Chemistry of transition-metal complexes containing functionalized phosphines. Part 2. Cationic rhodium(I) complexes stabilized by hemilabile diallylphosphines

• Diallylphosphines as bidentate ligands in cationic rhodium complexes has been studied.
• The hemilabile character of diallylphosphines is demonstrated by the reversible ligand exchange reaction with acetonitrile.
• The coordinated acetonitrile can be removed under vacuum.
• The ease of removal of the acetonitrile is a function of the donor character of the substituent on the phosphine.

Cationic rhodium(I) complexes of the type [Rh(COD){κ3(P,C,C)-RP(CH2CHCH2)2}][BF4] (R = tBu 3a, Ph 3b, iPr2N 3c) have been synthesized starting from the chloro-bridged dimer [Rh2(μ-Cl)2(COD)2] and fully characterized by 31P{1H}, 1H and 13C{1H} NMR. X-ray diffraction analysis of 3a and 3c showed a square planar geometry around of the rhodium atom, with allyl-phosphine ligands in a chelating fashion due to coordination of only one of the allylic double bonds while the other allyl moiety is located away from the metal center. Crystals of 3c showed the presence of the two enantiomers in the asymmetric unit. In solution, a dynamic equilibrium of exchange between the two allylic double bonds was detected by low temperature NMR analysis. Hemilabile properties of diallylphosphine ligands have been demonstrated by ligand exchange reactions and the reversible displacement of coordinated allylic double bond by acetonitrile have been observed. DFT calculations have been performed to explain the order of reactivity on removing the acetonitrile ligand under high vacuum.

Rhodium(I) complexes of the type [Rh(COD){η3(P,C,C)-RP(CH2CHCH2)2}][BF4] (R = tBu 3a, Ph 3b, iPr2N 3c) have been synthesized. X-ray diffraction analysis of 3a and 3c showed a square planar geometry around the rhodium with the coordination of one of the allyl substituents of the phosphine. Crystals of 3c showed the presence of the two enantiomers in the unit cell.Figure optionsDownload as PowerPoint slide