Towards a general solid phase approach for the iterative synthesis of conjugated oligomers using a germanium based linker - First solid phase synthesis of an oligo-(triarylamine)

Article abstract of DOI:10.1039/b703022c

The development of a germanium-based linker system for the solid phase synthesis (SPS) of 3-(n-hexyl)thiophene oligomers and the first SPS of triarylamine oligomers via iterative chain extension is described. The efficiency of the key steps in the oligomer syntheses and their compatibility with the germanium linker are demonstrated by the SPS of bi-[3-(n-hexyl) thiophene] 19 and ter-(triarylamine) 50. The use of a germanium-based linker in combination with appropriately selected silicon-based blocking/protecting groups allows double coupling to drive the key cross coupling steps to completion hence minimising deletion sequences and also allows for traceless and potentially functionalisative cleavage from the resin. The latter feature has yet to be fully explored but towards this end the first ipso-borodegermylation reaction of a 2-germyl-3-(n-hexyl)thiophene is presented. The Royal Society of Chemistry.

Full text of DOI:10.1039/b703022c

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www.rsc.org/obc | Organic & Biomolecular Chemistry
Towards a general solid phase approach for the iterative synthesis of
conjugated oligomers using a germanium based linker - first solid phase
synthesis of an oligo-(triarylamine)†
c
David J. Turner,‡d Re´mi Ane´mian,§ Philip R. Mackie,c Domenico C. Cupertino,c Stephen G. Yeates,b
Michael L. Turnerb and Alan C. Spivey*a
Received 27th February 2007, Accepted 11th April 2007
First published as an Advance Article on the web 30th April 2007
DOI: 10.1039/b703022c
The development of a germanium-based linker system for the solid phase synthesis (SPS) of
3-(n-hexyl)thiophene oligomers and the first SPS of triarylamine oligomers via iterative chain extension
is described. The efficiency of the key steps in the oligomer syntheses and their compatibility with the
germanium linker are demonstrated by the SPS of bi-[3-(n-hexyl)thiophene] 19 and ter-(triarylamine)
50. The use of a germanium-based linker in combination with appropriately selected silicon-based
blocking/protecting groups allows double coupling to drive the key cross coupling steps to completion
hence minimising deletion sequences and also allows for traceless and potentially functionalisative
cleavage from the resin. The latter feature has yet to be fully explored but towards this end the first
ipso-borodegermylation reaction of a 2-germyl-3-(n-hexyl)thiophene is presented.
transistors (FETs) and in electroreprographic/electroluminescent
devices, respectively.
Conventional solution phase chemistry has been used to
Introduction
p-Conjugated oligomers have received considerable attention
synthesise monodisperse oligomeric oligo-(3-alkylthiophene)s12–14
and oligo-(triarylamine)s15–17 using repetitive transition metal
catalysed cross-coupling. However, control over the structure
of such materials is notoriously arduous due to difficulties in
separating the target oligomer from residual lower molecular
weight truncated oligomers and starting materials with closely
similar chromatographic properties. At the outset of the work
described herein, there was emerging evidence from the labs of
Fre´chet,18 Tour19 and Ba¨uerle11,20–24 that Solid Phase Synthesis
(SPS)25 could constitute a useful technique for the preparation of
oligo-(3-alkyl/arylthiophene)s and provide an attractive solution
to some of these purification issues. However, the linker systems
employed in these pioneering studies offered little flexibility for
control over the end groups of the oligomers and limited prospects
for generalisation to other types of oligomer. We were therefore
inspired to try to develop a general SPS platform for the efficient
preparation of a variety of high purity, regioregular, homo- and
heteromonomer based p-conjugated oligomers. In addition, we
wanted to design a system that would allow for the formation of a,
x-differentiated telechelic units for block co-oligomer preparation
and for electronic property tuning as a function of the nature
of the end-capping unit. We were also particularly concerned to
develop protocols that would minimise the occurrence of truncated
oligomers as the result of incomplete conversion during each
iterative cross-coupling step.
recently as active materials for the construction of electronic and
photonic devices such as organic light emitting diodes (OLEDs),1
organic field-effect transistors (OFETs),2 and photovoltaic devices
(PVDs).3 The ideal materials for such devices should display high
stability and processibility during fabrication and high charge
mobility and environmental stability during operation.4 Many p-
conjugated oligomeric materials have been reported in the litera-
ture which satisfy these requirements to varying degrees, includ-
ing oligo-(3-alkylthiophene)s,5 oligo-(fusedthiophene)s,6 oligo-
(dialkylfluorene)s,7 oligo-(triarylamine)s8–10 and alternating and
block co-oligomers thereof. To obtain high charge mobilities,
long-range order in the solid state and very high levels of purity
are generally required.11 We have been interested both in oligo-
(3-alkylthiophene)s and oligo-(triarylamine)s as charge transport
materials for potential use as p-type materials in field effect
aDepartment of Chemistry, Imperial College London, South Kensington cam-
pus, London, UK SW7 2AZ. E-mail: a.c.spivey@imperial.ac.uk; Fax: (+)
44 (0)20 75945841; Tel: (+) 44 (0)20 75945841
bDepartment of Chemistry, University of Manchester, Oxford Road, Manch-
ester, UK M13 9PL
cMerck Chemicals Ltd, LC - Manchester Technical Centre, Hexagon Tower,
Blackley, Manchester, UK M9 8ZS
dDepartment of Chemistry, University of Sheffield, Brook Hill, Sheffield,
UK S3 7HF
† Electronic supplementary information (ESI) available: Experimental
procedures for 1b–c, 6, 8b–e, 9b–e, 10b–e, 12–20, 23–28; copies of 1H
and 13C spectra for new compounds 1b, 1c, 8a–e, 9a–e, 10a–e, 12–18, 20,
23–26, 28 and 50, 1H MAS NMR spectra for resins 30–36 and gel phase
13C spectra for resins 39–41 and 43–49, and HPLC traces for 19 and 50.
See DOI: 10.1039/b703022c
Here, we describe development of a germanium-based linker
suitable for the SPS of p-conjugated oligomers and proof of
concept for its employment for the SPS of an oligo-[3-(n-
hexyl)thiophene] and for the first SPS of an oligo-(triarylamine).
The chemistry employed for both the oligo-[3-(n-hexyl)thiophene]
and the oligo-(triarylamine) SPS was first developed on solution
model systems and this work has already been published.26,27
‡ Author to whom queries relating to the oligo-(thiophene) and linker
optimization work should be directed: david.x.turner@gsk.com.
§ Author to whom queries relating to the oligo-(triarylamine) work should
be directed: remi.anemian@merck.de.
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Consequently, the following provides full details of the evolution
of those solution protocols, in which a germanium-based linker
having two methyl ‘spectator’ groups was used, into more robust
SPS protocols employing a germanium-based linker having two p-
tolyl spectator groups.28 This change in linker was necessitated
by our finding in solution that the lability of immobilised
oligomers, particularly oligo-[3-(n-hexyl)thiophene]s, towards un-
wanted cleavage from the linker by adventitious acid increased as
the oligomers grew and our desire to develop a robust platform
for SPS of many varied oligomers with wide scope.
linker. However, as noted above, during the early development
of the oligomer chemistry in solution it became apparent that
susceptibility to cleavage by electrophiles was a property of the
linker that would require careful tuning to allow, on the one hand,
facile functionalisative cleavage from the solid support at the end
of the synthesis and, on the other hand, adequate stability during
the iterative oligomer extension steps.38
The iterative oligomer assembly processes that we developed
for the preparation of oligo-[3-(n-hexyl)thiophene]s and oligo-
(triarylamine)s in solution are summarised below (Scheme 1).
For the preparation of the ter-[3-(n-hexyl)thiophene] in solu-
tion, the synthesis involved coupling of lithiated trimethylsilyl
(TMS) blocked 3-(n-hexyl)thiophene ‘starter monomer’ 1a to a
dimethylgermylchloride linker model,39 chemoselective removal of
the TMS blocking group, activation of the ‘oligomer’ terminus as
an iodide, and then Suzuki double coupling with a TMS-blocked
3-(n-hexyl)thiophene boronate salt ‘extender monomer’ 2. The
sequence was then repeated on the resulting dimer, starting with
removal of the TMS blocking group. The resulting trimer was
then cleaved from the linker tracelessly using acid. The process
relies critically on the orthogonal susceptibility of the TMS and
aryldimethylgermyl groups towards ipso-protodegermylation by
fluoride ions: the TMS group is selectively removed by CsF in
DMF at 60 ◦C without affecting the linker. Additionally, the
double coupling process that is employed to drive the coupling
steps to completion (and so minimise formation of truncated
oligomers) relies on the stability of both these groups during
the activation and the Suzuki coupling steps.26 It was envisaged
that, in principle, once optimised for SPS, the iterative steps for
monomer introduction and activation could be repeated to provide
an oligomer of any desired length.
Results and discussion
Our choice of a germanium-based linker system29–31 as the
foundation on which to build our SPS approach to p-conjugated
oligomers was primarily influenced by the need to employ a linker
that would be robust to a wide range of aromatic/heteroaromatic
metalation conditions [e.g. halogen–metal exchange, directed
ortho metalation (DoM)]32 and to transition metal catalysed
cross-coupling conditions (e.g. Suzuki coupling, Buchwald–
Hartwig amination)33,34 and which would allow traceless35 and
functionalisative36 cleavage from the solid support. Germanium-
based linkers were considered to be excellent candidates for this
role as the key arylgermane bond connecting the solid support to
the growing oligomer terminus was expected to display excellent
stability towards strongly basic conditions whilst being susceptible
to cleavage (via ipso-substitution) by a wide range of electrophiles.
