Article pubs.acs.org/joc
Synthesis and C−H Functionalization Chemistry of ThiazoleSemicoronenediimides (TsCDIs) and -Coronenediimides (TCDIs) Qinqin Shi,† Eric S. Andreansky,† Seth R. Marder,‡ and Simon B. Blakey*,† †
Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
‡
S Supporting Information *
ABSTRACT: Coronenediimide (CDI) derivatives have a planar structure, a reasonably high electron affinity, and a rigid and extended delocalized π-system. Therefore, this core and variants thereof may be promising building blocks for the synthesis of electron transport materials. Herein, we have synthesized thiazole-semicoronenediimides (TsCDIs) and -coronenediimides (TCDIs) by a two-step process from a perylenediimide (PDI) precursor. Conditions for C−H arylation and heteroarylation of the thiazole moiety of this core were developed and were successfully used for the synthesis of dimer, triad, and polymeric materials. The optical and electrochemical properties of these materials and their monomers were examined as a function of sidechain modification and π-extension. With their broad optical absorption and low reduction potentials, these materials could be candidates as organic semiconductors for applications in OFETs and as nonfullerene acceptors.
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can provide access to π-expanded derivatives, such as semicoronenediimides (sCDIs) and corenenediimides (CDIs), that allow for tuning of material properties in addition to providing a possible functional handle for further derivatization. Additionally, the expanded core structure of these derivatives allows for greater planarity in aromatic-substituted derivatives.14−20 For example, Usta and co-workers reported dithienocoronenediimide-based copolymers, which exhibited ambipolar transport with electron mobilities up to 0.3 cm2 V−1 s−1.14 Due to our ongoing interest in developing new organic electronic materials, we desired access to substituted sCDI and CDI derivatives. In particular, we hypothesized that thiazolesemicoronenediimide (TsCDI) and -coronenediimide (TCDI) derivatives would lead to lower reduction potentials and greater planarity than previously reported sCDIs and CDIs. Additionally, selective functionalization of thiazole rings is well developed, providing readily available methods for building these derivatives.21−29 We hypothesized that complex TsCDI and TCDI materials could be readily assembled using C−H functionalization strategies. Methodologies for functionalizing simpler benzothiazole and benzobisthiazole derivatives have
INTRODUCTION π-Conjugated electron transport materials have been the subject of significant research interest due to their potential applications in organic field-effect transistors (OFETs), organic photovoltaic (OPV) cells, and organic light-emitting diodes (OLEDs).1−4 Traditional synthesis requires access to stannylated, borylated, and halogenated derivatives of electron deficient aromatic systems. Due to their low-lying frontier molecular orbitals, these molecules are often unreactive to typical electrophilic reagents used for functionalization in other systems in the absence of harsh conditions, and many desired derivatives decompose under the strongly basic conditions required for functionalization mediated by deprotonation. Therefore, there is a clear opportunity for novel synthetic methods that provide ready access to these materials. Perylene-3,4:9,10-bis(dicarboximide)s (PDIs) are one such electron-deficient aromatic system that has been widely used in OFETs and OPVs as electron transport materials due to their relatively high electron affinities and electron mobilities, as well as their chemical, thermal, and photochemical stability.5−8 However, like other electron deficient aromatic systems, PDIs can require harsh conditions to access brominated or borylated derivatives.9−13 Additionally, while PDIs themselves are planar, aromatic-substituted PDI derivatives often have large dihedral angles between the aryl and PDI units. Annulations on PDIs © 2017 American Chemical Society
Received: June 28, 2017 Published: September 8, 2017 10139
DOI: 10.1021/acs.joc.7b01604 J. Org. Chem. 2017, 82, 10139−10148
Article
The Journal of Organic Chemistry been previously developed,30,31 and we recently reported a C− H iodination methodology for electron-withdrawing aromatic systems, including a representative TsCDI and TCDI monomer.32 In addition, other C−H functionalization strategies have also been developed for similar compounds.33−36 These prior results all indicate the potential for C−H functionalization chemistry to be applied to the synthesis of TsCDI- and TCDI-based materials. Here, we describe the synthesis, C−H functionalization reactivity, and optical and electrochemical properties of TsCDIs and TCDIs and their derivatives.
