Organophosphorus compounds; 129. Mesitylphosphaacetylene: Synthesis and reactivity studies of a new phosphaalkyne

Article abstract of DOI:10.1055/s-1998-6089

Mesitylphosphaacetylene (1b) has been synthesized by AlCl₃ initiated elimination of bis(trimethylsilyl) ether from the phosphaalkene 2b. This new phosphaalkyne undergoes [3+2] cycloaddition reactions with diazo compounds (→ 6a,b), azides (→ 8a-c), and nitrile oxides (→ 10a,b) to yield five-membered heterocyclic products. The mesoionic reaction partners 11 and 13 react with 1b under elimination of CO₂ and COS, respectively, to furnish the 1,3-aza- and 1,3-thiaphospholes 12 and 14. Reaction of 1b with buta-1,3-diene leads to the diphosphatricyclooctene 18; it has been shown that the 1-phosphacyclohexa-1,4-diene 15 (characterized by an X-ray structure analysis of its W(CO)₅ complex 17) is an intermediate in the multistep reaction. Moreover, 1b has been characterized by Diels-Alder reactions with the cyclobutadiene 19 and the azacyclobutadiene 21 to afford the Dewar hetarenes 20 and 22.

Full text of DOI:10.1055/s-1998-6089

SYNTHESIS
September 1998
1305
Organophosphorus Compounds; 129.1 Mesitylphosphaacetylene: Synthesis and
Reactivity Studies of a New Phosphaalkyne
Andreas Mack, Elke Pierron, Thomas Allspach, Uwe Bergsträßer, Manfred Regitz*
Fachbereich Chemie der Universität Kaiserslautern, Erwin-Schrödinger-Straße, D-67663 Kaiserslautern, Germany
Fax + 49(631)3921; E-mail: regitz@rhrk.uni-kl.de
Received 6 February 1998
Abstract: Mesitylphosphaacetylene (1b) has been synthesized by
gate the synthetic potential of this aryl-substituted phos-
phaalkyne.
AlCl3 initiated elimination of bis(trimethylsilyl) ether from the
phosphaalkene 2b. This new phosphaalkyne undergoes [3+2]
cycloaddition reactions with diazo compounds (→ 6a,b), azides
(→ 8a–c), and nitrile oxides (→ 10a,b) to yield five-membered
heterocyclic products. The mesoionic reaction partners 11 and 13
react with 1b under elimination of CO2 and COS, respectively, to
furnish the 1,3-aza- and 1,3-thiaphospholes 12 and 14. Reaction
of 1b with buta-1,3-diene leads to the diphosphatricyclooctene 18;
it has been shown that the 1-phosphacyclohexa-1,4-diene 15
(characterized by an X-ray structure analysis of its W(CO)5 com-
plex 17) is an intermediate in the multistep reaction. Moreover, 1b
has been characterized by Diels–Alder reactions with the cyclo-
butadiene 19 and the azacyclobutadiene 21 to afford the Dewar
hetarenes 20 and 22.
In general, β-elimination reactions of suitably substituted
phosphaalkenes 2a,b have proved to be valuable for the
synthesis of kinetically substituted phosphaalkynes. In
particular, optimized elimination conditions for P/C triple
bond systems bearing tertiary alkyl groups consist of the
NaOH catalyzed elimination of hexamethyldisiloxane at
110–150°C in the absence of a solvent.8 This strategy was
also applied to the preparation of mesitylphosphaalkyne.8
However, we were not able to reproduce the reported syn-
thesis with a yield of 43%. Since 1b cannot be removed
rapidly enough from the reaction vessel due to its relative-
ly high boiling point of 50°C/10–3 mbar, the required re-
action temperature (150°C) always leads to a high per-
centage of polymerization products of 1b.
Key words: mesitylphosphaacetylene, heterophospholes, [3+2]
cycloaddition reactions, Diels–Alder reactions, Dewar hetarenes
Introduction
For this reason we sought an easier, alternative process
which avoids high temperatures. In 1996 Breit et al.
reported9 an efficient and quantitative synthesis of tert-
butylphosphaacetylene (1a) by elimination of hexameth-
yldisiloxane from 2a in the presence of a stoichiometric
amount of aluminum trichloride at comparably low tem-
peratures. However, in this case the phosphaalkyne could
not be separated from concomitantly formed chlorotrime-
thylsilane and the dichloromethane used as solvent. From
a mechanistic point of view, the initial step of this proce-
dure probably comprises the formation of the alanylphos-
phaalkene 3. Final elimination of AlCl2(OSiMe3) furnish-
es the phosphaacetylene 1a. Hence we have now investi-
gated the reactivity of the mesitylphosphaalkene 2b
towards aluminum trichloride.
tert-Butylphosphaacetylene (1a) has played a dominating
role in investigations on the chemistry of kinetically stabi-
lized phosphaalkynes. Its reactivity has been investigated
more thoroughly than that of any other compound with a
P/C triple bond.2–5 In general, phosphaalkynes bearing
tertiary alkyl substituents have an unusually high thermal
stability whereas the steric shielding of the bulky group in
1a has only a limited influence on the reactivity.
Synthesis of Mesitylphosphaacetylene (1b): Synthesis
of the E/Z-Mesitylphosphaalkene 2b
The phosphaalkene 2b is easily prepared by reaction of lith-
10
•
ium bis(trimethylsilyl)phosphide 2THF with mesitylene-
2-carboxylic acid chloride11 at –40°C. After the initial
In marked contrast to alkyl-substituted phosphaalkynes, elimination of lithium chloride the (not detectable)
our knowledge about phosphaalkynes bearing aryl acylphosphane undergoes spontaneous rearrangement to an
substituents is sparse: the rather unstable phenyl- E/Z-isomeric mixture of phosphaalkene 2b, which can be
phosphaacetylene6 is not accessible in the amounts need- isolated in good yields by bulb-to-bulb distillation. The
ed for reactivity studies and, although 2,4,6-tri-tert-but- pure E-isomer is obtained by crystallization from pentane.
ylphenylphosphaacetylene is more easily prepared, the However, in solution rapid (<15 min) isomerization occurs
reactivity of its P/C triple bond is markedly reduced by and the E/Z mixture is obtained again. E/Z-Mesitylphos-
the extreme shielding of the supermesityl group.7 In this phaalkene 2b was fully characterized by analytical and
context mesitylphosphaacetylene (1b) occupies an inter- spectroscopic data which are typical for phosphaalkenes12
mediate position and thus we were prompted to investi- and accordingly are not discussed further.

SYNTHESIS
Papers
1306
Synthesis of Mesitylphosphaacetylene (1b): Reaction tylphosphaacetylene toward numerous diazo compounds
of 2b with Aluminum Trichloride
has been investigated most thoroughly15, 16 and so we
have now studied analogous reactions with mesitylphos-
When a solution of 2b in dichloromethane is added drop- phaacetylene (1b).
wise to a suspension of aluminum trichloride/dichlo-
The use of α-diazoalkanes 4a,b gives rise to the selective
romethane at –40 °C, low temperature 31P NMR monitor-
ing of the reaction reveals the quantitative formation of
mesitylphosphaacetylene (1b). Workup by rapid distilla-
tion and subsequent filtration over silica gel with pentane
leads to the pure product 1b isolated in a yield of 30%. In
contrast to the thermal (NaOH catalyzed) process (with a
higher, but not reproducible yield of 43%), the described
aluminum trichloride initiated procedure is absolutely re-
liable.
formation of the 1,2,4-diazaphospholes 6a,b, which are
isolated in good yields by column chromatography. The
primary products of the reaction are the 3H-1,2,4-diaza-
phospholes of which 5b has been detected at –50°C by
NMR spectroscopy in the example of the cycloaddition of
mesitylphosphaacetylene (1b) with the diazo compound
4b. Thus, 5b exhibits a 31P NMR signal at remarkably low
field (δ = 297.6) compared to the tert-butyl derivative
(δ = 223.7). The sigmatropic [1,5]-proton shifts to furnish
6 are observed at 0 ˚C and are facilitated by the gain in
aromatization energy.
