Photoinduced Reactions of Diruthenium Tetrahydride Complexes: Carbon–Hydrogen Bond Cleavage of Tetrahydrofuran Leading to Bridging Cyclic Fischer-Type Carbene Complexes

Photochemical reactions of diruthenium tetrahydride complexes containing cyclopentadienyls as auxiliary ligands, CpsRu­(μ-H)₄RuCps (<b>1</b>) (<b>a</b>: Cps = C₅Me₅ (Cp*), <b>b</b>: C₅EtMe₄ (Cp^Et), and <b>c</b>: 1,2,4-C₅(<i>t</i>-Bu)₃H₂ (Cp^‡)), with tetrahydrofuran were studied for elucidation of the reaction mode of dinuclear complexes containing multiple bridging hydrides. Complexes <b>1a</b>–<b>c</b> reacted with tetrahydrofuran under UV irradiation (365 nm) to produce bridging cyclic Fischer-type carbene complexes, {CpsRu­(μ-H)}₂(μ-<i>cyclo</i>-CCH₂CH₂CH₂O−)­(μ-H)₂ (<b>5</b>), via consecutive C–H bond cleavage at the α-position of the oxygen atom. The characteristic cyclic structures of the bridging carbene ligands were unambiguously confirmed by X-ray diffraction studies. Line-shape analysis of the variable-temperature ¹H NMR spectra of <b>5c</b> demonstrated the rotation of the bridging carbene ligand