Organophosphorus compounds, part 150; imidovanadium(V)-complexes as reaction partners for kinetically stabilized phosphaalkynes. 1-Aza-2-phospha- 4-vanada(V)-cyclobutenes: Precursors in the synthesis of 1H-1,2-azaphospholes

Article abstract of DOI:10.1055/s-2000-6353

A new synthetic pathway to the 1H-1,2-azaphospholes 12a-m has been developed involving reactions of the 1-aza-2-phospha-4-vanada(V)-cyclobutenes 9a-g, generated in situ from the imidovanadium(V) complexes 7a-c and the phosphaalkynes 8a-e. with the acetylenes 10a-g. This synthesis affords the heterocyclic compounds 12a-m in good yields and allows variation of all substituents for the first time. The structure of the 1H-1,2-azaphosphole 12a has been confirmed by X-ray crystallographic analysis. A selective η¹- complexation of the azaphospholes 12a,b to afford the transition metal complexes 13a,b can be realized by reaction with diiron nonacarbonyl. While reactions of the alkyl trifluoromethanesulfonates 14a,b with the heterophosphole 12a result in the formation of the azaphospholium compounds 15a,b, the azaphosphole 12a reacts with the azo compound 16 to form the spirotricyclic betaine 17. Diels-Alder reactions occur when the heterophospholes 12a,b are treated with the electron-poor acetylenes 18a-e and furnish the 1,2-azaphosphanorbomadienes 19a-f, the structures of which have been confirmed by an X-ray crystallographic analysis of the bicyclic product 19e. The phosphorus atom of the azaphosphanorbornadiene 19a can be oxidized and sulfurized to form the bicyclic species 20 and 21 containing λ⁵σ⁴-phosphorus atoms.

Full text of DOI:10.1055/s-2000-6353

PAPER
417
Organophosphorus Compounds, Part 150;1 Imidovanadium(V)-Complexes as
Reaction Partners for Kinetically Stabilized Phosphaalkynes. 1-Aza-2-
phospha-4-vanada(V)-cyclobutenes: Precursors in the Synthesis of 1H-1,2-
Azaphospholes
Christoph Peters, Frank Tabellion, M. Schröder, U. Bergsträßer, Fritz Preuss,* Manfred Regitz*
Fachbereich Chemie der Universität Kaiserslautern, Erwin-Schrödinger-Straße, D-67663 Kaiserslautern, Germany
Fax +49(631)2053921; E-mail: regitz@rhrk.uni-kl.de
Received 2 November 1999
Abstract: A new synthetic pathway to the 1H-1,2-azaphospholes
12a-m has been developed involving reactions of the 1-aza-2-
phospha-4-vanada(V)-cyclobutenes 9a-g, generated in situ from
the imidovanadium(V) complexes 7a-c and the phosphaalkynes
8a-e, with the acetylenes 10a-g. This synthesis affords the hetero-
cyclic compounds 12a-m in good yields and allows variation of all
substituents for the first time. The structure of the 1H-1,2-azaphos-
phole 12a has been confirmed by X-ray crystallographic analysis. A
selective h1-complexation of the azaphospholes 12a,b to afford the
transition metal complexes 13a,b can be realized by reaction with
diiron nonacarbonyl. While reactions of the alkyl trifluoromethane-
sulfonates 14a,b with the heterophosphole 12a result in the forma-
tion of the azaphospholium compounds 15a,b, the azaphosphole
12a reacts with the azo compound 16 to form the spirotricyclic be-
taine 17. Diels-Alder reactions occur when the heterophospholes
12a,b are treated with the electron-poor acetylenes 18a-e and fur-
nish the 1,2-azaphosphanorbornadienes 19a-f, the structures of
which have been confirmed by an X-ray crystallographic analysis of
the bicyclic product 19e. The phosphorus atom of the azaphospha-
norbornadiene 19a can be oxidized and sulfurized to form the bicy-
clic species 20 and 21 containing l5s4-phosphorus atoms.
Key words: 1H-1,2-azaphospholes, 1,2-azaphosphanorborna-
dienes, heterophospholes, Diels-Alder reaction, phosphorus, orga-
nometallic reagents, azo compounds, heterocycles
Scheme 1
Introduction
Two major aspects of current research in the field of low-
coordinated phosphorus compounds are, on one hand, the
syntheses of phosphorus-containing cage compounds2
and of heterophospholes3-5 on the other hand. Although
the class of the 1,3-azaphospholes has been well investi-
gated from both synthetic and reactivity aspects,3a there
are as yet only two approaches to the class of constitution-
ally isomeric heterocyclic compounds, the 1H-1,2-aza-
phospholes.6,7 Of these two, however, only the synthetic
route to the 1H-1,2-azaphosphole-5-carbonitriles 5 and 6
from the easily accessible 1,3,2-diazaphosphole-4,5-dini-
triles 1 and acetylenes 2, (Scheme 1) is of preparative im-
portance.6
For example, they are not attacked by water, methanol,
sulfur, or mixtures thereof.
Having found and initiated investigations on the enor-
mous synthetic potential of imidovanadium(V) com-
pounds in reactions with phosphaalkynes8 and, in
particular, of 1-aza-2-phospha-4-vanada(V)-cyclobutenes
in reactions with phosphaalkynes to furnish 1,3,5-triphos-
phabenzenes,9 we have now turned our attention to their
reactions with alkynes. In this paper we report on the se-
lective synthesis of 1H-1,2-azaphospholes and their sur-
prising reactivity.
The subsequent chemistry of the 1H-1,2-azaphospholes is
also practically unexplored. All that is known is that the
1H-1,2-azaphosphole-5-carbonitriles 5 and 6 are color-
less, air-stable liquids possessing only very low reactivity.
New Approach to 1H-1,2-Azaphospholes 12a-m
When the 1:1 cycloadducts 9a-g, generated in situ by ad-
dition of an equimolar amount of a phosphaalkyne 8a-e
to the imidovanadium(V) complex 7a-c, are treated with
Synthesis 2000, No. 3, 417–428 ISSN 0039-7881 © Thieme Stuttgart · New York

418
C. Peters et al.
PAPER
an excess of an acetylene 10a-g quantitative reactions i.e., in the typical region for heterophospholes possessing
with formation of the 1H-1,2-azaphospholes 12a-m are a l3s2-phosphorus atom directly adjacent to a nitrogen
observed (Scheme 2). The pure products 12a-m are then and a carbon atom.10 The signals in the 13C{1H} NMR
isolated in 31-71% yields after workup.
spectra for the ring carbon atoms C(3), C(4), and C(5) are
of high diagnostic value. Thus, the sp2-carbon atom C(4)
produces a signal between d = 116.3 and 127.0 with a typ-
ical 2J(C,P) coupling constant of 4.8-6.3 Hz. As a result
of the direct adjacency to electronegative heteroatoms the
13C NMR signals of the atoms C(3) and C(5) appear at low
field: that of C(5) is seen as a singlet or doublet at
2
d = 142.4-149.7 with a J(C,P) coupling over the nitro-
gen atom of 4.0-0.0 Hz. The signal for C(3) is the most
significant; it appears, as expected, at lowest field
(d = 173.6-180.6) as a doublet with a characteristic
1J(C,P) coupling constant of 40.7-44.1 Hz. The 1H NMR
chemical shifts of the hydrogen atoms on the rings of
compounds 12a-f,h,i,l,m are in the range d = 6.33 - 6.72,
i.e., in the generally usual aromatic region for azaphos-
pholes.6 Since only one signal is seen for each proton in
these cases, the reaction must be regiospecific.
An X-ray crystallographic analysis of compound 12a (see
Fig. 1) was carried out in order to obtain unequivocal con-
firmation of the regiochemistry and structure.
Figure 1 Crystal structure of 12a. Selected bond lengths [Å] and
angles [°]: P(2)-N(1) 1.728(4), P(2)-C(3) 1.713(5), N(1)-C(5)
1.377(5), C(3)-C(4) 1.395(6), C(4)-C(5) 1.372(6), C(5)-N(1)-P(2)
112.3(3), N(1)-P(2)-C(3) 91.5(2), P(2)-C(3)-C(4) 109.7(4), C(3)-
C(4)-C(5) 115.3(4), C(4)-C(5)-N(1) 111.2(4)
This demonstrated conclusively in the case of 12a that the
product was the 5-phenyl-substituted regioisomer. The
central structural feature of 12a is the planar five-mem-
bered ring unit. When a least squares plane is defined
through N(1), P(2), C(3), C(4), and C(5), the mean devia-
tion is merely 0.34 pm. With an angle of 85.5°, the plane
of the phenyl system is almost orthogonal to that of the
five-membered ring. As expected, the bond lengths of the
ring atoms lie between the values for the corresponding
single and double bonds and, furthermore, are in good
Scheme 2
The compositions of the azaphospholes 12a-m are eluci-
dated unambiguously from their elemental analyses and
mass spectral data. The 31P{1H} NMR spectra of 12a-m
each show a singlet signal between d = 168.8 and 182.2,
Synthesis 2000, No. 3, 417–428 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Imidovanadium(V)-Complexes as Reaction Partners for Kinetically Stabilized Phosphaalkynes
419
agreement with the bond lengths in comparable hetero-
phospholes.3a Not only the planarity of the five-membered
ring but also the bond lengths confirm the aromaticity of
this heterocyclic skeleton.
Studies on the Reactivity of 1H-1,2-Azaphospholes
a)
Complexation of the Azaphospholes 12a,b
with Diiron Nonacarbonyl
Reactions of the heterophospholes 12a,b with an equimo-
lar amount of diiron nonacarbonyl furnish the h1-com-
plexes 13a,b selectively in 63 and 59% yield, respectively
(Scheme 3).
Scheme 4
(15a) and 114.5 (15b). Finally, the 1H and 13C{1H} NMR
spectra provide conclusive evidence for the constitutions
and prove the preservation of the azaphosphole skeleton.
In particular, the signals of the newly introduced methyl
or ethyl group are of major diagnostic relevance. Thus, the
P-methyl group of 15a gives rise to a signal at d = 15.7 in
the 13C{1H} NMR spectrum and unambiguously demon-
strates the alkylation at phosphorus with its characteristic
1J(C,P) coupling constant of 27.3 Hz. This alkylation po-
sition is also supported by the signals of the ethyl group in
15b: thus, the methylene group gives a doublet signal at
1
d = 23.8 with a significant J(C,P) coupling constant of
29.8 Hz, while the signal of the methyl group appears at
d = 7.4 with a 2J(C,P) coupling constant of 2.2 Hz.
Scheme 3
c)
Reaction of the 1H-1,2-Azaphosphole 12a
with the Azo Compound 16
The h1-complexation in 13a,b is apparent from the
31P{1H} NMR spectra with a pronounced high field shift
of the signals by Dd @ 55 - 60 ppm to d = 121.3 (13a) and The reaction of the azaphosphole 12a with two equiva-
126.2 (13b). On the other hand, the complexation is re- lents of the azo compound 16 occurs at 25°C and furnishes
flected in the 13C{1H} NMR spectra in some cases by a the zwitterionic 2:1-adduct 17, isolated in 37% yield after
marked shift of the ring carbon signals to lower field. This
phenomenon is particularly pronounced for the carbon
atom C(3), the signals of which are shifted by about 30
ppm to lower field and appear at d = 204.0 and 204.5, re-
spectively. Concomitantly, the 1J(C,P) coupling constants
decrease by about 20 Hz.
workup (Scheme 5).
b)
Alkylation of the Azaphosphole 12a with the
Alkyl Trifluoromethanesulfonates 14a,b
The azaphosphole 12a reacts under mild conditions and in
remarkable selectivity with alkyl trifluoromethane-
sulfonates 14a,b to afford the 1,2-azaphospholium com-
pounds 15a,b in quantitative yields (Scheme 4).
Scheme 5
The EI mass spectra of compounds 15a,b confirm the for-
mation of the cation unit from one equivalent of the het-
erophosphole 12a and a methyl or ethyl group,
respectively.
In addition to its EI mass spectrum which confirms its
composition, the structural elucidation of compound 17 is
based mainly on NMR spectral data.
The extreme high-field shift of the 31P NMR signal by
more than 220 ppm in comparison to that of the azaphos-
phole 12a confirms the formation of a betaine possessing
a hexacoordinated, negatively charged phosphorus atom.
