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A new addition reaction in organophosphorus chemistry
Tetrahedron Letters, Vol. 36, No. 12, pp. 2021-2024, 1995
Elsevier Science Ltd Printed in Great Britain 0040-4039/95 $9.50+0.00
Pergamon 0040-4039(95)00227-8
A New Addition Reaction in Organophosphorus Chemistry I Igor V. Shevchenko Southern Methodist University. Dallas, Texas 75275, U S A
Abstract: A new type of stepwise addition of alkylisocyanates 2a,b to two phosphorus atoms of methylenephosphinophosphorane I leads to the tbrmation of unusual compounds 4a, b and 5a,b with two phosphorus atoms of different coordination number ~.4P÷.k6P" and opposite formal charge Zwitterionic heterocyclic compounds with two phosphorus atoms of opposite charge and different coordination numbers in the cycle are a rarity. Only a few examples are known at present. 2 One possible method of synthesis would be the addition of unsaturated compounds to two phosphorus atoms of phosphinophosphoranes, containing tri- and penta-coordinate phosphorus atoms (Eq. l a). However, such a
(la)
/P
P~
(lb)
reaction was unknown until now. The only known reaction of similar type is the addition of alkynes to diphosphines (Eq. I b). 3 We have found that methylenephosphinophosphorane 14 reacts with methylisocyanate 2a and ethylisocyanate 2b via the unusual addition of a CN or CO double bond to two phosphorus atoms with the formation of the L4P +, k6P" zwitterionic compounds 4a,b and 5a,b (Eq. 2). These products are structural isomers and are formed in the ratio 7:1. This reaction is believed to proceed in two stages. First, the electrophilic carbon atom o f the isocyanate group attacks the trivalenl phosphorus atom forming the shortlived intermediate 3a,b whose negative charge can be delocalized over the unit O=C=N -. In the second stage, the nitrogen adds to the second phosphorus atom to give the major isomer as shown 4a,b. The formation of the minor isomer 5a,b is accounted
for by the alternative attack of the isocyanate oxygen at the second
phosphorus atom. The similar formation of two structural isomers depending on whether the O or N atom of [Me3Si(Me)N]2C=O adds to phosphorus was described by us earlier5
2021
2022
O
0
MexN"~N~Me
Me--N'~N~Me \/
R-N=C=O
(Et2N)2P--CH2--P--O
o' c,
1
C~
CI
2a,b
o'-" h
el = Me (a) R = Et (b) R
-
CI
_
3a,b
0
0
MexN-'~N~Me
Me",N~N~Me (2)
o
c,
o
5a,b
o \O c, 4a,b
The proposed structures of the isomers 4a,b and 5a,b are in agreement with the spectral data. For example, the 31p-NMR spectrum of 4a shows two doublets at 37 ppm and -140 ppm with a 2jpp value of 16.8 I-[z. These chemical shifts are in the usual regions for tetra- and hexa-coordinate phosphorus, respectively. The phosphonium diethylamino groups, the methyl groups of the urea unit and the protons of the bridging methylene group P-CH2-P are not equivalent in the I H-NMR spectrum. The lR-spectrum shows the band at 1660 cm -1, attributed to the CN double bond of the minor isomer. The rate of the reaction depends on the steric bulk of R. The reaction of methylisocyanate with 1 is complete within lh, whereas 4h is required with ethylisocyanate. In the case of tert-butylisocyanate the reaction does not occur at all. The reaction is reversible. In nonpolar solvents, such as hexane or ether, the equilibrium is shifted to the products 4a,b and 5a,b which precipitate from the reaction mixture as colourless crystals. Dissolving 4a, b and 5a,b in polar solvents, such as methylene chloride or chloroform, leads to their partial decomposition to the starting reagents. In fact, if sulfur is added to the reaction mixture, 1 is oxidised to give the known compound 6. 4 In this reaction 4a,b and 5a,b disappear within 12h leaving only 6 and the alkylisocyanate (Eq. 3). Compounds 4a,b and 5a,b are colourless crystalline products, stable in an inert atmosphere but decomposing when exposed to air. The structure of 4a was confirmed by X-ray analysis (Fig. 1).6 The phosphonium phosphorus atom, PI, is tetrahedrally coordinated, but the spread of angles is wide (99.9 - 110.9o), which is caused by incorporation of the phosphorus into the five-membered ring. A similar structure with the same distribution of angles was shown for the nonzwitterionic pentacyclic phosphonium cation "1
_Fn
[Et2P_CH2(CH2)2CH2 ] .6 The P1-CI-P2 angle of 108.6 ° suggests an overall tetrahedral geometry for the bridging methylene group. The coordination geometry at P2 is distorted octahedral with the major distortions
2023
0
1/8s8
s
4a,b ; 5a, b
=-
Me-.N/gXN...Me \ /
(Et2N)2P--CH2--P--O
6
+
2a, b
(3)
Cl~--~,~ CI CI
being associated with the four-membered ring (e.g. angle N3-P2-N4 is only 73.1o). This ring is planar (to within 0.014 A), with transoid methyl groups and a transannular P2...C6 distance of 2.29A. This geometry at P2
is
very
close
to
the
related
monocyclic
compound
of
six-coordinate phosphorus,
(CF3)2CI21~-N(C6H11)CCII'4(C6H11)9 Thus, it appears that the zwitterionic charge distribution in 4a has little effect on overall structure.
