Competitive Oxidation and Reduction of Aliphatic Alcohols over (WO3)3 Clusters

The reactions of C1−C4 aliphatic alcohols over (WO 3 ) 3 clusters were studied experimentally and theoretically using temperature-programmed desorption, infrared reflection−absorption spectroscopy, and density functional theory. The results reveal that all C1−C4 aliphatic alcohols readily react with (WO 3 ) 3 clusters by heterolytic cleavage of the RO−H bond to give alkoxy (RO−) bound to W(VI) centers and a proton (H + ) attached to the terminal oxygen atom of a tungstyl group ( W ═O). Two protons adsorbed onto the cluster readily react with the doubly bonded oxygen to from a water molecule that desorbs at 200−300 K and the alkoxy that undergoes decomposition at higher temperatures into the corresponding alkene, aldehyde, and/or ether. Our theory predicts that all three channels proceed over the W(VI) Lewis acid sites with energy barriers of 30−40 kcal/mol, where dehydration is favored over the others. We also present further analysis of the yield and reaction temperature as a function of the alkyl substituents and discuss the origin of the reaction selectivity among the three reaction channels.