The observed chemical shift of d = -41.0 is in good agree-
The functionalization at phosphorus is clearly demon-
strated in the 31P{1H} NMR spectra by the high-field shift
of the signals in comparison to that of the starting material
12a. Thus, the phosphorus signals appear at d = 103.4
Synthesis 2000, No. 3, 417–428 ISSN 0039-7881 © Thieme Stuttgart · New York

420
C. Peters et al.
PAPER
ment with literature data for related compounds.11,12 The and 13C NMR data support the conclusions drawn from
1H NMR spectrum is also in accord with the constitution the 31P NMR spectrum and a X-ray crystallographic anal-
of 17 and, in addition, demonstrates the existence of a bis- ysis of product 19e provided definitive confirmation of
adduct as a consequence of the correct integration ratio of the structure of the cage compounds 19a-f (see Figure 2).
the t-butyl to the ethyl protons. The 13C{1H} NMR spec-
trum again plays major role in the determination of the
constitution. Of particular diagnostic relevance is the sig-
nal of the carbon atom C(9) adjacent to the spiro center.
As a result of the increase of the coordination and the pres-
ence of a formal negative charge at phosphorus, this signal
experiences not only a shift to higher field of more than 75
ppm but also an appreciable increase in the magnitude of
1
the JC,P coupling constant to 113.7 Hz. Similar values
have been reported for a structurally related spirocyclic
betaine12 and are also found for zwitterionic 2:1-adducts
of tetrahalo-ortho-benzoquinones with 1,3-aza- and 1,2,4-
diazaphospholes.13
d)
Diels-Alder Reaction of the 1H-1,2-Aza-
phospholes 12a,b with Electron-Poor Acetyl-
enes 18a-e
When the azaphospholes 12a,b are allowed to react with
the electron-poor acetylenes 18a-e the azaphosphanor-
bornadienes 19a-f are obtained selectively and in high
yields (63 - 73%) (Scheme 6).
Figure 2 Crystal structure of 19e. Selected bond lengths [Å] and an-
gles [°]: P(1)-N(7) 1.737(2), P(1)-C(2) 1.855(2), P(1)-C(6)
1.895(2), N(7)-C(4) 1.508(2), C(2)-C(3) 1.331(2), C(3)-C(4)
1.555(2), C(4)-C(5) 1.555(2), C(5)-C(6) 1.317(3), N(7)-P(1)-C(2)
86.34(8), N(7)-P(1)-C(6) 91.91(7), C(2)-P(1)-C(6) 92.21(9),
C(4)-N(7)-P(1) 99.51(10), C(3)-C(2)-P(1) 108.04(14), C(2)-
C(3)-C(4) 110.90(2), N(7)-C(4)-C(3) 100.25(13), N(7)-C(4)-
C(5) 105.78(13), C(3)-C(4)-C(5) 102.42(14), C(4)-C(5)-C(6)
112.90(2), C(5)-C(6)-P(1) 106.17(13)
The central structural increment of compound 19e is a dis-
torted norbornadiene skeleton in which the phosphorus
atom is present at one bridgehead (position 1) and the ni-
trogen atom is in the bridge (position 7). The tert-butyl
group on the nitrogen atom is inclined towards the lesser
substituted double bond. The bond lengths P(1)-C(2)
[1.855(2) Å] and P(1)-C(6) [1.895(2) Å] are within the
range of the experimentally determined average value
(1.86 Å)15 and are markedly longer than the corresponding
bond lengths for C(3)-C(4) [1.555(2) Å] and C(4)-C(5)
[1.555(2) Å]. Together with the appreciably smaller bond
angle for C(2)-P(1)-C(6) [92.21(9)°] as compared with
C(3)-C(4)-C(5) [102.42(14)°], these bond length differ-
ences characterize the distortion of the norbornadiene
skeleton. In addition, the nitrogen bridge is not positioned
symmetrically between P(1) and C(4), as revealed by the
bond lengths P(1)-N(7) [1.737(2) Å] and N(7)-C(4)
[1.508(2) Å] in combination with the angle P(1)-N(7)-
C(4) of 99.51(10)°. The C/C double bond lengths of
Scheme 6
The 1:1 composition of the azaphosphanorbornadienes
19a-f from one equivalent of the azaphosphole 12a or
12b and one equivalent of the acetylene 18 is supported by
elemental analyses and mass spectral data.
The 31P{1H} NMR spectra of the bicyclic compounds 1.317(3) Å [C(5)-C(6)] and 1.331(2) Å [C(2)-C(3)] are
19a-f contain singlet signals at much higher field in com- of the usual size.15 A comparison of the geometric para-
parison to those of the starting compounds. The positions meters of the bicyclic product 19e with those of a 1-
of the signals, between d = 53.0 - 60.6, are typical for phosphanorbornadiene16 or, of a tungsten-complexed
aminophosphanes and thus unambiguously confirm the azaphosphanorbornadiene17 shows characteristic agree-
transition from l3s2- to l3s3-phosphorus atoms.14 The 1H ments for comparable structural increments.
Synthesis 2000, No. 3, 417–428 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
e)
Imidovanadium(V)-Complexes as Reaction Partners for Kinetically Stabilized Phosphaalkynes
421
1
2400. H NMR and 13C NMR spectra were recorded with Bruker
AC 200 and Bruker AMX 400 spectrometers and referenced to the
solvent as internal standard. 31P NMR spectra were measured on a
Bruker AC 200 (81.1 MHz) spectrometer with 85% H3PO4 as exter-
nal standard. MS were recorded on a Finnigan MAT 90 spectrome-
ter at 70 eV ionization voltage. IR spectra were measured on a
Perkin-Elmer 16 PC FT-IR spectrophotometer.
Oxidation and Sulfurization of the 1,2-Aza-
phosphanorbornadiene 19a
When the azaphosphanorbornadiene 19a is allowed to re-
act with an equimolar amount of an oxidizing agent such
as bis(trimethylsilyl) peroxide or sulfur in the presence of
an equimolar amount of triethylamine, the respective
chalcogen-containing bicyclic compounds 20 (58%) and
21 (71%) are obtained after workup (Scheme 7).
1H-1,2-Azaphospholes 12a-m, General Procedure
Method A: To a stirred solution of the imidovanadium(V) complex
7 in toluene was added an equimolar amount of the respective phos-
phaalkyne 8 at -78°C. The reaction mixture was allowed to warm
to 25°C and then a threefold excess of the respective alkyne 10 was
added. After 18 h all volatile components were removed at 25°C/
0.001mbar and the residue dissolved in toluene (25 mL). Impurities
were filtered over Celite and the solvent was evaporated. Depend-
ing on the constitution of the residue, the products were either puri-
fied by crystallization from CH2Cl2 at -30°C or by bulb-to-bulb
distillation (if the residue was dark-brown and oily).
Method B: To a stirred solution of the imidovanadium(V) complex
7 and a threefold excess of the respective alkyne 10 in toluene was
added an equimolar amount of the respective phosphaalkyne 8 (re-
lated to 7) at -78°C. The reaction mixture was allowed to warm to
r.t. and stirred for additional 18 h. The workup was analogous to that
of Method A.
1,3-Di-tert-butyl-5-phenyl-1H-1,2-azaphosphole (12a)
Scheme 7
Method B: From imidovanadium(V) complex 7a (0.28g, 1.20
mmol) in toluene (5 mL), phenylacetylene (10a; 0.37 g, 3.60 mmol)
and t-butylphosphaalkyne (8a; 0.12 g, 1.20 mmol); yield (bulb-to-
bulb distillation): 0.23 g (71%); bp 120°C/0.001 mbar.
The chalcogenation of 19a is immediately confirmed by
the mass spectra of products 20 and 21. Thus, the respec-
tive molecular ion peaks are seen in the EI mass spectra at
m/z = 431 (20) and 447 (21). The IR spectra of com-
pounds 20 and 21 also support the chalcogenation of
phosphorus by the appearance of characteristic and in-
tense P/chalcogen bands at 1267 cm-1 (20) and 1260
cm-1 (21), respectively.
1H NMR (C6D6, 25°C, 200.1 MHz): d = 1.40 [d, 9 H, 4J(H,P) = 1.4
4
Hz] and 1.50 [d, 9 H, J(H,P) = 1.5 Hz] (t-C4H9 at N-1 and C-3),
6.70 [d, 1 H, 3J(H,P) = 5.9 Hz, H-4], 7.10-7.30 (m, 5 H, C6H5).
13C{1H} NMR (C6D6, 25°C, 50.3 MHz): d = 33.0 [d, 3J(C,P) = 10.2
Hz] and 33.6 [d, 3J(C,P) = 11.4 Hz] [C(CH3)3 at N-1 and C-3], 34.4
[d, 2J(C,P) = 16.8 Hz, C(CH3)3 at C-3], 59.4 [d, 2J(C,P) = 11.4 Hz,
C(CH3)3 at N-1], 120.4 [d, 2J(C,P) = 6.0 Hz, C-4], 127.4 (s, Ph-C),
127.8 (s, Ph-C), 131.2 [d, 4J(C,P) = 1.8 Hz, Ph-C], 139.4 [d,
3J(C,P) = 4.2 Hz, Ph-C], 148.7 [d, 2J(C,P) = 1.8 Hz, C-5], 177.7 [d,
1J(C,P) = 43.7 Hz, C-3].
The 31P{1H} NMR spectra do not reveal a uniform trend
with regard to the chemical shifts of the phosphorus atoms
of 20 and 21 in comparison to that of the starting com-
pound 19a. While oxidation resulted in a slight shift to
higher field of the phosphorus atom of 20 (d = 42.6), the
sulfuration in compound 21 effected a slight deshielding
of the 31P NMR signal to d = 67.8. However, these obser-
vations are in good harmony with phenomena reported in
the literature, namely that the 31P NMR signal of a pen-
tavalent phosphorus atom bearing a doubly bonded chal-
cogen atom experiences a shift to lower field on going
31P{1H} NMR (C6D6, 25°C, 81.0 MHz): d = 182.2 (s).
Anal. Calcd for C17H24NP (273.4): C, 74.6; H, 8.9; N, 5.1. Found C,
74.1; H, 8.9; N, 5.2.
MS (EI, 70 eV): m/z (%) = 273 (M+, 100), 217 ([M - C4H8]+, 14),
202 ([M - C4H9N]+, 58).
1-tert-Butyl-3-(1,1-dimethylpropyl)-5-phenyl-1H-1,2-azaphos-
phole (12b)
Method A: From imidovanadium(V) complex 7a (0.664 g, 2.91
mmol) in toluene (18 mL), (1,1-dimethylpropyl)phosphaalkyne
(8b; 0.332 g, 2.91 mmol, as a 26% solution in hexamethyldisilox-
ane)), and phenylacetylene (10a, 0.892 g, 8.73 mmol); yield: 0.594
g (71%); mp 76°C (crystallization from CH2Cl2 at -30°C); bp
120°C/0.001 mbar.
from oxygen to sulfur.14,18 The H and 13C{1H} NMR
spectral data are also in accord with the constitutions of 20
and 21, thus unequivocally confirming the retention of the
bicyclic structure.
1
1H NMR (CDCl3, 25°C, 400.1 MHz): d = 0.86 [t, 3 H, 3J(H,H) = 7.5
Hz, CH2CH3], 1.32 [d, 6 H, 4J(H,P) = 1.6 Hz, C(CH3)2Et], 1.53 [d,
All reactions were performed under argon (purity >99.998%) using
Schlenk techniques. The solvents were dried by standard proce-
dures, distilled, and stored under argon until used. Compounds 7a,19
7b,20 7c,20 8a,21 8b,22 8c,23,24 8d,23,24 8e,21 18e,25 and bis(trimethyl-
silyl) peroxide26 were prepared by published methods. 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 2°C/min) and are uncorrect-
ed. Microanalyses were performed with a Perkin-Elmer Analyzer
4
3
9 H, J(H,P) = 1.1 Hz, t-C4H9 at N-1], 1.63 [q, 2 H, J(H,H) = 7.5
Hz, CH2CH3], 6.45 [d, 1 H, 3J(H,P) = 6.0 Hz, H-4), 7.31-7.39 (m,
5 H, C6H5).
13C{1H} NMR (CDCl3, 25°C, 100.6 MHz): d = 9.3 [d, 4J(C,P) = 1.8
Hz, CH2CH3], 29.6 [d, 3J(C,P) = 10.8 Hz, C(CH3)2Et], 33.4 [d,
3J(C,P) = 10.8 Hz, C(CH3)3 at N-1], 37.2 [d, 3J(C,P) = 9.9 Hz,
CH2CH3], 37.5 [d, 2J(C,P) = 6.2 Hz, C(CH3)2Et], 59.0 [d,
2J(C,P) = 10.8 Hz, C(CH3)3 at N-1], 120.0 [d, 2J(C,P) = 6.3 Hz, C-
Synthesis 2000, No. 3, 417–428 ISSN 0039-7881 © Thieme Stuttgart · New York

422
C. Peters et al.
PAPER
3-(1-Adamantyl)-1-tert-butyl-5-phenyl-1H-1,2-azaphosphole
4], 127.1 (s, Ph-C), 127.6 (s, Ph-C), 130.7 [d, 4J(C,P) = 2.7 Hz, Ph-
C], 138.8 [d, 3J(C,P) = 3.6 Hz, Ph-C], 148.3 [d, 2J(C,P) = 1.8 Hz, C-
5], 175.9 [d, 1J(C,P) = 44.0 Hz, C-3].