C8
C7
(34 C6~
N4
C9
C14 ~
C5
04
N5
CI3
Fig. 1. Crystal structure of 4a; selected bond lengths [A] and angles [o]: P1-N4 1.635(4), P1-N5 1.621(4), P1-CI 1.781(4), P1-C2 1.838(4), P2-NI 1.825(4), P2-C1 1.896(4), P2-N2 1.749(4), P2-N3 1.768(3), P2-O2 1.760(3), P2-O3 1.803(3), C2-N1 1.342(4X N4-P1-N5 110.9(2), C1-PI-C2 99.9(2), P1-C1-P2 108.6(2), P1-C2-N I 110.3(3), P2-N 1-C2 122.5(3), N 1-P2-C1 91.4(2), N2-P2-N3 73.1(2), O2-P2-O3 87.2(1 ). In a typical experiment, a solution of I (0.30g, 0.54 mmol) in 4 ml of ether was treated with 1.35 mmol of alkylisocyanate. The solution was allowed to stay 24h at 20 oc and then cooled for 24h at -20 oc. A colourless crystalline product was tbrmed, which was filtered and dried in vacuo at 5-10-2 mm. 4a + 5a: Yield 0.24 g (72%), m.p. 115-117 oc. IH-NMR (200MHz, CDC13, 8, ppm), the major isomer: 1.17 (t, 3JHH 7.1 Hz, 6H, Et2N), 1.22 (t, 3JHH = 7.1 Hz, 6H, Et2N), 2.19 (dt, 2JpH = 11.1 Hz, 2JHH = 15.5 Hz, 1H, PCH2P), 2.52 (d, 3JpH = 13.9 Hz, 3H, MEN), 2.72 (d, 3JpH - 15.2 Hz, 3H, MEN), 2.89 (dr, 2JpH - 15.6 Hz,
2024
2JHH = 15.5 Hz, IH, PCH2P), 3.04 (dd, 3JpH = 6.5 Hz, 4JpH = 1.1 Hz, 3H, MEN), 3.06-3.28 (m, 8H, Et2N). 31p-NMR (81MHz, CDCI 3, ppm); the major isomer: 37.35 (d, 2jpp _ 16.8 Hz), -140.55 (d, 2jpp = 16.8 Hz); the minor isomer: 37.03 (d, 2jpp - 31.2 Hz), -134.18 (d, 2jpp _ 31.2 Hz).
4b + 5b: Yield 0.21 g (63%),
decomposes at >85 oc. 1H-NMR (200MHz, CDCI 3, 6, ppm), the major isomer: 0.79 (t, 3JHH = 7.0 Hz, 3H, EtN), 1.15 (t, 3JHH = 7.1 Hz, 6H, Et2N), 1.20 (t, 3JI-IH = 7.1 Hz, 6H, Et2N), 2.13 (dt, 2JpH - 10.7 Hz, 2JHH = 15.3 Hz, 1H, PCH2P), 2.46 (d, 3JpH = 13.5 Hz, 31-t, MEN), 2.67 (d, 3JpH = 15.3 Hz, 3H, MEN), 2.88 (dl, 2JpH = 15.4 Hz, 2JHH - 15.3 Hz, 1H, PCH2P), 2.95-3.35 (m, 8H, Et2N), 3.50-3.77 (m, 2H, EtN).
