1,3,2-diazaphosphinines: New versatile precursors of 1,2-azaphosphinines and polyfunctional phosphinines

Full text of DOI:10.1021/ja962736v

11978
J. Am. Chem. Soc. 1996, 118, 11978-11979
conversion of 1,3-azaphosphinines into phosphinines.2,13,14
Upon further heating at higher temperature with a second
equivalent of alkyne, these 1,2-azaphosphinines can, in turn,
be converted into phosphinines. In such a way, we have
prepared several polyfunctional phosphinines,15 as shown in the
following equation (eq 3).
1,3,2-Diazaphosphinines: New, Versatile Precursors
of 1,2-Azaphosphinines and Polyfunctional
Phosphinines
Narcis Avarvari, Pascal Le Floch, and Franc¸ois Mathey*
Laboratoire “He´te´roe´le´ments et Coordination”
URA CNRS 1499, DCPH, Ecole Polytechnique
91128 Palaiseau Cedex, France
ReceiVed August 6, 1996
Whereas all of the possible azaphosphinines are known to
date,1-3 our knowledge of diazaphosphinines is presently limited
to a couple of examples.4 We wish to describe here a very
simple access to 1,3,2-diazaphosphinines and their use to prepare
1,2-azaphosphinines and polyfunctional phosphinines. Recently,
Doxsee et al. have described the synthesis of 1,3,2-diazatitana-
cyclohexa-3,6-dienes by reaction of nitriles with Cp2TidCH2
or Cp2TiMe2.5-9 The reaction of such compounds with PCl3
and triethylamine directly affords 1,3,2-diazaphosphinines (eq
1).
This new synthetic pathway to azaphosphinines and phos-
phinines offers several distinct advantages: (a) its simplicity,
all of the syntheses can be carried out in one pot; (b) its yields,
the [4 + 2] cycloadditions take place under relatively mild
conditions (compare with 1,3-azaphosphinines2,13,14) and this
means high yields; (c) its versatility, two different alkynes can
be used and the reaction tolerates several functional groups such
as CO2Et, 2-py (pyridine), SiMe3, PPh2, and CH(OEt)2; (d) its
regioselectivity, in almost all cases, essentially one regioisomer
is obtained. On the basis of simple electronegativity arguments,
it is clear that both 1,3,2-diaza- and 1,2-azaphosphinines are
highly polarized molecules with substantial positive charge at
P and negative charge at C5. This favors a good regioselectivity.
These very reactive heterocycles have been characterized by
1H, 13C, and 31P NMR spectroscopies and mass spectrometry.10
They readily react at room temperature with protic reagents to
give the corresponding 1,2-dihydro-1,3,2-diazaphosphinines11
(eq 2).
(11) For 2: 80% yield; 31P δ 81.9 (C6D6). For 3: 85% yield; 31P δ
90.3 (CDCl3). For 4: 90% yield; 31P δ -1.7, 1J(PH) ) 642.3 Hz (CDCl3).
(12) Typical procedure: A solution of diazaphosphinine 1a (0.5 g, 2.4
× 10-3 mol) and 3-hexyne (0.975 g, 11.9 × 10-3 mol) in toluene (8 mL)
was stirred at 70 °C for 10 h in a closed Schlenk tube filled with nitrogen.
After the solution was cooled, the evaporation of toluene and unreacted
hexyne left 0.3 g (ca. 60%) of crude 6 as an orange oil. For 5: 60% yield;
NMR (C6D6) 31P δ 273.1, 1H δ 1.38 (s, 9H, tBu), 6.98-7.45 (m, 6H, Ph +
1
HC5), 8.64 (d, J(HP) ) 31.1 Hz, 1H, HC3); 13C δ 30.0 (s, Me), 40.4 (d,
More interestingly, their reaction with alkynes affords 1,2-
azaphosphinines12 with extrusion of one molecule of nitrile. This
[4 + 2] cycloaddition-cycloreversion process mimics the
3J(CP) ) 7.7 Hz, Me3C), 117.4 (d, 3J(CP) ) 31.9 Hz, C5), 152.8 (d, 2J(CP)
)
1
2
10.6 Hz, C4), 153.5 (d, J(CP) ) 74.9 Hz, C3), 177.0 (d, J(CP) ) 29.0 Hz,
C6); MS (Cl, NH3) m/z 230 (M+ + 1, 100). The crude 1,2-azaphosphinine
5 contains ca. 10% of its 2-phenyl isomer 5′ (13P δ 261.1). For 6: NMR
1
(1) 1,4-Azaphosphinines: Ma¨rkl, G.; Matthes, D. Angew. Chem., Int.
