Synthesis, structure, and chemistry of 2-amino-substituted phosphirenes

Article abstract of DOI:10.1021/om900696p

The reaction of the bulky ynamine PhC≡C-NⁱPr₂ with terminal phosphinidene complexes [RP-W(CO)₅] affords the corresponding phosphirenes for R = Ph and OMe and the diphosphetene for R = Me. The structure of the 1-phenyl-phos

Full text of DOI:10.1021/om900696p

Organometallics 2009, 28, 5705–5708 5705
DOI: 10.1021/om900696p
Synthesis, Structure, and Chemistry of 2-Amino-Substituted
Phosphirenes
Duanghathai Panichakul and Franc-ois Mathey*
Division of Chemistry & Biological Chemistry, School of Physical & Mathematical Sciences, Nanyang
Technological University, 21 Nanyang Link, Singapore 637371
Received August 6, 2009
The reaction of the bulky ynamine PhCtC-NiPr2 with terminal phosphinidene complexes
[RP-W(CO)5] affords the corresponding phosphirenes for R=Ph and OMe and the diphosphetene
for R=Me. The structure of the 1-phenyl-phosphirene shows elongated P-C(N) and CdC ring
bonds. The reaction of this phosphirene with dimethyl acetylenedicarboxylate gives the phosphole
resulting from the insertion of the alkyne into the P-C(N) bond and the tetrafunctional arene
resulting from the [2þ2þ2] cycloaddition of one alkyne with two phosphirenes.
Introduction
to use the more bulky and slightly less electron-rich
PhCtC-NiPr2.5 We were immediately successful, as shown
in eq 1.
Some time ago, we had noticed that the chemistry of the
three-membered cycle of 2-amino-substituted phosphiranes
is highly perturbed by the amino substituent.1 The amino
substituent sharply destabilizes the P-C(N) ring bond and
ring-opening takes place very easily. We thought that it
would be quite interesting to check whether a similar drastic
perturbation would occur for the phosphirene ring. Indeed,
in this case, the nitrogen lone pair can also delocalize over the
CdC double bond of the ring, inducing a completely differ-
ent type of chemistry. A related investigation has been
performed by Averin et al. on the chemistry of 2-amino-
1-iminophosphirenes obtained by condensation of imino-
phosphines with ynamines,2 but it is known that pentavalent
phosphirenes show a high propensity to ring-opening3 and
that their chemistry is quite different from that of trivalent
phosphirenes. We describe our results in this report.
The presence of the three-membered ring in 2a,b is
immediately obvious from the 31P chemical shift at high
1
1
fields: 2a, δ -140.9, JPW=271.6 Hz; 2b, δ -56.1, JPW
=
325.6 Hz. If we compare these data with those of the
phosphirene complexes deriving from diphenylacetylene,6
we note that the replacement of the Ph by the NiPr2
substituent has a significant influence on the chemical
shifts but not on the 1JPW coupling constants. Since we know
that the magnitude of these couplings depends on the
donor-acceptor character of phosphorus,7 this observation
suggests that there is only a limited electronic interaction
between the amino substituent and phosphorus in these
species. The 13C NMR spectrum shows the huge polarization
of the CdC(N) double bond, for example for 2b: δ C(Ph)
102.57 (s), C(N) 141.52 (d, 1JCP=22.9 Hz). Wishing to have a
more complete insight into the structure of these amino-
substituted phosphirenes, we decided to perform the X-ray
Results and Discussion
As usual for this kind of strained phosphorus-carbon
heterocycles, we decided to work in the coordination
sphere of tungsten for convenience. The products are
easier to synthesize and more stable. In a previous publica-
tion,4 we investigated the reaction of [PhP-W(CO)5] with
MeCtC-NEt2 and were unable to isolate the phosphirene
because it readily inserts a second molecule of aminoalkyne
to give the corresponding phosphole. Thus, we decided
analysis of 2a (Figure 1). We note immediately that nitrogen
P
is planar ( C-N-C angles 358.5°), suggesting a strong
delocalization of the lone pair over the ring. The short N-C
connecting bond (1.332(4) A) confirms this delocalization.
˚
The P-C(N) ring bond is significantly longer than the
˚
P-C(Ph) bond (1.806 vs 1.769(3) A), implying rather easy
ring-opening or insertions. At the same time, the CdC
*Corresponding author. E-mail: fmathey@ntu.edu.sg.
