Tetrahedron Letters
Donor–acceptor ferrocenyl triazines: synthesis and properties
⇑
Ramesh Maragani, Rajneesh Misra
Department of Chemistry, Indian Institute of Technology Indore, MP 452017, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of star shaped donor–p–acceptor type symmetrical triazine was designed and synthesized by the
Received 11 June 2013
Revised 20 July 2013
Accepted 23 July 2013
Available online 30 July 2013
Pd-catalysed Sonogshira cross coupling reaction. The ferrocenyl moiety with different spacer groups acts
as donor and 1,3,5-triazine as acceptor. The photophysical results show intramolecular charge transfer
from ferrocene to the 1,3,5-triazine unit. The cyclic voltammetric analysis reveals substantial donor–
acceptor interaction. The triazines exhibit good thermal stability with high decomposition temperature.
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Keywords:
Donor–acceptor system
Triazine and ferrocenyl
Electrochemical properties
Donor–acceptor (D–A) organic materials have attracted sub-
stantial interest in opto-electronic applications such as organic
photovoltaics (OPV), organic light emitting diodes (OLED) and thin
trimethylsilylacetylene resulted in triazine 4 in 80% yield. The
deprotection of the trimethylsilylacetylene group by a mixture of
NaOH and methanol resulted in triazine 5 in 68% yield (Scheme 1).
The Sonogashira coupling reaction of triazine 3 with ethynyl
1
–3
film transistors (TFT).
The 1,3,5-triazine derivatives show excel-
lent photonic, and electronic properties due to the high electron
affinity, and symmetrical structure.4 The literature reveals that
integrating the donor groups into the triazine moiety results in do-
ferrocene in the presence of Pd(dba)
3
and AsPh
sulted in triazine 6 in 52% yield. The Suzuki coupling of triazine
3 with ferrocene boronic acid in the presence of Pd(PPh as a
3
as a catalyst re-
15
3 4
)
nor–acceptor system, which exhibits high two-photon absorbing
catalyst resulted in triazine 7 in 57% yield (Scheme 2). In order to
synthesize the tri substituted ferrocenyl triazine, the Suzuki
coupling reaction was repeated by conventional as well as the
5
(
2PA) cross-section.
Recently we have reported the donor–acceptor triazine, where
6
the donor group is connected via phenyl spacers to the triazine.
3 4 2
microwave method in the presence of Pd(PPh ) , Ag O and CsF
Our group is interested in molecular systems with strong elec-
with excess boronic acid. However the isolation of 2,4,6-tris(-5-fer-
rocene-thiophene-2-yl)-1,3,5-triazine (tri ferrocenyl substituted
triazine) resulted in failure.
The Sonogashira coupling reaction of triazine 5 with 1-ferro-
cene-4-iodo-phenyl, 1-ferrocene-3-iodo-phenyl and 1-ethynyl fer-
tronic communication.7
–11
The literature reveals that thiophene
spacers exhibit better communication compared to phenyl spacers
in donor–acceptor system.12
In order to enhance the electronic communication between the
donor and acceptor group, we have introduced the thiophene
bridge. Ferrocene is a widely studied strong donor. In this Letter
we have incorporated ferrocenyl moiety into the 1,3,5-triazine core
with different spacers and explored its photophysical and electro-
chemical properties.
rocene-4-iodo-phenyl in the presence of Pd(PPh
3 4
) catalyst
resulted in triazines 8, 9 and 10 in 39%, 40% and 32% yields, respec-
1
6
tively, (Scheme 3).
Triazines 5–10 were well characterized by 1H NMR, C NMR
and HRMS techniques (see Supplementary data). The H NMR
13
1
The donor substituted triazines 6–10 were synthesized by the
Pd-catalysed Suzuki and Sonogshira cross-coupling reaction of
triazine 3 and triazine 5 with the corresponding ferrocenyl deriva-
tives. Triazine 2 was synthesized by the trimerization reaction of
thiophene-2-carbonitrile in the presence of trifluoromethanesulfo-
nic acid in chloroform.13 The treatment of triazine 2 with threefold
excess of N-bromosuccinimide (NBS) resulted in triazine 3 in 87%
yield.1 The Sonogshira cross-coupling reaction of triazine 3 with
spectra of triazines 6–10 exhibit following types of signals; (a)
two characteristic doublets between 8.12–8.02 ppm and
7.43–7.02 ppm, corresponding to the thiophene unit; (b) the ferr-
ocenyl group exhibits three different types of peaks, the unsubsti-
tuted cyclopentadienyl moiety of ferrocene shows a sharp singlet
around 4.21–3.98 ppm the mono substituted cyclopentadienyl
ring exhibits two broad singlets around 4.66–4.48 ppm and
4.33–4.20 ppm.
4
The thermal properties of the ferrocenyl substituted triazines 6,
8
, 9 and 10 were evaluated using thermogravimetric analysis (TGA)
⇑
À1
at a heating rate of 10 °C min up to 800 °C under a nitrogen