Initiator Control of Conjugated Polymer Topology in Ring-Opening Alkyne Metathesis Polymerization

Article abstract of DOI:10.1021/jacs.6b02422

Molybdenum carbyne complexes [RCequiv;Mo(OC(CH₃)(CF₃)₂)₃] featuring a mesityl (R = Mes) or an ethyl (R = Et) substituent initiate the living ring-opening alkyne metathesis polymerization of the strained cyclic alkyne, 5,6,11,12-tetradehydrobenzo[a,e][8]annulene, to yield fully conjugated poly(o-phenylene ethynylene). The difference in the steric demand of the polymer end-group (Mes vs Et) transferred during the initiation step determines the topology of the resulting polymer chain. While [MesCequiv;Mo(OC(CH₃)(CF₃)₂)₃] exclusively yields linear poly(o-phenylene ethynylene), polymerization initiated by [EtCequiv;Mo(OC(CH₃)(CF₃)₂)₃] results in cyclic polymers ranging in size from n = 5 to 20 monomer units. Kinetic studies reveal that the propagating species emerging from [EtCequiv;Mo(OC(CH₃)(CF₃)₂)₃] undergoes a highly selective intramolecular backbiting into the butynyl end-group.

Full text of DOI:10.1021/jacs.6b02422

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Article
Initiator Control of Conjugated Polymer Topology
in Ring-Opening Alkyne Metathesis Polymerization
Stephen Winthrop von Kugelgen, Donatela E. Bellone,
Ryan R. Cloke, Wade Scott Perkins, and Felix R. Fischer
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.6b02422 • Publication Date (Web): 27 Apr 2016
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Initiator Control of Conjugated Polymer Topology in Ring-Opening
Alkyne Metathesis Polymerization
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⊥
* §
†
†‡
†‡
†
†
,
Stephen von Kugelgen , Donatela Bellone , Ryan R. Cloke , Wade Perkins Felix R. Fischer
†Department of Chemistry, University of California Berkeley, Berkeley, California 94720, United States
⊥Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
§Kavli Energy Nanosciences Institute at the University of California Berkeley and Lawrence Berkeley National Laboratory, Berkeley,
California 94720, United States
ABSTRACT: Molybdenum carbyne complexes [RC≡Mo(OC(CH3)(CF3)2)3] featuring a mesityl (R = Mes) or an ethyl (R = Et) substituent
initiate the living ring-opening alkyne metathesis polymerization of the strained cyclic alkyne, 5,6,11,12-tetradehydrobenzo[a,e][8]annulene,
to yield fully conjugated poly-(o-phenylene ethynylene). The difference in the steric demand of the polymer end-group (Mes vs. Et) trans-
ferred during the initiation step determines the topology of the resulting polymer chain. While [MesC≡Mo(OC(CH3)(CF3)2)3] exclusively
yields linear poly-(o-phenylene ethynylene), polymerization initiated by [EtC≡Mo(OC(CH3)(CF3)2)3] results in cyclic polymers ranging in
size from n = 5 to 20 monomer units. Kinetic studies reveal that the propagating species emerging from [EtC≡Mo(OC(CH3)(CF3)2)3] un-
dergoes a highly selective intramolecular backbiting into the butynyl end-group.
