Structure, Stereochemistry and Dynamics of Tetranuclear Polyhydride Clusters Containing Chiral Heterobidentate Phosphanes

A novel chiral phosphane (S)-2-(4-isopropyl-2-oxazoline-2-yl)phenyl-di-N-pyrrolylphosphane (S-PyrPOx) based on asymmetric oxazoline ring has been prepared and characterised. Reaction of this ligand and its phenyl-substituted analogue (S-PhPOx) with H4Ru4(CO)12 and H3RhOs3(CO)12 gave substituted derivatives H4Ru4(CO)10(1,1-PhPOx) (2), H4Ru4(CO)10(1,1-PyrPOx) (3), and H3RhOs3(CO)10(1,1-PyrPOx) (4), which were structurally characterised by X-ray crystallography in solid state and by a variety of multinuclear NMR spectroscopic measurements in solution. In all studied clusters the coordinated ligands form five-membered chelate rings through phosphorus and nitrogen atoms of oxazoline moiety to afford a novel chiral center associated with the substituted metal atom. The substitution reactions demonstrate extremely high stereoselectivity, which results in formation of only one diastereomer in all three cases to give S,S isomer in 2 and S,R isomer in 3 and 4.