In analogy to the reaction of 4a,b with alkyl-substituted
phosphaalkynes no 1,2,3-diazaphosphole is formed. Ab
initio calculations on the parent compounds show that the
observed regioselectivity results from the energy differ-
ence of the transition states. The barrier calculated for the
initial formation of 3H-1,2,4-diazaphosphole is lower
than that for 1,2,3-diazaphosphole. The [3+2] cycloaddi-
tion is therefore under kinetic control.17
Similar to the intermediates 5, the mesityl-substituted
1,2,4-diazaphospholes 6 show low field shifts in their 31
P
NMR spectra (∆δ = +8.1 for 5a) compared to the tert-but-
At room temperature, mesitylphosphaacetylene (1b) is a
colorless viscous oil which crystallizes at ca. –5 to –10°C
and is best stored as such at –78°C because it decomposes
slowly but noticeably at about 25°C. Having this reliable
and reproducible synthetic method at hand, detailed reac-
tivity studies of 1b became possible.
As previously mentioned, tert-butylphosphaacetylene (1a)
has been used mainly as the model substrate for studies on
the reactivity of phosphaalkynes.8 Compound 1a shows a
very pronounced tendency to undergo cycloaddition,2–5
ene,13 and cyclooligomerization5, 14 reactions. In this paper
we concentrate mainly on novel 1,3-dipolar and [4+2] cy-
cloaddition reactions of mesitylphosphaacetylene (1b).
[3+2] Cycloaddition Reactions with Diazo
Compounds, Azides, and Nitrile Oxides
Phospholes containing further heteroatoms in the ring
play a significant role in the development of the chemistry
of low-coordinated phosphorus.2–4 Since phosphaalkynes
possess a cycloaddition potential similar to that of alkynes
and since a large selection of 1,3-dipoles is available, the
range of accessible phospholes has been greatly expanded
by various [3+2] cycloaddition reactions.2–4 The [3+2] cy-
cloaddition potential of the model substrate tert-bu-

SYNTHESIS
September 1998
1307
yl-substituted rings15,16 (Table). This is most likely caused
by the negative inductive effect of the mesityl group as
opposed to the positive inductive effect of the tert-butyl
group. In the 13C NMR spectra both ring carbon atoms
(C3, C5) are detected as doublet signals with characteris-
tic 1J(C,P) coupling constants at δ = 167.9 [1J(C,P) = 61.0
Hz] and 175.3 [1J(C,P) = 53.8 Hz]. The NH absorption in
1
the IR (ν = 3165 cm–1) and the signals in the H NMR
spectra (δ = 11.36 for 6a) clearly indicate that the nitrogen
is bonded to the original diazomethyl hydrogen atom.
1,2,3,4-Triazaphospholes are easily accessible by reaction
of alkyl-substituted phosphaalkynes.15 Starting from 1b
regiospecific [3+2] cycloadditions with azides 7a–c take
place to furnish the mesityl-substituted 1,2,3,4-triaza-
phospholes 8a–c in good to high yields. The regiochemis-
try is easily deduced from the significant 3J(H,P) coupling
constant of 6.6 Hz for the methyl protons in 8a. Although
the 31P NMR signals are in the range typical for 1,2,3,4-
triazaphospholes15 comparison with the tert-butyl deriva-
tive again reveals a low-field shift of ∆δ = +9.0 (for 8a)
(Table). Interestingly, the 13C NMR signal of the mesityl-
substituted ring carbon C5 is observed at δ = 181.0, a no-
ticeably upfield shift (δ = 198.3 for tert-butyl substitu-
tion).
The well known 1,3-dipolar cycloadditions of tert-bu-
tylphosphaacetylene with nitrile oxides18 can also be
transferred to the novel phosphaalkyne 1b. Benzonitrile
oxide (9a) and mesitylene-2-carbonitrile oxide (9b) un-
dergo rapid addition to furnish the 3,5-diaryl-1,2,4-oxaza-
phospholes 10a,b, isolated in high yields by bulb-to-bulb
distillation or crystallization. The dipole orientation is
such as to provide an optimal separation between the ste-
rically demanding substituents and is the same as that for
1a.18 Although thermodynamically more favored, the
1,2,5-oxazaphosphole ring is not formed. In accordance
with the 1,2,4-diazaphospholes 6, the 3,5-diaryl com-
pounds 10 show significant shifts of the 31P NMR signals
to lower field (∆δ = +15.3) in comparison to those with
tert-butyl substitution at C5. In the 13C NMR spectrum of
10b the mesityl substitution leads to a significant upfield
shift of the signal for C5 (δ = 210.2) as compared to tert-
butyl substitution (δ = 226.5). The resonance for C3, how-
ever, has the same chemical shift of δ = 180.0 (Table).
Both ring carbon atom signals are typically split into dou-
1
blets with characteristic J(C,P) coupling constants of
about 60 Hz.
[3+2] Cycloaddition Reactions with Mesoionic
Compounds
δ
As reported for 1a,19 mesitylphosphaacetylene (1b) also
undergoes smooth reactions with the mesoionic com-
pounds 11 and 13 to furnish the 1,3-azaphosphole 12 or
the 1,3-thiaphosphole 14; the reactions proceeding at rel-
atively low temperatures (55°C). However, the primary
formed bicyclic adducts cannot be detected: spontaneous
extrusion of carbon dioxide (→ 12) or carbon oxide sul-

SYNTHESIS
Papers
1308
fide (→ 14) occurs. As expected from the results with the
above discussed heterophospholes, the 31P NMR signal of
the 1,3-azaphosphole 12 is shifted downfield to 106.0 ppm
(∆δ = +9.4 compared to tert-butyl substitution)19 (Table).
ion peak in mass spectrum indicates that 15 is a 1:1 adduct
of 1b with buta-1,3-diene.
The 1,3-thiaphosphole 14 is an exception: in this case the
31P NMR chemical shift of δ = 217.5 is similar to that of
the product formed from 1a (δ = 220.6). The 13C NMR
chemical shifts and J(C,P) coupling values of 12 and 14
unambiguously prove the formation of 1,3-azaphosphole
and 1,3-thiaphosphole ring systems. Each ring carbon sig-
nal is split into a doublet with characteristic J(C,P) values.
When compared to those of the tert-butyl derivative, the
13C NMR signals for C2 (δ = 170.8) and C5 (δ = 142.1) in
the nitrogen containing compound 12 are typical while
that of C4 (δ = 141.3) is significantly shifted upfield (∆δ
= –15.1).19 In the thiaphosphole 14, mesityl substitution at
C4 results in a marked upfield shift20 of the signal for ei-
ther C2 or C4 to δ = 157.4 while the other carbon shows a
typical value of δ = 177.4 (Table).
The stability of the Diels–Alder adduct 15 is increased
significantly by coordination of one tungsten pentacarbo-
nyl fragment at phosphorus. Complete purification of the
η1-complex 17 (63%) is possible by column chromatogra-
phy on silica gel and the complete set of analytical and
spectroscopic data can be obtained. The tungsten frag-
ment at phosphorus leads to a significant upfield shift to
1
δ = 170.0 in the 31P NMR spectrum. The J(P,W) cou-
[4+2] Cycloaddition Reactions with Buta-1,3-diene
pling constant of 259.6 Hz is typical for W(CO)5–phos-
phaalkene complexes.23 On comparison with the [2-meth-
The main purpose of the studies of reactions of kinetical- yl-1-phosphacyclohexene]pentacarbonyltungsten com-
ly stabilized phosphaalkynes with 1,3-dienes was to syn- plex [δ = 161.8, 1J(P,W) = 246.6 Hz]22 good agreement of
thesize 1-phosphacyclohexa-1,4-dienes. However, at the 31P and 13C NMR data for the phosphaalkene subunits
90°C these reactions lead exclusively to the unexpected is seen. In the phosphacyclohexadiene complex 17 the sp2-
diphosphatricyclooctenes.21 Their formation can be ra- carbon C2 appears as a doublet at δ = 181.4 with a charac-
1
tionalized by a reaction sequence starting with an initial teristic J(C,P) splitting of 47.5 Hz. The other carbon di-
[4+2] cycloaddition, which is followed by a phospha-ene rectly bonded to phosphorus (C6) is observed at δ = 37.5
reaction, and a final intramolecular [4+2] cycloaddition. with a small 1J(C,P) coupling of 9.3 Hz. The C3 signal is
In the case of alkyl-substituted phosphaalkynes the pri- seen at comparable field [δ = 31.4, 2J(C,P) = 2.6 Hz]. The
marily formed Diels–Alder adducts have not yet been de- two sp2-carbon atoms of the C/C double bond show typical
tected.22
signals at δ = 120.3 and 125.4 while the equatorial and axial
carbonyl carbons of the metal fragment are observed at δ =
194.5 and 198.8 with typical splitting patterns.