Semiconducting π-conjugated polymers have been widely ex-
plored as functional materials in advanced electronic devices. They
combine the superior processability and mechanical performance
of polymers with readily tunable optical, electrical, and magnetic
properties of small molecules.1 Applications for these polymers
include electronic devices such as organic photovoltaics (OPVs),2,3
organic light-emitting diodes (OLEDs),4,5 organic field-effect tran-
sistors (OFETs),6,7 photorefractive devices,8 and environmental
sensors.9–13 Among these materials, poly-(phenylene ethynylenes)
(PPE), a class of conjugated polymers featuring a pattern of alter-
nating aromatic rings and triple bonds, have stood out for their
stability, moderate fluorescence quantum yields,14,15 and readily
tunable band gap.16,17 The macromolecular assembly of PPEs in
solution and thin films can be tuned from densely packed linear
organizations to well defined helical coiled or zig-zag structures18 by
varying the substitution pattern (para-, meta-, ortho-) of the aro-
matic rings along the backbone of the polymer chain. The classical
syntheses of PPEs rely on step-growth polymerizations based on
either transition metal catalyzed cross-coupling reactions or alkyne
cross-metathesis (ACM).19,20 While ACM and cyclodepolymeriza-
tion of linear polymers have previously been used to access cyclic
topologies, the thermodynamic products of these reactions are
usually small cylic oligomers comprised of not more than 3–6 al-
kynes.21–24 Transition-metal catalyzed cross-coupling polymeriza-
tions of aryl halides with aromatic alkynes, instead, suffer from
undesired termination reactions, e.g. dehalogenation, and structur-
al defects along the polymer backbone such as butadiyne groups
emerging from oxidative coupling of terminal alkynes. While these
strategies benefit from readily accessible monomers, they lack the
precise control over degree of polymerization, molecular weight,
end-group functionality, and polydispersity unique to a controlled
ring-opening alkyne metathesis polymerization (ROAMP) mecha-
nism.25–27
In this study we report a novel route towards fully conjugated
PPE based on two ROAMP catalysts [MesC≡Mo(OC(CH3)
(CF3)2)3]
1
and [EtC≡Mo(OC(CH3)(CF3)2)3(DME)] (DME =
(Scheme 1) that selectively yield PPE
1,2-dimethoxyethane)
2
featuring either linear or cyclic polymer topology. Both catalysts
rapidly initiate the polymerization of ring-strained monomer
3
5,6,11,12-tetradehydrobenzo[a,e][8]annulene ( ) to form poly-
(ortho-phenylene ethynylene) (PoPE) featuring a mesityl or an
ethyl end-group, respectively. Time-resolved NMR spectroscopy
reveals that the active chain ends of the polymers featuring a mesit-
yl end-group are stable under the reaction conditions. In the ab-
sence of monomer, living polymers formed from instead undergo
2
highly regioselective backbiting into the least sterically hindered
alkyne (EtC≡C) at the end-group to give cyclic PoPE with n > 5
and the starting catalyst . We herein demonstrate an unprecedent-
2
ed structural control over polymer topology by taking advantage of
the unique selectivities of two ROAMP catalysts to form either
linear or cyclic fully conjugated polymers derived from ring-
strained monomers.
RESULTS AND DISCUSSION
Catalyst
1
was synthesized from Mo(CO)6 and MesLi following
a procedure described by Tamm.28 The DME adduct of catalyst
2
was obtained through cross-metathesis of the nitrido-complex
[N≡Mo(OC(CH3)(CF3)2)3] with hex-3-yne as described by John-
son.29 Orange prisms of
2
suitable for X-ray crystallography were
obtained from a saturated toluene solution at –35 °C. The geome-
try at the Mo center is pseudo-octahedral. X-ray crystallography of
2
(Figure 1) confirms the presence of a C(1)≡Mo(1) triple bond
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with a bond length of 1.736(2) Å and a C(2)–C(1)–Mo(1) angle
= 10) at 24 °C leads to the precipitation of polymers within 1 hour.
19
1H and F NMR indicate that
1
quantitatively initiates with a half-
1
2
3
4
5
6
7
8
of 176.44(19)°. Three hexafluoro-tert-butoxide ligands adopt a
meridional conformation featuring typical Mo(1)–O(1), Mo(1)–
O(2), and Mo(1)–O(3) distances of 1.9632(15) Å, 1.9326(15) Å
and, 1.9720(15) Å. In the crystal structure one equivalent of DME
is coordinated to the Mo complex. The bond distances are
2.2283(15) Å and 2.4526(15) Å for the Mo(1)–O(4) cis and
Mo(1)–O(5) trans to the carbyne, respectively. In solution the
life of t1/2 ≪ 1 min to form the propagating species. Monomer
3
is
consumed in less than 1 h at 24 °C. The active ROAMP catalyst
remains attached to the growing polymer chain. The molecular
weight of the resulting polymers scales linearly with monomer con-
version (Supporting Information Figure S2).
Table 1. Molecular weight analysis of poly-3a
.
octahedral complex
2
is in dynamic equilibrium with the penta-
coordinate monodentate DME complex and the fully DME disso-
9
c
[
3
]/[
1
]
Mn
Mn
Mw
Xn
PDI
GPCa
ciated tetracoordinate complex.30 At 24 °C in benzene, the equilib-
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theory GPCb GPCb
rium lies on the side of the associated complexes
2
(Kd = 6.2 × 10–5
mol L–1) (Supporting Information Figure S1). Variable tempera-
ture NMR reveals that the exchange is fast suggesting that an open
coordination site is readily available to bind the alkyne substrate.
