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Phosphorus Heterocycles
Jens Geier, Gilles Frison, and Hansjrg Grtzmacher*
Dedicated to Professor Horst Prinzbach
on the occasion of his “70 + ” birthday
Because of their frequently unusual properties, small heterocycles are of constant interest.[1] They also remain a challenge
to any synthetic chemist. Three-membered rings with phosphorus are less strained than their carbon analogues,[2]
tetrahedral P4 being the most prominent example.[2c] BabarPhos (I Scheme 1), a remarkable stable polycyclic phosphir-
For the synthesis of the dibenzo-1-phosphasemibullvalene
(4), we adopted a method developed by Niecke et al.
(Scheme 1).[8] As a precursor, we prepared the 5-bis(trimethylsilyl)phosphanyl-5H-dibenzo[a,d]cycloheptene
(troppSiMe3, 2)[9] which was converted into the highly air,
moisture, and temperature sensitive unsymmetrical tropp(Cl)SiMe3
compound 3. The yields of 2 and 3 are almost quantitative in
both reactions.
The controlled thermolysis of 3 at 90 8C gives only one
product, with a resonance in the 31P NMR spectra at d =
21.6 ppm, in quantitative yield. A phosphinidene, trop-P, a
plausible intermediate could not be trapped, however, and the
mechanism of this reaction is uncertain.
The product 4 can be isolated as a colorless, air-sensitive
solid but decomposes upon storage into a waxy insoluble
material. The 1H and 13C NMR spectra show that 4 has a
symmetric structure but the very unusual 31P chemical shift
left doubts that a dibenzo-1-phosphasemibullvalene was
obtained. Phosphiranes with alkyl or aryl substitutents on
the phosphorus atoms typically show 31P chemical shifts at
very low frequencies: d = 150– 250 ppm[1] (cage compounds such as phosphaprismanes IV (d = 100– 140 ppm)
and phosphabenzvalenes V (d = 80– 90 ppm) are more
deshielded).[10] The calculated 1H, 13C, and 31P chemical shifts
(GIAO-B3LYP/6-31 + G(d)//B3LYP-6-31G(d) level)[11] are
included in Figure 1 which shows the geometry optimized
structure of 4.[12] Selected bond lengths and angles are given in
Table 1. The agreement between the experimental values and
Scheme 1. Syntheses of tropp-type phosphanes 2 and 3 and the
dibenzo-1-phosphasemibullvalene 4.
ane,[3] has potential as a ligand for transition-metal complexes
in homogeneous catalysis.[3–5] This situation prompted us to
investigate the possibility of synthesizing the unknown
phosphorus analogue of dibenzosemibullvalene II (X =
CH).[6] Derivatives of dibenzoazasemibullvalene III (X =
N)[7] have been described as quite stable compounds.
[*] Prof. Dr. H. Gr6tzmacher, Dipl.-Chem. J. Geier, Dr. G. Frison+
Department of Chemistry, HCI
ETH H<nggerberg
8093 Z6rich (Switzerland)
Fax: (+ 41) 1-632-1032
Figure 1. Calculated structure and NMR chemical shifts of 4. Selected
experimental data are shown in bold, calculated data are given in italics.
Table 1: Bond lengths and angles of PC2 of 4 and as a ligand in 5.
[+] Present address: Laboratoire des MAcanismes RAactionnels–DCMR
Ecole Polytechnique
91128 Palaiseau Cedex (France)
[**] This work was supported by the ETH Z6rich. We are indebted to the
Swiss Center for Scientific Computing (CSCS) and the Competence
Centre for Computational Chemistry (C4) of the ETH Z6rich for
providing computer time.
Supporting information for this article is available on the WWW
under or from the author.
Angew. Chem. Int. Ed. 2003, 42, 3955 –3957
a [%]
b [%]
c [%]
a [8]
b [8]
g [8]
[a] Calculated values. [b] Experimental average values for both molecules
in the asymmetric unit.
DOI: 10.1002/anie.200351388
2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
calculated values is very satisfactory. Definitive proof for the
assignment of 4 as dibenzo-1-phosphasemibullvalene was
obtained in a complexation reaction with [W(CO)5(thf)]
which gave the complex [4-W(CO)5] (5). The result of the Xray structure analysis for 5 is shown in Figure 2;[13] selected
bond lengths and angles of 4 as ligand are listed in Table 1.
calculations, 51–55 kJ mol 1 in ref. [2a]; see the Supporting
Information for details.) In conclusion, the polycyclic framework in 4 does not exert any particular strain. In fact because
of conjugation of the PC2 cycle with the hydrocarbon
p system, 4 is even less strained and its instability must
therefore have different origins.
