The cyclometallation of benzoic acid to give rhodium, iridium, and osmium C,O-benzoates. X-Ray structure determination of the dibenzoate [(C5Me5)Rh(OOCPh)2(H2O)]

Abstract

The cyclometallated benzoate complexes [(C₅Me₅)[graphic omitted]H₄)(Me₂SO)][M = Rh (1a) or Ir (1b)] and [(p-MeC₆H₄CHMe₂)O[graphic omitted]C₆H₄)(Me₂SO)] were prepared by reaction of [(C₅Me₅)MMe₂(Me₂SO)] or [(p-MeC₆H₄CHMe₂)OsMe(Cl)(Me₂SO)] with benzoic acid or silver benzoate respectively. Methane was formed in these reactions. Complex (1b) was also prepared from [(C₅Me₅)IrCl₂( Me₂SO)] with silver benzoate. Complex (1a) reacted with water to give [{(C₅Me₅)Rh}₂(µ-OH)₃][OOCPh] and the dibenzoate hydrate [(C₅Me₅)Rh(OOCPh)₂(H₂O)](5a). Complex (5a) was also formed when (1a) was reacted with benzoic acid or when [(C₅Me₅)RhCl₂(Me₂SO)] reacted with two equivalents of silver benzoate. The structure of (5a) was determined by an X-ray study which showed two benzoates attached in a monodentate manner to the (C₅Me₅)Rh moiety; the rhodium also bore a co-ordinated water, which was also hydrogen-bonded to the two benzoate carbonyl oxygens. Both the rhodium and the iridium complexes (1a) and (1b), reacted with methyl iodide to give the cyclometallated methyl benzoate complexes [(C₅Me₅)[graphic omitted]H₄}(I)]. They also underwent carbonylation to give phthalic anhydride and [(C₅Me₅)]Rh(CO)₂ from (1a), and [(C₅Me₅)I[graphic omitted]H₄)(CO)] from (1b). Mechanismsofthe various transformations are discussed.