Methyllithium and Its Oligomers as Lewis Bases for Hydrogen and Halogen Bonding

When bonded to electropositive Li, the methyl C exhibits strong Lewis basicity. DFT calculations show a highly negative electrostatic potential on the C and a HOMO that closely resembles a C lone electron pair. LiMe and some of its oligomers are paired in the context of both halogen and hydrogen bonds with dihalogens and HX (X = F, I, Br, Cl). There is a wide variation of halogen bond strength from 1 to 20 kcal/mol, while the H‐bonds cover a narrower range between 4 and 10 kcal/mol. The electrostatic potential minimum and the binding of (LiMe) ₂ are weakened relative to its monomer. Electrostatic effects account for slightly less than half of the total attractive energy in the halogen bonds and just over half for the H‐bonds. Enlarging the cluster to four and six Li atoms has a very mild weakening effect on the binding, reaching its asymptote for some 6–8 Li.