Incorporating phosphaalkenes into oligoacetylenes

Article abstract of DOI:10.1002/anie.200802253

Mind the gap! Replacing the two terminal carbon atoms of a tetrayne-linked bis-alkene by two phosphorus centers leads to a decrease of the HOMO-LUMO gap by 0.5 eV. The acetylenic phosphaalkenes are accessible from an ambivalent carbene-type C₅ intermediate and are shown to be viable building blocks for the construction of elaborate phosphorus- and carbon-rich molecules (see picture; C gray, P purple). (Figure Presented).

Full text of DOI:10.1002/anie.200802253

Communications
DOI: 10.1002/anie.200802253
Phosphaorganic Chemistry
Incorporating Phosphaalkenes into Oligoacetylenes**
Bernhard Schꢀfer, Elisabet ꢁberg, Mikael Kritikos, and Sascha Ott*
First synthesized and isolated by Becker in 1976, and viewed
as something of a curiosity,[1] phosphaalkenes are now well-
established entities in organophosphorus chemistry. In many
cases, phosphaalkenes display a reactivity that is similar to
that of their all-carbon-based counterparts, that is, alkenes.[2,3]
Their use as ligands in homogenous catalysis has recently
obtained from a C-bromophosphaalkene.[16] The non-exis-
tence of APAs with more than one acetylene substituent and
the lack of more elaborate structures that are based on the
APA motif are presumably results of the reluctance of
halogenated phosphaalkenes to engage in metal-catalyzed
coupling reactions. C,C-Dibromophosphaalkenes, for exam-
ple, will isomerize to phosphaalkynes upon exposure to
palladium or platinum.[17]
We envisaged that APAs would be accessible through a
sequence of three steps from commercially available acety-
lenes and ethyl formate (Scheme 1). In the preparation of
carbinols 1a–d[18] it is important that the reaction times are
kept short and the temperature below room temperature to
avoid the previously described base-catalyzed ynol-to-enone
rearrangement.[19] Treatment of etheric solutions of the
carbinols with thionyl chloride affords the 3-chloropenta-
1,4-diynes 2a–d in acceptable yields.[20] NMR spectroscopic
studies of 2a–c show unambiguously that the compounds are
C2-symmetric and therefore consistent with the assigned
refueled interest in the chemistry of phosphaalkenes,[4,5]
a
trend that now also reaches into certain areas of material and
polymer science.[6] For example, phosphaalkenes have been
polymerized in reactions similar to those of ethylenes[7] or
incorporated as intact fragments in polyphenylenephosphaal-
kenes.[8–10] Phosphorus centers that have been implemented
into polyaromatic structures in the form of phospholes have
been shown to act as n-type dopants that lead to decreased
band gaps in p-conjugated assemblies.[11,12] The incorporation
of pyridines, thiophenes, and now phospholes is a prominent
way to alter the properties of polyaromatic p conjugates.
However, conjugated atom chains, that is, oligoacetylene
analogues that feature heavier main-group elements, are
virtually unknown. We have recently initiated a project with
the aim to incorporate phosphorus heteroatoms, in the form
=
structures. Finally, the P C bond can be established by
treating the chlorides with Mes*PCl2 in the presence of
lithium diisopropylamide (LDA).[21] The reaction proceeds
presumably through a carbene-type C5 intermediate which is
=
of phosphaalkenes (P C), into fully p-conjugated acetylenic
frameworks. In contrast to the classical all-carbon-based
designs,[13,14] our approach will enable us to
alter the electronic properties of the resulting
acetylenic phosphaalkenes (APAs) by coor-
dination of metal fragments to the phos-
phaalkene ligand. In this first report of a
heavy main-group element that is an intrinsic
part of an oligoacetylene, we also seek to
investigate the effect that the heavy alkene
has on the optical and electrochemical prop-
erties of the entire p conjugate.
