Synthesis and chemistry of trans-[RhX(CO)L2](X = anionic ligand, L = tertiary phosphine)

Abstract

The novel preparation of a wide variety of trans-[RhX(CO) L₂] complexes (X = anionic ligand, L = tertiary phosphine) from [Rh₄(CO)₁₂], phosphine (L), and acid (HX) is described. A plausible formation pathway is proposed. The electron density on the phosphorus atom in trans-[RhX(CO)L₂] decreases and the length of the Rh–P bond increases with an increase in the electronegativity of the anionic ligand, X, in a cis position to the phosphine ligand. The rhodium complexes (X = arylcarboxylate) are reduced to afford rhodate anions such as [Rh(CO)₃L]^– and [Rh (CO)₄]^– in hexamethylphosphoramide solution under CO–H₂. The rate of reduction increases with a decrease in the electron-withdrawing effect of the arylcarboxylate ligand.