inorganic chemistry

ligands were bleached, and other three absorption peaks (at
1970, 2017,2070 cm
^1 ) attributed to the lowest excited state,

(^3) MLCT, were produced. Although the additional three peaks
decayed at the same rate as that observed in the emission decay
experiment, the peak intensities of the ground state did not
recover to their original magnitudes. On the same timescale, a
new couple of IR absorption bands appeared (at 1876,
1951 cm
^1 ), which can be attributed to the ligand substitution
reaction product cis,trans-[Re(bpy)(CO) 2 {P(OEt) 3 }(CH 3 CN)]þ.
The rise of the IR absorption band of the product was propor-
tional to the amount of the^3 MLCT state complex formed imme-
diately after laser irradiation. This result suggested that this
photochemical ligand substitution reaction proceeds from the
(^3) MLCT state or the (^3) LF state, which is in thermal equilibrium
with the^3 MLCT state (Scheme 2).
As these excited states were attributed to the transitions from
the central metal dporbital to the bipyridinep orbital (^3 MLCT)
and to the central metal ds orbital (^3 LF), respectively, the state

• 40 –42

CO

Re

N

+

OC N

OC

P(OEt) 3

COax

(b)

(a)

–44 –46

d (ppm)

–48 –50

COeq

FIG. 9.^13 C NMR spectra of 3a in a degassed CDCl 3 solution
under^13 CO atmosphere: (a) before irradiation, (b) after 60-min irradia-
tion. Copyright 2002 American Chemical Society.

152 HIROYUKI TAKEDAet al.