Preparation of Cyclopentadienyltricarbonylrhenium Complexes Using a Double Ligand-Transfer Reaction

Abstract

A unique double ligand-transfer reaction is described for the preparation of substituted cyclopentadienyltricarbonylrhenium complexes. In the reaction, potassium perrhenate(VII) is reduced and carbonylated by treatment with chromium trichloride and chromium hexacarbonyl to provide a proposed alkoxy carbonyl rhenium(I) intermediate. It is believed that this intermediate then undergoes a Cp ligand-transfer reaction with an acyl-substituted ferrocene to provide the corresponding (acyl-cyclopentadienyl)tricarbonylrhenium complex. A strongly coordinating solvent such as methanol is necessary to promote the reduction of perrhenate, and a carbonyl substituent conjugated to the Cp ring is necessary to activate it for transfer from iron to rhenium. This method has potential value for the synthesis of rhenium and technetium organometallic radiopharmaceuticals.