31p.
NMR (81MHz, CDCI 3, ppm); the major isomer: 36.82 (d, 2jpp = 16. I Hz), -140.07 (d, 2jpp = 16.1 Hz); the minor isomer: 35.31 (d, 2jpp = 33.7 Hz), -132.84 (d, 2jpp _ 33.7 Hz). ACKNOWLEDGEMENTS The author thanks Dr. S.N.Sereda and E.B.Rusanov for the X-ray analysis of compound 4a, as well as Pro£ M.Lattman for the help in preparing this publication. REFERENCES AND NOTES 1.
Dedicated to Professor Alan H. Cowley on the occasion of his 60th birthday.
2.
a) Zal'tsman, I.S.; Bespal'ko, G. K ; Marchenko, A.P.; Pinchuk, A.M. Zh. Ohshch. Khim. 1990, 60, 21752176; b) Shevchenko, I.V.: Fischer, A.; Jones, P.G.; Schmutzler, R. ('hem. Ber. 1992, 125, 1325-1332; c) Boeske, J.; Niecke, E.: Krebs, B.; i,~ge, M.; Henkel, G. ("hem. Ber. 1992, 125, 2631-2634.
3.
a) Shaw, M.A.; Tebby, J.C.: Ward, R.S.; Williams, D.H J. f'hem. Soc. ((') 1970, 504-507; b) Hughes, A.N.; Jafry, S.W.S.J. Heterocyclic. ('hem. 1969, 6, 991-992.
4.
Shevchenko, I.V.; Schmutzler, R. Heteroatom ('hem. 1993, 4, 307-312.
5.
Shevchenko, I.V.; Krill, J.: Fischer A.; Jones, P.G.; Schmutzler, R. Heteroatom ('hem. 1993, 4, 565-569.
6.
Crystal structure analysis of 4a. Crystal data: C20H31CI4N504P 2, M - 609.26, monoclinic, a 9.801(9), b = 17.382(3), c = 17.201(4) A, f5 - 106.51(4) o V = 2809.4/~3, Z - 4, d c - 1.44 g cm -3, space group P21/c, p. = 5.7 cm -1, F(000) - 1264. A single crystal was mounted in a glass capillary and measured with an Enraf Nonius CAD-4 diffractometer; scan mode o)/20 (o)/O = 1.2), graphite monochromator, Mo-Kct radiation (~, = 0.71073 A), T = 293 OK, 1o < O < 26 o, 5510 unique measured reflections, 3355 with I > 3g(1). The structure was solved by direct methods and refined anisotropically (full matrix least squares). Positions of 70% of the H-atoms were located in the difference Fourier maps, while positions of the remaining atoms were calculated. All H-atoms were included in the final refinements with the fixed positional and thermal (Bis o = 5 A 2) parameters. R - 0.045, R w = 0.061, GOF =- 1.78 (316 refined parameters), the weightings scheme w = (cr2F + 0.0016F2) -1. The computer PDP-11/23+ and the SDP-PLUS programme package 7 were used. Further details of the crystal structure are available from the Cambridge Crystallographic Data Centre, University Chemical Lab., Lensfield Road, Cambridge CB2 IEW, U.K. Requests shoud be accopanied by a full literature citation for this communication.
7.
Frenz, B.A. in ¢ "ompmtng m ("r)'stallography: Schenk, H., Olthof-Hazekamp, R., van Koningsveld, H., Bassi, G.C.; Delft Univ. Press, Delft, Holland, 1976, 64-71.
8.
Gomelya, N.D.; Feshcbenko N.G.; Chernega, AN.; Antipin, M.Yu.; Struchkov, Yu.T.; Boldeskul, I.E .I. Obshch. Khtm. 1985, 55, 1733-1738.
9.
Kennepohl, D.K.; Santarsiero, B.D.; Cavell, R.G. lnorg. ("hem. 1990, 29, 5081-5087.
