The 1-silyl-1h-phosphirene/1,2-dihydrophosphasilete rearrangement and its preparative significance

Article abstract of DOI:10.1002/(SICI)1521-3765(19990503)5:5<1581::AID-CHEM1581>3.0.CO;2-2

Photolysis of the silyl-substituted 1H-phosphirene 3a proceeds selectively with cleavage of a silicon-silicon bond and ring expansion to furnish the 1,2-dihydro-1,2-phosphasilete 4a. The corresponding heterocyclic germanium product, 4b, is prepared analogously from 3b. The preparative significance of 4a is reflected not only in its numerous addition reactions to multiple-bond systems, such as alkynes 8 and 12 and ketene 10, but also in its substitution reactions with the chloro compounds 15, 18, and 21. The latter reactions proceed through the formation of chlorotrimethylsilane and the novel 1,2-dihydro-1,2-phosphasiletes (16, 19, and 22) which, depending on the substitution pattern at the phosphorus atom, undergo various isomerization reactions (16→17, 19→20). The hydrolysis of 4a to 23 by mere traces of water in carefully purified tetrahydrofuran demonstrates the extreme sensitivity of this compound towards moisture.

Full text of DOI:10.1002/(SICI)1521-3765(19990503)5:5<1581::AID-CHEM1581>3.0.CO;2-2

FULL PAPER
Organophosphorus Compounds, Part 135[=]
The 1-Silyl-1H-phosphirene/1,2-Dihydrophosphasilete Rearrangement
and Its Preparative Significance
Steffen Haber, Marion Schmitz, Uwe Bergsträûer, Jürgen Hoffmann, and
Manfred Regitz*[a]
Dedicated to Professor Edgar Niecke on the occasion of his 60th birthday
Abstract: Photolysis of the silyl-substi-
tuted 1H-phosphirene 3a proceeds se-
lectively with cleavage of a silicon ± sili-
con bond and ring expansion to furnish
the 1,2-dihydro-1,2-phosphasilete 4a.
The corresponding heterocyclic germa-
nium product, 4b, is prepared analo-
gously from 3b. The preparative signifi-
cance of 4a is reflected not only in its
numerous addition reactions to multi-
ple-bond systems, such as alkynes 8 and
12 and ketene 10, but also in its sub-
stitution reactions with the chloro com-
pounds 15, 18, and 21. The latter reac-
tions proceed through the formation of
chlorotrimethylsilane and the novel 1,2-
dihydro-1,2-phosphasiletes (16, 19, and
22) which, depending on the substitution
pattern at the phosphorus atom, under-
go various isomerization reactions
(16 !17, 19 !20). The hydrolysis of 4a
to 23 by mere traces of water in carefully
purified tetrahydrofuran demonstrates
the extreme sensitivity of this compound
towards moisture.
Keywords: electrophilic additions ´
phosphorus heterocycles ´ photoly-
sis ´ ring enlargement ´ silicon
metallic compounds, such as 2a and 2b, proceed under
formation of lithium chloride to afford the 1-silyl- and
1-germyl-1H-phosphirenes 3a and 3b, respectively (Sche-
me 1).[8, 9]
Introduction
We accomplished the synthesis of 1-chloro-1H-phosphirenes,
such as 1, by the addition of chlorocarbenes, generated in situ,
to l3s1-phosphaalkynes in 1989.[1, 2] In these reactions the
corresponding 2H-phosphirenes must be considered as inter-
mediates that undergo a rapid 1,3-chlorine shift to afford the
thermodynamically more favorable 1H-phosphirenes.[3] In the
meantime, the enormous synthetic potential of the 1-chloro-
1H-phosphirenes has been investigated intensively and has
been the subject of several review articles.[4±6] In particular,
the substitution of the chlorine atom on the phosphorus by
nucleophiles leads to a whole series of novelly substituted 1H-
phosphirenes.[7] In this way, for example, the syntheses of
cyano-, azido-, imido-, and phosphaalkene-substituted 1H-
phosphirenes became possible.[1, 2, 7, 8] Reactions with organo-
Scheme 1. Synthesis of the 1-silyl- and 1-germyl-1H-phosphirenes 3a and
3b.
[a] Prof. Dr. M. Regitz, Dr. S. Haber, Dr. M. Schmitz, Dr. U. Bergsträûer,
Dr. J. Hoffmann
While the 1-chloro-1H-phosphirenes preferentially take
part in substitution reactions and only exhibit ring open-
ing[10, 11] or ring expansion[5] behavior in isolated cases, we now
report the first ring expansion reactions of the 1-silyl- and
1-germyl-1H-phosphirenes 3a and 3b.[9]
Fachbereich Chemie der Universität Kaiserslautern
Erwin-Schrödinger-Strasse, D-67663 Kaiserslautern (Germany)
Fax: (‡49)631-205-3921
E-mail: regitz@rhrk.uni-kl.de
[=] Part 134: M. Regitz, U. Bergsträûer, Pol. J. Chem. 1998, 73, 135.
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on the solvent: if the reaction is performed in n-pentane the
molecule undergoes fragmentation so that only the alkyne 5
can be detected. Benzene presumably functions as a UV filter
for light with wavelengths shorter than 280 nm[12] and thus
prevents further decomposition of 3.
Results and Discussion
The rearrangement 3 !4: When the 1H-phosphirenes 3a,b
are irradiated in benzene they undergo isomerization to
furnish the 1,2-dihydro-1,2-phosphasilete 4a and the 1,2-
dihydro-1,2-phosphagermete 4b, respectively, within 40 hours
(Scheme 2). Ring opening occurs specifically at the phenyl-
substituted carbon ± phosphorus bonds of 3. The isomers 7,
The NMR spectroscopic data of 4a,b differ distinctly from
those of the isomeric starting materials 3a,b and are discussed
below for the example of product 4a. The shift of a silyl group
from silicon to phosphorus is apparent in the 1H NMR
spectrum from the splitting of a signal in the characteristic
region for trimethylsilyl protons with a 3J(H,P) coupling
constant of 4.0 Hz; this is a typical value for silylphos-
phanes.[13] The two silyl groups on the heterocyclic silicon do
not show separate signals at room temperature, while in the
low-temperature 1H NMR spectrum there are two singlets for
these now magnetically nonequivalent groups. When the
sample is warmed up again, these two signals become broader
and migrate towards a central position; coalescence occurs at
314 K. At temperatures above 363 K only a sharp singlet is
observed for the two groups on account of a rapid inversion at
the phosphorus atom. The inversion barrier for the phospho-
1
rus atom in 4a can thus be determined as 67.7 kJmol
(16.2 kcalmol ).[14] This value clearly shows the influence of
1
two effects in 4a: the substitution of carbon by silicon at the
phosphorus atom generally lowers the inversion barrier,[15±17]
while the incorporation of the inversion center in a small ring
tends to increase the barrier.[18] In the case of the heterocyclic
germanium compound 4b, two separate signals are observed
for the protons of the silyl groups on germanium even at room
temperature. This is indicative of a higher barrier to inversion
at phosphorus. The ring expansion in 4a is apparent from the
marked shift of the 31P NMR signal to low field: from d ˆ
205 in 3a[7] to d ˆ 131 in 4a. The 13C NMR data provide
further evidence for the constitution of the products: the
signals of the sp2 skeletal carbon atoms C3 and C4 are shifted
by more than 30 ppm to lower field in comparison with those
of 3a.[7] Additionally, the J(C,P) coupling constant for the
signal of C4 is only 22.1 Hz. Small coupling constants of this
type are a general feature of diphospha- and phosphacyclo-
butenes with l3s3 phosphorus atoms.[19, 20] The X-ray crystallo-
graphic analysis of 4a has already been described in a short
communication.[9]
Scheme 2. Irradiation and ring opening of the 1H-phosphirenes 3a,b to
give the 1,2-dihydro-1,2-phosphasiletes 4a,b.
which would arise through the opening of the tert-butyl-
substituted carbon ± phosphorus bonds in 3, could not be
detected. The alkyne 5 and the disilane 6 are formed as further
photolysis products. This photolysis is extremely dependent
Abstract in German: Die Photolyse des silylsubstituierten 1H-
Phosphirens 3a verläuft selektiv unter Spaltung einer Silicium-
Silicium-Bindung und Ringerweiterung zum 1,2-Dihydro-1,2-
phosphasilet 4a. Der entsprechende Germaniumheterocyclus
4b wird analog aus 3b erhalten. Die präparative Bedeutung
von 4a spiegelt sich nicht nur in den zahlreichen Additions-
reaktionen an Mehrfachbindungssysteme wie etwa Alkine 8
und 12 sowie Ketene 10 wider sondern auch in Substitutions-
reaktionen mit den Chlorverbindungen 15, 18 und 21. Die
letztgenannte Reaktion verläuft unter Bildung von Chlortrime-
thylsilan und der neuartigen 1,2-Dihydro-1,2-phosphasilete
(16, 19, 22), die in Abhängigkeit vom Substitutionsmuster
am Phosphoratom verschiedene Isomerisierungsreaktionen
eingehen (16 !17, 19 !20). Die Hydrolyse von 4a zu 23
durch Spuren von Wasser selbst in sorgfältig gereinigtem
Tetrahydrofuran demonstriert die extreme Empfindlichkeit
dieser Verbindung gegenüber Feuchtigkeit.
