Acetylene-expanded dendralene segments with exotopic phosphaalkene units

Article abstract of DOI:10.1002/chem.201101358

Bis-TMS protected C,C-diacetylenic phosphaalkene (A₂PA) 1 (Mes*P=C(C=CTMS)₂; Mes=2,4,6-tBu₃Ph) has been used as a building block for the construction of butadiyne-expanded dendralene fragments in which phosphaalkenes feature as exotopic double bonds. Treatment of 1 with CuCl gives rise to a Cu^I acetylide that is selectively formed at the acetylene trans to the Mes* group. The cis-TMS-acetylene engages in similar chemistry, albeit at higher temperatures and longer reaction times. The differentiation between the two acetylene termini of 1 allows for the controlled synthesis of the title compounds by a variety of different Cu- and Pd-catalyzed oxidative acetylene homo- and heterocoupling protocols. Crystallographic characterization of A₂PA 1 and dimeric Mes*P=C(C=CR¹)C₄(R²C=C)C=PMes* (3 b, R¹=R²=Ph; 6, R¹=R²=TMS), and 10 (R¹=R²=C=CPh) verifies that the stereochemistry across the P=C bond is conserved during the coupling reactions, whereas spectroscopic evidence reveals cis/trans isomerization in an iodo-substituted A₂PA intermediate 4 (Mes*P=C(C=CTMS)(C=CI). UV/Vis spectroscopic and electrochemical studies reveal that efficient π conjugation operates through the entire acetylenic phosphaalkene framework, even in the cross-conjugated dimeric structures. The P centers contribute considerably to the frontier molecular orbitals of the compounds, thereby leading to smaller HOMO-LUMO gaps than in all-carbon-based congeners. Phenyl- and/or ethynylphenyl substituents at the A₂PA framework influence the HOMO and LUMO to a varying degree depending on their relationship to the Mes* group, thus enabling a fine-tuning of the frontier molecular orbitals of the compounds.

Full text of DOI:10.1002/chem.201101358

FULL PAPER
DOI: 10.1002/chem.201101358
Acetylene-Expanded Dendralene Segments with Exotopic Phospha
Units
ACHTUNGTRNEaNUNG lkene
Xue-Li Geng and Sascha Ott*[a]
Abstract: Bis-TMS protected C,C-diac-
etylenic phosphaalkene (A2PA)
(Mes*P=C
(CꢀCTMS)2; Mes*=2,4,6-
catalyzed oxidative acetylene homo-
and heterocoupling protocols. Crystal-
lographic characterization of A2PA 1
N
R
1
ACHTUNGTRENNUNG
tBu3Ph) has been used as a building
block for the construction of buta-
diyne-expanded dendralene fragments
in which phosphaalkenes feature as
exotopic double bonds. Treatment of 1
with CuCl gives rise to a CuI acetylide
that is selectively formed at the acety-
lene trans to the Mes* group. The
cis-TMS-acetylene engages in similar
chemistry, albeit at higher tempera-
tures and longer reaction times. The
differentiation between the two acety-
lene termini of 1 allows for the con-
trolled synthesis of the title compounds
by a variety of different Cu- and Pd-
and dimeric Mes*P=CACHTUNGTRENNUNG
A
6, R1 =R2 =TMS), and 10 (R1 =R2 =
CꢀCPh) verifies that the stereochem-
istry across the P=C bond is conserved
during the coupling reactions, whereas
spectroscopic evidence reveals cis/trans
isomerization in an iodo-substituted
A2PA intermediate
4
(Mes*P=C-
Keywords: carbon-rich compounds ·
conjugation · dendralenes · oxida-
tive acetylene coupling · phospha-
a fine-
AHCTUNGTRENGNaUN lkenes
Introduction
tween structurally defined molecular chemistry and polymer
science.
Highly unsaturated linear, two- or three-dimensional com-
pounds with acetylene or ethylene subunits are appealing
for a myriad of different applications such as organic semi-
conductors, organic components in (opto)electronic devices,
or as sensor materials.[1,2] Despite having been a popular
field of research over the last decades,[3–13] the underlying
fundamental research on well-defined oligoacetylenes and
-vinylenes continues to fascinate chemists to date.[14–16] From
a structural viewpoint, one may divide the compounds into
those that contain arene moieties like oligo-phenylacety-
lenes or -vinylenes[14,17,18] or structures in which the p system
exclusively consists of acetylene and/or vinylene units, the
latter sometimes being referred to as “acetylenic scaffold-
ing.”[19,20] Many of these systems have reached an impressive
maturity, with elaborate systems approaching the effective
conjugation length of polymers, thereby bridging the gap be-
The incorporation of main-group elements other than
carbon into the p conjugates provides the possibility to alter
the electronic properties of the structures and to allow for
postsynthetic manipulations such Lewis acid coordination or
oxidations.[21,22] In the case of oligo-phenylacetylenes and
-vinylenes, the constituting arenes can formally be replaced
relatively easily by other heteroaromatic units such as pyri-
dines, thiophenes, and others.[1,2,11,23] The introduction of
heteroatoms in the form of higher alkenes as surrogates of
traditional alkenes has been explored to a much lesser
extent, despite the advantages in terms of lower HOMO–
LUMO gaps and polarizability that are offered by this strat-
egy.[24–26] The first oligo-phenylethylene analogues that fea-
ture disilenes,[27–29] phosphaalkenes,[30,31] and diphos-
phenes[32,33] instead of classical C=C bonds have emerged in
the literature only recently. The reason for the sporadic
presence of such structures is caused by a shortage of syn-
thetic protocols that allow for their preparation as well as
the general instability of higher element p bonds. The intro-
duction of heteroatoms into purely acetylenic scaffolds is
even more in its infancy. We have recently reported the in-
corporation of phosphaalkenes into acetylenic frameworks
to form acetylenic phosphaalkenes (AxPA, x=number of
acetylene substituents),[34–36] an effort that has now also been
extended into group 12 elements with the report of a disi-
[a] Dr. X.-L. Geng, Prof. S. Ott
Department of Photochemistry and Molecular Science
ꢀngstrçm Laboratories, Uppsala University
Regementsvagen 1, Box 523, 75120 Uppsala (Sweden)
Fax : (+)018-471-6844
E-mail: sascha.ott@fotomol.uu.se
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201101358.
Chem. Eur. J. 2011, 17, 12153 – 12162
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12153

lene analogue of (E)-enediyne by Sato et al.[37] The ultimate
goal of our program is to establish access to all geminal and
P,C-A2PAs and to use them as building blocks for the prepa-
ration of larger oligomeric, polymeric, and cyclic structures
of, for example, type I and II, the all-carbon analogues of
which are well-established entities with intriguing proper-
ties.[38,39]
tive acetylene homocoupling under the classical Eglinton
conditions (MeOH, py, Cu
(OAc)2; py=pyridine)[42] afforded
AHCTUNGTRENNUNG
the dimeric product 3a in good yield (Scheme 1).[41] When a
mixture of 2a and 2b was used in the experiment, only 2a
reacted and 2b remained unchanged. The work thus indicat-
ed that desilylation of the two TMS-acetylenes in 2a and 2b
proceeds at different rates—an encouraging finding as it po-
tentially enables site-selective
reactions and the controlled as-
sembly of elaborate structures.
