m. r. billa , s. p. kitney, s.m. kelly the university of hull, department of chemistry e-mail...
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Direct Heteroarylation: A Modern Synthetic Tool for the Synthesis of Liquid Crystalline Organic Semiconductors . M. R. Billa , S. P. Kitney, S.M. Kelly The University of Hull, Department of Chemistry E-mail address: [email protected]. - PowerPoint PPT PresentationTRANSCRIPT
The conventional method to synthesise liquid crystalline organic electronic materials uses traditional cross coupling reactions such as Suzuki and Stille couplings. However, these conventional methods have drawbacks including the use of organometallic reagents which generate a stoichiometric amount of metal waste which is often toxic, difficult to handle and requires the prior preparation of organometallic precursors and extra synthetic steps. To overcome these difficulties and to avoid using organometallic reagents Pd-catalysed direct heteroarylation is an alternative technique to traditional cross coupling. No preparation of an organometallic derivative is required and most importantly the number of reaction steps is reduced1, 2, 3.
M. R. Billa, S. P. Kitney, S.M. Kelly The University of Hull, Department of Chemistry E-mail address: [email protected]
References:
X-ray diffraction:
1. Derek J. Schipper and Keith Fagnou, Chem. Mater., 2011, 23 , 1594–16002. Yohei Fujinami, Junpei Kuwabara, Wei Lu, Hideki Hayashi, and Takaki Kanbara, ACS Macro Lett., 2012, 1, 67–70.3. Julien Roger, Franc Požgan and Henri Doucet Green Chem., 2009, 11, 425-432.4. J.K. Stille, Angew. Chem. Int. Ed. (1986), 25, p. 508.5. Philippe Berrouard, Dr. Ahmed Najari, Dr. Agnieszka Pron, David Gendron, Pierre-Olivier Morin, Jean-Rémi Pouliot, Justine Veilleux, Prof. Dr. Mario Leclerc, 2012, 51, 2068-2071.
Abstract:
Direct Heteroarylation Scheme-1
Conventional Stille/Suzuki coupling Sheme-2
Direct Heteroarylation: A Modern Synthetic Tool for the Synthesis of Liquid Crystalline Organic Semiconductors
HO Br
RO Br
RO S S
C6H13 C6H13
I Br
C8H17 C8H17
Br Br
C6H13 C6H13
BrSS
RO
S
RO SS
Sn(C4H9)3
S
SS
(C4H9)3Sn
C6H13 C6H13
BSS
RO O
O
C8H17 C8H17
SS S
S
C8H17 C8H17
SS S
SBrBr
C8H17 C8H17
SS S
SC6H13 C6H13
C6H13 C6H13
S
SS OR
SRO
1
S
C8H17 C8H17
Br Br
C6H13 C6H13
Br BrS
C6H13 C6H13
SS S
S
C8H17 C8H17
SS S
SC6H13 C6H13
C6H13 C6H13
S
SSS
RO OR
C8H17 C8H17
SS S
SC6H13 C6H13
C6H13 C6H13
S
SSS
RO Br
K2CO3, Pivalic acid
K2CO3, Pivalic acid
Pd(OAc)2, K2CO3, Pivalic acid
Pd(OAc)2
Pd(OAc)2
1
Advantages:1)Minimal
synthetic steps2)Higher yields3)Lower catalyst
loadings4)Does not employ
organometallic intermediate
5)Easy purification
6)Eco-friendly7)Faster8)Economical
Direct heteroarylation of 2,2’-bithiophene gives a bithiophene-fluorene based oligomer in good yields. The optimised reaction conditions were investigated in terms of the catalytic system and reaction times. The optimised reaction conditions allows the synthesis of 5',5'''-(9,9-dioctylfluorene-2,7-diyl-bis(5- 9,9-dihexyl-7-5'-(4-methoxyphenyl)-[2,2'-bithiophen]-5-yl-fluoren-2-yl -2,2'-bithiophene) in three synthetic reaction steps with an overall yield of 45%, scheme-1. This is in comparison to ten synthetic steps required for more conventional Stille4
or Suzuki-Miyaura aryl-aryl coupling reactions, scheme-2. The reactions all proceed without the addition of a phosphine ligand and the need for use of bifunctional organometallic reagents as reaction intermediates.
Conclusion : Ultimately, by merging the advantages of organic semiconductors with new eco-friendly synthetic procedures, new
opportunities for the production of green energy from green materials may emerge. The use of more environmentally friendly materials, which produce no tin/boronic by-products, could also show improved performance and stability.
The new synthetic procedure, i.e., direct heteroarylation (scheme-1) allows the synthesis of the same material (scheme-2) but on a larger scale and much more quickly and efficiently.
The direct heteroarylation condensation reaction is a very promising method to synthesize high molecular weight compounds as well as low molecular weight compounds with high yields in a more environmentally friendly and faster way5.
SS Br
SS
K2CO3, Pivalic acid
Pd(OAc)2
2
DSC thermograph of compound 2Smectic A phase of compound 2
Nematic phase of compound 1Single step synthesis of small molecularweight organic semiconductors
Optimised reactionConditions for
scheme-1:
Reaction time-3 hrs
Temperature-100 °C
Pd(OAc)2 -2 mol %
Pivalic acid-30 mol %
K2CO3-2.5 equiv
DMF -0.25 Molar