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-Rawashdeh 4 1 Department of Chemistry, United Arab Emirates University, Al Ain, Abu Dhabi, United Arab Emirates 2 Department of Chemical Engineering, United Arab Emirates University, Al Ain, Abu Dhabi, United Arab Emirates 3 Department of Inorganic Chemistry, University of Hamburg, Hamburg, Germany 4 Department 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 [2+2]-Photocycloaddition published previously What could be done, if [2+2]-photocycloaddition of 9-ethenylanthracenes were possible. Y R R R X X H O 2 H H x (H 2 C) x (H 2 C) Y Y Y R RO h ν R [2+2]photocycloaddition h ν O X h ν O H R R X Y H H R R RO H R R H H x (H 2 C) x (H 2 C) Y Y etc. R RO T. Thiemann, C. Thiemann, S. Sasaki, V. Vill, S. Mataka, M. Tashiro, Oligo ‐ /polymerisation of Cross ‐ linking of ethenyl ‐ substituted J. Chem. Res. , 1997 , 21 ( S ) 248 - 249; 1997 , 21 ( M ) 1736 - 1750 bis(ethenyl)anthracenes anthracenes on a solid support

Introduction (continued) In 2010, A. Marrocchi et al. 1 have studied 9,10 ‐ diaryl ‐ , 9,10 ‐ diarylethenyl, and 9,10 ‐ diarylethynylanthracenes as potential semiconducting materials. OCH 3 O 2 N OCH 3 H 3 CO OCH 3 H 3 CO OCH 3 H 3 CO OCH 3 H 3 CO OCH 3 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' =aryl R' R' h ν RO 2 C n h ν 2 2A CO 2 R h ν R = H, Et R' n = 1,2 R 1 10 3 RO 2 C 9 9 B R 2 head-to-head 1 or head-to-tail? A syn- or anti? Scheme 1. Possible photodimerisation products of anthranylacrylates

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

Ph 3 P CHCl 3 aq. Na 2 CO 3 Ph 3 PCH 2 CO 2 Et OEt PPh 3 + BrCH 2 CO 2 Et Br O Ph 3 P CHCl 3 aq. Na 2 CO 3 Ph 3 PCH 2 CO 2 Et PPh 3 + BrCH 2 CO 2 Et OEt Br O O O O Ph 3 P aq. Na 2 CO 3 Br Ph 3 P R R + NBS PPh 3 + R R O Br Preparation of the phosphorane reagents Ph 3 P OEt O 6 min. CHCl 3 or solventless 2a CHO 5 CO 2 Et CO Et Ph 3 P R O 7 solventless 8 CHO 5 R = F, Br, Cl, CH 3 O R Scheme 3. Synthesis of 9-aroylethenylanthracenes 8 and anthranylacrylates 2

Br Br Br 2 + + CHCl 3 Br 2a 9b 9a CO 2 Et 75% 15% CO 2 Et CO 2 Et 2 Br Br 2 CHCl 3 3 5 10 CHO Br Scheme 4. Bromination 9-substituted anthracenes 2a and 5 X Br Pd(PPh 3 ) 2 Cl 2 + X-Ph-B(OH) 2 X Ph B(OH) 2 PPh 3 , THF (or DME) 11 9a 12 CO 2 Et CO 2 Et 2 X = 4-CH 3 O, H, 3-Cl, 3-NO 2 , 4-C 22 H 45 O Scheme 5. Suzuki cross-coupling reactions to extended anthracenes

