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Nitrile Ylides and Azirines Gas-Phase Generation from 2 3-Dihydro-1 4 5-oxazaphospholes and Matrix Isolation.

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[XI SO. ( 2 0 m L ) was condensed at - 190°C into a pressure flask containing
l.Og (6.8 mmol) of 1 and I.0g (3.4mmol) of 3. The colorless solution
was allowed to warm up in the dark to room temperature and stirred for
18 h. The moderately soluble precipitate that formed was filtered off and
the soI\rnt was removed from the filtrate in vacuum. The residue was
recrystallized from SO?, affording 1.6 g (79%) of 4 as pale yellow crystals. m.p = I15 'C (decomposition at 125'C).-IR (nujol): v=2175, 700,
575,498,464, and 395 cm-'.-Raman: v=2175,683, 658,498,460,430,
and 206 cm '
[9] Freshly prepared 2 (1.56 g, 8.7 mmol), which had been dried in a vacu u m d t -30°C. was heated rapidly to the melting point (-3°C) and
then added under a stream of nitrogen to 3 (1.29 g, 4.3 mmol) in a pressure ilask at - 190°C. In the evacuated flask, 20 m L of SOz was condensed and the stirred solution was then slowly warmed in a cold bath
( - 50°C') in the dark over 4 h to room temperature. After two hours of
stirring. the sparingly soluble solid was filtered off and the solvent removed from the filtrate. Orange crystals of 5 were obtained by recrystallizing the residue from SO?. Yield: 1.9 g (67%). m.p.=92'C (decomposition dl IlO"C)-lR (nujol): v=2165, 705, 692, 685, 465, and 395
cm ' Raman: v=2165, 678, 506, 438,420, 401, 223, 189, 180, 127, 93,
and 78 cm . '.
[lo] The Raman- and IR-active v(C=N) vibrations are shifted by 19 ( 4 ) and
13 ( 5 ) cm I , respectively, to shorter wavelengths by complexation.
r,(C-S). v(S-S), &(C-S-S), and S(S-S-S) frequencies are also shifted;
the number of bands, however, remains the same, thereby confirming
that no sulfur-sulfur bonds are broken.
[ I I ] The crystal structure of 1 could only be imprecisely determined by Xray diffraction at -20°C (R=0.25), while that of 2 is unknown. Cf. F.
Feher. K. H. Linke, Z . Anorg. Allg. Chem. 327(1964) 151: 0. Foss, Acra
Chem S c a d 10 (1956) 136.
[I21 P. G. Jones, Acfa Crnra//ogr. A 4 0 (1984) 660.
1131 D. Rogers, Arru Crwallogr. A 3 7 (1981) 734.
1141 Further details of the crystal structure investigations are available on
request from the Fachinforrnationszentrum Energie, Physik, Mathemattk GmbH. D-7514 Eggenstein-Leopoldshafen2, on quoting the depository number CSD-51607, the names of the authors, and the journal
starting material, as seen by the simultaneous disappearance of the triplet and the appearance of a new band at
1620 c m - ' (characteristic of la). After warming to room
temperature and opening the apparatus, the sample remaining on the window was identified as pure l a .
In similar experiments, in which the pyrolysis products
were isolated in a cold trap at - 196"C, it was possible to
distill the new compound into a second cold trap in high
vacuum, thus freeing it from 2 and preventing the regeneration of l a . The sample thus obtained showed a I9F-NMR
signal at 6=73.07 as expected for a bis(trifluor0methyl)azirine;"] it was extremely sensitive to moisture and hydrolyzed to the amide 5a simply on exposing the apparatus to the atmosphere. On the basis of the spectroscopic
and chemical properties, the new compound is identified
as the azirine 3a. Hydrolysis with cleavage of the C-C
bond (3a + 5a) is normal for bis(trifluoromethy1)azirines.LS;!I
Nitrile Ylides and Azirines:
Gas-Phase Generation from
a, R
2,3-Dihydro-1,4,215-oxazaphospholes and
Matrix Isolation**
By Curt Wentrap,* Stephan Fischer,
Hans-Michael Berstermann, Martin Kuzaj, Holger Liierssen,
and Klaus Burger
Nitrile ylides are among the most important nitrilium
betaines.".'] Although nitrile ylides have been directly observed, mostly by UV spectroscopy following photochemical generation from 2H-azirines,[*]and a single example of
a stable nitrile ylide has been r e p ~ r t e d , 'there
~ ] has been no
direct observation of thermally generated nitrile ylides. We
now wish to report the first such example.