10/1
20/1
30/1a
2134
4134
6134
1700
4800
6600
3000
6400
9400
11
21
29
1.7
1.3
1.4
a
[3]/[1] loadings > 30 lead to precipitation of insoluble polymers be-
b
fore all monomer is consumed; calibrated to narrow polydispersity poly-
styrene standards; c degree of polymerization determined by 1H NMR end-
group analysis.
Figure 1. ORTEP representation of the X-ray crystal structure of 2
.
Thermal ellipsoids are drawn at the 50% probability level. Color cod-
ing: C (gray), O (red), F (green), Mo (turquoise). Hydrogen atoms
are omitted for clarity.
Figure 2. A) GPC traces for linear poly-3a and purified cyclic poly-3b
3 1 2
with catalyst and respectively; cali-
brated to polystyrene standards. B) MALDI mass spectrum of cyclic
poly-3b showing integer multiples of the mass of monomer
200 g mol–1) and the absence of end-groups.
obtained through ROAMP of
3
(MW =
Precipitation of the resulting polymer with MeOH affords poly-
3a in 82% isolated yield. Gel permeation chromatography (GPC)
3 1
analysis for various [ ]/[ ] loadings at 24 °C in toluene shows a
PDI of 1.3–1.7 (Table 1). The molecular weights of poly-3a deter-
mined by GPC, calibrated to polystyrene standards, scale with the
conversion of monomer, are proportional to the initial [ ]/[ ]
3 1
loading and show a unimodal distribution (Figure 2a). Extended
reaction times do not lead to a broadening of the PDI. Mass spec-
trometry of polymers that have been quenched with MeOH is con-
sistent with the characteristic signature for one mesityl end-group
and a statistical mixture of CH3, CH2OH, or CHO end-groups
resulting from the cleavage of the propagating molybdenum car-
Scheme 1. Synthesis of linear poly-3a and cylic poly-3b from ring
strained monomer
We studied
tetradehydrobenzo[a,e][8]annulene (
1).31 Addition of
to a solution of
3
using ROAMP catalyst
the ROAMP
) with
and .
1 2
of
and
5,6,11,12-
2
(Scheme
3
1
1
1
3
(50 mM) in toluene ([
3
]/[
1
]
byne species (Supporting Information Figure S3). While the H
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]/[ ] load-
3b. GPC analysis of samples prepared from various [3 2
NMR of poly-3a features two distinct resonance signals in the aro-
matic region, the C NMR reveals a characteristic upfield shift for
the alkyne carbon resonances (109.5 ppm in
3a) associated with the release of the ring-strain stored in
13
1
2
3
4
5
6
7
8
ings at 24 °C in toluene indicates the formation of discrete cyclic
oligomers (poly-3b) and some higher molecular weight linear pol-
ymers (Mn = 5,000–10,000) resulting from intermolecular cross-
metathesis of living polymer chains. The ratio of products emerging
from an intra- vs. intermolecular chain transfer is concentration
3
to 92.6 ppm in poly-
. No
3
evidence for branching or the formation of cyclic polymers could
1
be observed by H NMR analysis and mass spectrometry. End-
group analysis of the mesityl group resonance signals (1H NMR)
indicates that GPC overestimates the Mn of poly-3a. A correction
factor of 1.1–1.2 correlates well with the degree of polymerization
(Xn) determined by NMR analysis and the expected molecular
dependent ranging from 93% cyclic polymers at [
2
] = 1 mM to
1
86% at [ ] = 10 mM as determined by H NMR (Supporting In-
2
formation Table S1, Figure S4,S5). The linear polymers can be
removed by Soxhlet extraction or fractional precipitation to give
pure cyclic poly-3b in > 60% isolated yield (Figure 2a). Mass spec-
trometry of poly-3b shows evenly spaced peaks corresponding to
9
weight based on the initial [
If the polymerization of
propylidyne complex ([ ]/[
cipitation of polymers can be observed. Catalyst
reacts with to form a propagating molybdenum complex (t1/2
3
]/[
is initiated with the molybdenum
] = 10) at 24 °C in toluene no pre-
quantitatively
1
] loading.
