Stannyl derivatives of naphthalene diimides and their use in oligomer synthesis

Article abstract of DOI:10.1021/ol203432x

2-Stannyl and 2,6-distannyl naphthalene diimides (NDIs) can be synthesized through the palladium-catalyzed reaction of the appropriate bromo derivatives with hexabutylditin. The utility of these precursors in palladium catalyzed cross-coupling reactions is demonstrated by the synthesis of bi- and ter-NDI derivatives, UV - vis, cyclic voltammetry, and n-channel organic field-effect transistor data for which are compared to those of the monomeric parent NDI.

Full text of DOI:10.1021/ol203432x

ORGANIC
LETTERS
2012
Vol. 14, No. 3
918–921
Stannyl Derivatives of Naphthalene
Diimides and Their Use in Oligomer
Synthesis
Lauren E. Polander,† Alexander S. Romanov,‡ Stephen Barlow,† Do Kyung Hwang,§
Bernard Kippelen,§ Tatiana V. Timofeeva,‡ and Seth R. Marder*,†
School of Chemistry and Biochemistry, School of Electrical and Computer
Engineering, Center for Organic Photonics and Electronics, Georgia Institute of
Technology, Atlanta, Georgia 30332-0400, United States, and Department of
Chemistry, New Mexico Highlands University, Las Vegas, New Mexico 87701,
United States
seth.marder@chemistry.gatech.edu
Received December 22, 2011
ABSTRACT
2-Stannyl and 2,6-distannyl naphthalene diimides (NDIs) can be synthesized through the palladium-catalyzed reaction of the appropriate bromo
derivatives with hexabutylditin. The utility of these precursors in palladium catalyzed cross-coupling reactions is demonstrated by the synthesis
of bi- and ter-NDI derivatives, UVꢀvis, cyclic voltammetry, and n-channel organic field-effect transistor data for which are compared to those of
the monomeric parent NDI.
Tetracarboxylic diimide derivatives of rylenes, particu-
larly of napthalene and perylene (NDIs amd PDIs, respec-
tively), are extensively studied for organic electronics.1,2
Their thermal, chemical, and photochemical stability, high
electron affinities (EAs), and large charge-carrier mobility
values render these materials attractive for applications in
field-effect transistors (OFETs)3ꢀ15 and photovoltaic cells
(OPVs).12,16ꢀ20 They have also been widely used as accep-
tors in transient absorption studies of photoinduced elec-
tron transfer, again due to their redox potentials and to
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† School of Chemistry and Biochemistry, Center for Organic Photonics
and Electronics, Georgia Institute of Technology.
‡ Department of Chemistry, New Mexico Highlands University.
§ School of Electrical and Computer Engineering, Center for Organic
Photonics and Electronics, Georgia Institute of Technology.
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10.1021/ol203432x
Published on Web 01/24/2012
2012 American Chemical Society

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ruplex oligonucleotides.25ꢀ28
imidization with a primary amine in refluxing HOAc.5,31,36
NDA can also be brominated using Br2 in conc. H2SO4 or
oleum.5,37 The brominated NDI can then serve as an
intermediate for use in either nucleophilic substitutions,
to afford amino, thiol, or alkoxy derivatives,35,36 or
Pd-catalyzed coupling reactions, to yield cyano,5,33 phenyl,32,33
alkynyl,33 and thienyl11,14,32 products. However, the range
of conjugated species that can be obtained by Pd-catalyzed
methods is limited by the availability of appropriate candi-
date coupling partners. In particular, metalated reagents such
as stannanes and boronates can be difficult to obtain for
electron-poor (acceptor) building blocks. Accordingly, me-
talated NDI species would be valuable building blocks for
new types of conjugated NDI derivatives in which acceptor
groups are directly conjugated to the NDI core.
The N,N0-substituents of PDIs and NDIs generally have
only minimal influence on the optical and electronic pro-
perties of isolated molecules, although they can be used to
control solubility, aggregation, and intermolecular pack-
ing in the solid state. Core substitution of these species
typically has a much more significant effect on the redox
potentials (enabling air-stable OFET operation in some
cases5,13,29) and optical spectra. Moreover, core substitu-
tion can be used as a means of constructing more elaborate
architectures such as conjugated polymers7,11,20,30,31 and
donor- or acceptor-functionalized products.13,14,32ꢀ36
Functionalized NDIs are most effectively obtained
through the selective bromination of naphthalene-1,4:5,
8-tetracarboxylic dianhydride (NDA) with dibromoisocya-
nuric acid (DBI) in conc. H2SO4 or oleum, followed by
Here we report the synthesis, using Pd-catalyzed coupl-
ing38,39 of brominated NDIs and Sn2Bu6, of the first
stannyl derivatives of NDIs and their use in Stille reactions
to obtain bi- and ter-NDIs.
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Scheme 1. Preparation of Stannyl NDI Derivatives
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N,N0-Di-(n-hexyl)-2-tri(n-butyl)stannylnaphthalene-
1,4,5,8-bis(dicarboximide), 3, and N,N0-di(n-hexyl)-2,6-
bis(tri(n-butyl)stannyl)naphthalene-1,4,5,8-bis(dicarboxi-
mide), 4, were obtained in good to moderate yields,
respectively, according to Scheme 1: a mixture of the
appropriate mono- or dibromo derivative, 1 or 2, and
Sn2Bu6 (1 equiv per Br) was heated in toluene in the
presence of Pd2dba3 (0.05 equiv per Br) and P(o-tol)3
(0.2 equiv per Br). Purification of the products by silica
gel chromatography and recrystallization from MeOH
afforded the mono- and distannyl derivatives as long
yellow needles; these compounds were characterized by
NMR spectroscopy, mass spectrometry, elemental analy-
sis, and, in the case of 4, X-ray crystallography (Figure 1;
see Supporting Information (SI) for details).40 The
ability to isolate and thoroughly purify the distannyl
derivative is important for potential applications in
conjugated-polymer syntheses, where the ability to obtain
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(40) Under identicalconditions, the monobrominated PDI derivative
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sponding stannyl PDI intermediate cannot be isolated.
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Org. Lett., Vol. 14, No. 3, 2012
919