The ring expansion 3 !4 can be considered to be a
diotropic rearrangement which may be followed by a radical
fragmentation (3a !alkyne 5 ‡ disilane 6).
The dihydrophosphasilete 4a represents the starting point
for numerous transformations, for example, insertions into a
P/Si bond or substitutions at the silylated phosphorus atom
with subsequent reactions, as described below.
Addition to electron-poor multiple bond systems: The
reactions of the dihydrophosphasilete 4a with the electron-
poor alkynes 8a ± d are exothermic (Scheme 3). The 1-alken-
yl-1,2-dihydro-1,2-phosphasiletes 9a ± d are isolated in very
good yields (ꢀ90%) after workup by distillation. Products
9a ± c are colorless crystalline solids and 9d is a yellow oil.
Compounds 9 proved to be very stable: isomerization or
subsequent reactions did not occur, even after heating at
2008C for several days.
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Silylphosphirene Rearrangement
1581±1589
164.6. The occurrence of 1J(C,P) couplings of ꢀ46 Hz for the
hydrogen-substituted carbons C1' in 9c and 9d confirm the
direction of addition. The formation of a 1-allenyl-substituted
dihydrophosphasilete (the product of a 1,4-addition) is
excluded by the signal for the carbonyl carbon atom in the
benzoyl group of 9d at d ˆ 199.1 [3J(C,P) ˆ 16.2 Hz].[22] The
31P NMR signals are shifted to lower field on account of the
alkenyl substitution by ꢀ70 ppm for 9a,b and by ꢀ50 ppm for
9c,d as compared to the signals of the starting material 4a.
The reaction of diphenylketene (10) with 4a also proceeds
through 1,2-addition. After the dropwise addition of the
ketene to a solution of the dihydrophosphasilete at 788C,
the pure 1-alkenyl-1,2-dihydro-1,2-phosphasilete 11 was iso-
lated upon workup by distillation. Addition to the carbonyl
function of 10 is demonstrated by the absence of CO bands in
the IR spectrum of 11.
The remaining spectroscopic data of 11 are very similar to
those of the 1-alkenyl-1,2-dihydro-1,2-phosphasiletes 9 and
therefore do not need to be discussed in detail. Even so, a
characteristic effect for enol ethers was observed in the
13C NMR spectrum of 11: in comparison with the signals of the
other doubly bonded carbon atoms (C3, C4, and C1') the
signal for C2' (d ˆ 134.1) is shifted to higher field; this can be
attributed to the shielding effect of the oxygen atom in the b-
position to C4.[23] Also, the heterocyclic product 11 does not
undergo any further isomerization under thermal conditions.
When the 1,2-dihydro-1,2-phosphasilete 4a is cooled to
788C with dibenzoylacetylene (12) and the mixture sub-
sequently allowed to warm up, a reaction occurs and the
bicyclic compound 14 is obtained after crystallization from n-
pentane at 208C; the novel product possesses the structural
unit of a cyclic 3-phosphahexa-1,3,5-triene that also contains a
1-phospha-1,3-diene unit. Open-chain 1-phosphabutadienes
are extremely reactive and can behave not only as dienes but
also as dienophiles. However, systems of this type have been
stabilized by the introduction of sterically demanding sub-
stituents.[24] This and the incorporation of the reactive moiety
in a bicyclic system are apparently sufficient to prevent
further reaction of 14.
Scheme 3. Addition reactions of the dihydrophosphasilete 4a to electron-
poor multiple bond systems.
The first information on the structure of 14 was provided by
the 31P NMR spectrum in which the conversion of a l3s3- to a
l3s2-phosphorus atom is indicated by the shift of the signal
(d ˆ 214) to lower field. Additionally, there are no CO
absorptions shown in the IR spectrum.
The composition of the 1:1 addition products 9 was
confirmed by elemental analysis. The absence of 3J(H,P)
couplings in the 1H NMR spectra of 9 demonstrates the
cleavage of the exocyclic phosphorus ± silicon bond (cf. 4a);
only singlet signals are observed in the expected region. The
integration ratios also reveal the construction from one
molecule of alkyne and one molecule of dihydrophosphete.
The 13C NMR spectra clearly show the characteristic signals
of the skeletal carbon atoms, C3 and C4, in the olefinic region
at d ˆ 151.3 ± 169.9, with the corresponding coupling constants
[2J(C,P) ˆ 19.0 ± 20.1 Hz, 1J(C,P) ˆ 14.7 ± 23.2 Hz] (cf. 4a).
Furthermore, the carbonyl carbon atoms of the ester groups
The expansion of the four-membered ring is also revealed
by the 13C NMR spectrum: the carbon ± phosphorus couplings
of the C atoms originating from the double bond of the four-
membered ring are clearly changed. While C4 (d ˆ 165.8) in
1
14 has a J(C,P) coupling constant of 53.9 Hz, that is, almost
twice as large as the corresponding coupling constant in 4a
[1J(C,P) ˆ 22.1 Hz], the splitting pattern at C3 (d ˆ 153.3)
breaks down completely. The acetal carbon C8a gives a signal
at d ˆ 111.6 [2J(C,P) ˆ 13.2 Hz]. The signals for the carbon
atoms of the second alkene unit, C6 and C7, are seen at d ˆ
3
give rise to signals at d ' 165. By comparison of the J(C,P)
2
coupling constants of C2' in 9a ± d [3J(C,P) ˆ 14.6 ± 16.7 Hz]
with the corresponding values for phosphane-substituted
maleates and fumarates,[21] the formation of the Z isomers
may be deduced. The carbon atoms of the exocyclic alkene
unit, C1' and C2', give rise to signals between d ˆ 142.9 and
115.6 (C6) and d ˆ 168.6 (C7). The J(C,P) coupling constant
of 31.7 Hz for C6 is appreciably larger than those for C8a and
C3; this is due to the effect of the free electron pair on
phosphorus. In fixed bonds it increases the 2J(C,P) coupling if
the carbon atom involved is in a cis position.[25±27] Finally, the
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M. Regitz et al.
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signal of the skeletal phosphaalkene carbon atom C5 appears
at d ˆ 193.5 with the typical doublet structure for a phos-
phaalkene [1J(P,C) ˆ 51.3 Hz].
The crystals of 14, obtained from a cold n-pentane solution,
were analyzed by X-ray crystallography (Figure 1). This
confirmed the proposed constitutional assignments. Within
Figure 1. Molecular structure of 14 in the solid state. Selected bond lengths
[Š] and angles [8]: Si2 ± C3 1.890(5), C3 ± C4 1.338(7), C4 ± P5 1.841(6), P5 ±
C5a 1.675(5), C5a ± C8a 1.527(7), C5a ± C6 1.449(7), C6 ± C7 1.349(7), C7 ±
O8 1.356(6), O8 ± O8a 1.455(6), C8a ± O1 1.390(6), O1 ± Si2 1.670(3); O1-
Si2-C3 108.9(2), Si2-C3-C4 121.8(4), C3-C4-P5 120.5(4), C4-P5-C5a
108.9(3), P5-C5a-C8a 128.9(4), P-C5a-C6 124.2(4), C5a-C8a-O1 111.6(4),
C5a-C8a-O8 104.3(4), C5a-C6-C7 106.2(4), C6-C7-O8 115.3(4), C7-O8-C8a
108.1(4), O8-C8a-O1 104.3.
the limits of the standard deviations, the five-membered ring
is planar and the phosphorus atom also lies in the same plane,
thus providing the prerequisites for the interaction of the p
system with the 1-phosphabutadiene unit. This is, however,
not the case for the second phosphabutadiene increment
(C5a-P5-C4-C3) since C3 does not lie in the plane defined by
C4-P5-C5a; the dihedral angle C5a-P5-C4-C3 ˆ 58.48. The
C7 ± O8 bond [135.6(6) pm] is significantly shorter than the
C8a ± O8 bond [145.5(6) pm; average: 143.6 pm].[28] The C6 ±
C7 bond length of 134.9(7) pm is in the typical range (average:
135.4 pm) for enol ethers.[28] The significantly shorter C6 ± C5a
bond length of 144.9(7) pm is in accord with its position in a
conjugated 1-phosphabutadiene system (C7-C6-C5a-P5).
The formation of 14 can only be explained by the formation
of the intermediate 13 through the insertion of the triple bond
of 12 into the P ± Si bond of 4a; insertions of this sort are
known in principle.[29] The further reaction in the direction of
the arrows (see Scheme 3) requires a cis configuration of the
two benzoyl groups at the alkene unit of 13. The driving force
for this process is most certainly the formation of the silicon ±
oxygen bond.
