Structural and Energetical Characterization of the Methylbutadiene–Fe(CO)3 Isomers and Related Reactive Intermediates with Quantum Chemical Methods

Abstract

A theoretical investigation of isoprene–Fe(CO)3 (2), (E)-1,3-pentadiene–Fe(CO)3 (3), (Z)-1,3-pentadiene–Fe(CO)3 (4), and reactive intermediates derived from these complexes was undertaken, employing the HF/DFT hybrid functional Becke3LYP, and the results are presented. Special emphasis is placed on cationic, anionic, and radical intermediates formally derived by abstraction of a hydride, a proton, or a hydrogen atom from the methyl group of the parent complexes. The geometry, energy, and electronic situation of the calculated species are discussed in the context of experimental facts. This leads to a better mechanistic understanding of the chemistry of acyclic butadiene–Fe(CO)3 complexes, provides insights into structural details of the intermediates involved, and allows the evaluation of possible resonance formulae. The calculation of transition states of isomerization (or racemization) processes even permits a quantitative description of energy profiles. In this way, the configurational stability of relevant cationic, anionic and radical intermediates can be estimated.