Synthesis and structure of the first 2H-1,3,2-diazaphosphole complex
Hendrik Wilkens, Jo¨rg Jeske, Peter G. Jones and Rainer Streubel*
Institut fu¨r Anorganische und Analytische Chemie der Technischen Universita¨t Braunschweig, Postfach 3329, D-38023
Braunschweig, Germany
Thermal decomposition of the 2H-azaphosphirene tungsten
C(19)
complex
1 in benzonitrile and in the presence of
dimethylcyanamide yields the 2H-1,3,2-diazaphosphole
tungsten complex 4, containing a novel five-membered
heterocyclic ligand; the overall reaction may be described as
a 1,3-dipolar cycloaddition of an in situ generated nitrilium
phosphane ylide complex to benzonitrile.
O(3)
C(3)
C(18)
C(21)
Si(1)
C(17)
C(6)
Si(2)
Nitrilium ylides, like nitrile oxides,1 sulfides2 and nitrile-
imines,1,3 are versatile building blocks in heterocyclic che-
mistry. Very recently, we obtained the first evidence of a
nitrilium phosphane ylide complex as a reactive intermediate in
the thermolysis of 2H-azaphosphirene tungsten complexes in
the presence of dimethylacetylenedicarboxylate (DMAD) in
toluene.4 The formation of the 2H-1,2-azaphosphole tungsten
complexes, which were obtained as by-products, was explained
as a 1,3-dipolar cycloaddition of a nitrilium phosphane ylide
complex to the trapping reagent.4
We now report the first synthesis of a 2H-1,3,2-diazaphos-
phole tungsten complex 4, which has been obtained in good
yield by thermal decomposition of the 2H-azaphosphirene
tungsten complex 1 in benzonitrile and in the presence of 2
equiv. of dimethylcyanamide. Under these reaction conditions
the 1,3-dipolar cycloaddition is stereoselective and the ex-
clusive formation of this regioisomer was observed.
O(2)
C(2)
C(22)
C(4)
O(4)
N(1)
C(7)
C(20)
W
P
C(5)
O(5)
C(16)
N(2)
C(1)
N(3)
C(8)
C(15)
C(9)
O(1)
C(14)
C(10)
C(13)
C(11)
C(12)
This reaction is interpreted as a further example of a
1,3-dipolar cycloaddition of the transiently formed nitrilium
phosphane ylide tungsten complex 2b to benzonitrile (Scheme 1,
pathway (c)]. Pathways (a) and (b) seem less plausible,
especially, if taken into account that under these reaction
conditions the formation of the diphenyl-substituted
2H-1,3,2-diazaphosphole tungsten complex 3 was not observed
[pathway (a)].
Fig. 1 Molecular structure of complex 4 in the crystal. Radii are arbitrary.
Selected bond lengths (Å) and angles (°): P–W 2.479(11), P–N(1) 1.705(3),
P–N(2) 1.705(3), N(1)–C(7) 1.291(5), N(2)–C(8) 1.284(5), C(7)–C(8)
1.488(5); N(1)–P–N(2) 96.3(2), P–N(1)–C(7) 108.2(3), N(1)–C(7)–C(8)
114.0(3), N(2)–C(8)–C(7) 113.4(4), P–N(2)–C(8) 107.8(3).
NMR spectral data† in solution and was confirmed for the solid
state by a X-ray crystal structure analysis.‡ In comparison to
related 2H-1,2-azaphosphole tungsten complexes,4 the
2H-1,3,2-diazaphosphole tungsten complex 4 displays a low-
field shifted resonance signal of the phosphorus nucleus at d
149.8 (cf. d 102–1054) and a markedly increased phosphorus
tungsten coupling constant of 257.1 Hz (cf. 1JWP 236–238 Hz4).
The phosphorus–carbon coupling constants of the quaternary
ring carbon atoms are 2–10 Hz, which are characteristically
small for both five-membered heterocycles.
Remarkable features of the molecular structure of 4 and
2H-1,2-azaphosphole complexes4 are the planar five-membered
ring system and the localised double bonds; the latter being in
contrast to the situation of aromatic heterocycles like
2H-1,2,3-diazaphospholes5,6 and 2H-1,2,3-triazoles.7 The coor-
dination sphere of phosphorus is distorted tetrahedral and the
phosphorus–tungsten bond length is 2.479(11) Å.
The composition of 2H-1,3,2-diazaphosphole tungsten com-
plex 4 is confirmed by elemental analysis and mass spectrome-
try;† the structural formulation is based on the characteristic
(OC)5W
CH(SiMe3)2
CH(SiMe3)2
(OC)5W
P
P
3
N
N
C
N
Ph
C
C
(a) PhCN
Ph
Ph
1
75 °C
CH(SiMe3)2
(OC)5W
N
W(CO)5
–
+
N
(b) Me2NCN
P
Ph
C
P
N
CH(SiMe3)2
C
C
Ph
NMe2
2a
4
We are currently investigating the synthetic potential of
nitrilium phosphane ylide complexes in 1,3-dipolar cycloaddi-
tion reactions.
This work was supported by the Fonds der Chemischen
Industrie and by the Deutsche Forschungsgemeinschaft.
Me2NCN – PhCN
(c) PhCN
W(CO)5
–
P
+
N
Me2N
C
CH(SiMe3)2
2b
Footnotes and References
Scheme 1 Reagents and conditions: 1 mmol 1 was treated with 2 mmol
dimethylcyanamide in benzonitrile at 75 °C for 1.5 h. Work-up by column
chromatography at low temperature afforded 4 in good yield (67%, mp
90 °C).
* E-mail: streubel@mvs.anchem.nat.tu-bs.de
† Satisfactory elemental analysis was obtained for complex 4. NMR data
were recorded at room temp. in CDCl3 solution at 50.3 MHz (13C) and 81.0
Chem. Commun., 1997
2317
Wilkens, Hendrik
