Synthesis of a mixed phosphonium-sulfonium bisylide R3P=C= SR2

Article abstract of DOI:10.1002/anie.200704071

Mixing it up: The first persistent mixed phosphorus-sulfur bisylide has been synthesized (see scheme). Its formation was clearly demonstrated by its chemical reactivity, such as by methylation and complexation with Cu^I ions. DFT calculations on a model compound indicate that they are highly polarized species as a result of the interaction of the lone pairs of electrons on the central carbon atom with only the phosphonium function. (Chemical Equation Presented).

Full text of DOI:10.1002/anie.200704071

Communications
DOI: 10.1002/anie.200704071
Mixed Bisylides
= =
Synthesis of a Mixed Phosphonium–Sulfonium Bisylide R3P C SR2**
Sergio Pascual, Matthew Asay, Ona Illa, Tsuyoshi Kato, Guy Bertrand, Nathalie Saffon-
Merceron, VicençBranchadell, and Antoine Baceiredo*
Phosphonium and sulfonium ylides are highly nucleophilic
species, which feature a totally different reactivity. Whereas
the former have been used extensively for olefination
reactions,[1] the later have mostly been involved in epoxida-
tion reactions.[2] Carbodiphosphoranes (A) contain two
cumulated phosphorus ylide functions, and formally possess
a carbon atom with two negative charges, which are stabilized
by two phosphonium groups. Since their discovery in 1961 by
Ramirez et al.,[3] their unique bonding system and reactivity
have attracted considerable interest.[1a,4,5] In contrast, only
one example of a sulfur-containing bisylide (B) has been
reported.[6]
phosphorus-carbon-sulfur (PCS) skeleton, appeared to be a
potential precursor for the desired cumulene C.
Treatment of bis(diisopropylamino)phosphenium tri-
flate[7] with two equivalents of diphenylsulfonium ylide in
THF solution at À788Cgave C-phosphonium sulfonium ylide
1 in quantitative yield, which could be characterized in
solution (31P NMR: d = 53.0 ppm). However, ylide 1 appeared
to be thermally labile, and therefore was treated in situ with
one equivalent of MeOTf at À788C. The P-methyl derivative
2 was isolated as a white powder in 80% yield, and X-ray
quality single crystals were grown from a CH2Cl2 solution at
À208C(Scheme 1, Figure 1a). [8]
Here we report the synthesis and characterization of the
first persistent mixed phosphorus–sulfur bisylide (C). Such
compounds have never been isolated or even observed by
spectroscopic methods.
Scheme 1. Synthesis of sulfonium phosphaylide 2. Ph=phenyl, Tf=tri-
flate.
Abstraction of a proton from the corresponding conju-
gated acid is the classical method for preparing ylides; thus,
phosphonium salt 2, (Scheme 1) which already features the
[*] Dr. S. Pascual, Dr. O. Illa, Dr. T. Kato, Dr. N. Saffon-Merceron,
Dr. A. Baceiredo
Laboratoire HØtØrochimie Fondamentale et AppliquØe du CNRS
(UMR 5069)
UniversitØ Paul Sabatier
118 route de Narbonne, 31062 Toulouse Cedex 9 (France)
Fax: (+33)5-6155-8204
E-mail: baceired@chimie.ups-tlse.fr
Homepage: http://hfa.ups-tlse.fr
Figure 1. X-ray crystal structures of 2 (a) and 5 (b). H atoms and the
triflate anion (for 2) are omitted for clarity.[8] Thermal ellipsoids are
drawn at the 50% level. Selected bond lengths [Š] and angles [8].
2: P-C1 1.721(5), S-C1 1.690(4), P-C2 1.796(4), S-C3 1.810(5), P-C1-S
118.0(3). 5: P-C1 1.709(5), S-C1 1.677(5), P-C2 1.804(5), C1-Cu
1.903(4), N1-Cu1 1.874(4), P-C1-S 115.3(2), C1-Cu-N 176.97(18),
S-C1-Cu 125.7(3), P-C1-Cu 118.7(2).
