Modular Synthesis of Diarylalkynes and Their Efficient Conversion into Luminescent Tetraarylbutadienes

Article abstract of DOI:10.1021/acs.organomet.6b00298

A series of electronically distinct symmetrical diarylalkynes were prepared via a general Suzuki-Miyaura cross-coupling protocol. These alkynes underwent zirconium-mediated coupling to yield zirconacycles that afford new tetraaryl-1,3-butadienes upon subsequent protonolysis; these butadienes display deep blue or green emission and represent promising building blocks for light-emitting devices. The presented synthetic pathway allows access to new libraries of molecular light emitters with tunable luminescence and considerable thermal- and photostabilities.

Full text of DOI:10.1021/acs.organomet.6b00298

Article
pubs.acs.org/Organometallics
Modular Synthesis of Diarylalkynes and Their Efficient Conversion
into Luminescent Tetraarylbutadienes
†
§
†
†
†
Olena Shynkaruk, Yanyu Qi, Aiden Cottrell-Callbeck, William Torres Delgado, Robert McDonald,
†
,§
,†
Michael J. Ferguson, Gang He,* and Eric Rivard*
†
Department of Chemistry, University of Alberta, 11227 Saskatchewan Drive, Edmonton, Alberta, Canada T6G 2G2
§
Frontier Institute of Science and Technology, Xi’an Jiaotong University, Xi’an, Shaanxi Province 710054, People’s Republic of China
S Supporting Information
*
ABSTRACT: A series of electronically distinct symmetrical
diarylalkynes were prepared via a general Suzuki−Miyaura cross-
coupling protocol. These alkynes underwent zirconium-mediated
coupling to yield zirconacycles that afford new tetraaryl-1,3-
butadienes upon subsequent protonolysis; these butadienes display
deep blue or green emission and represent promising building
blocks for light-emitting devices. The presented synthetic pathway
allows access to new libraries of molecular light emitters with
tunable luminescence and considerable thermal- and photo-
stabilities.
INTRODUCTION
Scheme 1. Selected Examples of Diarylalkyne Synthesis
■
Diarylalkynes are important precursors for the synthesis of
1
,2
3
4
olefins, ketones, fused organic heterocycles as well as
functional inorganic heterocycles such as luminescent benzo-
5
6
7
fused heteroles, Te/B heterocycles, π-conjugated systems,
8
9
10
spirocycles, vinyl cations, arylalkene polymers, and materials
with a broad range of biological activities (e.g., 5-
azoindoles) and nonlinear optical properties.
1
1
1
2
13
In general, the most common route to yield diarylalkynes is
Sonogashira coupling: the palladium-catalyzed coupling of aryl
14
or alkenyl halides (or triflates) with terminal alkynes. Recent
developments in the Sonogashira methodology include nano-
particle-catalyzed, ligand-free, and/or metal-free coupling, as
well as photocatalyzed and microwave-assisted reactions in
1
4c
water.
Despite the common use of Sonogashira coupling to form
symmetric diarylalkynes, there are some drawbacks including
limitations in aryl halide substrate scope when using protected
1
5
acetylenes and the multistep nature of known protocols,
leading to low overall yields. In order to overcome these
1
5,16
17
limitations Lee
and others focused attention on the
development of decarboxylative alkyne coupling, where
propiolic acid is used as an alkyne source (Scheme 1). Other
methods of diarylalkyne synthesis (some of which are outlined
In this paper we report the coupling of the easily prepared
24
diborylethyne synthon PinBCCBPin (1) with various aryl
bromides in a general palladium-catalyzed Suzuki−Miyaura
cross-coupling reaction to construct symmetric diarylalkynes in
moderate to high yields (Scheme 2). Advantages of this
methodology include a timesaving one-pot procedure (i.e.,
reduction of workup and purification steps compared to the
Sonogashira method) and the use of commercially available aryl
1
8
in Scheme 1) include sila-Sonogashira coupling, 2S0 tille
8
c,19
coupling,
the use of organoaluminum alkyne or
21
alkynylsilanol reagents, the platinum-catalyzed alkynylation
2
2
23
of aryl iodides, and Suzuki−Miyaura cross-coupling. In the
latter method, Sun’s group employed a successful multistep
synthesis using boronic acids and thermally unstable acetylene
iodides as coupling partners to obtain unsymmetrical alkynes
Received: April 13, 2016
2
3b
(
Scheme 2).
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.6b00298
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Organometallics
Article
Scheme 2. Synthesis of Diarylalkynes Using Suzuki−Miyaura
Cross-Coupling
in the Supporting Information). In each trial, compound 1 was
dissolved in either THF or DMF (0.12 M solutions), and 6
equiv of oven-dried K PO was added. Upon the microwave
3
4
heating of 1/K PO in THF at 70 °C for 40 min, compound 1
3
4
30
completely decomposed into the bis-boryloxide PinBOBPin
and hydroxide HO-BPin; the same reaction carried out in DMF
gave only HOBPin as a boron-containing product. In addition,
heating 1/K PO to reflux in THF for 36 h led to partial
3
4
1
11
decomposition of 1 (11% according to H and B NMR
spectroscopy) into PinBOBPin. One possible explanation for
the formation of protodeboronation products with K PO
3
4
under seemingly nonaqueous conditions is the presence of
residual water in the potassium phosphate, despite prior heating
at 170 °C for 2 days. When 1 and CsF (2 equiv) were heated in
a microwave reactor to 70 °C for 40 min in THF, similarly
rapid protodeboronation to yield HOBPin transpired. Not
surprisingly, the use of aqueous potassium carbonate (6 equiv)
as a base under the same microwave reaction conditions
converted 1 into hydroxide HOBPin. These trials effectively
show that protodeboronation is a reaction that will compete
with C−C bond formation during Suzuki−Miyaura cross-
coupling, leading to some reduction in yield of the target
diarylalkyne (vide infra).
bromides as substrates. The resulting diarylalkynes can also be
used to prepare tetraaryl-substituted 1,3-butadienes that exhibit
color tunable luminescence and valuable solid-state emission
2
5,26
properties.
Accordingly our current study represents an
efficient general synthetic methodology for accessing a wide
library of luminogens.
RESULTS AND DISCUSSION
■
Synthesis of Diarylalkynes via Suzuki−Miyaura Cou-
pling. This project began with an evaluation of the stability of
24
the diborylethyne reagent 1 to base-induced pinacolboronate
BPin) cleavage, termed protodeboronation, as this is a
common side reaction during Suzuki−Miyaura cross-cou-
We chose 4-bromoisopropylbenzene as a substrate for cross-
(
coupling optimization trials, as the target diarylalkyne
i
i
2
7
(4- PrC H )CC(C H Pr-4) (2) could only be previously
6
4
6
4
pling. In order to minimize reaction time, microwave
irradiation was applied with compound 1 dissolved in either
predried THF or freshly distilled DMF (as these solvents
readily absorb microwave irradiation). When DMF solutions of
31
prepared via challenging multistep procedures. The catalytic
system Pd (dba) /XPhos (dba = dibenzylideneacetone) was
32
2
3
explored under different conditions, starting from microwave
heating at 100 °C for 20 min and up to 140 °C for 40 min in
different solvents (Table 1). The best isolated yield of 2
1
were heated to 100 °C for 20 min, compound 1 was
28
completely converted into the known hydroxide HOBPin (as
confirmed by multinuclear NMR spectroscopy), indicating the
likely presence of residual water in the DMF. Upon careful
examination of the protodeboronated product mixture, the
(
Scheme 3) was 55% and arose when a Pd (dba) −XPhos−
2
3
K PO precatalyst/ligand/base system was employed with
3
4
microwave heating to 140 °C for 40 min in THF. The
analogous reactions in DMF or toluene did not yield any
product. In the case of DMF, the complete protodeboronation
of 1 transpired, while in toluene, no reaction occurred, as
toluene is known to be a poor absorber of microwave
29
known alkyne HCCBPin could not be detected, suggesting
that the alkyne unit was eliminated as acetylene. In contrast, a
THF solution of PinBCCBPin (1) does not undergo
decomposition, even after prolonged heating in the microwave
reactor to 140 °C for 40 min; while under the same microwave
3
3
radiation. Interestingly, use of a THF/H O (3:1) solvent
2
i
conditions, 1 in a 3:1 THF/H O mixture completely converted
combination gave the desired product (4- PrC )CC-
(C H Pr-4) (2) in a 30% isolated yield after purification by
6 4
6
H
4
2
i
into HOBPin, indicating the key role of water in protodeboro-
nation.