31P{1H} NMR (CDCl3, 25°C, 81.0 MHz): d = 181.2 (s).
(12e)
Method A: From imidovanadium(V) complex 7a (0.457 g, 2.00
mmol) in toluene (15 mL), (1-adamantyl)methylidynephosphane
(8e; 0.340 g, 2.00 mmol), and phenylacetylene (10a; 0.613 g, 6.00
mmol); yield (bulb-to-bulb distillation): 0.260 g (37%); mp 93°C;
bp 170°C/0.001 mbar.
IR (CCl4): n = 2972 (C-H), 1622, 1532, 1298, 1216, 1186, 1113,
929, 790 cm-1.
1H NMR (C6D6, 25°C, 400.1 MHz): d = 1.42 (s, 9 H, t-C4H9 at N-1),
1.69 (br s, 6 H, Ad-H), 1.97 (br s, 3 H, Ad-H), 2.12 (br s, 6 H, Ad-
H), 6.68 [d, 1 H, 3J(H,P) = 6.0 Hz, H-4], 7.00-7.13 (m, 3 H, C6H5),
7.23-7.27 (m, 2 H, C6H5).
Anal. Calcd for C18H26NP (287.4): C, 75.23; H, 9.12; N, 4.87.
Found C, 74.81; H, 10.11; N, 4.96.
MS (EI, 70 eV): m/z (%) = 287 (M+, 20), 231 ([M - C4H8]+, 23),
216 ([M - C4H9N]+, 7), 202 ([M - C5H11N]+, 100).
13C{1H} NMR (C6D6, 25°C, 100.6 MHz): d = 29.5 [d, 4J(C,P) = 1.7
1-tert-Butyl-3-(1-methylcyclopentyl)-5-phenyl-1H-1,2-azaphos-
phole (12c)
3
Hz, Ad-C], 33.6 [d, J(C,P) = 11.0 Hz, C(CH3)3 at N-1], 36.6 [d,
3
2J(C,P) = 16.1 Hz, Ad-C], 37.1 (s, Ad-C), 45.6 [d, J(C,P) = 10.2
Method A: From imidovanadium(V) complex 7a (0.237 g, 1.04
mmol) in toluene (10 mL), (1-methylcyclopentyl)methylidynephos-
phane (8c; 0.131 g, 1.04 mmol, as a 16% solution in hexamethyl-
disiloxane), and phenylacetylene (10a; 0.319 g, 3.12 mmol); yield
(bulb-to-bulb distillation): 0.134 g (43%); mp 79°C; bp 140°C/
0.001 mbar.
2
Hz, Ad-C], 59.0 [d, J(C,P) = 11.0 Hz, C(CH3)3 at N-1], 119.2 [d,
2J(C,P) = 5.1 Hz, C-4], 127.4 (s, Ph-C), 128.5 (s, Ph-C), 131.2 [d,
4J(C,P) = 1.7 Hz, Ph-C], 139.6 [d, 3J(C,P) = 4.2 Hz, Ph-C], 148.4 (s,
C-5), 178.4 [d, 1J(C,P) = 43.2 Hz, C-3].
31P{1H} NMR (C6D6, 25 °C, 81.0 MHz): d = 181.7 (s).
1H NMR (CDCl3, 25°C, 400.1 MHz): d = 1.42 [s,
3 H,
IR (CCl4): n = 2963 (C-H), 2908 (C-H), 2850 (C-H), 1261, 1100,
C(CH2)2CH3], 1.57 [d, 9 H, 4J(H,P) = 1.2 Hz, t-C4H9 at N-1], 1.73-
2.05 (m, 8 H, cyclopentyl-CH2), 6.53 [d, 1 H, 3J(H,P) = 5.7 Hz, H-
4], 7.35-7.45 (m, 5 H, C6H5).
1032 cm-1.
MS (EI, 70 eV): m/z (%) = 351 (M+, 31), 295 ([M - C4H8]+, 100),
135 ([1-Ad]+, 27), 57 ([t-C4H9]+, 24).
13C{1H} NMR (CDCl3, 25°C, 100.6 MHz): d = 24.5 [s,
C(CH2)2CH3], 29.9 (s, cyclopentyl-CH2), 30.0 (s, cyclopentyl-
CH2), 33.5 [d, 3J(C,P) = 11.2 Hz, cyclopentyl-CH2], 42.4 [d,
1,3-Di-tert-butyl-5-p-tolyl-1H-1,2-azaphosphole (12f)
Method A: From imidovanadium(V) complex 7a (0.536 g, 2.35
mmol) in toluene (13 mL), t-butylphosphaalkyne (8a, 0.235 g, 2.35
mmol), and p-tolylacetylene (10b, 0.819 g, 7.05 mmol); yield
(bulb-to-bulb distillation): 0.257 g (38%), mp 79°C; bp 120°C/
0.001 mbar.
2
3J(C,P) = 10.8 Hz, C(CH3)3 at N-1], 45.2 [d, J(C,P) = 15.3 Hz,
2
C(CH2)2CH3], 59.0 [d, J(C,P) = 11.3 Hz, C(CH3)3 at N-1], 120.3
[d, 2J(C,P) = 5.6 Hz, C-4], 127.2 (s, Ph-C), 127.7 (s, Ph-C), 130.8
[d, 4J(C,P) = 1.4 Hz, Ph-C], 138.9 [d, 3J(C,P) = 3.2 Hz, Ph-C],
148.7 (s, C-5), 177.1 [d, 1J(C,P) = 43.4 Hz, C-3].
1H NMR (CDCl3, 25°C, 400.1 MHz): d = 1.35 [d, 9 H, 4J(H,P) = 1.4
4
Hz, t-C4H9 at C-3], 1.52 [d, 9 H, J(H,P) = 1.1 Hz, t-C4H9 at N-1],
31P{1H} NMR (CDCl3, 25 °C, 81.0 MHz): d = 179.7 (s).
3
2.39 (s, 3 H, Tol-CH3), 6.48 [d, 1 H, (H,P) = 6.0 Hz, H-4], 7.15
[AA´BB´ spin system, 2 H, 3J(H,H) = 8.3 Hz, Tol-H], 7.25
[AA´BB´ spin system, 2 H, 3J(H,H) = 8.3 Hz, Tol-H).
IR (CDCl3): n = 2964 (C-H), 1621, 1530, 1295, 1262, 1229, 1204,
1189, 1113, 1074, 1022, 810 cm-1.
MS (EI, 70 eV): m/z (%) = 299 (M+, 35), 243 ([M - C4H8]+, 100),
13C{1H} NMR (CDCl3, 25°C, 100.6 MHz): d = 21.2 (s, Tol-CH3),
228 ([M - C4H9N]+, 30), 57 ([t-C4H9]+, 21).
32.6 [d, 3J(C,P) = 9.9 Hz, C(CH3)3 at C-3], 33.4 [d, 3J(C,P) = 11.7
2
Hz, C(CH3)3 at N-1], 34.1 [d, J(C,P) = 7.3 Hz, C(CH3)3 at C-3],
1-tert-Butyl-3-(1-methylcyclohexyl)-5-phenyl-1H-1,2-azaphos-
phole (12d)
58.9 [d, 2J(C,P) = 11.7 Hz, C(CH3)3 at N-1], 120.0 [d, 2J(C,P) = 5.4
Hz, C-4], 127.8 (s, Tol-C), 130.5 [d, 4J(C,P) = 1.8 Hz, Tol-C], 135.7
[d, 3J(C,P) = 3.6 Hz, Tol-C], 137.4 (s, Tol-C), 148.5 (s, C-5), 177.6
[d, 1J(C,P) = 43.1 Hz, C-3].
Method A: From imidovanadium(V) complex 7a (0.396 g, 1.73
mmol) in toluene (12 mL), (1-methylcyclohexyl)methylidynephos-
phane (8d; 0.243 g, 1.73 mmol, as a 16% solution in hexamethyl-
disiloxane), and phenylacetylene (10a; 0.530 g, 5.19 mmol); yield:
(bulb-to-bulb distillation): 0.255 g (47%); mp 81°C; bp 140°C/
0.001 mbar.
1H NMR (CDCl3, 25°C, 400.1 MHz): d = 1.35 [d, 3 H, 4J(H,P) = 1.0
Hz, C(CH2)2CH3], 1.50-1.92 (m, 10 H, cyclohexyl-CH2), 1.57 [d, 9
H, 4J(H,P) = 1.7 Hz, t-C4H9 at N-1], 6.52 [d, 1 H, 3J(H,P) = 5.9 Hz,
H-4], 7.35-7.43 (m, 5 H, C6H5).
13C{1H} NMR (CDCl3, 25°C, 100.6 MHz): d = 23.7 [s,
C(CH2)2CH3], 27.4 (s, cyclohexyl-CH2), 30.4 (mc, cyclohexyl-
CH2), 34.4 [d, 3J(C,P) = 11.7 Hz, cyclohexyl-CH2], 38.4 [d,
2J(C,P) = 14.5 Hz, C(CH2)2CH3], 40.9 [d, 3J(C,P) = 9.9 Hz,
C(CH3)3 at N-1], 60.0 [d, 2J(C,P) = 10.8 Hz, C(CH3)3 at N-1], 120.5
[d, 2J(C,P) = 6.3 Hz, C-4], 128.1 (s, Ph-C), 128.6 (s, Ph-C), 131.7
[d, 4J(C,P) = 1.8 Hz, Ph-C], 139.9 [d, 3J(C,P) = 3.6 Hz, Ph-C],
149.2 [d, 2J(C,P) = 1.8 Hz, C-5], 178.8 [d, 1J(C,P) = 43.1 Hz, C-3].
31P{1H} NMR (CDCl3, 25 °C, 81.0 MHz): d = 178.5 (s).
IR (CDCl3): n = 2971 (C-H), 1621, 1536, 1504, 1321, 1296, 1216,
1185, 1112, 821 cm-1.
Anal. Calcd for C18H26NP (287.4): C, 75.23; H, 9.12; N, 4.87.
Found C, 74.13; H, 8.90; N, 3.80.
MS (EI, 70 eV): m/z (%) = 287 (M+, 32), 231 ([M - C4H8]+, 72),
216 ([M - C4H9N]+, 100).
1,3-Di-tert-butyl-4-methyl-5-phenyl-1H-1,2-azaphosphole (12g)
Method A: From imidovanadium(V) complex 7a (0.572 g, 2.50
mmol) in toluene (14 mL), t-butylphosphaalkyne (8a, 0.250 g, 2.50
mmol), and 1-phenylprop-1-yne (10c, 0.871 g, 7.50 mmol); yield
(bulb-to-bulb distillation): 0.295 g (41%); mp 75°C; bp 140°C/
0.001 mbar.
1H NMR (CDCl3, 25°C, 400.1 MHz): d = 1.44 [d, 9 H, 4J(H,P) = 2.4
4
31P{1H} NMR (CDCl3, 25°C, 81.0 MHz): d = 182.1 (s).
Hz] and 1.45 [d, 9 H, J(H,P) = 1.4 Hz] (t-C4H9 at N-1 and C-3),
2.78 (s, 3 H, CH3 at C-4), 7.22-7.25 (m, 2 H, C6H5), 7.34-7.38 (m,
3 H, C6H5).
IR (CCl4): n = 2932 (C-H), 1711, 1622, 1448, 1368, 1312, 1287,
1262, 1188, 1112, 944, 909 cm-1.
13C{1H} NMR (CDCl3, 25°C, 100.6 MHz): d = 14.8 (s, C-4-CH3),
MS (EI, 70 eV): m/z (%) = 313 (M+, 35), 257 ([M - C4H8]+, 100),
31.5 [d, 3J(C,P) = 13.7 Hz, (CH3)3 at C-3], 33.3 [d, 3J(C,P) = 11.2
242 ([M - C4H9N]+, 5), 57 ([t-C4H9]+, 87).