(Received in USA 14 September 1994; revised 24 January 1995; accepted 31 January 1995)
Elsevier Science Ltd Printed in Great Britain 0040-4039/95 $9.50+0.00
Pergamon 0040-4039(95)00227-8
A New Addition Reaction in Organophosphorus Chemistry I Igor V. Shevchenko Southern Methodist University. Dallas, Texas 75275, U S A
Abstract: A new type of stepwise addition of alkylisocyanates 2a,b to two phosphorus atoms of methylenephosphinophosphorane I leads to the tbrmation of unusual compounds 4a, b and 5a,b with two phosphorus atoms of different coordination number ~.4P÷.k6P" and opposite formal charge Zwitterionic heterocyclic compounds with two phosphorus atoms of opposite charge and different coordination numbers in the cycle are a rarity. Only a few examples are known at present. 2 One possible method of synthesis would be the addition of unsaturated compounds to two phosphorus atoms of phosphinophosphoranes, containing tri- and penta-coordinate phosphorus atoms (Eq. l a). However, such a
(la)
/P
P~
(lb)
reaction was unknown until now. The only known reaction of similar type is the addition of alkynes to diphosphines (Eq. I b). 3 We have found that methylenephosphinophosphorane 14 reacts with methylisocyanate 2a and ethylisocyanate 2b via the unusual addition of a CN or CO double bond to two phosphorus atoms with the formation of the L4P +, k6P" zwitterionic compounds 4a,b and 5a,b (Eq. 2). These products are structural isomers and are formed in the ratio 7:1. This reaction is believed to proceed in two stages. First, the electrophilic carbon atom o f the isocyanate group attacks the trivalenl phosphorus atom forming the shortlived intermediate 3a,b whose negative charge can be delocalized over the unit O=C=N -. In the second stage, the nitrogen adds to the second phosphorus atom to give the major isomer as shown 4a,b. The formation of the minor isomer 5a,b is accounted
for by the alternative attack of the isocyanate oxygen at the second
phosphorus atom. The similar formation of two structural isomers depending on whether the O or N atom of [Me3Si(Me)N]2C=O adds to phosphorus was described by us earlier5
2021
2022
O
0
MexN"~N~Me
Me--N'~N~Me \/
R-N=C=O
(Et2N)2P--CH2--P--O
o' c,
1
C~
CI
2a,b
o'-" h
el = Me (a) R = Et (b) R
-
CI
_
3a,b
0
0
MexN-'~N~Me
Me",N~N~Me (2)
o
c,
o
5a,b
o \O c, 4a,b
The proposed structures of the isomers 4a,b and 5a,b are in agreement with the spectral data. For example, the 31p-NMR spectrum of 4a shows two doublets at 37 ppm and -140 ppm with a 2jpp value of 16.8 I-[z. These chemical shifts are in the usual regions for tetra- and hexa-coordinate phosphorus, respectively. The phosphonium diethylamino groups, the methyl groups of the urea unit and the protons of the bridging methylene group P-CH2-P are not equivalent in the I H-NMR spectrum. The lR-spectrum shows the band at 1660 cm -1, attributed to the CN double bond of the minor isomer. The rate of the reaction depends on the steric bulk of R. The reaction of methylisocyanate with 1 is complete within lh, whereas 4h is required with ethylisocyanate. In the case of tert-butylisocyanate the reaction does not occur at all. The reaction is reversible. In nonpolar solvents, such as hexane or ether, the equilibrium is shifted to the products 4a,b and 5a,b which precipitate from the reaction mixture as colourless crystals. Dissolving 4a, b and 5a,b in polar solvents, such as methylene chloride or chloroform, leads to their partial decomposition to the starting reagents. In fact, if sulfur is added to the reaction mixture, 1 is oxidised to give the known compound 6. 4 In this reaction 4a,b and 5a,b disappear within 12h leaving only 6 and the alkylisocyanate (Eq. 3). Compounds 4a,b and 5a,b are colourless crystalline products, stable in an inert atmosphere but decomposing when exposed to air. The structure of 4a was confirmed by X-ray analysis (Fig. 1).6 The phosphonium phosphorus atom, PI, is tetrahedrally coordinated, but the spread of angles is wide (99.9 - 110.9o), which is caused by incorporation of the phosphorus into the five-membered ring. A similar structure with the same distribution of angles was shown for the nonzwitterionic pentacyclic phosphonium cation "1
_Fn
[Et2P_CH2(CH2)2CH2 ] .6 The P1-CI-P2 angle of 108.6 ° suggests an overall tetrahedral geometry for the bridging methylene group. The coordination geometry at P2 is distorted octahedral with the major distortions
2023
0
1/8s8
s
4a,b ; 5a, b
=-
Me-.N/gXN...Me \ /
(Et2N)2P--CH2--P--O
6
+
2a, b
(3)
Cl~--~,~ CI CI
being associated with the four-membered ring (e.g. angle N3-P2-N4 is only 73.1o). This ring is planar (to within 0.014 A), with transoid methyl groups and a transannular P2...C6 distance of 2.29A. This geometry at P2
is
very
close
to
the
related
monocyclic
compound
of
six-coordinate phosphorus,
(CF3)2CI21~-N(C6H11)CCII'4(C6H11)9 Thus, it appears that the zwitterionic charge distribution in 4a has little effect on overall structure.
