NEW OSCILLATING REACTION IN CATALYSIS BY METAL-COMPLEXES - A MECHANISM OF ALKYNE OXIDATIVE CARBONYLATION

The reaction of phenylacetylene carbonylation to phenyl maleate, pheny l fumarate, and dimethoxylactone in the homogeneous catalytic system P dI2-KI-O-2-NaOAc in methanol solution was found to exhibit oscillation s in the redox potential, pH, and rate of gaseous CO-O-2 mixture consu mption. This is the first example of an oscillating chemical reaction in typical metal-complex catalysis where a complex organic molecule is formed from simple reactants in solutions of metal complexes. Oscilla tions were observed for 3.5 h up to 95% conversion of alkyne. The oxid ation of CO to CO2 occurs in parallel with carbonylation. The products were analyzed by NMR spectroscopy and GLC coupled with mass spectrome try. The compositions of the gas and liquid phases were controlled by GC and GLC, respectively. The range of NaOAc concentrations within whi ch oscillations were observed was found to be very narrow: from 0 to 0 .01 mol/L. It was shown that oxygen transfer through the phase boundar y is not a cause of oscillations. The run where PdI2 was replaced by K 2Pd2I4 exhibited oscillations similar in shape and amplitude. A reacti on scheme was proposed, which includes the processes of Pd(II) reducti on to the active catalysts of carbonylation, Pd(I) complexes, followed by the oxidation of palladium(I) complexes by iodine.