12866
J. Am. Chem. Soc. 1996, 118, 12866-12867
First Characterization of a 10-P-5 Spirophosphorane
with an Apical Carbon-Equatorial Oxygen Ring.
Kinetic Studies on Pseudorotation of Stereoisomers
Satoshi Kojima, Kazumasa Kajiyama,†
Masaaki Nakamoto, and Kin-ya Akiba*
Department of Chemistry, Faculty of Science
Hiroshima UniVersity, 1-3-1 Kagamiyama
Higashi-Hiroshima 739, Japan
Figure 1. The ORTEP drawings of 3 and 4 showing the thermal
ellipsoids at the 30% probability level. All hydrogens have been omitted
for clarity. Selected bond distances (Å) and angles (deg): 3 P1-O1,
1.765(2); P1-O2, 1.753(2); P1-C1, 1.818(2); P1-C10, 1.820(2); P1-
C19, 1.818(2); O1-P1-O2, 175.79(6); O1-P1-C1, 87.32(8); O2-
P1-C10, 87.30(8); C1-P1-C10, 126.84(8), C10-P1-C19, 116.6(1);
C1-P1-C19, 116.6(1); 4 P1-O1, 1.768(3); P1-O2, 1.659(2); P1-
C1, 1.813(4); P1-C10, 1.863(4); P1-C19, 1.835(5); O1-P1-C10,
170.6(1); O1-P1-C1, 87.1(2); O2-P1-C10, 87.8(1); O2-P1-C1,
119.9(2), O2-P1-C19, 124.0(2); C1-P1-C19, 114.8(2).
ReceiVed June 25, 1996
ReVised Manuscript ReceiVed October 29, 1996
10-P-51 phosphoranes usually assume trigonal bipyramidal
structures in the ground state, in which there are two distinctive
sites, the apical and the equatorial positions.2 It is well-known
that a phosphorane bearing oxygen and carbon substituents
preferentially has oxygen atoms in the apical positions as the
most stable stereoisomer according to the apicophilicity of the
elements.2,3 Quite recently, it was reported that a specially
designed tetraoxyphosphorane in which a carbon substituent
occupies the apical position due to steric hindrance could be
isolated as the only detectable isomer.4 Here, we report on the
first isolation and characterization of a spirophosphorane having
an apical carbon-equatorial oxygen five-membered ring and
its thermodynamically more stable apical oxygen-equatorial
carbon isomer and discuss the relative thermal stability of these
stereoisomers on the basis of kinetic studies.
Scheme 1
Scheme 2
When P-H (equatorial) spirophosphorane 1 [31P NMR
(CDCl3) δ -45.8 (1JPH ) 729 Hz)]5,6 was treated with more
than 2 equiv of n-BuLi in ether and carefully treated with dilute
hydrochloric acid, we obtained monocyclic P-H (apical)
phosphorane 27 [90%; mp 119 °C; 31P NMR (CDCl3) δ -34.4
(1JPH ) 273 Hz); 19F NMR (CDCl3) δ -72.9 (br s, 3F), -76.3
4
4
(q, JFF ) 9.2 Hz, 3F), -76.8 (q, JFF ) 8.2 Hz, 3F), -77.0
4
9
(qq, JFF ) 9.2 Hz, JFF ) 4.9 Hz, 3F)] and spirophosphorane
3 bearing a butyl group [9%; mp 109 °C; 31P NMR (CDCl3) δ
-18.8; 19F NMR (CDCl3) δ -75.1 (q, 4JFF ) 9.3 Hz, 6F), -75.4
49 revealed that these compounds were stereoisomers with
trigonal bipyramidal structure, as shown in Figure 1. It is clearly
shown that the apical bonds of 4 are longer than the corre-
sponding equatorial bonds (i.e., P1-O1(ap) 1.768 > P1-O2-
(eq) 1.659 Å and P1-C10(ap) 1.863 > P1-C1(eq) 1.813 Å.
On the other hand, the pairs of bonds of 3 are almost equal
(i.e., P-O(ap) 1.753, 1.765 Å and P-C(aryl; eq) 1.818, 1.820
Å.
4
(q, JFF ) 9.3 Hz, 6F)] (Scheme 1).
