Photochemistry of 9-vinyl substituted anthracenes, of their reduced - - PowerPoint PPT Presentation

Photochemistry of 9-vinyl substituted anthracenes, of their reduced derivatives and of Diels Alder type adducts of 9-vinylanthracenes with activated dienophiles

Hasnaa Sadeq,1 Thies Thiemann,1* John P Graham,1 Yosef Al Jasem,2 Bernhard Bugenhagen,3 Nathir Al-Rawashdeh4

1Department of Chemistry, United Arab Emirates University, Al Ain, Abu Dhabi, United Arab Emirates 2Department of Chemical Engineering, United Arab Emirates University, Al Ain, Abu Dhabi, United Arab Emirates 3Department of Inorganic Chemistry, University of Hamburg, Hamburg, Germany 4Department of Applied Chemical Sciences, Jordan University of Science and Technology, Irbid, Jordan

Department of Applied Chemical Sciences, Jordan University of Science and Technology, Irbid, Jordan

Introduction

X Y

R

R R

[2+2]-Photocycloaddition published previously What could be done, if [2+2]-photocycloaddition of 9-ethenylanthracenes were possible.

X O H H H RO Y

2

R x(H2C)

Y

x(H2C)

Y X H O O

hν [2+2]photocycloaddition

hν

R

hν

R R H H RO X H H H Y

R R R R

RO

R

etc.

x(H2C)

Y

x(H2C)

Y

• T. Thiemann, C. Thiemann, S. Sasaki, V. Vill, S. Mataka, M. Tashiro,
• J. Chem. Res., 1997, 21(S) 248 - 249; 1997, 21(M) 1736 - 1750

Oligo‐/polymerisation of bis(ethenyl)anthracenes Cross‐linking of ethenyl‐substituted anthracenes on a solid support

In 2010, A. Marrocchi et al.1 have studied 9,10‐diaryl‐, 9,10‐diarylethenyl, and 9,10‐ diarylethynylanthracenes as potential semiconducting materials.

Introduction (continued)

OCH3 OCH3 O2N OCH3 H3CO OCH3 H3CO OCH3 OCH3 H3CO H3CO

In recent times, 9,10‐diaryl and 9,10‐diarylethenyl substituted anthracenes have been forwarded as potential constituent molecules in light‐harvesting devices for organic solar cell applications.2 So, it is of importance to understand whether such 9,10‐substituted anthracenes are stable under photoirradiation for a longer time and what type of reactions they could undergo. References: 1. A. Marrocchi et al., J. Photochem. Photobiol. 2010, 211, 162.

• 2. N. Belghiti et al., Mat. Environ. Sci. 2014, 5, 2191

R'

R' =aryl

R'

hν

CO2R

n

RO2C

hν 2 2A R = H, Et n = 1,2

R'

hν

R1

10

RO2C

3 9

B A

head-to-head

• r head-to-tail?

syn- or anti?

R2

9 1

Scheme 1. Possible photodimerisation products of anthranylacrylates

O OR O OR O O

2 4

OR OR O

Scheme 2. Possible competing [4+4]-photodimerisation of anthranylacrylates

PPh3 + BrCH2CO2Et Ph3PCH2CO2Et Br CHCl3

• aq. Na2CO3

Ph3P O OEt

PPh3 + BrCH2CO2Et Ph3PCH2CO2Et CHCl3

• aq. Na2CO3

Ph3P OEt Br O PPh3 +

O R + NBS O R Br O Ph3P R

Br Ph3P O

R

• aq. Na2CO3

Ph3P OEt

Preparation of the phosphorane reagents

CHO O

• min. CHCl3

CO Et 5 2a 6

• r

solventless CO2Et solventless Ph3P O R 7 CHO O R = F, Br, Cl, CH3 5 8 R

Scheme 3. Synthesis of 9-aroylethenylanthracenes 8 and anthranylacrylates 2

Br2 Br Br + CO2Et CHCl3 CO2Et CO2Et Br + 75% 15% 2a 9a 9b

2

Br2 CHCl3 Br CHO

3

Br 5 10 X

Scheme 4. Bromination 9-substituted anthracenes 2a and 5

Br + X-Ph-B(OH)2 Pd(PPh3)2Cl2 CO2Et CO2Et X Ph B(OH)2 PPh3, THF (or DME) 9a 12 11