Experimental Section
Figure 2. Molecular structure of 5. Thermal ellipsoids at 50 % probability. Hydrogen atoms have been omitted for clarity and only one of the
two crystallographically independent molecules is shown. Selected
mean values for the bond lengths [%] and angles [8] of the {W(CO)5}
fragments in both molecules are listed: W-P 2.462(3), W-Ceq 2.06(2),
W-Caxial 1.98(2), Ceq-O 1.12(2), Caxial-O 1.15(2), P-W-Caxial 177.7(4).
As observed for various Babar-Phos complexes, the P C
bonds a and c (see Table 1) are shortened and the basal C C
bond b of the PC2 cycle is elongated in the complex.[14] In 4
and 5 the sum of bond angles at the phosphorus center, 8(P),
is about 208 smaller than in monocyclic phosphiranes[1] or
Babar-Phos derivatives[14] and to our knowledge are the
smallest values reported to date for any PC2 heterocycle.
Noteworthy, the 31P chemical shift does not change
significantly when 4 serves as a ligand in 5 (31P: d =
20.7 ppm) while the change in chemical shift in BabarPhos complexes on coordination exceeds 50 ppm. The 183W31P
coupling constant is used as a sensitive measure for the
electronic properties of the phosphane ligands and increases
with the electronegativity of the phosphorus-bonded substituents.[15] The coupling constant in 5 (1J(P,W) = 238 Hz)
compares well with ordinary tri-alkyl/aryl phosphanes and is
significantly smaller than in [W(CO)5(Babar-Phos)] complexes (1J(P,W) > 285 Hz) which lie in the range of tris(amino)- or tris(alkoxy)phosphane–W(CO)5 complexes.[16]
Also, the calculated Naturall Bond Orbitals (NBO) charge
at the phosphorus center (qP = 0.75 at the B3LYP6-31G(d)
level) gives no indication that the electron density is
especially depleted from the phosphorus atom in 4. To this
end, the unexpectedly deshielded 31P resonance signal in
phosphasemibullvalenes such as 4 cannot be satisfactorily
The ring strain of 4 (ca. 28 kJ mol 1) was estimated by a set
of bond-separation reactions and is about 30 kJ mol 1 lower
than in the parent phosphirane, HPC2H4 (58 kJ mol 1 in our
2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Inert conditions (high vacuum or argon atmosphere) were maintained
throughout all operations. Additional spectroscopic data of 2–5 are
given in the Supporting Information.
2: 1[18] (5.00 g, 22.1 mmol) was stirred with tris(trimethylsilyl)phosphane[19] (13.82 g, 55.1 mmol, 2.5 equiv) in toluene (100 mL) at
room temperature for 2 days. After removal of the solvent and all
other volatile compounds under high vacuum the residue was
recrystallized from toluene/n-hexane to give 7.38 g (91 %) of 2 as
colorless, air-sensitive needles: 31P NMR (121.49 MHz, C6D6, 298 K):
d = 146.6 (s).
3: Compound 2 (500 mg, 1.4 mmol) was stirred at room temperature with hexachloroethane (355 mg, 1.5 mmol) in toluene (15 mL)
until the 31P NMR spectrum indicated quantitative conversion (1–
2 h). After removal of all volatiles under high vacuum, 3 was obtained
as spectroscopically pure, air-sensitive and thermally instable, colorless solid which was immediately used for the preparation of 4.
P NMR (121.49 MHz, C6D6, 298 k): d = 69.6 ppm (s).
4: 3 was dissolved in toluene (10 mL) and heated to 90 8C until the
P NMR spectrum indicated quantitative conversion into 4 (1–2 h);
longer heating results in decomposition. The dibenzophosphasemibullvalene 4 was isolated as a colorless, thermally unstable and airsensitive solid by rapidly removing the solvent and the formed
