10.1021/jp311732t.s001 Justin P. Lomont Justin P. Lomont Son C. Nguyen Son C. Nguyen Charles B. Harris Charles B. Harris Direct Observation of a Bent Carbonyl Ligand in a 19-Electron Transition Metal Complex American Chemical Society 2013 CO ligand electron picosecond time scale adduct Bent Carbonyl Ligand CH DFT CpRu TRIR spectra 2013-03-21 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Direct_Observation_of_a_Bent_Carbonyl_Ligand_in_a_19_Electron_Transition_Metal_Complex/2432092 The photochemistry of [CpRu­(CO)<sub>2</sub>]<sub>2</sub> in P­(OMe)<sub>3</sub>/CH<sub>2</sub>Cl<sub>2</sub> solution has been studied using picosecond time-resolved infrared (TRIR) spectroscopy. Photolysis at 400 nm leads to the formation of 17-electron CpRu­(CO)<sub>2</sub><sup>•</sup> radicals, which react on the picosecond time scale to form 19-electron CpRu­(CO)<sub>2</sub>P­(OMe)<sub>3</sub><sup>•</sup> adducts. The TRIR spectra of this adduct display an unusually low CO stretching frequency for the antisymmetric CO stretching mode, suggesting that one carbonyl ligand adopts a bent configuration to avoid a 19-electron count at the metal center. This spectral assignment is supported by analogous experiments on [CpFe­(CO)<sub>2</sub>]<sub>2</sub> in the same solvent, combined with DFT studies on the structures of the 19-electron adducts. The DFT results predict a bent CO ligand in CpRu­(CO)<sub>2</sub>P­(OMe)<sub>3</sub><sup>•</sup>, whereas approximately linear Fe–C–O bond angles are predicted for CpFe­(CO)<sub>2</sub>P­(OMe)<sub>3</sub><sup>•</sup>. The observation of a bent CO ligand in the 19-electron ruthenium adduct is a surprising result, and it provides new insight into the solution-phase behavior of 19-electron complexes. TRIR spectra were also collected for [CpRu­(CO)<sub>2</sub>]<sub>2</sub> in neat CH<sub>2</sub>Cl<sub>2</sub>, and it is interesting to note that no singly bridged [CpRu­(CO)]<sub>2</sub>(μ-CO) photoproduct was observed to form following 400- or 267-nm excitation, despite previous observations of this species on longer time scales.