M. Asay, Prof. G. Bertrand
UCR-CNRS Joint Research Chemistry Laboratory (UMI 2957)
Department of Chemistry
University of California
Riverside, CA 92521-0403 (USA)
The cumulene 3 was cleanly generated at À788Cby
deprotonation of the corresponding salt 2 with either
potassium or sodium hexamethyldisilazane (Scheme 2). The
neutral structure of 3 was indicated by its very high solubility
in nonpolar solvents such as pentane. Derivative 3 displays a
singlet signal at d = + 44.0 ppm in the 31P{1H} NMR spec-
trum, while the central carbon atom appears as a doublet at
d = 36 ppm (JPC = 86.4 Hz) in the 13CNMR spectrum.
Although 3 is stable for days at temperatures lower than
À208C, it decomposes (t1/2 = 10 h, in C6D6) at room temper-
ature to give a complex mixture.
Prof. V. Branchadell
Departament de Química
Universitat Autònoma de Barcelona
08193 Bellaterra (Spain)
[**] We thank Prof. H. Gornitzka for the X-ray diffraction studies of
derivatives 2 and 4. Financial support from the CNRS, LEA-368, NSF
(CHE 0518675), and Spanish Ministerio de Educación y Ciencia
(CTQ2004-01067/BQU) are gratefully acknowledged. We also thank
the French Minist›re des Affaires Etrang›res (Eiffel grant for M.A.),
and Spanish Ministerio de Educación y Ciencia (grant for S.P.).
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
9078
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2007, 46, 9078 –9080
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Angewandte
Chemie
Figure 3. Highest occupied molecular orbitals of 6: HOMO (left) and
HOMO-1 (right).
À
pair of electrons on the Catom, while HOMO-1 is the p(P C)
bonding orbital, which is strongly polarized towards the C
atom.
Scheme 2. Synthesis and reactivity of bisylide 3.
À À
In the P C S moiety of 6, the NBO procedure identified a
=
À
All attempts to grow X-ray quality single crystals for
diffraction analysis failed because of the high reactivity of 3.
However, the formation of 3 was clearly demonstrated by its
chemical reactivity. Addition of MeI to a solution of 3 in THF
cleanly and quantitatively gave the C-methylated salt 4, which
was fully characterized, including by X-ray diffraction anal-
ysis.[8] Furthermore, we also successfully synthesized the CuI
complex 5 by the reaction of 2 with copper chloride in the
presence of an excess of potassium hexamethyldisilazane
(KHMDS). X-ray quality crystals of 5 were grown from a
toluene solution, and its structure[8] (Figure 1b) showed a
similar geometry to that of a carbodiphosphorane–CuI com-
P Cbond and a C S bond, along with lone pair electrons on
À
Cand S atoms. The p(P C) orbital has a low occupancy
(1.663) and it is strongly polarized toward the Catom (88% of
contribution), which could also be viewed as a second lone
pair of electrons on the Catom. The occupancy of the
corresponding antibonding orbital (with an 88% contribution
from the P atom) is 0.171.
Contrary to the carbodiphosphorane case where the ns
orbital is stabilized by favorable interactions with s*P-R
orbitals (negative hyperconjugation),[10] the antiperiplanar
relationship between the nsC and nS orbitals in P,S bisylides is
destabilizing.[11] This finding explains the small variation of
plex.[9] The P1 C1 S1 angle is rather acute (115.38) and the
the S Cbond length compared to that of the P Cbond after
the deprotonation of 7 [Eq. (1)].
À
À
À
À
À
À
P C1 (1.709 Š) and S C1 bond lengths (1.677 Š) are slightly
shorter than those of the corresponding protonated cation 2.
To gain insight into the electronic structure of 3,
calculations by geometry optimization, natural population
analysis (NPA), and natural bond orbital (NBO) analysis
=
were performed on the model compound 6 (R NMe2) and its
protonated triflate salt 7. The geometries of 6 and 7 are shown
in Figure 2.
The NPA shows (Table 1) that the central carbon atom of
6 bears a strong negative charge (À1.357 a.u.), which is
compensated by the positive charges of the SPh2 and P(Me)-
(NMe2)2 fragments. Upon protonation, the negative charge of
the central carbon atom slightly decreases and most of the
positive charge (0.320 a.u.) goes to the P(Me)(NMe2)2 frag-
ment.
Table 1: Natural population analysis[a] of 6 and 7 (R=NMe2).
Figure 2. Structures of 6 (a) and 7 (b) optimized at the B3LYP/6-
31+G(d,p) level of calculation. Interatomic distances are in Š and
bond angle in degrees. H atoms and the triflate anion (for 7) are
omitted for clarity.