column chromatography, while on the other hand a DMF/H O
2
Next we evaluated the effect of added base on the stability of
(3:1) solvent medium did not lead to the formation of 2, with
1
under microwave-assisted reaction conditions (see Table S2
only protodeboronation transpiring. Overall the microwave-
Table 1. Optimization of Reaction Conditions to Synthesize Compound 2
a
b
entry
catalyst, mol % of Pd
Pd (dba) , 2
ligand, mol %
base, equiv
K PO , 6
solvent
THF
temperature (°C)
time (min)
purified yield, %
1
2
3
4
5
6
7
8
9
XPhos, 8
XPhos, 8
XPhos, 8
XPhos, 8
XPhos, 8
XPhos, 8
XPhos, 8
100
100
100
140
140
140
140
140
140
140
140
20
20
40
40
40
40
40
40
40
40
40
24
31
35
55
0
2
3
3
4
Pd (dba) , 2
K PO , 6
DMF
THF
2
3
3
4
Pd (dba) , 2
K PO , 6
3 4
2
3
Pd (dba) , 2
K PO , 6
THF
2
3
3
4
Pd (dba) , 2
K PO , 6
DMF
Toluene
THF
2
3
3
4
Pd (dba) , 2
K PO , 6
0
2
3
3
4
Pd (dba) , 2
K CO (aq), 6
0
2
3
2
3
t
Pd (dba) , 2
H Bu PBF , 8
K CO (aq), 6
THF
0
2
3
3
4
2
3
t
Pd (dba) , 2
H Bu PBF , 8
K CO (aq), 6
DMF
0
2
3
3
4
2
3
1
0
1
Pd (dba) , 2
XPhos, 8
K PO , 6
THF:H O = 3:1
33
0
2
3
3
4
2
1
Pd (dba) , 2
XPhos, 8
K PO , 6
DMF:H O = 3:1
2
3
3
4
2
a
K PO was dried in an oven at 170 °C for 48 h before use; a 2.0 M aqueous solution of K CO was freshly prepared and degassed prior to use.
3
4
2
3
b
THF was obtained from a Grubbs-type solvent purification system, and DMF was stirred overnight over CaH (5% w/v), filtered, and then freshly
2
distilled from CaSO and stored over molecular sieves.
4
B
DOI: 10.1021/acs.organomet.6b00298
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Scheme 3. Synthesis of the Symmetric Diarylalkynes 2−5
repeatedly the best isolated yields of analytically pure
bis(thienyl)alkynes 3 and 4 (40% and 51% yield, respectively)
after column chromatography. We also prepared the symmetric
alkyne 5 containing capping triphenylamine (TPA) groups due
to the use of TPA units to achieve two-photon absorption and
35
enhanced hole transport properties in optoelectronics. The
diarylalkynes 2−5 were obtained as very pure materials in ca.
3
0−50% yield after column chromatography; however one can
rapidly obtain alkynes 2, 3, and 5 in >90−95% purity
1
(
according to H NMR) by simply washing the crude alkynes
2
, 3, and 5 with Et O, leading to enhanced isolated yields of
2
7
3% (2), 40% (3), and 60% (5).
The structures of alkynes 2 and 5 were confirmed by single-
crystal X-ray crystallography (Figures S1 and 1, respectively)
assisted trial reactions summarized in Table 1 helped us to
identify a suitable solvent (THF) for future explorations.
In order to effectively scale up the reaction between 4-
bromoisopropylbenzene and PinBCCBPin (1), conventional
heating in refluxing THF for 36 h was applied with different
catalyst/base combinations examined. Specifically we explored
Pd catalysts that were commonly used in Suzuki−Miyaura
cross-coupling while using 6 equiv of K PO base in relation to
3
4
3
4a
1.
The Pd(OAc) /XPhos (1:4 ratio; 2 mol % of Pd) mixture
2
afforded pure 2 in a 40% isolated yield, which is comparable to
the yield obtained with the Pd (dba) /XPhos combination
2
3
mentioned above (35% isolated yield of 2; 2 mol % of Pd).
However, the use of 2 mol % of Pd(PPh ) as a catalyst gave 2
in a much lower isolated yield of 20% (Table 2). In addition,
3
4
Figure 1. Thermal ellipsoid plot (30% probability) of compound 5
with hydrogen atoms omitted for clarity; a crystallographic inversion
center (1/2, 0, 1/2) lies at the midpoint of the C(1)−C(1A) bond.
Selected bond lengths (Å) and angles (deg): C(1)−C(1A) 1.198(2),
C(1)−C(2) 1.4336(15).
the Pd(OAc) /XPhos catalyst combination when mixed with 2
2
equiv of CsF relative to 1 in THF afforded the target alkyne 2
34b
in an isolated yield of 40%. In order to facilitate the handling
of the reagents, we chose to use the air-stable precatalyst
Pd(OAc) in future coupling reactions instead of the air-
2
sensitive Pd (dba) . To investigate the effect of the Pd(OAc) /
and afforded expected metrical parameters; for example, the
CC bond lengths in 2 and 5 are the same within
experimental error [1.196(3) and 1.198(2) Å, respectively].
Tetraaryl-1,3-butadiene Synthesis. The preparation of
arylated 1,3-dienes has received somewhat limited attention in
2
3
2
XPhos/K PO mixture on the stability of 1, a THF solution of
3
4
1
in the presence of Pd(OAc) /XPhos (1:4 ratio; 2 mol % of
2
Pd) and K PO (6 equiv) was heated to reflux for 36 h, leading
3
4
to partial decomposition (ca. 40%) of 1 into PinBOBPin; this
represents a slight increase in protodeboronation when
compared to heating 1 with 6 equiv of K PO in the absence
26b,c
the literature,
despite their novel reversible mechanochro-
mic properties (i.e., changing emission color in response to
3
4
of Pd(OAc) /XPhos (only 11% decomposition occurred).
