have size-selectively synthesized [9]-, [12]-, [14]-, [15]-, and
1
8 h afforded the desired 1a in 96% yield. Then, 1a was
treated with Pd(dba) (2.0 equiv, dba = dibenzylidene-
acetone) and 2,2 -bipyridyl (bpy) in THF at 50 °C for 8 h.
After the solvent and free dba were removed by filtration,
5ꢀ19
20ꢀ22
[
utilize cyclic, cis-bisaryl-platinum complexes as precursors
16]CPPs
and their derivatives. In contrast, we
2
0
for CPPs, and reductive elimination from the complexes
2
3
selectively affords [8]- and [12]CPPs. Inaddition, we have
reported that the same strategy is effective for the random
the resulting solid material was treated with AgBF (2.2
4
equiv) at room temperature in CH Cl /acetone for 12 h.
2
2
8
synthesis of [8]ꢀ[13]CPPs. Isobe has utilized our strategy
Although we anticipated the formation of [8]-, [12]-, or
[16]CPP via the selective dimerization, trimerization, or
tetramerization of 1a, respectively, we found that [10]CPP
to prepare the first optically active, simplest structural unit
2
4
of helical single-walled carbon nanotubes. Despite these
developments, the availability of CPPs in terms of size and
quantity has been quite limited. Therefore, a size-selective
and high-yielding synthetic route for CPPs is needed.
We envisioned that L-shaped cis-substituted bis(para-
haloaryl) platinum complex 1 could be used as a precursor
for a cyclic platinum intermediate, such as 2, by selective CꢀC
bond formation through selective CꢀX bond manipulation
1
formed exclusively from H NMR and mass spectrosco-
pies. [10]CPP was isolated, by using silica gel chromato-
graphy, in 16% overall yield from 1a (13% from 3c) and
1
was fully characterized by using H NMR (7.56 ppm in
1
CDCl3), C NMR (127.5 and 138.3 ppm), and MALDI
3
TOF mass spectroscopies (m/z = 760.3136), the results of
8
which are identical to those in our previous report.
(
Scheme 1). Once 2 forms, reductive elimination of the pla-
Although a considerable amount of insoluble black solid,
presumably linear oligomers of biphenyls, was observed,
nootherCPPs, besides[10]CPP, formed. Use of AgSbF or
tinum from 2 should give a CPP. We report here the selective
synthesis of [10]CPP from 1a (X = I, n = 2, L = cycloocta-
diene [cod]) by using the palladium-mediated coupling reac-
6
AgOTf instead of AgBF gave [10]CPP selectively in 10%
4
25,26
tion developed by Osakada as the key step.
In addition, we
or 14% yield from 1a, respectively. In contrast, treatment
of 1a with Ni(cod) instead of Pd(dba) gave a mixture of
report the X-ray crystal structure of [10]CPP for the first time.
During our investigation, Itami and co-workers reported the
selective synthesis of [9]ꢀ[11]- and [13]CPPs by using their cis-
2
2
2
7
1
,4-diphenylcyclohexane-1,4-diyl based strategy.
Scheme 2. Selective Synthesis of [10]CPP
0
Commercially available 4,4 -diiodobiphenyl (3c) was
treated with BuLi (1.0 equiv) in THF at ꢀ78 °C, followed
by Me SnCl (1.0 equiv), to afford monostannylated
3
Scheme 1. Working Hypothesis on a New Synthetic Route for
CPPs
biphenyl 3d in 84% yield (Scheme 2). Subsequent treat-
ment of3dwithPt(cod)Cl (0.50equiv) in THF at 60°C for
2
(17) Segawa, Y.; Omachi, H.; Itami, K. Org. Lett. 2010, 12, 2262.
ꢀ
(18) Segawa, Y.; Miyamoto, S.; Omachi, H.; Matsuura, S.; Senel, P.;
Sasamori, T.; Tokitoh, N.; Itami, K. Angew. Chem., Int. Ed. 2011, 50,
244.
19) Segawa, Y.; Senel, P.; Matsuura, S.; Omachi, H.; Itami, K.
Chem. Lett. 2011, 40, 423.
3
ꢀ
(
(
20) Omachi, H.; Segawa, Y.; Itami, K. Org. Lett. 2011, 13, 2480.
21) Yagi, A.; Segawa, Y.; Itami, K. J. Am. Chem. Soc. 2012, 134,
(
962.
2
(
(
22) Matsui, K.; Segawa, Y.; Itami, K. Org. Lett. 2012, 14, 1888.
23) Yamago, S.; Watanabe, Y.; Iwamoto, T. Angew. Chem., Int. Ed.
2
010, 49, 757.
24) Hitosugi, S.; Nakanishi, W.; Yamasaki, T.; Isobe, H. Nat.
Commun. 2011, 2, 492.
(
(
25) Suzaki, Y.; Osakada, K. Organometallics 2003, 22, 2193.
Figure 2. ORTEP drawing of [10]CPP hexane. Thermal ellip-
soids are shown at 50% probability, and all hydrogen atoms are
omitted for clarity.
3
(26) Suzaki, Y.; Yagyu, T.; Osakada, K. J. Organomet. Chem. 2007,
6
92, 326.
(
27) Ishii, Y.; Nakanishi, Y.; Omachi, H.; Matsuura, S.; Matsui, K.;
Shinohara, H.; Segawa, Y.; Itami, K. Chem. Sci. 2012, 3, 2340.
Org. Lett., Vol. 14, No. 13, 2012
3285