Thiophene in Conducting Polymers: Synthesis of Poly(thiophene)s and Other Conjugated Polymers Containing Thiophenes, for Application in Polymer Solar Cells - Thiophenes - page 216

Br

S S N

Si N S

S

+ Br

Me 3 Sn

S SnMe 3

S

Pd(PPh 3 ) 4
PhMe, reflux

Si

S

S N

S

S

S

N S

n

Scheme 18 Synthesis of dithieno[3,2- b :20,30- d ]silole-alt-dithienylthiazolo[5,4- d ]thiazole copol-
ymer [ 95 ]

R 1 R 2

R 1 X

PdL n

reductive
elimination

oxidative
addition

R 2
R 2

R 1
X

Ln Pd

Ln Pd

NaOEt (or another base)

transmetallation

R 2 EtO B(OR) 2 B(OR) 2

+ NaX

Scheme 19 Suzuki cross-coupling catalytic cycle [ 96 , 97 ]

monomer) by Stille cross-coupling, obtaining an LBG polymer containing thio-
phene units shown in Scheme 18 .
Suzuki cross-coupling polymerization is also often used to synthesize conju-
gated polymers. In this case, a halide (or triflate) monomer is cross-coupled with an
organo-borane monomer under basic conditions and in the presence of a Pd(0) cat-
alyst. The mechanism, shown in Scheme 19 , is similar to Stille cross-coupling: the
first step is the oxidative addition of the organic halide (electrophile) to the Pd
(0) complex, generating a Pd(II) complex, which undergoes transmetallation with
the organometallic monomer. Reductive elimination of the product allows a new
cycle to start [ 96 , 97 ]. The step that differs in the two cross-couplings is the