Chemistry Reference
In-Depth Information
R
TMS
R
B(OH)
2
R
OTf
i, ii
iii, i
v
R
TMS
R
TMS
R
TMS
16
CsF, Pd(PPh
3
)
4
DMAD, MeCN, rt
CsF, Pd
2
(dba)
3
DMAD, MeCN, rt
F
-
,Pd(PPh
3
)
4
MeCN, rt
R
R
R
R
CO
2
Me
CO
2
Me
R
R
MeO
2
C
R
MeO
2
C
R
CO
2
Me
CO
2
Me
17a
:R=H,58%
17b
:R=C
6
H
13
,65%
18a
:R=H,85%
18b
:R=C
6
H
13
,62%
19a
:R=H,73%
19b
:R=C
6
H
13
,71%
R
R
R
R
Scheme 5 Pd-catalyzed cyclization of 2,3-dehydrobiphenylene derivatives [
33
]. Conditions: (
i
)
NBS, AgNO
3
, acetone, rt, (
ii
) (1) BuLi, THF,
78
C, (2) B(OMe)
3
,
78
C, (3) HCl (1 M), (
iii
)
oxone, NaHCO
3(aq)
, acetone-H
2
O, 0
C, (
iv
) DIPEA, Tf
2
O, CH
2
Cl
2
,
78
C. The source of F
is
TBAF for 17a and CsF for 17b
20
21
22
23
24
25
Fig. 4 Structure of [N]phenylenes 20-25 [
34
]
scope of this review; however, this foundation is important for understanding
properties observed in longer isomers. Biphenylene is only weakly fluorescent
(
10
4
)[
35
-
37
] and only low levels of triplet state population are
observed upon direction excitation (
f
F
ΒΌ
2
10
2
)[
38
-
41
].
The values corresponding to the energy of S
1
-S
0
transition in compounds 20-22
as well as zigzag [4]- (23) and [5]phenylene (24), and triangular [4]phenylene (25,
Fig.
4
) are summarized in Table
2
[
34
]. The bathochromic shift in energy going
from 20 to linear 21 is much larger (0.87 eV) than that from 20 to angular 22
(0.13 eV). The rapidly decreasing band gap with linear annulation is consistent with
the prediction that linear [N]phenylenes of infinite length could serve as conductive
organic wires [
20
]. Interestingly, angular [3]phenylene is emissive, while linear [3]
phenylene is not. The band gap does decrease with angular extension of the [N]
phenylene going from 22-24 but at a much slower rate.
f
ISC
<
