5-Carbaphosphatranes: The first main group atrane bearing a 1-5 covalent bond [2]

Full text of DOI:10.1021/ja0056264

J. Am. Chem. Soc. 2001, 123, 3387-3388
3387
Scheme 1a
5-Carbaphosphatranes: The First Main Group
Atrane Bearing a 1-5 Covalent Bond
Junji Kobayashi, Kei Goto, and Takayuki Kawashima*
Department of Chemistry, Graduate School of Science
The UniVersity of Tokyo, 7-3-1 Hongo, Bunkyo-ku
Tokyo 113-0033, Japan
ReceiVed September 20, 2000
ReVised Manuscript ReceiVed December 29, 2000
There have been extensive studies on a wide variety of main
group atranes, generally depicted as A.1 A number of their
derivatives bearing different ring sizes and other building elements
have also been reported so far. These studies established that the
nature of the NfE dative bond has a great influence on their
structures and reactivities. From such a viewpoint, it is particularly
intriguing how their properties will change when the dative bond
between the 5-nitrogen atom and the central atom is replaced by
a covalent bond with a group 14 element like carbon as shown
by a general formula B.
a a) n-BuLi: b) PCl3, rt, then H2O, 11% (2 steps); c) PCl3, 50 °C,
then H2O, 38% (2 steps); d) TMSI, rt, 38%; e) TMSI, rt, 39%; f) BBr3,
rt, then aq. NaHCO3, 54%; g) TMSI, 80 °C, in a sealed tube, 29%.
However, there has been no example of such an atrane bearing
a 1-5 covalent bond; the element at the 5-position of known
atranes has been limited almost exclusively to nitrogen with a
few exceptions of phosphorus.2 Here we report the synthesis of
5-carbaphosphatranes 1 and 2, presenting the first example of
5-carbon analogues of main group atranes. While they have an
isoelectronic structure with usual phosphatranes bearing a 5-ni-
trogen atom, they are expected to be quite different in reactivities
from usual ones reflecting the differences in the properties of the
1-5 bond.
Lithiation of triarylmethane 3 followed by the reaction with
phosphorus trichloride at room temperature afforded phosphinic
acid 4 after hydrolysis (Scheme 1). When the reaction was effected
at 50 °C, the cyclic phosphinate 5 was obtained as a result of
intramolecular cyclization with loss of chloromethane and hy-
drolysis.3 1-Hydro-5-carbaphosphatrane 1 was synthesized by
treatment of 4 or 5 with iodotrimethylsilane at room temperature
in CDCl3.4,5 In this reaction, the intermediary cyclic phosphonite
6 was observed by 31P NMR (δ 190), which is considered to react
with hydrogen iodide formed in situ to afford 1. On the other
hand, when the reaction of 5 with iodotrimethylsilane was carried
out at 80 °C in a sealed tube, 1-methyl-5-carbaphosphatrane 2
Figure 1. ORTEP drawings of 1 with thermal ellipsoid plot (50%
probability). Selected bond lengths (Å) and angles (deg): P1-C1,
1.921(2); P1-H1, 1.38(2); O1-P1-O2, 121.96(9); O1-P1-O3,
118.14(9); O2-P1-O3, 119.62(9); C1-P1-O1, 91.65(9); C1-P1-O2,
91.69(9); C1-P1-O3, 91.99(9); H1-P1-C1, 178.7(9).
was obtained instead of 1, probably as a result of the reaction of
the intermediate 6 with iodomethane generated in situ. Compound
1 was also obtained by the reaction of 5 with boron tribromide
in CHCl3. It was reported that the tribenzophosphatrane 7 bearing
a 5-nitrogen is observable by NMR spectroscopy in solution, but
too fragile to be isolated.6 In contrast, 5-carbaphosphatrane 1 was
obtained as stable crystals, showing the difference between a
phosphatrane with an NfP dative bond and that with a C-P
covalent bond.
(1) For reviews, see: (a) Verkade, J. G. Acc. Chem. Res. 1993, 26, 483-
489. (b) Verkade, J. G. Coord. Chem. ReV. 1994, 137, 233-295. (c) Alder,
R. W.; Read, D. Coord. Chem. ReV. 1998, 176, 113-133. For silatranes, see:
Voronkov, M. G. Pure Appl. Chem. 1966, 13, 35-59.
The structure of 1 was established by X-ray crystallographic
analysis as shown in Figure 1.7 The apical bond lengths of 1 are
1.921(2) and 1.38(2) Å for the P-C and P-H bonds, respectively,
and the sum of the angles between equatorial bonds is 359.7°.