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3
integer multiples of
3
(m/z = [n × 200] g mol–1, n = 5, 6, 7, …, 20;
2
3
2
Figure 2b). The absence of end-groups in poly-3b is further cor-
2
1
roborated by H and 13C NMR spectroscopy (Supporting Infor-
3
≪
mation Figure S15,S16) and highlights the unusual selectivity of
1
19
1 min) as indicated by H and F NMR. Addition of MeOH to the
homogeneous reaction mixture leads to the precipitation of poly-
catalyst
2
for the formation cyclic poly-3b over linear poly-3a.
1
Figure 3. ROAMP of isotopically labeled 3* with catalyst
tion of transient intermediates during the reaction of (C) and
1
(A) and
(D) with
2
(B) followed by time resolved H, 19F, and 13C NMR spectroscopy. Mole frac-
1
2
3
derived from 1H NMR. Isotopic labeling: * 99.5% 13C, u 50% 13C.
13
To gain insight into the reaction mechanism we studied the
ROAMP of C-labeled
resting state of the catalyst observed by C NMR is the intercon-
verting metallacyclobutadienes 1a and 1b (Figure 3a, Supporting
Information Figure S6,S8) characterized by two broad sets of H
and F resonances for the alkoxides (axial and equatorial) and two
molybdenum species observed in C NMR are the interconverting
13
3
* with
1
. In the presence of monomer the
metallacyclobutadienes 2a and 2b (Figure 3b, Supporting Infor-
mation Figure S7,S9). Following the consumption of monomer, 2b
undergoes a final cycloreversion to give the ring-opened molyb-
denum benzylidyne complex 2c. While 1c is stable in the reaction
mixture, 2c undergoes highly regioselective backbiting into the
butynyl end-group to give cyclic poly-3b and the original unlabeled
13
1
19
13
sets of C resonances for the metallacyclobutadiene carbons (one
β carbon and two α carbons).30,32 Following the consumption of 3*
the metallacyclobutadiene 1b undergoes a final cycloreversion to
give the labeled, ring-opened molybdenum benzylidyne complex
1c. In the absence of monomer, 1c is stable for > 10 h and remains
attached to one end of the polymer chain pending MeOH solvoly-
molybdenum propylidyne complex . The outstanding selectivity
2
of this backbiting reaction is reflected in the absence of half-integer
multiples of the monomer (m/z = [n × 200 + 100] g mol–1) in the
mass spectrum of poly-3b (Figure 2b). The increased steric de-
mand of internal alkynes lining the backbone of the growing poly-
mer chain (2c) prevents a stochastic backbiting process and directs
sis. If the same polymerization is performed with , the dominant
2
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the reaction exclusively towards the unhindered butynyl end-group.
Kinetic studies using [TolC≡Mo(OC(CH3)(CF3)2)3(DME)] (
and were used as received unless otherwise noted. Organic solvents
1
2
3
4
5
6
7
8
were dried by passing through a column of alumina and were de-
gassed by vigorous bubbling of N2 or Ar through the solvent for 20
min. Flash column chromatography was performed on SiliCycle
silica gel (particle size 40–63 μm). Thin layer chromatography was
carried out using SiliCycle silica gel 60 Å F-254 precoated plates
4
)
as a model complex for the propagating species 2c, show that the
rate of cross-metathesis with the sterically less demanding 1-(but-1-
yn-1-yl)-2-methylbenzene (5a) is ~200 times faster (k = 1.3 × 10–1
M–1s–1) than with 1,2-bis(o-tolyl)acetylene (5b) (k = 7.1 × 10–4 M–
1s–1) (Supporting Information Figure S10,S11). The subtle kinetic
selectivity that directs the intramolecular cross-metathesis of 2c
toward the sterically less hindered butynyl end-group has previous-
ly been observed for acyclic diyne metathesis (ADMET).21
1
(0.25 mm thick) and visualized by UV absorption. All H, {1H}13C,
19
and F NMR spectra were recorded on Bruker AV-600, DRX-500,
and AV-500 spectrometers, and are referenced to residual solvent
1
13
peaks (CDCl3 H NMR δ = 7.26 ppm, C NMR δ = 77.16 ppm;
9
1
13
1
C6D6 H NMR δ = 7.16 ppm, C NMR δ = 128.06 ppm; Tol-d8 H
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NMR δ = 2.08 ppm; THF-d8 H NMR δ = 1.78 ppm, 13C NMR δ =
1
67.21 ppm) or hexafluorobenzene (19F NMR δ = –162.90 ppm).