These expectations followed particularly from our previous work
in which a germanium-based linker was shown to exhibit enhanced
stability towards basic/nucleophilic conditions as compared to
silicon-based counterparts26 and model studies in which cleavage
of the same linker by TFA, NCS, Br2, ICl30 and RCOCl/AlCl3
37
For the preparation of the ter-(triarylamine) in solution, a simi-
lar sequence of steps was developed involving coupling of lithiated
tert-butyldimethylsilyl (TBS) ether blocked phenol ‘starter unit’ 3
could be effected with concomitant introduction of H, Cl, Br, I
and COR functions at the position of former attachment to the
Scheme 1 The preparation of a ter-[3-(n-hexyl)thiophene]26 and a ter-(triarylamine)27 in solution by iterative coupling processes. Reagents and conditions:
i) 1a, LDA, THF, −50 ◦C; ii) CsF, DMF, 60 ◦C; iii) n-BuLi, THF, −50 ◦C then ICH2CH2I, dark; iv) 2, Pd(PPh3)4, DMF, 60 ◦C; v) DCl, CDCl3; vi) 3,
n-BuLi, THF, −78 ◦C then toluene, RT; vii) TBAF, THF, RT; viii) Tf2O, pyridine, 0 ◦C; ix) 4 (or 5), Pd(PPh3)4, Na2CO3, DME, 80 ◦C; x) 1% TFA in
CH2Cl2, RT.
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to the same dimethylgermylchloride linker model, chemoselective
removal of the TBS-ether blocking group, activation of the
resulting phenol as a triflate ester, and then Suzuki coupling with a
TBS ether blocked triarylamine boronic ester extender monomer
4. The sequence was then repeated on the resulting monomer,
starting with removal of the TBS ether. The resulting dimer
was then TBS deprotected, activated and capped-off by Suzuki
coupling to triarylamine boronic ester ‘terminating monomer’ 5
to give the trimer which was then cleaved from the linker trace-
lessly using acid. This process relies critically on the orthogonal
susceptibility of the TBS ether and aryldimethylgermyl groups
towards cleavage by fluoride ions: the TBS ether is selectively
removed by tetra-n-butylammonium fluoride (TBAF) in THF
at RT without affecting the linker. For this ‘proof-of-principle’
synthesis, double coupling was not performed; however, the system
was designed to allow for this via reactivation of the crude coupled
product with trifluoromethanesulfonic anhydride and then re-
coupling to drive any phenol-terminated oligomer (from hydro-
lysis of the triflate during coupling) through to the homologated
product. Again, it was envisaged that, in principle, once optimised
for SPS, the iterative steps for monomer introduction and acti-
vation could be repeated to provide an oligomer of any desired
length.
However, despite the complete orthogonality of the linker to
the fluoride blocking group deprotection steps in these studies, the
TMS blocking group employed in the oligo-[3-(n-hexyl)thiophene]
sequence proved to be susceptible to partial cleavage by traces of
adventitious acid once the oligomer reached the tetramer length
(e.g. during NMR spectroscopy in CDCl3). This finding forced
us to develop a new thiophene silyl blocking group/germanium
linker combination which retained the orthogonal stability of the
silyl vs. germyl linkages towards fluoride ions but for which both
partners displayed enhanced stability towards acid.
Consequently, three silyl protected 3-(n-hexyl)thiophenes
(TMS, TES and TBS thiophenes 1a–c) and five germanium-based
linkers containing different spectator groups (dimethyl, diethyl,
di-iso-propyl, diphenyl and di-p-tolylgermylthiophenes 10a–e)
were prepared (Scheme 2). Noteworthy during the execution of
this chemistry was the high degree of selectivity achievable for
protonolysis of the p-anisole group over either phenyl or p-tolyl
groups when employing HCl in Et2O at RT (i.e. step iv).
These silyl and germyl thiophenes were evaluated for their
stability towards both acid (AcOH–CH2Cl2, 1 : 100) and fluoride
(∼0.3 M CsF in DMF). Screening consisted of monitoring by 1H
NMR while the temperature was stepped up from 25 to 60 to
110 ◦C over 72 h (Table 1).
Scheme 2 Preparation of silyl blocked 3-(n-hexyl)thiophenes 1a–d and linker candidates 10a–e. Reagents and conditions: i) n-BuLi, THF, −78 ◦C
then YX2SiCl → RT; ii) RꢀMgBr/Cl, toluene, 110 ◦C; iii) EtOCH2CH2Cl, n-Bu4NI, Cs2CO3, MeCN, 85 ◦C; iv) 1 M HCl, Et2O, RT; v) 5-lithio-
3-(n-hexyl)thiophene [from 3-(n-hexyl)thiophene and LDA], THF, −50 ◦C → RT.
Table 1 Acid and fluoride induced ipso-desilylation/degermylation of silylthiophenes 1a–c and germylthiophenes 10a–e
Cleavage conditionsa
AcOH
CsF
Substrate
25 ◦
C
60 ◦
C
110 ◦
C
25 ◦
C
60 ◦
C
110 ◦
C
1a (X = Y = Me, TMS)
1b (X = Y = Et, TES)
1c (X = Me, Y = t-Bu, TBS)
10a (Rꢀ = Me)
✗
—
✗
—
—
ꢀ
—
—
—
ꢀ
ꢀ
✗
✗
✗
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
—
—
—
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
—
—
—
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
∼
ꢀ
∼
∼
∼
ꢀ
ꢀ
ꢀ
✗
10b (Rꢀ = Et)
✗
✗
10c (Rꢀ = i-Pr)
10d (Rꢀ = Ph)
ꢀ
10e (Rꢀ = p-Tol)
ꢀ
a Key: ꢀ = stable; ∼ = partial cleavage; ✗ = complete cleavage; — = N/A.
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As a result of this stability screening process, the TBS group was
selected as the most suitable silyl blocking group for SPS since TBS
thiophene 1c was the most acid stable. As this group also showed
noticeably greater stability towards fluoride than the TMS group
it was decided to use it in combination with the linker having
p-tolyl spectator groups as the thiophene bound via this linker
(10e) was markedly more stable towards acid than the dialkyl
linkers and because the p-tolyl methyl groups were anticipated to
provide a convenient marker for NMR reaction monitoring (cf.
the diphenyl analogue 10d, which was equally acid stable). Using
this blocking group/germyl spectator group combination the key
iterative steps of the envisioned oligo-[3-(n-hexyl)thiophene] SPS
were re-investigated in solution (Scheme 3).
For this work, the position of the n-hexyl side chain of the
thiophene unit was reversed relative to that of the previous
solution phase work (i.e. Scheme 1, above). This change was made
mainly because 2-TBS-4-(n-hexyl)thiophene 12 could be obtained
on a preparative scale with very high purity more easily than
2-TBS-3-(n-hexyl)thiophene 1c.40 Additionally, we had shown
previously that the position of the n-hexyl chain had little effect
on the susceptibility of the linker towards cleavage,26 and with the
now more robust linker it was anticipated that these differences
would be insignificant. Thus, 2-TBS-4-(n-hexyl)thiophene 12 was
readily immobilised onto di-p-tolyl linker model by lithiation with
LDA then quenching with the germyl chloride derived from p-
anisylgermane 10e (73%) to give TBS protected compound 13.
TBS deprotection was achieved using CsF in DMF at 110 ◦C (cf.
60 ◦C previously) for 24 h to give germylthiophene 14 in 95%
yield and activation was achieved as in solution using LDA/1,2-
diiodoethane to give the iodide 15 (90%). In the previous solution
phase work it had been necessary to employ boronate salt 2
as the monomer such that Suzuki coupling could be achieved
under base-free conditions to avoid desilylation; with the new
blocking group/linker combination this was no longer necessary
and coupling to give bithiophene 17 (60%) could be achieved
without any traces of desilylation using pinacolato boronic ester
16 under fairly standard conditions employing K3PO4 as base. No
attempt was made to optimise this coupling at this stage as it was
decided that this would be best performed ‘on-resin’. Cleavage of
the TBS group from bithiophene was readily achieved once again
using CsF in DMF at 110 ◦C (→18, 99%) and cleavage of the
linker was readily achieved using TFA in CH2Cl2 at RT to give
bithiophene 19 in 97% yield.
Linker cleavage with concomitant introduction of a pinacolato
boronic ester at the previous point of attachment was also briefly
explored using germylthiophene 14 as a substrate. As indicated
above, it was envisaged that this type of functionalisative cleavage
would provide expeditious access to a, x-differentiated telechelic
oligo-(thiophene)s for block co-oligomer preparation. Although
ipso-borodesilylation has been reported previously,41–49 to the best
of our knowledge ipso-borodegermylation has not. We were able to
effect the desired transformation on germylthiophene 14 to give
pinacolato boronic ester 20 in an unoptimised 30% yield using
BCl3 in CH2Cl2–propylene oxide at −78 ◦C followed by addition
of pinacol. The mass balance was protodegermylated material
[i.e. 3-(n-hexyl)thiophene (11)]; no starting material remained
(Scheme 4).
Scheme 4 ipso-Borodegermylation of germylthiophene 14 to give boronic
ester 20 in solution. Reagents and conditions: i) propylene oxide, CH2Cl2,
BCl3, −78 ◦C, then pinacol, RT.
We were now in a position to transfer the chemistry to the
solid phase. Two resins were selected for these studies: Merrifield
R
and Quadragelꢀ. The former, has the advantage of low cost and
good handling properties but displays limited swelling in e.g.
THF. The latter, which is a TEG [tetra(ethyleneglycol)] grafted
p-hydroxy-PS resin, is more expensive and has a tendency to
stick to glassware, but has excellent swelling in e.g. THF. In the
event, initial studies using Merrifield demonstrated that although
the di-p-tolyl linker 8e could be readily introduced onto the
resin using n-Bu4NI, Cs2CO3, MeCN at 85 ◦C (i.e. Williamson
etherification), and could be activated as the germyl chloride
using excess HCl in Et2O–CH2Cl2, the subsequent reaction with
the lithiated TBS protected 4-(n-hexyl)thiophene 12 in THF at
−40 ◦C proceeded with only ∼25% conversion as judged by
Scheme 3 Solution studies on the iterative steps for oligo-[3-(n-hexyl)thiophene] synthesis using the TBS thiophene/di-p-tolylgermyl linker combination.