2
Hz, C(CH3)3 at N-1], 34.9 [d, J(C,P) = 8.4 Hz, C(CH3)3 at C-3],
58.9 [d, 2J(C,P) = 11.3 Hz, C(CH3)3 at N-1], 125.1 [d, 2J(C,P) = 5.6
Synthesis 2000, No. 3, 417–428 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Imidovanadium(V)-Complexes as Reaction Partners for Kinetically Stabilized Phosphaalkynes
423
4
Hz, C-4], 127.7 (s, Ph-C), 127.8 (s, Ph-C), 131.7 [d, J(C,P) = 1.6
Hz, Ph-C], 138.9 [d, 3J(C,P) = 3.2 Hz, Ph-C], 147.8 (s, C-5), 173.9
[d, 1J(C,P) = 41.8 Hz, C-3].
13C{1H} NMR (C6D6, 25°C, 50.3 MHz): d = 14.6 (s, CH3 at C-5),
3 3
16.9 [d, J(C,P) = 4.2 Hz CH3 at C-4], 31.9 [d, J(C,P) = 13.6 Hz]
and 32.0 [d, 3J(C,P) = 11.0 Hz] (C(CH3)3 at N-1 and C-3), 34.5 [d,
2
2J(C,P) = 11.0 Hz, C(CH3)3 at C-3], 57.2 [d, J(C,P) = 11.9 Hz,
31P{1H} NMR (C6D6, 25°C, 81.0 MHz): d = 170.7 (s).
C(CH3)3 at N-1], 123.8 [d, 2J(C,P) = 5.1 Hz, C-4], 142.4 [d,
2J(C,P) = 2.5 Hz, C-5], 173.6 [d, 1J(C,P) = 40.7 Hz, C-3].
IR (CDCl3): n = 2966 (C-H), 1693, 1622, 1539, 1477, 1396, 1367,
1282, 1111, 1008, 923, 757, 722, 644, 619 cm-1.
31P{1H} NMR (C6D6, 25°C, 81.0 MHz): d = 168.8 (s).
MS (EI, 70 eV): m/z (%) = 287 (M+, 43), 231 ([M - C4H8]+, 66),
MS (EI, 70 eV): m/z (%) = 225 (M+, 89), 168 ([M - C4H8]+, 100),
216 ([M - C4H9N]+, 100).
57 ([t-C4H9]+, 66).
5-Benzyl-1,3-di-tert-butyl-1H-1,2-azaphosphole (12h):
Method A: From imidovanadium(V) complex 7a (0.463 g, 2.03
mmol) in toluene (13 mL), t-butylphosphaalkyne (8a; 0.203 g, 2.03
mmol) and 3-phenylprop-1-yne (10d; 0.707 g; 6.09 mmol); yield
(bulb-to-bulb distillation): 0.274 g (47%); mp 78°C; bp 120°C/
0.001 mbar.
1,3-Di-tert-butyl-4,5-diphenyl-1H-1,2-azaphosphole (12k)
Method A: From imidovanadium(V) complex 7a (0.290 g, 1.29
mmol) in toluene (5 mL), t-butylphosphaalkyne (8a; 0.130 g, 1.30
mmol), and 1,2-diphenylacetylene (10g; 0.460 g, 2.56 mmol); yield
(bulb-to-bulb distillation): 0.240 g (67%); bp 220°C/0.001 mbar.
1H NMR (C6D6, 25°C, 200.1 MHz): d = 1.43 [d, 9H, 4J(H,P) = 1.5
Hz] and 1.48 [d, 9H, 4J(H,P) = 2.4 Hz, t-Bu at N-1 and C-3], 6.77-
7.23 (m, 10H, Ph-H).
1H NMR (CDCl3, 25°C, 400.1 MHz): d = 1.28 [d, 9 H, 4J(H,P) = 1.6
4
Hz, t-C4H9 at C-3], 1.67 [d, 9 H, J(H,P) = 1.6 Hz, t-C4H9 at N-1],
4.26 (s, 2 H, CH2 at C-5), 7.06-7.29 (m, 5 H, C6H5).
13C{1H} NMR (C6D6, 25°C, 50.3 MHz): d = 33.1 [d, 3J(C,P) = 13.6
Hz] and 33.5 [d, 3J(C,P) = 11.9 Hz, C(CH3)3 at N-1 and C-3], 35.7
[d, 2J(C,P) = 18.7 Hz, C(CH3)3 at C-3], 59.3 [d, 2J(C,P) = 11.0 Hz,
C(CH3)3 at N-1], 126.2 (s, Ph-C), 127.0 [d, 2J(C,P) = 5.9 Hz, C-4],
128.3 (s, Ph-C), 132.5 [d, J(C,P) = 2.6 Hz, Ph-C], 133.8 (s, Ph-C),
133.9 [d, J(C,P) = 5.9 Hz, Ph-C], 138.2 [d, J(C,P) = 3.4 Hz, Ph-C],
140.2 (s, Ph-C), 140.2 (s, Ph-C), 148.1 [d, 2J(C,P) = 1.7 Hz, C-5],
174.4 [d, 1J(C,P) = 44.1 Hz, C-3].
13C{1H} NMR (CDCl3, 25°C, 100.6 MHz): d = 32.6 [d,
3J(C,P) = 9.6 Hz], 32.7 [d, 3J(C,P) = 12.6 Hz] (C(CH3)3 at N-1 and
C-3), 34.0 [d, 2J(C,P) = 16.9 Hz, C(CH3)3 at C-3], 38.0 [d,
3J(C,P) = 4.0 Hz, CH2 at C-5], 57.9 [d, 2J(C,P) = 11.3 Hz, C(CH3)3
at N-1], 119.7 [d, 2J(C,P) = 4.8 Hz, C-4], 126.1 (s, Ph-C), 128.3 (s,
Ph-C), 128.5 (s, Ph-C), 140.3 (s, Ph-C), 146.9 [d, 2J(C,P) = 4.0 Hz,
C-5], 177.8 [d, 1J(C,P) = 43.4 Hz, C-3].
31P{1H} NMR (C6D6, 25 °C, 81.0 MHz): d = 179.4 (s).
31P{1H} NMR (C6D6, 25°C, 81.0 MHz): d = 173.4 (s).
IR (CDCl3): n = 2965 (C-H), 2867 (C-H), 1700, 1600, 1585, 1504,
1-(1-Adamantyl)-3-tert-butyl-5-phenyl-1H-1,2-azaphosphole
(12l)
Method A: From imidovanadium(V) complex 7b (0.100 g, 0.31
mmol) in toluene (15 mL), t-butylphosphaalkyne (8a; 0.031 g, 0.31
mmol), and phenylacetylene (10a; 0.095 g, 0.93 mmol); yield
(bulb-to-bulb distillation): 0.040 g (40%); bp 170°C/0.001 mbar.
1263, 1206, 1184, 1116, 1028, 1013, 919, 817, 733, 651 cm-1.
MS (EI, 70 eV): m/z (%) = 287 (M+, 47), 231 ([M - C4H8]+, 48),
216 ([M - C4H9N]+, 100), 91 ([Ph - CH2]+, 35).
1,3-Di-tert-butyl-5-propyl-1H-1,2-azaphosphole (12i)
Method A: From imidovanadium(V) complex 7a (0.776 g, 3.40
mmol) in toluene (15 mL), t-butylphosphaalkyne (8a; 0.340 g, 3.40
mmol), and pent-1-yne (10e; 0.695 g (10.20 mmol); yield (bulb-to-
bulb distillation): 0.439 g (51%); bp 70°C/0.001 mbar.
1H NMR (C6D6, 25°C, 200.1 MHz): d = 1.34 [t, 6 H, 3J(H,H) = 3.1
Hz, ad-H], 1.50 [d, 9 H, 4J(H,P) = 1.7 Hz, t-C4H9 at C-3], 1.80 (m,
3
3 H, ad-H), 2.26 [d, 6 H, J(H,H) = 3.1 Hz, Ad-H], 6.72 [d, 1 H,
3J(H,P) = 7.1 Hz, H-4], 7.02-7.36 (m, 5 H, C6H5).
1H NMR (CDCl3, 25°C, 400.1 MHz): d = 1.00 [t, 3 H, 3J(H,H) = 7.4
4
13C{1H} NMR (C6D6, 25°C, 50.3 MHz): d = 30.5 [d, 4J(C,P) = 2.2
Hz, CH2CH2CH3], 1.33 [d, 9 H, J(H,P) = 1.7 Hz, t-C4H9 at C-3],
1.68 [d, 9 H, 4J(H,P) = 1.7 Hz, t-C4H9 at N-1], 1.69 [tq, 2 H,
3
Hz, Ad-C], 33.0 [d, J(C,P) = 10.2 Hz, C(CH3)3 at C-3], 34.4 [d,
3
3J(H,H) = 8.0 Hz, J(H,H) = 7.4 Hz, CH2CH2CH3], 2.82 [dt, 2 H,
2J(C,P) = 17.4 Hz, C(CH3)3 at C-3], 36.1 (s, Ad-C), 46.0 [d,
3J(C,P) = 12.4 Hz, Ad-C], 60.6 [d, 2J(C,P) = 9.5 Hz, C(CH2)3 at N-
1], 120.4 [d, 2J(C,P) = 5.8 Hz, C-4], 127.4 (s, Ph-C), 128.1 (s, Ph-
4
3J(H,H) = 8.0 Hz, J(H,P) = 1.7 Hz, CH2 at C-5], 6.57 [d, 1 H,
3J(H,P) = 5.7 Hz, H-4].
4
3
13C{1H} NMR (CDCl3, 25 °C, 100.6 MHz): d = 14.1 (s,
C), 131.1 [d, J(C,P) = 2.2 Hz, Ph-C], 140.1 [d, J(C,P) = 3.6 Hz,
Ph-C], 148.2 (s, C-5), 177.7 [d, 1J(C,P) = 43.6 Hz, C-3].
3
CH2CH2CH3), 23.6 (s, CH2CH2CH3), 32.4 [d, J(C,P) = 11.4 Hz]
3
31P{1H} NMR (C6D6, 25°C, 81.0 MHz): d = 179.2 (s).
and 32.5 [d, J(C,P) = 9.5 Hz] (C(CH3)3 at N-1 and C-3), 33.8 [d,
2J(C,P) = 16.2 Hz, C(CH3)3 at C-3], 34.1 [d, 3J(C,P) = 3.8 Hz, CH2
MS (EI, 70 eV): m/z (%) = 351 (M+, 12), 135 ([C10H15]+, 26), 135
2
at C-5], 57.4 [d, J(C,P) = 11.4 Hz, C(CH3)3 at N-1], 116.3 [d,
([C8H6]+, 100).
2J(C,P) = 4.8 Hz, C-4], 149.7 (s, C-5), 177.6 [d, 1J(C,P) = 42.0 Hz,
C-3].
3-tert-Butyl-5-phenyl-1-isopropyl-1H-1,2-azaphosphole (12m)
Method B: From imidovanadium(V) complex 7c (0.210 g, 0.98
mmol) in toluene (5 mL), t-butylphosphaalkyne (8a; 0.098 g, 0.98
mmol), and phenylacetylene (10a; 0.100 g, 0.98 mmol); yield
(bulb-to-bulb distillation): 0.160 g (65%), bp 140°C/0.001 mbar.
1H NMR (C6D6, 25°C, 200.1 MHz): d = 1.27 [d, 6 H, 3J(H,H) = 6.6
Hz, CH(CH3)2], 1.49 [d, 9 H, 4J(H,P) = 1.7 Hz, t-C4H9 at C-3], 4.39
[pseudo-oct, 1 H, 3J(H,H) = 3J(H,P) = 6.6 Hz, CH(CH3)2], 6.77 [d,
1 H, 3J(H,P) = 6.1 Hz, H-4], 7.10-7.26 (m, 5 H, C6H5).
31P{1H} NMR (CDCl3, 25 °C, 81.0 MHz): d = 177.8 (s).
IR (CCl4): n = 2968 (C-H), 2906 (C-H), 2874 (C-H), 1711, 1476,
1463, 1396, 1368, 1291, 1269, 1206, 1131, 1068, 1059, 1027, 946,
910, 885, 843 cm-1.