Scheme 4. Hydrolysis and cleavage reactions of the 1,2-dihydro-1,2-
phosphasilete 4a.
Compounds 16 are unequivocally characterized by their
spectral data which, as far as the four-membered ring is
concerned, correspond closely to the data for the products 4a,
9, and 11. However, the presence of a second phosphorus
atom does give rise to some special features. Two doublet
signals are observed in the 31P NMR spectra: the signal for
each skeletal phosphorus atom experiences a paramagnetic
shift of ꢀ80 ppm compared to that of the starting material 4a
(16a: d ˆ 38; 16b: d ˆ 66), while the signals of the l3s2-
phosphorus atoms at d ˆ ‡459.0 (16a) and d ˆ ‡352.9 (16b)
are in the region typical for phosphane-substituted phos-
phaalkenes.[30] The presence of the P ± P bond is clearly
documented by the occurrence of 1J(P,P) couplings of
ꢀ271 Hz. Since the 31P NMR spectrum of 16b contains only
one set of signals, it may be assumed that only one isomer,
presumably the E isomer, has been formed.[31]
Reactions with cleavage of the exocyclic P-silyl group:
Reactions of the P-chlorophosphaalkenes 15a,b with the
dihydrophosphasilete 4a proceed with the formation of
chlorotrimethylsilane to yield the phosphaalkene-substituted
heterocyclic compounds 16a,b as yellow oils in quantitative
yields (Scheme 4). These products cannot be distilled; how-
ever, they can be stored for several weeks at 208C without
decomposition.
The 13C NMR signals for the ring carbon atoms, C3 and C4,
are similar to those of the starting material 4a except for the
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Silylphosphirene Rearrangement
1581±1589
splitting to a double doublet structure on account of the
presence of a further phosphorus atom. The sp2 carbon atoms
of the phosphaalkene unit give rise to doublet signals at
significantly low field (16a: d ˆ 211; 16b: d ˆ 207.6). The
typically large phosphaalkene P,C-coupling constants amount
to 96.5 (16a) and 83.3 Hz (16b). Surprisingly, no other
couplings with the l3s3-phosphorus atom were observed.
In contrast to the alkenyl-substituted heterocyclic com-
pounds 9 and 11, the products 16a,b do undergo thermal
isomerization: when heated for 2 hours at 1808C, they
transform into the bicyclic diphosphiranes 17a,b which were
isolated in 80 and 95% yields by distillation.
in the double bond moiety is provided by the reactions of 4a
with the acyl chlorides 18a ± c: the P-acyldihydrophospha-
siletes 19a ± c, most certainly formed initially along with
chlorotrimethylsilane, are not detectable, in contrast to the
situation with 16a,b. Instead spontaneous isomerization with
1,3-migration of the Si(Tms)2 moiety from phosphorus to the
carbonyl oxygen atom in 19a ± c takes place to furnish the
dihydrooxaphosphasilines 20a ± c, heterocyclic species con-
taining a 2-phospha-1,3-butadiene unit which have already
been reported.[38]
Spectral and analytical data for 20a ± c strongly support the
proposed structures. The transition from a l3s3 phosphorus to
a l3s2 phosphorus is reflected in a pronounced downfield shift
of the 31P NMR signal to d ˆ 91.0 and 92.0 for 20a and 20b,
respectively. This is a typical region for phosphaalkenes with
oxygen substitution on the sp2 carbon atom.[24, 28] The excep-
tionally low-field position of the 31P NMR signal for the
acceptor-substituted derivative 20c (d ˆ 172.0) may be attrib-
uted to a considerable participation of conceivable mesomeric
forms with negative partial charge on the oxygen atom.[39] This
assumption is also supported by the diamagnetic shift of the
13C NMR signal of C2 in 20c in comparison to the
corresponding signals for 20a,b as well as the shift to low
field of the signal for C5. The positions of the signals for the
olefinic carbon atom C4 in 20a ± c are almost identical.
The expansion from a four- to a six-membered ring
becomes apparent on consideration of the C,P coupling
constants: while the signal for the tert-butyl-substituted C4 in
4a exhibits only a small coupling (1J(C,P) ˆ 22.1 Hz), those of
This rather unexpected transformation of the phosphane-
substituted phosphaalkenes 16a,b to the diphosphiranes
17a,b is reflected in a dramatic shift to high field of the 31P
NMR signal of the original l3s2-phosphorus atom by more
than 600 ppm.[32] The signal at higher field (17a: d ˆ 261.5;
17b: d ˆ 283.5) is assigned to P1 on account of the silicon
substitution. The P ± P coupling of ꢀ185 Hz is of the magnitude
1
expected for a J(P,P) coupling in a diphosphirane.[33, 34]
The final configurational elucidation of the bicyclic prod-
1
ucts 17a,b was based on the H and 13C NMR data. In the
1H NMR spectrum of the bicyclic compound 17a signals for
the four trimethylsilyl groups appear at d ˆ 0.20, 0.35, 0.45,
and 0.50. The signal at d ˆ 0.35 is split by 1.8 Hz into a
pseudotriplet. A similar situation is observed in the spectrum
of 17b where the trimethylsilyl signal at d ˆ 0.30 is split by
1.2 Hz into a pseudotriplet. Since in phosphiranes only those
trimethylsilyl groups in a cis orientation to the free electron
pair on phosphorus exhibit a P,H coupling, in contrast to trans-
trimethylsilyl groups that do not experience any coupling,[35, 36]
the cis orientation of one of the trimethylsilyl groups to both
free electron pairs on the phosphorus may safely be assumed.
The 13C NMR spectral data are similar: the signals for the
cis-trimethylsilyl group have a pseudotriplet structure [17a:
3J(C,P) ˆ 8.1; 17b: 3J(C,P) ˆ 4.8 Hz], whereas that for the
trans-trimethysilyl group in 17a does not exhibit any coupling.
The proposed bicyclic structure of 17 is further supported by
the values for the ring carbon atoms: the signals for C3 and C4
appear in the olefinic region; those for C3 (17a: d ˆ 151.4;
17b: d ˆ 148.4) are not split by any carbon ± phosphorus
couplings and are diamagnetically shifted compared to the
signals of C4 (17a: d ˆ 165.5; 17b: d ˆ 160.4).[36] The signals
1
C4 in 20 have J(C,P) coupling constants in the range 54.8 ±
2
58.2 Hz. On the other hand, the J(C,P) couplings of 6.2 ±
7.8 Hz are conspicuously small. Final confirmation of the
constitutions of products 20 was provided by the single-crystal
X-ray crystallographic analysis of 20b (Figure 2).
1
for C4 are each split into doublets by J(C,P) couplings of
ꢀ70 Hz. The signal for the carbon atom of the three-
membered ring, C6, appears, as expected, at high field.[37] As
a result of the two neighboring phosphorus atoms, the signal
1
at d ˆ 16.4 (17a) is split into a pseudotriplet by a J(C,P)
1
coupling of 88 Hz [17b: d ˆ 30.6, J(C,P) ˆ 67.7 Hz].
The formation of 17 from 16 can formally be explained in
terms of a 1,2-shift of the ring silyl fragment in 16 with
subsequent ring closure to afford the bicyclic species 17. This
process requires the attack of the phosphaalkene phosphorus
atom at the silicon. The different reactivity of the phosphaal-
kenyl-substituted heterocyclic system 16 in comparison to the
alkenyl-substituted compounds 9 and 11 is thus caused by the
heteroatom in the vinyl unit.
Figure 2. Molecular structure of 20b in the solid state. Selected bond
lengths [Š] and angles [8]: P3 ± C2 1.678(4), C2 ± O1 1.339(3), O1 ± Si6
1.692(2), Si6 ± C5 1.866(4), C5 ± C4 1.336(4), C4 ± P3 1.845(2); C4-P3-C2
105.5(1), P3-C2-O1 129.1(2), C2-O1-Si6 117.5(2), O1-Si6-C5 105.0(1), Si6-
C5-C4 119.4(2), C5-C4-P3 123.0(3).
The phosphorus ± carbon bond lengths agree very well with
the average values of 167 pm for P ± C double bonds and
185 pm for P ± C single bonds.[40] The ring skeleton is not
planar but has a slight boat conformation.
Another example for the influence exerted on the 1-vinyl-
1,2-dihydro-1,2-phosphasilete isomerization by heteroatoms
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M. Regitz et al.
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with an Hg lamp (TQ150, Heraeus) for 40 h. The reaction was monitored
by 31P NMR. The solvent was removed at 208C (10 2 mbar) and the red-
brown oily residue was purified by bulb-to-bulb distillation. Recrystalliza-
tion from n-pentane at 788C yielded colorless crystals.
