Syntheses and structural characterizations of rhenium carbonyl complexes of a bitopic ferrocene-linked bis(pyrazolyl)methane ligand

The reaction between Fe[C5H4CH(pz)2]2 (pz = pyrazolyl ring) and two equivalents of Re(CO)5Br in refluxing toluene produces Fe[C5H4CH(pz)2Re(CO)3Br]2 (1) in high yield. A similar reaction with a ligand/rhenium ratio of slightly greater than one yields mainly 1 and a low yield of Fe[C5H4CH(pz)2Re(CO)3Br][C5H4CH(pz)2] (2). The compound H2C(pz)2Re(CO)3Br (3) was prepared by the reaction of H2C(pz)2 and Re(CO)5Br. Compounds 1 and 2 show a reversible oxidation at ca. 0.9 V (Ag/AgCl) that can be assigned to the oxidation of the ferrocene moiety and one irreversible oxidation at ca. 1.4 V assigned to the oxidation of the rhenium metal center. The solid-state structures of 1 · CH3NO2, 1 · 2CH3NO2, 1 · 2CH3CN and 2 · 1/2Et2O · 1/2C3H6O have been determined, with 1 · 2CH3NO2 and 1 · 2CH3CN being isomorphous. All four are organized into supramolecular structures by the interactions of the acidic hydrogens of the pyrazolyl and methine groups with either the bromine atoms or carbonyl ligand oxygen atoms, and in 2 the lone pairs on the uncomplexed bis(pyrazolyl)methane units.