The concentrations of ,
4
5a, and 5b were determined by 1H and 19F
NMR using the ERETIC method36 against an external standard of
18.2 mM 1,3,5-tris(trifluoromethyl)benzene in C6D6. ESI mass
spectrometry was performed on a Finnigan LTQFT (Thermo)
spectrometer in positive ionization mode. MALDI mass spectrom-
etry was performed on a Voyager-DE PRO (Applied Biosystems
Voyager System 6322) in positive mode using a matrix of dithranol.
Elemental analysis (CHN) was performed on a Perkin Elmer 2400
Series II combustion analyzer (values are given in %). Gel permea-
tion chromatography (GPC) was carried out on a LC/MS Agilent
1260 Infinity set up with a guard and two Agilent Polypore 300 x
7.5 mm columns at 35 °C. All GPC analyses were performed on a
0.2 mg/mL solution of polymer in chloroform. An injection vol-
ume of 25 μL and a flow rate of 1 mL/min were used. Calibration
was based on narrow polydispersity polystyrene standards ranging
from Mw = 100 to 4,068,981. X-ray crystallography was performed
on APEX II QUAZAR, using a Microfocus Sealed Source (In-
coatec IμS; Mo-Kα radiation), Kappa Geometry with DX (Bruker-
AXS build) goniostat, a Bruker APEX II detector, QUAZAR multi-
layer mirrors as the radiation monochromator, and Ox-
Figure 4. UV/Vis absorption and fluorescence emission (λex = 300 nm)
of linear poly-3a and cyclic poly-3b in chloroform solution (1.6 and 0.6
µg/mL poly-3a and poly-3b, respectively).
The topological difference of linear and cyclic polymers, poly-3a
and poly-3b, is reflected in their photophysical properties. Alt-
hough the UV-Vis absorption spectra of poly-3a and poly-3b ap-
pear similar (Figure 4), cyclic poly-3b exhibits a higher fluores-
cence quantum yield upon excitation at 300 nm (ΦF = 8.4% and
18.6% for poly-3a and poly-3b, respectively). As the emission spec-
trum does not shift to longer wavelengths, the observed enhance-
ment can not be explained by the formation of excimer complexes
between adjacent monomer units as has been observed for e.g.
cyclic polystyrene.33 Instead, enhanced quantum yield can be at-
ford Cryostream 700 for . Crystallographic data was refined with
2
SHELXL-97, solved with SIR-2007, visualized with ORTEP-32,
and finalized with WinGX. UV-Vis absorption spectra were ac-
quired in chloroform solution on a Varian Cary 50 spectrophotom-
eter (Agilent, USA). Fluorescence emissions spectra were acquired
at an excitation wavelength of 300 nm on a Fluoromax-4 spectro-
fluorometer equipped with automatic polarizers,1.0 nm slit widths
for excitation/emission and a 0.5 s integration time. Quantum
yields were calibrated to 1,4-bis(5-phenyloxazol-2-yl) benzene
tributed to the reduced conformational entropy of cyclic poly-3b
.
Cyclic poly-3b experiences less nonradiative relaxation than linear
poly-3a due to the restricted intramolecular rotation about the
polymer backbone.34,35 The unique control over polymer topology
enables tuning the mechanical and photophysical properties of
PoPEs with minimal effect on their electronic structure.
(POPOP) in cyclohexane (ΦF = 0.97).37 1 28
synthesized following literature procedures.
,
3 38
,
4,31 and 5b39 were
CONCLUSION
We describe the synthesis of a fully conjugated poly(o-phenylene
ethynylene) using living ring-opening alkyne metathesis polymeri-
zation. Tuning the steric demand of the molybdenum carbyne ini-
tiator directs the synthesis of either linear or cyclic polymers with
high selectivity. The polymerization mechanism and catalyst rest-
ing states were investigated through multinuclear NMR kinetic and
13C labeling studies. The catalyst system described herein repre-
sents an extraordinary access to the field of conjugated organic
materials, simultaneously enabling exceptional control over poly-
mer structure, sequence and topology.
(
Preparation of [EtC≡Mo(OC(CH3)(CF3)2)3(DME)] 2
). A
100 mL sealable Schlenk flask was charged under N2 with
N≡Mo(OC(CF3)2CH3)3 (1.00 g, 1.53 mmol) and 3-hexyne (1.25
g, 15.2 mmol) in toluene (50 mL) and heated to 95 °C for 20 h.