As a consequence of the strong oxophilicity of silicon, the
formation of 20 from 19 can be explained by the migration of
1,3-Si(Tms)2 from phosphorus to oxygen and ring closure. The
same driving force is responsible for the reaction of acyl
chlorides with silylphosphanes where the acylphosphane
primary products, which are difficult to detect, undergo
isomerization to phosphaalkenes by 1,3-silyl migration.[38]
When an equimolar amount of chloro(diphenyl)phosphane
(21) is added to 4a, the silyl group at phosphorus is again
replaced by the phosphane substituent to furnish product 22.
Ring opening (cleavage of the endocyclic P ± Si bond),
however, does not take place, as is clearly apparent from
4-tert-Butyl-3-phenyl-1,2,2-tris(trimethylsilyl)-1,2-dihydro-1,2-phosphasilete
(4a): From 3a (1.5 g, 3.4 mmol); to furnish 4a (0.5 g, 34%) as colorless
crystals. M.p. 758C; b.p. 1508C (10 3 mbar); 1H NMR (CD2Cl2): d ˆ 0.2 ±
0.4 [br, 18H, Si(CH3)3], 0.45 [d, 3J(H,P) ˆ 4.0 Hz, 9H, P-Si(CH3)3], 1.10 (s,
9H, tBu), 7.0 ± 7.2 (m, 5H, phenyl-H); 13C NMR (CD2Cl2): d ˆ 0.1, 1.2 [each
br, Si-Si(CH3)3], 2.0 [d, 2J(C,P) ˆ 10.3 Hz, P-Si(CH3)3], 31.5 [d, 3J(C,P) ˆ
5.0 Hz, C(CH3)3], 40.9 [d, 2J(C,P) ˆ 13.7 Hz, C(CH3)3], 124.6, 126.5, 127.5
(each s, phenyl-C), 145.2 [d, 3J(C,P) ˆ 4.5 Hz, ipso-C], 149.3 [d, 2J(C,P) ˆ
13.3 Hz, C3], 166.2 [d, J(P,C) ˆ 22.1 Hz, C4]; 31P NMR (C6D6): d ˆ 130.7
(s); IR (film): nÄ ˆ 3050 (w), 2950 (vs), 2900 (s), 1600 (m), 1480 (m), 1360
1
(m), 1250 (vs), 1190 (w), 1050 (s), 850 (vs), 760 (s), 690 (s), 620 (s) cm
;
1
the spectral data of 22. The H NMR spectrum no longer
inversion barrier at phosphorus (toluene): Tc ˆ 314 K, DG=(Tc) ˆ
shows any 3J(H,P) coupling and contains signals for only two
trimethylsilyl groups at d ˆ 0.20 and d ˆ 0.50. A 1J(P,P)
coupling of 186 Hz in the 31P NMR spectrum unequivocally
confirms the exchange of a silyl fragment on the ring
phosphorus atom for a phosphorus group (d ˆ 10.8 and
79.6). Retention of the dihydrophosphasilete skeleton is
demonstrated by a comparison of the 13C NMR data for the
ring carbon atoms with the corresponding values for 4a.
Although the former have double doublet structures on
account of the presence of two phosphorus atoms, the signals
occur in the same regions and reveal the characteristically
67.7 kJmol 1; C21H41PSi4 (436.9): calcd C 57.73, H 9.46; found C 57.4, H 9.4.
4-tert-Butyl-3-phenyl-1,2,2-tris(trimethylsilyl)-1,2-dihydro-1,2-phosphager-
mete (4b): From 3b (1.1 g, 2.3 mmol); to furnish 4b (50 mg, 5%) as
colorless crystals. M.p. 908C; b.p. 1808C (10 3 mbar); 1H NMR (C6D6): d ˆ
0.25, 0.37 [each s, 9H, Si(CH3)3], 0.5 [d, 3J(H,P) ˆ 4.0 Hz, 9H, P-Si(CH3)3],
1.2 (s, 9H, tBu), 7.0 ± 7.2 (m, 5H, phenyl-H); 13C NMR (C6D6): d ˆ 0.3 [s,
Ge-Si(CH3)3], 0.6 [d, 3J(C,P) ˆ 2.6 Hz, Ge-Si(CH3)3], 1.9 [d, 2J(C,P) ˆ
3
2
7.0 Hz, P-Si(CH3)3], 31.7 [d, J(C,P) ˆ 6.2 Hz, C(CH3)3], 40.8 [d, J(C,P) ˆ
13.3 Hz, C(CH3)3], 125.1 ± 128.2 (phenyl-C), 146.9 [d, 3J(C,P) ˆ 4.8 Hz,
ipso-C], 151.3 [d, 2J(C,P) ˆ 14.1 Hz, C3], 163.7 [d, 1J(C,P) ˆ 23.4 Hz, C4];
31P NMR (C6D6): d ˆ 92 (s).
General procedure for the reaction of 1,2-dihydro-1,2-phosphasilete 4a
with acceptor-substituted alkynes 8a ± d: A solution of alkyne 8 in diethyl
ether was added to a solution of 4a in diethyl ether at 788C. The mixture
was allowed to warm to room temperature and was then stirred for 4 h. The
reaction was exothermic and the color of the solution became darker. The
solvent was removed at 208C (10 2 mbar) and the oily residue then purified
by bulb-to-bulb distillation.
2
small J(C,P) coupling constants.
Hydrolysis of the 1,2-dihydro-1,2-phosphasilete 4a: The four-
membered heterocyclic product 4a proved to be extremely
sensitive to hydrolysis. Cleavage of the P-silyl group occurred
even in absolute tetrahydrofuran on moderate heating for a
few hours. The resultant hydrogen-substituted 1,2-dihydro-
1,2-phosphasilete 23 is obtained as a colorless, extremely
moisture-sensitive oil. For this reason only NMR data were
available for the elucidation of its structure and these
exhibited the already sufficiently discussed characteristic
features of a 1,2-dihydro-1,2-phosphasilete (see the Exper-
imental Section). The presence of the PH function results in a
splitting of the signal in the proton-coupled 31P NMR
spectrum by a 1J(P,H) coupling of 160 Hz (d ˆ 173.0), which
Dimethyl 1-[4-tert-butyl-3-phenyl-2,2-bis(trimethylsilyl)-1,2-dihydro-1,2-
phosphasilet-1-yl]-2-trimethylsilylmaleate (9a): From 8a (66 mg,
0.46 mmol) and 4a (200 mg, 0.46 mmol). Crystallization from n-pentane
at 208C yielded 9a (240 mg, 90%) as colorless crystals. M.p. 116.08C; b.p.
2008C (10 3 mbar); 1H NMR (C6D6): d ˆ 0.4, 0.5, 0.55 [each s, 9H,
Si(CH3)3], 1.2 (s, 9H, tBu), 3.55, 3.6 (each s, 3H, CO2Me), 7.0 ± 7.3 (m, 5H,
phenyl-H); 13C NMR (C6D6): d ˆ 0.14 [d, J(C,P) ˆ 2.7 Hz, Si(CH3)3], 0.4 [d,
J(C,P) ˆ 10.9 Hz, Si(CH3)3], 1.2 [s, Si(CH3)3], 31.0 [d, 3J(C,P) ˆ 4.7 Hz,
C(CH3)3], 40.6 [d, 2J(C,P) ˆ 13.1 Hz, C(CH3)3], 51.1, 51.3 (each s, CO2CH3),
125.5, 126.2, 127.7 (each s, phenyl-C), 144.7 [d, 3J(C,P) ˆ 5.3 Hz, ipso-C],
150.5 [d, 2J(C,P) ˆ 43.3 Hz, C2'], 152.8 [d, 1J(C,P) ˆ 60.9 Hz, C1'], 157.5 [d,
2J(C,P) ˆ 19.7 Hz, C3], 163.7 [d, 3J(C,P) ˆ 15.9 Hz, CO2CH3], 165.7 [d,
2J(C,P) ˆ 6 Hz, CO2CH3], 169.9 [d, 1J(C,P) ˆ 20.5 Hz, C4]; 31P NMR
(C6D6): d ˆ 63.5 (s); IR (film): nÄ ˆ 2950 (vs), 2900 (q), 1720 (vs), 1600
(w), 1530 (m), 1430 (s), 1360 (w), 1230 (vs), 1070 (m), 1020 (w), 850 (vs), 770
(s), 710 (s), 630 (m) cm 1; C27H47O4PSi4 (578.0): calcd C 56.0, H 8.1; found C
55.9, H 8.1.
1
is also seen in the H NMR signal at d ˆ 3.40.
