The chemistry of 3-aminophospholes

Article abstract of DOI:10.1021/om100085c

A 3-morpholinophosphole has been prepared from the appropriate 3-keto-4-phospholene oxide by reaction with morpholine in the presence of TiCl₄ as a catalyst, followed by reduction of the phosphoryl group by phenylsilane. Both theoretical and experimental studies show that the amino group enhances the reactivity of the diene but does not affect the lone pair at phosphorus. This observation has been used to devise a generating system for the transient phosphinidene complex [PhP-Fe(CO)₄] that has been trapped by alkynes and ethanol.

Full text of DOI:10.1021/om100085c

1862 Organometallics 2010, 29, 1862–1864
DOI: 10.1021/om100085c
The Chemistry of 3-Aminophospholes
Wei Luo, Ana Ciric, Rongqiang Tian, and Franc-ois Mathey*
Division of Chemistry & Biological Chemistry, School of Physical & Mathematical Sciences, Nanyang
Technological University, 21 Nanyang Link, Singapore 637371
Received February 3, 2010
Summary: A 3-morpholinophosphole has been prepared from
the appropriate 3-keto-4-phospholene oxide by reaction with
morpholine in the presence of TiCl4 as a catalyst, followed by
reduction of the phosphoryl group by phenylsilane. Both
theoretical and experimental studies show that the amino
group enhances the reactivity of the diene but does not affect
the lone pair at phosphorus. This observation has been used to
devise a generating system for the transient phosphinidene
complex [PhP-Fe(CO)4] that has been trapped by alkynes and
ethanol.
Introduction
Presently, only a few 2-aminophospholes have been des-
cribed in the literature, and no chemistry has ever been
developed around them.1 Moreover, 3-aminophospholes
are still completely unknown. Since it is well established that
phospholes are poorly aromatic,2 we can expect a strong
perturbation of their dienic system by a possible amino
Figure 1. Comparison between the frontier orbitals of phos-
pholes 1 and 2.
substituent. Such a substituent on the β position is expected
to sharply increase the basicity of the phosphorus lone pair,
which is normally rather low.3 Hereafter, we attempt to
partly fill this lack of data by describing the synthesis and
some chemistry of a 3-aminophosphole.
compare 1 and 2 by DFT computations at the B3LYP/
6-311þG(d,p) level.4
Results and Discussion
In order to have a better insight into the kind of electronic
perturbation that can be expected when grafting an amino
group on the β position of a phosphole ring, we decided to
The comparison between the frontier orbitals of 1 and 2 is
shown in Figure 1. The LUMO of 2 is shifted to higher
energy by 0.13 eV, but its shape is not significantly altered.
Whereas the HOMO of 1 is localized on the diene, the
HOMO of 2 contains significant contributions from the lone
pairs at P and N, and its energy sharply increases by 0.57 eV.
Finally, the HOMO-1, which corresponds to the lone pair at
P in 1, is not significantly boosted in energy. As we shall see,
these results nicely explain the chemistry of 3-aminophos-
pholes.
*Corresponding author. E-mail: fmathey@ntu.edu.sg.
(1) Tan, W. H.-L. W.; Foucaud, A. Tetrahedron Lett. 1988, 29, 4581.
~
(2) Cyranski, M. K.; Krygowski, T. M.; Katritzky, A. R.; Schleyer,
P. v. R. J. Org. Chem. 2002, 67, 1333. Mattmann, E.; Mathey, F.; Sevin, A.;
Frison, G. J. Org. Chem. 2002, 67, 1208.
(3) Quin, L. D.; Bryson, J. G.; Moreland, C. G. J. Am. Chem. Soc.
1969, 91, 3308.
(4) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo,
C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin,
A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma,
K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.;
Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.;
Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox,
D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong,
M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision B.05; Gaussian,
Inc.: Pittsburgh, PA, 2003.
The synthesis of our 3-aminophosphole starts from a
3-oxophosphol-4-ene oxide. Some work has been done on
such compounds in connection with the synthesis of phos-
phasugars.5 These products result from the allylic oxidation
(5) Reddy, V. K.; Rao, L. N.; Maeda, M.; Haritha, B.; Yamashita, M.