MS (EI, 70 eV): m/z (%) = 239 (M+, 7), 183 ([M - C4H8]+, 6), 168
([M - C4H9N]+, 15), 57 ([t-C4H9]+, 100).
1,3-Di-tert-butyl-4,5-dimethyl-1H-1,2-azaphosphole (12j)
Method A: From imidovanadium(V) complex 7a (0.250 g, 1.10
mmol) in toluene (5 mL), t-butylphosphaalkyne (8a; 0.110 g, 1.10
mmol), and but-2-yne (10f; 0.192 g, 3.30 mmol); yield (bulb-to-
bulb distillation): 0.080 g (31%); bp 140°C/0.001 mbar.
1H NMR (C6D6, 25°C, 200.1 MHz): d = 1.41 [d, 9 H, 4J(H,P) = 1.7
Hz] and 1.41 [d, 9 H, 4J(H,P) = 2.4 Hz, t-C4H9 at N-1 and C-3], 2.11
[d, 3 H, 4J(H,P) = 2.2 Hz, CH3 at C-4], 2.14 (s, 3 H, CH3 at C-5).
13C{1H} NMR (C6D6, 25°C, 50.3 MHz): d = 26.7 [d, 3J(C,P) = 10.5
Hz, CH(CH3)2], 33.1 [d, 3J(C,P) = 9.5 Hz, C(CH3)3 at C-3], 34.6 [d,
2
2J(C,P) = 17.2 Hz, C(CH3)3 at C-3], 50.0 [d, J(C,P) = 12.4 Hz,
CH(CH3)2], 116.7 [d, 2J(C,P) = 5.7 Hz, C-4], 127.8 (s, Ph-C), 128.5
(s, Ph-C), 129.5 [d, 4J(C,P) = 1.9 Hz, Ph-C], 135.7 [d, 3J(C,P) = 3.8
Hz, Ph-C], 149.2 (s, C-5), 180.6 [d, 1J(C,P) = 43.8 Hz, C-3].
31P{1H} NMR (C6D6, 25°C, 81.0 MHz): d = 172.5 (s).
Synthesis 2000, No. 3, 417–428 ISSN 0039-7881 © Thieme Stuttgart · New York

424
C. Peters et al.
PAPER
MS (EI, 70 eV): m/z (%) = 259 (M+, 94), 244 ([M - CH3]+, 100),
202 ([M - C4H9]+, 64), 77 ([C6H5]+, 5).
romethanesulfonate 14a,b at -78°C. The reaction mixture was al-
lowed to warm to 25°C and after 18 h all volatile components were
removed at 25°C/0.001 mbar, whereby the respective products
15a,b were obtained as colorless, viscous oils.
1H-1,2-Azaphospholetetracarbonyliron(0) Complexes 13a,b;
General Procedure
1,3-Di-tert-butyl-2-methyl-5-phenyl-1,2-azaphospholium Tri-
flate (15a)
From azaphosphole 12a (0.183 g, 0.67 mmol) in CH2Cl2 (8 mL) and
methyl triflate (14a; 0.110 g, 0.67 mmol); yield: 0.293 g (~100%);
bp >250°C/0.001 mbar.
1H NMR (C6D6, 25°C, 400.1 MHz): d = 1.18 (s, 9 H) and 1.35 (s, 9
H, t-C4H9 at N-1 and C-3), 2.06 [d, 3 H, 2J(H,P) = 5.7 Hz, CH3 at P-
2], 6.59 [d, 1 H, 3J(H,P) = 10.8 Hz, H-4], 7.30-7.36 (m, 3 H,C6H5),
7.63-7.70 (m, 2H,C6H5).
To a stirred suspension of nonacarbonyldiiron(0) in toluene was
added an equimolar amount of the respective 1H-1,2-azaphosphole
12a,b at 25°C. After 18 h the reaction mixture was filtered over
Celite and the solvent evaporated. The dark red residue was dis-
solved in pentane and crystallized at -30°C providing a black-red,
crystalline powder of the respective complex 13a,b.
(2-h1-1,3-Di-tert-butyl-5-phenyl-1H-1,2-azaphosphole)tetracar-
bonyliron(0) (13a)
From nonacarbonyldiiron(0) (0.265 g, 0.73 mmol) in toluene (12
mL) and azaphosphole 12a (0.199 g, 0.73 mmol); yield: 0.203 g
(63%); mp 105°C (dec.).
1H NMR (C6D6, 25°C, 400.1 MHz): d = 1.39 [d, 9 H, 4J(H,P) = 1.4
Hz] and 1.40 [d, 9 H, 4J(H,P) = 0.5 Hz, t-C6H4 at N-1 and C-3], 6.69
[d, 1 H, 3J(H,P) = 10.3 Hz, H-4], 6.99-7.17 (m, 5 H, C6H5).
13C{1H} NMR (CDCl3, 25°C, 100.6 MHz): d = 31.5 [d,
3J(C,P) = 8.7 Hz] and 32.7 [d, 3J(C,P) = 9.4 Hz, C(CH3)3 at N-1 and
C-3], 35.6 [d, 2J(C,P) = 13.1 Hz, C(CH3)3 at C-3], 62.2 [d,
2J(C,P) = 7.3 Hz, C(CH3)3 at N-1], 124.7 [d, 2J(C,P) = 5.1 Hz, C-4],
127.5 (s, Ph-C), 128.7 (s, Ph-C), 129.0 [d, 4J(C,P) = 5.1 Hz, Ph-C],
137.5 [d, 3J(C,P) = 5.8 Hz, Ph-C], 162.7 [d, 2J(C,P) = 8.7 Hz, C-5],
204.6 [d, 1J(C,P) = 25.5 Hz, C-3], 218.2 [d, 2J(C,P) = 5.8 Hz, CO].
13C{1H} NMR (C6D6, 25°C, 100.6 MHz): d = 15.7 [d,
1J(C,P) = 27.3 Hz, CH3 at P-2], 30.6 [d, 3J(C,P) = 6.4 Hz] and 31.6
[d, 3J(C,P) = 6.4 Hz, C(CH3)3 at N-1 and C-3], 36.5 [d,
2J(C,P) = 10.4 Hz, C(CH3)3 at C-3], 66.5 [d, 2J(C,P) = 7.2 Hz,
C(CH3)3 at N-1], 121.7 [q, 1J(C,F) = 322.2 Hz, CF3SO3 ], 127.5 [d,
-
2J(C,P) = 4.4 Hz, C-4], 128.4 (s, Ph-C), 130.8 (s, Ph-C), 132.7 (s,
3
2
Ph-C), 133.3 [d, J(C,P) = 4.0 Hz, Ph-C], 180.3 [d, J(C,P) = 8.8
Hz, C-5], 192.5 [d, 1J(C,P) = 24.9 Hz, C-3].
31P{1H} NMR (C6D6, 25°C, 81.0 MHz): d = 103.4 (s).
IR (CCl4): n = 2960 (C-H), 2926 (C-H), 2873 (C-H), 1495, 1262,
1098, 1030, 727, 694 cm-1.
MS (EI, 70 eV): m/z (%) = 288 (M+, 3), 217 ([M - CH3 - C4H8]+,
9), 202 ([M - CH3 - C4H9N]+, 13), 56 ([C4H8]+, 100).
31P{1H} NMR (C6D6, 25°C, 81.0 MHz): d = 121.3 (s).
1,3-Di-tert-butyl-2-ethyl-5-phenyl-1,2-azaphospholium Triflate
(15b)
From azaphosphole 12a (0.231 g, 0.84 mmol) in CH2Cl2 (10 mL)
and ethyl triflate (14b; 0.150 g, 0.84 mmol); yield: 0.381 g
(~100%); bp >250°C/0.001 mbar.
IR (CCl4): n = 2968 (C-H), 2047 (CO), 1969 (CO), 1940 (CO),
1186, 1028, 676, 634 cm-1.
Anal. Calcd for C21H24FeNO4P (441.3): C, 57.16; H, 5.48; N, 3.17.
Found C, 56.13; H, 5.64; N, 3.08.
MS (EI, 70 eV): m/z (%) = 441 (M+, 1), 273 ([M - Fe(CO)4]+, 27),
217 ([M - Fe(CO)4 - C4H8]+, 51), 202 ([M - Fe(CO)4 - C4H9N]+,
100), 57 ([t-C4H9]+, 5).
(2-h1-1-tert-Butyl-3-(1,1-dimethylpropyl)-5-phenyl-1H-1,2-aza-
phosphole)tetracarbonyliron(0) (13b)
1H NMR (CDCl3, 25°C, 400.1 MHz): d = 1.00 [dt, 3 H,
3J(H,P) = 10.4 Hz, 3J(H,H) = 7.3 Hz, CH2CH3 at P-2], 1.43 [d, 9 H,
4J(H,P) = 1.2 Hz, t-C4H9 at C-3], 1.61 (s, 9H, t-C4H9 at N-1), 2.93
2
3
[dq, 2 H, J(H,P) = 34.1 Hz, J(H,H) = 7.3 Hz, CH2CH3 at P-2],
7.03 [d, 1 H, 3J(H,P) = 10.3 Hz, H-4], 7.50-7.67 (m, 5 H, C6H5).
13C{1H} NMR (CDCl3, 25°C, 100.6 MHz): d = 7.4 [d, 2J(C,P) = 2.2
From nonacarbonyldiiron(0) (0.224 g, 0.78 mmol) in toluene (12
mL) and azaphosphole 12b (0.284 g, 0.78 mmol); yield : 0.210 g
(59%); mp 107°C (dec.).
1H NMR (C6D6, 25°C, 400.1 MHz): d = 0.84 [t, 3 H, 3J(H,H) = 7.4
Hz, CH2CH3], 1.36 [d, 6 H, 4J(H,P) = 1.7 Hz, C(CH3)2Et], 1.41 [d,
9 H, 4J(H,P) = 1.0 Hz, t-C4H9 at N-1], 1.68 [dq, 2 H, 3J(H,H) = 7.5
Hz, 4J(H,P) = 1.7 Hz, CH2CH3], 6.65 [d, 1 H, 3J(H,P) = 10.5 Hz, H-
4], 6.97-7.20 (m, 5 H, C6H5).
1
Hz, CH2CH3 at P-2], 23.8 [d, J(C,P) = 29.8 Hz, CH2CH3 at P-2],
30.5 [d, 3J(C,P) = 6.5 Hz] and 31.4 [d, 3J(C,P) = 6.5 Hz, C(CH3)3 at
N-1 and C-3], 36.9 [d, 2J(C,P) = 11.6 Hz, C(CH3)3 at C-3], 67.0 [d,
1
2J(C,P) = 7.3 Hz, C(CH3)3 at N-1], 120.5 [q, J(C,F) = 321.4 Hz,
-
CF3SO3 ], 126.7 [d, 2J(C,P) = 4.4 Hz, C-4], 128.6 (s, Ph-C), 131.1
(s, Ph-C), 132.1 [d, 3J(C,P) = 4.4 Hz, Ph-C], 134.4 (s, Ph-C), 181.7
[d, 2J(C,P) = 8.0 Hz, C-5], 190.8 [d, 1J(C,P) = 28.3 Hz, C-3].
31P{1H} NMR (CDCl3, 25°C, 81.0 MHz): d = 114.5 (s).
13C{1H} NMR (C6D6, 25°C, 100.6 MHz): d = 9.2 (s, CH2CH3), 28.9
[d, 3J(C,P) = 10.2 Hz, C(CH3)2Et], 32.9 [d, 3J(C,P) = 9.3 Hz,
IR (CCl4): n = 2960 (C-H), 2928 (C-H), 2872 (C-H), 1458, 1265,
2
1152, 1030, 909 cm-1.
C(CH3)3 at N-1], 36.9 [d, J(C,P) = 5.9 Hz, C(CH3)2Et], 39.6 [d,
3J(C,P) = 11.9 Hz, CH2CH3], 62.7 [d, 2J(C,P) = 7.6 Hz, C(CH3)3 at
N-1], 125.7 [d, 2J(C,P) = 5.5 Hz, C-4], 127.4 (s, Ph-C), 129.0 (s, Ph-
MS (EI, 70 eV): m/z (%) = 302 (M+, 2), 217 ([M - C2H5 - C4H8]+,
66), 202 ([M - C2H5 - C4H9N]+, 8), 56 ([C4H8]+, 54), 41 ([C3H5]+,
100).
