Synthesis and characterization of 2-oxacycloalkylideneruthenium(II) complexes: X-ray crystal structure of the 2-oxacycloheptylidene complex [Ru{COCH2(CH2)3CH2}(η5-C9H7)(PPh3)2][PF6]·CH2Cl2

The oxacyclocarbene complexes [Ru{H2}(η5-C9H7)LL′][PF6]·(L=L′=PPh3, n=1 (2a), 2 (3a), 3 (5a); L=L′=PMe2Ph, n=1 (2b), 2 (3b), 3 (5b); LL′=dppm, n=1 (2c), 2 (3c), 3 (5c); L=PPh3, L′=PMe3, n=1 (2d), 2 (3d), 3 (5d)) have been prepared by reaction of [RuCl(η5-C9H7)LL′] with 3-butyn-1-ol, 4-pentyn-1-ol and 5-hexyn-1-ol in refluxing ethanol and in the presence of NaPF6. The process involves alkyne to vinylidene tautomerization to give hydroxyalkylvinylidene intermediate complexes. The vinylidene complexes [Ru{CC(H)(CH2)3CH2OH}(η5-C9H7)LL′][PF6] (L=L′=PPh3 (4a), L=L′=PMe2Ph (4b), L=PPh3, L′=PMe3 (4d)) have been isolated from the reaction of [RuCl(η5-C9H7)LL′] with 5-hexyn-1-ol. The first structure for a 2-oxacycloheptylidene complex, 5a, has been determined by X-ray diffraction methods. The molecular structure shows the typical pseudooctahedral three-legged piano-stool geometry around the ruthenium atom, which is linked to the phosphorus atoms of the triphenylphosphine ligands and to the Cα of the oxacyclic carbene ligand; the coordination around the ruthenium atom is completed by a η5-bonded indenyl ligand with the benzo ring orientated nearly trans to the carbene group (CA=16.6(6)°). The RuC1 distance, 1.89(1) Å, is somewhat shorter than that found for other oxacyclic carbene ruthenium(II) complexes. The oxacycloheptylidene ring adopts a ‘pseudochair’ conformation for the seven member ring and shows an appreciable deviation from vertical orientation (DA=29.7(5)°).