high-molecular-weight material is critically dependent on
precise control of monomer stoichiometry.
As an example of the utility of stannyl NDI derivatives
as a reagent for cross-coupling with electron-poor moieties,
we carried out stannyl-NDI/bromo-NDI cross-couplings
to obtain N,N0,N00,N000-tetra(n-hexyl)-[2,20-binaphthalene]-
1,4:5,8:10,40:50,80-tetra(dicarboximide), 7, and N,N0,N00,
N000,N0000,N00000-hexa(n-hexyl)-[2,20:60,200-ternaphthalene]-1,4:-
5,8:10,40:50,80:100,400:500,800-hexa(dicarboximide) 8 (Scheme 3).
In addition to using the cross-coupling of 1 and 3
(Scheme 3, B), 7 was also obtained by the one-pot homo-
coupling of1 (Scheme 3, A ) using 5.0 mol % of Pd(PPh3)4,
10 mol % of CuI, and 0.5 equiv of Sn2Bu6 in hot toluene over
6 d, a reaction that presumably involves the in situ generation
and reaction of 3. Purification of the reaction mixture by
silica-gel chromatography and recrystallization from isopro-
panol afforded 7 in 25% yield. The cross-coupling of 1 and 3
was performed in the presence of 5.0 mol % of Pd(PPh3)4 and
10 mol % of CuI in hot toluene over only 3 h and afforded 7in
59% yield after identical purification procedures.
Figure 1. One of the independent molecules of compound 4
found in its crystal structure. Atoms are shown as spheres of
arbitrary size.
Scheme 3. Preparation of Bi- and Ter-NDI Derivatives
Moreover, the different chromatographic behavior of
3 (Rf = 0.3 on silica, eluting with 1:1 CH2Cl2/hexanes) and
4 (Rf = 0.3, silica, 1:10 CH2Cl2/hexanes) suggested to us the
possibility of carrying out this reaction using a mixture of
mono- and dibromo species obtained from bromination and
imidization of NDA, only purifying at the final stage. This
transformation can indeed be carried out without separation
of the mono- and difunctionalized intermediates to give iso-
lated yields of mono- and distannyl derivatives of ca. 20% and
5%, respectively (using 1 equiv of DBI as the brominating
agent).41 As shown in Scheme 2, N,N0-bis(n-dodecyl) analog-
ues 5 and 6 have also been obtained in the same way in
similar isolated yields. The facile separation of the highly
soluble mono- and distannyl NDI products via column
chromatography is an attractive alternative to the more dif-
ficult separation of the mono- and dibromo-NDI intermedi-
ates, such as 1 and 2, which are both less soluble in common
organic solvents and less well-differentiated in Rf (0.4 and 0.3
for 1and 2, silica, CH2Cl2). Thus, a two-step process involving
isolation and purification of the brominated species followed
by stannylation results in overall yields of ca. 9% and 2% for
the mono- and distannyl NDI, respectively.
8 was prepared by cross-coupling of 1 and 4 in the
presence of 5.0 mol % of Pd(PPh3)4 and 10 mol % of
CuI in hot toluene over 15 h. Purification of the reaction
mixture by silica-gel chromatography and recrystallization
from isopropanol afforded 8 in 56% yield.
The optical and electrochemical properties of 7 and 8
were compared to those of the corresponding mono-
meric parent NDI, N,N0-bis(n-hexyl)naphthalene-1,4:5,8-
bis(dicarboximide), 9. The UVꢀvis absorption spectra of
7 and 8 are similar in shape to that of 9 and the molar
absorptivity, εmax, increases with the number of NDI units,
suggesting that each NDI subunit behaves largely inde-
pendently of the other(s), consistent with inter-NDI
steric interactions leading to significant deviation of the
NDI subunits from coplanarity. However, the nonlinear
Scheme 2. Preparation of Stannyl NDI Derivatives from Com-
mercially Available NDA
(41) The relative yields can be tuned somewhat with respect to the
brominating agent, and yields of ca. 15ꢀ20% were obtained for both
mono- and distannyl derivatives using 2 equiv of DBI.
920
Org. Lett., Vol. 14, No. 3, 2012