APAs have only emerged very sporadi-
cally. A report by Appel et al. describes the
synthesis of P-acetylenic phosphaalkenes
from a P-chlorophosphaalkene,[15] whereas
the only C-acetylenic phosphaalkene was
Scheme 1. Synthesis of C,C-diacetylenic phosphaalkene 3 and 1-phosphahex-1-ene-3,5-
diyne 4b–d. 1) SOCl2, Et2O, 12 h, 208C. 2a 82%; 2c 71%; 2d 58%. 2) Mes*PCl2, LDA,
THF, 2 h, ꢀ100!ꢀ208C. 3 40%; 4b 48% over two steps; 4c 57%; 4d 52%.
Mes*=2,4,6-(tBu)3C6H2.
attainable from 3-chloropenta-1,4-diyne by a base-induced
a elimination.[22,23]
[*] Dr. B. Schꢀfer, E. ꢁberg, Dr. S. Ott
Department of Photochemistry and Molecular Science
ꢂngstrꢃm Laboratories
Since such a C5 fragment can react either at the central C3-
position or at the terminal C1 atom, the products of this
reaction have to be analyzed carefully. Common character-
ization techniques such as 1H, 13C, and 31P NMR spectroscopy
and mass spectrometry show that acetylenic phosphaalkenes
Uppsala University, Box 523, 75120 Uppsala (Sweden)
Fax: (+46)18-471-6844
E-mail: sascha.ott@fotomol.uu.se
Dr. M. Kritikos
Department of Physical, Inorganic and Structural Chemistry
Arrhenius Laboratory
Stockholm University, 10691 Stockholm (Sweden)
are obtained in all cases. A characteristic chemical shift for
=
the P C carbon atom at d = 142.6 ppm can be found in the
13C NMR spectrum of the product arising from 2a. In
contrast, the respective signals of the products arising from
2b–d are considerably shifted downfield to values beyond d =
160 ppm, supporting the notion that the APA portion of these
[**] This work was supported by the Swedish Research Council, the
Gꢃran Gustafssons Foundation, and the Carl Trygger Foundation.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200802253.
8228
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Angewandte
Chemie
products are regioisomers to 2a. Confirmation of the
product structures was obtained from X-ray crystal-
lography. Analysis of 3 revealed that a C,C-diacety-
lenic phosphaalkene had formed, that is, an isomer
that stems from the reaction of 2a at the central
position of the C5 reactant (Figure 1). Since 4b–d
yielded no crystals of sufficient quality, a correspond-
ing [Co2(CO)6] complex was prepared. X-ray analysis
of [Co2(CO)6(4b)] showed that 4b is a butadiyne-
substituted phosphaalkene and thus a regioisomeric
analogue of 3 (see the Supporting Information).
Remarkably, the reaction is not only regioselective
for the C1-position of the C5 fragment, but also
produces almost exclusively the isomer in which the
butadiyne is trans to the lone pair of electrons on the
phosphorus atom. A similar reactivity leads to 4c and
4d, the structures of which were assigned by 13C NMR
Scheme 2. Coupling reactions of 4d. 1) K2CO3, [Pd(PPh3)4] or [PdCl2(PPh3)2],
CuI, Et3N, THF, MeOH, 3–4 h, 508C. 5 68%; 6 59%. 2) K2CO3, Cu(OAc)2,
MeOH, pyridine, 1 h, 208C, 67%. TMS=trimethylsilyl
spectroscopic data and further crystallographic evidence (see
below). As the two silyl groups in 2a and 2c are electronically
very similar, it seems that the selectivity of this reaction is
solely determined by the steric bulk of the substituents.
Interestingly, Barluenga et al. have recently reported the site-
specific olefination of a chromium(0) alkynylcarbene that
isomerization is presumably aided by temporary coordination
2
[17]
=
of the palladium catalyst to the P C bond in an h fashion.
The electronic effect of the remote substituents in 5 and 6 is
communicated to the phosphorous centers as evidenced by a
difference of Dd = 14 ppm between their chemical shifts in the
respective 31P NMR spectra. It is thus clear that the phos-
phorus heteroatoms are an intrinsic part of the p-conjugated
system.