The reaction mixture was cooled to 24 °C, 1,2-dimethoxyethane
(156 mg, 1.73 mmol) was added, and stirred for 30 minutes. The
solvent was removed under vacuum. The residue was extracted
with Et2O (20 mL), filtered through Celite, concentrated to 5 mL
under vacuum and cooled to –35 °C. The precipitate was collected
by filtration. Recrystallization from pentane (–35 °C) yielded 2
(0.69 g, 0.90 mmol, 58%). Crystals for X-ray analysis were grown
EXPERIMENTAL SECTION
1
Materials and General Methods. Unless otherwise stated, all ma-
nipulations of air and/or moisture sensitive compounds were car-
ried out in oven-dried glassware, under an atmosphere of Ar or N2.
All solvents and reagents were purchased from Alfa Aesar, Spec-
trum Chemicals, Acros Organics, TCI America, and Sigma-Aldrich
from toluene. H NMR (600 MHz, C6D6, 22 °C) δ = 3.16 (s, 6H,
(CH3OCH2)2), 3.00 (s, 4H, (CH3OCH2)2, 2.65 (q, J = 7.6 Hz, 2H,
MoCCH2CH3), 1.71 (s, 9H, OC(CF3)2CH3), 0.59 (t, J = 7.6 Hz,
13
3H, MoCCH2CH3) ppm; C NMR (151 MHz. C6D6, 22 °C) δ =
309.8 (MoCEt), 124.5 (q, 1JCF = 289 Hz, OC(CF3)2CH3), 83.3 (m,
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2JCF = 29 Hz, OC(CF3)2CH3), 71.6 ((CH3OCH2)2), 63.8
Abramson Foundation. The authors acknowledge Dr. Christian
Canlas and Dr. Hasan Celik for support with NMR acquisition and
Dr. Antonio DiPasquale for assistance with X-ray analysis.
1
2
3
4
5
6
7
8
((CH3OCH2)2), 43.1 (MoCCH2CH3), 18.9 (OC(CF3)2CH3), 12.6
(MoCCH2CH3) ppm; 19F NMR (376 MHz, C6D6, 22 °C) δ = –
78.84
[EtC≡Mo(OC(CH3)(CF3)2)3]+
681.9710; found, 681.9720;
ppm;
FTMS
(ESI-TOF)
calcd. [C15H14F18MoO3],
Anal. calcd. for
(m/z):
REFERENCES
(1)
(2)
Scherf, U.; List, E. j. w. Adv. Mater. 2002, 14 (7), 477–487.
Cheng, Y.-J.; Yang, S.-H.; Hsu, C.-S. Chem. Rev. 2009, 109
[EtC≡Mo(OC(CH3)(CF3)2)3(DME)]: C, 29.62; H, 3.14. Found:
C, 29.35; H, 2.96; Crystal data: CCDC no., 1456633; formula,
C19H24F18MoO5; fw, 770.32 g mol–1; temp, 100(2) K; cryst. system,
monoclinic; space group, P2(1)/n; color, black; a, 11.4678(9) Å; b,
16.8911(14) Å; c, 13.8634(11) Å; α, 90.000°; β, 91.155(2)°; γ,
90.000°; V, 2684.8(4) Å3; Z, 4; R1, 0.0262; wR2, 0.0556; GOF,
1.197.
(11), 5868–5923.
(3)
6335.
(4)
Weber, J.; Thomas, A. J. Am. Chem. Soc. 2008, 130 (20), 6334–
9
Friend, R. H.; Gymer, R. W.; Holmes, A. B.; Burroughes, J. H.;
10
11
12
13
14
15
16
17
18
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60
Marks, R. N.; Taliani, C.; Bradley, D. D. C.; Santos, D. A. D.; Brédas, J. L.;
Lögdlund, M.; Salaneck, W. R. Nature 1999, 397 (6715), 121–128.
(5)
Lüssem, B.; Leo, K. Nature 2009, 459 (7244), 234–238.
(6) Kanimozhi, C.; Yaacobi-Gross, N.; Chou, K. W.; Amassian, A.;
Reineke, S.; Lindner, F.; Schwartz, G.; Seidler, N.; Walzer, K.;
Preparation of linear poly-(o-phenylene ethynylene) (poly-3a).
