Pentamethylcyclopentadienylrhodium bis-carboxylates: Monohapto carboxylate coordination, dihapto carboxylate coordination, and water coordination to Cp*Rh

Article abstract of DOI:10.1016/0020-1693(95)04793-X

Reaction between [Cp*RhCl₂]₂ and silver carboxylates in anhydrous, non-coordinating solvents produces Cp*Rh(η²-O₂CR) (η¹-O₂CR) complexes with the unusual feature of having both the η² and η¹ carboxylate ligands bound to the same metal. The benzoate complex Cp*Rh(η²-O₂CPh) (η¹-O₂CPh) was characterized crystallographically and its structure is discussed. Cp*Rh(η²-O₂CPh) (η¹-O₂CPh) was found to crystallize in the monoclinic space group P2₁/c with a=11.658(3), b=14.574(4), c=26.248(6) A, β=101.87(2)° and V=4364(2) A³ for Z=8. These bis-carboxylate compounds are very hygroscopic, reacting with water quite readily to form the aquo complexes, Cp*Rh(OH₂) (η¹-O₂CR)₂. The acetate aquo complex Cp*Rh(OH₂) (η¹-O₂CMe)₂ was characterized crystallographically and was found to crystallize in the monoclinic space group P2₁/c with a=8.910(2), b=12.854(4), c=14.710(3) A, β=106.82(2)° and V=1612.6(7) A³ for Z=4. The water molecule in Cp*Rh(OH₂) (η¹-O₂CMe)₂ was found to internally hydrogen bond to the coordinated acetate groups. The coordination of water in Cp*Rh(OH₂) (η¹-O₂CMe)₂ is unusual in that the Rh-O bond is perpendicular to the plane of the water molecule. The geometry of water coordination in these Cp*Rh complexes is compared with geometries found for water coordinated to other non-classical, organometallic compounds.