Cooperative Chemistry at the Hard–Soft Interface: Phosphine Oxide-Based Rare Earth–Transition Metal Complexes

A series of monometallic Al(III), Sm(III), Dy(III), Er(III), and Yb(III) complexes, featuring tetraphenyldiphosphine monoxide (PPO) as a ligand, were synthesised and characterised. These complexes served as precursors for the construction of heterobimetallic rare earth (RE)–transition metal (TM) assemblies. Attempts to introduce soft TMs, such as Cu(I) and Au(I), into the pre-formed RE–PPO synthons predominantly afforded equilibrium-driven TM-based POP species, underscoring the challenges of incorporating hard and soft metal centres directly. This observation led to an alternative route employing a pre-synthesised Mo–PPO synthon, which led to the successful formation of RE–Mo heterobimetallic complexes upon addition of the RE ions. The molecular structures of both mono- and heterobimetallic species were strongly influenced by the solvent environment. Notably, reactions in dichloromethane, a non-coordinating solvent, yielded RE2 complexes featuring chloride bridges, a motif absent when coordinating solvents, such as THF or MeCN were employed. This solvent-dependent structural divergence offers a straightforward strategy for modulating the metal nuclearity. ... mehrRemarkably, all RE ions in the resulting complexes adopt an uncommon octahedral coordination geometry, attributed to the steric and electronic constraints imposed by the PPO ligand at the hard–soft interface.