Hydroxyalkyl Complexes and Hemiaminal Formation in the Reaction of o-Diphenylphosphinobenzaldehyde with Rhodium(I) Dihydrazone Complexes

The diimino complex Rh(COD)(bdh)Cl (bdh:  H₂NNC(Me)C(Me)NNH₂) reacts with o-diphenylphosphino(benzaldehyde) (PCHO) in the presence of PPh₃ to give acylhydrido [Rh(H)(PCO)(PPh₃)(bdh)]⁺ species. When using Rh/PCHO = 1:2 stoichiometric ratios, oxidative addition of one PCHO and P-coordination of another PCHO occurs. The aldehyde group then undergoes two competitive reactions:  (i) addition of one free amino group to give a stable hemiaminal and a complex [Rh(H)(PCO)(Pbdh)]⁺ that contains a new PNN ligand coordinated via the imino nitrogens and the phosphorus atom or (ii) insertion into Rh−H to give the hydroxyalkyl complex [Rh(PCO)(PCHOH)(bdh)]⁺. The complexes have been fully characterized, and X-ray diffraction structures of both of them are reported. Some intermediates in the competitive reactions have been spectroscopically characterized, and the transformation of the hemiaminal group into imine to give a PaNN ligand in the complex [Rh(H)(PCO)(Pabdh)]⁺ has also been studied.