Me3SiCl under high vacuum. However, it cannot be stored and
decomposes within a few hours at room temperature: 31P{H} NMR
(101.25 MHz, C6D6, 298 K): d = 21.6 ppm (quintet, 2J(P,H-1) =
27.8 Hz, 2J(P,H-4) = 2J(P,H-5) = 13.9 Hz); 1H NMR (300.13 MHz,
C6D6, 298 K): d = 3.05 (d, J = 13.9 Hz, 2 H, H-4/5), 3.33 (d, J =
27.8 Hz, 1 H, H-1), 6.74–7.27 ppm (m, 8 H, Ar-H).
5: Freshly prepared 4 was stirred with an excess of
[W(CO)5(thf)][20] (1.5 equiv) in THF solution (200 mL) for 2 h at
room temperature. The solvent was removed in vacuum and the
brown residue was purified by column chromatography on neutral
aluminium oxide. After washing the column with n-hexane, the
product was eluted with toluene (31P NMR control). After three
recrystallizations from cyclopentane solution a rather low yield of
crystalline colorless, air-sensitive 5 (184 mg, 24 %) was obtained
although the initial yield in the crude reaction mixture was
quantitative (as judged from 31P NMR). M.p. 139 8C (dec.); 31P{H}
NMR (101.25 MHz, C6D6, 298 K: d = 20.7 ppm (d with 183W
J(P,W) = 238.3 Hz,
J(P,H-1) = 11.2 Hz);
(250.13 MHz, C6D6 298 K: d = 3.02 (s, 2 H, H-4/5), 4.02 (d, J =
11.2 Hz, 1 H, H-1), 6.71–7.02 ppm (m, 8 H, Ar-H); 13C NMR
(75.48 MHz, C6D6, 298 K): d = 42.8 (d, 1J(C-4/5,P) = 12.1 Hz, C-4/5),
59.3 (d, 1J(C-1,P) = 14.7 Hz, C-1), 122.3 (d, J(C,P) = 7.1 Hz), 127.0
(two nearly superimposed s), 127.1 (s), 135.4 (d, J(C,P) = 1.1 Hz),
149.8 (d, J(C,P) = 2.5 Hz), 194.8 (d with 183W satellites, 2J(C,P) =
8.1 Hz, 1J(C,W) = 125.3 Hz, cis CO), 198.7 ppm (d, 2J(C,P) =
32.4 Hz, trans CO); IR (neat): ñ = 2074s, 1996m, 1954w, 1889vs,
1600w, 1583w, 1474m, 1458m, 1340w, 1303w, 1260w, 934w, 880w, 789m,
755s, 588s, 569s, 562s cm 1; MS (70 eV): m/z (%): 546 (33) [M+], 191
(100) [C15H11+].
Received: March 13, 2003 [Z51388]
Keywords: ab initio calculations · cycloaddition · heterocycles ·
Angew. Chem. Int. Ed. 2003, 42, 3955 –3957
[1] a) For a discussion of the stability of strained heterocycles with
main-group element centers see: M. Driess, H. GrJtzmacher,
Angew. Chem. 1996, 108, 901; Angew. Chem. Int. Ed. Engl. 1996,
35, 828, and references therein; b) For reviews focusing on threemembered phosphorus heterocycles see: c) F. Mathey, M. Regitz
in Phosphorus Heterocyclic Chemistry: The Rise of a New
Domain (Ed.: F. Mathey), Pergamon, Amsterdam, 2001, pp. 17 –
55; d) F. Mathey, Chem. Rev. 1990, 90, 997. For a recent
computational work on the ring strain in three-membered rings
see: M. Alcamí, O. MM, M. YaNez, J. Comput. Chem. 1998, 19,
[2] a) M. T. Nguyen, A. Dransfeld, L. Landuyt, L. G. Vanquickenborne, P. von R. Schleyer, Eur. J. Inorg. Chem. 2000, 103;
b) M. T. Nguyen, E. Van Praet, L. G. Vanquickenborne, Inorg.
Chem. 1994, 33, 1153; c) The low ring strain of P4 can be ascribed
to the phenomenon of Non-Orbital-Hybridisation (NOH), see:
W. W. Schoeller, V. Staemmler, P. Rademacher, E. Niecke, Inorg.
Chem. 1986, 25, 4382.
[3] J. Liedtke, S. Loss, G. Alcaraz, V. Gramlich, H. GrJtzmacher,
Angew. Chem. 1999, 111, 1724; Angew. Chem. Int. Ed. 1999, 38,
[4] J. Liedtke, S. Loss, H. GrJtzmacher, Tetrahedron 2000, 56, 143.
[5] J. Liedtke, H. RJegger, S. Loss, H. GrJtzmacher, Angew. Chem.
2000, 112, 2596; Angew. Chem. Int. Ed. 2000, 39, 2479.
[6] a) G. F. Emerson, L. Watts, R. Pettit, J. Am. Chem. Soc. 1965, 87,
131; b) E. Ciganek, J. Am. Chem. Soc. 1966, 88, 2882; c) For
derivatives of dibenzosemibullvalene see: M. BOshar, H. Heydt,
M. Regitz, Tetrahedron 1986, 42, 1815.
[7] M. J. Haire, J. Org Chem. 1980, 45, 1310.
[8] R. Streubel, E. Niecke, Chem. Ber. 1990, 123, 1245.
[9] For the nomenclature used for (tropylidenyl)phosphanes =
tropp type phosphanes see: J. Thomaier, S. BoulmaPz, H.
SchOnberg, H. RJegger, A. Currao, H. GrJtzmacher, H. Hillebrecht, H. Pritzkow, New J. Chem. 1998, 22, 947.