Fragment
C[b]
H
S
SPh2
P
PMeR2
6
7
À1.357
À1.235
0.874
0.926
0.585
0.797
1.947
2.055
0.771
1.049
0.315
The optimized geometry of 7 agrees reasonably well with
the experimentally obtained structure of 2. Each molecule
[a] In arbitrary units (a.u.). [b] Central C atom.
À À
shows a strongly bent P C S arrangement. The deprotona-
À
tion essentially affects only the P Cbond, as can be seen by
As expected, because of the high negative charge density
on the central carbon atom, the gas-phase proton affinity of 6
(290.3 kcalmolÀ1) is larger than that of carbodiphosphoranes
(270–280 kcalmolÀ1).[12]
the larger variation in bond lengths (DP-C = 0.042 Š; DS-C
0.018 Š), and in the Wiberg bond indexes (DP-C: 0.320; DC-S
=
:
0.134).
Figure 3 shows the two highest occupied molecular
orbitals (HOMOs) of 6. The HOMO is an orbital of
s symmetry which corresponds mainly to the in-plane lone
The preparation of such derivatives should be of major
significance because of the synthetic impact of both types of
ylides (P and S).
Angew. Chem. Int. Ed. 2007, 46, 9078 –9080
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 9079
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Communications
PCH3), 7.07–7.24 (m, 6H, CHarom), 8.07–8.10 ppm (m, 4H, CHarom);
Experimental Section
13C NMR (CDCl3, 258C, 75 Hz): d = 11.3 (d, 2JCP = 11.1 Hz, CH3),
All manipulations were performed under an inert atmosphere of
1
3
17.9 (d, JCP = 96.1 Hz, PCH3), 24.3 (d, JCP = 2.8 Hz, CH3), 24.7 (d,
argon and by using standard Schlenk techniques. Dry, oxygen-free
solvents were employed. 1H, 13C, 31P NMR spectra were recorded on a
Bruker WM 250 and Bruker Avance 300 spectrometers. 1H and
13CNMR chemical shift were reported in ppm relative to Me 4Si as an
external standard. 31P NMR downfield chemical shifts are expressed
with a positive sign, in ppm, relative to the standard of 85% H3PO4.
2: A solution of nBuLi (1.6m in hexanes, 2.0 mmol) was added
dropwise to a solution of diphenylmethylsulfonium triflate (0.70 g,
2.0 mmol) in THF (10 mL) at À788C. After 15 min at À788C , a
solution of bis(diisopropylamino)phosphonium triflate (0.38 g,
1.0 mmol) in THF (20 mL) was added, and the mixture was then
stirred at the same temperature for 2 h. Then, methyl triflate (0.16 g,
1.0 mmol) was added and the reaction mixture was slowly warmed to
room temperature over 12 h. After removal of all volatiles under
vacuum, the product was extracted with CH2Cl2. Derivative 2 was
obtained in the solid state after crystallization from CH2Cl2/Et2O at
À308C(0.54 g, 91%). M.p. 102–103 8C; 31P{1H} NMR (CDCl3, 258C,
3JCP = 2.8 Hz, CH3), 48.0 (d, 2JCP = 6.5 Hz, NCH), 48.9 (d, 2JCP = 6 Hz,
NCH), 121.6 (q, JCF = 319 Hz, CF3), 128.5, 130.5, 131.9 (s, CHarom),
1
132.2 ppm (s, Cipso).
Received: September 4, 2007
Published online: October 24, 2007
Keywords: density functional calculations · heterocumulenes ·
.
phosphorus · sulfur · ylides
[1] a) O. I. Kolodiazhnyi in Phosphorus Ylides: Chemistry and
Application in Organic Synthesis, Wiley-VCH, Weinheim,
1999; b) A. D. Abell, M. K. Edmonds in Organophosphorus
Reagents (Ed.: P. J. Murphy), Oxford University Press, Oxford,
2004, pp. 99 – 127; c) M. Edmonds, A. Abell in Modern Carbonyl
Olefination (Ed.: T. Takeda), Wiley-VCH, Weinheim, 2004,
pp. 1 – 17; d) K. C. Nicolaou, M. W. Härter, J. L. Gunzner, A.
