Synthesis, characterization and structure of rhodium(I) carbonyl complexes with O,P-chelating 1′-(diphenylphosphino)ferrocenecarboxylate or P-monodentate 1′-(diphenylphosphino)ferrocenecarboxylic acid

Abstract

The reaction of 1′-(diphenylphosphino)ferrocenecarboxylic acid (Hdpf) with [{Rh(µ-X)(CO)₂}₂] (X = Cl or Br) afforded rhodium(I) complexes trans-[Rh(Hdpf-P)₂X(CO)] containing the ligand as the P-bonded phosphine. On the other hand, pentane-2,4-dionato rhodium(I) complexes reacted with Hdpf by an acid–base reaction yielding novel O,P-chelated rhodium(I) complexes and pentane-2,4-dione (Hacac). The compound [Rh(acac)(CO)₂] reacted with 2 equivalents of Hdpf to give trans-[Rh(dpf-O,P)(Hdpf-P)(CO)] which exhibits proton exchange between the two forms of the ligand. Likewise, related complexes [Rh(acac)(PR₃)(CO)], where PR₃ = PCy₃, PPh₃ or PPh₂Fc (Cy = cyclohexyl, Fc = ferrocenyl), afforded the corresponding complexes trans-[Rh(dpf-O,P)(PR₃)(CO)]. The formation of the O,P chelates is regioselective and might be considered as a rather unusual displacement of pentane-2,4-dionate by the phosphinocarboxylate dpf^– with concurrent proton exchange. All the compounds were characterized by ¹H, ¹³C, ³¹P and IR spectroscopies and by FAB mass spectrometry. The crystal structure determination of trans-[Rh(dpf-O,P)(PCy₃)(CO)] confirmed the presence of an unprecedented heteroannular O,P-chelating ferrocene ligand.