The TMS-acetylene trans to the
Mes* group is more reactive,
presumably due to an addition-
al steric protection of the TMS
group cis to the very bulky, ad-
jacent Mes*.
The first incentive of the cur-
rent work was thus to find syn-
thetic protocols to deprotect
the less reactive TMS-acetylene
cis to the Mes* and to engage
In this paper, we scrutinize the viability of this concept
and present an in-depth investigation of C,C-A2PAs that
engage in oxidative acetylene homo- and heterocoupling re-
actions. The synthesis, crystallographic, spectroscopic, and
electrochemical characterization of the first acetylene-ex-
panded dendralene fragments in which the exotopic C=C
double bonds have been replaced by P=C units is presented.
Results and Discussion
C,C-A2PA 1 is a promising building block for the construc-
tion of elaborate structures such as I and II due to the pres-
ence of the TMS groups that can presumably be removed
under mild conditions similar to what has been shown for
ene-1,1-diynes.[40] Single-crystal X-ray analysis of compound
1 (Figure 1) shows that the aromatic ring of the Mes* group
is almost perpendicular to the plane defined by P1-C1-C2-
C3-C4-C5 (hereafter referred to as the PC5 subunit). The in-
terplanar angle of 87.18 basically prevents all p conjugation
between the Mes* and PC5 subunits. In addition, the Mes*
ring resides on top of the TMS-acetylene that is cis relative
to the P=C double bond, thus leaving the trans-TMS-acety-
lene rather exposed. This feature suggests that the two TMS
groups may potentially be removed selectively, thereby ena-
bling a high degree of control in subsequent coupling
chemistry of the terminal acetylenes.
Figure 1. Molecular structure of A2PA 1 (35% probability ellipsoids). All
hydrogen atoms are omitted for clarity. Selected bond lengths [ꢀ] and
À
À
À
À
angles [8]: C1 C2 1.187(8), C2 C3 1.454(7), C3 C4 1.413(7), C4 C5
À
À
1.214(7), C3 P1 1.717(5); P1 C6 1.859(4); C2-C3-C4 117.5(4), C2-C3-P1
116.9(3), C4-C3-P1 125.6(4), C3-P1-C6 101.7(2), C4-C5-Si1 177.5(4). Di-
hedral angle [8]: Mes* aromatic ring to P1-C1-C2-C3-C4-C5 87.1(4).
the thus-formed terminal acetylene in coupling reactions. A
simple increase in reaction time and temperature using the
conditions described for the synthesis of 3a led to the con-
sumption of 2b, but did not result in the formation of isola-
ble amounts of desired product. Inspired by a report by
Mori and co-workers,[43,44] we attempted the direct transfor-
mation of the TMS-protected alkyne to a copper(I) acety-
lide by treating 2b with equimolar amounts of CuCl in
DMF. This protocol circumvents the use of K2CO3 and other
nucleophiles that we believe to promote decomposition.
Using these conditions, we were delighted to find that the
TMS group cis to the Mes* was removed at slightly elevated
temperatures, thereby forming a red Cu acetylide that is
Developing mild desilylation strategy for TMS-protected
C,C-A2PA and suitable oxidative acetylene coupling proto-
cols: In a previously reported paper, we could demonstrate
for the first time that the strategy to assemble larger struc-
tures from A2PA building blocks may indeed by viable.[41]
One-pot in situ deprotection of 2a with K2CO3 and oxida-
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Dendralene Segments
FULL PAPER
acetylene termini are rotated
out of their respective PC5
plane by 24.48, further decreas-
ing the conjugation level. In
contrast, the phenyl groups in
3a (Figure 2, top) are almost
coplanar with the plane of two
PC5 systems and deviate by
only 6.68.[41]
Encouraged by the synthesis
of 3b, we explored the Pd/
CuCl-catalyzed cross-coupling
of 2b with phenylacetylene.
Employing an excess amount of
phenylacetylene (5 equiv) in
the presence of [PdACTHNUTRGNEUNG(PPh3)2Cl2]
and 2 equiv of CuCl in DMF/
THF/N,N-diisopropylethyl-
amine (DIEA) (10:2:1) gave
dissatisfying results as the cou-
pling proceeded very slowly at
358C, and decomposition of
starting material dominated at
higher temperatures. The fail-
Scheme 1. Desilylation and coupling reactions on TMS-protected C,C-A2PA 2b; cis and trans are relative to
the 2,4,6-tBu3Ph (Mes*) substituent. Conditions: a) K2CO3, Cu
b) [Pd(PPh3)2Cl2], CuCl, air, DMF/THF, 388C, 2 h, 3b 87%. c) i) CuCl, DMF/THF, 408C, 1–2 h; ii) I2, RT, 1 h.
d) Phenylacetylene, [Pd(PPh3)2Cl2], CuCl, DIEA, DMF/THF, RT, 3–5 h, 5 71% (2 steps, 5a 27%, 5b 73%). ure is at least partially caused
ACHTUNGRTEN(NUNG OAc)2, MeOH, pyridine, 1 h, 208C, 3a 68%.
ACHTUNGTRENNUNG
G
by a difference in reactivity of
the CuI acetylide of 2b relative
available for subsequent coupling reactions. Unfortunately,
employing the Cu acetylide of 2b under customary Hay ho-
mocoupling conditions (CuCl, N,N,N’,N’-tetramethylethyle-
nediamine (TMEDA), O2) resulted either in no reaction or
decomposition. If CuCl and TMEDA were added in equi-
molar amounts, the reaction does not occur because Cu–
TMEDA will not lead to the formation of the Cu acetylide
of 2b. If CuCl is added in excess amount or before the addi-
tion of TMEDA, the Cu acetylide is formed; however, it de-
composes rapidly due to the presence of TMEDA and O2.
