inorganic chemistry

E. MULTINUCLEARRHENIUM(I) COMPLEXES

Because of the significant features of the rhenium(I)
complexes, such as strong photoabsorption, intense emission,
and catalytic activities, they have been adopted as building
blocks for constructing various multinuclear complexes. For
instance, rhenium complexes introduced as pendant molecules
on polymer chains have been reported (Fig. 13).
All these polymers, A( 39 ),B( 40 ),C(41,42),D( 43 ), showed dis-
tinctive absorption and emission due to the MLCT transition of
the rhenium(I) diimine complexes. Among these rhenium-con-
taining polymers, polymer C has the most notable emission pro-
perties, with an emission quantum yield and a lifetime
(Fe¼0.132,te¼2019 ns in a deaerated CH 2 Cl 2 solution) compa-
rable to those of the corresponding mononuclear complex
(Fe¼0.181,te¼2200 ns) ( 43 ).
fac-[Re(diimine)(CO) 3 X]mþ(m¼0, 1) type complexes have been
also employed as “L-shaped” building blocks for constructing

Weak

p-base p-acid

Strong

p-acid

Strong

p-acid

Re Re

N

CO CO

CI Strongp-acid

Strong

p-acid

Re

CO

PR 3

SCHEME4. Trans-effects of the ligands to the Re

CO bond.

TABLE V

PHOTOPHYSICAL ANDTHERMODYNAMICDATA FOR THEPHOTOCHEMICALLIGAND

SUBSTITUTIONREACTIONS OFfac-[Re(X 2 bpy)(CO) 3 (Y)]þINCH 3 CN.

Complex kd

(10^5 s
^1 )

E 00 (^3 MLCT)a

(cm
^1 )

DG6¼ 298 b

(cm
^1 )

XY n

1a H Cl
0 320 15,660 30 250  21
1b CF 3 Cl
0 4100 13,680 20 252  94
1c OMe Cl
0 520 16,320 1 252  40
2a H py 1 40 17,490 15
36  15
2b CF 3 py 1 400 15,090 15 84  8
3c CF 3 P(OEt) 3 1 60 17,270 50 4820  140

a 0 – 0 band energy gaps between the (^3) MLCT and the ground states.
bFree activation energy change at 298 K.
160 HIROYUKI TAKEDAet al.