Nadin, Liebigs Ann. 1997, 1283 – 1301; e) H. Pommer, Angew.
Chem. 1977, 89, 437 – 443; Angew. Chem. Int. Ed. Engl. 1977, 16,
423 – 429.
1
121 Hz): d = 53.0 ppm; H NMR (CDCl3, 258C, 300 Hz): d = 1.17 (d,
4JHH = 7 Hz, 24H, CH3), 2.02 (d, JPH = 12.9 Hz, 3H, PCH3), 2.42 (d,
2
2JPH = 13.9 Hz, 1H, CH), 3.52–3.74 (m, 4H, CH), 7.43–7.52 ppm (m,
10H, CHarom); 13C NMR (CDCl3, 258C, 75 Hz): d = 15.9 (d, JCP
=
1
1
109.0 Hz, CH3), 18.4 (d, JCP = 41.6 Hz, PCH), 23.4 (s, CH3), 46.9 (d,
2JCP = 5.5 Hz, NCH), 121.6 (q, 1JCF = 319 Hz, CF3), 127.1, 130.5, 131.7
(s, CHarom), 137.5 ppm (s, Cipso).
[2] For reviews on sulfonium ylides, see a) V. K. Aggarwal, C. L.
Winn, Acc. Chem. Res. 2004, 37, 611 – 620; b) Nitrogen, Oxygen,
and Sulfur Ylide Chemistry (Ed.: S. J. Clark), Oxford University
Press, Oxford, 2002; c) Y. G. Gololobov, A. N. Nesmeyanov, V. P.
Lysenko, I. E. Boldeskul, Tetrahedron 1987, 43, 2609 – 2651, and
references therein.
3: C6D6 (1 mL) was added to a mixture of KHMDS (0.12 g,
0.6 mmol) and phosphoniosulfonium ylide 2 (0.28 g, 0.5 mmol) at
08C, and the mixture was then warmed to room temperature. The
product 3 was characterized without any purification. 31P{1H} NMR
(CDCl3, 258C, 121 Hz): d = 44.6 ppm; 1H NMR (CDCl3, 258C,
[3] F. Ramirez, N. B. Desai, B. Hansen, N. McKelvie, J. Am. Chem.
Soc. 1961, 83, 3539 – 3540.
300 Hz): d = 1.17 (d, 4JHH = 6.0 Hz, 12H, CH3), 1.36 (d, JHH
=
4
2
6.0 Hz, 12H, CH3), 1.79 (d, JPH = 12.0 Hz, 3H, PCH3), 3.44 (d-sept,
3JPH = 15.0 Hz, 3JHH = 6.0 Hz, 4H, CH), 7.01 (t, 3JHH = 9.0 Hz, 2H,
CHarom), 7.19 (m, 4H, CHarom), 8.00 ppm (d, 3JHH = 6.0 Hz, 4H,
[4] For reviews on ylides and carbodiphosphoranes chemistry, see
a) O. I. Kolodiazhnyi, Tetrahedron 1996, 52, 1855 – 1929;
b) Ylides and Imines of Phosphorus (Ed.: A. W. Johnson),
Wiley, New York, 1993; c) H. Schmidbaur, Angew. Chem. 1983,
95, 980 – 1000; Angew. Chem. Int. Ed. Engl. 1983, 22, 907 – 927.
[5] Particularly, carbodiphosphoranes are electron-rich carbon-
centered ligands: a) S. Marrot, T. Kato, H. Gornitzka, A.
Baceiredo, Angew. Chem. 2006, 118, 2660 – 2663; Angew.
Chem. Int. Ed. 2006, 45, 2598 – 2601; b) K. Kubo, N. D. Jones,
M. J. Ferguson, R. McDonald, R. G. Cavell, J. Am. Chem. Soc.
2005, 127, 5314 – 5314; c) W. Petz, C. Kutschera, B. Neumüller,
Organometallics 2005, 24, 5038 – 5043; d) W. Petz, C. Kutschera,
M. Heitbaum, G. Frenking, R. Tonner, B. Neumüller, Inorg.
Chem. 2005, 44, 1263 – 1274.
[6] T. Fujii, T. Ikeda, T. Mikami, T. Suzuki, T. Yoshimura Angew.
Chem. 2002, 114, 2688–2690; Angew. Chem. Int. Ed. 2002, 41,
2576 – 2578; Angew. Chem. Int. Ed. 2002, 41, 2576 – 2578.