Mild and efficient homocoupling conditions were found
to that of the phenylacetylene, which, however, ought to be
similar for a heterocoupling to occur. To avoid unwanted
homocoupling reactions and the depletion of a coupling
partner in the reaction mixture, a differentiation of the two
reaction partners was desired. The selective heterocoupling
between a haloacetylene and a terminal acetylene similar to
what is achieved in the Cadiot–Chodkiewicz protocol,[46] and
a modified version using Pd catalysis was considered suita-
ble.[47] We therefore turned to synthesize the iodo-substitut-
ed A2PA 4 by quenching the Cu acetylide of 2b with I2
(Scheme 1c). The reaction is accompanied by a color change
from reddish-brown to reddish-yellow, and the appearance
of a new yellow spot on the TLC plates. NMR spectroscopic
analysis reveals the formation of two products with 31P
chemical shifts at d=341.6 (4a) and 342.8 ppm (4b). Nei-
ther of the products contains TMS groups, nor 1H NMR
spectroscopic signals in the diagnostic acetylene region that
point towards the formation of two isomers of 4. It thus
seems that the activation barrier for cis/trans isomerization
in iodo-acetylene 4 is lower than that in 2b and its Cu acety-
lide. The interconversion proceeds at ambient temperature
and can be followed by 31P NMR spectroscopy (Figure 3),
which shows that the steady-state equilibrium between 4a/
4b of 2:1 is reached after about 12 h.
when [PdACHTUNGTRENNUNG(PPh3)2Cl2] was added to an aerated solution of
the Cu acetylide of 2b in DMF/THF, thereby affording the
dimeric phosphaalkene 3b in 87% yield (Scheme 1b).[45] It
is interesting to note that the formation of the Cu acetylide
and its subsequent Pd-mediated coupling proceeds without
any isomerization across the P=C double bond, even though
the isomer in which the phenyl group is cis to Mes* can be
assumed to be thermodynamically more favorable.[41]
Single-crystal X-ray analysis of 3b illustrates the cis rela-
tionship between the butadiyne (C2’-C1’-C1-C2) and the
Mes* rings, thus verifying that the stereochemistry across
the P=C bond in compound 2b is conserved during the ho-
mocoupling reaction (Figure 2, bottom). The two bulky
Mes* rings of 3b reside above/under the butadiyne vector
and are almost orthogonal (91.18) to the planes defined by
their respective monomeric PC5 subunits. These two factors
lead to a solid-state conformation in which the two PC5
planes are twisted by an angle of 43.68, thus preventing effi-
cient p conjugation. Moreover, the phenyl groups at the
Iodo-substituted 4a,b possess limited stability, which once
more suggests a one-pot procedure for the preparation of
5a,b. Thus, when the crude reddish-yellow solution of 4a,b
was transferred directly into a suspension of phenylacety-
lene in DMF/THF/DIEA (10/1/1) in the presence of catalyt-
ic amounts (5 mol%) of [PdACHTUNGRTNEUNG(PPh3)2Cl2] and CuCl, 5a and
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12155

X.-L. Geng and S. Ott
Figure 3. Transformation of 4b (5 mm, CDCl3, 208C) to 4a. Shown are
the 31P NMR spectroscopic signals d=341.6 (4a) and 342.8 ppm (4b).
focus was turned to the bis-TMS-protected A2PA 1, that is,
the building block for I and II. Since 1 features a TMS-acet-
ylene trans to the Mes* group that resembles the situation
in 2a, synthesis of dimeric 6 was attempted by applying the
Eglinton procedure that was used for the formation 3a.
Much to our disappointment, complete decomposition of
bis-TMS A2PA 1 was observed within one hour under these
conditions. The phenyl substituent at the second, rather
remote and cross-conjugated acetylene in 2a is thus a crucial
factor that stabilizes reaction intermediates and enables the
synthesis of 3a under these conditions. Changing to modi-
fied, non-basic Hay coupling conditions (CuCl, air, DMF) to
avoid decomposition, A2PA 1 underwent oxidative homo-
coupling and up to 81% of desired dimeric 6 was obtained
by adding 15 equivalents of CuCl into the reaction within
8 h. The most reliable route for the synthesis of dimer 6 was
found when 1 in DMF was treated with CuCl and PdII, and
6 was obtained in almost quantitative yield within one hour
at room temperature (Scheme 2a). The procedure is the
same as described above for the preparation of 3b. Whereas
in the latter case, the reaction can only proceed at one acet-
ylene, it is noteworthy that in the case of 1, selectivity is ach-
ieved by the faster deprotection rate of the acetylene trans
to the Mes* group.
The solid-state structure of 6 (Figure 4) reveals that the
acetylene homocoupling of 1 proceeds as expected at the
sterically more exposed acetylene trans to the Mes* group.
The dimerization does not significantly alter the structural
features of the monomeric units. The Mes* groups in dimer-
ic 6 are still almost perpendicular to their respective PC5
planes with an interplanar angle of 87.48 (87.18 for mono-
mer 1). In addition, the two PC5 subunits are almost copla-
nar, being twisted only by 6.88, thereby allowing good conju-
gation between the two halves of the molecule. It is interest-
ing to note that the Si atom of the TMS group in compound
Figure 2. Molecular structure of phosphaalkene 3b (bottom) (35% prob-
ability ellipsoids). All hydrogen atoms are omitted for clarity. Selected
À
À
À
bond lengths [ꢀ] and angles [8]: C1 C1’ 1.374(5), C1 C2 1.206(6), C2
À
À
À
À
C3 1.425(5), C3 C4 1.442(6), C4 C5 1.214(6), C5 C6 1.440(6), C3 P1
À
1.719(4), P1 C7 1.846(4); C2-C3-P1 122.9(4), C2-C3-C4 120.4(4), C4-C3-
P1 116.6(3), C3-P1-C7 101.34(17). Dihedral angle [8]: C7 Mes* aromatic
ring to P1-C1-C2-C3-C4-C5 91.1(3), P1-C1-C2-C3-C4-C5 to P1’-C1’-C2’-
À
À
C3’-C4’-C5ꢂ 43.6(2), C6 Phenyl ring to P1-C1-C2-C3-C4-C5 24.4(3). The
molecular structure of 3a is included for comparison (top).[41]
5b are obtained in an overall yield of 71% from 2b
(Scheme 1d). Compounds 5a,b are the first examples of
APAs that have been realized through an oxidative hetero-
coupling reaction. It is noteworthy that the ratio of 4a and
4b determines the product distribution, thereby indicating
that no further cis/trans isomerization across the P=C bond
occurs under the coupling conditions. The two butadiyne-
substituted 5a and 5b can be separated by careful column
chromatography and their stereochemistry identified by
1H NMR spectroscopy. Whereas the ortho-phenyl protons at
the acetylene terminus cis to Mes* in 5a resonate at
d=6.86 ppm on account of the additional shielding above
the aromatic Mes* group, the signal of the corresponding
proton in 5b features at d=7.53 ppm.
