Dynamic Processes on the IR Time Scale: Coalescence of CO Stretching Vibrational Bands in [(η⁴‐Diene)Fe(CO)₃] Complexes

Complex chemists should check the temperature dependence of the IR spectra of their compounds more often . The IR spectra of the Fe(CO) 3 complexes with norbornadiene and 1,5‐cyclooctadiene at room temperature show only two CO bands, despite C s symmetry, whereas at ca. 10 K the expected three bands are observed with about equal intensities. That is, a coalescence must take place by a very rapid intramolecular rearrangement whose activation energy is only ca. 2. 2 kcal mol −1 .