Reagents and conditions: i) LDA, THF, TBSCl, −50 ◦C → RT; ii) LDA, THF, 2-isopropoxy-4,4,5,5-tetramethyl-[1,3,2]dioxaborolane, −50 ◦C → RT;
iii) 1 M HCl, Et2O, RT; iv) 5-lithio-2-TBS-4-(n-hexyl)thiophene (from 12 and LDA), THF, −50 ◦C → RT; v) CsF, DMF, 110 ◦C; vi) LDA, THF, −40 ◦C
then ICH2CH2I, dark; vii) 16, K3PO4, Pd(PPh3)4, DMF, 60 ◦C; vi) 33% TFA in CH2Cl2, RT.
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R
1H MAS NMR (integrating the TBS methyl groups against the
linker p-tolyl methyl groups). This was not entirely unexpected
due to the aforementioned limited swelling of the resin in THF,
particularly at the low temperature required for this reaction.
Bromination of Quadragelꢀ (29, 0.93 mmol g−1 → 30,
0.88 mmol g−1) proceeded smoothly as did the immobilisation of
the di-(p-tolyl)p-anisyl linker 8e by Williamson etherification. The
resulting resin 31 (0.52 mmol g−1) was activated with HCl in ether
(→32, 0.54 mmol g−1) and the starter monomer, TBS-blocked 4-(n-
hexyl)thiophene 12, was then efficiently introduced as its lithiated
derivative. Removal of the TBS blocking group from the resulting
resin bound thiophene proceeded selectively using CsF in DMF
R
Consequently, our attention turned to Quadragelꢀ. As this resin
is supplied hydroxyl terminated and our preference was to
employ the above Williamson etherification conditions for the
immobilisation step rather than Mitsunobu conditions31 on cost
grounds, the first step was to effect halogenation of the resin.
Initial trials at chlorination using SOCl2 in CCl4 with catalytic
DMF50 led to the appearance of an unexplained peak in the IR
spectrum of the product resin at 1725 cm−1 so we decided to use
triethyleneglycol etherified p-cresol 23 as a model compound on
which to optimise the procedure (Scheme 5).
The model compound 23 was readily prepared by the alkylation
of a two-fold excess of p-cresol (21) with chloride 22 (as the product
23 and the chloride 22 were essentially inseparable by chromatog-
raphy). Chlorination using SOCl2 in CCl4 with catalytic DMF
yielded the desired chloride 24 (89%) and formate ester 25 (9%).
The formate ester had a strong carbonyl stretching absorption
in the IR at 1725 cm−1 thereby explaining the result observed
on resin. As omitting the DMF resulted in an unacceptably
sluggish reaction, bromination using PPh3–CBr4 in CH2Cl2 was
investigated. This procedure resulted in very clean conversion
to the corresponding bromide 26 in 97% yield. The isolated
chloride 24 and bromide 26 were then subjected in parallel to
etherification with trimethylgermyl linker 27.50 As both reactions
gave comparable yields of the immobilised linker 28 (87% and 84%,
respectively) it was decided to employ the bromination procedure
for the SPS work. The SPS of bi-[3-(n-hexyl)thiophene] 19 using
iterative chain extension with double coupling is outlined below
(Scheme 6).
◦
at 110 C (33, 0.40 mmol g−1 → 34, 0.42 mmol g−1) without
detectable cleavage of the arylgermane. Sequential iodination
(→35, 0.40 mmol g−1) and Suzuki cross-coupling with TBS-
blocked thiophene boronic ester extender monomer 16 also
proceeded smoothly to give the resin bound bithiophene 36 with
high efficiency. It was found that no optimisation of this step
was required relative to the solution phase conditions (Scheme 3).
Indeed the cross-coupling was so efficient that the double-
coupling sequence was almost unnecessary for enhancing the
efficiency of coupling: after double coupling a final loading level
of 0.35 mmol g−1 was achieved and HPLC analysis of TFA cleaved
crude samples of bithiophene 19 before and after double coupling
had purities of 94% and 96%, respectively. Bithiophene 19 was
fully characterised by H NMR, 13C NMR, IR, and HRMS. All
1
the steps in the sequence were monitored by 1H MAS NMR and
appeared to proceed to ∼100% conversion (see Fig. 1, Electronic
Supplementary Information†). Loading levels were determined
by elemental analysis and/or NMR integration and/or recovery
of reagents (see experimental). The overall ‘yield’ for the double-
R
coupled material from Quadragelꢀ bromide (30) over the nine
steps was ∼28%.
For the oligo-(triarylamine) SPS, the same di-p-tolylgermyl
R
R
linker was employed but using HypoGelꢀ in place of Quadragelꢀ
R
as the solid support. HypoGelꢀ generally has similar properties
Scheme 5 Optimisation of the resin halodehydration/linker attachment steps using soluble model system 23. Reagents and conditions: i) n-Bu4NI,
Cs2CO3, MeCN, 85 ◦C; ii) SOCl2, DMF, CH2Cl2, RT; iii) PPh3, CBr4, CH2Cl2, RT.
Scheme 6 The preparation of bi-[3-(n-hexyl)thiophene] 19 by SPS on QuadragelꢀR . Reagents and conditions: i) PPh3, CBr4, CH2Cl2, RT; ii) 8e. n-Bu4NI,
Cs2CO3, MeCN, 85 ◦C; iii) 1 M HCl, Et2O, RT; iv) 5-lithio-2-TBS-4-(n-hexyl)thiophene (from 12 and LDA), THF, −40 ◦C → RT; v) CsF, DMF, 110 ◦C;
vi) LDA, THF, −40 ◦C then ICH2CH2I, dark; vii) 16, K3PO4, Pd(PPh3)4, DMF, 60 ◦C; viii) 33% TFA in CH2Cl2, RT.
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R
to Quadragelꢀ but differs in that it a polydisperse PEG grafted p-
triarylamine boronic ester terminating monomer 5 was cross-
coupled to triflate resin 48 to yield resin 49 (0.30 mmol g−1). Release
of oligomer from the resin 49 was achieved by electrophilic ipso-
protodegermylation using a 1% solution of trifluoroacetic acid
(TFA) in CH2Cl2. Purification by FC yielded the target H-capped
hydroxyethyl-PS resin having on average five oxyethyl repeat units
(cf. monodisperse TEG grafted p-hydroxy-PS). HypoGelꢀ was
preferred for this work because in our hands it provided superior
gel-phase 13C NMR spectra relative to Quadragelꢀ, allowing the
R
R
1
synthesis to be monitored without the need for regular access to
an NMR spectrometer with an MAS probe. For the envisaged
SPS it was not considered necessary to change the TBS ether
phenol blocking group employed in the solution phase studies as
this had proved amply robust and was anticipated to retain its
ability to be orthogonally removed by TBAF when paired with
the new linker. However, for the SPS it was decided to initiate the
synthesis by introduction of bromotriarylamine starter monomer
42 rather than the 4-bromophenol derivative 3 used in the solution
studies. This modification allows the oligomer synthesis to proceed
by immediate monomer introduction and requires no additional
‘off-resin’ monomer synthesis as the starter monomer 42 is an
intermediate in the synthesis of extender monomer 4.27 The SPS
of ter-(triarylamine) 50 using iterative chain extension is outlined
below (Scheme 7).
ter-(triarylamine) 50 which was characterised by H NMR, 13C
NMR and HRMS. Its purity was >97% by HPLC. All the steps
were conveniently monitored by 13C gel-phase NMR (see Figs
2 and 3, Electronic Supplementary Information†) and loading
levels were determined by elemental analysis (see experimental).
R
The overall ‘yield’ from HypoGelꢀ bromide (40) over the 10 steps
was ∼28%.
Conclusions
In summary, we have described the development of a germanium-
based linker system for the SPS of 3-(n-hexyl)thiophene oligomers
and for the first SPS of triarylamine oligomers via iterative
chain extension protocols. The germanium-based linker provides
a robust platform for the chain extension steps, allows orthogonal
removal of temporary TBS thiophene and TBS phenolic ether
blocking groups following each iteration using fluoride, and allows
for traceless or functionalisative cleavage from the resin. The
efficiency of the key steps in the oligomer syntheses and their
compatibility with the germanium linker have been demonstrated.
The key iterative steps in both processes are: i) cross coupling of a
terminally blocked extender monomer to a linker bound activated
oligomer terminus, ii) selective deprotection of the now terminal
blocking group, iii) activation of the resulting functionality to one
suitable for cross coupling and then repetition of the cycle for
the desired number of iterations. The use of a blocking group in
this fashion allows double coupling to drive each cross coupling
step to completion and hence minimise deletion sequences; this
tactic has been validated for the oligo-(thiophene) series. The first
ipso-borodegermylation reaction has also been performed in a
model study for the potential cleavage of a germanium bound
oligo-[3-(n-hexyl)thiophene] from the resin with concomitant
functionalisation of the oligomer as a terminal boronic ester; a
process of potential utility for block co-oligomer synthesis. We
are currently adapting these synthetic strategies to accommodate
other monomers and expanding the scope of the functionalisative
R
Bromination of HypoGelꢀ (38, 0.80 mmol g−1 → 39,
0.80 mmol g−1) and subsequent immobilisation of the di-(p-tolyl)p-
anisyl linker 8e by Williamson etherification (→40, 0.48 mmol g−1)
R
proceeded smoothly as on the Quadragelꢀ. Activation with HCl in
ether was also uneventful, providing the germyl chloride resin 41
cleanly (0.49 mmol g−1). Immobilisation of the starter monomer
using lithiated triarylamine bromide 42 afforded triarylamine TBS
ether resin 43 (0.37 mmol g−1). Selective cleavage of the TBS
ether group was achieved using TBAF to give phenol resin 44
(0.38 mmol g−1) with no detectable cleavage of the arylgermane
linkage. Conversion of the phenol function to the triflate derivative
using trifluoromethanesulfonic anhydride was carried out in
anhydrous pyridine to give resin 45 (0.37 mmol g−1) and set the
stage for the Suzuki cross-coupling step. Triarylamine boronic
ester extender monomer 4 was cross-coupled to aryl triflate resin
45 to give the triarylamine dimer resin 46 (0.34 mmol g−1) using
the same conditions developed for the preliminary solution studies
(Scheme 1).27 An excess of extender monomer 4 was used to drive
the reaction to completion. Deprotection of the TBS ether and
subsequent conversion to triflate was repeated to give resins 47
(0.33 mmol g−1) and 48 (0.30 mmol g−1), respectively. Finally,
Scheme 7 The preparation of ter-(triarylamine) 50 by SPS on HypoGelꢀR . Reagents and conditions: i) PPh3, CBr4, CH2Cl2, RT; ii) n-Bu4NI, Cs2CO3,
MeCN, 85 ◦C; iii) 1 M HCl in Et2O, RT; iv) n-BuLi, THF, −78 ◦C; v) TBAF, THF, RT; vi) Tf2O, pyridine, 0 ◦C; vii) Pd(PPh3)4, Na2CO3, DME, 80 ◦C;
vii) 1% TFA in CH2Cl2, RT.
