2011. 12. 14.

Tobe Laboratory

Kitabayashi Kenichi

1

Synthesis of Dizethrenylacetylene(Candidate for tetraradical)

Contents

1. Introduction - singlet diradical - zethrene - previous work in our laboratory2. Purpose of this work - tetraradical - zethrenedimers3. Experiment and discussion - synthetic route to dizethrenylacetylene - physical properties of dizethrenylbutadiyne 4. Future work and Summary

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t-Bu

t-Bu

t-Bu

t-Bu

t-Bu

t-Bu

t-Bu

t-Bu

Mes

MesMes

Mes

y = 1y = 0

closed shell singlet diradical

0 < y < 1

open shell

diradical character

y

Singlet Diradical

H H H H H H

p-quinodimethane3

閉殻 開殻一重項ジラジカル

　 y = 0.81

y = 0.76Kubo, T. et al. Angew. Chem. Int. Ed. 2005, 44, 6564.

Kubo, T. et al. J. Am. Chem. Soc. 2010, 132, 11021.

t-Bu

t-Bu

t-Bu

t-Bu

t-Bu

t-Bu

t-Bu

t-Bu

t-Bu = C CH3

CH3

CH3

Mes =

714

4

Moderate Singlet Diradical

Nakano, M. et al. Comp. Lett. 2007, 3, 333. zethrene(dibenzo[de,mn]tetracene)

7147 714

14

spin density

It is predicted theoretically that large spin density and frontier orbital coefficients of zethrene are located at the 7,14-positions.

LUMO −2.34 eVHOMO −4.56 eV (B3LYP/6-31G*)

Tobe, Y. et al. Pure Appl. Chem. 2010, 82, 871.

Zethrene is predicted to exhibit moderate singlet diradical character (y = 0.41) and high two-photon absorption property by computational studies.

Previous Syntheses of Zethrene

5

NC

CN

O

O

O

O(EtO2C)2HCOC

COCH(CO2Et)2

2 steps81%

2 steps1%>

Cu Cu

I I

pyridinerefluxCu

I

H(solvent)

(a)

(b)

Tetradehydrodinaphto[10]annulene

22% (a)50% (b)

Clar, E. et al. Chem. Ber. 1955, 88, 1520.

(a) Sondheimer, F. et al. Tetrahedron 1970, 26, 2141.(b) Staab, H. A. et al. Chem. Ber. 1971, 104, 1182.

Stepwise approach

Transannular cyclization

I2II

CHCl3

Ph

Ph

PhPd(PPh3)4, CuI

Et3N

1a ; R = H; 20%1b ; R = t-Bu; 22%

3a ; R = H; 65%3b ; R = t-Bu; 88%

I I

Me3Si SiMe3

Pd(PPh3)4, CuIDBU, NaOH aq.

benzene

R

RR

R R

R R

R R

R R

R R R

R R

R = H or t-Bu

2a ; R = H; 65%2b ; R = t-Bu; 68%

6

Synthesis and Physical Properties of 3b

transannular cyclization

crosscoupling

Ph =

crosscoupling

zethrene

TPAcross−section

492 GM(650 nm)

509 GM (604 nm)

1138 GM (604 nm)

diphenyl-zethrene

rubrene

67 GM (612 nm)

0.4320.407 0.324diradical character ̶K

GM = 10−50 cm4 s photon−1 molecule−1

3b

TPA cross−section : 二光子吸収断面積

PhPh

Tobe, Y. et al. Org. Lett. 2009, 11, 4104.

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A Stable Tetraradical

Bertrand, G. et al. Angew. Chem. Int. Ed. 2004, 43, 4876.Bertrand, G. et al. Dalton Trans. 2008, 4482.

1.547Å

1.404Å1.411Å 1.383Å

quinoid structure

There is only a weak interaction between both diradical sites.

・ B2−C2 bond length is a little shorter than normal B−C bond length.