Heteroat. Chem. 2003, 14, 320. Yamashita, M.; Rao, L. N.; Reddy, V. K.;
Maeda, M.; Oshikawa, T.; Takahashi, M. Phosphorus Sulfur Silicon 2002,
177, 1661. Reddy, V. K.; Rao, L. N.; Maeda, M.; Oshikawa, T.; Takahashi,
M.; Yamashita, M. Synth. Commun. 2002, 32, 69. Bodalski, R.; Janecki, T.;
Galdecki, Z.; Glowka, M. Phosphorus Sulfur 1982, 14, 15. Kashman, Y.;
Awerbouch, O. Tetrahedron Lett. 1973, 34, 3217.
r
pubs.acs.org/Organometallics
Published on Web 03/05/2010
2010 American Chemical Society

Note
Organometallics, Vol. 29, No. 7, 2010 1863
of 2-phospholenes by CrO3. We have devised a new approach
based on the ozone cleavage of the exocyclic CdC double
bond of the easily accessible isomeric phosphole sulfide (3)6
(eq 1).
generation and trapping of [iPr2N-P-Fe(CO)4] from Na2Fe-
(CO)4.9 Although quite simple, his approach is restricted to
the amino substituent. The reaction of 5 with Fe2(CO)9
affords the [Fe(CO)4] complex 7. Upon complexation, the
31P resonance of 5 is shifted from -7 to þ61 ppm. Since the
reaction is clean and quantitative, the complex was used
without further purification. It readily reacts with dimethyl
acetylenedicarboxylate at 70 °C, but it appears that the
resulting 7-phosphanorbornadiene complex 8 is unstable
even under these mild conditions. Thus we followed the
same approach as for the study of the generation and
trapping of [ClP-W(CO)5].10 The reaction with DMAD
was performed in the presence of the trapping reagents. In
so doing, we were able to obtain the phosphirene complexes 9
and 10 from the appropriate alkynes and the secondary
phosphinite complex from ethanol (eq 3). It must be stressed
that the same scheme does not work when applied to
1-phenyl-3,4-dimethylphosphole, thus highlighting the higher
reactivity of 5. In line with the findings of Lammertsma, we
were unable to obtain the phosphirane complexes when using
the alkenes as trapping reagents.
The conversion of 4 into the corresponding 3-aminophos-
phole 5 is then carried out by reaction with morpholine with
TiCl4 as a catalyst, followed by in situ reduction of the
phosphoryl group by phenylsilane (eq 2).
Phosphole 5 displays two vinylic protons at 6.59 (2JHP=35
Hz) and 5.75 ppm (2JHP=30 Hz). The 13C spectrum shows a
β dC(N) at 160.77 and the corresponding R dCH at 109.09
ppm with no detectable C-P coupling. Due to its high
sensitivity toward hydrolysis and oxidation, phosphole 5
was more fully characterized as its P-W(CO)5 complex 6.
The 1JPW coupling of 219 Hz is especially noteworthy. It can
be compared with the similar coupling in the 1-phenyl-3,4-
dimethylphosphole P-W(CO)5 complex (214.7 Hz). Since
this value is correlated with the basicity of the P lone pair,7 it
seems to indicate that the amino substitution does not
significantly alter the basicity of P, contrary to what we
expected. It must be recalled that the lone pair orbital of 2 is
almost at the same level of energy as that of the correspond-
ing orbital of 1. Since we know that the electronic delocaliza-
tion is weak within the phosphole ring, this might explain this
observation.
Our theoretical results suggest that the main change in the
chemistry of 2 versus 1 is the boosted reactivity of the dienic
system. The main use of the dienic reactivity of phospholes is
the synthesis of the 7-phosphanorbornadiene precursors of
terminal phosphinidene complexes.8 This scheme is charac-
terized by the wide range of possible substituents at phos-
phorus but is limited to a few complexing groups, in practice
only Cr, Mo, and W(CO)5. We decided to check whether it
was possible to use a phosphole such as 5 to build a precursor
of [PhP-Fe(CO)4]. Lammertsma has already studied the
The modest yields probably reflect the modest stability of
the products. A generalization of this approach to other
complexing groups appears possible.
