On the existence of collective interactions reinforcing the metal-ligand bond in organometallic compounds

Abstract

Recently, Sowlati-Hashjin et al.1 concluded that the nature of the Li-C chemical bond in LiCF3 differs significantly from that in LiCPh3 (Ph = phenyl). Whereas the Li-C bond of LiCF3 is classified as a conventional two-center two-electron bond (exchange-correlation interaction collectivity index, ICIXC = 0.910, ICIXC > 0.9 and close to 1), that of LiCPh3 is categorized as a collective bond (ICIXC = 0.393). The authors claim that collective bonds take place in systems composed of MAR3 (M = metal; A = C, B or Al; R = substituent) when M forms a stronger bond with the substituents R than with the central atom A. They claim the M-A interaction is either destabilizing or weakly stabilizing, whilst the 1,3-M R interactions are strongly stabilizing, but their method does not provide a causal mechanism that would demonstrate the correctness of this interpretation of the ICIXC index. Here, we prove the opposite, namely, that the Li-CPh3 bond is not reinforced or provided by collective interactions, but that it is weakened by 1,3-M R contacts, which reduce the bond overlap. On top of that, there is 1,3-M R closed-shell overlap that further reduces the stability through Pauli repulsion. Taken together, our results suggest that there is no need to define the collective interaction as a new type of chemical bond