isomer shown);32 2-octyldodecyl-substituted TsCDI derivative 4 was synthesized in a similar fashion. Beginning from 1bromo-PDI 3,13 we initially attempted a C−H arylation protocol27 to install the thiazole ring, but no reaction was observed. Instead, Stille coupling of 3 with 5-(tributylstannyl)thiazole provided the crude thiazole substituted PDI derivative. Dilution of this reaction mixture with dichloromethane and subsequent cyclization with UV light in the presence of catalytic iodine provided the desired TsCDI derivative 4 in 60% yield for the two steps. We next explored conditions for the C−H functionalization of these intermediates, initially examining the C−H arylation of TsCDI 4 with 4-tert-butyl-bromobenzene (Table 1). Examination using conditions developed for the direct arylation of benzobisthiazoles31 did not lead to significant quantities of observable product. Alternative conditions using catalytic PXPd,30 catalytic copper(II) acetate, and triphenylphosphine gave significant quantities of phenyl-substituted TsCDI 6 (45% yield) in addition to the desired 4-(tert-butyl)phenylsubstituted derivative 5 in 22% yield (Entry 1). This phenylsubstituted byproduct is believed to be the result of phenyl transfer from the phosphine ligand.37 To alleviate this, an alternative ligand system for the copper cocatalyst was examined. Switching Cu(OAc)2 and PPh3 for CuI(Xantphos) led to exclusive formation of the 4-(tert-butyl)phenylsubstituted TsCDI 5 in 60% yield, with no phenyl-substituted byproduct observed (Entry 2). PXPd was found to be necessary for good yields in this transformation, with palladium(II) acetate providing only 17% yield of the desired product (Entry 3). Additionally, the elevated temperatures used (135 °C) were also required, with no reaction being observed at 90 °C (Entry 4). Alternative solvents were also explored (Entries 5−6). No reactivity was observed in toluene, while the product was obtained cleanly in N,N-dimethylacetamide, albeit in diminished yields (43%). Finally, the loading of the copper catalyst was found to be crucial for good yields and clean reactivity (Entries 7−8). Elevating the loading of CuI(Xantphos) to 5 mol% provided the desired product 5 in increases the yield to 80%. Additionally, a trace amount of phenyl transfer product 6 was also observed at this loading (Entry 7). When copper loading was further increased to 20 mol%, significant quantities of phenyl-substituted product 6 began to again be observed (40% yield), eroding the yield of the desired product to 55% (Entry 8). Having developed a robust C−H functionalization protocol for our TsCDI substrate, we next explored the scope of aryl halide coupling partners for this reaction (Figure 2). Electron rich aromatic rings, such as 4-methoxybromobenzene and 4methoxyiodobenzene, were able to be coupled successfully, providing the 4-methoxyphenyl-substituted TsCDI derivative 7 in 35% and 55% yield, respectively. 2-Bromothiophene, containing an electron rich heterocyclic motif important in many materials applications, coupled in very high yield to provide 2-thienyl-TsCDI 8 (95%), an intriguing result in terms of the potential application in the synthesis of complex materials fragments. Electron deficient arenes also were successfully coupled, with 4-nitrobromobenzene and 4trifluoromethylbromobenzene providing products 9 and 10 in 57% and 85% yields, respectively. The very electron poor substrate pentafluoroiodobenzene did not provide any product 11 under our optimized reaction conditions.32 We also hypothesized that these C−H functionalization conditions could be adapted for use in an oxidative C−H/C-H
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RESULTS AND DISCUSSION To simplify the initial optimization of our desired C−H functionalization reaction, we wished to first explore these reactions on a TsCDI substrate (Figure 1). We previously have disclosed the synthesis of TsCDI monomer 1 and 2 (isolated as a 3:1 mixture of anti-/syn-thiazolyl isomers, with the major
Figure 1. (A) Previously synthesized TsCDI monomer 1 and TCDI monomer 2. (B) Synthesis of TsCDI monomer 4. 10140
DOI: 10.1021/acs.joc.7b01604 J. Org. Chem. 2017, 82, 10139−10148
Article
The Journal of Organic Chemistry Table 1. Optimization of Reaction Conditions
entry
PdLn
CuLn
solvent
ligand
Temp (° C)
% yieldb (5/6)
1 2 3 4 5 6 7 8
PXPdc PXPd Pd(OAc)2g PXPd PXPd PXPd PXPd PXPd
Cu(OAc)2d CuI(Xantphos)f CuI(Xantphos) CuI(Xantphos) CuI(Xantphos) CuI(Xantphos) CuI(Xantphos)h CuI(Xantphos)i
DMF DMF DMF DMF PhCH3 DMAc DMF DMF
PPh3e
135 135 135 90 135 135 135 135
22/45 60/0 17/0 0/0 0/0 43/0 80/