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cleavage protocols to provide new oligomers of potential utility as
novel electroactive materials.
The residue was purified by FC (pentane) to give silylthiophene
1a as a colourless oil (329 mg, 87%). Rf 0.85 (pentane); 1H NMR
(250 MHz, CDCl3): d 0.03 (s, 9H), 0.58 (t, J = 6.5, 3H), 0.95–1.10
(6H), 1.27 (m, 2H), 2.36 (t, J = 8, 2H), 6.73 (d, J = 4.5, 1H), 7.14
(d, J = 4.5, 1H); MS (CI+) m/z 240 (M+); HRMS (CI+) calcd.
for C13H24SSi (M+) 240.1368, found 240.1361.
Experimental
General directions
All reactions were performed under anhydrous conditions and an
inert atmosphere of N2 in the oven or flame dried glassware. Yields
refer to chromatographically and spectroscopically (1H NMR)
homogenous materials, unless otherwise indicated. Reagents were
used as obtained from commercial sources or purified according
General procedure B
reaction of germyldichloride 7 with a Grignard reagent.
4-{2-[(4-Methoxyphenyl)dimethylgermanyl]ethyl}phenol 8a. A
solution of MeMgBr (40.0 mL, 3.0 M, 1.20 mmol) in
Et2O was added to a solution of 4-{[2-dichloro-(4-methoxy-
phenyl)germanyl]ethyl}phenol (7)38 (9.00 g, 24.2 mmol) in toluene
(50 mL). The mixture was then refluxed at 110 ◦C for 16 h before
partitioning between sat. NH4Cl (aq) (250 mL) and Et2O (200 mL).
After extracting further with Et2O (2 × 200 mL) the combined
organic extracts were dried (MgSO4) and concentrated in vacuo.
The residue was purified by FC (petrol–EtOAc, 3 : 1) to give
dimethylgermane 8a as a pale yellow oil (7.55 g, 84%). Rf 0.40
R
to known procedures.51 Quadragelꢀ resin was purchased from
Avecia Ltd. [nominal loading level (LL) 930 lmol g−1] and
is a DVB crosslinked p-hydroxy-PS-based resin etherified with
a monodisperse TEG [tetra(ethyleneglycol)] graft terminating
R
with a OH group. HypoGelꢀ resin was purchased from Fluka
Ltd. (nominal LL 800 lmol g−1) and is a DVB crosslinked p-
hydroxyethyl-PS-based resin etherified with a polydisperse PEG
graft containing on average five oxyethyl repeat units terminating
with a hydroxyl group. Flash chromatography (FC) was carried
out using Merck Kiesegel 60 F254 (230–400 mesh) silica gel. Only
distilled solvents were used as eluents. Thin layer chromatography
(TLC) was performed on Merck DC-Alufolien or glass plates
pre-coated with silica gel 60 F254 which were visualised either
by quenching of ultraviolet fluorescence (kmax = 254 nm) or by
charring with 5% w/v phosphomolybdic acid in 95% EtOH,
10% w/v ammonium molybdate in 1 M H2SO4, or 10% KMnO4
in 1 M H2SO4. Observed retention factors (Rf ) are quoted to
the nearest 0.05. All reaction solvents were distilled before use
1
(petrol–EtOAc, 3 : 1); H NMR (250 MHz, CDCl3): d 0.25 (s,
6H); 1.14 (m, 2H), 2.54 (m, 2H), 3.73 (s, 3H), 4.67 (broad s, 1H),
6.64 (d, J = 8.5, 2H), 6.84 (d, J = 9, 2H), 6.95 (d, J = 8.5, 2H),
7.29 (d, J = 9, 2H); 13C NMR (62.8 MHz, CDCl3) d −3.6 (q,
2C), 18.2 (t), 30.2 (t), 55.1 (q), 113.8 (d, 2C), 115.1 (d, 2C), 128.9
(d, 2C), 132.2 (s), 134.5 (d, 2C), 137.0 (s), 153.5 (s), 159.9 (s); IR
(neat) 3401 (broad, O–H), 3020–2835 (C–H), 1612, 1592, 1569,
1513, 1500, 1462, 1443, 1358, 1279, 1246 cm−1; MS (EI+) m/z
332 (M+); HRMS calcd. for C17H22Ge74O2 (M+) 332.0832, found
332.0824; Anal. calcd. for C17H22GeO2: C 61.7, H 6.7, found C
62.0, H 6.6%.
˚
and stored over activated 4 A molecular sieves, unless otherwise
indicated. Anhydrous CH2Cl2 was obtained by refluxing over
CaH2. Anhydrous THF and Et2O were obtained by distillation,
immediately before use, from sodium/benzophenone ketyl under
an inert atmosphere of N2. Anhydrous DMF was obtained by
distillation from CaH2 under reduced pressure. Ethylene glycol
was distilled immediately prior to use. Petrol refers to the fraction
of light petroleum boiling between 40–60 ◦C. NMR J values
are given in Hz. High Resolution Mass Spectrometry (HRMS)
measurements are valid to 5 ppm. Microanalyses were performed
using a LECO CHNS 932 Analyser (N), an Atomscan 16 ICP-OES
(Ge), an Orion Ion Analyser (F), and a Metrohm 716 DMS (Cl,
Br). Results are quoted to the nearest 0.1%, and are valid to
0.5% (N, Cl, Br, F) and 1.5% (Ge) of theory.
General procedure C
Williamson etherification with 2-chloroethyl ethyl ether.
{2-[4-(2-Ethoxyethoxy)phenyl]ethyl}-(4-methoxyphenyl)dimethyl-
germane 9a. To a solution of phenol 8a (96.1 mg, 290 lmol) in
acetonitrile (65 mL) was added 2-chlorodiethyl ether (70.0 lL,
638 lmol), TBAI (10.7 mg, 29.0 lmol) and caesium carbonate
◦
(153 mg, 434 lmol). The mixture was refluxed at 85 C for 17 h
then cooled and filtered. The solvent was removed in vacuo and
the residue purified by FC (petrol–EtOAc, 20 : 1) to give ether
9a as a pale yellow oil (105 mg, 90%). Rf 0.30 (petrol–EtOAc, 9 :
1
1); H NMR (250 MHz, CDCl3): d 0.25 (s, 6H), 1.16 (m, 5H),
2.54 (m, 2H), 3.52 (q, J = 7, 2H), 3.70 (t, J = 4.5, 2H), 3.73 (s,
3H), 4.01 (t, J = 4.5, 2H), 6.64 (d, J = 8.5, 2H), 6.84 (d, J =
8.5, 2H), 6.95 (d, J = 9, 2H), 7.29 (d, J = 9, 2H); 13C NMR
(62.8 MHz, CDCl3) d −3.5 (q, 2C), 15.2 (q), 18.2 (t), 30.2 (t),
55.1 (q), 66.9 (t), 67.5 (t), 69.1 (t), 113.8 (d, 2C), 114.6 (d, 2C),
128.7 (d, 2C), 132.0 (s), 134.5 (d, 2C), 137.1 (s), 156.9 (s), 159.9
(s); IR (neat) 2930–2870 (C–H), 1611, 1593, 1568, 1511, 1500,
1458, 1280, 1247 cm−1; MS (EI+) m/z 404 (M+); HRMS calcd.
for C21H30Ge74O3 (M+) 404.1407, found 404.1393.
General procedure A
Lithiation of bromide 6 and subsequent reaction with a chlorosi-
lane.
[3-(n-Hexyl)thiophen-2-yl]trimethylsilane 1a52. A solution of
n-BuLi (787 lL, 2.2 M, 1.57 mmol) in hexanes was added dropwise
to a degassed solution of bromide 6 (387 mg, 1.57 mmol) in
THF (3 mL) at −78 ◦C. The reaction mixture was stirred for
40 min at this temperature, and then trimethylchlorosilane (600 lL,
4.73 mmol) added dropwise at −78 ◦C. The resulting mixture was
stirred for 1 h at this temperature, warmed to RT and stirred for
a further 1 h. After quenching with sat. NH4Cl (aq) (100 mL),
the mixture was extracted with Et2O (3 × 100 mL), the combined
organic extracts dried (MgSO4) and the solvent removed in vacuo.