Flash vacuum pyrolysis of 5-tert-butyl-3,3-bis(trifluoromethyl)-2,3-dihydro- 1,4,2hs-oxazaphosphole
laf4] at
400°C/10-3 torr with isolation of the products on a KBr
window at -196°C for IR spectroscopy resulted in the
quantitative formation of trimethyl phosphate 2 and a new
species characterized by a triplet at v= 1740 (m), 1715 (s),
and 1695 (m) cm-'. On warming the window to -7O"C,
this species reacted with the phosphate 2 to regenerate the
Prof. Dr. C . Wentrup [+I, DipLChem. S. Fischer,
Dip1 -C'hem. H.-M. Berstermann, DiplLChem. M. Kuzaj,
DipLChem. H. Liierssen
Fachhereich Chemie der Universitat
Hans-Meerwein-Strasse. D-3550 Marburg (FRG)
Prof. Dr. K. Burger
lnstitut fur Organische Chemie der Technischen Universitat Miinchen
D-8046 Carching (FRG)
New dddress: Department of Chemistry, University of Queensland
St Lucia. Briabane.. Old.
(Australia) 4067
[**I This work was supported by the Deutsche Forschungsgemeinschaft, the
Fonds der Chemischen Industrie, and the University of Queensland.
Anyen Chem. I n f . Ed. Engl. 25 11986) No. I
b, R = C&
When the pyrolysis of l a was carried out at 700-860°C
and the products examined by IR spectroscopy at
- 196"C, the azirine 3a was no longer observed; instead, a
species absorbing strongly at v= 2250 cm ' had appeared.
This species, too, was sensitive to moisture and hydrolyzed
on warming up (-90 to - 50°C) to give the same product
(5a), as seen by the disappearance of the band at
v=2250 c m - ' simultaneous with the appearance of a band
at v = 1680 c m - ' (characteristic of 5a). The 'H-NMR spectrum of the isolated product established its identity as 5a,
formed in virtually quantitative yield.['I
On the basis of the IR spectrum and the reactivity we
identify the high temperature species as the nitrile ylide
4a. The asymmetric stretching vibration at v=2250 c m - '
is similar to that reported for the only nitrile ylide isolated
so far.131Further bands belonging to 4a appear at v= 1460
(m), 1365 (m), 1345 (m), 1280 (s), 1250 (m), 1225 (m), 1215
(m), 1180 (vs), 1095 (s), 995 (vs), 890 (m), 770 (m) e m - ' .
Trapping reactions of thermally generated 4a in solution
have been described previously.[41
Further proof for the identity of the nitrile ylide 4a is
given by its photochemical formation from the matrix-isolated azirine 3a. The azirine was generated at 400°C and
isolated in argon on a BaF2 window at I 1 K. Subsequent
irradiation with a low-pressure Hg lamp (/1=254 nm) resulted in the slow disappearance of the azirine triplet concomitant with the appearance of the bands due to the nitrile ylide 4a.I"
The corresponding 5-phenyloxazaphosphole l b reacted
similarly to give the azirine 3b (IR: v = 1730, 1690 c m - ' ;
F-NMR: 6 = 72.88), which reverted quantitatively to l b
on warming u p and reacted with water to give 5b. In this
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case, however, high-temperature pyrolysis (870°C) did not
lead to the clean formation of the ylide 4b.
In continuation of our studies of thermally generated nitrilium betaines"' we have also prepared nitrile
Received: August 19, 1985 [Z 1435 IE]
German version: Angew. Chem. 98 (1986) 99
The anion of the complex has-according to an X-ray
structure analysis of 2 - an approximate C, symmetry
(Fig. 1). This is evident from the well-ordered propellertype arrangement of the three SCH2CH2S ligands:
S-Nb-S, 81.58(4)-82.14(4)"; S-Nb-S (trans), 156.29(4)157.55(4)". The torsional angles (4)of the three chelate li-
[ I ] R. Huisgen, Angew. Chem. 75 (1963) 604; Angew Chem. Inr. Ed. En# 2
(1963) 565.
[2] H:J. Hansen, H. Heimgartner in A. Padwa (Ed.): 1.3-Dipolar Cycloaddition Chemi.ctry. Vol. 1. Wiley, New York 1984, p. 177ff.
[3] E. P. Janulis, Jr., S. R. Wilson, A. J. Arduengo 111, Tetrahedron Lett. 25
(1984) 405.
[4] K. Burger, J. Fehn, Chem. Ber. I05 (1972) 3814. K. Burger, J. Albanbauer,
F. Manz, ihid. 107 (1974) 1823.
151 a) C . G. Krespan, J . Org Chem. 34 (1969) 1278: b) C. S. Cleaver, C. G.
Krespan, J . Am. Chem. Soc. 87 (1965) 3716.
161 3 reacts laster with 2 than does 4. It is not at present possible to determine whether 4 also reacts with 2 to regenerate 1, or whether this occurs
via the reversion 4 - 3 - 1 .
[7] C. Wentrup, S. Fischer, A. Maquestiau, R. Flammang, Angew. Chem. 97
(1985) 74; Angew. Chem. Int. Ed. Engl. 24 (1985) 56.
[8] C. Wentrup et al., unpublished.