Reactions with bis-TMS A2PA 1: Having established mild
conditions for the in situ desilylation of the less reactive
TMS-acetylene and for the subsequent coupling steps, our
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Dendralene Segments
FULL PAPER
be inapplicable to the A2PAs
because of their incompatibility
with secondary amine. In seek-
ing neutral and mild conditions,
it was found that Scott and co-
workers described a modified
Cadiot–Chodkiewicz conditions
for the synthesis of polydiacety-
lenes by coupling separately
prepared copper(I) acetylides
with bromoalkynes in pyri-
dine.[50] With slight modifica-
tions to these conditions, A2PA
1 was converted to its Cu acety-
lide by the continuous addition
of an excess amount of CuCl in
degassed DMF at room temper-
ature over 5 min, followed by
quenching with a solution of an
Figure 4. Molecular structure of 6 (35% probability ellipsoids). All hydrogen atoms are omitted for clarity. Se-
À
À
À
À
lected bond lengths [ꢀ] and angles [8]: C1 Si1 1.8437(18), C1 C2 1.209(2), C2 C3 1.429(2), C3 C4 1.422(2),
À
À
À
À
C4 C5 1.209(2), C5 C6 1.362(2), P1 C3 1.7170(17), P1 C11 1.8426(16); C2-C1-Si1 169.27(16), C1-C2-C3
175.83(17), C3-P1-C11 102.10(8), C2-C3-C4 116.82(14), C2-C3-P1 125.94(12), C4-C3-P1 117.22(12). Dihedral
À
angle [8]: C11 Mes*aromatic ring to P1-C1-C2-C3-C4-C5 87.40(2), P1-C1-C2-C3-C4-C5 to P2-C6-C7-C8-C9-
C10 6.80(10).
6 was found to bend 118 away from the acetylenic chain of
C1-C2-C3 to minimize the steric repulsion between Mes*
and TMS group. This bending is significantly bigger than
that observed for 1 (2.58).
The rate of Cu acetylide formation of the acetylene trans
to Mes* in 1 is similar to that of the trans acetylene in 2a,
thus enabling the synthesis of unsymmetrically terminated 7.
Compound 7 is the first report of a dimeric A2PA that stems
from an oxidative acetylene heterocoupling. The 31P NMR
spectrum of 7 features a pair of doublets at d=348.5 and
356.3 ppm due to the presence of chemically different P=C
excess amount of phenylethynyl iodide in degassed pyridine
(Scheme 2c), thereby affording 8 in 52% overall yield based
on A2PA 1. The same protocol can be used a second time
on compound 8 to afford the bis- butadiyne-substituted
phosphaalkene 9 (Scheme 2d). However, the direct synthesis
of 9 from 1 by heating the reaction to 35–408C results in
very low yields of 9. The homocoupling of 8 proceeds
smoothly under the Pd/CuCl-mediated coupling conditions
that were developed for the reaction of acetylenes cis to
Mes*, and dimeric 10 was obtained in 68% isolated yield
(Scheme 2e).
units. Considering the P···P distance of 8.7 ꢀ (as deduced
X-ray analysis of a single crystal of 10, grown from a mix-
ture of CH2Cl2 and acetonitrile, revealed that the cis rela-
tionship of two bulky Mes* groups forces dimeric 10 to
adopt a somewhat twisted geometry around the central bu-
tadiyne vector, similar to what is observed for 3b (Figure 5).
The two PC5 planes (defined by P1-C1-C2-C3-C4-C5 and
P2-C1’-C2’-C3’-C4’-C5’, respectively) describe an interplanar
angle of 50.28, thus limiting the communication between the
two P=C units in the solid state. It is interesting to note that
the phenyl substituents at the terminal butadiynes are not
7
from 3b and 6), the coupling constant of J
N
stunningly large, which indicates that the two P centers in 7
are part of one common p system that provides a large
degree of communication. If the P centers were not part of
the same p system, a much lower coupling constant would
be expected, for example, that between two tertiary s3l3
phosphanes that are bridged by a butadiyne linker (5J
2.3 Hz).[48] The 7J
(P,P) coupling in 7 is comparable to the
ACHTUNGTRNE(NUNG P,P)=
ACHTUNGTRENNUNG
2J
ACHTUNGTRENNUNG(P,P) of 32 Hz that has been reported between the two en-
docyclic P centers of a 1,3,6-triphosphafulvene.[49]
symmetrical (Figure 5, bottom, side view). The C8 Ph group
À
To further develop the chemistry of A2PAs while main-
taining a large degree of reaction control, we started to ex-
plore the possibility of A2PA 1 to engage in heterocoupling
reactions of differentially polarized acetylenes. Unfortunate-
ly, attempts to convert A2PA 1 into an iodo-substituted
product by treating the former with CuCl and quenching the
copper acetylide with iodine at room temperature failed,
presumably due to the low stability of the formed iodo-sub-
stituted A2PA. Again, the only difference between 4a,b and
the elusive iodo-substituted analogue of 1 is the phenyl
group at the cross-conjugated acetylene terminus of the
former, which seems to be crucial for the stability of such an
intermediate. Having identified this shortcoming, the inverse
reaction of a copper acetylide of 1 with 1-haloalkynes was
investigated. The widely used Cadiot–Chodkiewicz coupling
protocol for unsymmetrically terminated alkynes seemed to
is twisted out of its PC5 plane by 67.78, whereas the other
À
C8’ Ph group almost lies within its PC5 plane and deviates
by only 7.28, thus allowing the participation of the C8’-
phenyl ring in p conjugation.
Electronic absorption spectroscopy: The electronic absorp-
tion spectra of A2PAs 3b and 5–10 are shown in Figure 6. In
contrast to the observations from the solid-state structures
of 3a and 3b (Figure 2), which indicated different degrees
of p conjugation within the two compounds, their UV/Vis
spectra are literally identical. The unfavorable conformation
caused by steric repulsion between the two Mes* groups in
3b thus seems to be obsolete in solution. In contrast, 5a and
5b show somewhat different longest-wavelength absorption
maxima of 383 and 379 nm, respectively. The spectrum of 5a
is more similar to that of 8 and points towards a negligible
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12157

X.-L. Geng and S. Ott
Scheme 2. Synthesis of dimeric phosphaalkenes from bis-TMS-protected A2PA 1; cis and trans are relative to the Mes* substituent. Conditions: a) [Pd-
A
ACHTUGNTRENUN(GN PPh3)2Cl2], CuCl, DIEA, DMF/THF, RT, 1–2 h, 7 76% (based on 2a). c) i) CuCl,
ACHTUNGTRENNUNG
contribution of the second phenyl group at the acetylene cis
to the Mes* group in the overall p conjugation of 5a.
ble to that imposed by two additional tetrathiafulvalene
units that formally replace the P centers of 10 at an other-
wise identical acetylene skeleton (lmax =354, shoulder at 425
and 460 nm).[53]
Due to the larger p-conjugation system, dimeric 3, 6, and
10 exhibit longest-wavelength absorption maxima at 446,
441, and 456 nm, which are considerably redshifted by 79,
94, and 83 nm, respectively, compared to the corresponding
monomers.[35,41] The presence of two additional phenyl
groups that extend the p system in 3a relative to that in 6
has only a small effect on the observed absorption maxima
with a Dlmax of 5 nm. By contrast, in comparing the UV/Vis
spectra of 10 and 3, it becomes apparent that the two addi-
tional acetylenes in 10 lead to a greater redshift of 9 nm rel-
ative to that in 3b, and a remarkable increase in molar ex-
tinction coefficient, both indicative of a more extended p
system in 10 than that of 3.
