molybdenum and ruthenium complexes of chloranilic acid

Abstract

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 μB. 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(μ-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.