NDIs indicated by the optical data. The slight anodic shift
in the oligomeric species is perhaps attributable to the
inductive electron-withdrawing effect of one NDI upon
another, while the separation between the multiple reduc-
tions is likely to be due to electrostatic effects, given the
close proximity of the multiple redox centers.
Table 1. Optical and Electrochemical Properties of Mono-,
Bi-, and Ter-NDIs
no. of
a
a
0/ꢀb
E1/2 /
NDI
λmax
/
εmax
/
λmax,solid
/
compd
units
nm
104 Mꢀ1 cmꢀ1
nm
V
9
7
8
1
2
3
380
381
383
2.76
4.10
6.09
393
388
389
ꢀ1.13
ꢀ1.03
ꢀ1.00
a CH2Cl2. b 0.1 M nBu4NPF6/CH2Cl2 vs FeCp2
.
þ/0
Top-gate, bottom-contact geometry organic field-effect
transistors were fabricated with a CYTOP (45 nm)/Al2O3
(50 nm) bilayer gate dielectric, 7 or 8 asthe activelayer, and
Au source and drain electrodes. The materials were spin-
coated from 1,1,2,2-tetrachloroethane solutions to yield
devices with n-channel characteristics with moderate elec-
tron mobility values, μe, of up to 0.34 and 0.014 cm2 Vꢀ1
s
ꢀ1 for 7 and 8, respectively (see SI). Although μe for 7 falls
short of the state of the art for solution-processed n-chan-
nel devices (1.5 cm2 Vꢀ1 sꢀ1),14 it is an order of magnitude
higher than the highest value reported for solution-
processed devices based on a simple N,N0-alkyl NDI with-
out core substitution (0.01 cm2 Vꢀ1 sꢀ1).3
To conclude, we have developed an efficient and
straightforward synthesis of 2-stannyl and 2,6-distannyl
NDIs. Their use in Pd-catalyzed coupling reactions was
demonstrated by the synthesis of bi- and ter-NDI.
These stannyl NDI derivatives may be useful building
blocks for new small-molecule and polymeric NDIs and
may facilitate structures that are otherwise difficult to
obtain.
Figure 2. UVꢀvis spectra in CH2Cl2 (top) and cyclic voltammo-
grams in CH2Cl2/nBu4NPF6 (bottom) of 7 and 8.
increase of εmax with the degree of oligomerization, some
broadening seen in the spectra of 7 and 8, and the ap-
pearance of a distinct shoulder on the low-energy side of
the main absorption of 8 indicate that there are some in-
teractions, possibly excitonic coupling, between the NDI
subunits (differences in band shape are more clear-
ly seen in normalized spectra of 7, 8, and 9; see
Figure S2).
Cyclic voltammetry showed four reversible reduction
waves for 7 and six reversible reduction waves for 8
corresponding to the sequential reduction of each NDI
to its radical anion and then to its dianion (Figure 2). No
oxidation could be observed in the potential window
investigated. The first halfwave reduction potentials are
reported in Table 1. 7 and 8 are reduced at very a similar
potential to one another and at only a marginally more
anodic potential than the monomeric NDI, 9, suggesting
no significant delocalization of the charge between the
NDIs, consistent with the picture of weakly interacting
Acknowledgment. We thank Solvay S.A. and the NSF
(STC Program, DMR-0120967; PREM program, DMR-
0934212) for support, Yulia Getmanenko for helpful dis-
cussions, and Brian Seifried for the scale-up of some
intermediates.
Supporting Information Available. Full details of the
synthesis and characterization of 1ꢀ8. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
Org. Lett., Vol. 14, No. 3, 2012
921