external mechanical stimuli) and occasionally high fluorescence
2
26a
To further investigate the developed synthetic procedure, the
thiophene-substituted acetylenes 3 and 4 were prepared
according to the conditions presented in Scheme 3 and in
Table S5 of the Supporting Information. After slight variations
in the catalytic loadings and reaction times, we found that a
quantum yields in the solid state. Scheme 4 outlines the
overall procedure used to prepare the symmetric tetraaryl-1,3-
butadienes 7a, 7b, and 8 reported in this paper. To begin, the
i
cumyl-substituted zirconacycle Cp ZrC (4- PrC H ) 6a and
2
4
6
4 4
the previously reported tetrathiophene zirconacycle 6b
32
reaction mixture with a 1:4 ratio of the Pd(OAc) precatalyst to
(Cp ZrC T ; T = 2-thienyl) were obtained by combining 2
2
2 4 4
the XPhos ligand in THF that is refluxed for 36 h gave
equiv of the alkynes 2 and 3 each with in situ generated “Cp Zr”
2
Table 2. Catalyst and Base Screening Trials for the Synthesis of 2 in Refluxing THF
a
b
entry
catalyst, mol % of Pd ligand, mol % base, equiv solvent, time refluxed (h)
purified yield, %
1
2
3
4
5
6
7
8
9
Pd (dba) , 2
XPhos, 8
XPhos, 8
XPhos, 8
K PO , 6
THF, 36
THF, 36
THF, 36
THF, 36
THF, 36
THF, 18
THF, 36
THF, 18
THF, 36
35
40
40
20
15
2
3
3
4
Pd(OAc) , 2
K PO , 6
3 4
2
Pd(OAc) , 2
CsF, 2
2
Pd(PPh ) , 2
K PO , 6
3
4
3
4
Pd(PPh ) , 2
CsF, 2
3
4
K PO , 6
9% decomp of 1 into O(BPin)2
11% decomp of 1 into O(BPin)2
33% decomp of 1 into O(BPin)2
40% decomp of 1 into O(BPin)2
3
4
K PO , 6
3
4
(no 4-bromoisopropylbenzene added)
(no 4-bromoisopropylbenzene added)
Pd(OAc) , 2
XPhos, 8
XPhos, 8
K PO , 6
3 4
2
Pd(OAc) , 2
K PO , 6
3 4
2
a
b
K PO and CsF were dried in an oven at 170 °C for 48 h before use. THF was obtained from a Grubbs-type purification system.
3
4
C
DOI: 10.1021/acs.organomet.6b00298
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Scheme 4. Synthetic Route to the 1,3-Butadienes 7a/b and
Structures of the Known Analogues 9−11
hexanes solution of the reaction products through a silica gel
plug. Compound 7a was obtained as a white solid (57% yield)
after further washing with hexanes, while compound 7b was
isolated as a yellow solid (40% yield) after washing the crude
material with cold (−35 °C) Et O. Both the cumyl-substituted
2
butadiene 7a and the thiophene-capped analogue 7b yielded
crystals of suitable quality for X-ray analysis, and their
respective structures are found as Figures 3 and 4. As in the
Figure 3. Thermal ellipsoid plot (30% probability) of compound 7a
with selected hydrogen atoms omitted for clarity; remaining hydrogen
atoms presented with arbitrarily small thermal parameters. Only the
major orientation of the disordered isopropyl groups is shown.
Selected bond lengths (Å) and angles (deg): C(1)−C(2) 1.347(3),
C(2)−C(3) 1.477(3), C(3)−C(4) 1.347(3); C(2)−C(3)−C(4)
121.07(17), C(1)−C(2)−C(3) 121.70(17).
n
36a
(
made from Cp ZrCl /2 BuLi) in THF. The new zircona-
2 2
cycle 6a was isolated as an air- and moisture-sensitive red solid
in a high yield of 90%, and its structure was determined by
single-crystal X-ray crystallography (Figure 2). The average
Figure 4. Thermal ellipsoid plot (30% probability) of compound 7b
with selected hydrogen atoms omitted for clarity; remaining hydrogen
atoms presented with arbitrarily small thermal parameters. Only the
major orientation of the disordered thienyl groups is shown. A
crystallographic inversion center (1/2, 0, 1/2) lies at the midpoint of
the C(1)−C(1A) bond. Selected bond lengths (Å) and angles (deg):
C(1)−C(1A) 1.477(2), C(1)−C(2) 1.351(2), C(2)−C(3)
Figure 2. Thermal ellipsoid plot (30% probability) of compound 6a
with hydrogen atoms omitted for clarity; only one molecule of the two
in the asymmetric unit is shown. Selected bond lengths (Å) and angles
1
1
.4489(19); C(2)−C(1)−C(1A) 121.31(15), C(1)−C(1A)−C(2A)
21.31(15).
(
deg) with metrical parameters for the second molecule in the
asymmetric unit are listed in square brackets: Zr−C(1) 2.269(2)
[
[
[
2.259(3)], Zr−C(4) 2.267(3) [2.259(3)], C(1)−C(2) 1.363(4)
1.369(4)], C(2)−C(3) 1.489(3) [1.494(3)], C(3)−C(4) 1.366(3)
1.368(4)]; C(1)−Zr−C(4) 77.50(9) [78.27(9)].
previously characterized tetratolyl-1,3-butadiene 9 and tetra-
26b,c
phenyl-1,3-butadiene 11 (Scheme 4),
one of the four aryl
rings in compound 7a (containing C(41), Figure 3) is nearly
coplanar with the butadiene core (dihedral angle of 4°), while
the remaining rings are twisted from the diene unit by 34.9°,
67°, and 87.5°. Due to the significant twisting of the aryl groups
and the presence of sterically encumbered isopropyl groups in
7a, there is a lack of substantial intermolecular π−π stacking;
however significant intermolecular aryl---(H−C)aryl contacts
are present (as short as 2.46 Å). In the case of 7b, the two
terminally positioned thienyl groups are only slightly twisted
from the butadiene core by 8.8°, while the two remaining
thienyl rings are arranged in a nearly perpendicular fashion.
Although the TPA-functionalized butadiene 8 could be
Zr−C bond lengths in the five-membered ZrC ring in 6a are
4
2
.264(4) Å and in accordance with the reported Zr−C bond
37
lengths in pinacolboronate-functionalized zirconacycles. The
cumyl groups adjacent to the Cp Zr unit are twisted from the
2
five-membered zirconacycle core by 55.80(6)° and 58.25(8)°,
while the remaining cumyl-based rings are also canted by
5
5.80(8)° and 54.90(9)° to yield an overall propeller
arrangement of the four cumyl groups in 6a.
Conversion of the zirconacycles 6a and 6b into the target
1
,3-butadienes 7a and 7b with exclusive cis−trans−cis geo-
metries of the appended aryl groups was readily accomplished
by adding an excess of HCl in Et O (Scheme 4). The Cp ZrCl
obtained using the zirconium source “Cp Zr” (generated from
2
n
Cp ZrCl /2 BuLi in situ), it could also be obtained via a slightly
2
2
2
2
2
byproduct was effectively removed by filtration of a CH Cl /
different one-pot procedure starting from the thermally stable
2
2
D
DOI: 10.1021/acs.organomet.6b00298
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Article
36b
26c
and isolable Cp Zr source Cp Zr(pyridine)(Me SiCCSiMe )
of for sensing applications. When 8 is dissolved in THF,
2
2
3
3
(
Scheme 4). Specifically, Cp Zr(pyridine)(Me SiCCSiMe )
blue-green emission is observed (λemis = 472 nm, Φ
=
2
3
3
absolute
and 2 equiv of (TPA)CC(TPA) 5 were combined in THF
to yield a red solution containing the zirconacycle
Cp ZrC (TPA) , which was reacted in situ with an excess of
34.6%, τ = 2.1 ns); however in the film state there is a
substantial red-shift in λemis to 516 nm, corresponding to bright
green emission (Figure 6). As a comparison, the relative
2
4
4
HCl to give crude 8 as an orange solid. The resulting product
contained Cp ZrCl byproduct as well as unreacted 5; thus
2
2
additional purification by multiple washes with cold (−30 °C)
Et O, followed by washing with acetone at room temperature,
2
was required to afford pure 8 as a bright yellow solid in a 26%
yield. Unfortunately, we have not been able to obtain crystals of
8
of suitable quality for single-crystal X-ray crystallographic
analysis.
