3622 Organometallics, Vol. 20, No. 17, 2001
Communications
Sch em e 1
vinylidene system with a bent structure at Câ, the
isonitrile ligand is linear. Therefore, the deprotonation
step should yield a bent transient zwitterionic nitrile
ylide X with an anionic charge most likely located at
the methyne carbon atom of the isonitrile ligand (see
Scheme 1), thus facilitating formation of the azirinyl
ring.10
At -20 °C, the 31P NMR spectrum of 3c displays three
sets of mutually coupled doublet pairs assigned to three
isomers, possibly the 2H-azirinyl isomers 3c-I (δ 51.89,
49.72;) and 3c-II (δ 51.98, 48.82) and the 1H-azirinyl
isomer 3c-III (δ 51.17, 50.15) (Scheme 1), in a ratio of
1
3:2:2, each with a stereogenic center. In the H NMR
spectrum two sharp resonances at δ 4.71 and 4.89 are
assigned to CH of the azirinyl groups of 3c-I and 3c-II,
respectively, and a broad resonance at δ 3.23 is assigned
to the NH of 3c-III. Upon addition of D2O the NH
resonance disappears immediately at -20 °C; then
within 20 min the two CH resonances also vanish,
indicating interconversion of three isomers. As the
temperature was lowered to -30 °C, 3c-III disappears,
and then at -40 °C only 3c-I is observed. The stereo-
genic nitrogen center in the 1H-azirinyl ligand of 3c-
III may originate from hindered pyramidal inversion.
A molecular orbital calculation showed that the organic
1H-azirine is approximately 30 kcal less stable than 2H-
azirine because of ring strain and an electronically less
favorable structure;11 previously the presence of 1H-
azirine was only inferred by indirect evidence.12 In our
system, the Ru center and the phenyl substituent on
the ring could stabilize the 1H-azirinyl ligand, possibly
by an extended conjugation of the phenyl group and
metal d electron connected by the CdC double bond of
the 1H-azirinyl ligand. The M-C(sp2) bonding in 3c-
III also enhances stability of the 1H-azirinyl ligand via
a d-π interaction. For 3c-I, a similar d-π interaction
combined with the more stable character of the 2H-
azirinyl ligand leads us to believe that it is the most
stable isomer. This explains the fact that, out of three
isomers of 3c, only one is observed at -40 °C. Transi-
tion-metal-induced reactions of organic azirine have
been reported for Fe,13 Mo,14 and Rh, Mo, and Pd.15
Treatment of 2d with n-Bu4NOH afforded [Ru]-
of several new ruthenium azirinyl complexes and the
insertion reaction of the carbonyl group of ketones,
aldehydes, or esters into the C-C bond of the azirinyl
ring, yielding a metal-coordinated oxazoline complex.6
The regiospecificity of this insertion is opposite that
observed in the organic azirine system and may be used
for the coupling of organic halide with carbonyl-contain-
ing compounds.7
Reactions of [Ru]CN (1; [Ru] ) (η5-C5H5)(PPh3)2Ru)
with XCH2R readily gives the green isonitrile complexes
{[Ru]CNCH2R}X (2a , R ) CN, X ) Br; 2b, R )
CHdCH2, X ) I; 2c, R ) C6H5, X ) Br; 2d , R )
COOCH3, X ) Br). Upon treatment with base (n-
Bu4NOH or n-Bu4NF) at 0 °C, complexes 2a -c afforded
[Ru]CNCHR (3a -c), respectively (Scheme 1). Com-
plexes 3 decompose at room temperature and are
1
characterized by spectroscopic methods. In the H NMR
spectrum of 3b the ddd coupling pattern of the reso-
nance at δ 5.73, assignable to the vinyl methine proton,
reveals the site of deprotonation at the NCH2 group. For
comparison the corresponding resonance of 2b exhibits
a ddt pattern. Formation of the azirinyl ring should
generate a stereogenic center, which is revealed by a
pattern of two doublet resonances in the 31P NMR
1
spectra of 3a and 3b. The singlet H NMR resonance of
the ring proton of 3a appears at δ 2.98, similar to that
of organic azirine systems.8 In the 2D HMQC NMR
spectrum this resonance is correlated to the 13C reso-
nance at δ 11.3 assignable to the sp3 carbon of the
azirinyl ring.