In comparison with structurally closely related all-carbon-
based reference compounds, the longest-wavelength absorp-
tion maxima of all A2PAs are generally redshifted, thus fur-
ther supporting the notion that the HOMO–LUMO gaps of
oligoacetylenes can be lowered dramatically by replacing
some of the constituting alkenes by heavier congeners such
as phosphaalkenes. For example, bis-phenylbutadiyne-substi-
tuted phosphaalkene 9 shows a lowest-energy absorption
maximum at 396 mm that is thus considerably redshifted rel-
Electrochemistry: Electrochemical measurements of A2PAs
3b and 5–10 were performed to further investigate their
electronic properties and to evaluate the role of the phos-
phorus centers (Table 1). A2PAs 3, 5, and 7 that contain a
phenylacetylene subunit directly at the P=C feature oxida-
tion potentials that are noticeably shifted cathodically com-
pared to those of the TMS-terminated compounds. This ob-
servation thus suggests that the HOMOs of these com-
pounds experience additional contributions from the phenyl
groups. However, if the phenyl group is separated by a buta-
diyne like in 8, its contribution to the HOMO becomes neg-
ligible, as the oxidation potential of 8 remains unchanged
compared to that of 1 (Ep,a =1.16 V),[35] consistent with a
previous finding for another butadiynylphenyl-substituted
phosphaalkene.[35] An additional trend that is visible from
the anodic scans is that the dimeric A2PAs 3b, 6, and 10 ex-
hibit milder oxidation potentials than their monomeric
building blocks 2b, 1, and 8 by 80, 90 and 110 mV, respec-
tively. It is thus clear that the HOMO of the dimeric species
extends well beyond the monomeric subunits, thereby pro-
viding a viable communication path between the two P=C
units.
ative to that of its all-carbon endiyne analogue (lmax
=
330 nm, shoulder at 350 nm).[51] The effect is even more dra-
matic in the dimeric systems with phosphaalkene 6, which
features an end absorption that is bathochromically shifted
by Dlmax =112 nm relative to a suitable reference with a sim-
ilar all-carbon-based p framework.[52] Similarly, A2PAs 3 and
10 are also bathochromically shifted by more than 100 nm
An evaluation of the cathodic scans reveals that the ob-
served reduction potentials are considerably more sensitive
measures for the extent of p conjugation in the A2PAs than
the oxidation potentials. In comparisons with A2PAs 1 and
2b, extending the p system by one additional acetylene
group as in 5 and 8 results in sizeable anodic shifts of the
observed reduction potentials of 200–300 mV. The second
À
compared to their all-carbon-based analogues with NO2 or
À
NMe2 substituents at the phenyl groups.[51] The effect of
the P=C units on the HOMO–LUMO gap in 10 is compara-
12158
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 12153 – 12162

Dendralene Segments
FULL PAPER
acetylene in 9 leads to an addi-
tional shift of roughly the same
magnitude. Homo-dimeric 3b,
6, and 10 feature anodically
shifted reduction potentials
greater than 400 mV relative to
their
monomeric
building
blocks. These often reversible
reductions are typically fol-
lowed by a second, irreversible
electron uptake at roughly
500 mV more negative poten-
tial. The large separation of
these
two-electron
uptake
events is consistent with a de-
localization of the primarily ob-
tained radical anion across the
entire p system, because locali-
zation on one side of the mole-
cules would presumably give
rise to a smaller separation of
the two cathodic waves.
The expanded dendralene
fragment 10 with the largest
p system also features the least
negative reduction potential as
expected. However, comparing
the data of 10 with that of 3b,
which possesses the same ste-
reochemistry and only differs in
two acetylenes, a stunning pos-
sibility to tune the absolute en-
ergies of the frontier molecular
Figure 5. Molecular structure of phosphaalkene 10 (30% probability ellipsoids). All hydrogen atoms are omit-
ted for clarity in front view and Mes* groups are further omitted for clarity in side view. Selected bond lengths
À
À
À
À
À
À
[ꢀ] and angles [8]: C1 C1’ 1.373(4), C1 C2 1.210(4), C2 C3 1.416(4), C3 C4 1.429(4), C4 C5 1.198(4), C5
À
À
À
À
À
À
C6 1.379(4), C6 C7 1.190(4), C7 C8 1.443(7), C3 P1 1.715(3), P1 C9 1.848(3), C3’ P2 1.705(3), P2 C9’
1.844(3); C2-C3-C4 118.0(2), C2-C3-P1 123.5(2), C4-C3-P1 118.5(2), C3-P1-C9 99.80(12). Dihedral angles [8]:
À
orbitals
(FMOs)
emerges.
the plane of P1-C1-C2-C3-C4-C5 to P2-C1’-C2’-C3’-C4’-C5’ 129.8(2), the aromatic ring of C9 Mes* to the
À
plane of P1-C1-C2-C3-C4-C5 90.1(2), the aromatic ring of C9’ Mes* to the plane of P1’-C1’-C2’-C3’-C4’-C5’
Whereas the HOMO is only
sensitive to phenyl groups that
are separated from the P=C by
not more than one acetylene,
the LUMO contains contribu-
À
À
93.1(2), C8 phenyl ring to the plane of P1-C1-C2-C3-C4-C5 112.30(11), C8’ phenyl ring to the plane of P1’-
C1’-C2’-C3’-C4’-C5’ 7.2(2).
Table 1. Electrochemical data for 1 mm solutions in CH2Cl2 (0.1m
NBu4PF6).[a]
1
Compound
Reduction E = [V]
Oxidation Ep,a [V]
2
1[35]
2b[41]
3a[41]
3b
5a
5b
6
7
8
9
10
À2.07[b]
1.16
1.02
0.95
0.94
1.00
0.96
1.07[d]
1.00
1.17
1.05
1.06
À2.04[b]
À1.67
À1.59
À1.89[b]
À1.77
À1.59
À1.63
À2.02[b]
À1.61
À1.47
À2.2[b,c]
À2.00[b,c]
À2.17[b]
À2.23[b]
À1.91
[a] Glassy carbon electrode, scan rate (n)=100 mVsÀ1. All potentials are
given versus Fc+/0. E = =(Epa +Epc)/2. [b] Irreversible peak potentials Ep,c
.
1
2
Figure 6. UV/Vis absorption spectra of compounds 3a and 5–10 in
CH2Cl2 at 258C.
[c] Reversible at v>1 VsÀ1. [d] A second oxidation potential was ob-
served at +1.33 V.
Chem. Eur. J. 2011, 17, 12153 – 12162
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
12159

X.-L. Geng and S. Ott
a 400 MHz spectrometer. Chemical shifts (ppm) were reported and refer-
enced to the internal signal of residual protic solvent. UV/Vis spectra
were recorded in a 1ꢃ1 cm2 optical quartz cell as solutions in CH2Cl2.