Experimental Section
NMR spectra were obtained on a JEOL ECA400 or JEOL
ECA400SL spectrometer. All spectra were recorded at 298 K
unless otherwise specified. HRMS spectra were obtained in ESI
mode on a Finnigan MAT95XP HRMS system (Thermo Elec-
tron Corp.). All reactions were performed under argon. Silica
gel (230-400 mesh) was used for the chromatographic separa-
tions. All commercially available reagents were used as received
from the suppliers. Most of the products show a high sensitivity
toward moisture, and their elemental analyses have been
replaced by exact mass measurements.
Isomeric Phosphole Sulfide 3. To a solution of 1-phenyl-3,
4-dimethylphosphole sulfide (2.0 g, 9.1 mmol) in 30 mL of THF
at -78 °C and under argon was added sodium bis(trimethyl-
silyl)amide (5 mL of a 2 M solution in THF) via a syringe. After
stirring for about 10 min, 4 mL of 3 N HCl was added via a
syringe; the mixture was stirred for another 10 min at -78 °C,
then slowly warmed to room temperature. After extraction, the
organic layer was dried with MgSO4. The residue was chromato-
graphed with CH2Cl2-hexane (70:30) to give 3. Yield: 1.4 mg,
70%. 31P NMR (162 MHz, CDCl3): δ 49.2. 1H NMR (400 MHz,
CDCl3): δ 2.10 (s, 3H, CH3), 3.11-3.21 (m, 2H, P-CH2), 5.24 (d,
J=1.84 Hz, 1H, dCH2), 5.40 (s, 1H, dCH2), 6.06 (d, J=25.64
Hz, 1H, P-CH), 7.40-7.47 (m, 3H, Ph), 7.75-7.81 (m, 2H, Ph).
13C NMR (100 MHz, CDCl3): δ 16.53 (d, J=17.2 Hz, CH3),
40.36 (d, J=60.35 Hz, P-CH2), 113.04 (d, J=13.42 Hz, dCH2),
127.52 (d, J = 78.55 Hz, P-CH), 128.61 (d, J = 12.46, Ph),
(6) Mathey, F. Tetrahedron 1972, 28, 4171.
(7) Mercier, F.; Mathey, F.; Afiong-Akpan, C.; Nixon, J. F.
J. Organomet. Chem. 1988, 348, 361.
(8) (a) Mathey, F.; Tran Huy, N. H.; Marinetti, A. Helv. Chim. Acta
2001, 84, 2938. (b) Lammertsma, K.; Vlaar, M. J. M. Eur. J. Org. Chem.
2002, 1127. (c) Lammertsma, K. Top. Curr. Chem. 2003, 229, 95. (d)
Mathey, F. Dalton Trans. 2007, 1861.
(9) Wit, J. B. M.; van Eijkel, G. T.; de Kanter, F. J. J.; Schakel, M.;
Ehlers, A. W.; Lutz, M.; Spek, A. L.; Lammertsma, K. Angew. Chem.,
Int. Ed. 1999, 38, 2596. Wit, J. B. M.; van Eijkel, G. T.; Schakel, M.;
Lammertsma, K. Tetrahedron 2000, 56, 137. Borst, M. L. G.; van der Riet,
N.Lemmens, R. H.; de Kanter, F. J. J.; Schakel, M.; Ehlers, A. W.; Mills, A. M.;
Lutz, M.; Spek, A. L.; Lammertsma, K. Chem.;Eur. J. 2005, 11, 3631.
(10) Duffy, M. P.; Mathey, F. J. Am. Chem. Soc. 2009, 131, 7534.

1864 Organometallics, Vol. 29, No. 7, 2010
Luo et al.
130.93 (d, J = 11.49 Hz, Ph), 131.76 (d, J = 28.7 Hz, Ph),
132.81 (d, J = 79.52, Ph), 145.48 (d, J = 9.58 Hz), 156.70 (d,
J=12.46 Hz).
are double due to the presence of two almost undistinguish-
able diastereomers. Exact mass: calcd for C20H18NO6P183W,
582.0374; found, 582.0372.
4-Ketophospholene (4). A 2.0 g (9.1 mmol) amount of 3 was
dissolved in 50 mL of CH2Cl2. A stream of ozone was bubbled
through the solution at -78 °C. Ozone treatment was termi-
nated when the mixture turned blue. A stream of O2 removed the
excess ozone; then an excess of dimethyl sulfide was added. The
mixture was slowly warmed to room temperature and stirred
overnight. After removal of the solvent, the product was puri-
fied by column chromatography with CH2Cl2-EtOH (40:1).
