inorganic chemistry

photochemical reactions. Irradiation of1ausing 313-nm light in
an Ar-saturated acetonitrile solution gave (OC-6-34)-[Re(bpy)
(CO) 2 (CH 3 CN)Cl] ( 4 ), which is a CO ligand substitution product
and (OC-6-24)-[Re(bpy)(CO) 2 Cl(CH 3 CN)] ( 5 ), an isomer of 4
(Eq. 11). Complex 5 was isomerized to (OC-6-44)-[Re(bpy)
(CO) 2 (CH 3 CN)Cl] ( 6 ) even in the dark ( 51 ). The reaction quan-
tum yield evaluated from the consumption of complex1awas
0.010.001, which increased using higher-energy light.

CO

CO

CO CO CO

CO

CO

CO

Re Re

Re

CO+

N N

N

in the dark N

5

6

N

N

NCCH 3

NCCH 3

NCCH 3

1a 4

hn (313 nm)

in CH 3 CN

Cl Ar sat. Cl

Cl

Cl

N

N

Re

ð 11 Þ

Photochemical isomerization of1ato themer-isomer ( 7 ) in a CO-
saturated THF solution proceeded by 313-nm irradiation instead
of the ligand substitution reaction (Eq. 12) ( 52 ).

CO

CO in THF

under CO

fac-[Re(bpy)(CO) 3 Cl] mer-[Re(bpy)(CO) 3 Cl]

hn (313 nm)

CO

Cl

N Re

N

CO

Cl

CO

CO

1a 7

N Re

N

ð 12 Þ

The photochemical ligand substitution reaction of 1a was
investigated by ultrafast TR-IR spectroscopy (Fig. 16) ( 51 ). An
acetonitrile solution of1awas irradiated by a 266-nm laser pulse
(150 fs pulse width). A broad IR absorption band which was
attributed to the reaction products in higher vibrational excited
states was produced within 1 ps after the laser flash. The broad
band sharpened and a n 00 peak at 1828 cm
^1 of the reaction
product was observed in the 50- to 100-ps duration. This time
scale is much shorter than the decay of the lowest^3 MLCT excited
state (right-hand side of Fig. 16). The TR-IR results indicate that
this photochemical reaction proceeds from higher vibrational
states or high-energy electronic excited states instead of the
lower vibrational excited states of^3 MLCT and thermal accessible
states from^3 MLCT such as the^3 LF state.

RHENIUM(I) DIIMINE COMPLEXES 165