Experimental Section
Di-tert-butyl [4-tert-butyl-3-phenyl-2,2-bis(trimethylsilyl)-1,2-dihydro-1,2-
phosphasilet-1-yl)-trimethylsilylmaleate (9b): From 8b (52 mg, 0.23 mmol)
and 4a (100 mg, 0.23 mmol). Crystallization from n-pentane at 08C yielded
9b (130 mg, 86%) as colorless crystals. M.p. 153.58C; b.p. 2508C
General: All experiments were carried out under argon (purity >99.998%)
in previously evacuated and baked Schlenk vessels. The solvents were
anhydrous and stored under argon until used. Melting points were
determined on a Mettler FP61 apparatus (heating rate 28Cmin 1) and
are uncorrected. NMR spectra were recorded on Varian EM360, Varian
EM390, Bruker WP200, and Bruker AM400 instruments. Chemical shifts
for 1H and 13C are reported in ppm relative to tetramethylsilane as the
internal standard; the chemical shifts for 31P are expressed relative to
external 85% orthophosphoric acid. Elemental analyses were performed
on Perkin ± Elmer analysers EA240 and 2400CHN. Bulb-to-bulb distil-
lations were carried out in a Büchi GKR50 apparatus (temperatures given
refer to the heating mantle). IR spectra were determined on Perkin ± Elmer
710B or Perkin ± Elmer IR394 spectrophotometers. Mass spectra were
recorded on a Finnigan MAT90 spectrometer. Compounds 3a,b[7] were
prepared by published methods. All other starting materials were
purchased from commercial sources.
1
(10 3 mbar); H NMR (C6D6): d ˆ 0.4, 0.5 [each s, 9H, Si(CH3)3], 0.55 [d,
J(H,P) ˆ 2 Hz, 9H, Si(CH3)3], 1.3, 1.5, 1.7 (each s, 9H, tBu), 7.0 ± 7.3 (m, 5H,
phenyl-H); 13C NMR (C6D6): d ˆ 0.3 [s, Si(CH3)3], 1.4 [d, J(C,P) ˆ 12 Hz,
Si(CH3)3], 1.7 [s, Si(CH3)3], 28.6 [s, C(CH3)3], 31.2 [d, 3J(C,P) ˆ 3.2 Hz,
C(CH3)3], 41.3 [d, 2J(C,P) ˆ 13.8 Hz, C(CH3)3], 80.8, 82.1 [each s,
CO2C(CH3)3], 125.8, 126.4, 127.7 (each s, phenyl-C), 145.5 [d, 3J(C,P) ˆ
5 Hz, ipso-C], 149.2 [d, 2J(C,P) ˆ 45.6 Hz, C2'], 153.8 [d, 1J(C,P) ˆ 58.4 Hz,
C1'], 157.8 [d, 2J(C,P) ˆ 18.7 Hz, C3], 164.3 [d, 3J(C,P) ˆ 16.7 Hz, CO2tBu],
166.0 [d, 2J(C,P) ˆ 5.5 Hz, CO2tBu], 168.9 [d, 1J(C,P) ˆ 23.2 Hz, C4]; 31P
NMR (C6D6): d ˆ 60.2 (s); IR (KBr): nÄ ˆ 2900 (vs), 1710 (vs), 1600 (w),
1540 (w), 1425 (w), 1350 (w), 1240 (s), 1050 (m), 840 (s), 770 (m), 710 (m),
630 (w) cm 1; C33H59O4PSi4 (663.1): calcd C 59.77, H 9.0; found C 57.8, H 8.7.
Methyl (Z)-3-[4-tert-butyl-3-phenyl-2,2-bis(trimethylsilyl)-1,2-dihydro-1,2-
phosphasilet-1-yl)-2-trimethylsilylprop-2-enoate (9c): From 8c (40 mg,
0.48 mmol) and 4a (200 mg, 0.46 mmol), to afford 9c (220 mg, 90%) as
General procedure for the photolytic isomerization of 3a,b: A solution of
1-silyl-1H-phosphirene 1 in benzene (5 mL) in an NMR tube was irradiated
1586
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0947-6539/99/0505-1586 $ 17.50+.50/0
Chem. Eur. J. 1999, 5, No. 5

Silylphosphirene Rearrangement
1581±1589
colorless crystals. M.p. 958C; b.p. 2008C (10 3 mbar); 1H NMR (C6D6): d ˆ
16a as a nondistillable red oil. 1H NMR (C6D6): d ˆ 0.35 [s, 18H, Si(CH3)3],
0.4 [d, J(H,P) ˆ 2 Hz, 9H, Si(CH3)3], 0.55 [s, 9H, Si(CH3)3], 1.2 (s, 9H, tBu),
7.0 ± 7.3 (m, 5H, phenyl-H); 13C NMR: d ˆ 0.35, 1.4 [each s, Si(CH3)3], 1.9
[d, 3J(C,P) ˆ 12.4 Hz, Si(CH3)3], 3.0 [d, 3J(C,P) ˆ 8.9 Hz, Si(CH3)3], 31.6 [d,
3J(C,P) ˆ 4.7 Hz, C(CH3)3], 41.5 [d, 2J(C,P) ˆ 11.8 Hz, C(CH3)3], 125.8,
126.9, 128.2 (each s, phenyl-C), 145.2 [d, 3J(C,P) ˆ 3.3 Hz, ipso-C], 152.4
0.4, 0.5, 0.6 [each s, 9H, Si(CH3)3], 1.2 (s, 9H, tBu), 3.6 (s, 3H, CO2Me), 7.0 ±
2
7.3 (m, 5H, phenyl-H), 8.7 [d, J(H,P) ˆ 5 Hz, 1H, C CH]; 13C NMR
ˆ
(C6D6): d ˆ 0.2 [s, Si(CH3)3], 0.5 [s, Si(CH3)3], 1.0 [d, J(C,P) ˆ 8.8 Hz,
Si(CH3)3], 31.3 [d, 3J(C,P) ˆ 4.8 Hz, C(CH3)3], 41.4 [d, 2J(C,P) ˆ 12.7 Hz,
C(CH3)3], 51.1 (s, CO2CH3), 125.8, 126.5, 128.4 (each s, phenyl-C), 142.9 [d,
2J(C,P) ˆ 28.5 Hz, C2'], 144.9 [d, 3J(C,P) ˆ 5.5 Hz, ipso-C], 151.3 [d,
2J(C,P) ˆ 20.1 Hz, C3], 164.6 [d, 1J(C,P) ˆ 46.3 Hz, 1J(C,H) ˆ 154.0 Hz,
2
1
[dd, J(C,P) ˆ 14.6 Hz, 3J(C,P) ˆ 5.8 Hz, C3], 168.9 [dd, J(C,P) ˆ 23.7 Hz,
2
1
J(C,P) ˆ 6.8 Hz, C4], 211.2 [d, J(C,P) ˆ 96.4 Hz, P C]; 31P NMR (C6D6):
ˆ
C CH], 169.2 [d, 3J(C,P) ˆ 14.6 Hz, CO2Me], 169.7 [d, 1J(C,P) ˆ 17.0 Hz,
d ˆ ‡459.0, 33.0 [each d, 1J(P,P) ˆ 270.5 Hz].
ˆ
C4]; 31P NMR (C6D6): d ˆ 82 (s); IR (film): nÄ ˆ 3050 (w), 2950 (s), 2900
(m), 1700 (s), 1590 (w), 1510 (w), 1430 (w), 1350 (w), 1250 (s), 1200 (s), 830
(vs), 760 (w), 700 (m) cm 1; C25H45O2PSi4 (521.0): calcd C 57.6, H 8.7; found
C 57.1, H 8.8.
4-tert-Butyl-3-phenyl-2,2-bis(trimethylsilyl)-1-(trimethylsilylbenzylidene-
phosphanyl)-1,2-dihydro-1,2-phosphasilete (16b): Yield: 250 mg, 95% of
1
16b as a nondistillable red oil. H NMR (C6D6): d ˆ 0.3 [s, 9H, Si(CH3)3],
0.4 [d, J(H,P) ˆ 2 Hz, 9H, Si(CH3)3], 0.5 (s, 9H, Si(CH3)3], 1.25 (s, 9H, tBu),
7.0 ± 7.4 (m, 10H, phenyl-H); 13C NMR (C6D6): d ˆ 0.2, 0.1 [each s,
Si(CH3)3], 1.8 [d, J(C,P) ˆ 2.8 Hz, Si(CH3)3], 31.6 [s, C(CH3)3], 41.5 [d,
2J(C,P) ˆ 12 Hz, C(CH3)3], 125.2 ± 129.1 (phenyl-C), 145.2 [d, 2J(C,P) ˆ
3 Hz, ipso-C], 147.6 [dd, J(C,P) ˆ 11.6 Hz, J(C,P) ˆ 12.6 Hz, ipso-C], 151.2
(Z)-3-[4-tert-Butyl-3-phenyl-2,2-bis(trimethylsilyl)-1,2-dihydro-1,2-phospha-
silet-1-yl)-2-trimethylsilyl-1-phenylpropen-1-one (9d): From 8d (45 mg,
0.35 mmol) and 4a (150 mg, 0.35 mmol), to furnish 9d (180 mg, 90%) as a
1
yellow oil. B.p. 2008C (10 3 mbar); H NMR (C6D6): d ˆ 0.35, 0.4 [each s,
[d, 2J(C,P) ˆ 12 Hz, C3], 167.5 [dd, 1J(C,P) ˆ 21.6 Hz, 2J(C,P) ˆ 6.6 Hz, C4],
9H, Si(CH3)3], 0.6 [s, 9H, Si(CH3)3], 1.2 (s, 9H, tBu), 7.1 ± 7.4 (m, 8H,
2
ˆ
1
207.6 [d, J(C,P) ˆ 81.3 Hz, P C]; 31P NMR (C6D6): d ˆ ‡352.9, 66.2
phenyl-H), 7.7 [d, J(H,P) ˆ 4 Hz, 1H, C CH], 8.0 ± 8.2 (m, 2H, phenyl-H);
ˆ
13C NMR (C6D6): d ˆ 0.4 [d, J(C,P) ˆ 8.1 Hz, Si(CH3)3], 0.8, 1.4 [each s,
Si(CH3)3], 31.4 [d, 3J(C,P) ˆ 4.6 Hz, C(CH3)3], 41.4 [d, 2J(C,P) ˆ 13 Hz,
C(CH3)3], 125.8, 126.4, 128.3, 128.5, 130.1, 132.6 (each s, phenyl-C), 138.0 (s,
ipso-C), 144.8 [d, 3J(C,P) ˆ 6 Hz, ipso-C], 151.8 [d, 2J(C,P) ˆ 19 Hz, C3],
1
[each d, J(P,P) ˆ 271.6 Hz].
