Abstract
The reduction of carbon dioxide to chemical fuels such as carbon monoxide is an
important challenge in the field of renewable energy conversion. Given the
thermodynamic stability of carbon dioxide, it is difficult to efficiently activate this
substrate in a selective fashion and the development of new electrocatalysts for CO2
reduction is of prime importance. To this end, we have prepared and studied a new
fac-ReI(CO)3 complex supported by a bipyridine ligand containing ancillary BODIPY
moieties ([Re(BB2)(CO)3Cl]). Voltammetry experiments revealed that this system
displays a rich redox chemistry under N2, as [Re(BB2)(CO)3Cl] can be reduced by
up to four electrons at modest potentials. These redox events have been
characterized as the ReI/0 couple, and three ligand based reductions – two of which
are localized on the BODIPY units. The ability of the BB2 ligand to serve as a noninnocent
redox reservoir is manifest in an enhanced electrocatalysis with CO2 as
compared to an unsubstituted Re-bipyridine complex lacking BODIPY units
([Re(bpy)(CO)3Cl]). The second order rate constant for reduction of CO2 by
[Re(BB2)(CO)3Cl] was measured to be k = 3400 M–1s–1 at an applied potential of –
2.0 V versus SCE, which is roughly three times greater than the corresponding
unsubstituted Re-bipyridine homologue. Photophysical and photochemical studies
were also carried out to determine if [Re(BB2)(CO)3Cl] was a competent platform for
CO2 reduction using visible light. These experiments showed that this complex
supports unusual excited state dynamics that are not typically observed for fac-
ReI(CO)3 complexes.