Optical Properties of the Tetraaryl-1,3-butadienes 7a,
b, and 8. Tetraarylbutadienes are an emerging class of solid-
7
state emitters with high photoluminescence quantum yield;
thus the optical properties of 7a, 7b, and 8 were studied in
more detail. Compounds 7a and 7b undergo a drastic change
from a nonemissive state in THF solution to highly emissive
aggregated states in THF/H O mixtures when the water
2
Figure 6. Normalized PL excitation and emission spectra of 8 with λex
content exceeded 60% v/v and 80% v/v, respectively; this effect
=
423 nm in THF and λex = 423 nm in the film state.
25
is termed aggregation-induced emission and was previously
26
observed for butadienes 9−11. The fluorescence emission
quantum yield of the TPA-containing butadiene 10 (Scheme 4)
spectra of 7a/b in THF/H O are presented in Figures 5 and
2
in THF (Φ = 4.7%; λ = 545 nm) is about 7-fold lower as in
emis
8
; thus the added TPA units and overall steric bulk in 8 appear
26a
to hinder nonradiative decay pathways. Similarly to 5 and
1
26a
0, the UV/vis spectrum of 8 shows absorption peaks at 305
and 380 nm in THF (Figure S30); however in line with the
dramatic changes in emission data in the solid state, the longer
wavelength absorption is red-shifted by ca. 30 nm to 410 nm;
thus aggregation triggers enhanced conjugation within 8. The
aggregation behavior of compound 8 is very different compared
to the butadienes 7a/b and 9−11, which do not show a change
in photoluminescence color upon aggregation, but rather only
26
an enhancement of emission intensity. Under UV irradiation
8
undergoes a change from blue emission in pure THF (λemis
=
4
72 nm) to green (λemis = 505 nm) when the water
composition exceeds 60% v/v (Figure 7), in line with
aggregation promoting restricted intramolecular motion and
enhanced conjugation in 8.
The solid-state emission spectra for the butadienes 7a,b and
8 were recorded from amorphous films (with amorphous
Figure 5. Photoluminescence spectra of 7a in different THF/water
ratios (listed as % water content). Inset: Emission intensity of 7a as the
THF/water ratio is altered. Inset photo: Aggregates under UV light
−4
(λex = 365 nm); [7a] = 10 M.
S34 in the Supporting Information. In addition, compound 7a
emits a bright blue color in the solid state (λemis = 426 and 463
nm) due to the restricted rotation of the peripheral cumyl
groups (Figure S32). As a comparison, bright green photo-
luminescence (λemis = 506 nm) is noted in the solid state for 7b
with a spectral tail that extends to ca. 650 nm (Figure S33).
Given the emissive nature of unsaturated compounds bearing
TPA substituents, we decided to investigate the luminescence
of the alkyne 5 and its 1,3-butadiene derivative 8. In agreement
35b
with previously reported emission data for 5 in CHCl3,
alkyne 5 displays blue emission in THF when irradiated at 267
and 322 nm (λemis = 413 nm, Φ = 79.7%; Figure S31);
absolute
however this emission maxima is slightly blue-shifted when
compared to that in CHCl , where λ = ca. 430 nm. The
3
emis
relative quantum yield of 5 (vs quinine sulfate in 1.0 N H SO )
2
4
38
is lower within predicted error than its absolute quantum
yield and is presented in the Experimental Section. The 1,3-
butadiene analogue 8 shows a change of luminescence color
upon aggregation, which one could conceivably take advantage
Figure 7. Photoluminescence spectra of 8 in different THF/water
ratios (listed as % water content). Inset: Aggregates under UV light
−4
(λex = 365 nm); [8] = 10 M.
E
DOI: 10.1021/acs.organomet.6b00298
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
character confirmed by X-ray powder diffraction; Figure S35).
Compounds 5, 7a, 7b, and 8 all show fluorescence in the solid
state according to the lifetimes found: 2.4, 1.0, 1.2, and 2.1 ns,
respectively. The 1,3-butadiene analogue 7a has the highest
absolute quantum yield of 24.8% in the solid state, while the
thiophene-capped analogue 7b and alkyne 5 have similarly low
quantum yields of 1.5% and 1.7%. Even though in solution the
quantum yield of 8 was higher than that of 10 (Φ = 34.6%
versus 4.7%), in the solid state 8 has quantum yield of 10.7%,
while the previously reported TPA-substituted butadiene 10
has a solid-state photoluminescence quantum yield of
Thermal stability is another important parameter to consider
when selecting emitters for full-color displays. The onset of
thermal decomposition (5% weight loss, T ) of compounds 7a/
d
b and 8 was evaluated under nitrogen using thermal gravimetric
analysis (Figure 9). The TPA-functionalized butadiene 8 has
2
6c,39
40.1%.
Given the lack of X-ray data for 8, it is difficult
to provide a convincing reason for the reduced fluorescence
efficiency of 8 in the solid state.
Photooxidation and Thermal Stability of Function-
alized Tetraaryl-1,3-butadienes. To determine how the
incorporation of cumyl, thienyl, or triphenylamine groups
within a butadiene framework affects the photostability, thin
amorphous films of 7a/b and 8 were irradiated under air. In
−3
each photostability trial, 30 μL of a 2.0 × 10 M THF solution
of the butadiene was drop-casted onto a glass slide, and each
experiment was conducted in triplicate under aerobic
conditions (see Figures 8, S36, and S37). To the best of our
Figure 9. TGA thermograms of 7a, 7b, and 8 measured under N2
(scan rate = 10 °C/min).
the highest thermal stability (T = 401 °C) in the series,
d
followed by the cumyl-substituted butadiene 7a (T = 267 °C)
d
and thienyl analogue 7b (T = 241 °C). This trend is mirrored
d
by the precursor diarylalkynes 2−5 (Figure S41), albeit with
lower thermal stabilities. The most thermally stable diarylalkyne
is (TPA)CC(TPA) (5), with a T of 206 °C, followed by the
d
cumyl-substituted alkyne 2 (T = 186 °C) and the thiophene-
d
appended alkyne 3 (T = 118 °C). Surprised by the low
d
apparent decomposition temperature of (2-thienyl)CC(2-
thienyl) (3), we measured its melting point in a sealed capillary
tube under a nitrogen atmosphere and found that this
compound melts at 97−100 °C without any decomposition;
notable discoloration started at 175 °C, and the melt became
dark brown at 230 °C. Based on the DSC measurements under
a nitrogen atmosphere, the alkyne 3 melts at 97−100 °C (in
agreement with melting point data) and decomposes at 179 °C;
thus 118 °C is the temperature at which 5% weight loss is most
likely due to the evaporation of the alkyne. Compound 3 was
also heated in refluxing toluene (ca. 110 °C) for 24 h with no
sign of decomposition; such a result is important, as this alkyne
is being increasingly used as a reagent in the chemical
community, for instance in the preparation of conducting and
Figure 8. Time dependence of the fluorescence emission intensity of a
−3
drop-cast thin film of 7b (from 30 μL of a 2.0 × 10 M THF
solution) upon exposure to a 65 W xenon lamp in air. Film distance
from lamp was 130 cm.
knowledge, this is the first example of such a study for tetraaryl-
substituted 1,3-butadienes and helps identify candidates for the
development of LEDs that work without substantial encapsu-
33
fluorescent polymers.
