Hexafluoroacetylacetonate (hfac) as ligand for pentamethylcyclopentadienyl (Cp*) rhodium and iridium complexes: Some surprising results, including an Ir3Na1O4 cubane structure

Abstract

Attempts to prepare hexafluoroacetylacetonate (hfac) piano stool complexes of pentamethylcyclopentadienyl Cp* iridium and rhodium led to a surprising array of unexpected products. The desired complex, Cp*M(hfac)Cl, was obtained following the reaction of sodium hexafluoroacetylacetonate (hfacNa) with [Cp*MCl2]2 in dichloromethane. Variations of this synthetic method resulted in twelve unique crystallographically identified products, eleven of which contain the hfac ligand or a trifluoroacetylacetonate (TFA) ligand, either coordinated to the metal or as a non-coordinating anion. Five dinuclear Cp* iridium hydroxo-bridged products with various fluorinated non-coordinating anions were obtained. The most intriguing two complexes are trinuclear Cp*IrIII hydroxo-bridged clusters that have, at their core, an Ir3NaO4 cubane structure. Attempts to devise rational syntheses of the hydroxo-bridged cluster compounds were not successful. Generation of the TFA moieties likely occurred following degradation of Cp*Ir(hfac)Cl. The reaction between [Cp*MCl2]2 and 1,1,1-trifluoroacetylacetonate (tfac) proceeded as expected to give Cp*M(tfac)Cl with no observed side product formation, indicating that the metal-coordinated tfac moiety is significantly more stable than the metal-coordinated hfac moiety.