{2-[4-(2-Ethoxyethoxy)phenyl]ethyl}-(4-hexylthiophen-2-yl)di-
methylgermane 10a. To germyl-p-anisole 9a (1.16 g, 2.01 mmol)
was added HCl in Et2O (40.2 mL, 1.0 M, 40.2 mmol) and the
reaction mixture left to stir for 16 h. The solvent was then removed
in vacuo to give the crude germyl chloride as a brown oil [1H NMR
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(250 MHz, CDCl3): d 0.59 (s, 6H), 1.20–1.27 (m, 3H), 1.45–
1.55 (m, 2H), 2.80 (t, J = 8, 2H), 3.59 (q, J = 7, 2H), 3.77
(t, J = 5, 2H), 4.10 (t, J = 5, 2H), 6.85 (d, J = 8.5, 2H),
7.10 (d, J = 8.5, 2H); MS (EI+) m/z 332 (M+); HRMS (EI+)
calcd. for C14H23ClGe74O2 (M+) 332.0598, found 332.0586]. In a
separate flask, a solution of LDA (3.99 mL, 2.0 M, 7.98 mmol)
in hexanes–THF–ethylbenzene (6 : 5 : 3) was added dropwise to
a degassed solution of 3-(n-hexyl)thiophene (1.34 g, 7.98 mmol)
in THF (5 mL) at −50 ◦C. This solution was stirred for 40 min at
CDCl3) d 29.8, 30.5, 40.6, 44.5, 46.3, 55.4, 61.9, 67.4, 70.1, 70.8,
71.3, 72.7, 77.2, 77.5, 78.2, 79.3, 114.3, 125.7, 128.4, 133.5, 137.7,
145.4, 156.8; IR (neat) 3030–2865 (C–H), 1601, 1509, 1492, 1452,
1350, 1244, 1101, 697 (strong) cm−1.
R
Quadragelꢀ-di-para-tolylgermyl-para-anisole 31. To bromi-
nated resin 30 (20.0 g, LL = 880 lmolg−1, 17.6 mmol) swollen
in a minimum of acetonitrile (200 mL) was added germylphenol
8e (19.4 g, 81.2 mmol), tetra-n-butylammonium iodide (740 mg,
2.00 mmol) and caesium carbonate (26.2 g, 74.3 mmol) and the
◦
−40 C, and then transferred by cannula to a degassed solution
◦
resulting mixture heated at 85 C for 20 h. The reaction mixture
of the crude germyl chloride in THF (5 mL) at −50 ◦C. The
resulting mixture was stirred for 1 h at −40 ◦C, warmed to RT
and stirred for a further 1 h. After quenching with sat. NH4Cl (aq)
(100 mL), the mixture was extracted with Et2O (3 × 100 mL), the
combined organic extracts dried (MgSO4) and the solvent removed
in vacuo. The residue was purified by FC (petrol–EtOAc, 9 : 1) to
give dimethylgermylthiophene 10a as a brown/yellow oil (741 mg,
60%). Rf 0.40 (petrol–EtOAc, 9 : 1); 1H NMR (250 MHz, CDCl3):
d 0.38 (s, 6H), 0.88 (t, J = 7, 3H), 1.23 (t, J = 7, 3H), 1.25–1.30
(8H), 1.58 (m, 2H), 2.62 (t, J = 8, 2H), 2.67 (t, J = 8.5, 2H), 3.59
(q, J = 7, 2H), 3.77 (t, J = 5.5, 2H), 4.09 (t, J = 5.5, 2H), 6.83
was cooled and the resin was washed successively with MeCN (3 ×
350 mL), DMF (3 × 350 mL), THF–water (1 : 1, 3 × 350 mL),
THF (3 × 350 mL), MeOH (3 × 350 mL) and then dried in vacuo to
give resin 31 as light brown granules (13.4 g, 74% conversion by the
weight increase of the resin and the amount of phenol returned,
1
LL = 0.52 mmol g−1). H MAS NMR (400 MHz, CDCl3): d
1.15–1.65 [CH(Ar)CH2], 1.65–2.10 [ArCH2, CH(Ar)CH2], 2.37
(s, ArCH3), 2.70–2.80 (GeCH2), 3.50–4.15 (OCH3, OCH2), 6.10–
6.70 (ArH), 6.70–7.30 (m, ArH), 7.41 (d, J = 4.5, ArH); 13C gel
phase NMR (75 MHz, d8-THF) d 17.6, 21.8, 31.7, 37.4, 41.6, 71.7,
72.2, 128.9; IR (neat) 3030–2865 (C–H), 1593, 1510, 1494, 1453,
1281, 1245, 698 (strong) cm−1.
(d, J = 8, 2H), 6.96 (s, 1H), 7.06 (s, 1H), 7.11 (d, J = 8, 2H); 13
C
NMR (62.8 MHz, CDCl3) d −2.3 (q, 2C), 14.1 (q), 15.2 (q), 19.1
(t), 22.6 (t), 29.2 (t), 30.1 (t, 2C), 30.7 (t), 31.7 (t), 66.8 (t), 67.5 (t),
69.1 (t), 114.6 (d, 2C), 124.5 (d), 128.7 (d, 2C), 134.5 (d), 136.8 (s),
139.6 (s), 144.5 (s), 157.00 (s); IR (neat) 2930–2855 (C–H), 1611,
1511, 1246 cm−1; MS (EI+) m/z 464 (M+); HRMS (EI+) calcd.
for C24H38Ge74O2S (M+) 464.1804, found 464.1798.
R
Quadragelꢀ-di-para-tolylgermyl chloride 32. To germyl-p-
anisole resin 31 (13.1 g, LL = 0.52 mmol g−1, 6.8 mmol) swelled in
CH2Cl2 (50 mL) was added HCl (65 mL, 1.0 M, 65 mmol) in Et2O
and the reaction mixture left to stir for 16 h. The solvent was then
removed by filtration to give resin 32 as brown granules (11.7 g,
1
1
100% conversion by H NMR, LL = 0.54 mmol g−1). H MAS
NMR (400 MHz, CDCl3): d 1.00–2.30 [ArCH2, CH(Ar)CH2],
2.47 (s, ArCH3), 2.85–2.95 (GeCH2), 3.60–4.20 (OCH2), 6.10–
6.70 (ArH), 6.70–7.30 (ArH), 7.56 (d, J = 4.5, ArH); IR (neat)
3030–2865 (C–H), 1601, 1509, 1493, 1452, 1243, 697 (strong) cm−1.
Typical procedure A
Assessment of AcOH stability of a germyl/silyl thiophene.
(Table 1, entry 3). To silylthiophene 1c (10.5 mg, 37 lmol) was
added CH2Cl2 (500 lL) and then AcOH (5 lL). The mixture was
stirred at 25 ◦C for 24 h, then at 60 ◦C for 24 h and then at 110 ◦C
R
Quadragelꢀ-di-para-tolylgermyl monothiophene (a-TBS) 33.
A solution of LDA (1.11 mL, 2.0 M, 2.21 mmol) in hexanes–
THF–ethylbenzene (6 : 5 : 3) was added dropwise to a degassed
solution of silylthiophene 12 (616 mg, 2.18 mmol) in THF (4 mL)
at −50 ◦C. This solution was warmed to −40 ◦C, stirred for 40 min
at this temperature and recooled to −50 ◦C. The solution was then
transferred by cannula to a degassed suspension of germylchloride
resin 32 (777 mg, LL = 0.54 mmol g−1, 0.42 mmol) in THF (10 mL)
at −50 ◦C. The reaction mixture was stirred for 1 h at −40 ◦C,
warmed to RT and stirred for a further 1 h. After quenching with
sat. NH4Cl (aq) (50 mL), the solvent was removed by filtration
and the resin washed with DMF (50 mL × 3), THF : water
1 : 1 (50 mL × 3), THF (50 mL × 3) and MeOH (50 mL ×
3). The resin was then dried in vacuo at 60 ◦C to give resin 33
as yellow/orange granules (876 mg, 83% conversion by weight
increase of resin, LL = 0.40 mmol g−1). 1H MAS NMR (400 MHz,
CDCl3): d 0.41 [s, Si(CH3)2], 0.91 (t, J = 4.5, CH2CH3), 0.95–
2.30 [C(CH3)3, (CH2)4CH3, ArCH2CH2Ge, CH(Ar)CH2], 2.47 (s,
ArCH3), 2.54 [t, J = 5, CH2(CH2)4CH3], 2.80–2.95 (GeCH2),
3.60–4.25 (OCH2), 6.10–6.80 (ArH), 6.80–7.30 (ArH), 7.53 (d,
J = 4.5, ArH); IR (neat) 3030–2865 (C–H), 1601, 1509, 1492,
1451, 1244, 697 (strong) cm−1.
1
for a further 24 h, analysing by H NMR (CDCl3) for extent of
conversion to 3-(n-hexyl)thiophene 11.53
Typical procedure B
Assessment of CsF stability of a germyl/silyl thiophene.
(Table 1, entry 3). To silylthiophene 1c (7.6 mg, 27 lmol) was
added DMF (500 lL) and CsF (20 mg, 0.13 mmol). The mixture
was sti◦rred at 25 ◦C for 24 h, then at 60 ◦C for 24 h and then
1
at 110 C for a further 24 h, analysing by H NMR (CDCl3) for
extent of conversion to 3-(n-hexyl)thiophene 11.53
R
R
Quadragelꢀ-Br 30. To a suspension of Quadragelꢀ (29, 38.7 g,
LL = 930 lmol g−1, 36.0 mmol) in CH2Cl2 (220 mL) at 0 ◦C
was added triphenylphosphine (10.3 g, 39.3 mmol) and carbon
tetrabromide (26.0 g, 78.4 mmol). The orange reaction mixture was
warmed to RT and left to stir for 24 h. The solvent was removed
by filtration and the resin washed sequentially with CH2Cl2 (3 ×
300 mL), DMF (300 mL), THF–H2O (1 : 1, 2 × 300 mL), THF
(2 × 300 mL, and MeOH (2 × 300 mL). The resin was then dried
in vacuo to give resin 30 as yellow grains (37.5 g, LL = 880 lmolg−1.
