Diastereomeric chiral diphosphine chioro(η5-cyclopentadienyl)ruthenium(II) complexes and the crystal structure of [(S)RuCl(η5-C5H5){(R)Ph2PCH(Me)CH2PPh2}]

Abstract

Diastereomeric [RuCl(η⁵-C₅H₅){Ph₂PCH(R)CH₂PPh₂}] chelate complexes (where R = CH₃, cyclo-C₆H₁₁, or C₆H₅) form in nearly equimolar amounts in the displacement reaction of triphenylphosphine from [RuCl(η⁵-C₅H₅)(PPh₃)₂]. The diastereomers were separated by fractional crystallization. Diastereomeric composition at the equilibrium showed a low asymmetric induction (28–41%) by the optically active diphosphine ligand on the chiral ruthenium atom. The absolute configuration at the ruthenium atom has little influence on the chiroptical properties of the complexes, which appear to be dominated, at least in the visible region, by the chiral conformation of the chelate ligand. The crystal structure of the title diastereomer, [(S)RuCl(η⁵-C₅H₅){(R)Ph₂PCH(Me)CH₂PPh₂}], has been investigated. It is monoclinic, space group P2₁, with a= 9.688(3), b= 15.037(4), c= 10.556(2)Å, β= 113.54(2)°, and Z= 2. The structure was solved by Patterson and Fourier methods, and refined by least squares on the basis of 2 000 significant counter data, to a final R value of 0.042. The complex shows a distorted λ conformation of the diphosphine ligand in the chelate five-membered ring, in the solid state. The Ru–Cl and Ru–P interactions are 2.444(2) and 2.277 Å(mean value), respectively.