Reaction of (S)-BINAP with H₄Ru₄(CO)₁₂. The First Example of Face-Bridging BINAP Coordination and 100% Stereoselectivity in Formation of a Chiral Tetranuclear Cluster Framework

The reaction of H₄Ru₄(CO)₁₂ with (S)-BINAP in the presence of Me₃NO affords the cluster H₄Ru₄(CO)₁₀(μ-(S)-BINAP) (2) in good yield. Gentle heating of a benzene−ethanol solution of 2 results in the dissociation of CO and coordination of a naphthyl fragment of BINAP to give H₄Ru₄(CO)₉(μ₃-(S)-BINAP) (3) with face-bridging coordination of the diphosphine ligand. The solid-state structures of both clusters have been determined by X-ray crystallography. Their structures in solution and some details of ligand sphere dynamics have been elucidated using 1D variable-temperature ¹H and ³¹P NMR spectroscopy together with selective decoupling measurements and ¹H COSY and NOESY experiments. The difference ¹H nuclear Overhauser effect (NOE) spectra provide additional support for the structural models suggested by visualization of important intramolecular nonbonding contacts in the molecules under study. The metal frameworks in 2 and 3 are chiral, due to the chemical difference of the ruthenium atoms induced by asymmetry of their ligand environments. The chemical reactions, which result in the formation of 2 and 3, display exceptional stereoselectivity to give a unique S,S configuration of the two ((S)-BINAP and cluster framework) stereogenic centers in the both compounds. The NMR and CD spectroscopic studies indicated that the S,S configuration observed in the solid state remains unchanged in solution. The cluster 3, containing face-bridging BINAP, demonstrates exceptional thermal stability and does not undergo metal framework racemization up to 343 K.