[7] A. H. Cowley, R. Kemp, Chem. Rev. 1985, 85, 367 – 382.
[8] CCDC-659272 (2), -659273 (4), and -659994 (5) contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[9] H. Schmidbaur, C. E. Zybill, G. Müller, C. Krüger, Angew.
Chem. 1983, 95, 753 – 755; Angew. Chem. Int. Ed. Engl. 1983, 22,
729 – 730.
CHarom); 13C NMR (CDCl3, 258C, 75 Hz): d = 21.5 (d, JCP = 75.7 Hz,
1
PCH3), 23.4 (d, 2JCP < 1 Hz, CH3), 24.0 (s, CH3), 35.9 (d, JCP
=
1
86.6 Hz, PCS), 45.5 (s, NCH), 123.0, 128.3, 128.6 (s, CHarom),
151.2 ppm (d, 3JCP = 23.7 Hz, Cipso).
4: Methyl iodide (0.14 g, 1.0 mmol) was added to the solution of 2
in THF (2 mL), generated from 3 (0.59 g, 1.0 mmol) in the presence of
KHMDS (0.24 g, 1.2 mmol) at À788C. After warming the solution to
room temperature, all volatiles were removed under vacuum. The
product was extracted with CH2Cl2 and the pure product 5 was
obtained after drying under vacuum (0.35 g, 57%). X-ray quality
crystals were grown from CH2Cl2/Et2O solution at À308C; 31P{1H}
NMR (CDCl3, 258C, 121 Hz): d = 66.1 ppm; 1H NMR (CDCl3, 258C,
300 Hz): d = 1.19 (d, 3JHH = 7 Hz, 12H, CH3), 1.23 (d, 3JHH = 7 Hz,
12H, CH3), 1.54 (d, 3JPH = 11.9 Hz, 3H, PCH3), 2.10 (d, 3JPH = 13.5 Hz,
3H, CCH), 3.44 (d-sept, 3JPH = 12.4 Hz, 3JHH = 6.7 Hz, 4H, CH),
3
7.34–7.53 ppm (m, 10H, CHarom); 13C NMR (CDCl3, 258C, 75 Hz):
2
1
d = 11.3 (d, JCP = 11.1 Hz, CH3), 17.9 (d, JCP = 96.1 Hz, PCH3), 24.3
(d, 3JCP = 2.8 Hz, CH3), 24.7 (d, 3JCP = 2.8 Hz, CH3), 48.0 (d, JCP
=
2
6.5 Hz, NCH), 48.9 (d, 2JCP = 6 Hz, NCH), 121.6 (q, 1JCF = 319 Hz,
CF3), 128.5, 130.5, 131.9 (s, CHarom), 132.2 ppm (s, Cipso).
5: A mixture of phosphonium salt 2 (0.20 g, 3.31 mmol), excess
KHMDS (0.20 g, 9.94 mmol), and anhydrous copper(I) chloride
(0.033 g, 3.31 mmol) were cooled to À788Cand then THF (4 mL)
was added. The mixture was stirred and warmed to room temperature
over 12 h. All volatiles were removed under vacuum and the product
was extracted with toluene (3 mL). Pale yellow crystals were grown
from a concentrated toluene solution (139 mg, 63%). M.p. 78–798C;
31P{1H} NMR (CDCl3, 258C, 121 Hz): d = 66.5 ppm; 1H NMR (C6D6,
258C, 300 Hz): d = 0.63 (s, 18H, SiCH3), 1.07 (d, 3JHH = 6.7 Hz, 12H,
[10] D. G. Gilheany, Chem. Rev. 1994, 94, 1339 – 1374.
[11] S. Wolfe, A. Stolow, L. A. LaJohn, Tetrahedron Lett. 1983, 24,
4071 – 4074.
[12] R. Tonner, F. ꢀxler, B. Neumüller, W. Petz, G. Frenking, Angew.
Chem. 2006, 118, 8206 – 8211; Angew. Chem. Int. Ed. 2006, 45,
8038 – 8042.
3
3
CH3), 1.25 (d, JHH = 6.7 Hz, 12H, CH3), 2.04 (d, JPH = 12.4 Hz, 3H,
9080 www.angewandte.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2007, 46, 9078 –9080
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