Compounds 7a/b also yielded dramatic weight losses (up to
4
0
lation. After drop-casting, the resulting amorphous films of
a, 7b, and 8 were irradiated in air with a 65 W xenon lamp
95%) when subjected to TGA under N (Figure 9). Upon
2
7
heating from ambient temperature to 800 °C, the onset of
thermal decomposition/weight loss for 7a/b and 8 was found
at 230, 271, and 308 °C. The melting points of these species
were extracted from DSC data and afforded values of 209, 218,
and 274 °C, respectively (Figures S45−S47), in agreement with
those measured in sealed capillary tubes. Compound 7a also
found within our fluorimeter. The resulting I/I ratios were
0
derived from the recorded photoluminescence intensity at the
emission wavelength, λmax. The cumyl (4-isopropylbenzene)-
substituted butadiene 7a showed rapid degradation with 50%
retention of emission intensity (I/I = 0.50) after 23 min of
o
exposure (Figure S36); the TPA-functionalized butadiene 8
retains half of the initial photoluminescence (PL) intensity after
showed a crystallization temperature (T ) of 130 °C, which
c
emerged upon cooling of the melt. To test possible
decomposition, compounds 7a/b and 8 where subjected to
repeated heating and cooling cycles in the DSC to temperatures
ca. 10 °C above noticeable melting events; the weight loss after
these measurements was negligible (<2%), excluding the
evaporation of butadienes 7a/b and 8 during heating. It was
found that the cumyl-capped butadiene 7a has a stable melt, as
1
6 min of exposure (Figure S37). The thiophene-appended
41
butadiene 7b shows considerably enhanced photostability
relative to 7a and 8, with a 50% reduction in PL after 75 min of
sustained exposure to the xenon lamp (Figure 8). A decrease of
the emission intensity due to degradation of the butadienes was
also verified by UV/vis spectroscopy (Figures S38−S40).
F
DOI: 10.1021/acs.organomet.6b00298
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
noted by reoccurring melting/recrystallization after the first
cycle. In contrast, recrystallization and melting were not
observed after the first heating for compounds 7b and 8, thus
confirming their decomposition upon melting. Thus, the weight
loss in 7a noted during TGA could be due to evaporation
hexanes, 75 mmol). Then 2.25 mL (25 mmol) of trichloroethylene in
2
5 mL of Et O was added dropwise over 15 min with stirring. After the
2
addition was completed, the cooling bath was removed immediately
and the resulting pale yellow mixture was stirred overnight to give a
white slurry. The mixture containing dilithioacetylide was then
transferred via cannula to a precooled (−78 °C) solution of 2-
isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (10 mL, 49 mmol)
(which is rapid above 230 °C), while in 7b decomposition
occurs upon melting.
in Et O (100 mL), followed by stirring at −78 °C for 4 h. Next the
2
mixture was warmed to room temperature and stirred for 4 h. The
reaction mixture was then cooled to −78 °C, 20 mL of HCl (4.0 M in
dioxane, 80 mmol) was added, and the flask was stirred for 3 h at room
temperature. The LiCl precipitate was allowed to settle, and the
supernatant was filtered through a pad of Celite. The volatiles were
then removed from the filtrate under reduced pressure to give 1 as a
brown semisolid, which was washed with cold pentane (2 × 10 mL;
−30 °C) to give 1 as an air-stable, light beige powder (5.195 g, 75%).
CONCLUSIONS
■
We have developed a general synthetic protocol to yield
diarylalkynes and functionalized tetraaryl-1,3-butadienes via
sequential Suzuki−Miyaura and zirconium-mediated alkyne
coupling. Altering the nature of the peripheral substituents
appended to the butadiene unit leads to blue or green
photoluminescence in the solid state. Future work will involve
incorporating these emissive units into polymeric structures for
the fabrication of mechanically robust LEDs.
The corresponding 1H and C{ H} NMR spectral data in C D
13
1
6
6
24
1
matched those reported previously by the Therien group. H NMR
400 MHz, CDCl ): δ 1.25 (s, 24H, CH ). C{ H} NMR (100 MHz,
1
3
1
(
3
3
11
1
CDCl ): δ 84.7 (C(CH ) ), 24.6 (CH ). B{ H} NMR (160 MHz,
3
3
2
3
CDCl ): δ 23.3 (br).
3
EXPERIMENTAL SECTION
Materials and Instrumentation. All reactions were performed
using standard Schlenk and glovebox (MBraun) techniques under a
nitrogen atmosphere. Solvents were all dried and degassed using a
Synthesis of 1,2-Bis(4-isopropylphenyl)ethyne (2). Compound 1
1.00 g, 3.60 mmol), 4-bromoisopropylbenzene (1.09 mL, 7.20
■
(
mmol), K PO (4.58 g, 21.6 mmol), palladium(II) diacetate (0.016 g,
3
4
0
.072 mmol), and 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbi-
4
2
phenyl (XPhos) (0.137 g, 0.288 mmol) were mixed in a 100 mL
Grubbs-type solvent purification system manufactured by Innovative
Technology, Inc., and stored under an atmosphere of nitrogen prior to
use. 4-Bromoisopropylbenzene was obtained from TCI America,
palladium(II) diacetate and zirconocene dichloride were from Strem
Chemicals Inc., 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
was from Oakwood Chemicals, and pyridine was from Caledon
Laboratory Chemicals; all other chemicals were obtained from Aldrich.
