10.1021/ic4013729.s001
Chern-Hooi Lim
Chern-Hooi
Lim
Aaron
M. Holder
Aaron
M.
Holder
James T. Hynes
James T.
Hynes
Charles B. Musgrave
Charles B.
Musgrave
Roles of
the Lewis Acid and Base in the Chemical Reduction of CO<sub>2</sub> Catalyzed by Frustrated Lewis Pairs
American Chemical Society
2013
Frustrated Lewis PairsWe
quantum chemical calculations
FLP
HT
LA
AB
LB
catalyzes hydride transfer
CO 2 reductions
CO 2
LUMO
CO 2 Catalyzed
2013-09-03 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Roles_of_the_Lewis_Acid_and_Base_in_the_Chemical_Reduction_of_CO_sub_2_sub_Catalyzed_by_Frustrated_Lewis_Pairs/2382052
We employ quantum
chemical calculations to discover how frustrated Lewis pairs (FLP)
catalyze the reduction of CO<sub>2</sub> by ammonia borane (AB); specifically,
we examine how the Lewis acid (LA) and Lewis base (LB) of an FLP activate
CO<sub>2</sub> for reduction. We find that the LA (trichloroaluminum,
AlCl<sub>3</sub>) alone catalyzes hydride transfer (HT) to CO<sub>2</sub> while the LB (trimesitylenephosphine, PMes<sub>3</sub>) actually
hinders HT; inclusion of the LB increases the HT barrier by ∼8
kcal/mol relative to the reaction catalyzed by LAs only. The LB hinders
HT by donating its lone pair to the LUMO of CO<sub>2</sub>, increasing
the electron density on the C atom and thus lowering its hydride affinity.
Although the LB hinders HT, it nonetheless plays a crucial role by
stabilizing the active FLP·CO<sub>2</sub> complex relative to
the LA dimer, free CO<sub>2</sub>, and free LB. This greatly increases
the concentration of the reactive complex in the form FLP·CO<sub>2</sub> and thus increases the rate of reaction. We expect that the
principles we describe will aid in understanding other catalytic CO<sub>2</sub> reductions.