inorganic chemistry

D. PHOTOCHEMICALLIGANDSUBSTITUTIONREACTION OF
fac-[Re(DIIMINE)(CO) 3 PR 3 ]þ

Recently, the excited states of the rhenium complexes have
been investigated by using advanced computational methods,
which can handle chemical systems that contain heavy atoms.
Although direct observation of the reactive states remains impor-
tant in order to confirm the photochemical reaction mechanism,
it is sometimes very difficult because the concentrations of reac-
tive states are very small when their potential curves are repul-
sive. Systematic investigations of the effects of various
experimental parameters on reaction yields are also useful for
getting mechanistic information. For example, energetic cha-
racteristics of the reactive states can be elucidated by
investigating the dependence of emission and reaction quantum
yields on temperature and chemical modification of the ligands.
Most rhenium diimine tricarbonyl complexes were considered
to be relatively stable against photosubstitution, with some
exceptions described above, until the photochemical ligand sub-
stitution reactions of complexes with phosphorous ligands, phos-
phorous complexes, andfac-[Re(LL)(CO) 3 (PR 3 )]þwere reported.
When the complex3awith triethylphosphite as a monodentate
ligand was irradiated at 365 nm in MeCN, the UV/Vis absorption
spectrum changed with some isosbestic points (Fig. 8). This pho-
tochemical reaction gave exclusively cis,trans-[Re(bpy)(CO) 2 {P

300

0.0

0.2

0.4

0.6

Absorbance

0.8

1.0

1.2

1.4

350

Wavelength (nm)

400 450 500

70

40

30

20

10

0

Irradn. time / min

FIG. 8. UV/Vis absorption spectral changes of an CH 3 CN solution con-
taining1a(0.12 mM) under an Ar atmosphere during 365-nm irradiation
(4.24 1015 photon s
^1 ). Copyright 2002 American Chemical Society.

150 HIROYUKI TAKEDAet al.