ꢁ
involves a formal 1,2-migration of a C C bond and thus
exhibits a regioselectivity that is comparable to that of our
system.[24]
Compound 4d was also found to undergo homocoupling
when exposed to K2CO3 under the classical Eglinton con-
Having succesfully synthesized 4d, we explored its suit-
ability as a building block for the construction of more
elaborate APAs (Scheme 2). In situ protodesilylation of 4d
with potassium carbonate afforded the terminal acetylene
which was found to engage in Sonogashira–Hagihara coupling
reactions.
Thus, a solution of compound 4d in THF/MeOH and Et3N
was treated with 4-iodonitrobenzene and 4-iodo-N,N-dime-
thylaniline in the presence of excess potassium carbonate and
catalytic amounts of [PdCl2(PPh3)2] and copper iodide in a
one-pot reaction to afford compounds 5 and 6 in 68% and
59% yield, respectively. A small amount of an isomeric by-
product in which the butadiyne is cis to the phosphorus lone
pair of electrons was detected after the reaction. This
=
ditions. No isomerization of the P C bond was detected under
these conditions and the octatetrayne-linked bis(phosphaal-
kene) 7 was isolated in 67% yield after chromatographic
purification. In the solid state, the octatetrayne in 7 adopts a
slightly twisted conformation, with the two phosphorus
centers separated by 13.3 ꢀ (Figure 2). Alternating single
and triple bonds are evidenced by typical bond lengths of 1.37
ꢀ
ꢁ
and 1.20 ꢀ for the C(sp) C(sp) and C C bonds, respectively.
Figure 3 shows the UV/Vis absorption spectra of com-
pounds 4b and 5–7. As expected, 4b has its longest wave-
length absorption maximum at higher energy than the
substituted analogues 5–7. N,N-Dimethylamino-substitution
in 6 leads to a red-shift of the lowest energy absorption band
by 65 nm. Octatetrayne 7 absorbs at 485 nm and thus at a
wavelength that is even further bathochromically shifted as a
result of the large delocalized p system.
The UV/Vis spectra of all the APAs show lowest energy
absorption bands that are generally red-shifted compared to
all-carbon-based reference compounds. For example, com-
pared to a dodec-1,11-diene-3,5,7,9-tetrayne, which exhibits
its longest wavelength absorption maximum at 405 nm,[25] the
substitution of the two terminal carbon atoms by phosphorus,
as in 7, leads to a bathochromic shift of the lowest energy
absorption maximum of 80 nm, which corresponds to a
difference in HOMO–LUMO gap between the two com-
pounds of 0.50 eV. The doping strength of the two phosphaal-
kenes in 7 is similar to that of two dithiafulvenes that, when
implemented at the termini of octatetraynes, result in a shift
of the respective absorption maximum to 484 nm.[26] This
wavelength is similar to that for the corresponding absorption
of compound 7. In contrast to these studies, however, the
doping effect is an intrinsic property of APAs.
Figure 1. ORTEP view of diacetylenic phosphaalkene 3. Thermal ellip-
soids set at 20% probability level. Hydrogen atoms removed for clarity
ꢀ
ꢀ
Selected bond lengths [ꢂ] and angles [8]: P1 C1 1.68, P1 C24 1.85,
ꢀ
ꢀ
ꢀ
ꢀ
C1 C2 1.46, C1 C13 1.46, C2 C3 1.20, C13 C14 1.20, P1–C1–C2 127,
P1–C1–C13 117, C2–C1–C13 116.