[10] a) K. Blatter, W. ROsch, U.-J. Vogelbacher, J. Fink, M. Regitz,
Angew. Chem. 1987, 99, 67; Angew. Chem. Int. Ed. Engl. 1987,
26, 85; b) M. Regitz in Multiple Bonds and Low Coordination in
Phosphorus Chemistry (Eds.: M. Regitz, O. J. Scherer), Thieme,
Stuttgart, 1990, pp. 78 – 80.
[11] R. Ditchfield, Mol. Phys. 1974, 27, 789.
[12] All calculations were carried out with the Gaussian 98 suite of
programs: Gaussian 98 (Revision A.9), M. J. Frisch, G. W.
Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Montgomery, R. E. Stratmann, J. C.
Burant, S. Dapprich, J. M. Millam, A. D. Daniels, K. N. Kudin,
M. C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R.
Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J.
Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui, K. Morokuma,
D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J.
Cioslowski, J. V. Ortiz, B. B. Stefanov, G. Liu, A. Liashenko, P.
Piskorz, I. Komaromi, R. Gomperts, R. L. Martin, D. J. Fox, T.
Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, C.
Gonzalez, M. Challacombe, P. M. W. Gill, B. G. Johnson, W.
Chen, M. W. Wong, J. L. Andres, M. Head-Gordon, E. S.
Replogle, J. A. Pople, Gaussian, Inc., Pittsburgh, PA, 1998.
Further details are given in the Supporting Information.
[13] Crystal structure data for 5: C20H11O5PW, Mr = 546.1 g mol 1;
colourless, irregular shaped, crystal size 0.40 S 0.39 S 0.37 mm;
monoclinic, space group P21/c, a = 13.644(3), b = 11.448(2), c =
24.129(5) T,
V = 3731(1) T3,
Z = 8,
1calcd = 1.945 g cm 3,
F(000) = 2080, m = 6.31 mm 1. The data were collected on a
STOE IPDS I diffractometer in 300 frames separated by 18 in fdirection: l(MoKa) = 0.71073 T, T = 293 K, 2qmax = 47.948,
2qmin = 3.948, number of collected (independent) reflections =
13 994 (5579), Rint = 0.1042. The structure was solved by direct
methods and refined against F2 with the full-matrix least-squares
Angew. Chem. Int. Ed. 2003, 42, 3955 –3957
method (SHELXS-97, SHELXL-97; G. Sheldrick, GOttingen,
Germany, 1997). All non-hydrogen atoms were found in difference fourier synthesis and were refined anisotropically, while the
hydrogen atoms were added to the structure at calculated
positions and then refined according to a riding model. Number
of refined parameters = 487, R1 = 0.0589 for 3718 reflections
with I > 2s, wR2 = 0.1778 for all data, GooF on F2 = 1.072, max./
min. residual electron density = 3.16/ 1.73 e T 3. CCDC-209240
(5) contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge via (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+ 44) 1223-336-033; or deposit@
C. Laporte, G. Frison, H. GrJtzmacher, A. C. Hillier, W.
Sommer, S. P. Nolan, Organometallics 2003, 22, 2202.
The range is defined by the extremes (Me3Sn)3P: 1J(W,P) = 142
and PF3 : 1J(W,P) = 485 Hz; a) E. O. Fischer, L. Knauss, R. I.
Keiter, J. G. Verkade, J. Organomet. Chem. 1972, 37, C7; b) H.
Schumann, H.-J. Kroth, Z. Naturforsch. B 1972, 32, 768.
J. Liedtke, Dissertation, ETH ZJrich, No. 13688, 2000. In this
context, we mention that the A1-symmetric CO stretching mode
of 5 (ñ = 2074 cm 1) is comparable to [W(CO)5(Babar-Phos)]
complexes (ñ = 2074–2078 cm 1) and other W(CO)5–phosphirane complexes and is, in general, a poor measure for the
electronic properties of phosphanes.
Note, that the benzo groups are unlikely to contribute to the
deshielding since, a) a calculation of the 31P chemical shift of the
parent phosphasemibullvalene PC7H7 gives an even higher
frequency shifted value (d = 14.6 ppm), and b) such an effect
is not seen in Babar-Phos which shows usual low frequency 31P
resonances (d = 140–230 ppm).
G. Berti, J. Org. Chem. 1957, 22, 230.
H. H. Karsch, F. Bienlein, T. Rupprich, F. Uhlig, E. Herrmann,
M. Scheer in Synthetic Methods of Organometallic and Inorganic
Chemistry, Vol. 3 (Eds.: W. A. Herrmann, G. Brauer), Georg
Thieme, Stuttgart, 1996, p. 58.
For the preparation of [W(CO)5(thf)] we used the method
described in: G. BalVzs, H. J. Breunig, E. Lork, Z. Anorg. Allg.
Chem. 2001, 627, 1855.
2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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