In contrast, the analogous reaction of mesitylphosphaacet-
ylene (1b) now provides the first access to a 1-phosphacy-
clohexa-1,4-diene when the reaction is performed at rela- The constitution of 17 suggested by the NMR data has
tively low temperatures (55 ˚C) in toluene as a solvent. been confirmed by a crystal structure analysis (Figure),
The phosphaalkene 15 can be isolated and characterized which shows a planar 1-phosphacyclohexa-1,4-diene
by 1H, 31P NMR, and mass spectroscopy. However, com- ring: The mean deviation from the best plane is 0.005 Å; all
plete purification of 15 is not possible due to unselective torsion angles are in the range of –1.2 to +0.7°. The plane
decomposition processes occurring during bulb-to-bulb of the mesityl ring at C2 is perpendicular to that of the phos-
distillation or column chromatography. The 31P NMR sig- phacyclohexadiene ring as can be deduced from the torsion
nal at δ = 215.7 clearly indicates that a phosphaalkene unit angles (C3/C2/C21/C22 –87.9°, C3/C2/C21/C26 90.4°, P1/
is present in the product. Moreover, the 100% molecular C2/C21/C22 92.5°, P1/C2/C21/C26 –89.2°).

SYNTHESIS
September 1998
1309
carboxylate 19 to give the 2-Dewar-phosphinine 20 regio-
selectively and in quantitative yield. However, purifica-
tion of the bicyclic compound 20 by bulb-to-bulb distilla-
tion is not possible due to thermal decomposition at the
required high temperatures.
Again the mesityl substitution leads to a marked low-field
shift (δ = 335.9) in the 31P NMR spectrum when compared
with the tert-butyl derivative (δ = 314.0). In the 13C NMR
spectrum of 20 the former sp-carbon of 1b (now C3) is
observed at δ = 224.0, i.e., a dramatic upfield shift (∆δ =
–15.8 vs. tert-butyl substitution). The same effect has
been observed in the heterocyclic compounds 6, 8, 10, 12,
14, and 22 (Table). In contrast to C3, 13C NMR data of the
remaining skeletal carbon atom are in good agreement
with those of the tert-butyl derivative.
Figure. Structure of 17 in the crystal. Selected bond lengths [Å] and
bond angles [˚]: P1–C2 1.670 (6), P1–C6 1.826(6), P1–W1 2.467(2),
C2–C3 1.504(8), C3–C4 1.483(9), C4–C5 1.321(10), C5–C6
1.484(9), C2–C21 1.481(8); C2–P1–C6 107.9(3), C2–P1–W1
132.8(2), C6–P1–W1 119.3(2), P1–C6–C5 115.3(4), P1–C2–C3
124.2(4), P1–C2–C21 119.7(4), C3–C2–C21 116.2(5), C2–C3–C4
118.2(5), C3–C4–C5 126.2(6), C4–C5–C6 128.3(6).42
As expected, the organophosphorus ligand 15 occupies an
axial position on the tungsten pentacarbonyl fragment
with a typical planar coordination geometry. The P1/C2
bond length of 1.670(6) Å is typical for η1-complexed24
and non-complexed25 phosphaalkenes and clearly indi-
cates that the coordination of W(CO)5 in 17 has no signi-
ficant effect on the geometry of the phosphaalkene sub-
unit. However, the P1/W1 bond distance of 2.467(2) Å is
somewhat shorter in comparison to the average values re-
ported in the literature.24 The C4/C5 bond length of
1.321(10) Å and the P1/C6 bond length are of normal
magnitudes for C/C double and P/C single bonds.
Tri-tert-butylazete (21) also reacts regioselectively with
mesitylphosphaacetylene to afford the expected Dewar-
1,3-azaphosphabenzene 22, isolated in 91% yield as col-
orless crystals. As is the case of the Dewar-2-phosphaben-
zene 20, the 31P NMR signal of the 1-aza derivative 22 at
δ = 230.4 shows a dramatic low field shift (∆δ = +28.2
compared to tert-butyl substitution).28 The 13C NMR res-
onances and J(C,P) coupling values of the skeletal carbon
atoms are in good accord with those of the tert-butyl de-
rivative, with the exception of C2: the phosphaalkene car-
bon atom is found at δ = 225.9, i.e., a remarkable upfield
resonance shift (∆δ = –16.9) (Table).
Even though the ene/[4+2] cycloaddition reaction with a
further equivalent of mesitylphosphaacetylene (1b) is
slow, it is possible to synthesize the 1,7-diphosphatricy-
clooctene 18. This cage compound is characterized by
mass spectrometry (m/z = 378) and characteristic doublet
resonances in the 31P NMR spectrum at δ = –168.0 and
–163.1 with 1J(P,P) couplings of 158.3 Hz. On compari-
son with the tert-butyl derivative (δ = –210.6 and –
165.6)20 it is seen that one 31P NMR signal of 18 is shifted
significantly downfield while the other has a comparable
chemical shift of around δ = –165.
Conclusions
This new synthesis of mesitylphosphaacetylene (1b) me-
diated by aluminum trichloride has made extensive reac-
tivity studies possible. In the investigated [3+2] and [4+2]
cycloaddition reactions 1b shows parallels to tert-but-
ylphosphaalkyne (1a). However, 1b is generally slightly
less reactive so that the reactions proceed more slowly
than those of 1a. In the case of buta-1,3-diene, formation
of the [4+2]-cycloadduct 1b is faster than the subsequent
ene-reaction, thus the reaction can be stopped at this stage
(using one equivalent of 1b). This led to the first synthesis
and isolation of a 1-phosphacyclohexa-1,4-diene 15 and
[4+2] Cycloaddition Reactions with Cyclobutadienes
Just as the reactant pair “cyclobutadiene/acetylene”
opened an access to the chemistry of the valence isomers
of benzene,26 valence isomers of (hetero)phosphaben-
zenes are obtained by using alkyl-substituted phos-
phaalkynes and cyclic 1,3-dienes such as 1927 and 21.28
Mesitylphosphaacetylene (1b) undergoes an analogous
reaction with the kinetically stabilized cyclobutadiene-

SYNTHESIS
Papers
1310
(10 mL) was added dropwise under vigorous magnetic stirring at –
40°C. The mixture was held for 2 h at this temperature. The solvent
and TMSCl were removed at –20°C/10–3 mbar to leave a dark brown
residue. Immediate distillation (50 – 70°C/10–3 mbar) gave a color-
less oil. Further purification was achieved by filtration through a D3
sinter filled with silica gel and pentane (50 mL) as eluent. The solvent
was finally removed at 25°C/10–3 mbar to give 1b as a colorless oil
which crystallized at around –5°C; yield: 299 mg (30%; 1b is best
stored at –78°C).
its W(CO)5 complex 17. This example shows that the
electronically altered P/C triple bond resulting from mes-
ityl substitution may facilitate the synthesis of structurally
new compounds. For this reason we will investigate the
reactivity of mesitylphosphaalkyne 1b in more detail. In-
vestigations on thermally induced and metal-mediated cy-
clooligomerization reactions are underway and may pro-
vide further promising results.
IR (film): ν = 2942, 2917 (CH), 1603, 1551 (P≡C), 1460, 851,
738 cm–1.
31P NMR (C6D6): δ = 2.5 (s).
All reactions were performed under argon (purity >99.998%) using
Schlenk techniques. The solvents were dried by standard procedures,
distilled, and stored under argon. Compounds 4a,29 4b,30 7a,31 7b,32
7c,33 9b,34 11,35 13,36 19,26 21,37 lithium bis(trimethylsilyl)-
phosphide•2 THF,10 mesitylene-2-carboxylic acid chloride,11 benzo-
hydroxamic acid chloride,38 and W(CO)5(THF)39 were prepared by
the published methods. Column chromatography was performed in
water-cooled glass tubes under argon. The eluate was monitored with
a UV absorbance detector (λ = 254 nm). Silica gel was heated for 3 h
in vacuo and then deactivated with 4% water (Brockmann activity II).