A 5 mL vial was charged under N2 with
3
(0.02 g, 0.10 mmol) in
Anthopoulos, T. D.; Patil, S. J. Am. Chem. Soc. 2012, 134 (40), 16532–
16535.
toluene (1.50 mL). (3.8 mg, 5.0 μmol) in toluene (0.60 mL) was
1
added at 24 °C and the mixture was stirred for 3 h. The reaction
mixture was quenched with MeOH (10 mL). The solid precipitate
was isolated by filtration and washed with MeOH (30 mL) to yield
(7)
G.; Mei, J.; Lei, T.; Pei, J.; Bao, Z. Nat. Commun. 2014, 5, 2954.
(8) Fuller, M. J.; Walsh, C. J.; Zhao, Y.; Wasielewski, M. R. Chem.
Mater. 2002, 14 (3), 952–953.
Knopfmacher, O.; Hammock, M. L.; Appleton, A. L.; Schwartz,
1
poly-3a (0.02 g, 82%) as a brown solid. H NMR (500 MHz,
(9)
Yang, J.-S.; Swager, T. M. J. Am. Chem. Soc. 1998, 120 (46),
CDCl3, 22 °C) δ = 7.56–7.45 (br, 56H), 7.20–7.09 (br, 56H), 6.81
(s, 2H), 2.46 (s, 6H), 2.24 (s, 3H) ppm; 13C NMR (126 MHz,
CDCl3, 22 °C) δ = 132.3, 128.1, 125.8, 92.6, 21.3 ppm.
11864–11873.
(10) Smith, R. C.; Tennyson, A. G.; Lim, M. H.; Lippard, S. J. Org.
Lett. 2005, 7 (16), 3573–3575.
(11) Wosnick, J. H.; Mello, C. M.; Swager, T. M. J. Am. Chem. Soc.
2005, 127 (10), 3400–3405.
(12) Hussain, S.; De, S.; Iyer, P. K. ACS Appl. Mater. Interfaces
2013, 5 (6), 2234–2240.
(13) Ryu, S.; Yoo, I.; Song, S.; Yoon, B.; Kim, J.-M. J. Am. Chem.
Soc. 2009, 131 (11), 3800–3801.
(14) Intemann, J. J.; Hellerich, E. S.; Tlach, B. C.; Ewan, M. D.;
Barnes, C. A.; Bhuwalka, A.; Cai, M.; Shinar, J.; Shinar, R.; Jeffries-EL, M.
Macromolecules 2012, 45 (17), 6888–6897.
(15) Jagtap, S. P.; Mukhopadhyay, S.; Coropceanu, V.; Brizius, G. L.;
Brédas, J.-L.; Collard, D. M. J. Am. Chem. Soc. 2012, 134 (16), 7176–7185.
(16) Zhao, X.; Pinto, M. R.; Hardison, L. M.; Mwaura, J.; Müller, J.;
Jiang, H.; Witker, D.; Kleiman, V. D.; Reynolds, J. R.; Schanze, K. S. Mac-
romolecules 2006, 39 (19), 6355–6366.
(17) Guo, X.; Watson, M. D. Macromolecules 2011, 44 (17), 6711–
6716.
(18) Kübel, C.; Mio, M. J.; Moore, J. S.; Martin, D. C. J. Am. Chem.
Soc. 2002, 124 (29), 8605–8610.
(19) Bunz, U. H. F. Macromol. Rapid Commun. 2009, 30 (9-10),
772–805.
(20) Yang, H.; Jin, Y.; Du, Y.; Zhang, W. J. Mater. Chem. A 2014, 2
(17), 5986–5993.
(21) Zhang, W.; Moore, J. S. J. Am. Chem. Soc. 2005, 127 (33),
11863–11870.
(22) Zhang, W.; Brombosz, S. M.; Mendoza, J. L.; Moore, J. S. J. Org.
Chem. 2005, 70 (24), 10198–10201.
(23) Gross, D. E.; Moore, J. S. Macromolecules 2011, 44 (10), 3685–
3687.
(24) Yang, H.; Liu, Z.; Zhang, W. Adv. Synth. Catal. 2013, 355 (5),
885–890.
(25) Zhang, W.; Moore, J. S. Adv. Synth. Catal. 2007, 349 (1–2), 93–
120.
(26) Jyothish, K.; Zhang, W. Angew. Chem. Int. Ed. 2011, 50 (37),
8478–8480.
Preparation of cyclic poly-(o-phenylene ethynylene) (poly-3b).
