Reaction of [RhCl(CO)2]2 or [RhCl(COD)]2 with o-(diphenylphosphino)benzaldehyde. Formation of hemiaminals in the subsequent reaction with dihydrazones

[RhCl(CO)2]2 reacts with o-(diphenylphosphino)benzaldehyde (PCHO) to afford a monocarbonylated rhodium(I) complex containing P-monodentate PCHO, trans-[RhCl(CO)(PCHO)2] (1) while [RhCl(COD)]2 undergoes the oxidative addition of one PCHO, with displacement of 1,5-cyclooctadiene, and coordination of the second PCHO molecule as P-(σ-aldehyde) chelate to give [RhH(PCO)Cl(PCHO)] (2) which contains trans P-atoms. Compound 2 reacts with H2NNCHCHNNH2 (gdh) to give selectively a complex [RhH(PCO)(Pgdh)]+ containing a stable hemiaminal in a new tridentate ligand, Pgdh, coordinated via the imino nitrogens and the phosphorus and the atom. The reaction of Rh(COD)(gdh)Cl with PCHO gives a mixture of the hemiaminal containing compound and the hydroxyalkyl complex [Rh(PCO)(PCHOH)(gdh)]+ which contains trans P-atoms and is formed from precursors containing cis P-atoms. The transformation of the hemiaminal group in [RhH(PCO)(PNN)]+ (PNN=Pgdh or Ppvdh (pvdh, H2NNCHC(CH3)NNH2)) into imine to give new tridentate PaNN ligands in complexes [RhH(PCO)(PaNN)]+ has also been studied.