1H MAS NMR (400 MHz, CDCl3): d 1.00–1.75 [CH(Ar)CH2],
1.75–2.20 [CH(Ar)CH2], 3.50–3.60 (OCH2), 3.75–4.20 (OCH2),
6.30–6.85 (ArH), 6.85–7.30 (ArH); 13C gel phase NMR (125 MHz,
R
Quadragelꢀ-di-para-tolylgermyl monothiophene (a-H) 34. To
germylthiophene resin 33 (642 mg, LL = 400 lmolg−1, 257 lmol)
swollen in DMF (8 mL) was added caesium fluoride (341 mg,
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2.24 mmol) and the mixture left to stir for 72 h at 110 ◦C. The
solvent was then removed by filtration and the resin washed with
DMF (2 × 75 mL), THF–H2O (1 : 1, 3 × 75 mL), THF (3 × 75 mL)
and MeOH (3 × 75 mL). The resin was then dried in vacuo at 60 ◦C
to give germylthiophene resin 34 as brown granules (560 mg, 100%
conversion by integrals in 1H NMR, LL = 420 lmolg−1). 1H MAS
NMR (400 MHz, CDCl3): d 0.82 (t, J = 7.0, CH2CH3), 0.85–
2.20 [(CH2)4CH3, ArCH2CH2Ge, CH(Ar)CH2], 2.37 (s, ArCH3),
2.48 [m, CH2(CH2)4CH3], 2.77 (m, GeCH2), 3.60–4.15 (OCH2),
6.10–7.30 (ArH), 7.44 (d, J = 4.5, ArH), 7.53 (m, SCH); IR (neat)
3030–2865 (C–H), 1601, 1508, 1492, 1451, 1242, 697 (strong) cm−1.
diiodoethane (124 mg, 440 lmol) in THF (1 mL) was added by
cannula at −50 C. The reaction mixture was stirred in the dark
◦
for 1 h at −40 ◦C, warmed to RT and stirred for a further 1 h.
The solvent was then removed by filtration and the resin washed
with Na2S2O3 (aq) (3 × 50 mL), THF–H2O (1 : 1, 3 × 50 mL),
THF (3 × 50 mL) and MeOH (3 × 50 mL). The resin was then
dried in vacuo at 60 ◦C to give brown grains (221 mg) which
were then swollen in DMF (1.5 mL). To this swollen resin was
added boronic ester 16 (96.0 mg, 235 lmol) and K3PO4 (37.2 mg,
273 lmol), the reaction mixture degassed and [Pd(PPh3)4] (4.5 mg,
3.89 lmol) added. The resulting mixture was stirred at 60 ◦C for
48 h. The solvent was then removed by filtration and the resin
washed with DMF (2 × 50 mL), THF–H2O (1 : 1, 3 × 50 mL),
THF (3 × 50 mL) and MeOH (3 × 50 mL). The resin was then
dried in vacuo at 60 ◦C to give bithiophene resin 36 as dark brown
grains [196 mg, LL = 350 lmol g−1 by mass of bithiophene 19
cleaved from the resin (see ‘3,4ꢀ-di-(n-hexyl)-[2,2ꢀ]bithiophenyl 19
Method 2’, below)]. Spectroscopic data as above.
R
Quadragelꢀ-di-para-tolylgermyl monothiophene (a-I) 35.
A
solution of LDA (315 lL, 2.0 M, 630 lmol) in hexanes–THF–
ethylbenzene (6 : 5 : 3) was added dropwise to a suspension of
germylthiophene resin 34 (526 mg, LL = 420 lmolg−1; 221 lmol)
in THF (4 mL) at −50 ◦C. After stirring for 2 h at −30 ◦C, a
solution of degassed 1,2-diiodoethane (296 mg, 1.05 mmol) in
THF (2 mL) was added by cannula at −50 ◦C. The resulting
mixture was stirred in the dark for 2 h at −30 ◦C, warmed to RT
and stirred for a further 1 h. The solvent was then removed by
filtration and the resin washed with Na2S2O3 (aq) (3 × 75 mL),
THF–H2O (1 : 1, 3 × 75 mL), THF (3 × 75 mL) and MeOH (3 ×
75 mL). The resin was then dried in vacuo at 60 ◦C to give iodide
resin 35 as orange grains (533 mg, 100% conversion by integrals
R
Quadragelꢀ-di-para-tolylgermyl bithiophene (a-H) 37. To
germylthiophene resin 36 (165 mg, LL = 350 lmol g−1, 578 lmol)
swollen in DMF (2 mL) was added caesium fluoride (50.0 mg,
329 lmol) and the mixture left to stir for 72 h at 110 ◦C. The
solvent was then removed by filtration and the resin washed with
DMF (2 × 75 mL), THF–H2O (1 : 1, 3 × 75 mL), THF (3 × 75 mL)
and MeOH (3 × 75 mL). The resin was then dried in vacuo at 60 ◦C
to give germylthiophene resin 37 as a dark brown beads (157 mg,
∼100% conversion by integrals in 1H NMR, LL = 360 lmol g−1).
1H MAS NMR (400 MHz, CDCl3): d 0.75–2.50 [(CH2)5CH3,
ArCH2CH2Ge, CH(Ar)CH2, ArCH3], 2.80 (m, GeCH2), 3.50–
4.15 (OCH2), 6.10–7.40 (ArH), 7.47 (d, J = 6.5, ArH); IR (neat)
3030–2865 (C–H), 1601, 1508, 1492, 1451, 1243, 697 (strong) cm−1.
1
1
of H NMR, LL = 400 lmolg−1). H MAS NMR (400 MHz,
CDCl3): d 0.82 (t, J = 4.5, CH2CH3), 0.85–2.20 [(CH2)5CH3,
ArCH2CH2Ge, CH(Ar)CH2, ArCH3], 2.77 (m, GeCH2), 3.60–
4.15 (OCH2), 6.10–7.30 (ArH), 7.42 (d, J = 7.0, ArH); IR (neat)
3030–2865 (C–H), 1601, 1509, 1493, 1452, 1243, 697 (strong) cm−1.
R
Quadragelꢀ-di-para-tolylgermyl bithiophene (a-TBS) 36. To
a degassed solution of boronic ester 16 (242 mg, 592 lmol),
K3PO4 (134 mg, 985 lmol) and iodide resin 35 (493 mg, LL =
400 lmol g−1, 197 lmol) swollen in DMF (4 mL) was added
[Pd(PPh3)4] (11.6 mg, 10.0 lmol) and the resulting mixture stirred
at 60 ◦C for 48 h. The solvent was then removed by filtration and
the resin washed with DMF (2 × 50 mL), THF–H2O (1 : 1, 3 ×
50 mL), THF (3 × 50 mL) and MeOH (3 × 50 mL). The resin was
then dried in vacuo at 60 ◦C to give bithiophene resin 36 as dark
brown grains [508 mg, 87% conversion by mass of bithiophene
19 cleaved from the resin (see ‘3,4ꢀ-di-(n-hexyl)-[2,2ꢀ]bithiophenyl
19 Method 2’, below), LL = 350 lmol g−1]. 1H MAS NMR
(CDCl3): d 0.31 [s, Si(CH3)2], 0.75–2.50 [C(CH3)3, (CH2)5CH3,
ArCH2CH2Ge, CH(Ar)CH2, ArCH3], 2.80 (m, GeCH2), 3.50–
4.20 (OCH2), 6.10–7.35 (ArH), 7.47 (d, J = 7, ArH); 13C MAS
NMR (100 MHz, CDCl3) d −4.5, 14.5, 17.3, 18.6, 21.9, 22.9,
23.0, 26.8, 29.6, 29.7, 30.0, 30.8, 31.1, 31.7, 32.0, 32.2, 40.9, 43.6,
67.9, 70.2, 71.1, 71.2, 115.0, 126.1, 128.4, 128.8, 129.1, 129.5,
133.6, 135.1, 137.4, 138.7, 139.3, 140.6, 141.5, 145.7, 151.4, 157.3;
IR (neat) 3030–2865 (C–H), 1601, 1509, 1492, 1452, 1244, 697
(strong) cm−1.
General procedure D
TFA mediated cleavage of 3,4ꢀ-di-(n-hexyl)-[2,2ꢀ]bithiophene 1954
from resin 36 (Method 1).
3,4ꢀ-Di-(n-hexyl)-[2,2ꢀ]bithiophene 1954 from mono-coupled resin
36. To bithiophene resin 36 (35.7 mg, 14.3 lmol) was added a
33% v/v solution of TFA in CH2Cl2 (750 lL) and the mixture left
to stir at RT for 2 h. The solvent was then removed by filtration and
the resin washed with CH2Cl2 (3 × 50 mL). These washings were
then passed through a plug of silica and concentrated in vacuo to
give bithiophene 19 as a yellow oil [3.1 mg, >94.0% pure by HPLC:
Jupiter ODS-C18 column (250 × 0.46 cm), UV 254 nm detection,
1 mL min−1, 5 → 100% MeCN in H2O + 0.1% formic acid, Rt =
17.1 min.]. Rf 0.60 (pentane); 1H NMR (250 MHz, CDCl3): d 0.34
(s, 9H), 0.84–0.92 (6H), 1.20–1.35 (12H), 1.52–1.70 (4H), 2.63 (t,
J = 8.5, 2H), 2.74 (t, J = 8, 2H), 6.90 (d, J = 5.5, 1H), 7.03 (s,
1H), 7.12 (d, J = 5.5, 1H); 13C NMR (62.8 MHz, CDCl3) d 14.1
(q, 2C), 22.6 (t), 29.0 (t), 29.1 (t), 29.2 (t), 29.7 (t), 30.4 (t), 30.5
(t), 30.7 (t), 31.6 (t), 31.7 (t), 119.9 (s), 123.4 (s), 127.3 (s), 129.9
(s), 130.9 (d), 135.8 (d), 139.3 (d), 143.5 (d); IR (neat) 2950–2850
(C–H), 1457, 1377 cm−1; MS (EI+) m/z 334 (M+); HRMS calcd.
for C20H30S2 (M+) 334.1789, found 334.1784.
R
Double-couple procedure on Quadragelꢀ-di-para-tolylgermyl
bithiophene (a-TBS) 36. A solution of LDA (130 lL, 2.0 M,
260 lmol) in hexanes–THF–ethylbenzene (6 : 5 : 3) was added
dropwise to a suspension of germylthiophene resin 36 ◦(219 mg,
LL = 350 lmol g−1, 76.7 lmol) in THF (2 mL) at −50 C. After
stirring for 40 min at −40 ◦C, a solution of degassed 1,2-
3,4ꢀ-Di-(n-hexyl)-[2,2ꢀ]bithiophene 1954 from double-coupled resin
36. According to the general procedure D, bithiophene resin 36
(40.4 mg, 16.2 lmol) in TFA in CH2Cl2 (750 lL) gave bithiophene
1760 | Org. Biomol. Chem., 2007, 5, 1752–1763
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◦
19 as a yellow oil [6.1 mg, >96.0% pure by HPLC (same conditions
and Rt as above)]. Spectroscopic data as above.