4
3
C), 129.6 [d, J(C,P) = 5.1 Hz, Ph-C], 138.2 [d, J(C,P) = 5.1 Hz,
2
1
Ph-C], 163.1 [d, J(C,P) = 9.3 Hz, C-5], 204.0 [d, J(C,P) = 24.6
Hz, C-3], 219.2 [d, 2J(C,P) = 5.9 Hz, CO].
6,9-Di-tert-butyl-2,2´-diethoxy-4,4´-bis(ethoxycarbonyl)-7-phe-
nyl-1,1´-dioxa-3,3´,4,4´,6-pentaaza-5-phosphaspiro[4.4.4]tride-
ca-2,2´,7-triene (17)
31P{1H} NMR (C6D6, 25°C, 81.0 MHz): d = 126.2 (s).
IR (CCl4): n = 2965 (C-H), 2047 (CO), 1970 (CO), 1960 (CO),
1940 (CO), 1479, 1190, 1029, 705, 634 cm-1.
Diethyl azodicarboxylate (16, 0.293 g, 1.68 mmol)) was added to a
stirred solution of azaphosphole 12a (0.230 g, 0.84 mmol) in Et2O
(5 mL) at 25°C. After 3 d all volatile components were removed at
25°C/0.001 mbar and the residue was suspended in cold (3°C) hex-
ane (3 mL), whereby a colorless precipitate was separated. The pre-
cipitate was washed with cold hexane (3 × 3 mL) and then dried at
25°C/0.001 mbar providing the spirotricyclic betaine 17; yield:
0.193 g (37%); mp 103°C.
MS (EI, 70 eV): m/z (%) = 455 (M+, 16), 437 ([M - CO]+, 59), 287
([M - Fe(CO)4]+, 100), 231 ([M - Fe(CO)4 - C4H8]+, 32), 216 ([M
- Fe(CO)4 - C4H9N]+, 32), 57 ([t-C4H9]+, 50).
1,2-Azaphospholium Triflates 15a,b; General Procedure
To a stirred solution of the 1H-1,2-azaphosphole 12a in CH2Cl2 was
added an equimolar amount of the respective alkyl trifluo-
Synthesis 2000, No. 3, 417–428 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Imidovanadium(V)-Complexes as Reaction Partners for Kinetically Stabilized Phosphaalkynes
425
1H NMR (C6D6, 25°C, 400.1 MHz): d = 0.92 [t, 6 H, 3J(H,H) = 7.1
Hz, OCH2CH3], 1.01 [t, 6 H, 3J(H,H) = 7.1 Hz, OCH2CH3], 1.30 (s,
9 H, t-C4H9 at C-9), 1.56 (s, 9 H, t-C4H9 at N-6), 3.64-4.12 (m, 8 H,
OCH2CH3), 6.45 [d, 1 H, 3J(H,P) = 73.0 Hz, H-8], 7.09-7.23 (m, 3
H, C6H5), 7.89-7.93 (m, 2 H, C6H5).
Dimethyl 7-tert-Butyl-6-(1,1-dimethylpropyl)-4-phenyl-7-aza-
1-phosphabicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate
(19b)
From azaphosphole 12b (0.188 g, 0.65 mmol) in toluene (5 mL)
and dimethyl acetylenedicarboxylate (18a; 0.093 g, 0.65 mmol);
yield: 0.204 g (73%); mp 83°C.
1H NMR (CDCl3, 25°C, 400.1 MHz): d = 0.63 [t, 3 H, 3J(H,H) = 7.4
Hz, CH2CH3], 0.80 (s, 9 H, t-C4H9 at N-7), 1.03 [s, 3 H,
C(CH3)(CH3)Et], 1.13 [s, 3 H, C(CH3)(CH3)Et], 1.37-1.49 (m, 2 H,
CH2CH3), 3.56 (s, 3 H, OCH3), 3.69 (s, 3 H, OCH3), 7.20 [d, 1 H,
3J(H,P) = 8.1 Hz, H-5], 7.23-7.29 (m, 3 H, C6H5),), 7.51-7.55 (m,
2 H, C6H5).
13C{1H} NMR (C6D6, 25°C, 100.6 MHz): d = 14.0 (s, OCH2CH3),
14.1 (s, OCH2CH3), 14.2 (s, OCH2CH3), 14.3 (s, OCH2CH3), 29.7
[d, 3J(C,P) = 4.6 Hz, C(CH3)3 at C-9], 31.4 [s, C(CH3)3 at N-6], 38.1
2
[d, J(C,P) = 15.3 Hz, C(CH3)3 at C-9], 58.3 [s, C(CH3)3 at N-6],
63.1 (s, OCH2CH3), 64.9 (s, OCH2CH3), 100.4 [d, 1J(C,P) = 113.7
Hz, C-9], 124.7 [d, 2J(C,P) = 4.0 Hz, C-8], 127.7 (s, Ph-C), 128.1 (s,
Ph-C), 128.8 (s, Ph-C), 141.7 (s, Ph-C), 148.5 (s, C-7), 150.4 (s) and
153.4 [d, 2J(C,P) = 14.5 Hz] (C2 and C2´), 156.2 [d, 2J(C,P) = 10.7
Hz] and 156.9 [d, 2J(C,P) = 25.2 Hz] (CO2Et at N-4 and N-4´).
13C{1H} NMR (CDCl3, 25°C, 100.6 MHz): d = 8.6 (s, CH2CH3),
3
25.6 [d, 3J(C,P) = 4.8 Hz, C(CH3)(CH3)3Et], 27.2 [d, J(C,P) = 6.4
31P{1H} NMR (C6D6, 25 °C, 81.0 MHz): d = -41.0 (s).
Hz, C(CH3)(CH3)3Et], 32.1 [d, 3J(C,P) = 11.2 Hz, C(CH3)3 at N-7],
3
2
34.1 [d, J(C,P) = 4.8 Hz, CH2CH3], 37.9 [d, J(C,P) = 15.3 Hz,
CMe2Et], 51.9 [d, 2J(C,P) = 9.6 Hz, C(CH3)3 at N-7], 56.2 (s,
OCH3), 56.3 (s, OCH3), 92.9 [d, 2J(C,P) = 10.4 Hz, C-4], 128.0 (s,
Ph-C), 128.5 (s, Ph-C), 129.9 (s, Ph-C), 137.4 (s, Ph-C), 143.5 (s,
C-5), 155.2 [d, 1J(C,P) = 34.5 Hz, C-2], 164.5 [d, 2J(C,P) = 19.3 Hz,
C-3], 167.4 (s, CO2Me), 168.7 (s, CO2Me), 176.2 [d, 1J(C,P) = 37.7
Hz, C-6].
IR (CCl4): n = 2978 (C-H), 2936 (C-H), 2910 (C-H), 1747 (CO),
1669, 1478, 1428, 1382, 1369, 1346, 1320, 1306, 1271, 1247, 1176,
1145, 1072, 1017, 696, 644 cm-1.
MS (EI, 70 eV): m/z (%) = 621 (M+, 1), 564 ([M - C4H9]+, 5), 390
([M - C6H10N2O4 - C4H9]+, 11), 273 ([M - 2(C6H10N2O4)]+, 37),
202 ([M - 2(C6H10N2O4) - C4H9N]+, 37), 185 ([M - 2(C6H10N2O4)
- C7H4]+, 100), 57 ([C4H9]+, 33).
31P{1H} NMR (CDCl3, 25°C, 81.0 MHz): d = 53.7 (s).
IR (CCl4): n = 2967 (C-H), 1731 (CO), 1653, 1435, 1363, 1263,
7-Aza-1-phosphanorbornadienes 19a-d; General Procedure
To a stirred solution of the respective 1H-1,2-azaphosphole 12a,b
in toluene was added an equimolar amount of the respective dialkyl
acetylenedicarboxylate 18a-d at -78°C. The reaction mixture was
allowed to warm to 25°C and after 18 h all volatile components
were removed at 25°C/0.001 mbar. The residue was dissolved in
pentane and impurities were filtered over Celite. The filtrate was
concentrated and the azaphosphanorbornadienes 19a-d were ob-
tained by crystallization at -30°C as colorless to yellow, microcrys-
talline solids.
1239, 1197, 1028, 909, 701, 668 cm-1.
Anal. Calcd for C24H32NO4P (429.5): C, 67.12; H, 7.51; N, 3.26.
Found C, 66.51; H, 7.41; N, 3.28.
MS (EI, 70 eV): m/z (%) = 429 (M+, 1), 287 ([M - C6H6O4]+, 28),
231 ([M - C6H6O4 - C4H8]+, 24), 216 ([M - C6H6O4 - C4H9N]+, 9),
202 ([M - C6H6O4 - C4H9N - CH3]+, 100), 57 ([C4H9]+, 83).
Diethyl 6,7-Di-tert-butyl-4-phenyl-7-aza-1-phosphabicyclo-
[2.2.1]hepta-2,5-diene-2,3-dicarboxylate (19c)
From azaphosphole 12a (0.347 g, 1.27 mmol) in toluene(8 mL) and
diethyl acetylenedicarboxylate (18b; 0.216 g, 1.27 mmol); yield:
0.377 g (67%); mp 87°C.
Dimethyl 6,7-Di-tert-butyl-4-phenyl-7-aza-1-phosphabicyclo-
[2.2.1]hepta-2,5-diene-2,3-dicarboxylate (19a)
From azaphosphole 12a (0.772 g, 2.83 mmol) in toluene (10 mL)
and dimethyl acetylenedicarboxylate (18a; 0.402 g (2.83 mmol);
yield: 0.835 g (71%); mp 85°C.
1H NMR (C6D6, 25°C, 400.1 MHz): d = 0.88 [t, 3 H, 3J(H,H) = 7.2
Hz, OCH2CH3], 0.93 [d, 9 H, 4J(H,P) = 1.2 Hz, t-Buat N-7], 0.97 [t,
3
3 H, J(H,H) = 7.2 Hz, OCH2CH3], 1.15 (s, 9 H, t-C4H9 at C-6),
1H NMR (C6D6, 25°C, 400.1 MHz): d = 0.91 [d, 9 H, 4J(H,P) = 0.5
Hz, t-C4H9 at N-7], 1.12 [d, 9 H, 4J(H,P) = 0.5 Hz, t-C4H9 at C-6],
3.39 (s, 3 H, OCH3), 3.46 (s, 3 H, OCH3), 7.13-7.20 (m, 3 H, C6H5),
7.32 [d, 1 H, 3J(H,P) = 8.1 Hz, H-5], 7.61-7.65 (m, 2 H, C6H5).
13C{1H} NMR (C6D6, 25°C, 100.6 MHz): d = 28.9 [d, 3J(C,P) = 5.1
Hz, C(CH3)3 at C-6], 32.0 [d, 3J(C,P) = 11.0 Hz, C(CH3)3 at N-7],
34.4 [d, 2J(C,P) = 16.1 Hz, C(CH3)3 at C-6], 51.3 (s, OCH3), 51.4 (s,
OCH3), 56.1 [d, 2J(C,P) = 8.5 Hz, C(CH3)3 at N-7], 93.1 [d,
2J(C,P) = 11.0 Hz, C-4], 128.1 (s, Ph-C), 128.5 (s, Ph-C), 130.1 (s,
Ph-C), 137.8 (s, Ph-C), 142.2 (s, C-5), 156.0 [d, 1J(C,P) = 33.9 Hz,
C-2], 164.3 [d, 2J(C,P) = 20.3 Hz, C-3], 166.9 (s, CO2Me), 168.1 (s,
CO2Me), 177.4 [d, 1J(C,P) = 33.9 Hz, C-6].
3.84-4.16 (m, 4 H, OCH2CH3), 7.10-7.14 (m, 3 H, C6H5), 7.36 [d,
1 H, 3J(H,P) = 8.1 Hz, H-5], 7.66-7.71 (m, 2 H, C6H5).
13C{1H} NMR (C6D6, 25°C, 100.6 MHz): d = 13.1 (s, OCH2CH3),
14.3 (s, OCH2CH3), 29.4 [d, 3J(C,P) = 4.6 Hz, C(CH3)3 at C-6], 32.6
[d, 3J(C,P) = 11.4 Hz, C(CH3)3 at N-7], 35.0 [d, 2J(C,P) = 16.0 Hz,
C(CH3)3 at C-6], 56.6 [d, 2J(C,P) = 8.4 Hz, C(CH3)3 at N-7], 60.9 (s,
2
OCH2CH3), 61.0 (s, OCH2CH3), 93.6 [d, J(C,P) = 10.7 Hz, C-4],
128.4 (s, Ph-C), 128.8 (s, Ph-C), 130.8 (s, Ph-C), 138.4 (s, Ph-C),
141.8 (s, C-5), 156.2 [d, 1J(C,P) = 32.0 Hz, C-2], 164.4 [d,
2J(C,P) = 19.8 Hz, C-3], 166.7 (s, CO2Et), 168.9 (s, CO2Et), 178.0
[d, 1J(C,P) = 35.1 Hz, C-6].