(1) Marinetti, A.; Mathey, F. Organometallics 1984, 3, 1492.
(2) Averin, A. D.; Lukashev, N. V.; Borisenko, A. A.; Kazankova,
M. A.; Beletskaya, I. P. Zh. Org. Khim. 1995, 31, 404. Averin, A. D.;
Lukashev, N. V.; Borisenko, A. A.; Kazankova, M. A.; Beletskaya, I. P.
Zh. Org. Khim. 1995, 31, 400. Averin, A. D.; Lukashev, N. V.; Kazankova,
M. A.; Beletskaya, I. P. Mendeleev Commun. 1993, 2, 68.
(3) Reviews on phosphirenes: Mathey, F. Chem. Rev. 1990, 90, 997.
Heydt, H. Sci. Synth. 2001, 9, 85.
(5) Strobach, D. R. J. Org. Chem. 1971, 36, 1438.
(6) Alcaraz, J.-M.; Svara, J.; Mathey, F. New J. Chem. 1986, 10, 321.
Borst, M. L. G.; Bulo, R. E.; Winkel, C. W.; Gibney, D. J.; Ehlers, A. W.;
Schakel, M.; Lutz, M.; Spek, A. L.; Lammertsma, K. J. Am. Chem. Soc.
2005, 127, 5800.
(4) Tran Huy, N. H.; Mathey, F. Phosphorus Sulfur Silicon 1990, 47,
477.
(7) Mercier, F.; Mathey, F.; Afiong-Akpan, C.; Nixon, J. F.
J. Organomet. Chem. 1988, 348, 361.
r
2009 American Chemical Society
Published on Web 09/09/2009
pubs.acs.org/Organometallics

5706 Organometallics, Vol. 28, No. 19, 2009
Panichakul and Mathey
Figure 3. X-ray crystal structure analysis of diphosphetene 3.
Ellipsoids are scaled to enclose 50% of the electronic density.
Significant distances (A) and angles (deg): P1-P2 2.2185(9),
Figure 1. X-ray crystal structure analysis of phosphirene 2a.
Ellipsoids are scaled to enclose 50% of the electronic density.
Significant distances (A) and angles (deg): P1-W1 2.5132(8),
˚
˚
P1-C8 1.872(3), P2-C1 1.809(3), C1-C8 1.381(4), C8-N1
1.353(4), P1-W1 2.5063(7), P2-W2 2.4833(8), P1-C15
1.835(3), P2-C21 1.834(3); P1-P2-C1 77.35(9), P2-P1-C8
76.00(9), P1-C8-C1 101.5(2), P2-C1-C8 104.3(2); C15-P1-
P2-C21 164.26, C1-P2-P1-C8 5.42.
P1-C15 1.833(3), P1-C7 1.806(3), P1-C8 1.768(3), C7-C8
1.343(4), C7-N1 1.332(4), N1-C2 1.485(4), N1-C4 1.480(4);
C7-P1-C8 44.12(4), C2-N1-C7 118.8(3), C4-N1-C7
120.6(3), C2-N1-C4 119.1(3).
conditions (P/ynamine ratio), we always obtained the diphos-
phetene (3) as the sole important product (eq 2).
The product shows two nonequivalent phosphorus nuclei
at δ -0.8 and þ28.0 ppm with a very small P-P coupling of
8.7 Hz, which is characteristic of this type of ring.9 The
structure was fully established by X-ray crystal structure
analysis (Figure 3). A significant conjugation exists between
the nitrogen lone pair and the CdC double bond of the ring
(planar nitrogen, short N-C connecting bond with the ring,
elongated CdC double bond). The ring is slightly nonplanar
(C1-C8-P1-P2 7.37°). The two Me-P substituents are in
a trans disposition. Similar insertions of a second phosphi-
nidene unit into a phosphirene ring have already been
observed when a alkynyl substituent is grafted on one carbon
of the cycle.10,11 But we have two questions to answer. The
first one is why this insertion exclusively takes place with the
methylphosphinidene complex. The second one is why, in
this case, we get the trans R-P-P-R product whereas, in
the previous cases described in the literature, only or mainly
the cis product was obtained. In order to know on what side
(P-C(Ph) or P-C(N)) the insertion takes place, we perfor-
med the reaction of 1c with 2a, but we did not get the
expected insertion product. In the alkynyl case, the insertion
takes place on the side of the elongated bond substituted
by the sterically small triple bond. If we admit the same
Figure 2. Higher occupied Kohn-Sham orbitals of 1-methyl-
2-dimethylaminophosphirene pentacarbonyltungsten complex
as computed by DFT.