4227 (2.53 g, 5.4 mmol) in THF (20 mL) at −78 C. After being
stirred for 45 min, the mixture was transferred by cannula to a
suspension of resin 41 (3.00 g, LL = 0.49 mmol g−1, 1.5 mmol) in
toluene (30 mL) at −78 ◦C. The resulting mixture was stirred for
18 h at RT. An aqueous solution of 1 M HCl was then added and
the mixture stirred another 30 min. After removal of the solvent
by filtration, the resin was washed extensively with DMF (75 mL),
THF–water (1 : 1) (2 × 75 mL), THF (2 × 75 mL), MeOH (2 ×
75 mL) and was dried for 18 h at 50 ◦C in vacuo to give resin 43 as
pale yellow granules (3.23 g, LL = 0.37 mmol g−1). 13C gel-phase
NMR (75 MHz, d8-THF) d −4.1, 17.5, 19.0, 21.1, 21.7, 26.3, 31.4,
36–52, 69.0, 70.8, 71.7, 115.33, 121.65, 125.60, 128.02, 129.81,
130.81, 133.37, 135,35, 135.83, 136.48, 139.23, 142.28, 146.33,
150.19, 153.09 ppm; Anal. C, 80.2%; H, 8.0%; N, 0.5%; Ge, 2.7%.
R
R
HypoGelꢀ-Br 39. To a suspension of HypoGelꢀ 38 (24.55 g,
LL = 0.80 mmol g−1, 19.6 mmol) in CH2Cl2 (250 mL) at 0 ◦C
was added triphenylphosphine (10.30 g, 39.3 mmol) and carbon
tetrabromide (26 g, 78.4 mmol). The reaction mixture was stirred
at RT under N2 for 24 h. After removal of the solvent by filtration,
the resin was washed with DMF (300 mL), THF–water (1 : 1)
(2 × 300 mL), THF (2 × 300 mL) and MeOH (2 × 300 mL)
◦
and was dried for 16 h at 50 C in vacuo to give the brominated
resin 39 as pale yellow granules (25 g, 100% conversion by 13C
NMR, LL = 0.80 mmol g−1). 1H MAS NMR (400 MHz, CDCl3):
d 1.00–1.75 [CH(Ar)CH2], 1.15–1.60 [CH(Ar)CH2], 1.60–2.10
[CH(Ar)CH2], 3.50–3.60 (OCH2), 3.60–3.90 (CH2CH2O), 6.20–
6.80 (ArH), 6.80–7.30 (ArH); 13C gel-phase NMR (75 MHz, d8-
THF) d 31.7, 32–56, 71.7, 72.3, 120–135, 146.3 ppm; IR (neat)
3030–2865 (C–H), 1601, 1493, 1452, 1349, 1296, 1249, 1101
(strong) cm−1; Anal. C, 76.5%, H 7.7%, Br 6.4%.
R
HypoGelꢀ-di-para-tolylgermyl mono(triarylamine) (p-OH) 44.
TBAF (1.34 g, 4.25 mmol) was added to a suspension of resin
43 (2.43 g, LL = 0.37 mmol g−1, 1.22 mmol) in THF (20 mL).
This mixture was stirred under N2 at RT for 20 h. After removal
of the solvent by filtration, the resin was washed extensively with
DMF (75 mL), THF–water (1 : 1) (2 × 75 mL), THF (2 × 75 mL),
MeOH (2 × 75 mL) and was dried for 16 h at 50 ◦C in vacuo to give
R
HypoGelꢀ-di-para-tolylgermyl-para-anisole 40. Germylphe-
nol 8e (17.8 g, 36.8 mmol), tetra-n-butylammonium iodide
(680 mg, 1.84 mmol) and cesium carbonate (19.5 g, 55.2 mmol)
were added to a suspension of brominated resin 40 (24.5 g, LL =
0.80 mmol g−1, 18.4 mmol) in acetonitrile (150 mL). This mixture
was stirred at 85 ◦C for 22 h. After removal of the solvent by
filtration, the resin was washed extensively with acetonitrile (3 ×
300 mL), DMF (2 × 300 mL), THF–water (1 : 1) (3 × 300 mL),
THF (2 × 300 mL), MeOH (2 × 300 mL) and was dried for 16 h
at 50 ◦C in vacuo to give resin 40 as pale yellow granules (29.0 g,
99% conversion by the amount of germylphenol returned and
Ge elemental, LL = 0.48 mmol g−1). 1H MAS NMR (400 MHz,
CDCl3): d 1.00–1.65 [CH(Ar)CH2], 1.65–2.10 [ArCH2CH2Ge,
CH(Ar)CH2)], 2.37 (s, ArCH3), 2.80 (m, GeCH2), 3.40–4.15
(OCH3, CH2CH2O), 6.10–6.70 (ArH), 6.70–7.30 (ArH), 7.41 (d,
J = 6.5, ArH); 13C gel-phase NMR (75 MHz, d8-THF) d 17.6,
21.8, 31.4, 36–52, 55.4, 69.0, 70.8, 71.7, 114.9, 115.3, 128.6, 129.5,
129.9, 135.0, 135.8, 137.0, 139.3, 161.7 ppm; IR (neat) 3030–2865
(C–H), 1593, 1509, 1493, 1452, 1349, 1281, 1245, 1102 (strong),
698 (strong) cm−1; Anal. C 78.0%, H 7.7%, Ge 3.5%.
resin 44 as pale yellow granules (2.33 g, LL = 0.38 mmol g−1). 13
C
gel-phase NMR (75 MHz, d8-THF) d 17.5, 21.1, 21.8, 31.5, 36–
52, 68.5, 70.8, 71.7, 115.33, 117.29, 121.08, 125.13, 128.92, 129.80,
130.63, 132.86, 135.35, 135.85, 139.17, 146.53, 150.42, 156.54 ppm;
Anal. C, 80.8%; H, 7.7%; N, 0.7%; Ge, 2.8%.
R
HypoGelꢀ-di-para-tolylgermyl mono(triarylamine) (p-OTf) 45.
Trifluoromethanesulfonic anhydride (0.50 mL, 2.97 mmol) was
added slowly to a suspension of resin 44 (1.61 g, LL =
0.38 mmol g−1, 0.81 mmol) swollen in pyridine (10 mL) at 0 ◦C. The
◦
resulting mixture was stirred at 0 C for 5 min, then allowed to
warm to RT and stirred at this temperature for a further 16 h.
After removal of the solvent by filtration, the resin was washed
extensively with DMF (75 mL), THF–water (1 : 1) (2 × 75 mL),
THF (2 × 75 mL), MeOH (2 × 75 mL) and was dried for 16 h at
50 ◦C in vacuo to give resin 45 as pale yellow granules (1.73 g, LL =
0.37 mmol g−1). 13C gel-phase NMR (75 MHz, d8-THF) d 17.5,
21.2, 21.8, 31.4, 36–52, 68.5, 70.8, 71.7, 115.25, 117.84, 123.08,
124.39, 127.14, 129.84, 131.35, 132.72, 135.83, 136.97, 139.09,
145.44, 146.82, 148.97 ppm; 19F gel-phase NMR (75 MHz, d8-
THF) d −76.4 ppm; Anal. C, 76.3%; H, 6.7%; N, 0.7%; S, 1.3%;
F, 2.2%; Ge, 2.7%; N, 0.7%.
R
HypoGelꢀ-di-para-tolylgermyl chloride 41. A solution of 1 M
HCl in diethyl ether (150 mL, 150 mmol) was added to a
suspension of resin 40 (27.0 g, LL = 0.48 mmol g−1, 14.9 mmol) in
CH2Cl2 (500 mL). This mixture was stirred at RT under N2 for 20 h.
After removal of the solvent by filtration, the resin was washed with
anhydrous diethyl ether (2 × 200 mL) and dried at 50 ◦C in vacuo
for 16 h to give resin 41 as pale yellow granules (25.0 g, 100%
R
HypoGelꢀ-di-para-tolylgermyl di(triarylamine) (p-OTBS) 46.
Resin 45 (1.34 g, LL = 0.37 mmol g−1, 0.67 mmol), triarylamine
boronic ester 4 (1.73 g, 3.35 mmol), Pd(PPh3)4 (0.15 g, 0.13 mmol),
aqueous Na2CO3 (2 M, 10 mL) in 1,2-DME (10 mL) were stirred
1
1
conversion by H NMR, LL = 0.49 mmol g−1). H MAS NMR
(400 MHz, CDCl3): d 1.20–2.20 [ArCH2CH2Ge, CH(Ar)CH2],
2.38 (s, ArCH3), 2.90 (m, GeCH2), 3.40–4.20 (CH2CH2O), 6.10–
6.70 (ArH), 6.70–7.30 (ArH), 7.49 (d, J = 7, ArH); 13C gel-phase
NMR (75 MHz, d8-THF) d 21.8, 22.0, 30.2, 36–52, 69.0, 70.7,
71.7, 115.4, 129.7, 130.2, 133.6, 134.4, 136.3, 141.1, 158.4 ppm;
IR (neat) 3030–2865, 1601, 1510, 1493, 1452, 1349, 1245, 1102
(strong), 607 (strong) cm−1; Anal. C 76.7%, H 7.9%, Cl 2.2%, Ge
3.6%.
◦
at 80 C for 18 h. After removal of the solvent by filtration, the
resin was washed extensively with DMF (50 mL), THF–water (1 :
1) (2 × 50 mL), THF (2 × 50 mL), MeOH (2 × 50 mL) and
was dried for 16 h at 50 ◦C in vacuo to give resin 46 as dark
brown granules (1.25 g, LL = 0.34 mmol g−1). 13C gel-phase NMR
(75 MHz, d8-THF) d −4.0 (b), 17.5 (b), 19.0 (b), 21.6 (b), 26.4 (b),
31.5 (b), 36–52, 71.6 (b), 110.1 (b), 129.7 (b), 135.40 (b), 146.5 (b)
ppm; Anal. C, 77.1%; H, 7.0%; N, 1.0%; Ge, 2.5%.