General procedure for the isomerization of 16 to 17: 1,2-Dihydro-1,2-
phosphasilete 16 was heated for 2 h at 175 ± 1908C in a bulb-to-bulb
distillation apparatus. Distillation at 2008C (10 3 mbar) gave 17 as a
colorless oil. Product 17b was crystallized from n-pentane at 208C.
1
1
2
ˆ
155.3 [d, J(C,P) ˆ 45.8 Hz, J(C,H) ˆ 152.7 Hz, C CH], 155.8 [d, J(C,P) ˆ
1
3
27.7 Hz, C2'], 168.9 [d, J(C,P) ˆ 14.7 Hz, C4], 199.1 [d, J(C,P) ˆ 16.2 Hz,
COPh]; 31P NMR (C6D6): d ˆ 82.3 (s); IR (film): nÄ ˆ 3080 (w), 2950 (s),
4-tert-Butyl-3-phenyl-2,2,6,6-tetrakis(trimethylsilyl)-1,5,2-diphosphasilabi-
cyclo[3.1.0]-hex-3-ene (17a): From 16a (240 mg, 0.43 mmol), to afford 17a
2900 (w), 1650 (m), 1600 (w), 1260 (s), 1250 (s), 1170 (m), 1050 (m), 830 (s),
1
770 (w), 700 (m) cm
.
1
(190 mg, 80%). B.p. 1808C (10 3 mbar); H NMR (C6D6): d ˆ 0.20 [s, 9H,
4
4-tert-Butyl-1-(2',2'-diphenyl-1'-trimethylsiloxyethenyl)-3-phenyl-2,2-bis-
(trimethylsilyl)-1,2-dihydro-1,2-phosphasilete (11): A solution of diphenyl-
ketene (10) (70 mg, 0.36 mmol) in diethyl ether (2 mL) was added to a
solution of 4a (150 mg, 0.35 mmol) in diethyl ether (5 mL) at 788C. The
mixture was allowed to warm to room temperature and was stirred for 12 h.
The solvent was removed at 208C (10 2 mbar) and the residue then purified
by bulb-to-bulb distillation to afford 11 (130 mg, 60%) as a yellow oil. B.p.
2508C (10 3 mbar); 1H NMR (CD2Cl2): d ˆ 0.0, 0.1, 0.35 [each s, 9H,
Si(CH3)3], 1.0 (s, 9H, tBu), 7.0 ± 7.3 (m, 15H, phenyl-H); 13C NMR
(CD2Cl2): d ˆ 0.2 [d, J(C,P) ˆ 3 Hz, Si(CH3)3], 1.5, 2.5 [each s, Si(CH3)3],
Si(CH3)3], 0.35 [t, J(H,P) ˆ 1.8 Hz, 9H, Si(CH3)3], 0.45 [s, 9H, Si(CH3)3],
0.50 [s, 9H, Si(CH3)3], 1.35 (s, 9H, tBu), 7.0 ± 7.3 (m, 5H, phenyl-H);
13C NMR (C6D6): d ˆ 1.7 [d, 3J(C,P) ˆ 4.2 Hz, Si(CH3)3], 2.5 [dd, 3J(C,P) ˆ
8.1 Hz, 3J(C,P) ˆ 8.5 Hz, Si(CH3)3], 2.8 [s, Si(CH3)3], 6.8 [s, Si(CH3)3], 16.4
1
3
(pseudo-t, J(C,P) ˆ 88 Hz, C6], 34.2 [d, J(C,P) ˆ 10.1 Hz, C(CH3)3], 43.9
[d, 2J(C,P) ˆ 27.2 Hz, C(CH3)3], 127.2 (s, para-phenyl-C), 129.7 (s, meta-
phenyl-C), 126.3, 129.7 (each br, ortho,ortho'-phenyl-C), 146.1 (s, ipso-C),
151.4 (s, C3), 165.5 [d, 1J(P,C) ˆ 71.7 Hz, C4]; 31P NMR (C6D6): d ˆ 59.8,
261.5 [each d, 1J(P,P) ˆ 195.3 Hz]; IR (film): nÄ ˆ 3050 (w), 2950 (vs), 2900
(m), 1590 (m), 1470 (w), 1440 (w), 1400 (w), 1350 (w), 1250 (vs), 1070 (m),
31.4 [d, 3J(P,C) ˆ 4.6 Hz, C(CH3)3], 41.5 [d, 2J(C,P) ˆ 15 Hz, C(CH3)3],
1030 (m), 920 (s), 840 (vs), 760 (m), 700 (m), 690 (m) cm
.
1
2
ˆ
125.4 ± 131.0 (phenyl-C), 134.1 [d, J(C,P) ˆ 38.1 Hz, C CPh2], 124.6 [d,
4-tert-Butyl-3,6(b)-diphenyl-2,2,6(b)-tris(trimethylsilyl)-1,5,2-diphosphasi-
labicyclo-[3.1.0]hex-3-ene (17b): From 16b (200 mg, 0.36 mmol), to afford
17b (190 mg, 95%) as colorless crystals. M.p. 788C; b.p. 2008C (10 3 mbar);
3J(C,P) ˆ 6.8 Hz, ipso-C], 144.1 [d, 3J(C,P) ˆ 9.9 Hz, ipso-C], 145.6 [d,
3
1
ˆ
J(C,P) ˆ 4.8 Hz, ipso-C], 153.3 [d, J(C,P) ˆ 62.0 Hz, C COTms], 153.4 [d,
2J(C,P) ˆ 20.4 Hz, C3], 166.5 [d, 1J(C,P) ˆ 19.6 Hz, C4]; 31P NMR (CD2Cl2):
4
1H NMR (C6D6): d ˆ 0.10 [s, 9H, Si(CH3)3], 0.30 [t, J(H,P) ˆ 1.2 Hz, 9H,
d ˆ 58 (s); IR (film): nÄ ˆ 3050 (w), 2950 (s), 2900 (m), 1600 (m), 1550 (w),
4
Si(CH3)3], 0.50 [s, 9H, Si(CH3)3], 1.5 [d, J(H,P) ˆ 2 Hz, 9H, tBu], 7.0 ± 7.6
1
1440 (w), 1250 (s), 1200 (b), 960 (m), 800 (s), 700 (s) cm
.