Commercially obtained chemicals were used as received except for
pyridine (pyr), which was freshly distilled under nitrogen from
flask under N . Degassed THF (20 mL) was then added, and the
2
mixture was stirred for 30 min at room temperature (for catalyst
4
7
activation). The flask was then immersed in a preheated oil bath, and
the solvent was refluxed for 36 h. Afterward the reaction mixture was
cooled to room temperature, poured into 100 mL of water, and
extracted with 30 mL of chloroform. The organic layer was washed
with 100 mL of water and 2 × 100 mL of brine. The aqueous fractions
were combined and extracted with 20 mL of chloroform, and the
organic layer was washed with 2 × 100 mL of brine. Then all
43
potassium hydroxide. Bis(cyclopentadienyl)zirconium(2,3,4,5-tetra-
3
2
combined organic fractions were dried over MgSO . The solvent was
removed in vacuo, and the residue was purified by column
chromatography (silica gel, ethyl acetate:hexanes = 1:20, R = 0.74)
to give 2 as a light yellow solid (0.417 g, 44%). X-ray quality colorless
crystals were obtained upon recrystallization from ethyl acetate/
hexanes at room temperature. In addition, the crude mixture can also
be purified by washing with cold (−30 °C) diethyl ether (2 × 4 mL)
to yield 2 as a pale brown solid (1.003 g of 1 gives 0.687 g of 2, 73%
(
2-thienyl)methanide) (Cp ZrC T ),
Cp Zr(pyr)(Me SiC
4
2
4
4
2
3
4
4
45
CSiMe ), 2-bromo-3-hexylthiophene, and 4-bromotriphenyl-
amine were prepared according to literature procedures. H, C-
H}, and B{ H} NMR spectra were recorded on a Varian DD2MR-
3
4
6
1
13
f
1
11
1
{
1
13
1
4
00 spectrometer and referenced externally to SiMe ( H, C{ H})
4
11
1
and F B·OEt ( B{ H}). Elemental analyses were performed by the
3
2
Analytical and Instrumentation Laboratory at the University of
Alberta. Mass spectrometry were performed using a MS-50G system
Kratos Analytical). Melting points were obtained in sealed glass
1
yield, ca. 95% purity; see Figures S7 and S8). The corresponding H
(
NMR spectral data matched those reported previously in the
capillaries under nitrogen using a MelTemp melting point apparatus
and are uncorrected. UV/vis measurements were recorded using a
Varian Cary 300 Scan spectrophotometer. The fluorescence measure-
ments were conducted on a Photon Technology International (PTI)
MP1 fluorescence system. All relative solution quantum yields were
measured in comparison to quinine sulfate in 1 N H SO as a
standard, assuming a quantum yield of 0.55. Photoluminescence
lifetimes were measured on a time-correlated single-photon-counting
fluorescence spectrometer (Edinburgh Instruments FLS920) using an
EPL-375 ps pulsed diode laser with vertical polarization (70.3 ps pulse
width) as an excitation source; absolute quantum yields were measured
with an integrating sphere system within the same fluorescence
spectrometer. The X-ray powder diffraction patterns were collected on
an Inel diffractometer equipped with a curved position-sensitive
3
1
1
literature. TGA: Tdec = 186 °C. H NMR (400 MHz, CDCl ): δ
3
3
3
7
2
1
1
.46 (d, J = 7.9 Hz, 4H, ArH), 7.21 (d, J = 8.0 Hz, 4H, ArH),
HH HH
3
3
.92 (sept, J = 6.9 Hz, 2H, CH(CH ) ), 1.26 (d, J = 6.9 Hz,
2H, CH3). C{ H} NMR (100 MHz, CDCl ): δ 149.1, 131.6, 126.5,
HH
3
2
HH
1
3
1
3
20.9 (Ar-C), 88.9 (−CC−), 34.1 (CH(CH ) ), 23.9 (CH ). HR-
3
2
3
2
4
38a
MS (EI): m/z 262.1721; C H calcd 262.1722. Anal. Calcd (%) for
20 22
C H : C, 91.55; H, 8.45. Found: C, 90.73; H, 8.54.
20 22
Synthesis of 1,2-Bis(thiophen-2-yl)ethyne (3). In a 100 mL flask,
compound 1 (1.00 g, 3.60 mmol), 2-bromothiophene (731 μL, 7.56
mmol), K PO (4.58 g, 21.6 mmol), palladium(II) diacetate (0.016 g,
3
4
0
.072 mmol), and 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbi-
phenyl (XPhos) (0.137 g, 0.288 mmol) were mixed. Degassed THF
20 mL) was then added, and the mixture was stirred for 30 min at
(
4
7
detector (CPS 120) and a Cu Kα radiation source. Thermogravi-
room temperature (for catalyst activation). Then the flask was
inserted in a preheated oil bath, and the solvent was refluxed for 36 h.
Afterward the reaction mixture was cooled to room temperature,
poured into 100 mL of water, and extracted with 30 mL of chloroform.
The organic layer was washed with 100 mL of water and 2 × 100 mL
of brine. The aqueous fractions were combined and extracted with 20
mL of chloroform, and the organic fractions were washed with 2 × 100
mL of brine. Then all combined organic fractions were dried over
1
metric analysis was performed under a nitrogen atmosphere on a
PerkinElmer Pyris 1 TGA. Differential scanning calorimetry measure-
ments were conducted under a nitrogen atmosphere on a PerkinElmer
Pyris 1 DSC. Microwave reactions were performed using a Biotage
Initiator Classic microwave reactor (Biotage, LLC, Charlotte, NC,
USA). Photobleaching experiments on films were performed with a
PTI MP1 fluorescence system (xenon lamp, 65 W).
Synthesis of 1,2-Bis(4′,4′,5′,5′-tetramethyl[1′,3′,2′]dioxaborolan-
MgSO . The solvent was removed in vacuo, and the residue was
4
2
′-yl)ethyne (1). This compound was synthesized according to a
purified by column chromatography (silica gel, hexanes, R = 0.35) to
give 3 as a pale yellow solid (0.275 g, 40%). In addition, the crude
residue can also be purified by washing with cold (−30 °C) diethyl
f
2
4
modification of a known procedure. To a 100 mL 1:1 mixture of
n
THF and Et O at −78 °C was added a solution of BuLi (2.5 M in
2
G
DOI: 10.1021/acs.organomet.6b00298
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
ether (2 × 4 mL) to yield 3 as a dark brown solid (0.999 g of 1 gives
ns. Fluorescence emission (film) (λex = 380 nm): λemis = 424 nm.
Lifetime (film): τ = 2.4 ns. Absolute quantum yield (film) = 1.7%. The
optical data matched those previously reported. HR-MS (EI): m/z
0.274 g of 3, 40% yield, ca. 95% purity; Figures S8 and S9). The
1
13
1
35b
corresponding H and C{ H} NMR spectral data matched those
15,48
1
reported previously in the literature.
NMR (400 MHz, CDCl ): δ 7.31 (dd, J = 5.1 Hz, J = 1.1 Hz,
H, ThienylH), 7.29 (dd, JHH = 3.7 Hz, JHH = 1.2 Hz, 2H,
ThienylH), 7.02 (dd, J = 5.1 Hz, J = 3.7 Hz, 2H, ThienylH).
TGA: Tdec =4 179 °C. H
512.2239; C H N calcd 512.2252. Anal. Calcd (%) for C H N : C,
38
28
2
38 28
2
3
89.03; H, 5.51; N, 5.46. Found: C, 88.27; H, 5.37; N, 5.43.