31P{1H} NMR (C6D6, 25°C, 81.0 MHz): d = 54.0 (s).
31P{1H} NMR (C6D6, 25°C, 81.0 MHz): d = 54.0 (s).
IR (CCl4): n = 2965 (C-H), 2903 (C-H), 1717 (CO), 1620, 1473,
IR (CCl4): n = 2964 (C-H), 1731 (CO), 1652, 1474, 1458, 1434,
1462, 1447, 1391, 1364, 1292, 1276, 1228, 1198, 1035 cm-1.
1363, 1261, 1234, 1197, 1029 cm-1.
Anal. Calcd for C25H34NO4P (443.5): C, 67.70; H, 7.73; N, 3.16.
Found C, 66.47; H, 7.40; N, 3.00.
MS (EI, 70 eV): m/z (%) = 443 (M+, 1), 273 ([M - C8H10O4]+, 46),
217 ([M - C8H10O4 - C4H8]+, 53), 202 ([M - C8H10O4 - C4H9N]+,
100), 57 ([C4H9]+, 83).
Anal. Calcd for C23H30NO4P (415.5): C, 66.49; H, 7.28; N, 3.37.
Found C, 66.51; H, 7.41; N, 3.28.
MS (EI, 70 eV): m/z (%) = 415 (M+, 5), 273 ([M - C6H6O4]+, 34),
217 ([M - C6H6O4 - C4H8]+, 67), 202 ([M - C6H6O4 - C4H9N]+,
100), 57 ([C4H9]+, 83).
Di-tert-butyl 6,7-Di-tert-Butyl-4-phenyl-7-aza-1-phosphabicyc-
lo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate (19d)
From) azaphosphole 12a (0.161 g, 0.59 mmol) in toluene (4 mL)
and di-tert-butyl acetylenedicarboxylate (18c; 0.133 g, 0.59 mmol);
yield: 0.186 g (63%); mp 93 °C.
Synthesis 2000, No. 3, 417–428 ISSN 0039-7881 © Thieme Stuttgart · New York

426
C. Peters et al.
PAPER
1H NMR (C6D6, 25°C, 400.1 MHz): d = 0.97 [d, 9 H, 4J(H,P) = 1.1
Hz, t-Bu at N-7], 1.23 (s, 9 H, t-C4H9 at C-6), 1.32 [s, 9 H,
OC(CH3)3], 1.46 [s, 9 H, OC(CH3)3], 7.11-7.20 (m, 3 H, C6H5),
7.37 [d, 1 H, 3J(H,P) = 8.2 Hz, H-5], 7.69-7.74 (m, 2 H, C6H5).
filtered over Celite. The filtrate was concentrated and the azaphos-
phanorbornadiene 19f was obtained by crystallization at -78°C as
pale yellow crystals; yield: 0.308 g (63%); mp 105°C.
1H NMR (C6D6, 25°C, 400.1 MHz): d = 0.64 [d, 9 H, 4J(H,P) = 1.4
Hz, t-C4H9 at N-7], 0.87 (s, 9H, t-C4H9 at C-6), 6.65 [d, 1H,
3J(H,P) = 7.8 Hz, H-5], 7.02-7.18 (m, 5H, C6H5).
13C{1H} NMR (C6D6, 25°C, 100.6 MHz): d = 27.8 [s, OC(CH3)3],
28.1 [s, OC(CH3)3], 29.4 [d, 3J(C,P) = 4.8 Hz, C(CH3)3 at C-6], 32.6
[d, 3J(C,P) = 10.5 Hz, C(CH3)3 at N-7], 34.9 [d, 2J(C,P) = 16.2 Hz,
C(CH3)3 at C-6], 56.3 [d, 2J(C,P) = 8.6 Hz, C(CH3)3 at N-7], 80.7 [s,
13C{1H} NMR (C6D6, 25°C, 100.6 MHz): d = 27.7 [d, 3J(C,P) = 6.4
Hz, C(CH3)3 at C-6], 30.8 [d, 3J(C,P) = 10.4 Hz, C(CH3)3 at N-7],
33.9 [d, 2J(C,P) = 17.7 Hz, C(CH3)3 at C-6], 56.6 [d, 2J(C,P) = 8.8
2
OC(CH3)3], 81.4 [s, OC(CH3)3], 93.2 [d, J(C,P) = 10.5 Hz, C-4],
128.2 (s, Ph-C), 128.6 (s, Ph-C), 138.5 (s, Ph-C), 140.2 (s, C-5),
2
Hz, C(CH3)3 at N-7], 92.8 [d, J(C,P) = 12.9 Hz, C-4], 113.6 (s,
1
2
155.9 [d, J(C,P) = 29.6 Hz, C-2], 163.6 [d, J(C,P) = 20.0 Hz, C-
3], 165.1 (s, CO2tBu), 169.3 (s, CO2tBu), 177.7 [d, 1J(C,P) = 38.1
Hz, C-6].
CN), 113.7 (s, CN), 128.0 (s, Ph-C), 129.0 (s, Ph-C), 129.8 (s, Ph-
C), 134.4 (s, Ph-C), 144.7 (s, C-5), 151.9 [d, 2J(C,P) = 4.8 Hz, C-3],
152.7 [d, 1J(C,P) = 47.4 Hz, C-2], 177.0 [d, 1J(C,P) = 29.7 Hz, C-6].
31P{1H} NMR (C6D6, 25°C, 81.0 MHz): d = 60.6 (s).
31P{1H} NMR (C6D6, 25°C, 81.0 MHz): d = 54.2 (s).
IR (CCl4): n = 2970 (C-H), 2933 (C-H), 1712 (CO), 1624, 1476,
IR (CCl4): n = 2930 (C-H), 2857 (C-H), 2179, 1684, 1636, 1447,
1459, 1392, 1367, 1299, 1259, 1167, 1113, 1028, 702 cm-1.
1360, 1264, 1216, 1089, 1030, 726, cm-1.
Anal. Calcd for C29H42NO4P (499.6): C, 69.72; H, 8.48; N, 2.80.
Found C, 68.23; H, 8.27; N, 3.57.
MS (EI, 70 eV): m/z (%) = 499 (M+, 3), 273 ([M - C12H18O4]+, 31),
217 ([M - C12H18O4 - C4H8]+, 59), 202 ([M - C12H18O4 - C4H9N]+,
100), 57 ([C4H9]+, 78).
Anal. Calcd for C21H24N3P (349.4): C, 72.19; H, 6.92; N, 12.03.
Found C, 70.43; H, 7.28; N, 10.89.
MS (EI, 70 eV): m/z (%) = 349 (M+, 8), 292 ([M - C4H9]+, 12), 273
([M - C4N2]+, 24), 217 ([M - C4N2 - C4H8]+, 56), 202 ([M - C4N2
- C4H9N]+, 100), 57 ([C4H9]+, 15).
6,7-Di-tert-butyl-2,3-bis(trifluoromethyl)-4-phenyl-7-aza-1-
phosphabicyclo[2.2.1]hepta-2,5-diene (19e)
Dimethyl 6,7-Di-tert-butyl-1-oxo-4-phenyl-7-aza-1l5-phospha-
bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate (20)
Hexafluorobut-2-yne (18d; 0.240 g, 1.48 mmol) was condensed at
-196°C in a glass-pressure tube and then warmed up to -78°C.
Then the azaphosphole 12a (0.403 g, 1.48 mmol dissolved in
CH2Cl2 (5 mL) was added at -78°C and the reaction mixture was al-
lowed to warm to 25°C. After 18 h all volatile components were re-
moved at 25°C/0.001 mbar, the residue was dissolved in pentane
and filtered over Celite. Crystallization at -28°C from CH2Cl2 pro-
vided the azaphosphanorbornadiene 19e as colorless crystals; yield:
0.470 g (73%); mp 93°C.
Bis(trimethylsilyl) peroxide (0.049 g, 0.28 mmol) was added to a
stirred solution of the azaphosphanorbornadiene 19a (0.115 g, 0.28
mmol) in hexane (4 mL) at 0°C. The reaction mixture was allowed
to warm to 25°C and after 18 h all volatile components were re-
moved at 25°C/0.001 mbar. The residue was dissolved in pentane
and the solution cooled to -28°C, whereby a colorless precipitate
formed. The oxidized bicyclic product 20 was obtained as a yellow
solid after evaporation of the solvent; yield: 0.070 g (58%); mp
103°C.
1H NMR (C6D6, 25°C, 400.1 MHz): d = 0.86 [d, 9 H, 4J(H,P) = 1.6
Hz, t-C4H9 at N-7], 1.15 (s, t-C4H9 at C-6), 7.15-7.18 (m, 3 H,
1H NMR (C6D6, 25°C, 400.1 MHz): d = 1.14 (s, t-C4H9 at N-7), 1.32
(s, t-C4H9 at C-6), 3.28 (s, 3H, OCH3), 3.44 (s, 3 H, OCH3), 7.02-
7.45 (m, 5H, C6H5), 7.56 [d, 1H, 3J(H,P) = 38.4 Hz, H-5).
3
C6H5), 7.27 [d, 1 H, J(H,P) = 8.4 Hz, H-5], 7.56-7.62 (m, 2 H,
C6H5).
13C{1H} NMR (C6D6, 25°C, 100.6 MHz): d = 27.8 [d, 3J(C,P) = 5.1
13C{1H} NMR (C6D6, 25°C, 100.6 MHz): d = 29.2 [d, 3J(C,P) = 5.1
Hz, C(CH3)3 at C-6], 32.6 [d, 3J(C,P) = 11.3 Hz, C(CH3)3 at N-7],
34.9 [d, 2J(C,P) = 15.3 Hz, C(CH3)3 at C-6], 57.1 [d, 2J(C,P) = 8.9
Hz, C(CH3)3 at N-7], 94.3 [dq, 2J(C,P) = 12.7, 3J(C,F) = 1.3 Hz, C-
3
Hz, C(CH3)3 at C-6], 31.5 [d, J(C,P) = 4.5 Hz, C(CH3)3 at N-7],
34.3 [d, 2J(C,P) = 8.9 Hz, C(CH3)3 at C-6], 51.5 (s, OCH3), 51.6 (s,
OCH3), 58.7 [d, 2J(C,P) = 1.3 Hz, C(CH3)3 at N-7], 68.9 [d,
2J(C,P) = 35.0 Hz, C-4], 127.3 (s, Ph-C), 127.8 (s, Ph-C), 128.6 (s,
Ph-C), 136.0 [d, 3J(C,P) = 12.7 Hz, Ph-C], 142.3 [d, 1J(C,P) = 83.9
Hz, C-2], 147.9 [d, 2J(C,P) = 8.9 Hz, C-5], 157.4 [d, 1J(C,P) = 85.8
Hz, C-6], 162.8 (s, CO2Me), 165.0 (s, CO2Me), 168.0 [d,
2J(C,P) = 6.5 Hz, C-3].
1
4
4], 121.8 [qq, J(C,F) = 274.3 Hz, J(C,F) = 1.5 Hz, CF3 at C-3],
1
2
4
124.2 [qdq, J(C,F) = 270.2 Hz, J(C,P) = 21.6 Hz, J(C,F) = 1.5
Hz, CF3 at C-2], 127.5 (s, Ph-C), 129.3 (s, Ph-C), 136.4 (s, Ph-C),
139.3 (d, 2J(C,P) = 1.9 Hz, C-5), 160.0 (mc) and 163.3 (mc, C-2 and
C-3), 179.8 [d, 1J(C,P) = 38.2 Hz, C-6].
31P{1H} NMR (C6D6, 25°C, 81.0 MHz): d = 42.6 (s).
31P{1H} NMR (C6D6, 25°C, 81.0 MHz): d = 53.0 [q, 3J(P,F) = 15.8
Hz].
IR (CCl4): n = 2960 (C-H), 1730 (CO), 1685, 1670, 1635, 1603,
1594, 1552, 1538, 1433, 1395, 1368, 1267 (P = O), 1257, 1193,
1094, 1030, 1019, 975, 867 cm-1.
IR (CCl4): n = 2966 (C-H), 2905 (C-H), 1651, 1463, 1450, 1364,
1299, 1253, 1168, 1150, 1017, 703 cm-1.