IEt4NIIM(SCH,CH,S),I (M = Nb, Ta),
Homoleptic 1,2-Ethanedithiolate Complexes of
Niobium and Tantalum**
By Kazuyuki Tatsumi. Yoitsu Sekiguchi,
Akira Nakarnura,* Roger E. Cramer,* and John J. Rupp
Very few niobium and tantalum complexes with thiolate
ligands have so far been reported.['-31 During investigations of dithiolates of metals of the vanadium group we
were able to synthesize 1-3, the first homoleptic 1,2-ethanedithiolate complexes of niobium and tantalum, by reaction of NbCIs (or TaCI,) with LiSCH2CHzSLi.14"1
[Li(thf)3][Nb(SCH2CH2S)3] [Et,NI[M(SCH,CH,S),]
2, M = N b ; 3, M = T a
When NbCls was allowed to react with Li2SZC2H4in
benzene and then in THF, the air-sensitive compound 1
was obtained.14h'Cation exchange of 1 with Et,NCI in acetonitrile yielded the tetraethylammonium salt 2,'4'1 which
is relatively air-stable (several hours). With the stoichiometry established, it was found that 2 could be synthesized
more readily from a 1 : 3 : 1 mixture of NbCI5, Li2SzC2H,,
and Et4NCI in acetonitrile. A similar procedure with TaCI,
instead of NbCls afforded the Ta complex 3.l4''l
brown powder
gands are 31.4, 30.6, and 29.41 indicating that the coordination sphere defined by the six sulfur atoms is midway
between trigonal-prismatic (4 = Oo) and octahedral
(@=60"). For the very recently described Ti complex 4,I5l
the torsional angles are similar, ranging from 4 ~ 3 5 "to
42". However, this stereochemistry contrasts with the trigonal-prismatic geometry found for the niobium complex
@=0.7" (av.).
2, M = N b ; 3, M = T a
[*] Prof. Dr. A. Nakamura, Dr. K. Tatsumi, Y . Sekiguchi
Department of Macromolecular Science, Faculty of Science,
Osaka University
Toyonaka, Osaka 560 (Japan)
Prof Dr. R. E. Cramer, Dr. J. J. Rupp
Department of Chemistry, University of Hawaii
Honolulu, H I 96822 (USA)
[**I This work was supported by the Japanese Society for the Promotion of
Science and the National Science Foundation (NSF) of the USA in connection with the Japan-United States Cooperative Science Program
[joint research between K . Tatsumi and A . Nakamura in Osaka and J .
W . Gilje and R . E. Cramer in Honolulu). R . 6.C. acknowledges partial
support from a n NSF grant (CHE 8210244).
Fig I. An ORTEP representation of the structure of the complex anion in 2
with 50% probability ellipsoids. Monoclinic, space group C2, a = 19.920(3),
= 1.503 g cm-',
b=8.0424(9), c = 14.070(2)A, fl= 101.55(5)', pc,,iL
p(MoKn)=l0.06 c m - ' . The structure was solved by MULTAN 80 and refined to R,=0.0292 and R,; =0.0294 using the SHELX program system with
all atoms anisotropically refined except for hydrogen atoms. In this figure,
the thermal parameters of the H atoms are arbitrarily fixed at 0.05 (3702 observed reflections I > 3c(I), 4228 measured reflections, 328 refined parameters). Selected bond lengths [A]: Nb-S 2.425(1)-2.4422(9); C-S, 1.81 l(5)1.823(5); C-C, 1.493(8)-1.499(7): C-H, 0.87(5)-1.04(5). The locations of hydrogen atoms are normal. The absolute configuration of the complex anion
was determined to be A by refinement of both configurations using the complete data set which spanned Friedel pairs. Further details of the crystal
structure investigation are available on request from the Director of the Cambridge Crystallographic Data Centre, Lensfield Road, Cambridge CB2 I EW
(England) on quoting the full citation of this journal.
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Apart from the complexes [Ta( I,2-S2CsH4)3]-[3"1and
[Zr( l,2-S2C6H4)3]Z-J'oldithiolate chelates having n-conjugated bridges prefer to form trigonal-prismatic complexes,'61 while those without n-systems, e.g. 1-3, distort
from trigonal-prismatic. The C-S bond distances in 2 (av.
are substantially longer than those in 5 (av.
since the S atoms in SCHzCHzShave a different a donor ability than the S atoms in 1,2-SzC6H4.However, the observed Nb-S distances in 2 (av. 2.434(7)) are surprisingly close to those of 5 (av. 2.44(1) A). Nevertheless,
because of the decreased steric bulk of SCHzCHzS compared to that of lr2-S2C6H4,and the longer C-S distance in
the former compound, we anticipate that the anions of 2
(and 3) are more reactive than [Nb(S2C6H4)3]-,the anion
of 5.1'11
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Angew. Chem. Inr. Ed. Engl. 25 (1986) No. I
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dihydro, nitrile, matrix, azirine, isolation, generation, oxazaphospholes, gas, ylide, phase
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