Catalytic isomerization of 1-hexene to 2-hexene by halide clusters of Nb, Mo, Ta and W possessing an octahedral metal core

Abstract

Halide clusters, [(M 6Cl 12)Cl 2(H 2O) 4]·4H 2O (M: Nb, Ta) and (H 3O) 2[(M 6Cl 8)Cl 6]·6H 2O (M: Mo, W) with an octahedral metal framework, develop catalytic activity for the isomerization and slight hydrogenation of olefinic double bonds when the halide clusters are treated in a stream of hydrogen at elevated temperatures. In the case of Nb clusters, treatment above 200 °C produces the catalytic activity. Raman spectra of such heat-treated clusters show that the cage breathing motion of Nb 6 remains intact, whereas the breathing vibrations of the edge bridging Nb–Cl of [Nb 6Cl 12] disappear. In the case of W clusters, the catalytic activity appears at 300 °C, at which temperature the structure of [(W 6Cl 8)Cl 4(H 2O) 2] begins to decay to form W 6Cl 12. Maximum activity emerges at 450 °C, at which temperature the structure of W 6Cl 12 begins to decay. Elemental analyses of both clusters show the loss of Cl atoms. Thus, activation of these clusters occurs by partial loss of the halogen ligands, leaving the cluster framework intact.