Yield: 1.46 mg, 78%. 31P NMR (162 MHz, CDCl3): δ 31.12. 1H
NMR (400 MHz, CDCl3): δ 2.08 (s, 3H, CH3), 2.79-2.99 (m,
2H, CH2), 7.22 (d, J=16.48 Hz, 1H, P-CH), 7.48-7.56 (m, 5H,
Ph). 13C NMR (100 MHz, CDCl3): δ 13.82 (d, J=16.11 Hz,
CH3), 37.78 (d, J=73.64 Hz, P-CH2), 129.21 (d, J=12.65 Hz,
Ph), 130.76 (d, J=10.36 Hz, Ph), 132.84 (d, J=2.3 Hz, Ph),
143.42 (d, J=82.84 Hz, P-CH), 158.03 (d, J=5.75 Hz), 197.12 (d,
J=19.56, CdO).
3-Aminophosphole (5). A 0.2 g (0.97 mmol) amount of 4 was
dissolved in 10 mL of CH2Cl2, followed by 1 mL (excess) of
morpholine. Then 0.4 mL of TiCl4 (1 M in toluene) was added
slowly at 0 °C. The mixture was slowly warmed to room
temperature, stirred for 4 h, and then filtered. The solvent was
evaporated, and the residue was dissolved in 10 mL of toluene.
PhSiH3 (0.2 mL, excess) was added to the solution, which was
refluxed for 6 h. The solvent was evaporated, and phosphole 5
was extracted with hexane. 31P NMR (162 MHz, CDCl3): δ
-7.6. 1H NMR (400 MHz, CDCl3): δ 2.16 (dd, J=1.4 and 2.7
Hz, 3H, CH3), 2.85-3.04 (dm, 4H, NCH2), 3.78-3.84 (m, 4H,
OCH2), 5.75 (dd, J=2.7, 30 Hz, 1H, P-CH), 6.59 (dm, J=35.26
Hz, 1H, P-CH), 7.23-7.47 (m, 5H, Ph). 13C NMR (100 MHz,
CDCl3): δ 17.45 (s, CH3), 51.75 (s, NCH2), 67.02 (s, OCH2),
109.09 (s, P-CHd), 145.77 (s, Me-Cd), 160.76 (d, J=10.5 Hz, d
C-N).
Triphenylphosphirene Iron Complex 9. Phosphole 5 was
obtained from 0.2 g of starting material 4. The phosphole was
dissolved in 10 mL of THF, Fe2(CO)9 (0.3 g, 0.82 mmol) was
added, the mixture was stirred for 2 h at room temperature and
monitored by 31P, and the peak at -7 shifted to 61 ppm. The
solvent was removed under vacuum, the residue was dissolved in
10 mL of toluene, and an excess of dimethyl acetylenedicarboxy-
late and diphenylacetylene were added. The reaction mixture
was then heated under argon at 70 °C overnight. After removal
of the solvent, the product was purified by chromatography with
hexane-CH2Cl2 (40:3). Yield: 83 mg, 18.9% (overall). 31P
NMR (162 MHz, CDCl3): δ -90.3. 1H NMR (400 MHz,
CDCl3): δ 7.33-7.88 (m, 15H, Ph). 13C NMR (100 MHz,
CDCl3): δ 127.02 (d, J=5.73 Hz, Ph), 128.42 (d, J=8.59 Hz,
Ph), 129.55 (s, Ph), 128.77 (d, J=11.45 Hz), 130.47 (d, J=5.72
Hz, Ph), 130.62 (d, J=6.68 Hz, Ph), 131.07 (s, Ph), 131.71 (s, Ph),
132 (d, J=14.31 Hz), 135.98 (d, J=17.18 Hz, P-C(Ph)), 213.22
(d, J = 22.9, CdO). Exact mass: calcd for C24H16O4PFe,
455.0136; found, 455.0145.