double bond of the ring is sizably elongated when compared
to that of the triphenylphosphirene pentacarbonyltungsten
complex8 (1.343(4) vs 1.307(6) A), suggesting possible
˚
enamine reactivity. We shall demonstrate this dual re-
activity hereafter. In order to complete the picture, we also
studied [1-methyl-2-dimethylaminophosphirene]pentacar-
bonyltungsten by DFT at the B3LYP/6-31G(d)-Lanl2dz
(W) level. The computed structure is close to the X-ray
structure of 2a. The two highest occupied orbitals are shown
in Figure 2. The highest corresponds to the antisymmetric
combination of the two P-C ring bonds, while the next one
depicts the conjugation between the p lone pair at nitrogen
with the CdC π bond.
Averin et al.2 have reported that, in some cases, the
reaction of iminophosphines with ynamines yields a 1,2-di-
phosphetene. A similar observation was made when allowing
[MeP-W(CO)5] to react with the ynamine. Whatever the
(9) Charrier, C.; Mathey, F.; Robert, F.; Jeannin, Y. J. Chem. Soc.,
Chem. Commun. 1984, 1707.
(10) Tran Huy, N. H.; Ricard, L.; Mathey, F. Organometallics 1997,
16, 4501.
(11) Wang, B.; Nguyen, K. A.; Srinivas, G. N.; Watkins, C. L.;
(8) Marinetti, A.; Mathey, F.; Fischer, J.; Mitschler, A. J. Am. Chem.
Soc. 1982, 104, 4484.
Menzer, S.; Spek, A. L.; Lammertsma, K. Organometallics 1999, 18, 796.

Article
Organometallics, Vol. 28, No. 19, 2009 5707
regiochemistry, the presence, in our case, of the very bulky
diisopropylamino group might explain the change of stereo-
chemistry. If we use the level of the LUMO of the phosphi-
nidenes as a probe for their electrophilicity, then DFT
computations at the B3LYP/6-31G(d)-Lanl2dz level indi-
cate that the electrophilicity decreases in the order [MeP-
Cr(CO)5] > [PhP-Cr(CO)5] > [MeOP-Cr(CO)5]. The ring
expansion would take place only with the most electrophilic
species in the tungsten case.
Having in hand a 2-aminophosphirene like 2a, we decided
to check whether it was possible to insert a alkyne unit into
the ring to get a series of amino-substituted phospholes.
Indeed, the chemistry of this type of phospholes is presently
almost unknown.12 We observed no reaction with diphenyl-
acetylene in boiling toluene for 15 h. This underlines the
stability of 2a in contrast with the very high reactivity of
2-aminophosphiranes.1 On the contrary, we got unexpected
results with the electrophilic dimethyl acetylenedicarboxy-
late (eq 3)
Figure 4. X-ray crystal structure analysis of arene 4. Ellipsoids
are scaled to enclose 50% of the electronic density. Significant
˚
distances (A) and angles (deg): C1-C2 1.393(4), C2-C3
1.389(4), C3-C4 1.402(4), C4-C5 1.423(4), C5-C6 1.415(4),
C6-C1 1.395(4), C4-N1 1.432(4), C6-N2 1.421(4); C1-C2-
C9-O3 60.70, C2-C1-C7-O1 114.07, C1-C6-N2-C32
91.05, C6-C5-C23-C24 169.52, C5-C4-N1-C20 87.78,
C4-C3-C11-C12 108.10.
The structure of 4 was established by X-ray crystal struc-
ture analysis (Figure 4). The C-C bonds of the ring are
significantly nonequivalent between 1.389(4) and 1.423(4) A.