Angew. Chem. Int. Ed. 2008, 47, 8228 –8231
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www.angewandte.org 8229

Communications
Table 1: Electrochemical data for solutions of 4b, 5–7.[a]
Compound
Reduction E1/2 [V]
= ꢀ
Oxidation Ep,a [V]
= ꢀ
C6H4NO2
P C C4
C6H4NMe2
P C C4
4b
5
6
ꢀ1.98
1.05
1.08
1.07
1.06
ꢀ1.40
ꢀ1.84
ꢀ2.04
0.47[b]
7
ꢀ1.62, ꢀ1.96
[a] 1 mm solutions in CH2Cl2 (0.1m NBu4PF6), n=100 mVsꢀ1. All
potentials are given versus ferrocene/ferrocenium. [b] The irreversible
oxidation becomes reversible at scan rates higher than 1 Vsꢀ1
.
The common potential found for the oxidations of 4b and
5–7 points towards a localization of this process on the
phosphorus heteroatom. In agreement with the electronic
absorption spectra, the electrochemical data show that
octatetrayne 7 is the APA with the smallest HOMO–
LUMO gap of the series and comparable to the bis(dithia-
fulvene)-substituted octatetrayne reference.[26]
Figure 2. ORTEP view of 1,12-diphosphadodeca-1,11-diene-3,5,7,9-tet-
rayne 7. Thermal ellipsoids set at 20% probability level. Hydrogen
atoms removed for clarity. Selected bond lengths [ꢂ] and angles [8]:
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
P1 C1 1.69, P1 C12 1.84, C1 C2 1.42, C1 C6 1.49, C2 C3 1.20, C3
ꢀ
C4 1.37, C4 C5 1.20, P1–C1–C2 121, P1–C1–C6 121, C2–C1–C6 118.
In summary, we have introduced the first heavy alkene
into an oligoacetylene framework and have thus established
an access to a new class of p-conjugated molecules. The
synthesis was aided by the ambivalent reactivity of a carbene-
type C5 intermediate that leads to C,C-diacetylenic, as well as
to butadiyne-substituted phosphaalkenes. Compounds of the
latter type have been shown to engage in various coupling
reactions and are thus appealing building blocks for the
construction of larger assemblies based on the APA motif. As
evident from the electrochemical data, the HOMO of the
APAs is mainly localized on the phosphorus center, while the
LUMO has significant p* character. In comparison with all-
carbon-based reference compounds, it was established that
the phosphorus centers act as n-dopants to the conjugated
acetylene scaffold and lead to decreased HOMO–LUMO
gaps in the APAs. Future work will include an in-depth
investigation of the reactivity of the C5 carbene, the con-
struction of cyclic assemblies based on the APA building
blocks, and the synthesis of other members of the APA family,
that is, P,C-diacetylenic and peracetylenic phosphaalkenes.
Figure 3. UV/Vis spectra of solutions of compounds 4b (g),
5 (a), 6 (b), and 7 (c) in CH2Cl2 at 258C.
Further information about how phosphorus influences the
electronic properties of the APAs was sought using voltam-
metric measurements (Table 1). As anticipated, electron-rich 6
features the most negative reduction potential of the series at
ꢀ2.04 V. In contrast, the first reversible reduction of electron-
deficient 5 occurs at ꢀ1.40 V. This reduction is assigned to a
localized electron uptake of the nitrophenyl substituent.[27] The
second reversible reduction of 5, however, can safely be
assigned to the conjugated backbone of the molecule. In spite
of the charge of the radical anion, this second process occurs at
a potential that is 140 mV more positive than the first reductive
process of phenyl-substituted 4b. A further anodic shift of the
potential required for the reduction of the p-conjugated
framework occurs in octatetrayne 7, which is reduced at
ꢀ1.62 V. The subsequent electron uptake at ꢀ1.96 V is
assigned to a second reduction of the strongly coupled, dimeric
APA portion of 7. The reduction potential is thus a sensitive
measure of the electronic content of the entire p conjugate,
including the substituents at the butadiyne. In contrast, the
irreversible oxidations of 4b and 5–7 are largely invariant to
the substitution pattern. The cyclic voltammogram of the
anilino-substituted compound 6 features a preceding oxidation
at 0.47 V that can be assigned to the redox-independent anilino
group.[26]
Experimental Section
Compounds 3 and 4b–d were synthesized from 2a–d in a procedure
[21]
=
similar to that described for the synthesis of Mes*P CBr2.