Thermal reactions of 2 in refluxing toluene afforded 3,
quantitatively (Scheme 2). However, when 2 was treated with
2 equiv of pyridine in tetrahydrofuran at 60 °C for 20 min, a
new species (4) [71%; mp 115 °C; 31P NMR (CDCl3) δ -3.5]
was obtained along with 3 (29%) after separation by TLC
(hexane/CH2Cl2 2:1; SiO2). X-ray structural analysis of 38 and
1
The observation at room temperature (rt) that the JC(aryl)P
for 3 (160 Hz) and 4 (88 Hz)10 are quite different while the
1JC(alkyl)P are essentially the same (116 and 114 Hz, respectively)
indicates that the solution structures of these compounds are
also trigonal bipyramids.
† Research Fellow of the Japan Society for the Promotion of Science.
(1) For N-X-L designation, see: Perkins, C. W.; Martin, J. C.; Arduengo,
A. J.; Lau, W.; Alegria, A.; Kochi, J. K. J. Am. Chem. Soc. 1980, 102,
7753.
(2) Holmes, R. R. Pentacoordinated Phosphorus - Structure and
Spectroscopy; ACS Monograph 175, 176; American Chemical Society:
Washington, DC, 1980; Vols. I, II.
(3) (a) Trippett, S. Phosphorus Sulfur 1976, 1, 89. (b) McDowell, R. S.;
Streitwieser, A., Jr. J. Am. Chem. Soc. 1985, 107, 5849. (c) Wang, P.; Zhang,
Y.; Glaser, R.; Reed, A. E.; Schleyer, P. v. R.; Streitwieser, A. J. Am. Chem.
Soc. 1991, 113, 55. (d) Thatcher, G. R. J.; Campbell, A. S. J. Org. Chem.
1993, 58, 2272.
(4) Timosheva, N. V.; Prakasha, T. K.; Chandrasekaran, A.; Day, R.
O.; Holmes, R. R. Inorg. Chem. 1995, 34, 4525.
(5) (a) Kojima, S.; Kajiyama, K.; Akiba, K.-y. Tetrahedron Lett. 1994,
35, 7037. (b) Kojima, S.; Kajiyama, K.; Akiba, K.-y. Bull. Chem. Soc. Jpn.
1995, 68, 1785. (c) Kojima, S.; Nakamoto, M.; Kajiyama, K.; Akiba, K.-y.
Tetrahedron Lett. 1995, 36, 2261.
(6) Ross, M. R.; Martin, J. C. J. Am. Chem. Soc. 1981, 103, 1234.
(7) See Supporting Information for the ORTEP figure and crystal-
lographic data.
(8) Crystal data for 3: monoclinic, P21/a, colorless, a ) 19.522(4) Å, b
) 11.819(2) Å, c ) 10.596(2) Å, â ) 103.50(2)°, V ) 2377.4(8) Å3, Z )
4, R ) 0.045, Rw ) 0.081, GOF ) 2.70.
19F NMR spectra of compound 4 at rt showed only a pair of
quartets [19F NMR (CDCl3, 293 K) δ -74.9 (q, 4JFF ) 8.5 Hz,
4
6F), -76.2 (q, JFF ) 8.5 Hz, 6F)] for the four anisochronous
CF3 groups. At low temperatures, the CF3 groups decoalesced
into four signals [19F NMR (toluene-d8, 193 K) δ -74.3 (brs,
3F), -74.5 (brs, 3F), -75.5 (brs, 3F), -76.0 (brs, 3F)], whereas
a sole 31P signal [31P NMR (toluene-d8, 219 K) δ -3.6] could
be observed for the compound throughout the temperature range.
This can only be rationalized as due to interconversion between
(9) Crystal data for 4: monoclinic, P21/n, colorless, a ) 12.041(2) Å, b
) 16.936(3) Å, c ) 11.401(2) Å, â ) 96.05(1)°, V ) 2311.9(6) Å3, Z )
4, R ) 0.066, Rw ) 0.093, GOF ) 2.67.
(10) Low temperature (to 203 K) 13C NMR spectra were broad and did
not give well-resolved signals for the two inequivalent Martin ligand carbons
1
in 4. If we assume that the equatorial JC(aryl)P is 160 Hz as in 3, then the
1
axial JC(aryl)P ) 16 Hz.
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