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-2:2-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, = 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(µ3-2:2:2-C6H6)]3a and in a terminal mode in [Ru5C(CO)12(6-C6H6)]3b, respectively. Compound 3a is triclinic, space group P1–, a= 9.525(2), b= 14.574(3), c= 9.484(4)Å, = 96.29(2), = 112.37(3), = 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, = 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(6-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, = 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.