2

X = 4-CH3O, H, 3-Cl, 3-NO2, 4-C22H45O

Scheme 5. Suzuki cross-coupling reactions to extended anthracenes

CHO

354 (3620) 370 (6080) 400 (6680) 405 (6700) λmax [nm] (ε mol-1cm-1) 352 (3300) 370 (6135) 400 (6670) λmax [nm] (ε mol-1cm-1) 351 (5545) 366 (8400) 385 (10370) 358 (4415) 379 (7410) 385 (9010)

• Fig. 1

CHO

(CH2Cl2)

1 1

CO2Et

(CH3CN) (CH3CN)

UV band maxima of selected compounds in CH2Cl2 and

X = CH3 351 (4700) 370 (6688) 391 (8500) 405 (8719) X = OCH3 300 (15333) 305 (15305) 352 (5350) 371 (7180) λmax [nm] (ε mol-1cm-1) X = H 330 (2750) 355 (4430) 371 (6090) 391 (8330)

O

X = Cl 350 (4740) 371 (6160) 390 (7240) 410 (7310) X = Br 354 (5160) 370 (6440) 391 (8100) 415 (9395)

CH3CN.

(CH2Cl2) 391 (9440) 405 (9660) (CH2Cl2) 410 (9225) (CH2Cl2)

X

(CH2Cl2) (CH2Cl2) X = F 351 (4095) 369 (5810) X = CH3 352 (4100) 371 (6170) X = 3-NO2 352 (4435) 387 (5760) 369 (5810) 391 (8190) 410 (9490) (CH2Cl2) 371 (6170) 405 (8510) (CH3CN) 387 (5760) 425(7690) (CH2Cl2)

O O

λmax [nm] (ε mol-1cm-1) 336 (3900) 351 (5700) 370 (7300) 390 (6900) (CH Cl )

O O

340 (560) λmax [nm] (ε mol-1cm-1)

CH3

(CH2Cl2)

O NO2

O O

2a

Fig 2. Crystal packing of ethyl 3-(anthran-9-yl)acrylate showing intermolecular distances that are too large for photochemical dimerisation reactions in the crystal.

Br O O O O

9a

Fig 3. Crystal packing of ethyl 3-(9-bromoanthran-10-yl)acrylate showing g y p g y ( y ) y g intermolecular distances that are too large for photochemical dimerisation reactions in the crystal.

hν

O O

hν CH2Cl2

O X

l = 254 nm

O X

X= H, 4-CH3, 3-NO2, 4-Br, 4-F E-8 Z-8

Scheme 6. Photochemical cis-trans isomerisation of 9-aroylethenylanthracenes Scheme 6. Photochemical cis trans isomerisation of 9 aroylethenylanthracenes See also: H.-D. Becker, H. C. Becker, K. Sandros, K. Andersson, Tetrahedron Lett., 1985, 26, 1589.

• H. Bouas-Laurent, A. Castellan, J. P. Desvergne, and R. Lapouyade,, Chem. Soc. Rev., 2000, 29, 43 (review).
• H. Bouas-Laurent, A. Castellan, J. P. Desvergne, and R. Lapouyade, Chem. Soc. Rev., 2001, 30, 248 (review).

O O hν CH2Cl2

Scheme 7.

O and/or head-to-head

4

Slow build‐up of a [2+2] photodimer in CH2Cl2

O head to head dimer hν CH2Cl2

( l ) (slow)

O O

3

hν

O

benzene [O2] 13

O H3CO O

8

O

14

Scheme 8. Long‐time Photoirradiation of aroylethenylanthracene (8) in benzene in presence of air oxygen at λ = 352 nm.

X X X Y

Diels-Alder +

Y R

Diels Alder ∆ 2/8 15 16

R R X Y

?

hν retro- Diels-Alder

R

16 S h 7 Pl t d [2 2] l dd t f th th l th Fi t “ t t” th Scheme 7. Plan to produce [2+2]-cycloadducts from the ethenylanthracenes: First “protect” the anthranyl unit in a Diels-Alder reaction, then carry out the photochemistry, then “deprotect” the anthranyl unit in a retro-Diels-Alder reaction.

