This Perspective
discusses oriented external-electric-fields (OEEF),
and other electric-field types, as “smart reagents”,
which enable in principle control over wide-ranging
aspects of reactivity and structure. We discuss the potential of OEEFs
to control nonredox reactions and impart rate-enhancement and selectivity.
An OEEF along the “reaction axis”, which is the direction
whereby electronic reorganization converts reactants’ to products’
bonding, will accelerate reactions, control regioselectivity,
induce spin-state selectivity, and elicit mechanistic crossovers. Simply flipping the direction of the OEEF will lead to
inhibition. Orienting the OEEF off the reaction axis
enables control over stereoselectivity, enantioselectivity, and product
selectivity. For polar/polarizable reactants, the OEEF itself will act as tweezers, which orient the reactants
and drive their reaction. OEEFs also affect bond-dissociation energies
and dissociation modes (covalent vs ionic), as well as alteration
of molecular geometries and supramolecular aggregation. The “key”
to gaining access to this toolbox provided by OEEFs is microscopic
control over the alignment between the molecule and the applied field.
We discuss the elegant experimental methods which have been used to
verify the theoretical predictions and describe various alternative
EEF sources and prospects for upscaling OEEF catalysis in solvents.
We also demonstrate the numerous ways in which the OEEF effects can
be mimicked by use of (designed) local-electric fields (LEFs), i.e., by embedding charges or dipoles into molecules. LEFs and OEEFs are shown to be equivalent and to obey the same
ground rules. Outcomes are exemplified for Diels–Alder cycloadditions,
oxidative addition of bonds by transition-metal complexes, H-abstractions
by oxo-metal species, ionic cleavage of halogen bonds, methane activation,
etc.