Initial metal–metal bond breakage detected by fs X-ray scattering in the photolysis of Ru3(CO)12 in cyclohexane at 400 nm

Using femtosecond resolution X-ray solution scattering at a free electron laser we were able to directly observe metal–metal bond cleavage upon photolysis at 400 nm of Ru3(CO)12, a prototype for the photochemistry of transition metal carbonyls. This leads to the known single intermediate Ru3(CO)11(μ-CO)*, with a bridging ligand (μCO) and where the asterisk indicates an open Ru3-ring. This loses a CO ligand on a picosecond time scale yielding a newly observed triple bridge intermediate, Ru3(CO)8(μ-CO)3*. This loses another CO ligand to form the previously observed Ru3(CO)10, which returns to Ru3(CO)12via the known single-bridge Ru3(CO)10(μ-CO). These results indicate that contrary to long standing hypotheses, metal–metal bond breakage is the only chemical reaction immediately following the photolysis of Ru3(CO)12 at 400 nm. Combined with previous picosecond resolution X-ray scattering data and time resolved infrared spectroscopy these results yield a new mechanism for the photolysis of Ru3(CO)12.