Chemistry Reference
In-Depth Information
Mg / THF
Ni(bipy)
2
Cl
2
Yama moto
Route
Br
Br
S
Mg / THF
M(acac)
n
M=Pd,Ni,CoorFe
Lin and Dudek
Route
Br
Br
n
S
S
Mg or Zn
Dehalogenation
Hal
Hal
[M] catalyst
M=Pd,Ni,Co,Feetc.
S
Scheme 1 Organometallic polycondensation of 2,5-dihalo-thiophenes
BuLi then ClSnMe
3
Br
Br
Me
3
Sn
SnMe
3
S
S
2
1
Br
O
S
Cl
Br
O
S
To s O H ,
glycol
benzene, 80 °C, 2 d
AlCl
3
, CH
2
Cl
2
0 °C
O
+
Br
O
S
Br
Br
S
S
Cl
3
4
5
6
O
O
O
O
Me
3
Sn SnMe
3
Pd(PPh
3
)
4
DMF/toluene
S
O
S
S
O
TFA
DCB
LR
heat
O
S
n
S
n
S
S
S
n
O
7
8
O
O
Scheme 2 Synthesis of high molecular weight PT from a soluble prepolymer obtained via Stille
couplings [
32
]
(MgHal
2
, ZnHal
2
, etc.). By changing the type of halogen, the catalyst employed,
the metal, or the reaction conditions in general, different yields and molecular
weights of the PT can be achieved; however, all these routes result in low
molecular weight polymers (around 3,000-4,000 g mol
1
) due to the low solubility
of PT, and thus efforts have been made to increase the molecular weight [
31
]. For
example, the strategy shown in Scheme
2
was used to obtain high molecular weight
PT [
32
]. The first monomer, 2,5-bis(trimethylstannyl)thiophene (2), was synthe-
sized from 2,5-dibromothiophene (1) via metal-halogen exchange followed by
reaction with trimethyltin chloride. For the synthesis of the second monomer
6, 2-bromothiophene (3) was first subjected to a Friedel-Crafts acylation with
succinyl chloride (4) to give the 1,4-dione 5, which was then protected as a
bis-acetal, 6. The monomers were then combined in a Stille cross-coupling poly-
merization to give 7, which was further treated with acid to reveal the
1,4-dicarbonyl system in PT precursor 8. This was thiated through reaction with
Lawesson's reagent to form a thiophene ring from the 1,4-dicarbonyl system and
thus obtain PT with a high molecular weight (
M
n
of about 36,000 g mol
1
)[
32
].
Another method gives PT, from thiophene, as nanoparticles, by a chemical
oxidative reaction in aqueous medium in the presence of surfactants and oxidants
