inorganic chemistry

CO

CO

CO

TEA/DMF

Ar sat.

Re

Br

N

N

CO

CO

CO

Re

Br

C 2 H 5

N

hn (l> 400 nm) N

ð 14 Þ

The formation yield was 10–43% depending on reaction
conditions. This reaction is also initiated by photochemical
reduction of the Re(I) complex by TEA. Interestingly, the ethyl
group was only introduced at the 5-position of the bpy ligand.
Thetrans–cisphotoisomerization of the“stilbene-type”ligand
in the Re(I) diimine complexes has been reported( 55 ).

R

R

N

Re

N

hn

N N

N

N

CO CO

OC

OC

Re

OC

OC

ð 15 Þ

For instance, fac-[Re(phen)(CO) 3 (trans-stpy)]þ (phen¼1, 10-
phenanthroline, trans-stpy¼trans-4-styrylpyridine) was
irradiated at three different wavelengths (313, 334, and
365 nm) in an acetonitrile solution. Although there is no absorp-
tion by freetrans-stpy at 365 nm, isomerization of thetrans-stpy
ligand to thecis-form proceeded with reaction quantum yields of
0.35, 0.36, and 0.31, respectively( 56 ). The photochemical isomer-
ization proceeds via intramolecular sensitization, that is,

(^1) MLCT, (^1) pp! (^3) MLCT! (^3) pp(trans-stpy)! (^3) pp* of which trans-
stpy ligand is twisted ( 57 ).
IV. Rhenium(I) Complexes as Highly Efficient Photocatalyst
As noted above (Section II), rhenium(I) complexes have
relatively long excitation lifetimes in solution at room tempera-
ture and can be used as redox photosensitizers that drive
RHENIUM(I) DIIMINE COMPLEXES 167