R
R
HypoGelꢀ-di-para-tolylgermyl mono(triarylamine) (p-OTBS)
HypoGelꢀ-di-para-tolylgermyl di(triarylamine) (p-OH) 47.
43. A solution of n-butyllithium (2.5 M in hexane) (3.4 mL, 5.4 ×
TBAF (0.74 g, 2.35 mmol) was added to a suspension of resin
46 (0.94 g, LL = 0.34 mmol g−1, 0.47 mmol) in THF (10 mL).
10−3 mol) was added dropwise to a solution of triaryl bromide
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This mixture was stirred under N2 at RT for 20 h. After removal
of the solvent by filtration, the resin was washed extensively with
DMF (30 mL), THF–water (1 : 1) (2 × 30 mL), THF (2 × 30 mL),
Acknowledgements
The authors acknowledge Jon Cobb (King’s College London)
for help with the MAS NMR experiments and Andrea J. Keeley
(Avecia Ltd., Blackley, Manchester) for the gel phase 13C NMR
NMR experiments. RA acknowledges the European Commission
for a Marie Curie Fellowship (G5TR-CT-2000-00036) and DJT
acknowledges the EPSRC and Avecia Ltd. (Electronic Materials
Business) for a CASE award. This work was also supported
by the Organic Materials for Electronics Consortium (OMEC,
http://www.omec.org.uk/).
◦
MeOH (2 × 30 mL) and was dried for 16 h at 50 C in vacuo to
give resin 47 as dark brown granules (0.91 g, LL = 0.33 mmol g−1).
13C gel-phase NMR (75 MHz, d8-THF) d 17.5 (b), 21.8 (b), 31.5
(b), 36–52, 71.6 (b), 110.1 (b), 115–117 (b), 129.8 (b), 135.6 (b),
146.0 (b) ppm; Anal. C, 78.5%; H, 7.0%; N, 1.0%; Ge, 2.4%.
R
HypoGelꢀ-di-para-tolylgermyl di(triarylamine) (p-OTf) 48.
Trifluoromethanesulfonic anhydride (0.30 mL, 1.75 mmol) was
added slowly to a suspension of resin 47 (0.70 g, LL =
0.33 mmol g−1, 0.35 mmol) swollen in pyridine (10 mL) at 0 ◦C. The
References
◦
resulting mixture was stirred at 0 C for 5 min, then allowed to
1 A. Kraft, A. C. Grimsdale and A. B. Holmes, Angew. Chem., Int. Ed.,
1998, 37, 402–428.
2 C. D. Dimititrakopoulos and D. J. Mascaro, IBM J. Res. Dev., 2001,
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3 C. Winder and N. S. Sariciftci, J. Mater. Chem., 2004, 14, 1077–1086.
4 H. E. Katz, Z. Bao and S. L. Gilat, Acc. Chem. Res., 2001, 34, 359–369.
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warm to RT and stirred at this temperature for a further 16 h.
After removal of the solvent by filtration, the resin was washed
extensively with DMF (30 mL), THF–water (1 : 1) (2 × 30 mL),
THF (2 × 30 mL), MeOH (2 × 30 mL) and was dried for 16 h at
◦
50 C in vacuo to give resin 48 as brown granules (0.65 g, LL =
0.30 mmol g−1). 13C gel-phase NMR (75 MHz, d8-THF) d 17.5 (b),
21.9 (b), 31.4 (b), 36–52, 71.7 (b), 113.9 (b), 115.2 (b), 126.4 (b),
129.4 (b), 135.5 (b), 145.9 (b) ppm; 19F gel-phase NMR (75 MHz,
d8-THF)) d −74.6 ppm; Anal. C, 67.9%; H, 6.3%; N, 1.1%; S,
1.1%; F, 1.8%; Ge, 2.2%.
8 J. V. Allen, J. Fergus, S. W. Leeming, J. D. Morgan and M. Thomas,
WO99/35537, 1999, Avecia Ltd.
9 S. W. Leeming, J. Veres, J. D. Morgan, E. Wright and B. A. Brown,
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10 M. J. Plater and T. Jackson, Tetrahedron, 2003, 59, 4687–4692 and
references therein.
R
HypoGelꢀ-di-para-tolylgermyl tri(triarylamine) (p-Me) 49.
Resin 48 (0.53 g, LL = 0.30 mmol g−1, 0.35 mmol), triarylamine
boronic ester 5 (1.73 g, 3.35 mmol), Pd(PPh3)4 (0.15 g, 0.13 mmol),
aqueous Na2CO3 (2 M, 5 mL) in 1,2-DME (5 mL) were stirred
11 C. A. Briehn, T. Kirschbaum and P. Ba¨uerle, J. Org. Chem., 2000, 65,
352–359.
12 W. Li, T. Maddux and L. Yu, Macromolecules, 1996, 29, 7329–7334.
13 G. Bidan, A. De Nicola, V. Enee and S. Guillerez, Chem. Mater., 1998,
10, 1052–1058.
14 P. Ba¨uerle, Handbook of Oligo- and Polythiophenes, ed. D. Fichou,
Wiley-VCH,Weinheim, 1999.
◦
at 80 C for 18 h. After removal of the solvent by filtration, the
resin was washed extensively with DMF (30 mL), THF–water (1 :
1) (2 × 30 mL), THF (2 × 30 mL), MeOH (2 × 30 mL) and was
dried for 16 h at 50 ◦C in vacuo to give resin 49 as brown granules
(0.41 g, LL = 0.30 mmol g−1). 13C gel-phase NMR (75 MHz, d8-
THF) d 17.5 (b), 21.0 (b), 22.5 (b), 31.4 (b), 36–52, 71.7 (b), 115.3
(b), 125.5 (b), 128.1 (b), 129.8 (b), 130.9 (b), 133.1 (b), 135.4 (b),
136.6 (b), 146.5 (b) ppm; Anal. C, 72.3%; H, 6.2%; N, 1.3%; Ge,
2.2%.
15 J. P. Sadighi, R. A. Singer and S. L. Buchwald, J. Am. Chem. Soc., 1998,
120, 4960–4976.
16 F. E. Goodson, S. I. Hauck and J. F. Hartwig, J. Am. Chem. Soc., 1999,
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17 J. Louie and J. F. Hartwig, Macromolecules, 1998, 31, 6737–6739.
18 P. R. L. Malenfant and J. M. J. Fre´chet, Chem. Commun., 1998, 2657–
2658.
19 S. Huang and J. M. Tour, J. Org. Chem., 1999, 64, 8898–8906.
20 T. Kirschbaum, C. A. Briehn and P. Ba¨uerle, J. Chem. Soc., Perkin
Trans. 1, 2000, 1211–1216.
N4ꢀ -[4ꢀ -(Di-para-tolylaminobiphenyl-4-yl]-N4-(4ꢀ -phenyl)-N4,
N4ꢀ-di-para-tolylbiphenyl-4,4ꢀ-diamine 50. A suspension of resin
49 (0.33 g, LL = 0.30 mmol g−1, 0.10 mmol) in trifluoroacetic acid
(10% in CH2Cl2) (5 mL) was stirred at RT for 16 h. The resin was
separated off by filtration and washed with CH2Cl2. The organic
washings were concentrated 50 ◦C in vacuo to give a dark brown
oil. The crude material was purified by FC (hexane–ethyl acetate,
10 : 1) to give the expected product as a white solid [0.07 g, 90%,
>97% pure by HPLC: Jupiter ODS-C18 column (250 × 0.46 cm),
UV 300 nm detection, 1 mL min−1, 5 → 100% MeCN in H2O +
0.1% formic acid, Rt = 9.7 min.]. 1H NMR (400 MHz, CDCl3) d
2.30 (s, 6H), 2.31 (s, 3H), 2.32 (s, 3H), 6.95–7.12(m, 27H), 7.21–
7.24 (m, 2H), 7.39–7.43 (m, 8H); 13C NMR (100 MHz, CDCl3) d
20.82, 20.85, 20.87, 122.37, 122.90, 123.57, 123.68, 123.78, 124.58,
125.05, 125.10, 127.12, 127.20, 127.22, 129.16, 129.88, 129.97,
130.00, 132.47, 132.89, 132.99, 133.87, 134.40, 134.51, 134.67,
145.05, 145.15, 145.33, 146.64, 146.75, 146.89, 147.15, 147.93 ppm;
HRMS (EI+) calcd. for C58H49N3 (M+) 787.3926; found 787.3923.
21 T. Kirschbaum and P. Ba¨uerle, Synth. Met., 2001, 119, 127–128.
22 C. A. Briehn, M.-S. Schiedel, E. M. Bonsen, W. Schuhmann and
P. Ba¨uerle, Angew. Chem., Int. Ed., 2001, 40, 4680–4683.
23 C. A. Briehn and P. Ba¨uerle, J. Comb. Chem., 2002, 4, 457–469.
24 C. A. Briehn and P. Ba¨uerle, Chem. Commun., 2002, 1015–1023.
25 K. Burgess, Solid-Phase Organic Synthesis, Wiley, New York, 2000.
26 A. C. Spivey, D. J. Turner, M. L. Turner and S. Yeates, Org. Lett., 2002,
4, 1899–1902.
27 R. Anemian, D. C. Cupertino, P. R. Mackie and S. Yeates, Tetrahedron
Lett., 2005, 46, 6717–6721.
28 Part of the work described here relating to the development of the SPS
of oligo-(3-alkylthiophene)s has been published in preliminary form
(ref. 38).
29 M. J. Plunkett and J. A. Ellman, J. Org. Chem., 1997, 62, 2885–2893.
30 A. C. Spivey, C. M. Diaper and A. J. Rudge, Chem. Commun., 1999,
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