The ring is slightly distorted (C1-C6-C4-C3 3.24°). All of
the substituents are tilted out of the ring plane to reduce
steric congestion. According to the 13C NMR spectrum, the
rotation of the phenyl substituents is blocked. As far as we
know, this type of hexasubstituted arene has not been
described in the literature. The proposed mechanism of
formation is depicted in eq 4.
˚
Here, we have a clear example of insertion into the weak
P-C(N) ring bond.
As a conclusion, this study clearly demonstrates that
2-aminophosphirenes have very different properties from
2-aminophosphiranes. The conjugation of the nitrogen lone
pair with the double bond of the ring partly switches off the
interaction between nitrogen and phosphorus through the
P-C(N) ring bond, which governs the chemistry of 2-ami-
nophosphiranes and induces a high propensity to ring-open-
ing. This tendency does not exist to the same extent in the
2-aminophosphirenes, which are much more stable and react
through both their enamine functionality and their P-C(N)
ring bond.
Experimental Section
NMR spectra were obtained on a JEOL ECA400 or JEOL
ECA400SL spectrometer. All spectra were recorded at 298 K
unless otherwise specified. Elemental analyses were performed
in the Division of Chemistry and Biological Chemistry,
Nanyang Technological University. HRMS spectra were ob-
tained in ESI mode on a Finnigan MAT95XP HRMS system
(Thermo Electron Corp.). X-ray crystallographic analyses were
performed on a Bruker X8 APEX diffractometer. All reactions
were performed under argon. Silica gel (230-400 mesh) was
used for the chromatographic separations. All commercially
available reagents were used as received from the suppliers.
General Procedure for the Preparation of Compounds 2a,b and
3. The 7-phosphanorbornadiene complex (1) (0.084 mmol) and
N-isopropyl-N-(phenylethynyl)propan-2-amine (34 mg, 0.168
mmol) were heated at 110 °C for 15 h in 1 mL of toluene. After
evaporation of the solvent, the residue was chromatographed
with hexane-ethyl acetate (90:10) to give the product.
The loss of phosphinidene complexes from phosphirane
complexes has some precedents.13 We have here an example
of reaction induced by the enamine subunit. The formation
of the phosphole 5 is easier to explain. Its formula is
proposed on the basis of its 13C NMR spectrum. The three
carbons connected to phosphorus give resonances at 145.91
(J=37.2 Hz, C-CO2Me), 134.57 (J=35.3 Hz, C ipso-PhP),
and 127.38 ppm (J=39.1 Hz, P-C-Ph). The high shielding
and coupling of the ring carbon substituted by the phenyl
group implies that the amino group occupies the β position
on the ring. The carbon bearing the amino group appears at
157.47 with a coupling of 9.5 Hz. In addition, both the ipso
and the ortho carbons of the R-phenyl substituent are sizably
coupled to phosphorus, by 14.3 and 10.5 Hz, respectively.
Phosphirene 2a. Yield: 35 mg, 54%. 31P NMR (162 MHz,
1
CDCl3): δ -140.9 (t, J=271.6 Hz, 1P). H NMR (400 MHz,
(12) Tan, W. H.-L. W.; Foucaud, A. Tetrahedron Lett. 1988, 29, 4581.
(13) Mercier, F.; Deschamps, B.; Mathey, F. J. Am. Chem. Soc. 1989,
111, 9098.
CDCl3): δ 7.55-7.48 (m, 4H, ArH), 7.40-7.35 (m, 5H, ArH),
7.25-7.21 (m, 1H, ArH), 3.89 (sep, 2H, 2 ꢀ CH), 1.32 (d, J=6.8

5708 Organometallics, Vol. 28, No. 19, 2009
Panichakul and Mathey
Hz, 6H, 2 ꢀ CH3), 1.19 (d, J=6.8 Hz, 6H, 2 ꢀ CH3). 13C NMR
(100 MHz, CDCl3): δ 200.4 (d, J=29.7 Hz, trans CO), 198.6 (d,
J=8.6 Hz, cis CO), 141.3 (d, J=13.4 Hz, dC(N)), 133.8 (d,
J=8.6 Hz, ipso C(PhP)), 133.1 (d, J=15.3 Hz, ortho CH (PhP)),
132.3 (s, para CH (PhP)), 132.0 (d, J=5 Hz, ipso C (PhC)), 130.8
(s, meta CH (PhC)), 130.4 (d, J=10.6 Hz, meta CH(PhP)), 130.0
(d, J=6.7 Hz, ortho CH (PhC)), 128.2 (s, para CH(PhC)), 115.8
(s, dC(Ph)P) 53.9 (2 ꢀ CH), 24.5 (2 ꢀ CH3), 24.0 (2 ꢀ CH3).
