Synthesis and reactivity of formamidinato rhodium(I) complexes

The syntheses of Rh(diol)(formamidine)]₂ complexes (diol  cycloocta-1,5-diene (1); diol  norbornadiene (2); formamidine  N,N′-di-p-tolylformamidine) are reported. These complexes are dimeric and contain the bridging formamidino ligand. They react with CO, dppe and PPh₃ with displacement of the diene ligand to yield the known Rh(CO)₂(formamidine)]₂, Rh(dppe)₂]⁺ and Rh(PPh₃)₂(formamidine)], respectively; the last complex, in which the formamidine acts as a chelating ligand, was isolated only as the O₂ adduct. With HCl or HBF₄ aqueous 1 and 2 do not form hydrides but instead the formamidino cation p-tolyl-NHCHNHtolyl-p]⁺ and the complexes Rh(diol)X]₂ (X  Cl, F); a possible scheme for the reaction with HCl is proposed. The Rh(C₈H₁₂)(formamidine)]₂ complex reacts with heterocumulenes as CS₂, SO₂, PhNCS and PhNCO with diene displacement; the only product isolated was Rh(CS₂)₂(formamidine], to which a polymeric structure is assigned.