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 (1) (a: Cps = C5Me5 (Cp*), b: C5EtMe4 (CpEt), and c: 1,2,4-C5(t-Bu)3H2 (Cp‡)), with tetrahydrofuran
were studied for elucidation of the reaction mode of dinuclear complexes
containing multiple bridging hydrides. Complexes 1a–c reacted with tetrahydrofuran under UV irradiation (365 nm)
to produce bridging cyclic Fischer-type carbene complexes, {CpsRu­(μ-H)}2(μ-cyclo-CCH2CH2CH2O−)­(μ-H)2 (5), 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 5c demonstrated the rotation of the
bridging carbene ligand.