O O X

+

N-Ph-X O N O

neat 2b 15

CO2CH3 O CO2Me

X = H, 4-Br, 4-CH3, 4-OCH3, 2-CH3, 2,4-Di-F, 2,6-Di-F 2b 15a 16a

O O O

+

O O O

xylene reflux 2a 15b 16b

CO2Et CO2Et

Scheme 8. Facile Diels-Alder reactions of 9-substituted anthracenes with doubly activated dienophiles.

Fig 4. Spatial distribution and energies of HOMO – LUMO for representative anthranylacrylates and phenacyl and

• acetylethenylanthracenes. It can be seen that the HOMOs and the LUMOs, respectively, for the compounds are similar in energy

and spatial distribution. All calculations were performed using the Gaussian 09W C01 program. Geometry optimizations for the each molecule were performed without symmetry constraints in the gas-phase using the B3LYP hybrid functional and 6-31G(d) basis set. Optimized structures were confirmed to be energy minima through vibrational frequency calculations Orbital energies and LUMO (eV) HOMO (eV) Str1 ‐2.17 ‐5.39 isosurfaces were calculated using the same functional and basis set. Str2 ‐2.05 ‐5.32

O

Str3 ‐2.02 ‐5.25

O O O O

Str4 ‐2.12 ‐5.33

O O

O

O X N O X N O

hν

O O

hν CH2Cl2

O Y

E-16 Z-16

Y

E‐/Z‐isomerisation of 16 upon photoirradiation at λ = 254 nm. Arrows i di di i

1H

d 13C NMR k d b d i Scheme 9. indicate disappearing 1H and 13C NMR peaks due extreme broadening.

hν CHO CHO CH2Cl2 CHO CHO CHO O

+ 5 17

O

14

Scheme 10. Known photodimerisation of 9-formylanthracene in CH2Cl2 at λ = 352 nm.

NaBH4, AcOH Pd/C, toluene

CO2R CO2R

R = Et, Aryl Scheme 11. Hydrogenation of anthranyl acrylates and aroylethenylanthracenes with NaBH4, AcOH, Pd/C 18 2/8

CO2Et CO2Et

hν benzene

CO2Et CO2Et

Scheme 12. Photodimerisation of ethyl anthranylpropionate (18-Et) at λ = 352 nm 18-Et 19-Et

OCH3 O OCH3 O O

hν benzene

18-Ar-OMe 19-Ar-OMe

O O OCH3

Scheme 13. Photodimerisation of 4-methoxybenzoylethylanthracene (18-Ar-OMe) at λ = 352 nm

OCH3

3

• H. Bouas-Laurent, A. Castellan, J. P. Desvergne, and R. Lapouyade,, Chem. Soc. Rev., 2000, 29, 43 (review).
• H. Bouas-Laurent, A. Castellan, J. P. Desvergne, and R. Lapouyade, Chem. Soc. Rev., 2001, 30, 248 (review).

see also:

A view of the molecular structure of the molecule 19‐Ar‐OMe, with non‐hydrogen atom labelling. Displacement ellipsoids are shown at the 50% probability level. Disorder is clear at only one methoxyphenyl group.

Conclusions:

1.) A larger number of aroyl and ester substituted 9‐ethenylanthracenes could be synthesized via ) g y y y solventless Wittig‐olefination.

O O O

2.) X‐ray crystal structures of two of them showed the molecules too far apart in the crystal for them to photodimerize. 3.) The keto substituted 9‐ethenylanthracenes undergo photochemical E‐/Z‐isomerisation at λ 2 h b i d l l d l l i i h 9 l = 254 nm, the ester substituted molecules undergo a slow polymerisation. The 9‐aroyl‐ ethenylanthracenes undergo a slow [2+2]‐cycloaddition, but in very low yield. 4.) 9‐Ethenylanthracenes were submitted facilely to Diels‐ Alder reactions with maleimides. The photoreaction of the cycloadducts, which still carry an α,β‐enone or an α,β‐unsaturated ester f i li l d i l id E/Z i i i functionality, leads mainly to rapid E/Z‐isomerisation. 5.) When photoirradiated at λ = 352 nm, 9‐ketoethylanthracenes (ie., the hydrogenated 9‐ ethenylanthracenes) undergo [4+4]‐cycloaddition with the formation of head‐to‐tail cycloadducts. 6.) 9‐Ethenylanthracenes are photoreactive under UV‐irradiation. This can lead to aging of such ethenylanthracene containing material and should be taken into account when using these in

• rganic solar cells.

y

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