CdNCH2COO (4), which is rationalized by hydrolysis
of the ester group followed by oxygen atom attack at
CR. The 31P NMR spectrum of 4 displays a singlet
resonance (δ 50.5), unlike the two-doublet pattern of 3.
Previously, in the deprotonation reaction of vinylidene
with an ester group, we observed an ester-substituted-
cyclopropenyl complex as a kinetic product, which
transformed to a furanyl complex as a thermodynamic
A number of general methods9 are available for the
synthesis of organic 2H-azirines. These include the
modified Neber reaction, thermolysis and photolysis of
vinyl azide and isoxazoles, and thermolysis of oxaza-
phospholines. Using the strategy illustrated in the
synthesis of cyclopropenyl complexes, we have prepared
the azirinyl complexes 3. In contrast to the metal
(10) (a) Yamamoto, Y. Coord. Chem. Rev. 1980, 32, 193. (b)
Singleton, E.; Oosthuizen, H. E. Adv. Organomet. Chem. 1983, 22, 209.
(c) Carnahan, E.; Lippard, S. J . J . Am. Chem. Soc. 1990, 112, 3230.
(d) Aharonian, G.; Hubert-Pfalzgraf, L. G.; Zaki. A.; Le Borgne, G.
Inorg. Chem. 1991, 30, 3105.
(11) (a) Gilchrist, T. L.; Gymer, G. E.; Rees, C. W. J . Chem. Soc.,
Perkin Trans. 1 1973, 555. (b) Hopkinson, A. C.; Lien, M. A.; Yates,
K.; Csizmadia, J . G. Int. J . Quantum Chem. 1977, 12, 355.
(12) Regitz, M.; Arnold, B.; Danion, D.; Schubert, H.; Fusser, G. Bull.
Soc. Chim. Belg. 1981, 90, 615.
(13) Alper, H.; Prickett, J . E. J . Chem. Soc., Chem. Commum. 1976,
191.
(14) Inada, A.; Heimgartner, H.; Schmid, H. Tetrahedron Lett. 1979,
2983.
(6) (a) Bolm, C. Angew. Chem., Int. Ed. Engl. 1991, 30, 542. (b) Gant,
T. G.; Meyers, A. I. Tetrahedron 1994, 50, 2297. (c) Ghosh, A. K.;
Mathivanan, P.; Cappiello, J . Tetrahedron: Asymmetry 1998, 9, 1. (d)
Evans, D. A.; Miller, S. J .; Lectka, T. J . Am. Chem. Soc., 1993, 115,
6460. (e) Bremberg, U.; Larhed, M.; Moberg, C.; Hallberg, A. J . Org.
Chem. 1999, 64, 1082. (f) Lightfoot, A.; Schnider, P.; Pfaltz, A. Angew.
Chem., Int. Ed. Engl. 1998, 37, 2897. (g) Williams, J . M. J . Synlett
1996, 705.
(7) (a) Chan, T. H.; Yang, Y. J . Am. Chem. Soc. 1999, 121, 3228. (b)
Evans, W. J .; Allen, N. T. J . Am. Chem. Soc. 2000, 122, 2118.
(8) Banert, K.; Hagedorn, M. Angew. Chem., Int. Ed. Engl. 1990,
29, 103.
(9) (a) Padwa, A.; Carlsen, P. H. J .J . Org. Chem. 1978, 43, 2029.
(b) Nishiwaki, T. Tetrahedron Lett. 1969, 2049. (c) Singh, B.; Zweig,
A.; Gallivan, J . B. J . Am. Chem. Soc. 1972, 94, 1199. (d) Hassner, A.;
Alexanian, V. J . Org. Chem. 1979, 44, 3861.
(15) (a) Alper, H.; Prickett, J . E. Tetrahedron Lett. 1976, 2589. (b)
Isomura, K.; Uto, K.; Taniguchi, H. J . Chem. Soc., Chem. Commum.
1977, 664.