SYNTHESIS AND PROPERTIES OF PI-BONDED OLEFIN AND ACETYLENE COMPLEXES OF RUTHENIUM(II) - CRYSTAL AND MOLECULAR-STRUCTURE OF THE PENTAAMMINERUTHENIUM(II) FUMARIC-ACID COMPLEX, [(NH3)5RU(C4H4O4)]S2O6.2H2O

Alkenes and alkynes react with the pentaamminemonoaquoruthenium(II) ion to form complexes containing the irbonded unsaturated organic molecule as a ligand. Syntheses and spectroscopic properties of the complexes with ethylene, iso-butene, 1,4-cyclohexadiene, fumaric acid, acetylene, phenylacetylene, and 3-hexyne are reported. The electronic spectra are dominated by an intense band at about 220 nm ascribed to a ύ(d)→-ύ*(L) charge transfer. The coordination of the multiple bond to ruthenium is demonstrated by a shift of the C≡C and C≡C stretching frequencies by 100-200 cm-1 to lower energies. 1H NMR spectra are consistent with an edge-on bonding arrangement. Formal reduction potentials obtained by cyclic voltammetry are between 0.6 and 1.40 V (vs. N HE) showing the stabilization of the divalent state of ruthenium by the strong back bonding to the ligand. The crystal and molecular structure of the particular case of the fumaric acid complex has been determined by a single-crystal X-ray study to R ≡ 0.034 and Rw ≡ 0.040 for 1242 unique reflections. The compound crystallizes in the orthorhombic system with four molecules in space group D25-C2221. Cell dimensions are a = 9.840 (3). b = 10.887 (4), c = 15.970 (4) Å. The five Ru-N distances are between 2.143 (6) and 2.154 (5) Å, the two equivalent Ru-C distances are 2.172 (6) Å, and the C-C bond length of the olefinic group is 1.413 (8) Å. © 1979, American Chemical Society. All rights reserved.