The radical complex (C5Ph5)Cr(CO)3 reacts with small, neutral, monodentate Lewis bases (PMe3, PMe2Ph, P(OMe)3) in THF at −78 °C (PMe2Ph reacts at ambient temperature) to yield the monomeric substitution products (C5Ph5)Cr(CO)2L·THF as thermally stable solids. Electrochemical and spectroscopic data are provided. An X-ray crystal structure of the hemisolvate (C5Ph5)Cr(CO)2PMe3·0.5THF was obtained. Frozen-solution ESR spectra of (C5Ph5)Cr(CO)2L in toluene are comparable to those of other low-spin d5 “piano-stool” complexes. Rotation of the Cr(CO)2L moiety relative to the C5Ph5 ring is rapid on the ESR time scale in low-temperature liquid solutions and leads to axial powderlike spectra. Analysis of this effect leads to significant insights into the electronic structure.
Hammack, D. J.; Dillard, M. M.; Castellani, M. P.; Rheingold, A. L.; Rieger, A. L.; Rieger, P. H., Substitution Reactions of (C5Ph5)Cr (CO)3: Structural, Electrochemical, and Spectroscopic Characterization of (C5Ph5)Cr(CO)2L (L= PMe3, PMe2Ph, P (OMe)3). Organometallics 1996, 15 (22), 4791-4797.