・ There is an alternation between slightly shorter and longer in the phenylene ring.

t-BuBP

PBt-Bu

i-Pr i-Pr

i-Pr i-Pr

BBP

PB

PB

PHt-But-Bu

i-Pr i-Pr

i-Pr i-Pr i-Pr i-Pr

i-Pr i-Pr

BBHP

PB

PB

Pt-But-Bu

i-Pr i-Pr

i-Pr i-Pr i-Pr i-Pr

i-Pr i-Pr

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Zethrene Dimers (Candidates for tetraradical)

・Zethrenylzethrene

tert-Butyl groups are omitted for clarity.

・ Dizethrenylacetylene (n = 1) Dizethrenylbutadiyne (n = 2)

Interaction between diradicals

・ The two zethrene backbones of 4a would be considerably twisted because of strong steric repulsion.・ Since the steric repulsion of the 4b would be small because of the acetylene spacer, two zethrene backbones would adopt a co-planar conformation. Therefore, interaction between two diradicals would become stronger as expressed by the cumulenic resonance structure.

H2C C C CH2

cumulene

Ph

Ph

Ph

Ph

4a

Ph

Ph

Ph

Ph

Ph

Ph

CC

n

n

n4b ; n = 14c ; n = 2

PhPhX

t-Bu

t-Bu t-Bu

t-Bu

6a ; X = Br6b ; X =Cl

TMS

PhPh

4b

Ph

6aor6b

t-Bu t-Bu

t-Bu t-But-Bu t-Bu

t-Bu t-Bu

t-Bu t-Bu

t-Bu t-Bu

desilylation

t-Bu

t-Bu

Ph

t-But-Bu

t-But-Bu

Ph

4a

t-Bu

t-Bu

XI

t-Bu

t-Bu t-Bu

t-Bu

7a ; X = Br7b ; X = Cl

5a

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Retrosynthetic Analyses of Zethrene Dimers

TMS = Si CH3

CH3

CH3

homo coupling

crosscoupling

precursors of4a and 4b

My first project is to synthesize asymmetric 7,14-dihalozethrenes 7a and 7b.

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Synthetic Studies for Asymmetric Disubstituted Zethrenes

Transannular cyclization of 1b with IBr and ICl did not give asymmetric 7,14-dihalozethrenes.

XI

t-Bu

t-Bu t-Bu

t-Bu

7a ; X = Br, 7b ; X = Cl

t-Bu

t-Bu t-Bu

t-Bu

IXXX

t-Bu

t-Bu t-Bu

t-Bu

2c ; X = Br; 60%2d ; X = Cl; 36%

IX

CHCl3 CHCl3

1b

PhPd(PPh3)4,

CuI

Et3N

PhXXX

t-Bu

t-Bu t-Bu

t-Bu t-Bu

t-Bu t-Bu

t-Bu

2b ; X = I; 68%2c ; X = Br; 60%

6c ; X = I6a ; X = Br

2bPh

t-Bu

t-Bu t-Bu

t-Bu

3b

Ph 2c1b

I2 or IBr

CHCl3

startingmaterial

phenyl-acetylene

halophenylethynyl-zethrene 3b starting material

2b2c

0.7 eq

1.0 eq

6c ; 8%

6a ; 17%

16%

6%

2b ; 60% recovery

2c ; 45% recovery

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Synthetic Route to Dizethrenylacetylene

Quast, H. et al.J. Org. Chem. 2008, 73, 4956.(*)

PhPd(PPh3)4,

CuI

Et3N

PhX

Pd(PPh3)4,CuI

Et3N

TMS

Ph

TMS

K2CO3 Ph

THF,MeOH

Ph

Ph

Pd(0),Cu(I)

CHCl3XX

t-Bu

t-Bu t-Bu

t-Bu t-Bu

t-Bu t-Bu

t-Bu t-Bu

t-Bu t-Bu

t-Bu

t-Bu

t-Bu t-Bu

t-Bu t-Bu

t-Bu t-Bu

t-But-Bu

t-Bu t-Bu

t-Bu

t-Bu

t-Bu t-Bu

t-Bu

I2 or IBr

(CH3)3CClAlCl3

t-Bu

NO2NO2 NH2NH2H2, Pd-C

fuming HNO3

I I1) H2SO42) NaNO23) KI

H2O, EtOH

TMS TMSTMSPdCl2(PPh3)2,

CuIPd(PPh3)4, CuIDBU, NaOH aq

benzene,pyridine

977%

829%

Ac2Ot-Bu t-Bu t-Bu t-Bu t-Bu t-Bu t-Bu

t-Bu t-Bu

Et3N

1b22%

2b ; X = I; 68%2c ; X = Br; 60%

6c ; X = I; 8%6a ; X = Br; 17%

(X = Br)