λ max [nm] ( ε mol -1 cm -1 ) λ max [nm] ( ε mol -1 cm -1 ) 354 (3620) 352 (3300) 358 (4415) 351 (5545) 379 (7410) 370 (6080) 370 (6135) 366 (8400) 385 (9010) 400 (6680) 400 (6670) 385 (10370) 405 (6700) Fig. 1 CHO CHO (CH 2 Cl 2 ) (CH 3 CN) (CH 3 CN) CO 2 Et UV band maxima of selected compounds in CH 2 Cl 2 and λ max [nm] ( ε mol -1 cm -1 ) 1 1 CH 3 CN. X = Br X = H X = Cl X = OCH 3 X = CH 3 351 (4700) 300 (15333) 354 (5160) 350 (4740) 330 (2750) 370 (6688) 305 (15305) 370 (6440) 355 (4430) 371 (6160) 391 (8500) 352 (5350) 391 (8100) 371 (6090) 390 (7240) 405 (8719) 371 (7180) 415 (9395) O 391 (8330) 410 (7310) 391 (9440) 410 (9225) (CH 2 Cl 2 ) (CH 2 Cl 2 ) X 405 (9660) (CH 2 Cl 2 ) (CH 2 Cl 2 ) (CH 2 Cl 2 ) X = 3-NO 2 X = F X = CH 3 351 (4095) 352 (4100) 352 (4435) 369 (5810) 369 (5810) 371 (6170) 371 (6170) 387 (5760) 387 (5760) 391 (8190) 405 (8510) 425(7690) 410 (9490) (CH 2 Cl 2 ) (CH 3 CN) (CH 2 Cl 2 ) O λ max [nm] ( ε mol -1 cm -1 ) λ max [nm] ( ε mol -1 cm -1 ) O 340 (560) 336 (3900) O 351 (5700) O 370 (7300) 390 (6900) (CH Cl ) (CH 2 Cl 2 ) NO 2 O CH 3

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.

h ν h ν O O CH 2 Cl 2 X l = 254 nm O O X X= H, 4-CH 3 , 3-NO 2 , 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 h ν CH 2 Cl 2 Scheme 7. Slow build ‐ up of a [2+2] photodimer in CH 2 Cl 2 4 and/or O head to head head-to-head O dimer h ν CH 2 Cl 2 ( l (slow) ) O O 3

h ν benzene [O 2 ] 13 O O O H 3 CO 8 14 O Scheme 8. Long ‐ time Photoirradiation of aroylethenylanthracene ( 8 ) in benzene in presence of air oxygen at λ = 352 nm.

X X Y X Diels-Alder Diels Alder + ∆ Y 2/8 15 16 R R R X Y retro- h ν Diels-Alder ? 16 R S h Scheme 7. Plan to produce [2+2]-cycloadducts from the ethenylanthracenes: First “protect” the 7 Pl t d [2 2] l dd t f th th l th Fi t “ t t” th anthranyl unit in a Diels-Alder reaction, then carry out the photochemistry, then “deprotect” the anthranyl unit in a retro-Diels-Alder reaction.

O X O O N neat + N-Ph-X O 2b 2b 15a 15 O CO 2 CH 3 16a CO 2 Me X = H, 4-Br, 4-CH 3 , 4-OCH 3 , 2-CH 3 , 2,4-Di-F, 2,6-Di-F O O O O + O xylene reflux 2a 16b 15b O CO 2 Et CO 2 Et 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 isosurfaces were calculated using the same functional and basis set. LUMO (eV) HOMO (eV) Str1 ‐ 2.17 ‐ 5.39 O Str2 ‐ 2.05 ‐ 5.32 O O Str3 ‐ 2.02 ‐ 5.25 O O O O Str4 ‐ 2.12 ‐ 5.33 O

O X O X N N O h ν h ν O CH 2 Cl 2 O O Y Z -16 E -16 Y E ‐ / Z ‐ isomerisation of 16 upon photoirradiation at λ = 254 nm. Arrows Scheme 9. i di indicate disappearing 1 H and 13 C NMR peaks due extreme broadening. di i 1 H d 13 C NMR k d b d i

CHO CHO h ν CH 2 Cl 2 CHO CHO 5 CHO + O 17 14 O Scheme 10. Known photodimerisation of 9-formylanthracene in CH 2 Cl 2 at λ = 352 nm.

NaBH 4 , AcOH Pd/C, toluene 18 2/8 R = Et, Aryl CO 2 R CO 2 R Scheme 11. Hydrogenation of anthranyl acrylates and aroylethenylanthracenes with NaBH 4 , AcOH, Pd/C CO 2 Et CO 2 Et h ν benzene 18-Et 19-Et CO 2 Et CO 2 Et Scheme 12. Photodimerisation of ethyl anthranylpropionate ( 18-Et ) at λ = 352 nm

OCH 3 OCH 3 O O O h ν benzene 18-Ar-OMe 19-Ar-OMe O O OCH 3 3 OCH 3 Scheme 13. Photodimerisation of 4-methoxybenzoylethylanthracene ( 18-Ar-OMe ) at λ = 352 nm see also: 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).

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.