(m, 10H, phenyl-H); 13C NMR (C6D6): d ˆ 1.3 [t, 3J(C,P) ˆ 4.8 Hz,
Si(CH3)3], 0.7 [d, 3J(C,P) ˆ 3.6 Hz, Si(CH3)3], 30.6 [pseudo-t, 1J(C,P) ˆ
67.7 Hz, C6], 33.6 [d, 3J(C,P) ˆ 12.2 Hz, C(CH3)3], 42.4 [d, 2J(C,P) ˆ
25.8 Hz, C(CH3)3], 125.3 ± 134.6 (phenyl-C), 134.6, 140.9 (each s, ipso-C),
148.4 (s, C3), 160.4 [d, 1J(C,P) ˆ 69.3 Hz, C4]; 31P NMR (C6D6): d ˆ 87.9,
283.5 [each d, 1J(P,P) ˆ 177 Hz]; IR (film): nÄ ˆ 3050 (m), 2950 (s), 2900
(s), 1590 (s), 1470 (w), 1430 (w), 1390 (m), 1350 (m), 1240 (s), 1070 (w), 1030
(w), 910 (w), 900 (w), 820 (s), 760 (m), 700 (s), 620 (w) cm 1; MS (70 eV, EI):
4-tert-Butyl-3,7-diphenyl-2,2,6-tris(trimethylsilyl)-2,8a-dihydrofuro[2,3-b]-
[1,4,7]oxaphosphasilaepine (14): A solution of dibenzoylacetylene (12)
(170 mg, 0.73 mmol) in dichloromethane (3 mL) was added to a solution of
4a (300 mg, 0.69 mmol) in dichloromethane (3 mL) at 788C. The red
reaction mixture was allowed to warm to room temperature. The solvent
was removed at 208C (10 2 mbar) and the residue was dissolved in n-
pentane (20 mL). Filtration through Celite and recrystallization from n-
pentane afforded 14 (280 mg, 60%) as colorless crystals. M.p. 157.28C;
1H NMR (C6D6): d ˆ 0.2, 0.55, 0.65 [each s, 9H, Si(CH3)3], 1.1 (s, 9H, tBu),
6.8 ± 8.2 (m, 15H, phenyl-H); 13C NMR (C6D6): d ˆ 0.5 [s, Si(CH3)3], 1.3
[d, J(C,P) ˆ 8.2 Hz, Si(CH3)3], 1.9 [d, J(C,P) ˆ 4 Hz, Si(CH3)3], 32.6 [d,
‡
‡
‡
m/z (%) ˆ 556 (25) [M ], 483 (15) [M
Tms], 396 (12) [M
Tms
‡
PhC], 73 (100) [Tms ].
2,4-Di-tert-butyl-5-phenyl-6,6-bis(trimethylsilyl)-6H-1,3,6-oxaphosphasi-
line (20a): A solution of 18a (42 mg, 0.35 mmol) in tetrahydrofuran (1 mL)
was added slowly to a solution of 4a (150 mg, 0.35 mmol) in tetrahydrofur-
an (1 mL) at 788C. The reaction mixture was allowed to warm to room
temperature and was then stirred for 12 h at 208C. The solvent was
removed at 208C (10 2 mbar) and the residue was purified by bulb-to-bulb
distillation to afford 20a (80 mg, 51%) as a yellow oil. B.p. 2008C
(10 3 mbar); 1H NMR (CD2Cl2): d ˆ 0.15 [s, 18H, Si(CH3)3], 1.15 (s, 9H,
tBu), 1.3 [d, 4J(H,P) ˆ 2.0 Hz, 9H, tBu], 7.0 ± 7.4 (m, 5H, phenyl-H);
13C NMR (CD2Cl2): d ˆ 0.62 [s, Si(CH3)3], 29.1 [d, 3J(C,P) ˆ 13.7 Hz,
C(CH3)3], 32.8 [d, 3J(C,P) ˆ 14 Hz, C(CH3)3], 42.8 [d, 2J(C,P) ˆ 27.3 Hz,
C(CH3)3], 43.1 [d, 2J(C,P) ˆ 24.1 Hz, C(CH3)3], 125.6, 127.9, 128.2, 145.1
(each s, phenyl-C), 134.6 [d, 2J(C,P) ˆ 7.3 Hz, C5], 161.5 [d, 1J(C,P) ˆ
58.2 Hz, C4], 217.6 [d, 1J(C,P) ˆ 79.3 Hz, C2]; 31P NMR (CD2Cl2): d ˆ
2
3J(C,P) ˆ 9.6 Hz, C(CH3)3], 42.4 [d, J(C,P) ˆ 22.1 Hz, C(CH3)3], 111.6 [d,
2J(C,P) ˆ 13.2 Hz, C8a], 115.6 [d, 2J(C,P) ˆ 31.7 Hz, C6], 125.8, 126.8, 126.9,
127.9, 128.6, 129.6, 130.0, 133.0, 146.3 (each s, phenyl-C), 142.9 [d, J(C,P) ˆ
6.1 Hz, ipso-phenyl-C], 153.3 (s, C3), 165.8 [d, 1J(C,P) ˆ 53.9 Hz, C4], 168.6
[d, 3J(C,P) ˆ 31.9 Hz, C7], 193.5 [d, 1J(C,P) ˆ 51.3 Hz, C5a]; 31P NMR
(C6D6): d ˆ ‡214 (s); IR (KBr): nÄ ˆ 3050 (w), 2950 (s), 1600 (w), 1580 (w),
1450 (m), 1370 (w), 1250 (s), 1050 (s), 950 (w), 830 (s), 760 (m), 690
(m) cm 1; C37H51O2PSi4 (671.1): calcd C 66.2, H 7.6; found C 65.3, H 7.5.
General procedure for the reaction of 4a with chloromethylenephosphanes
15: To a solution of 4a (200 mg, 0.46 mmol) in diethyl ether (3 mL) was added
an equimolar amount of chloromethylenephosphane 15. After stirring for
12 h at room temperature the solvent was removed at 208C (10 2 mbar).
4-tert-Butyl-3-phenyl-2,2-bis(trimethylsilyl)-1-[bis(trimethylsilyl)methylene-
phosphanyl]-1,2-dihydro-1,2-phosphasilete (16a): Yield: 240 mg, 93% of
‡91.0 (s); IR (film): nÄ ˆ 2950 (s), 2900 (w), 1700 (m), 1470 (w), 1400 (w),
1
1360 (w), 1250 (s), 1070 (s), 840 (s), 700 (m) cm
.
Chem. Eur. J. 1999, 5, No. 5
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1587

M. Regitz et al.
FULL PAPER
1-(4-tert-Butyl-5-phenyl-6,6-bis(trimethylsilyl)-6H-1,3,6-oxaphosphasilin-
2-yl)ferrocene (20b): A solution of 18b (87 mg, 0.36 mmol) in tetrahy-
drofuran (1 mL) was added slowly to a solution of 4a (150 mg, 0.35 mmol)
in tetrahydrofuran (1 mL) at 788C. The reaction mixture was allowed to
warm to room temperature and was then stirred for 24 h at 208C. The
solvent was removed at 208C (10 2 mbar) and the residue was purified by
chromatography (silica gel (12 g), n-pentane/diethyl ether 5:1) followed by
recrystallization from n-pentane at 788C to afford 20b (140 mg, 70%) as
red crystals. M.p. 1358C; 1H NMR (C6D6): d ˆ 0.4 [s, 18H, Si(CH3)3], 1.5 (s,
9H, tBu), 4.2 ± 4.5 (m, 7H, cyclopentadienyl-H), 5.1 (m, 2H, cyclopenta-
dienyl-H), 7.1 ± 7.4 (m, 5H, phenyl-H); 13C NMR (C6D6): d ˆ 0.3 [s,
SHELXTL (Vers.4.2); molecule plots were obtained with the program XP
from SHELXTL.[41]
Data for 14: C37H51O2PSi4 (Mr ˆ 671.1), colorless prisms; a ˆ 12.247(4), b ˆ
15.282(5), c ˆ 21.096(6) Š, b ˆ 96.20(2)8, Vˆ 3925(2) Š3, 1calcd
ˆ
1.136 gcm 3, monoclinic, P21/n (No. 14), Z ˆ 4, F(000) ˆ 1440, w-scan, m ˆ
0.22 mm 1, no absorption correction. In the range 48 ꢁ 2q ꢁ 488 4525
reflections were measured, of which 4386 (Rint ˆ 0.0212) were independent
and 3835 [with I > 1.5s(I)] were used for the refinement; 397 parameters,
3
R ˆ 0.0626, Rw ˆ 0.1031, residual density: 0.36 and 0.32 eŠ
.
Data for 20b: C29H41FeOPSi3 (Mr ˆ 576.7), red prisms; a ˆ 11.561(3), b ˆ
15.343(5), c ˆ 10.504(3) Š, a ˆ 99.25(2), b ˆ 111.87(2), g ˆ 106.55(2), Vˆ
3
2
Si(CH3)3], 33.4 [d, J(C,P) ˆ 14.1 Hz, C(CH3)3], 42.8 [d, J(C,P) ˆ 25.8 Hz,
C(CH3)3], 67.7 [d, 3J(C,P) ˆ 13.7 Hz, C2'], 70.5 (s, C4'), 70.6 (s, C3'), 86.7 [d,
2J(C,P) ˆ 38.0 Hz, C1'], 125.8, 127.6, 128.5 (each s, phenyl-C), 136.0 [d,
2J(C,P) ˆ 7.8 Hz, C5], 145.8 (s, ipso-C), 163.4 [d, 1J(C,P) ˆ 57.3 Hz, C4],
204.3 [d, 1J(C,P) ˆ 66.4 Hz, C2]; 31P NMR (C6D6): d ˆ ‡92.0 (s); IR (film):
nÄ ˆ 3080 (w), 3060 (w), 3040 (w), 2950 (vs), 2895 (s), 1700 (w), 1650 (m),
1590 (m), 1476 (s), 1390 (m), 1360 (m), 1240 (vs), 1190 (m), 1160 (m), 1100
(s), 1060 (s), 1025 (s), 1000 (w), 980 (w), 910 (w), 885 (s), 840 (vs), 770 (s),
750 (s), 700 (s) cm 1; C29H41FeOPSi3 (576.7): calcd C 60.4, H 7.2; found C
60.4, H 7.3.
