Carbon as an Electron Donor Atom
NSF, Division of Chemistry (CHE) 1954310
NSF, Division of Chemistry (CHE)
There are a number of C-containing entities which can donate electrons. The C atom of the CN− anion contains a lone pair which can be transferred to a Lewis acid. Even if the acid molecule is anionic, short-range attractive forces can overcome the long-range ion-ion repulsion to approach close enough to engage in a strong bonding interaction. The CN− anion can be surrounded by a number of ligands that interact through a host of different types of bonds. The C lone pair of the MeCH2− carbanion is also available for donation. Neutral C-containing molecules can function as electron source as well. Despite the absence of any C lone pair, a CH3M unit can donate electron density from its σ-bonding orbitals to a neutral molecule within the framework of a ditetrel bond. The C lone pairs of carbenes may also be donated to form strong bonds within the covalent range. The π-systems of alkenic or aromatic molecules represent an alternate source, although generally weaker than the interactions arising from C lone pairs.
Scheiner, Steve. “Carbon as an Electron Donor Atom.” Polyhedron, vol. 193, Jan. 2021, p. 114905. DOI.org (Crossref), https://doi.org/10.1016/j.poly.2020.114905.