The figure clearly shows that 1 has a nearly ideal trigonal
bipyramidal structure, where the apical positions are occupied
by hydrogen and carbon atoms, while three oxygen atoms are
located at the equatorial positions. It is well-known that phos-
phoranes usually bear electronegative atoms at the apical positions
and electropositive atoms at the equatorial positions, according
to the apicophilicity of the elements.8,9 The structure of 1 in the
(2) (a) Tzschach, A.; Jurkschat, K. Comments Inorg. Chem. 1983, 3, 35-
50. (b) Clark, K. A. (Fusie); George, T. A.; Brett, T. J.; Ross, C. R., II;
Shoemaker, R. K. Inorg. Chem. 2000, 39, 2252-2253.
(3) For a similar reaction, see: Yoshifuji, M.; Nakazawa, M.; Sato, T.;
Toyota, K. Tetrahedron, 2000, 56, 43-55.
(4) For a demethylation reaction of anisole derivatives with iodotrimeth-
ylsilane, see: Jung, M. E.; Lyster, M. A. J. Org. Chem. 1977, 42, 3761-
3764.
(5) 1: colorless crystals, mp 272-274 °C. 1H NMR (500 MHz, CDCl3,
27 °C) δ 1.32 (s, 27H), 6.76 (d, 1H, JPH ) 852 Hz), 6.95 (d, 3H, J ) 8.4 Hz),
7.14 (dd, 3H, J ) 8.4, 2.1 Hz), 7.88 (brd, 3H); 13C{1H} NMR (125 MHz,
CDCl3, 27 °C) δ 31.52 (s), 34.47 (s), 39.21 (d, JPC ) 125 Hz), 112.41 (d, JPC
) 10.3 Hz), 122.20 (d, JPC ) 22.3 Hz), 124.59 (s), 131.95 (d, JPC ) 13.3
Hz), 146.39 (s), 149.70(s); 31P NMR (109 MHz, CDCl3, 27 °C) δ 2.6. HRMS-
(70 eV) m/z 488.2491, calcd for C31H37O3P 488.2480. Anal. Calcd for
C31H37O3P: C, 76.20; H, 7.63. Found: C, 76.48; H, 7.61.
(6) Mu¨ller, E.; Bu¨rgi, H.-B. HelV. Chim. Acta 1987, 70, 1063-1069.
(7) Crystal data for 1: monoclinic, P21/c, colorless, a ) 15.963(1) Å, b )
11.278(1) Å, c ) 15.269(1) Å, â ) 93.842(4)°, V ) 2742.7(3) Å3, 123 K, Z
) 4, R ) 0.055, RW ) 0.058, GOF ) 3.84.
10.1021/ja0056264 CCC: $20.00 © 2001 American Chemical Society
Published on Web 03/16/2001

3388 J. Am. Chem. Soc., Vol. 123, No. 14, 2001
Communications to the Editor
Scheme 3
Figure 2. Coupling constants of the related compounds.
Scheme 2
afforded the cyclic phosphonothioate 12 via the corresponding
anion 13. These results can be reasonably explained by assuming
the tautomerization between the five-coordinate carbaphosphatrane
1 and the three-coordinate phosphonite 14 (Scheme 3); the
tautomer 14 is deprotonated with amines to give the ionic species
15,15 which is irreversibly oxidized or sulfurized to 11 or 13,
respectively. The tautomerization between 1 and 14 was further
demonstrated by the desulfurization reaction of phosphonothioate
12. Treatment of 12 with triphenylphosphine in CDCl3 at 85 °C
afforded the parent carbaphosphatrane 1 almost quantitatively,
which is most probably formed via tautomerization of the three-
coordinate species 14 first generated in the reaction (Scheme 3).
Furthermore, the H-D exchange in the P-H bond of 1 was
observed when the CDCl3 solution of 1 was allowed to stand for
2 months in the presence of D2O. This reaction was remarkably
accelerated by acid, and in the presence of DCl/D2O, the exchange
was completed within 15 h at room temperature. These results
are also consistent with the equilibrium between 1 and 14.
Phosphonite 14 was not observed in any spectroscopic measure-
ment of 1, and no significant change was observed in the variable
temperature 1H NMR spectra of 1 in the range of -80 to 80 °C.
These observations are reasonable, however, if the tautomer 1 is
thermodynamically much more favorable than 14. While such
tautomerization between five-coordinate and three-coordinate
species has never been described for the usual phosphatranes with
an NfP dative bond, it is no wonder that a neutral phosphorane
1 with a C-P covalent bond undergoes such isomerization. The
reaction involving similar tautomerization was reported for an
o-phosphinobenzoic acid.16
perfectly “anti-apicophilic”10 arrangement is particularly note-
worthy in this connection.