Synthesis of Bis(cyclopentadienyl)zirconium(2,3,4,5-tetra(4-
isopropylphenyl)methanide) (6a). To a solution of Cp ZrCl
2
3
HH
HH
3
4
2
3
4
HH
HH
2
1
3
1
C{ H} NMR (100 MHz, CDCl ): δ 132.1, 127.6, 127.2, 122.9
(0.183 g, 0.63 mmol) in THF (10 mL) at −78 °C was added
3
n
(
Thienyl-C), 86.3 (−CC−). HR-MS (EI): m/z 189.9915; C H S
dropwise a solution of BuLi (0.49 mL, 2.5 M solution in hexanes, 1.2
10
6 2
calcd 189.9911. Anal. Calcd (%) for C H S : C, 63.12; H, 3.18; S,
mmol). After the reaction mixture was stirred at −78 °C for 1 h, a
solution of 2 (0.328 g, 1.25 mmol) in THF (10 mL) was added at −78
°C. The temperature was allowed to rise to room temperature, and the
mixture was stirred for another 24 h. The solvent was removed under
reduced pressure, the product was extracted with 15 mL of toluene,
and the resulting extract was filtered through Celite. The volatiles were
then removed from the filtrate under reduced pressure to give 6 as a
red powder (0.420 g, 90%). This compound was recrystallized from
hexanes at −35 °C to yield red crystals that were of suitable quality for
10
6 2
3
3.70. Found: C, 63.28; H, 3.13; S, 33.64.
Synthesis of 1,2-Bis(3-hexyl-2-thienyl)ethyne (4). Compound 1
1.013 g, 3.64 mmol), 2-bromo-3-hexylthiophene (1.892 g, 7.65
mmol), K PO (4.642 g, 21.8 mmol), palladium(II) diacetate (0.016 g,
(
3
4
0
.073 mmol), and 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbi-
phenyl (XPhos) (0.139 g, 0.292 mmol) were mixed in a 100 mL
flask under N . Degassed THF (20 mL) was then added, and the
2
mixture was stirred for 30 min at room temperature (for catalyst
47
1
activation) and then heated to reflux for 36 h. Afterward the reaction
mixture was cooled to room temperature, poured into 100 mL of
water, and extracted with 30 mL of chloroform. The organic layer was
washed with 100 mL of water and 2 × 100 mL of brine. The aqueous
fractions were combined and extracted with 20 mL of chloroform, and
X-ray crystallography. Mp: 119−124 °C (dec). H NMR (400 MHz,
3
C
D
): δ 6.95 (two overlapping doublets, 8H, ArH), 6.73 (d, JHH
=
6
6
3
8.1 Hz, 4H, ArH), 6.71 (d, JHH = 8.1 Hz, 4H, ArH), 6.07 (s, 10H,
3
3
CpH), 2.66 (sept, JHH = 6.9 Hz, 2H, CH(CH
)
), 2.50 (sept, JHH
), 0.99 (d,
): δ 194.2,
=
3
2
3
6.9 Hz, 2H, CH(CH
)
2
), 1.11 (d, JHH = 6.9 Hz, 12H, CH
). C{ H} NMR (100 MHz, C
3
3
3
13
1
the CHCl layer was washed with 2 × 100 mL of brine. Then all
J
HH = 6.9 Hz, 12H, CH
3
6
D
6
3
combined organic fractions were dried over MgSO . The solvent was
146.3, 144.8, 143.3, 142.9, 139.6, 131.2, 127.8, 125.9, 125.0 (Ar-C),
112.1 (Cp), 33.81, 33.78 (CH(CH ) ), 24.2, 24.0 (CH ). UV/vis
4
removed in vacuo, and the residue was purified by column
3
2
3
3
−1
−1
chromatography (silica gel, petroleum ether, R = 0.62) to give 4 as
(THF): λmax (ε) = 374 nm (6.78 × 10 mol L cm ). HR-MS
(MALDI): m/z 744.3271; C H Zr calcd 744.3284. Anal. Calcd (%)
f
1
13
1
a pale yellow oil (0.667 g, 51%). The corresponding H and C{ H}
50
54
NMR spectral data matched those reported previously in the
for C H Zr: C, 80.48; H, 7.29. Found: C, 79.93; H, 7.50.
50
54
3
3,49
1
3
literature.
H NMR (400 MHz, CDCl ): δ 7.20 (d, J = 5.2
Synthesis of cis,cis-1,2,3,4-Tetrakis(4-isopropylbenzene)-1,3-bu-
tadiene (7a). To a solution of 6a (0.421 g, 0.56 mmol) in 15 mL of
3
HH
3
Hz, 2H, ThienylH), 6.91 (d, J = 5.2 Hz, 2H, ThienylH), 2.78 (t,
HH
3
JHH = 7.7 Hz, 4H, Thienyl-CH ), 1.66−1.72 (m, 4H, Thienyl-
Et O was added a solution of HCl (0.9 mL, 2.0 M solution in Et O, 1.8
2
2
2
CH (CH ) -CH ), 1.33−1.42 (m, 12H, Thienyl-CH (CH ) -CH ),
mmol). The red color of 6a immediately disappeared to give a yellow
slurry. The mixture was stirred for 12 h at room temperature, and then
the solvent was removed under vacuum. The residue was dissolved in a
2
2
4
3
2
2
4
3
3
13
1
0
.92 (t, J = 7.1 Hz, 6H, Thienyl-(CH ) -CH ). C{ H} NMR
HH 2 5 3
(
(
(
3
100 MHz, CDCl ): δ 147.6, 128.3, 126.1, 118.4 (Thienyl-C), 88.0
3
−CC−), 31.7, 30.4, 29.7, 29.1, 22.7 (Thienyl-(CH ) -CH ), 14.1
2:1 CH Cl /hexanes solvent mixture (5 mL) and filtered through a 1
2 2
2
5
3
Thienyl-(CH ) -CH ). HR-MS (EI): m/z 358.1785; C H S calcd
cm plug of silica gel. The solvent was removed from the filtrate, and
the resulting solid (0.220 g, 74%) was washed with hexanes (2 × 5
mL) to yield 7a as a white solid (0.168 g, 57%). The product was
crystallized from hexanes at −35 °C to give X-ray quality colorless
2
5
3
22 30 2
58.1789. Anal. Calcd (%) for C H S : C, 73.69; H, 8.43; S, 17.88.
22
30 2
Found: C, 73.92; H, 8.39; S, 17.48.
Synthesis of 1,2-Bis(triphenylamine)ethyne (5). In a 100 mL flask,
compound 1 (1.015 g, 3.65 mmol), 2-bromo-3-hexylthiophene (2.412
g, 7.44 mmol), K PO (4.737 g, 22.3 mmol), palladium(II) diacetate
1
crystals of 7a. Mp: 198−201 °C. TGA: Tdec = 267 °C. H NMR (400
3
3
MHz, CDCl ): δ 7.29 (d, JHH = 8.1 Hz, 4H, ArH), 7.24 (d, JHH = 8.1
3
4
3
3
3
(
0.017 g, 0.074 mmol), and 2-dicyclohexylphosphino-2′,4′,6′-triiso-
Hz, 4H, ArH), 6.89 (d, JHH = 8.1 Hz, 4H, ArH), 6.66 (d, JHH = 8.1
3
propylbiphenyl (XPhos) (0.142 g, 0.298 mmol) were mixed. Degassed
THF (20 mL) was then added, and the mixture was stirred for 30 min
Hz, 4H, ArH), 6.24 (s, 2H, CH−), 3.00 (sept, JHH = 6.9 Hz, 2H,
3
3
CH(CH
)
), 2.76 (sept, JHH = 6.9 Hz, 2H, CH(CH
)
), 1.35 (d, JHH
3
2
3
2
47
3
13
1
at room temperature (for catalyst activation) and then heated to
reflux for 36 h. Afterward the reaction mixture was cooled to room
temperature, poured into 100 mL of water, and extracted with 30 mL
of chloroform. The organic layer was washed with 100 mL of water
and 2 × 100 mL of brine. The aqueous fractions were combined and
extracted with 20 mL of chloroform, and the organic layer was washed
with 2 × 100 mL of brine. Then all combined organic fractions were
= 6.9 Hz, 12H, CH
NMR (100 MHz, CDCl
130.2, 129.5, 126.8, 125.9 (Ar-C), 34.0, 33.7 (CH(CH
3
), 1.16 (d, JHH = 6.9 Hz, 12H, CH
3
). C{ H}
): δ 147.8, 147.2, 145.2, 137.6, 135.1, 131.2,
3
)
2
), 24.2, 23.8
3
4
−1
−1
(CH ). UV/vis (THF): λ (ε) = 327 nm (3.06 × 10 mol L cm ),
3
max
4
−1
−1
4
−1
339 nm (3.49 × 10 mol L cm ), and 356 nm (2.38 × 10 mol
L
−
1
cm ). UV/vis (film): λ = 331, 346, and 367 nm. Fluorescence
max
emission (film) (λex = 380 nm): λemis = 426 and 463 nm. Lifetime
(film): τ = 1.0 ns. Absolute quantum yield (film) = 24.8%. HR-MS
dried over MgSO . The solvent was removed in vacuo, and the residue
4
was purified by column chromatography (silica gel, hexanes/CH Cl =
(EI): m/z 526.3597; C H calcd 526.3600. Anal. Calcd (%) for
2
2
40 46
8
:2, R = 0.38) to give 5 as a pale yellow solid (0.572 g, 31%). Slow
C H : C, 91.20; H, 8.80. Found: C, 91.26; H, 9.01.
