Reaction of Secondary Phosphine Oxides with Rhodium(I)

Five secondary phosphine oxides (SPOs) differing in the steric and electronic properties of the P-substituents were reacted with [Rh(acac)(cod)]. Due to the tautomeric equilibrium, SPOs are able to coordinate to metal atoms via their trivalent tautomers. Their complexation behavior is strongly dependent on the substituents at the phosphorus atom. Electron-rich tertiary alkyl groups do not favor the reaction, whereas electron-poor phosphinous acids immediately coordinate, resulting in “quasi-chelate” complexes with a hydrogen bond in the backbone. The latter remains intact even in alcohols. Additionally, the SPOs were reacted with [Rh(cod)2]BF4, resulting in the corresponding BF2-capped complexes.