Cyclic voltammetry (CV) was carried out using a computer-controlled
potentiostat (Autolab) and a standard three-electrode arrangement. All
electrochemical measurements were carried out in Ar-purged dry di-
chloromethane with 100 mm Bu4NPF4 as the supporting electrolyte. The
working electrode was a glassy carbon disc (diameter 3 mm). Potentials
were measured against an Ag/Ag+ reference electrode (10 mm AgNO3 in
CH3CN) with ferrocenium/ferrocene (Fc+/0) as internal standard. High-
resolution mass spectral analyses (HRMS) were performed using a high-
resolution ESI-FTICR mass spectrometer (Varian 7.0 T) and an FTMS+
pNSI mass spectrometer (OrbitrapXL).
tions from the entire p system. The extra acetylenes in 10
thus prevent contributions of the phenyl group in the
HOMO and 10 is more difficult to oxidize than 3b. In con-
trast, the extra acetylene in 10 renders its reduction more
facile than that of 3b. As a result, HOMO and LUMO of 10
are both anodically shifted relative to the respective FMOs
of 3b, thereby opening an option to tune the energy levels
of the FMOs while keeping the HOMO–LUMO gaps more
or less constant.
Compound (1E,1’E)-3b: CuCl (29 mg, 0.3 mmol, 3 equiv) and [Pd-
AHCTUNGTRENN(GUN PPh3)2Cl2] (15 mg, 0.02 mmol, 20 mol%) were added successively to a
Conclusion
degassed solution of 2b (49 mg, 0.1 mmol) in THF/DMF (1:5 v/v) at
room temperature under Ar. The resultant solution was allowed to react
at 358C for 1 h and quenched by the addition of aqueous NH4Cl. The re-
action mixture was extracted with hexane (3ꢃ50 mL), the combined or-
ganic phases was dried over Na2SO4 and concentrated in vacuo. The
product was purified by column chromatography (silica, 2% EtOAc in
hexane) to afford 6 as a yellow solid (72 mg, 87%). M.p. 171–1738C
(decomp); Rf =0.1 (hexane); 1H NMR (CDCl3, 400 MHz): d=1.28 (s,
18H), 1.48 (s, 36H), 7.35–7.37 (m, 6H), 7.38 (s, 4H), 7.51–7.53 ppm (m,
4H); 13C NMR (CDCl3, 100 MHz): d=31.4, 33.2, 35.0, 37.9, 85.9 (d, J=
14.0 Hz), 87.9, 88.7 (d, J=27.6 Hz), 96.7 (d, J=16.1 Hz), 122.4, 123.2,
128.3, 128.5, 131.6, 133.8 (d, J=57.4 Hz), 140.9 (d, J=37.4 Hz), 151.3,
153.5 ppm; 31P NMR (CDCl3, 162 MHz): d=351.1 ppm; UV/Vis: l (e,
103 mÀ1 cmÀ1): 273 (25), 372 (20), 446 nm (13); HRMS (ESI): m/z: calcd
for C58H68P2 [M+Na]+: 849.4688; found: 849.4699.
By taking advantage of different rates for the deprotection
of the two TMS-acetylene termini in 1, a series of buta-
diyne-expanded dendralene fragments with exotopic phos-
phaalkene units have been successfully prepared. The bulky
Mes* that kinetically stabilizes the P=C bond in 1 also de-
creases the reactivity of the TMS acetylene in the cis posi-
tion, thereby enabling selective deprotection and coupling
reactions. Crucial synthetic steps include the mild in situ for-
mation of CuI acetylides from the TMS-acetylenes by treat-
ment with CuCl in DMF, followed by immediate Pd-/Cu-cat-
alyzed coupling protocols. Although the stereochemistry
across the P=C double bond is conserved during the oxida-
tive acetylene couplings, cis/trans isomerization occurs in io-
doacetylene-containing A2PA 4 at room temperature.
All spectroscopic, electrochemical, and crystallographic
studies show that the s2l3 phosphorous centers are integral
parts of the p systems of the compounds. Mixing the phos-
phaalkene-based fragment orbitals with those of the ap-
pended acetylene framework leads to smaller HOMO–
LUMO gaps in the entire p conjugates than in the all-
carbon-based reference compounds. Furthermore, communi-
cation between the two P=C units is effectively mediated by
Synthesis of 5: CuCl (29 mg, 0.3 mmol, 3 equiv) was added to a degassed
solution of 2b (54 mg, 0.1 mmol) in THF/DMF (1:5 v/v). The reaction
mixture was heated to 408C for 1–2 h. I2 (39 mg, 0.3 mmol, 3 equiv) was
added to the reaction mixture. CuCl (2 mg, 0.02 mmol, 20%) and [Pd-
AHCTUNGTREN(GNUN PPh3)2Cl2] (15 mg, 0.02 mmol, 20 mol%) were added to another de-
gassed solution of phenylacetylene (31 mg, 0.3 mmol, 3 equiv) in DIEA
(0.5 mL)/THF (5 mL) in a second flask. The solution from step 1 was
then added dropwise into the second. The reaction was allowed to stir at
room temperature for 2–4 h and quenched by the addition of aqueous
NH4Cl. The reaction mixture was extracted with hexane (3ꢃ50 mL), and
then the combined organic phases were dried over Na2SO4 and concen-
trated in vacuo. The product was purified by column chromatography
(silica, hexane) to afford 5a (19%, 10 mg) and 5b (52%, 27 mg) as light
yellow foam.
the central butadiyne as evidenced by the unexpectedly
7
large coupling constant of J
spectrum of 7.
(P,P)=25.8 Hz in the 31P NMR
ACHTUNGTRENNUNG
Compound 5a (Z isomer): Rf =0.3 (hexane); 1H NMR (CDCl3,
400 MHz): d=1.32 (s, 9H), 1.52 (s, 18H), 6.86 (d, J=8 Hz, 2H), 7.13–
7.21 (m, 3H), 7.32–7.36 (m, 3H), 7.48 (s, 2H), 7.52 ppm (d, J=7.8 Hz,
Depending on their separation from the P=C units either
by an ethyne (as in 3b) or a butadiyne (as in 10), terminal
phenyl groups affect the energy levels of the frontier molec-
ular orbitals of the A2PAs to a varying degree, thus offering
the possibility to fine-tune their energy levels. Synthetically,
phenyl groups at the cross-conjugated acetylene terminus
have been found to stabilize the reaction intermediates and
are crucial for the oxidative acetylene coupling of the CuI
acetylides in some instances. This finding suggests synthetic
strategies for future oligomeric structures of type I and II in
which extra phenyl groups are introduced into every second
butadiyne to increase the stabilities of the structures.