A 20 mL vial was charged under N2 with
toluene (1.50 mL). (43.4 mg, 55.0 μmol) in toluene (0.50 mL)
3
(0.06 g, 0.30 mmol) in
2
was added at 24 °C and the mixture was stirred for 24 h. The reac-
tion mixture was quenched with MeOH (10 mL). The solid precip-
itate was isolated by filtration and washed with MeOH (30 mL).
Soxhlet extraction (hexane) of the crude mixture yielded poly-3b
(0.01 g, 18%) as a brown solid. The polymer remaining in the ex-
traction thimble (30 mg) was dissolved in chloroform (15 mL) and
precipitated with pentane (60 mL). After filtering off the precipi-
tate, the filtrate was evaporated to yield additional pure poly-3b
1
(0.02 g, total yield 50%). H NMR (600 MHz, CDCl3, 22 °C) δ =
7.48–7.44 (m, 2H), 7.13–7.09 (m, 2H) ppm; 13C NMR (126 MHz,
CDCl3, 22 °C) δ = 132.2, 128.1, 125.7, 92.5 ppm.
ASSOCIATED CONTENT
Figures S1 to S11, Table S1, methods and instrumentation, synthetic
7 8 3* 5a and characterization, kinetic experiments,
procedures for , , ,
DME dissociation studies, NMR spectra (Figures S12 to S20), and X-
ray crystallographic data (Table S2 to S6) are included in the support-
ing information. This material is available free of charge via the WWW
at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
* ffischer@berkeley.edu
Author Contributions
‡ These authors contributed equally.
ACKNOWLEDGMENT
(27) Fürstner, A. Angew. Chem. Int. Ed. 2013, 52 (10), 2794–2819.
(28) Haberlag, B.; Freytag, M.; Daniliuc, C. G.; Jones, P. G.; Tamm,
M. Angew. Chem. Int. Ed. 2012, 51 (52), 13019–13022.
(29) Gdula, R. L.; Johnson, M. J. A. J. Am. Chem. Soc. 2006, 128
(30), 9614–9615.
Research supported by the National Science Foundation under
contract number CHE-1455289, Berkeley NMR Facility is sup-
ported in part by NIH grant SRR023679A, and X-Ray Facility is
supported in part by NIH Shared Instrumentation Grant S10‐
RR027172. D.E.B. acknowledges fellowship support through the
(30) Freudenberger, J. H.; Schrock, R. R.; Churchill, M. R.;
Rheingold, A. L.; Ziller, J. W. Organometallics 1984, 3 (10), 1563–1573.
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(31) Bellone, D. E.; Bours, J.; Menke, E. H.; Fischer, F. R. J. Am.
Chem. Soc. 2015 137 (2), 850–856. Strained 5,6,11,12-
tetradehydrobenzo[a,e][8]annulene ( ) decomposes rapidly at T > 40 °C
,
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3
4
5
6
7
3
and was thus incompatible with the ROAMP catalyst reported in reference
31.
(32) O’Reilly, M. E.; Ghiviriga, I.; Abboud, K. A.; Veige, A. S. Dalton
Trans. 2013, 42 (10), 3326–3336.
(33) Gan, Y.; Dong, D.; Carlotti, S.; Hogen-Esch, T. E. J. Am. Chem.
Soc. 2000, 122 (9), 2130–2131.
(34) Hong, Y.; Lam, J. W. Y.; Tang, B. Z. Chem. Commun. 2009, No.
29, 4332–4353.
(35) Zhu, X.; Zhou, N.; Zhang, Z.; Sun, B.; Yang, Y.; Zhu, J.; Zhu, X.
Angew. Chem. Int. Ed. 2011, 50 (29), 6615–6618.
(36) Akoka, S.; Barantin, L.; Trierweiler, M. Anal. Chem. 1999, 71
(13), 2554–2557.
(37) Lakowicz, J. R. Principles of Fluorescence Spectroscopy (2nd)
Second Edition, First Printing edition.; Kluwer Acacemic Publishers, 1999.
(38) Orita, A.; Hasegawa, D.; Nakano, T.; Otera, J. Chem. – Eur. J.
2002, 8 (9), 2000–2004.
(39) Chuentragool, P.; Vongnam, K.; Rashatasakhon, P.; Sukwatta-
nasinitt, M.; Wacharasindhu, S. Tetrahedron 2011, 67 (42), 8177–8182.
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