40 46
f
evaporation of a solution of 5 in 8:2 hexanes/CH Cl2 at room
temperature resulted in the formation of colorless crystals of X-ray
Synthesis of cis,cis-1,2,3,4-Tetrakis(2-thienyl)-1,3-butadiene (7b).
To a solution of 6b (0.202 g, 0.34 mmol) in 10 mL of THF was
2
3
2
quality (0.286 g, 15%). The crude mixture can also be purified by
added a solution of HCl (0.54 mL, 2.0 M solution in Et O, 1.09
2
washing with Et O (2 × 15 mL) to yield 5 as a light brown solid of ca.
mmol). The red color of 6b immediately disappeared to give a yellow
slurry. The mixture was stirred for 12 h at room temperature, and the
solvent was removed under vacuum; the pale yellow residue was then
dissolved in dichloromethane (5 mL) and filtered through a 1 cm plug
2
9
0% purity in 60% yield (1.015 g of 1 gives 1.116 g of 5; see Figure
1
S17). TGA: T = 206 °C. H NMR (400 MHz, CDCl ): δ 7.38 (d,
dec
3
3
JHH = 8.6 Hz, 4H, ArH), 7.29−7.31 (m, 8H, ArH), 7.07−7.14 (m,
2H, ArH), 7.03 (d, J = 8.6 Hz, 4H, ArH). C{ H} NMR (100
3
13
1
1
of silica gel with a CH Cl /hexanes = 2:1 solvent mixture (30 mL).
2 2
HH
MHz, CDCl ): δ 147.7, 147.3, 132.4, 129.4, 124.9, 123.5, 122.6, 116.7
The solvent was removed from the filtrate, and the product was
3
(
Ar-C), 88.9 (−CC−). UV/vis (THF): λ (ε) = 301 nm (4.02 ×
washed with cold (−35 °C) Et O (5 mL) to yield 7b as a bright yellow
max
2
4
−1
−1
4
−1
−1
1
1
0 mol L cm ) and 369 nm (6.65 × 10 mol L cm ). UV/vis
solid (0.051 g, 40%). Mp: 198−200 °C. TGA: T = 241 °C. H NMR
dec
3
4
(film): λmax = 312 and 367 nm. Fluorescence emission (THF) (λex
=
(400 MHz, CDCl ): δ 7.62 (dd, J = 5.1 Hz, J = 1.1 Hz, 2H,
3 HH HH
3
4
2
67, 322 nm): λemis = 413 nm. Fluorescence quantum yield: Φ = 48%,
ThienylH), 7.25 (dd, J = 5.1 Hz, J = 3.4 Hz, 2H, ThienylH),
HH HH
7.13 (dd, J = 5.0 Hz, J = 1.1 Hz, 2H, ThienylH), 7.05 (dd, J
3
4
3
relative to quinine sulfate in 1.0 N H SO . Absolute quantum yield
2
4
HH HH
HH
HH
THF): Φ = 79.7%. Lifetime (1 × 10− M solution in THF): τ = 1.4
5
= 3.4 Hz, J = 1.1 Hz, 2H, ThienylH), 6.85 (dd, J = 3.7 Hz, J
HH HH
4
3
4
(
H
DOI: 10.1021/acs.organomet.6b00298
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3
=
1.3 Hz, 2H, ThienylH), 6.80 (dd, J = 3.6 Hz, 4JHH = 0.7 Hz, 2H,
Cambridge CB2 1EZ, UK; fax: +44-1223/336-033; e-mail:
deposit@ccdc.cam.ac.uk).
HH
13
1
ThienylH), 6.73 (s, 2H, CH−). C{ H} NMR (100 MHz, CDCl ):
3
δ 140.9, 137.8, 134.3, 130.0, 129.3, 128.2, 128.1, 128.0, 127.8, 126.2.
4
UV/vis (THF): λ (ε) = 350, 367, and 387 nm (2.65 × 10 , 3.61 ×
max
ACKNOWLEDGMENTS
4
4
−1
−1
1
4
0 and 2.81 × 10 mol L cm ). UV/vis (film): λ = 364, 384, and
■
max
10 nm. Fluorescence emission (film) (λex = 383 nm): λem = 506 nm.
This work was supported by Natural Sciences and Engineering
Research Council (NSERC) of Canada (Discovery and
CREATE grants to E.R.), the Canada Foundation for
Innovation, and Alberta Innovates-Technology Futures (New
Faculty Award to E.R.). E.R. also thanks the Faculty of Science
at the University of Alberta for a Research Fellowship (2015-
2020). A.C. received support from the Women in Scholarship,
Engineering, Science and Technology program. We are also
grateful to Prof. Yu Fang (Key Laboratory of Applied Surface
and Colloid Chemistry, Shaanxi Normal University) for his
assistance with optical measurements. We are also very grateful
to Dr. Wayne Moffat for useful discussions.
Lifetime (film): τ = 1.2 ns. Absolute quantum yield (film) = 1.5%. HR-
MS (EI): m/z 381.9979; C H S calcd 381.9978. Anal. Calcd (%) for
C H S : C, 62.79; H, 3.69; S, 33.52. Found: C, 62.76; H, 3.70; S,
2.98.
Synthesis of cis,cis-1,2,3,4-Tetrakis(4-triphenylamine)-1,3-buta-
diene (8). Compound 5 (0.316 g, 0.62 mmol) and Cp Zr(pyr)
20
14 4
20
14 4
3
2
44
(
Me SiCCSiMe ) (0.145 g, 0.31 mmol) were dissolved in 10 mL
3
3
of THF, and the resulting mixture was allowed to stir for 12 h to give a
dark red solution. A solution of HCl (0.6 mL, 2.0 M solution in Et O,
.2 mmol) was added followed by stirring for 12 h at room
temperature, resulting in an orange mixture. The solvent was removed
under reduced pressure, and the residue was washed with cold Et O (2
2
1
2
×
5 mL, −35 °C) and then acetone (3 × 5 mL) to yield 8 as a bright
1
yellow solid (0.083 g, 26%). Mp > 250 °C. TGA: T = 401 °C. H
dec
3
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■
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HH
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(
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(
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1
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AUTHOR INFORMATION
■
Corresponding Authors
E-mail (G. He): ganghe@mail.xjtu.edu.cn. Tel: +86
8591980278.
E-mail (E. Rivard): erivard@ualberta.ca. Tel: +1 (780) 492-
255.
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Notes
The authors declare no competing financial interest.
CCDC reference numbers 1472248 (2), 1472249 (5), 1472250
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supplementary crystallographic data for the X-ray studies
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DOI: 10.1021/acs.organomet.6b00298
Organometallics XXXX, XXX, XXX−XXX