2H); 13C NMR (CDCl3, 100 MHz): d=29.7, 31.3, 33.2 (d,
JACHTUNGTRENNUNG
6.0 Hz), 38.2, 74.4 (d, J
(P,C)=24.4 Hz), 86.1 (d,
103.5 (d, J
ACHTUGTNREN(UNG P,C)=12.7 Hz), 80.4 (d, JACTHUNGTRENNUNG
J
N
J
A
JACHTUNGTRENNUNG
AHCTUNGTRENNUNG
A
JACHTUNGTRENNUNG
154.3 ppm; 31P NMR (CDCl3, 162 MHz): d=349.1 ppm; UV/Vis: l (e,
103 mÀ1 cmÀ1)=262 (29), 283 (21), 308 (shoulder, 16), 379 nm (18); EIMS
(70 eV): m/z (%): 514 (42) [M]+, 515 (14) [M+H]+, 458 (34)
[M+HÀtBu]+, 275 (100) [Mes*PÀ2H]+; HRMS (FTMS+pNSI): m/z:
calcd for C37H39PAg: 623.18369; found: 623.18230 (in CHCl3/MeOH with
CF3COOAg).
Compound 5b (E isomer): Rf =0.28 (hexane); 1H NMR (CDCl3,
400 MHz): d=1.36 (s, 9H), 1.53 (s, 18H), 7.30–7.35 (m, 8H), 7.49 (s,
2H), 7.52 ppm (d, J=7.8 Hz, 2H); 13C NMR (CDCl3, 100 MHz): d=29.7,
31.4, 33.4 (d, J
(P,C)=21.4 Hz), 81.2 (d, J
(d, J(P,C)=16.6 Hz), 96.6 (d, J
129.2, 131.5, 131.7, 132.6, 134.1 (d, 1J
37.0 Hz), 151.4, 154.2 ppm; 31P NMR (CDCl3, 162 MHz): d=349.6 ppm;
UV/Vis:
(e, 103 mÀ1 cmÀ1)=274 (30), 292 (22), 308 (shoulder, 18),
383 nm (19); EIMS (70 eV): m/z (%): 514 (54) [M]+, 515 (18) [M+H]+,
G
ACHTUNGTRENNUNG
E
R
ACHTUNGTRENNUNG
Experimental Section
G
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
General: All reactions were performed under argon using Schlenk tech-
niques. Diethyl ether and THF were freshly distilled from sodium/benzo-
phenone prior to use. 1H, 13C, and 31P NMR spectra were recorded using
l
12160
www.chemeurj.org
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 12153 – 12162

Dendralene Segments
FULL PAPER
458 (40) [M+HÀtBu]+, 275 (100) [Mes*PÀ2H]+; HRMS (FTMS+
pNSI): m/z: calcd for C37H39PAg: 621.18403, 623.18369; found: 621.18348,
623.18371 (in CHCl3/MeOH with CF3COOAg).
Compound 9: CuCl (60 mg, 0.6 mmol, 3 equiv) was added to a degassed
solution of 8 (104 mg, 0.2 mmol) in THF/DMF (1:5 v/v). The reaction
was allowed to stir at 358C for 30 min, after which a degassed solution of
iodophenylacetylene (228 mg, 1 mmol, 5 equiv) in pyridine was added
dropwise. The resulting solution was stirred at room temperature over-
night and quenched with aqueous NH4Cl. The reaction mixture was ex-
tracted with hexane (3ꢃ50 mL), then the combined organic phases were
dried over Na2SO4 and concentrated in vacuo. The product was purified
by column chromatography (silica, 4% CH2Cl2 in hexane) to afford 9
(27%, 29 mg) as a yellow foam. Rf =0.1 (hexane); 1H NMR (CDCl3,
400 MHz): d=1.35 (s, 9H), 1.50 (s, 18H), 7.30–7.35 (m, 8H), 7.48 (s,
2H), 7.49 (d, J=2.2 Hz, 2H), 7.50 ppm (d, J=1.4 Hz, 2H); 13C NMR
(CDCl3, 100 MHz): d=29.8, 31.4, 33.3 (d, 1J=5.4 Hz), 38.1, 74.1 (d, J=
9.2 Hz), 74.2 (d, J=15.3 Hz), 78.4 (d, J=19.9 Hz), 80.7 (d, J=23.7 Hz),
80.9 (d, J=19.4 Hz), 86.4 (d, J=7.7 Hz), 86.9 (d, J=9.9 Hz), 87.9 (d, J=
4.8 Hz), 121.9, 122.0, 122.6, 128.4, 128.5, 129.2, 129.4, 132.2, 132.5, 133.5
(d, 1J=54.3 Hz), 138.7 (d, J=37.5 Hz), 151.6, 153.9 ppm; 31P NMR
(CDCl3, 162 MHz): d=366.3 ppm; MS (EI; 70 eV): m/z (%): 538 (100)
[M]+, 539 (40) [M+H]+, 482 (54) [M+HÀtBu]+, 275 (90) [Mes*PÀ2H]+
, 262 (90) [Mes*PÀCH3]+; UV/Vis: l (e, 103 mÀ1 cmÀ1): 274 (35), 295 (23),
316 (19), 336 (18), 396 nm (broad, 20); HRMS (FTMS+pNSI): m/z:
calcd for C39H39PSiAg: 645.18403, 647.18369; found: 645.18339, 647.18321
(in CHCl3/MeOH with CF3COOAg).
Compound (1E,1’E)-6: CuCl (79 mg, 0.8 mmol, 4 equiv) and [Pd-
ACHTUNGTRENNUNG(PPh3)2Cl2] (30 mg, 0.04 mmol, 20 mol%) were added to a degassed solu-
tion of 1 (97 mg, 0.2 mmol) in THF/DMF (1:5 v/v) successively at room
temperature. The reaction was monitored by TLC (1% EtOAc in
hexane, 1 h) and quenched by the addition of aqueous NH4Cl. The reac-
tion mixture was extracted with hexane (3ꢃ50 mL). Then the combined
organic phases were dried over Na2SO4 and concentrated in vacuo. The
product was purified by column chromatography (silica, 1% EtOAc in
hexane) to afford 6 as a yellow foam. Yield: 95%; m.p. 166–1688C
(decomp); Rf =0.18 (hexane); 1H NMR (CDCl3, 400 MHz): d=À0.11 (s,
18H), 1.33 (s, 18H), 1.48 (s, 36H), 7.46 ppm (s, 4H); 13C NMR (CDCl3,
100 MHz): d=0.5, 31.4, 33.0, 35.0, 38.2, 81.4, 86.7 (m), 101.6 (m), 108.6,
122.6, 134.6 (m), 139.6 (m), 150.7, 153.6 ppm; 31P NMR (CDCl3,
162 MHz): d=355.9 ppm; UV/Vis: l (e, 103 mÀ1 cmÀ1)=345 (13), 405 (14),
441 nm (16); HRMS (ESI): m/z: calcd for C52H76P2Si2 [M+Na]+:
841.4853; found: 841.4852.
Compound (1E,1’E)-7: CuCl (79 mg, 0.8 mmol) and [PdACHTUNGTRNEG(UN PPh3)2Cl2]
(30 mg, 0.04 mmol, 20 mol%) were added to a degassed solution of 1
(170 mg, 0.4 mmol) and 2a (54 mg, 0.1 mmol) in THF/DMF (1:5 v/v) suc-
cessively at room temperature. The reaction was monitored by TLC (1%
EtOAc in hexane, 20–30 min) and quenched by the addition of aqueous
NH4Cl. The reaction mixture was extracted with hexane (3ꢃ50 mL).