3: 1H NMR (CDCl3, 400 MHz): d = 0.8–0.9 (m, 21H; iPr), 1.12 (s,
ꢀ
21H; iPr), 1.31 (s, 9H; tBu), 1.51 (s, 18H; tBu), 7.43 ppm (s, 2H; CH
Mes*); 13C NMR (CDCl3, 100 MHz): d = 11.4, 11.6, 18.7, 18.9, 31.5,
4
33.3 (d, J(P,C) = 6.5 Hz), 35.2, 38.3, 97.7 (d, J(P,C) = 15.4 Hz), 103.2
(d, J(P,C) = 11.9 Hz), 105.8 (d, J(P,C) = 19.6 Hz), 107.8 (d, J(P,C) =
25.8 Hz), 122.5, 135.1 (d, 1J(P,C) = 57.3 Hz), 142.6 (d, 1J(P,C) =
33.8 Hz), 150.4, 153.7 ppm; 31P NMR (CDCl3, 162 MHz): d =
331.0 ppm; EI MS (70 eV): m/z (%): 650.43 (100) [M+]. Elemental
analysis (%) calcd for (C41H71PSi2): 75.63, 10.99; found: C 75.89, H
11.13.
1
4d: H NMR (CDCl3, 400 MHz): d = 0.19 (s, 9H; TMS), 1.45 (s,
ꢀ
9H; tBu), 1.56 (s, 18H, tBu), 7.36–7.4 (m, 3H; Ph), 7.56 (s, 2H, CH
Mes*), 7.85–7.89 ppm (m, 2H, Ph); 13C NMR (CDCl3, 100 MHz): d =
ꢀ0.2, 31.6, 33.3 (d, 4J(P,C) = 6.5 Hz), 35.2, 38.2, 75.7 (d, J(P,C) =
21.1 Hz), 88.4 (d, J(P,C) = 8.5 Hz), 91.1 (d, J(P,C) = 10.4 Hz), 96.9
(d, J(P,C) = 3.5 Hz), 122.6, 125.5 (d, 3J(P,C) = 20.4 Hz), 128.7 (d,
J(P,C) = 1.5 Hz), 128.9 (d, J(P,C) = 5.8 Hz), 135.3 (d, 1J(P,C) =
52.7 Hz), 139.9 (d, J(P,C) = 21.1 Hz), 150.9, 154.1, 162.2 ppm (d,
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Angewandte
Chemie
1J(P,C) = 43.4 Hz); 31P NMR (CDCl3, 162 MHz): d = 313.6 ppm;
EI MS (70 eV): m/z (%): 486.54 (38) [M+], 472 (15) [MꢀCH3]+, 430
(93) [MHꢀtBu]+, 276 (100) [Mes*P]+. Elemental analysis (%) calcd
for 5(C32H43PSi)·CH3OH: 78.42, 8.95; found: C 78.45, H 8.80.
Keywords: p interactions · alkynes · cross-coupling ·
molecular electronics · phosphaalkenes
.
5: [Pd(PPh3)2Cl2] (6.5 mg, 9.25 mmol, 3 mol%), CuI (3.5 mg,
18.5 mmol, 6 mol%), and aqueous K2CO3 (1m, 3 mL) were added to a
degassed solution of 4-iodonitrobenzene (0.077 g, 0.31 mmol) and 4d
(0.15 g, 0.31 mmol) in THF (30 mL), MeOH (10 mL), and triethyl-
amine (10 mL). The reaction was monitored by thin-layer chroma-
tography (TLC; 5% EtOAc in pentane) and quenched after 3 h by
the addition of brine (40 mL). The reaction mixture was extracted
with EtOAc (3 ꢁ 30 mL), the combined organic phases dried over
Na2SO4, filtered, and concentrated in vacuo. The product was purified
by column chromatography (silica, 5% EtOAc in pentane) and
recrystallized from CH2Cl2 and MeOH. Yellow solid, yield 68%.