Anal. Calcd for C25H24NO5PW: C, 47.41; H, 3.82. Found: C,
47.62; H, 4.02.
the residue was chromatographed with hexane-ethyl acetate
(90:10) to give 4 as a colorless solid and 5 as an orange solid.
Arene 4. Yield: 6.2 mg, 24%. 1H NMR (400 MHz, CDCl3): δ
7.32-7.27 (m, 10H, ArH), 3.75 (s, 3H, CO2CH3), 3.35 (s, 3H,
CO2CH3), 3.16 (sep, 2H, 2 ꢀ CH), 3.00 (sep, 2H, 2 ꢀ CH), 0.76
(dd, J=23.8, 6.5 Hz, 12H, 4 ꢀ CH3), 0.51 (dd, J=19.2, 6.5 Hz,
12H, 4 ꢀ CH3). 13C NMR (100 MHz, CDCl3): δ 169.0 (CO),
168.5 (CO), 150.7 (C), 149.2 (C), 146.3 (C), 141.1 (C), 140.0 (C),
135.9 (C), 135.7 (C), 133.7 (C) 131.3 (2 ꢀ CH), 130.2 (CH), 129.3
(CH), 128.2 (CH), 127.5 (CH), 127.4 (CH), 127.1 (CH), 127.0
(CH), 126.7 (CH), 52.0 (OCH3), 51.9 (OCH3), 50.9 (2 ꢀ CH),
50.3 (2 ꢀ CH), 22.6 (2 ꢀ CH3), 22.3 (2 ꢀ CH3), 21.9 (2 ꢀ CH3),
21.8 (2 ꢀ CH3). Anal. Calcd for C34H44N2O4: C, 74.97; H, 8.14.
Found: C, 75.08; H, 7.75.
Phosphirene 2b. Yield: 40 mg, 68%. 31P NMR (162 MHz,
1
CD2Cl2): δ -56.1 (t, J=325.6 Hz, 1P). H NMR (400 MHz,
CD2Cl2, -40 °C): δ 7.44-7.37 (m, 4H, ArH), 7.27-7.23 (t, J=
7.1 Hz, 1H, ArH), 4.19 (sep, 1H, CH), 3.77 (sep, 1H, CH), 3.12
(d, J=13.7 Hz, 3H, OCH3), 1.44 (d, J=6.4 Hz, 3H, CH3), 1.35
(dd, J=11.9, 6.6 Hz, 6H, 2 ꢀ CH3), 1.26 (d, J=6.9 Hz, 3H, CH3).
13C NMR (100 MHz, CD2Cl2, -60 °C): δ 199.9 (d, J=37.2 Hz,
trans CO), 196.3 (td, J=63.0, 9.5 Hz, cis CO), 141.5 (d, J=22.9
Hz, =C(N)), 131.3 (s, ipso C(Ph)), 128.9 (s, meta CH(Ph)), 127.8
(d, J=6.7 Hz, ortho CH (Ph)), 126.8 (s, para CH (Ph)), 102.6
(s, dC(Ph)), 55.6 (CH), 52.1 (d, J=11.5 Hz, OCH3), 47.2 (CH),
25.7 (CH3), 21.6 (CH3), 21.4 (CH3), 21.0 (CH3). Anal. Calcd for
C20H22NO6PW: C, 40.91; H, 3.78. Found: C, 40.25; H, 3.50.
