Theoretical investigations of the reactivity of neutral molecules that feature an MM (M = B, Al, Ga, In, and Tl) double bond

Abstract

The geometry, the electronic structure and the reactivity of compounds that feature a central MM (M = group 13 element) double bond with two sterically bulky ligands (L₁ = ^tBu₂MeSi and L₂ = NHC^iPr), L₁L₂MML₁L₂ (Rea-MM) are studied at the B3LYP-D3(BJ)/def2-SVP level of theory. The computational results show that the presence of a lighter group 13 M element (such as B, Al, and Ga) in Rea-MM results in a significant EE double bond character and a planar structure. However, Rea-InIn and Rea-TlTl adopt a trans-bent structure, which weakens the MM 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-MM for its [2+2] cycloaddition reaction with ethylene. The ETS-NOCV analysis shows that only Rea-BB is inert in this cycloaddition reaction because it has large destabilizing interactions (ΔE_Pauli and ΔE_dist) 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 L₁L₂MML₁L₂ (in particular for M = Ga and In) compound should be undoubtedly one of the intriguing research targets.