Synthesis and structural characterization of diene and benzene pentaruthenium clusters

Abstract

Reaction of the square-pyramidal cluster [Ru₅C(CO)₁₅]1 with cyclohexa-1,3-diene and Me₃NO in CH₂Cl₂ at ambient temperature affords the novel species [Ru₅C(CO)₁₃(µ-η²:η²-C₆H₈)]2 which has been fully characterized by X-ray diffraction studies [monoclinic, space group P2₁/n, a= 16.193(3), b= 9.897(2), c= 19.536(4)Å, β= 98.80(3)° and Z= 4]. Further reaction of compound 2 with Me₃NO in the same solvent results in the dehydrogenation of the C₆H₈ ligand and the production of two isomers 3a and 3b of the benzene derivative [Ru₅C(CO)₁₂(C₆H₆)]. In agreement with mass spectroscopic and ¹H NMR data, the X-ray diffraction analysis shows that the benzene ligand is bound in a face-capping mode in [Ru₅C(CO)₁₂(µ₃-η²:η²:η²-C₆H₆)]3a and in a terminal mode in [Ru₅C(CO)₁₂(η⁶-C₆H₆)]3b, respectively. Compound 3a is triclinic, space group P1^–, a= 9.525(2), b= 14.574(3), c= 9.484(4)Å, α= 96.29(2), β= 112.37(3), γ= 82.33(2)° and Z= 2; 3b is monoclinic, space group P2₁/c, a= 15.26 (2), b= 16.675(9), c= 19.016(9)Å, β= 96.04(7)° and Z= 8. On heating 3a in hexane a quantitative and irreversible conversion to 3b is observed. Treatment of 3b with carbon monoxide produces the adduct [Ru₅C(CO)₁₃(η⁶-C₆H₆)]4a, which, on the basis of a single crystal X-ray diffraction study, has been shown to contain a ‘bridged-butterfly’ arrangement of five ruthenium atoms. Compound 4a is monoclinic, space group P2₁/n, a= 9.792(4), b= 15.718(2), c= 16.446(3)Å, β= 96.37(2)° and Z= 4. On standing in CH₂Cl₂, 4a undergoes loss of carbon monoxide to give the apical isomer [Ru₅C(CO)₁₂(C₆H₆)]3c. On heating in hexane over a prolonged period 3c undergoes quantitative isomerization to 3b.