The bulb-to-bulb distillations were carried out in a Büchi GKR 50
apparatus, the temperatures stated are oven temperatures. Mps were
determined on a Mettler FP61 apparatus (heating rate 3°C/min) and
are uncorrected. Microanalyses were performed with a Perkin–Elmer
1H NMR (C6D6): δ = 1.98 (s, 3H, p-CH3), 2.39 (s, 6H, o-CH3), 6.56
(s, 2H, aryl-H).
13C NMR (C6D6): δ = 21.6 (s, o-CH3), 21.8 (s, p-CH3), 128.3 (d,
4J(C,P) = 2.1 Hz, m-C), 129.5 (s, p-C), 139.6 (d, 3J(C,P) = 6.2 Hz, o-
2
1
C), 142.7 (d, J(C,P) = 6.9 Hz, i-C), 163.4 [d, J(C,P) = 45.8 Hz,
P≡C].
MS (EI, 70 eV): m/z (%) = 162 (100.0) [M+], 147 (78.8) [M+ – CH3],
133 (10.9) [MesCP+ – CH2 +– CH3], 129 (21.4), 115 (14.0), 119 (12.2)
[Mes+], 91 (3.0) [C6H4CH3 ], 77 (5.2) [C6H5 ].
+
C10H11P
(162.17)
calcd
found
C
74.06
73.80
H
6.84
6.88
5-Mesityl-1H-1,2,4-diazaphospholes 6a,b; General Procedure:
To a magnetically stirred solution of phosphaalkyne 1b in Et2O
(3 mL) at –78°C was added dropwise a solution of α-diazo ester 4 in
Et2O (2 mL). After the mixture had been allowed to warm up to r.t.
over a period of 24 h, all volatile components were removed at 25°C/
10–3 mbar. The purification of the residue was achieved by column
chromatography (silica gel, pentane/Et2O 3:1) to give 6a,b.
1
Analyser 2400. H NMR and 13C NMR spectra were recorded with
Bruker AC 200 and Bruker AMX 400 spectrometers using TMS or
solvent as internal standard. 31P NMR spectra were measured on a
Bruker AC 200 (80.8 MHz) spectrometer with 85% H3PO4 as exter-
nal standard. MS were recorded with a Finnigan MAT 90 spectrome-
ter at 70 eV. IR spectra were measured on Perkin–Elmer 16 PC FT-
IR and Perkin–Elmer 1310 spectrophotometers.
Methyl 5-Mesityl-1H-1,2,4-diazaphosphole-3-carboxylate (6a):
From methyl diazoacetate (4a) (62 mg, 0.62 mmol) and phos-
phaalkyne 1b (100 mg, 0.62 mmol), 6a was obtained as a yellow oil;
yield: 108 mg (67%).
(E,Z)-[Mesityl(trimethylsiloxy)methylene]trimethylsilylphos-
phane (2b):
Lithium bis(trimethylsilyl)phosphide•2 THF (9.85 g, 30 mmol) in
pentane (150 mL) was added dropwise under magnetic stirring to a
cooled solution (–40°C) of mesitylene-2-carboxylic acid chloride
(5.48 g, 30 mmol) in pentane (150 mL). LiCl precipitated in the
course of the reaction. The mixture was then allowed to warm up to
25°C and stirring was continued for 30 min. After concentration of
the suspension, LiCl was removed by centrifugation. The solvent was
then removed at 25°C/10–3 mbar and the oily residue purified by
bulb-to-bulb distillation at 150–160°C/10–2 mbar to furnish a pale
yellow oil which partially crystallized; yield: 7.11 g (73%) of the E/
Z-isomeric mixture.
IR (Et2O): ν = 3165 (NH), 2995–2800, 1723 (CO), 1440, 1350, 1324,
1152 cm–1.
31P NMR (C6D6): δ = 105.7 (s).
1H NMR (CDCl3): δ = 2.04 (s, 6H, o-CH3), 2.21 (s, 3H, p-CH3), 3.93
(s, 3H, OCH3), 6.92 (s, 2H, aryl-H), 11.36 (s, 1H, NH).
13C NMR (CDCl3): δ = 20.5 [d, 5J(C,P) = 1.6 Hz, o-CH3], 20.8 (s, p-
CH3), 52.45 (s, OCH3), 128.2 [d, 2J(C,P) = 14.5 Hz, i-C, Mes], 128.4
(s, m-C, Mes), 137.2 [d, 3J(C,P) = 3.2 Hz, o-C, Mes], 139.1 (s, p-C,
Mes), 163.4 [d, 2J(C,P) = 22.5 Hz, CO], 167.9 [d, 1J(C,P) = 61.0 Hz,
C3/5], 175.3 [d, 1J(C,P) = 53.8 Hz, C3/5].
Isomer E-2b was isolated as such by crystallization from pentane; mp
77°C.
MS (EI, 70 eV): m/z (%) = 262 (100.0) [M+], 219 (27.8) [M+ – N2 –
CH3], 175 (44.9) [M+ – N2 – CO2CH3], 144 (43.7) [MesCCH+], 91
IR (film): ν = 2950, 1605, 1370, 1250, 1205, 1175, 1000, 980, 940 cm–1.
31P NMR (C6D6): δ = 126.3 (s, E-2b, 64%), 122.4 (s, Z-2b, 36%).
1H NMR (C6D6): E-2a: δ = 0.05 [d, 3J(H,P) = 4.4 Hz, 9H, PSi(CH3)3],
0.47 [d, 5J(H,P) = 1.1 Hz, 9H, OSi(CH3)3], 2.10 (s, 3H, p-CH3), 2.43
(s, 6H, o-CH3), 6.70 (s, 2H, aryl-H).
+
+
(28.0) [C6H4CH3 ], 77 (11.6) [C6H5 ].
C13H15N2O2P calcd
(262.25) found
C
59.54
59.52
H
5.76
5.80
N
10.68
10.12
3
Ethyl 5-Mesityl-1H-1,2,4-diazaphosphole-3-carboxylate (6b):
From ethyl diazoacetate (4b) (70 mg, 0.62 mmol) and phosphaalkyne
1b (100 mg, 0.62 mmol), 6b was obtained as a yellow oil; yield:
124 mg (73%).
Z-2a: δ = –0.04 [s, 9H, OSi(CH3)3], 0.50 [d, J(H,P) = 3.6 Hz, 9H,
PSi(CH3)3], 2.10 (s, 3H, p-CH3), 2.36 (s, 6H, o-CH3), 6.70 (s, 2H,
aryl-H).
13C NMR (C6D6): E,Z-2b: δ = 0.7–1.1 [2 Si(CH3)3 (E), 2 Si(CH3)3
(Z), due to overlap no exact assignment possible], 20.3 (s, o-CH3),
IR (CH2Cl2): ν = 3369 (NH), 3298, 3216, 2990–2800, 1748, 1723,
3
1467, 1446, 1383, 1199, 1165, 1110 cm–1.
21.6 (s, p-CH3), 128.6 (s, m-C), 134.2 [d, J(C,P) = 4.2 Hz, o-C],
2
1
31P NMR (C6D6): δ = 106.0 (s).
137.6 (s, p-C), 143.4 (d, J(C,P) = 9.7 Hz, i-C], 198.2 [d, J(C,P) =
1H NMR (CDCl3): δ = 1.42 [t, 3H, 3J(H,H) = 7.2 Hz, CH2CH3], 2.07
54.1 Hz, P=C(E)], 205.5 [d, 1J(C,P) = 61.7 Hz, P=C(Z)].
3
(s, 6H, o-CH3), 2.27 (s, 3H, p-CH3), 4.45 [q, 2H, J(H,H) = 7.1 Hz,
C16H29OPSi2 calcd
(324.55) found
C
59.21
58.90
H
9.01
8.96
CH2CH3], 6.94 (s, 2H, aryl-H), 10.45 (s, 1H, NH).
13C NMR (CDCl3): δ = 14.3 (s, CH2CH3), 20.6 (s, o-CH3), 21.0 (s, p-
CH3), 61.7 (s, CH2CH3), 128.9 [d, 2J(C,P) = 14.5 Hz, i-C, Mes], 128.4
(s, m-C, Mes), 137.2 [d, 3J(C,P) = 3.2 Hz, o-C, Mes], 139.1 (s, p-C,
Mes), 163.3 [d, 2J(C,P) = 22.5 Hz, CO], 167.9 [d, 1J(C,P) = 57.0 Hz,
C3], 175.3 [d, 1J(C,P) = 55.4 Hz, C5].