1581.1(8) Š3, 1calcd ˆ 1.211 gcm , triclinic, P1 (No. 2), Z ˆ 2, F(000) ˆ 614, w-
3
Å
scan, m ˆ 0.66 mm 1, no absorption correction. In the range 48 ꢁ 2q ꢁ 488
4887 reflections were measured, of which 4601 (Rint ˆ 0.0266) were
independent and 4295 [with I >1.5s(I)] were used for the refinement;
316 parameters, R ˆ 0.0430, Rw ˆ 0.0595, residual density: 0.41 and
3
0.41 eŠ
.
Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge Crystallo-
graphic Data Centre as supplementary publication nos. CCDC-103016 (14)
and CCDC-103015 (20b). Copies of the data can be obtained free of charge
on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK [fax:
(‡44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk].
Methyl 4-tert-butyl-5-phenyl-6,6-bis(trimethylsilyl)-6H-1,3,6-oxaphospha-
siline-2-carboxylate (20c): A solution of 18c (30 mg, 0.25 mmol) in diethyl
ether (2 mL) was added dropwise to a solution of 4a (110 mg, 0.25 mmol) in
diethyl ether (3 mL) at 788C. The color of the reaction mixture changed
to yellow. The solution was allowed to warm to room temperature, the
solvent was removed at 208C (10 2 mbar), and the residue was dissolved in
n-pentane (10 mL). Filtration through Celite and recrystallization from n-
pentane gave 20c (80 mg, 72%) as yellow crystals. M.p. 838C; 1H NMR
(C6D6): d ˆ 0.3 [s, 18H, Si(CH3)3], 1.3 (s, 9H, tBu), 3.55 (s, 3H, CO2Me),
7.0 ± 7.3 (m, 5H, phenyl-H); 13C NMR (C6D6): d ˆ 0.36 [s, Si(CH3)3], 33.1
[d, 3J(C,P) ˆ 13.5 Hz, C(CH3)3], 42.7 [d, 2J(C,P) ˆ 27.1 Hz, C(CH3)3], 51.7
(s, CO2CH3), 126.3, 127.1, 128.6 (each s, phenyl-C), 142.6 [d, 2J(C,P) ˆ
6.2 Hz, C5], 144.3 (s, ipso-C), 161.5 [d, 1J(C,P) ˆ 54.8 Hz, C4], 165.3 [d,
2J(C,P) ˆ 33.4 Hz, CO2Me], 187.1 [d, 1J(C,P) ˆ 64.7 Hz, C2]; 31P NMR
(C6D6): d ˆ ‡172.0 (s); IR (film): nÄ ˆ 2950 (s), 2900 (m), 1750 (s), 1720 (s),
Acknowledgments
We thank the Fonds der Chemischen Industrie for generous financial
support (postgraduate grant for J.H.), the Deutsche Forschungsgemein-
schaft (Graduate College Phosphorus as Connecting Link Between Various
Chemical Disciplines, postgraduate grant for M.S.), as well as to the
Landesregierung von Rheinland-Pfalz (postgraduate grant for S.H.).
[1] O. Wagner, M. Ehle, M. Regitz, Angew. Chem. 1989, 101, 227; Angew.
Chem. Int. Ed. Engl. 1989, 28, 225.
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Clark, M. Regitz, Chem. Ber./Recueil 1997, 130, 711.
1470 (w), 1430 (w), 1390 (w), 1360 (w), 1250 (s), 1070 (s), 1020 (s), 830 (vs),
1
700 (m), 620 (w) cm
.
4-tert-Butyl-1-diphenylphosphano-3-phenyl-2,2-bis(trimethylsilyl)-1,2-di-
hydro-1,2-phosphasilete (22): Compound 21 (75 mg, 0.34 mmol) was added
to a solution of 4a (150 mg, 0.35 mmol) in diethyl ether (3 mL) at 08C. The
reaction mixture was allowed to warm to room temperature and was then
stirred for 12 h at 208C. The solvent was removed at 208C (10 2 mbar) and
the residue was purified by bulb-to-bulb distillation to furnish 22 (150 mg,
80%) as a yellow oil. B.p. 1758C (10 3 mbar); 1H NMR (C6D6): d ˆ 0.20,
0.50 [each s, 9H, Si(CH3)3], 1.1 (s, 9H, tBu), 7.0 ± 8.3 (m, 15H, phenyl-H);
13C NMR (C6D6): d ˆ 0.06 [s, Si(CH3)3], 1.1 [d, 3J(C,P) ˆ 4.9 Hz, Si(CH3)3],
31.6 [d, 3J(C,P) ˆ 4.5 Hz, C(CH3)3], 41.1 [d, 2J(C,P) ˆ 13.3 Hz, C(CH3)3],
125.6 ± 136.6 (phenyl-C), 141.4 [dd, 1J(C,P) ˆ 22.6 Hz, 2J(C,P) ˆ 5.8 Hz,
ipso-C], 142.2 [dd, 1J(C,P) ˆ 28.8 Hz, 2J(C,P) ˆ 9.8 Hz, ipso-C], 145.3 [d,
3J(C,P) ˆ 4.4 Hz, ipso-C], 151.6 [dd, 2J(C,P) ˆ 19.0 Hz, 3J(C,P) ˆ 8.6 Hz,
C3], 167.9 [dd, 1J(C,P) ˆ 27.1 Hz, 2J(C;P) ˆ 8.6 Hz, C4]; 31P NMR (C6D6):
d ˆ 10.8, 79.6 [each d, 1J(P,P) ˆ 186.2 Hz]; IR (film): nÄ ˆ 3050 (m), 2950
[8] M. Regitz, H. Heydt, O. Wagner, W. Schnurr, M. Ehle, J. Hoffmann,
Phosphorus Sulfur Silicon 1990, 49/50, 341.
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(vs), 2900 (s), 1600 (m), 1580 (w), 1570 (w), 1480 (s), 1430 (s), 1360 (w), 1250
1
(s), 1070 (w), 1030 (w), 840 (vs), 770 (m), 740 (s), 700 (s) cm
.
4-tert-Butyl-3-phenyl-2,2-bis(trimethylsilyl)-1,2-dihydro-1,2-phosphasilete
(23): A solution of 4a (100 mg, 0.23 mmol) in tetrahydrofuran (1 mL) was
stirred for 12 h at 708C. After removal of the solvent at 208C (10 2 mbar),
the remaining oil was purified by bulb-to-bulb distillation to furnish 23
(70 mg, 80%) as a colorless oil. Compound 23 is extremely sensitive to
[12] M. Klessinger, J. Michl, Lichtabsorption und Photochemie organischer
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Georg Thieme, Stuttgart, New York, 1983.
1
moisture. B.p. 1308C (10 3 mbar); H NMR (C6D6): d ˆ 0.20, 0.35 [each s,
1
9H, Si(CH3)3], 1.20 (s, 9H, tBu), 3.40 [d, J(H,P) ˆ 160 Hz, 1H, PH], 7.0 ±
[15] K. Mislow, Trans. N.Y. Acad. Sci. 1973, 35, 227.
7.3 (m, 5H, phenyl-H); 13C NMR (C6D6): d ˆ 0.6, 0.5 [each s, Si(CH3)3],
30.4 [d, 3J(C,P) ˆ 4 Hz, C(CH3)3], 40.4 [d, 2J(C,P) ˆ 13.3 Hz, C(CH3)3],
125.3, 126.4, 127.8 (each s, phenyl-C), 145.0 [d, 3J(C,P) ˆ 5 Hz, ipso-C],
148.9 [d, 2J(C,P) ˆ 18.9 Hz, C3], 164.8 [d, 1J(C,P) ˆ 17 Hz, C4]; 31P NMR
(C6D6): d ˆ 173.2 [1J(P,H) ˆ 160 Hz].
[16] R. D. Baechler, K. Mislow, J. Am. Chem. Soc. 1970, 92, 4758.
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Crystallographic data: Data collection was performed on a four-circle
diffractometer (Enraf ± Nonius CAD4) with MoKa radiation (l ˆ
0.71073 Š) at room temperature. The structures were solved by direct
methods and refined by the full-matrix least-squares method on F with
1588
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0947-6539/99/0505-1588 $ 17.50+.50/0
Chem. Eur. J. 1999, 5, No. 5

Silylphosphirene Rearrangement
1581±1589
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[26] V. Galasso, J. Magn. Reson. 1979, 34, 199.
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[41] SHELXTL (Vers. 4.2-IRIS), Siemens Analytical X-ray Instruments
1991.
Received: September 10, 1998 [F1339]
Chem. Eur. J. 1999, 5, No. 5
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0947-6539/99/0505-1589 $ 17.50+.50/0
1589