Coordination and Atom Transfer Chemistry at Surfaces of Polyoxometalate Anions

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This award from the Inorganic, Bioinorganic and Organometallic Chemistry Program is in the area of inorganic chemistry and deals with large clusters of either molybdenum or tungsten atoms tied together by oxygen atoms, known as polyoxoanions. These species have become the focus of much attention recently as models of catalytic metal oxide surfaces, and are also under intensive investigation as highly active and versatile homogeneous catalysts. Development of reactivity on the surfaces of large polyoxoanions of molybdenum and tungsten in aqueous and nonaqueous solvents is seen as a way (a) to lead to new classes of compounds and homogeneous catalysts and (b) to model processes that are important in heterogeneous catalysis on metal oxides. "Activation" of polyanion surfaces is achieved by reduction, e.g. oxomolybdenum(VI) to aquomolybdenum(IV), or by synthesis of polyanions containing one or more lower-valent heteroatoms in place of W(VI) or Mo(VI). The activated polyanions bind a variety of neutral ligands, especially in anhydrous solvents. With appropriate choice of heteroatom and oxidation state, polyanion-ligand complexes undergo atom transfer, either to or from the ligand. This tendency toward atom transfer will be used to develop stoichiometric or catalytic oxygen atom transfer involving one or several adjacent sites on the polyanion surface. An extension of this work is expected to lead to rational synthesis of polyanions containing terminal multiply-bonded groups other than oxo oxygen (e.g. imido, hydrazido) with consequent novel reactivity.