1H NMR (CDCl3, 400 MHz): d = 1.36 (s, 9H; tBu), 1.53 (s, 18H; tBu),
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7.36–7.40 (m, 3H; Ph), 7.5 (d, 3J(H,H) = 8.9 Hz, 2H; p-NO2Ph), 7.52
3
ꢀ
(s, 2H; CH Mes*), 7.81–7.86 (m, 2H; Ph), 8.17 ppm (d, J(H,H) =
8.9 Hz, 2H; p-NO2Ph); 13C NMR (CDCl3, 100 MHz): d = 31.5, 33.3
(d, 4J(P,C) = 6.5 Hz), 35.2, 38.2, 79.7 (d, J(P,C) = 8.5 Hz), 83.6 (d,
J(P,C) = 20.8 Hz), 85.5 (d, J(P,C) = 4.6 Hz), 89.4 (d, J(P,C) = 10.0 Hz),
122.6, 123.8, 125.5 (d, 3J(P,C) = 19.6 Hz), 128.9 (d, J(P,C) = 1.5 Hz),
129.1 (d, J(P,C) = 5.8 Hz), 129.4 (d, J(P,C) = 1.9 Hz), 132.8 (d,
7J(P,C) = 1.5 Hz), 135.1 (d, 1J(P,C) = 52.7 Hz), 139.6 (d, J(P,C) =
20.8 Hz), 147.3, 151.0, 154.2, 161.4 ppm (d, 1J(P,C) = 44.6 Hz);
31P NMR (CDCl3, 162 MHz): d = 318.7 ppm; EI MS (70 eV): m/z
(%): 535 (10) [M+], 479 (28) [MHꢀtBu]+, 277 (100) [Mes*PH]+.
Elemental analysis (%) calcd for C35H38NO2P: 78.48, 7.15, 2.61;
found: C 78.41, H 7.16, N 2.60.
6: 1H NMR (CDCl3, 400 MHz): d = 1.44 (s, 9H; tBu), 1.57 (s,
18H; tBu), 3.01 (s, 6H; CH3), 6.6 (d, 3J(H,H) = 8.8 Hz, 2H; p-
3
ꢀ
ꢀ
N(Me)2 Ph), 7.29 (d, J(H,H) = 8.8 Hz, 2H; p-N(Me)2 Ph), 7.35–7.41
(m, 3H; Ph), 7.56 (s, 2H; CH Mes*), 7.88–7.93 ppm (m, 2H; Ph);
ꢀ
13C NMR (CDCl3, 100 MHz): d = 31.6, 33.3 (d, 4J(P,C) = 6.5 Hz), 35.2,
38.2, 40.2, 73.2 (d, J(P,C) = 8.5 Hz), 80.6 (d, J(P,C) = 21.9 Hz), 90.5 (d,
J(P,C) = 4.2 Hz), 92.4 (d, J(P,C) = 10.0 Hz), 108.7 (d, J(P,C) = 1.9 Hz),
111.7, 122.5, 125.6 (d, 3J(P,C) = 20.4 Hz), 128.7, 128.7, 133.6 (d,
J(P,C) = 1.2 Hz), 135.8 (d, 1J(P,C) = 52.3 Hz), 140.3 (d, J(P,C) =
21.14 Hz), 150.5, 150.7, 154.1, 163.2 ppm (d, 1J(P,C) = 42.7 Hz);
31P NMR (CDCl3, 162 MHz): d = 304.3 ppm. Elemental analysis (%)
calcd for C37H44NP: C 83.26, H 8.31, N 2.62; found: C 83.14, H 8.36, N
2.60.