Mesitylphosphaacetylene (1b):
To a suspension of freshly sublimed AlCl3 (822 mg, 6.16 mmol) in
CH2Cl2 (15 mL) a solution of 2b (2.0 g, 6.16 mmol) in CH2Cl2

SYNTHESIS
September 1998
1311
MS (EI, 70 eV): m/z (%) = 276 (100.0) [M+], 219 (46.5) [M+ – N2 –
3J(C,P) = 4.0 Hz, o-C, Mes], 138.9 (s, p-C, Mes), 145.2 [d, 2J(C,P) =
9.4 Hz, i-C, Ph], 147.1 (s, p-C, Ph), 182.2 [d, 1J(C,P) = 49.8 Hz, P=C].
MS (EI, 70 eV): m/z (%) = 326 (1.8) [M+], 298 (100.0) [M+ – N2], 297
(42.2) [M+ – N2 – H], 251 (52.1) [M+ – N2 – H – NO2], 236 (20.6) [M+
– N2 – H – NO2 – CH3], 147 (12.9) [MesCP+ – CH3].
CH2CH3], 177 (60.0) [MesCPNH+], 175 (63.8) [M+ – N2
–
CO2CH2CH3], 144 (56.3) [MesCCH+], 91 (19.4) [C6H4CH3 ], 77
+
+
+
(15.5) [C6H5 ], 57 (24.6) [COCH2CH3 ].
5-Mesityl-1,2,3,4-triazaphospholes 8a–c; General Procedure:
To a magnetically stirred solution of phosphaalkyne 1b (0.62 mmol)
in Et2O (3 mL) at –78°C was added dropwise the azide 7a in pentane
(3 mL) or 7b,c (0.62 mmol) in Et2O (2 mL). The solution was allowed
to warm up to r.t. and stirred for 24 h. All volatile components were
removed at 25°C/10–3 mbar. Purification of the crude materials was
as described below.
C16H15N4O2P calcd
(326.30) found
C
58.89
58.87
H
4.63
4.61
N
17.17
17.06
5-Mesityl-3-phenyl-1,2,4-oxazaphosphole (10a):
To a solution of phosphaalkyne 1b (324 mg, 2.00 mmol) and triethyl-
amine (250 mg, 2.50 mmol) in Et2O (10 mL) a solution of benzohy-
droxamic acid chloride (310 mg, 2.00 mmol) in Et2O (5 mL) was add-
ed dropwise at 0°C. Stirring was continued for 1 h at the same tem-
perature. After separation of the precipitate by filtration the solvent
was removed at 25°C/10–3 mbar. Bulb-to-bulb distillation (200°C/
10–2 mbar) furnished 10a as a colorless oil; yield: 510 mg (90%).
IR (film): ν = 2960, 2930, 1615, 1465, 1317, 1270, 1145, 1005, 855,
765, 695, 680 cm–1.
5-Mesityl-3-methyl-1,2,3,4-triazaphosphole (8a):
From methyl azide (7a) (140 mg, 2.5 mmol) and phosphaalkyne 1b
(324 mg, 2.0 mmol) 8a was obtained after bulb-to-bulb distillation
(160°C/10–2 mbar) as a yellow oil; yield: 410 mg (93%).
IR (film): ν = 2943, 2915, 1610, 1440, 1375, 1235, 1188, 1008, 853,
813, 684 cm–1.
31P NMR (CDCl3): δ = 82.9 (s).
31P NMR (CDCl3): δ = 182.5 (s).
1H NMR (C6D6): δ = 2.23 (s, 3H, o-CH3), 2.30 (s, 6H, p-CH3), 6.94
(s, 2H, aryl-H, Mes), 7.30–8.10 (m, 5H, aryl-H, Ph).
1H NMR (CDCl3): δ = 2.08 (s, 6H, o-CH3), 2.31 (s, 3H, p-CH3), 4.28
[d, 3J(H,P) = 6.6 Hz, 3H, NCH3], 6.91 (s, 2H, aryl-H).
13C NMR (CDCl3): δ = 21.0 (s, p-CH3), 21.1 (s, o-CH3), 38.5 [d,
C17H16NOP
(281.29)
calcd
found
C
72.59
72.30
H
5.73
5.75
N
4.98
4.50
2
2J(C,P) = 15.7 Hz, NCH3], 128.3 (s, m-C), 128.9 [d, J(C,P) = 18.0
3
Hz, i-C], 136.5 [d, J(C,P) = 3.9 Hz, o-C], 137.8 (s, p-C), 181.0 [d,
3,5-Dimesityl-1,2,4-oxazaphosphole (10b):
1J(C,P) = 49.0 Hz, C5].
At –78°C a solution of mesitylcarbonitrile oxide (9b) (69 mg,
0.43 mmol) in toluene (3 mL) was added dropwise to a stirred solu-
tion of 1b (70 mg, 0.43 mmol) in toluene (2 mL). The mixture was
allowed to warm up to 25°C overnight and the solvent was then re-
moved at 25°C/10–3 mbar. The colorless residue was washed with
cold pentane affording the 1,2,4-oxazaphosphole 10b as a colorless
powder which was crystallized from Et2O at –30°C; yield: 124 mg
(89%), mp 155°C (dec.).
C11H14N3P
(219.23)
calcd
found
C
60.27
60.30
H
6.44
6.39
N
19.17
19.20
3-Butyl-5-mesityl-1,2,3,4-triazaphosphole (8b):
From butyl azide (7b) (62 mg, 0.62 mmol) and phosphaalkyne 1b
(100 mg, 0.62 mmol), 8b was obtained after chromatography (silica
gel, pentane/Et2O 3:1) after evaporation at 25°C/10–3 mbar as a yel-
low oil; yield: 121 mg (75%).
IR (pentane): ν = 1413, 1380, 1099, 1019, 866, 850, 807, 730, 703,
668 cm–1.
IR (film): ν = 2958, 2872, 2854, 1612, 1457, 1376, 1208, 1033, 1002,
851, 735 cm–1.
31P NMR (C6D6): δ = 92.2 (s).
31P NMR (C6D6): δ = 178.4 (s).
1H NMR (C6D6): δ = 2.07, 2.13 (each s, 3H, p-CH3), 2.19, 2.23 (each
s, 6H, o-CH3), 6.70, 6.77 (each s, 2H, aryl-H).
1H NMR (C6D6):
δ = = 6.5 Hz,
1.00 [t, 3H, 3J(H,H)
13C NMR (CDCl3): δ = 20.4, 20.5 (each s, o-CH3), 21.1, 21.1 (each s,
p-CH3), 127.4 [d, 2J(C,P) = 5.1 Hz, i-C], 127.7 (s, i-C), 128.5, 128.7
(each s, m-C), 136.4 [d, 3J(C,P) = 2.6 Hz, o-C], 137.0 [d, 3J(C,P) = 4.2
Hz, o-C], 138.6, 139.8 (each s, p-C), 180.0 [d, 1J(C,P) = 62.7 Hz, C3],
210.2 [d, 1J(C,P) = 58.5 Hz, C5].
CH2CH2CH2CH3], 1.39–1.49 (m, 2H, CH2CH2CH2CH3), 2.00–2.08
(m, 2H, CH2CH2CH2CH3), 2.11 (s, 6H, o-CH3), 2.33 (s, 3H, p-CH3),
4.67 (pseudo-q, 2H, CH2CH2CH2CH3), 6.97 (s, 2H, aryl-H).
13C NMR (CDCl3): δ = 13.4 (s, CH2CH2CH2CH3), 19.7 (s,
CH2CH2CH2CH3), 20.9 (s, p-CH3), 21.0 [d, 4J(C,P) = 2.4 Hz, o-CH3],
34.3 [d, 3J(C,P) = 3.2 Hz, CH2CH2CH2CH3], 52.2 [d, 2J(C,P) = 11.3
Hz, CH2CH2CH2CH3], 128.4 (s, m-C, Mes), 129.2 [d, 2J(C,P) = 18.5
Hz, i-C, Mes], 136.8 [d, 3J(C,P) = 4.0 Hz, o-C, Mes], 138.0 (s, p-C,
Mes), 180.7 [d, 1J(C,P) = 49.8 Hz, C5].
