title: Altered torquoselectivity of fluorine in the iron-tricarbonyl-mediated thermal ring opening of 3-fluorocyclobutene: a density-functional exploration.
abstract: There are eight possible pathways for the iron-tricarbonyl-assisted thermal electrocyclic ring opening of fluorocyclobutene due to variations in the orientation of the binding of Fe(CO)3relative to the fluorine substituent (R1or R2), stereoselectivity (conrotatory or disrotatory, i.e., C or D), and the torquoselectivity of fluorine (inward-facing or outward-facing, i.e., in or out). A density functional study revealed that the energetically favored pathway is R1Din. Not only is the D mode favored energetically, but the in configuration was observed to be the lowest-lying mode of R1, despite the general tendency of fluorine substituents to prefer an out configuration. Data on the activation hardness and aromaticity indices such as BAC and HOMA lead to the same conclusion. However, the R2mode surprisingly shows no particular preference for either the Cout or the Dout pathway (i.e., the R2mode shows less stereoselectivity than R1). This behavior occurs due to the influences of both the fluorine substituent and metal coordination. Also, the geminal bond orbitals σ(C-F) and σ*(C-F) appear to participate in ring opening, given the excellent correlation of ∆BE with the activation barrier of the transition state.
authors.affiliation: Department of Chemistry, Sri Sarada College for Women, Salem, 636016, Tamilnadu, India.
authors.forename: Chandresakaran
authors.initials: C
authors.lastname: Prathipa
authors.affiliation: Department of Chemistry, Sri Sarada College for Women, Salem, 636016, Tamilnadu, India. akilchem@gmail.com.
authors.forename: Lakshminarayanan
authors.initials: L
authors.lastname: Akilandeswari
keywords: DFT; Electrocyclic ring opening; Fe(CO)3; Torquoselectivity