Chemistry Reference
In-Depth Information
CoCp
CoCp
CoCp
R
R
R
R
R
R
R
R
R
R
35a
36a
37a
h
h
h
CoCp
CoCp
CoCp
R
R
R
R
R
R
R
R
R
R
35b
36b
37b
4
-CpCo-complexed linear [N]phenylenes, for 35 and 36
Scheme 11 Photo-thermal IRHR of
Z
R
¼
TMS, for 37 R
¼
H or TMS [
55
]
Table 4 Photostationary state of IRHR of [N]phenylenes 35-37 [
55
]
[N]Phenylene-CpCo
D
H
6¼
(c)
D
H
c
Haptomer a
Haptomer b
35
a
1
1
26.9
0
36
a
1
2
27.1
7.6
37
b
7
3
27.3
9.7
Irradiated with
a
350 nm lamp,
b
310 + 365 nm lamp
c
Calculated values for R
¼
H in kcal mol
1
Fig. 6 Structures of
anti
-
[2.2]-(1,4)-biphenylenophane
38 and parent [2.2]
paracyclophane 39 [
57
]
38
39
Table 5 Photophysical and electrochemical properties of 38, 39, and 20 [
57
]
Compound
E
ox
(V vs Ag/Ag
+
)
Lowest E
l
max
(nm)
l
em
(nm)
t
(ps)
38
378
537
229
1.37, 1.55
39
-
-
-
1.59
20
359
518
194
1.72
synthesized
anti
-[2.2]-(1,4)-biphenylenophane (38), employing the biphenylene
framework to investigate the phane properties of antiaromatics (Fig.
6
). An X-ray
crystal structure of 38 confirmed the
anti
relationship of the biphenylene rings. The
inter-ring distance of 3.09
˚
is identical to that of the parent [2.2]paracyclophane;
however, the ethano C-C bridge in 38 is significantly shorter, likely due to the
increased flexibility of biphenylene [
58
]. Additional thermal stability is imparted to
38 by a decrease in the strain of this bond.
The photophysical properties of 38 as compared to those of biphenylene 20
and the electrochemical properties of 38 as compared to 20 and 39 are
summarized in Table
5
[
57
]. A bathochromic shift and spectral broadening in
going from 20 to 39 is consistent with ground-state interactions between the
biphenylene units in the cyclophane. Since the Stokes shifts in 38 and 20 are
