Heterogenized polymetallic catalysts .3. Catalytic air oxidation of alcohols by Pd(II) complexed to a polyphenylene polymer containing beta-di- and tri-ketone surface ligands

This paper describes further studies on mono- and bi-metallic catalysts attached to a polymer support by beta-di- and tri-ketone surface Ligands. The previous two papers described the oxidation of catechol by the heterogeneous catalysts using Cu(II), Fe(III) and Pd(II) as the metal species, The present study expands these studies to a series of mono- and polyfunctional alcohols using Pd(II) as the metal species. The final catalytic surfaces were prepared by treatment of the modified polymer with a very reactive form of Pd(II), [Pd(CH3CN)(4)](2+). The simple alcohols gave increases in rates of up to 5-fold for the bimetallic systems. As might be expected glycols and alpha-D-glucose gave even higher increases in rate in going from the mono- to the bi-metallic catalyst. For ethylene glycol the factor was 30. Unsaturated alcohols gave the most dramatic results, With the monometallic catalyst, the products from allyl alcohol consisted of 25% acrolein resulting from direct alcohol oxidation and 75% 3-hydroxypropanal resulting from Wacker-type oxidation of the double bond. With the bimetallic catalyst the overall rate increased by a factor of 10 and the products consisted of 80% acrolein and 20% 3-hydroxypropanal, The actual rate increase for the direct alcohol oxidation is calculated to be a factor of 32. 4-Penten-2-ol and 4-penten-1-ol gave rates that were lower than the monofunctional alcohols. This is attributed to inhibition by olefin pi-complex formation with the Pd(II).