In 31P NMR spectra, 5-carbaphosphatranes 1 and 2 showed
1
their signals at δ 2.6 and 21, respectively. The JPH value of 1
and the 1JPC(P-CH3) value of 2 are 852 and 215 Hz, respectively,
which are extraordinarily large for the apical P-H and P-C
coupling constants of phosphoranes.11 The 1JPH value of 1 is more
than three times as large as that of the neutral phosphorane 9
(1JPH ) 266 Hz) bearing an apical P-H bond,12 whereas it is
similar to those of phosphatranes 7 (1JPH ) 853 Hz)6 and 8 (1JPH
) 791 Hz).13 Although there is a difference that 1 is a neutral
phosphorane and compounds 7 and 8 are ionic, these results
indicate that the spectroscopic properties of 1 are similar to those
of usual phosphatranes rather than to those of known neutral
phosphoranes.
It has been reported that usual phosphatranes bearing a
5-nitrogen do not react with bases such as NaOMe and proton
sponge.14 In contrast, when 5-carbaphosphatrane 1 was treated
with amino bases such as proton sponge, DBU, and triethylamine
in the open atmosphere, the phenolate anion 11 (δP 43) was
formed and converted to the cyclic phosphonate 10 after hydroly-
sis with hydrochloric acid (Scheme 2).
In summary, we synthesized 5-carbaphosphatranes 1 and 2,
the first example of 5-carbon analogues of main group atranes.
While the spectroscopic and structural properties of 1 are rather
similar to those of usual phosphatranes, 1 showed characteristics
as a neutral phosphoranes with respect to the reactivity. The
present results revealed that 5-carbaphosphatranes constitute a
novel class of highly coordinated phosphorus compounds bearing
the properties both as a phosphatrane and as a neutral phospho-
rane.
Similarly, the reaction of 1 with amino bases in the presence
of elemental sulfur followed by treatment with hydrochloric acid
(8) Holmes, R. R. Pentacoordinated Phosphorus - Structure and Spec-
troscopy; ACS Monograph 175, 176; American Chemical Society: Wash-
ington, DC, 1980; Vols. I, II.
(9) (a) Trippett, S. Phosphorus Sulfur 1976, 1, 89-98. (b) McDowell, R.
S.; Streitwieser, A., Jr. J. Am. Chem. Soc. 1985, 107, 5849-5855. (c) Wang,
P.; Zhang, Y.; Glaser, R.; Reed, A. E.; Schleyer, P. v. R.; Streitwieser, A. J.
Am. Chem. Soc. 1991, 113, 55-64. (d) Thatcher, G. R. J.; Campbell, A. S. J.
Org. Chem. 1993, 58, 2272-2281.
(10) For example of other phosphoranes with an apical P-C bond, see:
(a) Antipin, M. Yu.; Chernega, A. N.; Struchkov, Yu. T.; Kozlov, E. S.;
Boldeskul, I. E. Zh. Strukt. Khim. 1987, 28, 105-8. (b) Francke, R.; Sheldrick,
W. S.; Ro¨schenthaler, G.-V. Chem. Ber. 1989, 122, 301-306. (c) Timosheva,
N. V.; Chandrasekaran, A.; Prakasha, T. K.; Day, R. O.; Holmes, R. R. Inorg.
Chem. 1996, 35, 6552-6560. (d) Kojima, S.; Kajiyama, K.; Nakamoto, M.;
Akiba, K.-y. J. Am. Chem. Soc. 1996, 118, 12866-12867. (e) Vollbrecht, S.;
Vollbrecht, A.; Jeske, J.; Jones, P. G.; Schmutzler, R.; du Mont, W.-W. Chem.
Ber. 1997, 130, 819-822.
(11) Kawashima, T. Chemistry of HyperValent Compounds; Akiba, K.-y.,
Ed.; John Wiley and Sons: New York, 1999; pp 171-210 and references
therein.
(12) Ross, M. R.; Martin, J. C. J. Am. Chem. Soc. 1981, 103, 1234-1235.
(13) Clardy, J. C.; Milbrath, D. S.; Springer, J. P.; Verkade, J. G. J. Am.
Chem. Soc. 1976, 98, 623-624.
(14) Milbrath, D. S.; Verkade, J. G. J. Am. Chem. Soc. 1977, 99, 6607-
6613.
Acknowledgment. This work was partly supported by a Grant-in-
Aid for Scientific Research (A) No. 12304037 (T.K.) from the Ministry
of Education, Science, Sports and Culture, Japan. We also thank Shin-
etsu Chemical Co., Ltd. and Tosoh Finechem Corporation, for the
generous gifts of iodosilanes and alkyllithiums, respectively.
Supporting Information Available: Experimental procedure for the
synthesis and reactions of 1 and 2 with physical properties of structural
information on 1 (PDF). An X-ray crystallographic file (CIF). This
material is available free of charge via the Internet at http://pubs.acs.org.
JA0056264
(15) As for the structure of anion 15, there is a possibility that it exists as
a phosphoranide form. Theoretical study on the structure of 15 will be reported
elsewhere.
(16) Kemp, R. A. Phosphorus, Sulfur, and Silicon 1994, 87, 83-92.