Ed. Engl. 1972, 11, 1019.
(C6D6) 31P δ 270.5; H δ 0.97 (t, 3H, Me), 1.14 (t, 3H, Me), 1.42 (s, 9H,
tBu), 2.37 (m, 2H, CH2), 2.63 (m, 2H, CH2), 7.05 (s, 1H, HC5); 13C: δ:
3
2
(2) 1,3-Azaphosphinines: Ma¨rkl, G.; Dorfmeister, G. Tetrahedron Lett.
1987, 28, 1093.
15.6 (s, Me), 18.0 (d, J(C-P) ) 12.6 Hz, Me), 24.8 (d, J(C-P) ) 27.3 Hz,
CH2), 27.6 (s, CH2), 31.0 (s, Me3C), 40.6 (d, 3J(C-P) ) 8.7 Hz, Me3C), 119.2
3
2
1
(3) 1,2-Azaphosphinines: Bourdieu, C.; Foucaud, A. Tetrahedron Lett.
1987, 28, 4673.
(d, J(C-P) ) 29.8 Hz, C5), 155.1 (d, J(C-P) ) 6.1 Hz, C4), 174.8 (d, J(C-P)
2
) 77.0 Hz, C3), 175.4 (d, J(C-P) ) 27.2 Hz, C6); MS (Cl, NH3) m/z 210
(4) A 1,2,4-diazaphosphinine has been mentioned in a review: Mem-
mesheimer, H.; Regitz, M. ReV. Heteroat. Chem. 1994, 10, 61. 2,4,6-
Triaryl-1,3,5-diazaphosphinines have been synthesized: Ma¨rkl, G.; Do¨rges,
C. Angew. Chem., Int. Ed. Engl. 1991, 30, 106. The λ5-derivatives are
better known: Granier, M.; Baceiredo, A.; Nieger, M.; Bertrand, G. Angew.
Chem., Int. Ed. Engl. 1990, 29, 1123.
(M+ + 1, 100).
(13) Ma¨rkl, G.; Do¨rges, C.; Riedl, T.; Kla¨rner, F.-G.; Lodwig, C.
Tetrahedron Lett. 1990, 31, 4589.
(14) Ma¨rkl, G.; Dorsch, S. Tetrahedron Lett. 1995, 36, 3839.
(15) For 7: 2-ethynylpyridine was heated with 1a in toluene at 100 °C
for 15 h; 85% yield; NMR (C6D6) 31P δ 202.5; 1H δ 9.57 (dd, 2J(HP) ) 37.3
Hz, 4J(HH) ) 1.4 Hz, H2, H6). Compound 7 contains 5% of the 2,5-isomer
(δ 201.3). For 8: Bis(trimethylsilyl)acetylene was heated with 1a in toluene
at 80 °C for 15 h. The 1,2-azaphosphinine thus formed (31P δ 305.5) was
further heated in toluene with more alkyne at 120 °C for 20 h (overall
yield 85%, 31P δ 266.5). For 9: (1) PhCtCSiMe3, 70 °C, 10 h, toluene;
1,2-azaphosphinine (31P δ 303.6); (2) PhCtCSiMe3, 90 °C, 10 h, toluene;
80% yield; NMR (C6D6) 31P δ 269.4; 1H δ 0.26 (d, 4J(HP) ) 1.6 Hz, SiMe3);
13C δ 3.0 (d, 3J(CP) ) 9.5 Hz, SiMe3). In 8, only the R- but not the â-silyl
groups are coupled with P. For 10: (1) HCtCSiMe3, 70 °C, 3 h, toluene;
1,2-azaphosphinine (31P δ 300.0); (2) HCtCSiMe3, 75 °C, 5 h, toluene;
85% yield; NMR (C6D6) 31P δ 254.6; 1H δ 0.36 (d, 4J(HP) ) 0.8 Hz, SiMe3),
(5) Doxsee, K. M.; Farahi, J. B. J. Am. Chem. Soc. 1988, 110, 7239.