1,2-Diphenylphosphirene Iron Complex 10. The same experi-
ment as for 9 was used, with phenylacetylene instead of diphe-
nylacetylene. The product was purified by chromatography
with hexane-CH2Cl2 (35:5). Yield: 50 mg, 13.6% (overall).
1
31P NMR (162 MHz, CDCl3): δ -85.5. H NMR (400 MHz,
CDCl3): δ 8.50 (d, J=19.68, 1H, dCH-), 7.39-7.72 (m, 10H,
Ph). 13C NMR (100 MHz, CDCl3): δ 120.20 (d, J=4.77 Hz,
P-CHd), δ 125.65 (d, J=6.68 Hz, Ph), 128.62 (d, J=11.45 Hz),
129.43 (s, Ph), 130.43 (d, J=4.77, Ph), 131.13 (s, Ph), 131.81 (d,
J = 6.67 Hz, Ph), 131.99 (s, Ph), 136.94 (d, J = 18.3 Hz,
P-C(Ph)), 141.84 (d, J = 9.54 Hz), 213.15 (d, J = 22.9 Hz,
CdO). Exact mass: calcd for C18H12O4PFe, 378.9823; found,
378.9821.
3-Aminophosphole Tungsten Complex 6. Phosphole 5 was
made from 0.2 g of starting material 4 as described before. Then
0.5 mmol of [W(CO)5(THF)] in 10 mL of THF was added to the
phosphole 5, and the mixture was stirred overnight at room
temperature. Complex 6 was recrystallized from CH2Cl2. Yield:
169.6 mg, 30% overall. 31P NMR (162 MHz, CD2Cl2): δ 4.73
(JP-W=219.1 Hz). 1H NMR (400 MHz, CD2Cl2): δ 2.21 (s, 3H,
CH3), 2.93-3.04 (dm, 4H, NCH2), 3.77-3.79 (m, 4H, OCH2),
5.67 (d, J=32.28 Hz, 1H, P-CH), 6.63 (d, J=33.44 Hz, 1H,
P-CH), 7.37-7.38 (m, 3H, Ph), 7.49-7.54 (m, 2H, Ph). 13C
NMR (100 MHz, CD2Cl2): δ 17.06 (d, J=11.5 Hz, CH3), 51.40
(d, J=2.87 Hz, NCH2), 66.48 (d, J=1.92 Hz, OCH2), 107.1 (d,
J=49.8 Hz, P-CHd), 128.74 (d, J=10.54 Hz, Ph), 130.3 (s, Ph),
131.11 (d, J=12,46 Hz, Ph), 132.17 (d, J=40.29 Hz, P-C(Ph)),
133.21 (d, J=41.68 Hz, P-CHd), 147.78 (d, J=5.75 Hz, C-Me),
161.05 (d, J = 15.33 Hz, N-C), 199.56 (d, J = 18.2 Hz, trans
CdO), 196.59 (d, J=6.71 Hz, cis CdO). Most of the resonances
Secondary Phosphinite Iron Complex 11. The same experi-
ment as for 9 was used, with EtOH instead of diphenylacetylene.
The product was purified by chromatography with hexa-
ne-CH2Cl2 (35:5). Yield: 70 mg, 21.8% (overall). 31P NMR
(162 MHz, CDCl3): δ 153.34. 31P{1H} NMR: δ 153.36 (d, JP-H
=390). 1H NMR (400 MHz, CDCl3): δ 1.30 (t, J=6.88 Hz, 3H,
CH3), 3.84 (q, J=8.72 Hz, 2H, CH2), 7.92 (d, JP-H=391.4, 1H,
P-H), 7.54 (s, 3H, Ph), 7.70-7.75 (m, 2H, Ph). 13C NMR (100
MHz, CDCl3): δ 16.12 (d, J=7.66 Hz, CH3), 67.14 (d, J=11.5
Hz, CH2), 129.14 (d, J=10.54 Hz, Ph), 130.42 (d, J=10.54 Hz,
Ph), 132.19 (d, J = 1.91 Hz, Ph), 134.33 (d, J = 52.69 Hz,
P-C(Ph)), 212.37 (d, J = 22.04 Hz, CdO). Exact mass: calcd
for C12H12O5PFe, 322.9772; found, 322.9778.
Acknowledgment. The authors thank the Nanyang
Technological University in Singapore for the financial
support of this work.