inorganic chemistry

17-electron species that reacts directly with CO 2. For the OER
species to serve these two roles (1) requires stability while (2)
requires instability, demanding contradicting features. Based
on this consideration, high photocatalytic attributes have been
achieved by employment of a mixture of two rhenium complexes
(MS), each with optimized functions. fac-[Re{4,4^0 -(MeO) 2 bpy}
(CO) 3 {P(OEt) 3 }]þ (3j) yields the corresponding OER species
with high efficiency (F¼1.6) under photocatalytic reaction
conditions, and this OER species has a strong oxidation power
(E1/2red¼
1.67V vs. Ag/AgNO 3 ). Although the CO 2 reduction
quantum yield using this complex alone is fairly high at 0.33,
the addition of a small amount offac-[Re(bpy)(CO) 3 (CN 3 CN)]þ
( 13 ), which shows nearly no CO 2 reducing ability, led to the most
efficient CO 2 photoreduction among known homogeneous
photocatalysts (FCO¼0.59) ( 64 ). Complex3jfunctions as a photo-
sensitizer for single-electron transfer in this mixed photocatalyst
system. However, fac-[Re(bpy)(CO) 3 (CN 3 CN)]þ ( 13 ) forms 17-
electron species efficiently, as elimination of the monodentate
ligand occurs rapidly after receiving one electron from the OER
species of3j. After reacting with CO 2 , the CO 2 adduct receives
another electron from the OER species of3jto produce CO and
complete its role as a catalyst (Scheme 7).
One drawback of rhenium tricarbonyl complexes,fac-[Re(bpy)
(CO) 3 L]nþ, is that their absorption of visible light is weak (see

+

CO

CO

CO

NN Rel COCO MeO

MeO

CO

NN Rel

CO

CO

CO

P(OEt) 3

NN Rel

CO

CO

CO

NN Rel

MeO

MeO

CO

CO

CO

3j

13

P(OEt) 3

hn

NN Rel

CO 2

[CO 2 adduct]

CO

L L

Fco= 0.59!!

L

e–

e–

L

e–

SCHEME7. Schematic representation of multicomponent system with
3jas photosensitizer and 13 as catalyst of which acetonitrile ligand can
be substituted with L such as DMF and TEOA in the reaction solution.
Adapted with permission from Ref. ( 64 ). Copyright 2008 American
Chemical Society.

RHENIUM(I) DIIMINE COMPLEXES 177