(6) Doxsee, K. M.; Farahi, J. B. J. Chem. Soc., Chem. Commun. 1990,
1452.
(7) Doxsee, K. M.; Farahi, J. B.; Hope, H. J. Am. Chem. Soc. 1991,
113, 8889.
(8) Doxsee, K. M.; Juliette, J. J. J.; Mouser, J. K. M.; Zientara, K.
Organometallics 1993, 12, 4682.
(9) Petasis, N. A.; Fu, D.-K. Organometallics 1993, 12, 3776.
(10) Typical procedure: A solution of Cp2TiMe2 (1.9 g, 9 × 10-3 mol)
and pivalonitrile (1.52 g, 18 × 10-3 mol) in toluene (50 mL) was stirred at
65-68 °C for 4-5 d under nitrogen in a Schlenk tube. After the solution
was cooled to -20 °C, degassed PCl3 (1.25 g, 9 × 10-3 mol) was added
to the solution via a syringe. After the solution was to room temperature
and NEt3 (15-20 equiv) was added, the mixture was further heated for
2-3 h at 70 °C. After the reaction mixture was cooled, the resulting
suspension was filtered on a glass frit and the solvent evaporated under
vacuum. Crude 1a was thus obtained in 45% yield as an orange oil, very
sensitive to air and moisture. For 1a: NMR (C6D6) 31P δ 267.5; 1H δ 7.22
(d, 1H, 4J(HP) ) 4.4 Hz, C5H); 13C δ 29.5 (s, Me), 39.9 (d, 3J(CP) ) 4.5 Hz,
4
3
3
7.22 (dt, J(HP) ) 2.1 Hz, J(HH) ) 8.0 Hz, H4), 7.92 (dd, J(HP) ) 9.4 Hz,
H3, H5); 13C δ 0.7 (d, J(CP) ) 6.1 Hz, SiMe3). For 11: (1) PhCtCPPh2,
3
70 °C, 12 h, toluene; 1,2-azaphosphinine (31P δ 289.5 and -19.0, 2J(PP)
)
10.0 Hz); (2) PhCtCPPh2, 120 °C, 20 h, toluene; 80% yield; NMR (CDCl3)
31P δ 254.7 and -10.7, J(PP) ) 22.0 Hz; 13C δ 153.0 (dd, J(CP) ) 10.7
2
2
1
and 26.4 Hz, C3, C5), 166.7 (dd, J(CP) ) 26.0 and 88.7 Hz, C2, C6). For
12: (1) PhCtCCtCPh, 70 °C, 8 h, toluene; 1,2-azaphosphinine (31P δ
262.9); (2) PhCtCCtCPh, 100 °C, 8 h, toluene; 80% yield; NMR (CDCl3)
31P δ 198.1; 13C δ 89.3 (d, 3J(CP) ) 4.6 Hz, sp C), 95.0 (s, sp C), 141.9 (d,
2J(CP) ) 23.4 Hz, C ipso).
3
2
CMe3), 111.3 (d, J(CP) ) 44.1 Hz, C5H), 182.1 (d, J(C-P) ) 18.1 Hz, C4
and C6). For 1b: 31P NMR (toluene) δ 269.2.
S0002-7863(96)02736-9 CCC: $12.00 © 1996 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 118, No. 47, 1996 11979
Acknowledgment. We are grateful for financial support of this work
from the Ecole Polytechnique and CNRS.
Except in the case of diynes, it appears that the most shielded
sp carbon of the alkyne is connected to phosphorus in the final
phosphinine.
In addition to allowing us to study in depth the almost
unknown chemistry of 1,2-azaphosphinines and to prepare either
mono-, bi-, tri-, or tetrafunctional phosphinines, this synthetic
scheme underlines several interesting applications in coordina-
tion chemistry and might be generalized to other heteroatoms.
Supporting Information Available: Experimental data for 1a, 1b,
and 3-12 (3 pages). See any current masthead page for ordering and
Internet access instructions.
JA962736V