C8
C7
(34 C6~
N4
C9
C14 ~
C5
04
N5
CI3
Fig. 1. Crystal structure of 4a; selected bond lengths [A] and angles [o]: P1-N4 1.635(4), P1-N5 1.621(4), P1-CI 1.781(4), P1-C2 1.838(4), P2-NI 1.825(4), P2-C1 1.896(4), P2-N2 1.749(4), P2-N3 1.768(3), P2-O2 1.760(3), P2-O3 1.803(3), C2-N1 1.342(4X N4-P1-N5 110.9(2), C1-PI-C2 99.9(2), P1-C1-P2 108.6(2), P1-C2-N I 110.3(3), P2-N 1-C2 122.5(3), N 1-P2-C1 91.4(2), N2-P2-N3 73.1(2), O2-P2-O3 87.2(1 ). In a typical experiment, a solution of I (0.30g, 0.54 mmol) in 4 ml of ether was treated with 1.35 mmol of alkylisocyanate. The solution was allowed to stay 24h at 20 oc and then cooled for 24h at -20 oc. A colourless crystalline product was tbrmed, which was filtered and dried in vacuo at 5-10-2 mm. 4a + 5a: Yield 0.24 g (72%), m.p. 115-117 oc. IH-NMR (200MHz, CDC13, 8, ppm), the major isomer: 1.17 (t, 3JHH 7.1 Hz, 6H, Et2N), 1.22 (t, 3JHH = 7.1 Hz, 6H, Et2N), 2.19 (dt, 2JpH = 11.1 Hz, 2JHH = 15.5 Hz, 1H, PCH2P), 2.52 (d, 3JpH = 13.9 Hz, 3H, MEN), 2.72 (d, 3JpH - 15.2 Hz, 3H, MEN), 2.89 (dr, 2JpH - 15.6 Hz,
2024
2JHH = 15.5 Hz, IH, PCH2P), 3.04 (dd, 3JpH = 6.5 Hz, 4JpH = 1.1 Hz, 3H, MEN), 3.06-3.28 (m, 8H, Et2N). 31p-NMR (81MHz, CDCI 3, ppm); the major isomer: 37.35 (d, 2jpp _ 16.8 Hz), -140.55 (d, 2jpp = 16.8 Hz); the minor isomer: 37.03 (d, 2jpp - 31.2 Hz), -134.18 (d, 2jpp _ 31.2 Hz).
4b + 5b: Yield 0.21 g (63%),
decomposes at >85 oc. 1H-NMR (200MHz, CDCI 3, 6, ppm), the major isomer: 0.79 (t, 3JHH = 7.0 Hz, 3H, EtN), 1.15 (t, 3JHH = 7.1 Hz, 6H, Et2N), 1.20 (t, 3JI-IH = 7.1 Hz, 6H, Et2N), 2.13 (dt, 2JpH - 10.7 Hz, 2JHH = 15.3 Hz, 1H, PCH2P), 2.46 (d, 3JpH = 13.5 Hz, 31-t, MEN), 2.67 (d, 3JpH = 15.3 Hz, 3H, MEN), 2.88 (dl, 2JpH = 15.4 Hz, 2JHH - 15.3 Hz, 1H, PCH2P), 2.95-3.35 (m, 8H, Et2N), 3.50-3.77 (m, 2H, EtN).