Then the combined organic phases were dried over Na2SO4 and concen-
trated in vacuo. The product was purified by column chromatography
(silica, 1% EtOAc in hexane) to afford 7 as a yellow solid (62 mg, 76%,
based on 2a). M.p. 106–1098C (decomp); Rf =0.1 (hexane); 1H NMR
(CDCl3, 400 MHz): d=0.12 (s, 9H), 1.32 (s, 9H), 1.33 (s, 9H), 1.48 (s,
18H), 1.50 (s, 18H), 6.85 (d, J=8.0 Hz, 2H), 7.13–7.21 (m, 3H), 7.47 (s,
2H), 7.48 ppm (s, 2H); 13C NMR (CDCl3, 100 MHz): d=0.36, 31.3, 31.4,
Compound (1Z,1’Z)-10: CuCl (30 mg, 0.3 mmol, 3 equiv) and [Pd-
AHCTUNGTRENN(GUN PPh3)2Cl2] (15 mg, 0.02 mmol, 20 mol%) were added to a degassed solu-
tion of 8 (51 mg, 0.1 mmol) in THF/DMF (1:5 v/v) successively. The re-
sulting solution was allowed to react at 358C for 4 h and quenched by the
addition of aqueous NH4Cl. The reaction mixture was extracted with
hexane (3ꢃ50 mL), the combined organic phases were dried over
Na2SO4 and concentrated in vacuo. The product was purified by column
chromatography (silica, 1% EtOAc, 5% CH2Cl2 in hexane) to afford 10
(68%, 29 mg) as a yellow powder. Rf =0.3 (1% EtOAc in hexane); m.p.
171–1758C (decomp); 1H NMR (CDCl3, 400 MHz): d=1.33 (s, 18H),
1.43 (s, 36H), 7.36–7.38 (m, 6H), 7.38 (s, 4H), 7.52 (d, J=1.6 Hz, 2H),
7.54 ppm (d, J=1.6 Hz, 2H); 13C NMR (CDCl3, 100 MHz): d=31.4, 33.2,
35.1, 37.9, 75.4, 80.4–80.6 (m), 81.4–81.5 (m), 85.2–85.4 (m), 86.3, 87.8,
33.0 (d, 4J
38.20, 81.2–81.4 (m, 2C), 86.7–86.6 (m, 2C), 88.1 (d, J
101.6 (d, J(P,C)=20.6 Hz), 103.5 (d, J(P,C)=13.5 Hz), 108.8 (d, J
10.7 Hz), 119.5, 122.4 (2C), 127.9, 128.3, 131.4, 134.1 (d, 1J
64.6 Hz), 134.6 (d, 1J(P,C)=54.8 Hz), 139.5 (d, 1J
(P,C)=34.0 Hz), 139.8
(d, 1J(P,C)=35.6 Hz) 150.8, 150.9, 153.7 (2C), 154.3 ppm (2C); 31P NMR
(CDCl3, 162 MHz): d=348.5 (d, J(P,P)=25.8 Hz), 356.3 ppm (d, J(P,P)=
25.8 Hz); UV/Vis:
(e, 103 mÀ1 cmÀ1): 300 (13), 367 (18), 404 (17),
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(P,C)=5.4 Hz), 33.2 (d, 4J
AHCTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
122.0, 122.7, 129.4, 132.5, 133.1 (d, 1J
ACHTNUTRGENNUG(P,C)=60.0 Hz), 138.9 (d, JACHTUNGTRENNUNG(P,C)=
AHCTUNGTRENNUNG
29.1 Hz), 151.9, 153.6 ppm; 31P NMR (CDCl3, 162 MHz): d=368.2 ppm;
UV/Vis: l (e, 103 mÀ1 cmÀ1)=294 (43), 320 (37), 347 (37), 371 (37), 416
(30), 456 nm (23); elemental analysis calcd (%) for 2C62H68P2·CH3CN: C
84.22, H 7.87; found: C 84.43, H 7.92.
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
l
X-ray crystallography CCDC-823771 (1), 823772 (10), 823773 (3b) and
823774 (10) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
443 ppm (18); HRMS (FTMS+pNSI): m/z: calcd for C55H72P2SiAg:
929.39294; found: 929.39240; m/z: calcd for C55H72P2SiAg2CF3COO:
1151.28274; found: 1151.28219 (in CHCl3/MeOH with CF3COOAg); ele-
mental analysis calcd (%) for C55H72P2Si·2CH3OH·2H2O:
C 74.15,
H 9.17; found: C 73.84, H 9.54.
Compound (Z)-8: CuCl (150 mg, 1.6 mmol, 8 equiv) was added to a de-
gassed solution of 1 (98 mg, 0.2 mmol) in THF/DMF (1:5 v/v). The reac-
tion was allowed to stir at room temperature for 3 min, then a degassed
solution of iodophenylacetylene (364 mg, 1.6 mmol, 8 equiv) in pyridine
was added dropwise. The resulting solution was stirred for 3–5 h and
quenched with aqueous NH4Cl. The reaction mixture was extracted with
hexane (3ꢃ50 mL), then the combined organic phases were dried over
Na2SO4 and concentrated in vacuo. The product was purified by column
chromatography (silica, hexane) to afford 8 (52%, 53 mg) as a yellow
foam. Rf =0.35 (hexane); 1H NMR (CDCl3, 400 MHz): d=À0.1 (s, 9H),
1.33 (s, 9H), 1.49 (s, 18H), 7.33–7.36 (m, 3H), 7.48 (s, 2H), 7.49 (d, J=
1.8 Hz, 1H), 7.51 ppm (d, J=1.6 Hz, 1H); 13C NMR (CDCl3, 100 MHz):
Acknowledgements
This work was supported by the Swedish Research Council, the Gçran
Gustafsson Foundation, the Carl Trygger Foundation (X.-L.G.), COST
action 0802 PhoSciNet, and Uppsala University through the U3MEC mo-
lecular electronics priority initiative. We thank Dr. Jin-Li Cao and Prof.
Jin Qu (Nankai University, China) for the X-ray structure determination
of 1, 3b, 6, and 10 and Dr. Heinrich Luftmann (WWU Mꢄnster, Germa-
ny) for HRMS measurements of 5a, 5b, 7, 8, and 9.
d=À0.36, 31.5, 33.1 (d, 4J
A
ACHTUNGTRNE(NUNG P,C)=
13.8 Hz), 80.7 (d, JACHTUNGTRENNUNG(P,C)=17.6 Hz), 81.8 (d, JACHTUGNTRENNNUG
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Received: May 4, 2011
Revised: June 15, 2011
Published online: September 14, 2011
12162
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Chem. Eur. J. 2011, 17, 12153 – 12162