5b24%

5a95%

(*)EtOH,THF

8

4b

6c or 6a

PhPhX

Pd(PPh3)4,CuI

t-Bu t-Bu

t-Bu t-Bu

t-Bu t-Bu

t-Bu t-Bu

Ph

Pht-Bu

t-Bu t-Bu

t-Bu

t-Bu t-Bu

t-But-Bu

R

4c5a ; R = H5b ; R = TMS

6a ; X = Br6c ; X = I

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Sonogashira Coupling for Dizethrenylacetylene

dizethrenylbutadiyne

Attempted Sonogashira coupling of 6 and 5 did not give 4b but 4c which is a homocoupled product of 5a.

6 5 solvent additive temperature 4c6a 5a Et3N - 50 °C

10 ~ 15 %6a 5b benzene

DBUH2O 60 °C

6a 5bbenzenepyridine

DBUNaOH aq

95 °Creflux

6c 5bbenzenepyridine

DBUNaOH aq 70 °C

-2.3 -1.8 -1.3 -0.8 -0.3 0.2 0.7 1.2voltage /V

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300 350 400 450 500 550 600 650 700 7500

0.2

0.4

0.6

0.8

1

1.2

1.4

wave length / nm

Nor

mal

ized

inte

nsity

/ a.

u.UV Spectra and CV of Dizethrenylbutadiyne

UV spectra of 4c (red) and 3b (blue) in CH2Cl2 at 25 ˚C

Cyclic voltammogram of 4c and 3b in CH2Cl2 (1.0 mM, V vs. Ag/Ag+ in CH2Cl2 containing nBu4NClO4

as a supporting electrolyte, scan rate: 100 mV/s, Fc/Fc+ = 0 V)

Ph

Ph

t-Bu

t-Bu t-Bu

t-Bu

3b

lmax / nm Ered2 / V Ered1 / V Eox1 / V Eox2 / V Eox3 / V

+0.36 +0.71+0.21-1.54-1.68561

578 -1.81 +0.16 +0.65

・ Absorption maximum of 4c was blue shifted compared to that of 3b.・ Small shoulders were observed in the long-wave length region for 4c.

・ Splits of two oxidation waves and reduction waves indicate electron interaction between two zethrene backbones in 4c.

Ph

Pht-Bu

t-Bu t-Bu

t-Bu

t-Bu t-Bu

t-But-Bu

4c

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Future Work・ Synthesis of dizethrenylacetylene by Negishi coupling will be carried out.

・ Physical properties of dizethrenylbutadiyne and dizethrenylacetylene will be investigated.

・ Zethrenylzethrene will be synthesized.

Ph

t-Bu

t-Bu t-Bu

t-Bu

n-BuLi

THFZnCl2

Ph

t-Bu

t-Bu t-Bu

t-Bu

ZnCl

PhX

t-Bu

t-Bu t-Bu

t-Bu

6c ; X = I6a ; X = Br

Pd(PPh3)4

THF, toluene

Ph

Ph

t-Bu

t-Bu t-Bu

t-Bu

t-Bu

t-Bu t-Bu

t-Bu

4b

5a

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Summary

・ Recently, tetra-tert-butyl-7,14-bis(phenylethynyl)zethrene derivatives which exhibited high stability, high solubility, and high two-photon absorption property were synthesized.

・ Transannular cyclization of the [10]annulene with ICl and IBr did not give asymmetric 7,14-dihalozethrenes.

・ Attempted Sonogashira coupling of 7-ethynyl-14-(phenylethynyl)zethrene and 7-halo-14-(phenylethynyl)zethrene did not give dizethrenylacetylene but dizethrenylbutadiyne which is a homocoupled product of 7-ethynyl-14-(phenylethynyl)zethrene.

・ UV spectrum and Cyclic voltammogram of dizethrenylbutadiyne indicated electron interaction between two zethrene backbones in dizethrenylbutadiyne.

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