MS (EI, 70 eV): m/z (%) = 431 (M+, 1), 375 ([M - C4H8]+, 100),
Anal. Calcd for C21H24F6NP (435.4): C, 57.93; H, 5.56; N, 3.22.
Found C, 57.63; H, 5.52; N, 3.70.
343 ([M - C4H9 - OCH3]+, 57), 57 ([C4H9]+, 17).
MS (EI, 70 eV): m/z (%) = 435 (M+, 5), 273 ([M - C4F6]+, 26), 217
([M - C4F6 - C4H8]+, 62), 202 ([M - C4F6 - C4H9N]+, 100), 162
([C4F6]+, 15), 57 ([C4H9]+, 39).
Dimethyl 6,7-Di-tert-butyl-4-phenyl-1-thio-7-aza-1l5-phospha-
bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate (21)
Sulfur (S8) (0.120 g, 0.47 mmol) and Et3N (0.048 g, 0.47 mmol)
were added to a stirred solution of the azaphosphanorbornadiene
19a (0.196 g, 0.47 mmol) in toluene (4 mL) at 25°C. After 7 d all
volatile components were removed at 25°C/0.001 mbar. The resi-
due was dissolved in pentane and filtered over Celite. After concen-
trating the filtrate, crystallization at -28°C afforded the sulfurized
azaphosphanorbornadiene 21 as an orange-red solid; yield: 0.149 g
(71%); mp 96°C.
6,7-Di-tert-butyl-4-phenyl-7-aza-1-phosphabicyclo[2.2.1]hepta-
2,5-diene-2,3-dinitrile (19f)
To a stirred solution of the azaphosphole 12a (0.332 g, 1.40 mmol)
in CH2Cl2 (5 mL) was added dicyanoacetylene (18e; 0.106 g, 1.40
mmol) at -78°C. The reaction mixture was allowed to warm to
25°C and after 18 h all volatile components were removed at 25°C/
0.001 mbar. The residue was dissolved in pentane/Et2O (3:1) and
Synthesis 2000, No. 3, 417–428 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Imidovanadium(V)-Complexes as Reaction Partners for Kinetically Stabilized Phosphaalkynes
427
1H NMR (C6D6, 25°C, 400.1 MHz): d = 1.18 (s, 9 H, t-C4H9 at N-7),
1.40 (s, ) H, t-C4H9 at C-6), 3.22 (s, 3 H, OCH3), 3.52 (s, 3 H,
OCH3), 6.98-7.26 (m, 5 H, C6H5), 7.63 [d, 1 H, 3J(H,P) = 38.4 Hz,
H-5].
References
(1) Part 149, see: Ruf, S. G.; Mack, A.; Steinbach, J.; Bergsträßer,
U.; Regitz, M. Synthesis 2000, 360.
(2) Mack, A.; Regitz M. Chem. Ber. 1997, 130, 823.
(3) (a) Schmidpeter A.; Karaghiosoff K. In Multiple Bonds and
Low Coordination in Phosphorus Chemistry; Regitz M.;
Scherer, O. J., Eds.; Thieme: Stuttgart 1990; p 258.
(b) Regitz, M. In Multiple Bonds and Low Coordination in
Phosphorus Chemistry; Regitz, M.; Scherer, O. J., Eds.;
Thieme: Stuttgart 1990; p 58.
(4) Regitz, M.; Krill S. Phosphorus, Sulfur, and Silicon 1996,
115, 99.
(5) Asmus, S. M. F.; Bergsträßer, U.; Regitz, M. Synthesis 1999,
1642.
(6) Karaghiosoff, K.; Klehr, H.; Schmidtpeter, A. Chem. Ber.
1986, 119, 410.
(7) Rösch, W.; Facklam, T.; Regitz, M. Tetrahedron 1987, 43,
3247.
(8) Peters, C.; Tabellion, F.; Nachbauer, A.; Fischbeck, U.;
Leininger, S.; Preuss, F.; Regitz, M.; J. Org. Chem.,
submitted.
13C{1H} NMR (C6D6, 25°C, 100.6 MHz): d = 28.0 [d, 3J(C,P) = 4.4
3
Hz, C(CH3)3 at C-6], 32.2 [d, J(C,P) = 5.2 Hz, C(CH3)3 at N-7],
35.5 [d, 2J(C,P) = 9.6 Hz, C(CH3)3 at C-6], 51.6 (s, OCH3), 51.9 (s,
OCH3), 60.8 [d, 2J(C,P) = 1.2 Hz, C(CH3)3 at N-7], 76.2 [d,
2J(C,P) = 26.1 Hz, C-4], 128.2 (s, Ph-C), 128.3 (s, Ph-C), 128.8 (s,
3
2
Ph-C), 136.9 [d, J(C,P) = 11.7 Hz, Ph-C], 146.5 [d, J(C,P) = 8.4
Hz, C-5], 147.5 [d, 1J(C,P) = 66.3 Hz, C-2], 160.1 [d, 1J(C,P) = 60.6
Hz, C-6], 163.0 [d, 2J(C,P) = 13.1 Hz, CO2Me], 163.6 [d,
3J(C,P) = 4.0 Hz, CO2Me], 164.2 [d, 2J(C,P) = 14.9 Hz, C-3].
31P{1H} NMR (C6D6, 25°C, 81.0 MHz): d = 67.8 (s).
IR (CCl4): n = 2954 (C-H), 1733 (CO), 1435, 1295, 1260 (P = S),
1192, 1105, 1019, 949 cm-1.
MS (EI, 70 eV): m/z (%) = 447 (M+, 12), 391 ([M - C4H8]+, 14),
359 ([M - C4H8 - S]+, 37), 215 ([M - C6H6O4 - S - C4H9 - H]+,
100), 57 ([C4H9]+, 72).
Crystal Structure Analysis of 12a
(9) Tabellion, F.; Peters, C.; Regitz, M.; Preuss, F. Chem. Eur. J.,
submitted.
(10) Arbuzov, B. A.; Dianova, E. N.; Zabotina, E. Ya. Dokl. Akad.
Nauk SSSR 1983, 273, 613.
(11) Karaghiosoff, K.; Sheldrick, W. S.; Schmidpeter, A.
Phosphorus Sulfur 1987, 30, 780.
(12) Nießen, W. Ph. D. Thesis, 1996, University of Kaiserslautern.
(13) Burkhart, B. Ph. D. Thesis, 1990, University of
Kaiserslautern.
(14) Tebby, J. C. In CRC Handbook of Phosphorus-31 Nuclear
Magnetic Resonance Data; CRC Press: Florida, 1991.
(15) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.;
Orpen, A. G.; Taylor, R. J. Chem. Soc. Perkin Trans. 2 1987,
1.
(16) Mathey, F.; Mercier, F.; Charrier, C. J. Am. Chem. Soc. 1981,
103, 4595.
(17) Rohde, U.; Ruthe, F.; Jones, P. G.; Streubel, R. Angew. Chem.,
Int. Ed. Engl. 1999, 38, 218.
Crystal Data: C17H24NP, Mr = 273.37, monoclinic, space group
P21/C, a = 5.925(2), b = 10.3776(14), c = 26.598(4) Å, a = 90°,
b = 90.140(13)°, g = 90°, V = 1635.4(5) Å3, Z = 4, dc = 1.100 Mg/
m3.
Data Collection: The data collection was performed using an auto-
matic four circle diffractometer (Siemens P4) at r.t. Crystal dimen-
sions:0.30 ¥ 0.20 ¥ 0.15 mm. The measurements were made in
the range 1.53<q<25.00°, l = 0.71073 Å MoKa (graphite mono-
chromator), -1 £ h £ 7, -1 £ k £12, -31 £ l £ 31, a total of 4278
reflections, of which 2847 were independent reflections.
Structure Solution and Refinement: The structure was solved using
direct methods (SHELX-86)27 and refined with the full matrix least
squares procedure against F2 (SHELXL-93).28 The anisotropic re-
finement converged at R1 = 0.0840 and wR2 = 0.1150 [I>2s(I)]
and R1 = 0.1797, wR2 = 0.1557 [all data]. The difference Fourier
synthesis on the basis of the final structural model showed a maxi-
mum of 0.183 e/Å3 and a minimum of -0.231 e/Å3.29
(18) Berger, S.; Braun, S.; Kalinowski, H.-O. In NMR-
Spektroskopie von Nichtmetallen, 31P NMR-Spektroskopie,
Bd. 3, Berger, S.; Braun, S.; Kalinowski, H.-O., Eds.; Thieme:
Stuttgart 1993; p 61.
(19) (a) Preuss, F.; Towae, W. Z. Naturforsch. B 1981, 36, 1130.
(b) Preuss, F.; Fuchslocher, E.; Towae, W.; Leber, E. Z.
Naturforsch. B 1989, 44, 271.
Crystal Structure Analysis of 19e
Crystal Data: C21H24F6NP, Mr = 435.38, monoclinic, space group
C2/C, a = 14.719(3), b = 11.771(2), c = 24.879(5) Å, a = 90.0°,
b = 94.78(3)°, g = 90.0°, V = 4296(2) Å3, Z = 8, dc = 1.346 Mg/m3.
Data Collection: The data collection was performed using a STOE-
IPDS diffractometer at r.t. Crystal dimensions: 0.30 ¥ 0.20 ¥ 0.20
mm. The measurements were made in the range 2.33<q<26.05°,
l = 0.71073 Å MoKa (graphite monochromator), -18 £ h £ 18, -14
£ k £13, -30 £ l £ 30, a total of 16994 reflections, of which 4138
were independent reflections.
(20) Tabellion, F.; Fishbeck, U.; Regitz, M.; Preuss, F. Z. Anorg.
Allg. Chem., in preparation.
(21) Rösch, W.; Allspach, T.; Bergsträßer, U.; Regitz, M. Synthetic
Methods in Organometallic and Inorganic Chemistry, Vol. 3,
Karsch, H. H., Ed.; Thieme: Stuttgart 1996; p 11.
(22) Allspach, T. Ph. D. Thesis, 1986, University of
Kaiserslautern.
Structure Solution and Refinement: The structure was solved using
direct methods (SHELXS-86)27 and refined with the full matrix
least squares procedure against F2 (SHELXL-93).28 The anisotropic
refinement converged at R1 = 0.0444 and wR2 = 0.1327 [I>2s(I)]
and R1 = 0.0602, wR2 = 0.1430 [all data]. The difference Fourier
synthesis on the basis of the final structural model showed a maxi-
mum of 0.295 e/Å3 and a minimum of -0.190 e/Å3.29
(23) Rösch, W.; Vogelbacher, U.-J.; Allspach, T.; Regitz, M. J.
Organomet. Chem. 1986, 306, 39.
(24) Regitz, M.; Rösch, W.; Allspach, T.; Annen, U.; Blatter, K.;
Fink, J.; Hermesdorf, M.; Heydt, H.; Vogelbacher, U.-J.;
Wagner, O. Phosphorus Sulfur 1987, 30, 479.
(25) Witulski, B. Ph. D. Thesis, 1992, University of Braunschweig.
(26) Jackson, W.-P. Synlett 1990, 536.
(27) Sheldrick, G. M., Fortran Program for the Solution of Crystal
Structures from Diffraction Data, Institute for Organic
Chemistry, University of Göttingen, 1986.
(28) Sheldrick, G. M., Fortran Program for Crystal Structure
Refinement, Institute for Organic Chemistry, University of
Göttingen, 1993.
Acknowledgement
We are grateful to the Fonds der Chemischen Industrie for a post-
graduate grant (C. P.). We are also indebted to the Deutsche For-
schungsgemeinschaft (Graduiertenkolleg “Phosphor als Bindeglied
verschiedener chemischer Disziplinen“) for the generous financial
support and a postgraduate grant (M. S.).
Synthesis 2000, No. 3, 417–428 ISSN 0039-7881 © Thieme Stuttgart · New York

428
C. Peters et al.
PAPER
(29) Crystallographic data (excluding structure factors) for the
structure reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC-136910 (12a) and CCDC-136909
(19e). Copies of the data can be obtained free of charge on
application to The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [fax: int. code +44(1223)336-033,
e-mail:deposit@chemcrys.cam.ac.uk].
Article Identifier:
1437-210X,E;2000,0,03,0417,0428,ftx,en;Z08099SS.pdf
Synthesis 2000, No. 3, 417–428 ISSN 0039-7881 © Thieme Stuttgart · New York