Photoreactivity of bis(tricyclohexylphosphine)benzylidene ruthenium dichloride (Grubbsʹs catalyst)

The carbene complex RuII(CHPh)(PCy3)2Cl2 (Cy=cyclohexyl) in benzene undergoes a photochemical release of a phosphine ligand with φ=2.5×10−3 at λirr=546 nm. The reactive excited state is assumed to be a ligand field triplet. It is suggested that the photodissociation is initiated by a distortion of the complex from a square-planar towards a trigonal-bipyramidal structure.