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

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 ∗MCl 2 ] 2 in dichloromethane. Variations of this synthetic method resulted in twelve unique crystal- lographically 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 in- triguing two complexes are trinuclear Cp ∗Ir III hydroxo-bridged clusters that have, at their core, an Ir 3 NaO 4 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 ∗MCl 2 ] 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.