Diphosphetene 3. Yield: 27 mg, 57%. 31P NMR (162 MHz,
CDCl3): δ 28.0 (td, J=230.0, 8.7 Hz, 1P), -0.83 (td, J=230.0,
8.7 Hz, 1P). 1H NMR (400 MHz, CDCl3): δ 7.36-7.30 (m, 3H,
ArH), 7.19 (d, J=7.3 Hz, 2H, ArH), 3.90- 3.83 (sep, 2H, 2 ꢀ
CH), 2.38 (dd, J=17.8, 5.5 Hz, 3H, P-CH3), 2.24 (dd, J=17.8,
5.5 Hz, 3H, P-CH3), 1.24 (d, J=6.8 Hz, 6H, 2 ꢀ CH3), 1.19 (d,
J=6.8 Hz, 6H, 2 ꢀ CH3). 13C NMR (100 MHz, CDCl3): δ 198.2
(d, J=23.9 Hz, trans-CO), 197.6 (d, J=23.9 Hz, trans-CO),
196.1 (d, J=5.7 Hz, cis-CO), 195.9 (d, J=6.7 Hz, cis-CO), 150.1
(dd, J=38.2, 22.9 Hz, dC-N), 137.8 (dd, J=15.3, 8.6 Hz, ipso
C(Ph)), 129.0 (2 ꢀ CH), 128.9 (m, ortho and meta CH(Ph)),
128.3 (para CH(Ph)), 116.1 (dd, J=42.0, 20.4 Hz, dC(Ph)), 52.2
(d, J=4.8 Hz, 2 ꢀ CH), 26.8 (dd, J=10.5, 8.6 Hz, P-CH3),
24.0-23.7 (m, P-CH3, 2 ꢀ CH3), 21.7 (2 ꢀ CH3). Anal. Calcd
for C26H25NO10P2W2: C, 33.18; H, 2.68; N, 1.49. Found: C,
33.10; H, 1.94; N, 1.27.
Phosphole 5. Yield: 37 mg, 50%. 31P NMR (162 MHz,
1
CD2Cl2): δ 24.5 (t, J = 245.4 Hz, 1P). H NMR (400 MHz,
CDCl3): δ 7.62-7.57 (m, 3H, ArH), 7.50-7.46 (m, 3H, ArH),
7.24-7.13 (m, 4H, ArH), 3.96 (s, 3H, CO2CH3), 3.63 (s, 3H,
CO2CH3), 3.49-3.42 (sep, 2H, 2 ꢀ CH), 1.16 (d, J=6.6 Hz, 6H,
2 ꢀ CH3), 1.00 (d, J=6.6 Hz, 6H, 2 ꢀ CH3). 13C NMR (100
MHz, CDCl3): δ 197.8 (d, J=23.9 Hz, trans-CO), 195.8 (d, J=
6.7 Hz, cis-CO), 166.1 (d, J=16.2 Hz, RCOO), 161.8 (d, J=11.5
Hz, βCOO), 157.5 (d, J=9.5 Hz, dC(N)), 148.0 (d, J=16.2 Hz,
βC(COOMe)), 145.9 (d, J=37.2 Hz, RC(COOMe)), 134.5 (d, J=
35.5 Hz, ipso C(PhP)), 133.8 (d, J=14.3 Hz, ipso C (PhC)), 132.7
(d, J = 13.4 Hz, ortho CH(PhP)), 131.7 (d, J = 1.9 Hz, para
CH(PhP)), 129.5 (d, J=10.5 Hz, ortho CH(PhC)), 129.3 (d, J=
5.7 Hz, meta CH(PhC)), 128.9 (para CH(PhC)), 128.4 (meta
CH(PhP)), 126.3 (d, J=39.1 Hz, P-C(Ph)), 53.0 (OCH3), 52.3
(OCH3), 51.2 (2 ꢀ CH-N), 23.6 (2 ꢀ CH3), 22.2 (2 ꢀ CH3).
Exact mass: calcd for C31H30NO9P183W, 774.1161; found,
774.1141. Anal. Calcd for C31H30NO9PW: C, 48.02; H, 3.90;
N, 1.81. Found: C, 47.62; H, 3.78; N, 1.89.
Acknowledgment. The authors thank the Nanyang
Technological University in Singapore for the financial
support of this work and Dr. Li Yong Xin for the X-ray
crystal structure analyses.
Reaction of Aminophosphirene 2a with Dimethyl Acetylenedi-
carboxylate. Complex 2a (60 mg, 0.094 mmol) and dimethyl
acetylenedicarboxylate (27 mg, 0.188 mmol) were heated at
110 °C for 15 h in 1 mL of toluene. After evaporation of the solvent,
Supporting Information Available: X-ray crystal structure
analysis of compounds 2a, 3, and 4. This material is available
free of charge via the Internet at http://pubs.acs.org.