ALKANE REACTIONS WITH PHOTOACTIVATED DECATUNGSTATE IN NEUTRAL AND ACID-SOLUTION - MOLECULAR-ORBITAL THEORY

O- hole centers produced by charge-transfer photoexcitation in W10O324- abstract H from alkanes as do O- in numerous solid-state and molecular analogues. Upon protonation, forming H2W10O324-, this activity increases, and this has been modeled with atom superposition and electron delocalization molecular orbital (ASED-MO) calculations by shifting the polyoxometalate valence bands by an amount suggested by the observed decrease in first reduction potential. This strengthens the OH bond that forms at the anion surface when an alkane H is abstracted and lowers the activation energy for the process. The calculations show that in the absence of acid the resulting alkyl radicals bind weakly to the polyanions because the binding is reductive, promoting an electron to the empty W 5d band, but electron transfer to this band is possible for secondary and tertiary carbon radicals in the case of W100324-, yielding carbocations. In acidic media, the stronger oxidant H2W10O322- is likely to be capable of oxidizing primary carbon radicals and methyl radicals.