MS (EI, 70 eV): m/z (%) = 323 (6.7) [M+], 178 (10.9) [M+ – MesCN],
147 (100.0) [MesCO+], 145 (5.0) [MesCN+], 119 (12.2) [Mes+].
C20H22NOP
(323.37)
calcd
found
C
74.29
74.46
H
6.86
6.66
N
4.33
4.37
MS (EI, 70 eV): m/z (%) = 261 (22.3) [M+], 219 (29.4) [M+ – N3], 177
(93.7), 162 (22.1) [MesCP+], 144 (63.2) [MesCCH+], 119 (32.6)
4-Mesityl-1-methyl-2,5-diphenyl-1,3-azaphosphole (12); Typical
Procedure:
[Mes+], 91 (28.4) [C6H4CH3 ], 77 (20.3) [C6H5 ], 57 (44.9) [n-Bu+].
+
+
C14H20N3P
(261.31)
calcd
found
C
64.35
64.19
H
7.71
7.82
N
16.08
15.97
To a magnetically stirred solution of phosphaalkyne 1b (100 mg,
0.62 mmol) in toluene (2 mL) at r.t. was added dropwise a solution of
the münchnone 11 (155 mg, 0.62 mmol) in toluene (1 mL). After the
mixture had been heated at 55°C for 6 d, the volatile components
were removed at 25°C/10–3 mbar and the remaining oil was purified
by column chromatography (silica gel, pentane/Et2O 20:1) to give 12
as a yellow oil; yield: 105 mg (46%).
5-Mesityl-3-(4-nitrophenyl)-1,2,3,4-triazaphosphole (8c):
From 4-nitrophenyl azide (7c; 101 mg, 0.62 mmol) and phos-
phaalkyne 1b (100 mg, 0.62 mmol), 8c was obtained after chromato-
graphy (silica gel, pentane/Et2O 3:1) and evaporation of the eluent at
25°C/10–3 mbar as a yellow oil; yield: 139 mg (69%).
IR (CH2Cl2): ν = 3776, 3076, 2999, 2963, 1596 (NO2), 1529 (NO2),
1495, 1351, 1255, 1035, 854, 805 cm–1.
IR (CH2Cl2): ν = 3081, 2960, 2922, 1474, 1446, 1353, 1257, 1074,
1020, 856, 808 cm–1.
31P NMR (C6D6): δ = 106.0 (s).
31P NMR (C6D6): δ = 177.7 (s).
1H NMR (CDCl3): δ = 2.19 (s, 6H, o-CH3), 2.30 (s, 3H, p-CH3), 3.64
(s, 3H, NCH3), 6.86 (s, 2H, aryl-H, Mes), 7.21–7.56 (m, 10H, aryl-H,
Ph).
1H NMR (C6D6): δ = 2.17 (s, 6H, o-CH3), 2.35 (s, 3H, p-CH3), 7.02
(s, 2H, aryl-H, Mes), 8.14–8.17 (m, 2H, o-H, Ph), 8.40–8.42 (m, 2H,
m-H, Ph).
13C NMR (CDCl3): δ = 21.0 (s, p-CH3), 21.5 (s, o-CH3), 37.9 (s,
NCH3), 127.6 (s, aryl-C), 127.7 (s, aryl-C), 127.8 (s, aryl-C), 128.1 (s,
aryl-C), 128.3 (s, aryl-C), 129.5 [d, 2J(C,P) = 8.0 Hz, aryl-C], 129.7
13C NMR (CDCl3): δ = 21.1 (s, p-CH3), 21.2 [d, 4J(C,P) = 2.4 Hz, o-
CH3], 122.0 [d, 2J(C,P) = 8.0 Hz, o-C, Ph], 125.4 (s, m-C, Ph), 128.0
[d, 2J(C,P) = 17.7 Hz, i-C, Mes], 128.8 (s, m-C, Mes), 136.9 [d,
2
(s, aryl-C), 133.8 [d, J(C,P) = 15.3 Hz, aryl-C], 134.0 (s, aryl-C),

SYNTHESIS
Papers
1312
135.6 (s, aryl-C), 135.7 (s, aryl-C), 136.9 [d, 2J(C,P) = 3.3 Hz, aryl-
C], 141.3 [d, 1J(C,P) = 43.8 Hz, C4], 142.1 [d, 2J(C,P) = 4.6 Hz, C5],
170.8 [d, 1J(C,P) = 47.1 Hz, C2].
[MesCPC4H4+ – CH3], 91 (16.7) [C6H4CH3 ], 77 (11.7) [C6H5 ], 56
(23.2) [C4H6 ], 55 (63.6) [C4H5 ].
+
+
+
+
C19H17O5PW calcd
(326.30) found
C
42.25
41.79
H
3.17
3.15
MS (EI, 70 eV): m/z (%) = 369 (40.3) [M+], 251 (43.0) [M+ – Mes +
H], 118 (100.0) [Mes+ – H], 91 (7.4) [C6H4CH3 ], 77 (29.4) [C6H5 ].
+
+
2,8-Dimesityl-1,7-diphosphatricyclo[3.2.1.02,7]oct-3-ene (18):
A solution of phosphaalkyne 1b (134 mg, 0.62 mmol) in toluene
(2 mL) was stirred at 55°C for 1 week. The solvent was then removed
at 25°C/10–3 mbar. Further purification of the orange, oily residue by
bulb-to-bulb distillation (50 – 250°C/10–3 mbar) or by column chro-
matography (silica gel, pentane/Et2O) was not possible due to unse-
lective decomposition.
4-Mesityl-2,5-diphenyl-1,3-thiaphosphole (14):
The reaction and workup of phosphaalkyne 1b (100 mg, 0.62 mmol)
in toluene (2 mL) and the mesoionic compound 13 (157 mg,
0.62 mmol) in toluene (1 mL) were analogous to the preceding proce-
dure and furnished 14 as a yellow oil; yield: 135 mg (59%).
IR (Et2O): ν = 2976, 2944, 2923, 2840, 1474, 1449, 1378, 850, 756,
691 cm–1.
1
31P NMR (C6D6): δ = –168.0 [d, J(P,P) = 158.3 Hz], –163.1 [d,
31P NMR (C6D6): δ = 217.5 (s).
1J(P,P) = 158.3 Hz].
1H NMR (C6D6): δ = 2.11 (s, 6H, o-CH3), 2.33 (s, 3H, p-CH3), 6.91
(s, 2H, aryl-H, Mes), 7.24–7.40 (m, 10H, aryl-H, Ph).
13C NMR (CDCl3): δ = 21.1 (s, p-CH3), 21.2 (s, o-CH3), 125.9 [d,
2J(C,P) = 13.3 Hz, aryl-C], 128.0 (s, aryl-C), 128.2 (s, aryl-C), 128.4
MS (EI, 70 eV): m/z (%) = 378 (42.9) [M+], 363 (13.0) [M+ – CH3],
216 (100.0) [M+ – MesCP], 162 (44.5) [MesCP+], 119 (13.8) [Mes+],
+
+
91 (16.7) [C6H4CH3 ], 77 (11.2) [C6H5 ].
2
[d, J(C,P) = 2.0 Hz, aryl-C], 128.5 (s, aryl-C), 129.0 (s, aryl-C),
Methyl 1,5,6-Tri-tert-butyl-3-mesityl-2-phosphabicyc-
lo[2.2.0]hexa-2,5-diene-4-carboxylate (20):
133.2 [d, 2J(C,P) = 19.2 Hz, aryl-C], 134.1 (s, aryl-C), 136.3 (s, aryl-
2
C), 136.4 [d, J(C,P) = 4.0 Hz, aryl-C], 136.5 (s, aryl-C), 136.9 (s,
To a magnetically stirred solution of cyclobutadiene 19 (172 mg,
0.62 mmol) in pentane (3 mL) at –78°C was added dropwise a solution
of phosphaalkyne 1b (100 mg, 0.62 mmol) in pentane (3 mL). The mix-
ture was then allowed to warm to 25°C over 4 h and stirred for 2 h at
r.t. The volatile components were removed at 25°C/10–3 mbar. Purifi-
cation of the remaining oil 20 was not possible by bulb-to-bulb distilla-
tion (50–250°C/10–3 mbar) due to thermal decomposition.
