The Theoretical Investigations of The Reactivity of Neutral Molecules that Feature an E=E (E = B, Al, Ga, In, and Tl) Double Bond
The geometry, the electronic structure and the reactivity of compounds that feature a central E=E (E = group 13 element) double bond with two sterically bulky ligands (L1 = tBu2MeSi and L2 = NHCiPr) , L1L2E=EL1L2 (Rea-EE)) are studied at the B3LYP-D3(BJ)/def2-SVP level of theory. The computational results show that the presence of a lighter group 13 E element (such as B, Al, and Ga) in Rea-EE results in a significant E=E double bond character and a planar structure. However, Rea-InIn and Rea-TlTl adopt a trans-bent structure, which weakens the E=E double bond. The ETS-NOCV (extended transition state–natural orbitals for chemical valence) method is used to determine the key factors that affect the reactivity of Rea-EE for its [2 + 2] cycloaddtion reaction with ethylene. The ETS-NOCV analysis shows that only Rea-BB is inert in this cycloaddtion reaction because it has large destabilizing interactions (ΔEPauli and ΔEdist) that result in a high activation barrier. This occurs because of the small radius of the B atom in the group 13 elements, which results in severe steric congestion between Rea-BB and ethylene. The present theoretical conclusions suggest that the formation of the double-bonded neutral L1L2E=EL1L2 (in particular for E = Ga and In) compound should be undoubtedly one of intriguing research targets.