Visible-light photocatalysis and electrocatalysis are
two powerful
strategies for the promotion of chemical reactions that have received
tremendous attention in recent years. In contrast, processes that
combine these two modalities, an area termed electrophotocatalysis,
have until recently remained quite rare. However, over the past several
years a number of reports in this area have shown the potential of
combining the power of light and electrical energy to realize new
catalytic transformations. Electrophotocatalysis offers the ability
to perform photoredox reactions without the need for large quantities
of stoichiometric or superstoichiometric chemical oxidants or reductants
by making use of an electrochemical potential as the electron source
or sink. In addition, electrophotocatalysis is readily amenable to
the generation of open-shell photocatalysts, which tend to have exceptionally
strong redox potentials. In this way, potent yet selective redox reactions
have been realized under relatively mild conditions. This Perspective
highlights recent advances in the area of electrophotocatalysis and
provides some possible avenues for future work in this growing area.
The conversion of carbonyls to olefins is a transformation of great importance for complex molecule synthesis. Standard methods use stoichiometric reagents that have poor atom economy and require strongly basic conditions, which limit their functional group compatibility. An ideal solution would be to catalytically olefinate carbonyls under nonbasic conditions using simple and widely available alkenes, yet no such broadly applicable reaction is known. Here, we demonstrate a tandem electrochemical/electrophotocatalytic reaction to olefinate aldehydes and ketones with a broad range of unactivated alkenes. This method involves the oxidation-induced denitrogenation of cyclic diazenes to form 1,3-distonic radical cations that rearrange to yield the olefin products. This olefination reaction is enabled by an electrophotocatalyst that inhibits back-electron transfer to the radical cation intermediate, thus allowing for the selective formation of olefin products. The method is compatible with a wide range of aldehydes, ketones, and alkene partners.
The efficient and regioselective
hydrosilylation of epoxides co-catalyzed
by a pentacarboxycyclopentadienyl (PCCP) diamide nickel complex and
Lewis acid is reported. This method allows for the reductive opening
of terminal, monosubstituted epoxides to form unbranched, primary
alcohols. A range of substrates including both terminal and nonterminal
epoxides are shown to work, and a mechanistic rationale is provided.
This work represents the first use of a PCCP derivative as a ligand
for transition-metal catalysis.
The
efficient and regioselective hydrosilylation of epoxides co-catalyzed by a
pentacarboxycyclopentadienyl (PCCP) diamide nickel complex and Lewis acid is
reported. This method allows for the
reductive opening of terminal, monosubstituted epoxides to form unbranched,
primary alcohols. A screen of diamide
PCCP ligands revealed a correlation of steric demand and regioselectivity, with
smaller ligands being optimal, while the addition of Lewis acid enabled
efficient reactions at room temperature.
A range of substrates including both terminal and non-terminal epoxides
are shown to work, and a mechanistic rationale is provided. This work represents the first use of a PCCP
derivative as a ligand for transition metal catalysis.
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