Density functional insights on the role of iron tricarbonyl in manipulating the ring opening of 4π-hetero cyclobutane analogues – a shift from pseudopericyclic to pericyclic

The π-binding of iron tricarbonyl, Fe(CO)₃, tripod is known to effectively alter the stereoselectivity and torquoselectivity of electrocyclic ring opening (ERO) of cyclobutene and its derivatives by changing the mechanism. Representative examples of pseudopericyclic and also borderline pericyclic ERO reactions were chosen for the present study to establish the role of Fe(CO)₃ in manipulating the reactions. The parameters like nucleus-independent chemical shift (NICS), natural bond orbital (NBO) analysis, and topological parameters like ∇²ρ(r) (Laplacian) and ε (ellipticity) have revealed marked drifting of the reaction lying on the pseudopericyclic end to the borderline pericyclic end, which is due to Fe(CO)₃ binding.

Graphical abstract

Iron tricarbonyl alters the nature of pseudopericyclic reaction by making it borderline pericyclic. Activation barrier increases for pseudopericyclic case which is very low in the absence of Fe(CO)_3. No disconnection of orbitals is observed for pseudopericyclic system when complexed with Fe(CO)₃.