31P NMR (C6D6): δ = 335.9 (s).
aryl-C), 150.3 [d, 2J(C,P) = 10.0 Hz, C5], 157.5 [d, 1J(C,P) = 46.4 Hz,
C4], 177.4 [d, 1J(C,P) = 58.4 Hz, C2].
MS (EI, 70 eV): m/z (%) = 372 (33.3) [M+], 340 (6.9) [M+ – S], 147
(31.0) [MesCP+ – CH3], 119 (23.5) [Mes+], 91 (30.7) [C6H4CH3 ], 77
+
+
(39.9) [C6H5 ], 73 (100.0), 57 (69.7).
2-Mesityl-1-phosphacyclohexa-1,4-diene (15):
1H NMR (C6D6): δ = 1.23, 1.26, 1.41 (each s, each 9H, t-Bu), 2.15 (s,
3H, p-CH3), 2.42 (s, 6H, o-CH3), 3.20 (s, 3H, OCH3), 6.85 (s, 2H,
aryl-H).
At –78°C buta-1,3-diene (700 mg, 12.9 mmol) was condensed into a
pressure tube and a solution of phosphaalkyne 1b (100 mg,
0.62 mmol) in toluene (3 mL) added. The mixture was allowed to
warm to r.t. and then heated for 2 d at 55°C. After evaporation of the
solvent and excess buta-1,3-diene at 25°C/10–3 mbar a yellow/orange
oily residue was obtained which could not be purified by bulb-to-bulb
distillation (200°C/10–3 mbar), by column chromatography (silica
gel, pentane/Et2O), or by crystallization (toluene).
13C NMR (CDCl3): δ = 21.1 (s, p-CH3), 22.8 (s, o-CH3), 50.8 (s,
1
2
OCH3), 72.8 [d, J(C,P) = 19.3 Hz, C1], 78.5 [d, J(C,P) = 5.6 Hz,
C4], 136.3(s, m-C, Mes), 138.4 [d, 4J(C,P) = 5.6 Hz, o-C, Mes], 147.5
(s, p-C, Mes), 152.7 [d, J(C,P) = 20.1 Hz, C6], 158.8 [d, J(C,P) =
5.6 Hz, C5], 172.0 [d, J(C,P) = 4.8 Hz, CO], 224.0 [d, J(C,P) =
29.7 Hz, C3].
2
3
3
1
31P NMR (C6D6): δ = 215.7 (s).
MS (EI, 70 eV): m/z (%) = 216 (100.0) [M+], 201 (17.0) [M+ – CH3],
Due to impurities the remaining data could not be assigned.
MS (EI, 70 eV): m/z (%) = 440 (48.6) [M+], 425 (8.3) [M+ – CH3],
243 (78.7) [M+ – t-BuCCt-Bu, – CO2CH3], 207 (64.6) [M+ – MesCP
– CCO2CH3], 147 (19.3) [MesCP+ – CH3], 119 (8.1) [Mes+], 84
162 (61.1) [MesCP+], 147 (34.0) [MesCP+ – Me], 119 (56.3) [Mes+],
+
+
91 (27.2) [C6H4CH3 ], 77 (5.7) [C6H5 ].
1-η1-[2-Mesityl-1-phosphacyclohexa-1,4-diene]pentacarbonyl-
tungsten (17):
(100.0) [t-BuCHCH2 ], 57 (89.6) [t-Bu+].
+
Compound 15 (216 mg, 1.0 mmol) in THF (5 mL) was added to a
solution of W(CO)5•THF, prepared by irradiation of W(CO)6
(387 mg, 1.1 mmol) in THF (60 mL). After 5 h at r.t. the solvent was
removed at 25°C/10–3 mbar, the oily residue was eluted with pentane
(20 mL) and subjected to chromatography (silica gel, column: 1.8 ×
30 cm, pentane 200 mL) to furnish a pale yellow oil, which crystal-
lized from pentane at 2°C; yield: 340 mg (63%); mp 97°C.
IR (Et2O): ν = 3030–2860, 2076(CO), 1992 (CO), 1668, 1611, 1567,
1467, 1463, 1459, 1263, 1164, 1005, 849, 746, 667, 621 cm–1.
31P NMR (C6D6): δ = 170.0 [s, 1J(P,W) = 259.6 Hz].
4,5,6-Tri-tert-butyl-2-mesityl-1-aza-3-phosphabicyclo[2.2.0]-
hexadiene (22):
A solution of tri-tert-butylazete (21) (80 mg, 0.36 mmol) in pentane
(2 mL) was added dropwise to a solution of phosphaalkyne 1b
(59 mg, 0.36 mmol) at –78 ˚C in pentane (4 mL). Warming to r.t.
overnight was followed by removal of the solvent at 25°C/10–3 mbar.
The residue was extracted with pentane (5 mL) and then separated
from insoluble material by filtration through a D3 sinter filled with
Celite. Removal of the solvent at 25°C/10–3 mbar furnished 21 as a
colorless powder; yield: 127 mg (91%).
1H NMR (C6D6): δ = 2.10 (s, 6H, o-CH3), 2.11 (s, 3H, p-CH3), 2.40–
2.48, 2.63–2.75 (each m, 4H, 3,6-CH2), 5.17–5.26, 5.40–5.46 (each
m, 2H, H4,5), 6.77 (s, 2H, aryl-H).
31P NMR (C6D6): δ = 230.4 (s).
1H NMR (C6D6): δ = 0.98, 1.25, 1.28 (each s, each 9H, t-Bu), 2.06 (s,
3H, CH3), 2.42 [d, 5J(C,P) = 2.0 Hz, 3H, o-CH3], 2.70 (s, 3H, CH3),
6.74, 6.77 (each s, 2H, aryl-H).
13C NMR (CDCl3): δ = 19.6 (s, o-CH3), 21.0 (s, p-CH3), 31.4 [d,
2J(C,P) = 2.6 Hz, C3], 37.5 [d, 1J(C,P) = 9.3 Hz, C6], 120.3 [d,
3J(C,P) = 8.5 Hz, C4], 125.4 [d, 2J(C,P) = 11.9 Hz, C5], 129.2 (s, m-
C, Mes), 134.9 [d, 2J(C,P) = 12.7 Hz, i-C, Mes], 137.7 (s, p-C, Mes),
13C NMR (CDCl3): δ = 21.5 (s, p-CH3), 22.7 (s, o-CH3), 27.9 [d,
J(C,P) = 3.4 Hz, C(CH3)3], 30.0, 30.7 [each s, C(CH3)3], 31.3, 34.0
[each s, C(CH3)3], 36.7 [d, J(C,P) = 5.1 Hz, C(CH3)3], 89.7 [d, 1J(C,P)
4
1
137.9 [d, J(C,P) = 3.4 Hz, o-C, Mes], 181.4 [d, J(C,P) = 47.5 Hz,
C2], 194.5 [d, 2J(C,P) = 9.8 Hz, 1J(C,W) = 124.2 Hz, COeq], 198.8
[d, 2J(C,P) = 28.8 Hz, 1J(C,W) = 45.8 Hz, COax].
2
= 23.7 Hz, C4], 127.6 (s, m-C), 128.8 [d, J(C,P) = 12.7 Hz, i-C],
137.4 [d, 3J(C,P) = 5.1 Hz, o-C], 137.8 (s, p-C), 139.5 [d, 2J(C,P) =
3.4 Hz, C5], 162.1 [d, 3J(C,P) = 19.5 Hz, C6], 225.9 [d, 1J(C,P) = 37.3
Hz, C2].
MS (EI, 57 eV): m/z (%) = 540 (53.0) [M+], 484 (30.4) [M+ – 2 CO],
456 (35.2) [M+ – 3 CO], 428 (75.9) [M+ – 4 CO], 426 (85.6) [M+ – 3
CO – 2 CH3], 400 (49.1) [M+ – 5 CO], 398 (96.2) [M+ – 4 CO – 2
CH3], 396 (100), 393 (27.1) [M+ – CO – Mes], 199 (15.4)
MS (EI, 70 eV): m/z (%) = 383 (6.7) [M+], 178 (10.9) [M+ – MesCN],
147 (100.0) [MesCO+], 145 (5.0) [MesCN+], 119 (12.2) [Mes+].

SYNTHESIS
September 1998
1313
X-ray Crystal Structure Analysis of 17:
(19) Rösch, W.; Richter, H.; Regitz, M. Chem. Ber. 1987, 120, 1809.