7: Cu(OAc)2 (1.5 g, 8.23 mmol) and K2CO3 (0.85 g, 6.17 mmol)
were suspended in argon-degassed, distilled pyridine (17 mL) and
MeOH (17 mL). 4d (0.1 g, 0.2 mmol) was added in one portion under
a stream of argon. After stirring the reaction mixture at room
temperature for 1 h, it was quenched by the addition of water
(120 mL). The aqueous layer was extracted with n-pentane (3 ꢁ
50 mL) and Et2O (2 ꢁ 50 mL), the combined organic phases dried
over Na2SO4 and concentrated in vacuo (408C). The product was
purified by column chromatography (silica, eluent n-pentane).
Orange solid, yield: 57 mg, 67%.
[22] a) Y. Hori, K. Noda, S. Kobayashi, H. Taniguchi, Tetrahedron
Lett. 1969, 10, 3563 – 3566; b) N. P. Bowling, R. J. Halter, J. A.
Hodges, R. A. Seburg, P. S. Thomas, C. S. Simmons, J. F. Stanton,
R. J. McMahon, J. Am. Chem. Soc. 2006, 128, 3291 – 3302.
[23] The presence of a C5-carbene intermediate is also supported by
the fact that a mixture of dimerization products that arise from
the C5 carbene is obtained when the reaction is conducted in the
absence of Mes*PCl2. See also the Supporting Information.
[24] J. Barluenga, P. Garcꢃa-Garcꢃa, D. de Sꢂa, M. A. Fernꢂndez-
Rodrꢃguez, R. Bernardo de La Rffla, A. Ballesteros, E. Aguilar,
M. Tomꢂs, Angew. Chem. 2007, 119, 2664 – 2666; Angew. Chem.
Int. Ed. 2007, 46, 2610 – 2612.
1H NMR (CDCl3, 400 MHz): d = 1.38 (s, 18H; tBu), 1.51 (s, 36H;
ꢀ
tBu), 7.36–7.40 (m, 6H; Ph), 7.51 (s, 4H; CH Mes*), 7.78–7.82 ppm
(d, 3JH,H = 5.9 Hz, 4H, Ph); 13C NMR (CDCl3, 100 MHz): d = 31.5,
33.3 (d, 4J(P,C) = 5.7 Hz), 35.3, 38.2, 67.3 (d, J(P,C) = 5.3 Hz), 75.1,
78.4 (d, J(P,C) = 20.7 Hz), 91.7 (d, J(P,C) = 7.3 Hz), 122.9, 125.5 (d,
J(P,C) = 19.9 Hz), 128.9, 129.1 (d, 5J(P,C) = 4.6 Hz), 134.7 (d, 1J(P,C) =
53.4 Hz), 139.2 (d, J(P,C) = 21.1 Hz), 151.3, 154.2, 160.8 ppm (d,
1J(P,C) = 45.5 Hz); 31P NMR (CDCl3, 162 MHz): d = 330.5 ppm;
EI MS (70 eV): m/z (%): 770 (16) [MꢀtBu]+, 714 (57)
[25] Y. Zhao, R. McDonald, R. R. Tykwinski, J. Org. Chem. 2002, 67,
2805 – 2812.
[26] M. B. Nielsen, N. F. Utesch, N. N. P. Moonen, C. Boudon, J.-P.
Gisselbrecht, S. Concilio, S. P. Piotto, P. Seiler, P. Günter, M.
Gross, F. Diederich, Chem. Eur. J. 2002, 8, 3601 – 3613.
[27] A. Hilger, J.-P. Gisselbrecht, R. R. Tykwinski, C. Boudon, M.
Schreiber, R. E. Martin, H. P. Lüthi, M. Gross, F. Diederich, J.
Am. Chem. Soc. 1997, 119, 2069 – 2078.
+
+
+
ꢀ
[MHꢀ2tBu] , 658 (40) [M 3tBu+2H] , 602 (32) [Mꢀ4tBu+3H] .
Elemental analysis (%) calcd for C58H68P2·1= CH3OH: C 83.34, H
2
8.37; found: C 83.31, H 8.58.
Received: May 14, 2008
Published online: September 24, 2008
Angew. Chem. Int. Ed. 2008, 47, 8228 –8231
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
8231