31p.
NMR (81MHz, CDCI 3, ppm); the major isomer: 36.82 (d, 2jpp = 16. I Hz), -140.07 (d, 2jpp = 16.1 Hz); the minor isomer: 35.31 (d, 2jpp = 33.7 Hz), -132.84 (d, 2jpp _ 33.7 Hz). ACKNOWLEDGEMENTS The author thanks Dr. S.N.Sereda and E.B.Rusanov for the X-ray analysis of compound 4a, as well as Pro£ M.Lattman for the help in preparing this publication. REFERENCES AND NOTES 1.
Dedicated to Professor Alan H. Cowley on the occasion of his 60th birthday.
2.
a) Zal'tsman, I.S.; Bespal'ko, G. K ; Marchenko, A.P.; Pinchuk, A.M. Zh. Ohshch. Khim. 1990, 60, 21752176; b) Shevchenko, I.V.: Fischer, A.; Jones, P.G.; Schmutzler, R. ('hem. Ber. 1992, 125, 1325-1332; c) Boeske, J.; Niecke, E.: Krebs, B.; i,~ge, M.; Henkel, G. ("hem. Ber. 1992, 125, 2631-2634.
3.
a) Shaw, M.A.; Tebby, J.C.: Ward, R.S.; Williams, D.H J. f'hem. Soc. ((') 1970, 504-507; b) Hughes, A.N.; Jafry, S.W.S.J. Heterocyclic. ('hem. 1969, 6, 991-992.
4.
Shevchenko, I.V.; Schmutzler, R. Heteroatom ('hem. 1993, 4, 307-312.
5.
Shevchenko, I.V.; Krill, J.: Fischer A.; Jones, P.G.; Schmutzler, R. Heteroatom ('hem. 1993, 4, 565-569.
6.
Crystal structure analysis of 4a. Crystal data: C20H31CI4N504P 2, M - 609.26, monoclinic, a 9.801(9), b = 17.382(3), c = 17.201(4) A, f5 - 106.51(4) o V = 2809.4/~3, Z - 4, d c - 1.44 g cm -3, space group P21/c, p. = 5.7 cm -1, F(000) - 1264. A single crystal was mounted in a glass capillary and measured with an Enraf Nonius CAD-4 diffractometer; scan mode o)/20 (o)/O = 1.2), graphite monochromator, Mo-Kct radiation (~, = 0.71073 A), T = 293 OK, 1o < O < 26 o, 5510 unique measured reflections, 3355 with I > 3g(1). The structure was solved by direct methods and refined anisotropically (full matrix least squares). Positions of 70% of the H-atoms were located in the difference Fourier maps, while positions of the remaining atoms were calculated. All H-atoms were included in the final refinements with the fixed positional and thermal (Bis o = 5 A 2) parameters. R - 0.045, R w = 0.061, GOF =- 1.78 (316 refined parameters), the weightings scheme w = (cr2F + 0.0016F2) -1. The computer PDP-11/23+ and the SDP-PLUS programme package 7 were used. Further details of the crystal structure are available from the Cambridge Crystallographic Data Centre, University Chemical Lab., Lensfield Road, Cambridge CB2 IEW, U.K. Requests shoud be accopanied by a full literature citation for this communication.
7.
Frenz, B.A. in ¢ "ompmtng m ("r)'stallography: Schenk, H., Olthof-Hazekamp, R., van Koningsveld, H., Bassi, G.C.; Delft Univ. Press, Delft, Holland, 1976, 64-71.
8.
Gomelya, N.D.; Feshcbenko N.G.; Chernega, AN.; Antipin, M.Yu.; Struchkov, Yu.T.; Boldeskul, I.E .I. Obshch. Khtm. 1985, 55, 1733-1738.
9.
Kennepohl, D.K.; Santarsiero, B.D.; Cavell, R.G. lnorg. ("hem. 1990, 29, 5081-5087.
(Received in USA 14 September 1994; revised 24 January 1995; accepted 31 January 1995)