Ability of Carbenes to Act as Lewis Base within a Halogen Bond

Abstract

A halogen bond is formed by a wide range of divalent CR 2 carbenes with ICN as Lewis acid, and the results examined by DFT calculations. These carbenes form much stronger halogen bonds than more common Lewis bases such as NH 3 and OH 2 . The binding occurs through the carbene C lone pair and is enhanced if the central C is covalently attached to C on the R substituent, as compared to O or N. Interaction energies are as high as 30 kcal/mol, and the C••I bond contains a certain degree of covalent character. The two lone pairs on the C atom of the carbene, when connected through dative bonds to units such as NH 3 and OH 2 , make this C especially strongly nucleophilic, enough so as to partially extract the I from the ICN unit. The carbene halogen bonds have all of the characteristics of their classic counterparts, including a high dependence upon Coulombic interaction.