(20) An exact assigment to C2 or C4 is not possible.
(21) Fuchs, E. P. O.; Rösch, W.; Regitz, M. Angew. Chem. 1987, 99,
1058; Angew. Chem., Int. Ed. Engl. 1987, 26, 1011.
Heydt, H.; Bergsträßer, U.; Fäßler, R.; Fuchs, E. P. O.; Kamel,
N.; Mackewitz, T. W.; Michels, G.; Rösch, W.; Regitz, M.; Ma-
zerolles, P.; Laurent, C.; Faucher, A. Bull. Soc. Chim. Fr. 1995,
132, 652.
(22) When the reaction of 1a with buta-1,3-diene is carried out at
55°C, 2-tert-butyl-1-phosphacyclohexa-1,4-diene (15, t-Bu in-
stead of Mes) can be detected spectroscopically (31P δ = 204.1).
However, no isolation is possible as the subsequent ene reac-
tion/[4+2] cycloaddition process is much faster for the tert-bu-
tyl derivative 1a than for the mesitylphosphaacetylene (1b).
(23) Marinetti, A.; Le Floch, P.; Mathey, F. Organometallics 1991,
10, 1190.
Crystal data: C19H17OPW, Mr = 540.15; triclinic; space group P; a =
757.34(10), b = 1063.93(7), c = 1366.9(2) pm, α = 71.080(10)°, β =
84.993(9)°, χ = 75.304(10)°, V = 1.0078 (2) nm3; Z = 2, dc
=
1.780 Mg/m3.
Data collection: The data collection was performed using an automat-
ic four circle diffractrometer (Siemens P 4) at r.t.. Crystal dimensions:
0.45 × 0.30 × 0.15 mm. The measurements were made in the
range1.57<Θ <25.00°, λ = 0.71073 MoKα (graphite monochroma-
tor), –1≤h≤8, –11≤k≤11, –16≤l≤16, a total of 4457 reflections, of
which 3458 were independent reflections.
Structure solution and refinement: The structure was solved using di-
rect methods (SHELXS-86)40 and refined with the full matrix least
squares procedure against F2 (SHELXL-93)41. The anisotropic re-
finement converged at R1 = 0.0280 and wR2 = 0.0742 [I>2σ(I)] and
R1 = 0.0327, wR2 = 0.0907 [all data]. The difference Fourier syn-
thesis on the basis of the final structural model showed a maximum of
729 e/nm3 and a minimum of –695 e/nm3.42
(24) Marinetti, A.; Bauer, S.; Ricard, L.; Mathey, F. Organometal-
lics 1990, 9, 793.
(25) Appel R. In Multiple Bonds and Low Coordination in Phospho-
rus Chemistry; Regitz, M.; Scherer, O. J., Eds.; Thieme: Stutt-
gart, 1990; p 157.
We thank the Deutsche Forschungsgemeinschaft (Graduiertenkolleg
“Phosphor als Bindeglied verschiedener chemischer Disziplinen”)
and the Fonds der Chemischen Industrie for generous financial sup-
port of our work. A. M. is grateful to the Fonds der Chemischen
Industrie for a postgraduate grant. E. P. thanks the Landesregierung
of Rheinland-Pfalz for similar support.
(26) Wingert, H.; Regitz, M. Chem. Ber. 1986, 119, 244.
Maier, G.; Bauer, J.; Huber-Patz, U.; Jahn, R.; Kallfaß, D.; Ro-
dewald, H.; Irngartinger, H. Chem. Ber. 1986, 119, 1111.
Wingert, H.; Regitz, M.; Z. Naturforsch. B 1986, 41, 1306.
Wingert, H.; Maas, G.; Regitz, M. Tetrahedron 1986, 42, 5341.
(27) Fink, J.; Rösch, W.; Vogelbacher, U.-J.; Regitz, M. Angew.
Chem. 1986, 98, 265; Angew. Chem., Int. Ed. Engl. 1986, 25,
280.
(1) Part 128, see: Simon, J.; Bergsträßer, U.; Regitz, M. J. Chem.
Soc., Chem. Commun. 1998, 867.
(28) Vogelbacher, U.-J.; Ledermann, M.; Schach, T.; Michels, G.;
Hees, U.; Regitz, M. Angew. Chem. 1988, 100, 304; Angew.
Chem., Int. Ed. Engl. 1988, 27, 272.
(2) Regitz, M. Angew. Chem. 1988, 100, 1541; Angew. Chem., Int.
Ed. Engl. 1988, 27, 1484.
(3) Regitz, M. Chem. Rev. 1990, 90, 191.
(29) Regitz, M.; Hocker, J.; Liedhegener, A. Org. Synth. Coll. Vol. V
1968, 48, 36.
(30) Searle, N. E. Org. Synth. 1953, 36, 25.
(4) Regitz, M. In Multiple Bonds and Low Coordination in Phos-
phorus Chemistry; Regitz, M.; Scherer, O. J., Eds.; Thieme:
Stuttgart, 1990; p 77.
(31) Dimroth, O.; Wislicensius, W. Ber. Dtsch. Chem. Ges. 1905,
38, 1573.
(5) Regitz, M.; Hoffmann, A.; Bergsträßer, U. In Modern Acetylene
Chemistry: Stang, P. J.; Diederich, F., Eds.; VCH: Weinheim,
1995; p 173.
(6) Appel, R.; Maier, G.; Reisenauer, H.-P.; Westerhaus, A. Angew.
Chem. 1981, 93, 215; Angew. Chem., Int. Ed. Engl. 1981, 20,
197.
(7) Märkl, G.; Sejpka, H. Tetrahedron Lett. 1986, 27, 171.
(8) Veeck, W. G.; Regitz, M. In Comprehensive Organic Functio-
nal Group Transformations; Katritzky, A. R.; Meth-Cohn, O.;
Rees, C. W., Eds.; Pergamon: Oxford, 1995; Vol. 5; p 1151.
(9) Breit, B.; Regitz, M. Chem. Ber. 1996, 129, 489.
(10) Fritz, G.; Hölderich, W. Z. Anorg. Allg. Chem. 1976, 422, 104.
(11) Barnes, R. P. Org. Synth. 1941, 21, 77.
(12) Becker, G. Z. Anorg. Allg. Chem. 1977, 430, 66.
(13) Mackewitz, T. W.; Regitz, M. Synthesis 1998, 125.
(14) Mack, A.; Regitz, M. Chem. Ber. 1997, 130, 823.
(15) Rösch, W.; Regitz, M. Angew. Chem. 1984, 96, 898; Angew.
Chem., Int. Ed. Engl. 1984, 23, 903.
(32) Boyer, J. H.; Hamer, H. J. Am. Chem. Soc. 1955, 77, 951.
(33) Smith, P. A. S.; Bayer, J. H. Org. Synth. Coll. Vol. IV 1963, 75.
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Ber. 1970, 103, 2611.
(36) Gotthardt, H.; Weishuhn, M. C.; Christl, B. Chem. Ber. 1976,
109, 740.
(37) Vogelbacher, U.-J.; Regitz, M.; Mynott, R. Angew. Chem.
1986, 98, 835; Angew. Chem., Int. Ed. Engl. 1986, 25, 842.
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(40) Sheldrick, G. M. Fortran Program for the solution of Crystal
Structures from Diffraction Data; Institute for Organic Chemis-
try, University of Göttingen, 1986.
(41) Sheldrick, G. M. Fortran Program for Crystal Structure Refine-
ment; Institute for Organic Chemistry, University of Göttingen,
1993.
(42) Further details of the crystal structure determination are availa-
ble on request from the Fachinformationszentrum Karlsruhe,
Gesellschaft für wissenschaflich-technische Information mbH,
D-76344 Eggenstein-Leopoldshafen, on quoting the depository
number CSD-408229, the authors, and the journal citation.
Rösch, W.; Facklam, T.; Regitz, M. Tetrahedron 1987, 43,
3247.
(16) Rösch, W.; Hees, U.; Regitz, M. Chem. Ber. 1987, 120, 1645.
(17) Nyulászi, L.; Várnai, P.; Eisfeld, W.; Regitz, M. J. Comput.
Chem. 1997, 18, 609.
(18) Rösch, W.; Regitz, M. Synthesis 1987, 689.