Assignment of pre-edge features in the Ru K-edge X-ray absorption spectra of organometallic ruthenium complexes

The nature of the lowest energy bound-state transition in the Ru K-edge X-ray absorption spectra for a series of Grubbs-type ruthenium complexes was investigated. The pre-edge feature was unambiguously assigned as resulting from formally electric dipole forbidden Ru 4d ← 1s transitions. The intensities of these transitions are extremely sensitive to the ligand environment and the symmetry of the metal centre. In centrosymmetric complexes the pre-edge is very weak since it is limited by the weak electric quadrupole intensity mechanism. By contrast, upon breaking centrosymmetry, Ru 5p–4d mixing allows for introduction of electric dipole allowed character resulting in a dramatic increase in the pre-edge intensity. The information content of this approach is explored as it relates to complexes of importance in olefin metathesis and its relevance as a tool for the study of reactive intermediates.

Graphical abstractThe lowest energy transitions in Ru K-edge XAS for a series of Grubbs-type ruthenium complexes have been assigned: the pre-edge feature results from formally electric dipole forbidden Ru 4d ← 1s transitions. The intensities of these transitions are extremely sensitive to the ligand environment due to Ru 5p–4d mixing, which allows for electric dipole allowed character and results in a dramatic increase in the pre-edge intensity. The information content of this approach is explored as it relates to complexes of importance in olefin metathesis and its relevance as a tool for the study of reactive intermediates.Figure optionsDownload full-size imageDownload as PowerPoint slide