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.