Synthesis, characterization and catalytic epoxidation properties of lanthanide-stabilized peroxoisopolytungstates

Abstract

A series of new lanthanide-containing peroxoisopolyoxotungstates, K₆Na₄[H₃₂{Ln₄(WO₄)(H₂O)₁₆[W₇O₂₂(O₂)₂]₄}₃]·105H₂O [Ln = Ce^III (1), Nd^III (2), Sm^III (3), Tb^III (4), Er^III (5)], have been successfully synthesized and structurally characterized. All polyanions [Ln^III₄(WO₄)(H₂O)₁₆{W₇O₂₂(O₂)₂}₄]¹⁴⁻ are isostructural and consist of a central [Ln^III₄(WO₄)(H₂O)₁₆]¹⁰⁺ cluster surrounded by four peripheral [W₇O₂₂(O₂)₂]⁶⁻ units. They could act as efficient recyclable catalysts for the epoxidation of various alkenes including different cycloalkenes, styrene derivatives, internal and long-chain alkenes. Under optimal conditions, catalyst 2 displays the best catalytic activity for the oxidation of cyclooctene with high cyclooctene conversion (98.3%) and excellent selectivity (up to 99%) and could be reused for three cycles with a negligible decrease in reactivity.