J . Am. Chem. SOC.1986, 108, 7032-7038
7032
50-52 load resistor and was analyzed by using a Tektonix 7912 AD transient digitizer liked to a Tektronix WP2252 signal processing system. All alkenes were distilled before use, and spectrograde solvents were employed. Further details appear above (see Discussion section), where particulars of the studies with p-CF3C6H4CBrand p-CH30C6H4CFare described.
Acknowledgment. W e thank the National Science Foundation for support of this work a t both Rutgers and Columbia Universities. Additionally, the Columbia authors thank the Air Force
Office of Scientific Research for financial support. Registry NO.1,9591 1-65-2; 2, 87282-19-7; 3, 4460-46-2; 4,4222-25-7; 5, 9591 1-64-1; TME, 563-79-1; p-F3CC6H4CBr,104197-52-6; PhCBr,
14541-26-5; PhCCI, 19807-41-1; PhCF, 17825-75-1; p-MeOC,H,CF, 104197-53-7; 1-hexene, 592-41-6; I-bromo-I-@-trifluoromethy1)phenyl)-2-n-butylcyclopropane, 104197-48-0; 1-fluoro- 1-@-methoxyphenyl)-2-n-butylcyclopropane, 104197-49-1; I-fluoro-1-(p-methoxyphenyl)-2,2,3,3-tetramethylcyclopropane,104197-50-4; I-bromo-I-@(trifluoromethyl)phenyl)-2,2,3,3-tetramethylcyclopropane,104197-5 1-5.
Electronic Structure of Cyclic Bicalicenes Toyonari Sugimoto,' Mitsuhiro Shibata,+ Shigeo Yoneda,+ Zen-ichi Yoshida,*+ Yasushi Kai,t Kunio Miki,t Nobutami Kasai,** and Tsunetoshi Kobayashi*§ Contribution from the Department of Synthetic Chemistry, Kyoto University, Yoshida. Kyoto 606, Japan, the Department of Applied Chemistry, Osaka University, Yamadaoka, Suita, Osaka 565, Japan, and The Institute of Physical and Chemical Research, Wako, Saitama 351 -01 Japan. Received June 9, 1986 I
Abstract: The novel n-electron system, pentacyclo[ 1 1.3.0.02*4.05*9.0'0~12]hexadeca1,3,5,7,9,11,I 3,15-octaene ("cyclic bicalicene") has been prepared, in which two calicene units are joined in a head-to-tail manner. The X-ray crystallographic analysis indicates that the cyclic bicalicene skeleton is completely planar; Le., the molecule has DZhsymmetry. Cyclic bicalicene is shown to have a characteristic absorption band a t around 500 nm, which is interpreted as an intramoleculer charge-transfer band by a SCF-CI M O method. From the 'HN M R spectra, the paramagnetic ring current due to peripheral 1 6 conjugation ~ is not observed. The 'Hand 13CN M R chemical shifts suggest that a considerably large polarization of each calicene unit occurs in the cyclic system. The alternating polarization in cyclic bicalicene is also supported by the graph-theoretical and S C F M O calculations.
Cyclopropenylidenecyclopentadienide (calicene) (1) is a cross-conjugated T system, whose synthesis and characterization have been of keen interest.' Thus far, the parent calicene has not been isolated. However, a number of calicene derivatives substituted with strong electron-donating and/or electron-withdrawing groups a t the cyclopropenyl and/or cyclopentadienyl rings have been isolated as stable compounds. From the investigation of their electronic character, it has been shown that a polar structure (1B) contributes significantly to the ground state.* ( 2 a ) : X=SBu t
-
(2b):
A Recently, we have succeeded in the isolation of the 3,ll-bis(tert-butylthio) derivative 2a as a stable crystalline c ~ m p o u n d . ~ This compound contrasts in stability to 5,6-bis(tert-butylthio)calicene," which is unstable even a t -78 O C and which evidences a large contribution of covalent structure (1A) based on N M R and I R spectral data. Furthermore, the parent system 2b has been isolated as stable crystals by the reductive desulfurization of 2a.j As we briefly reported before, since 2b is an unprecedented "aromatic" system with a 16n-electron periphery, we have investigated its electronic structure and n-conjugatin mode based on 'H and I3CNMR spectral data, X-ray structural analysis, and Kyoto University. 'Osaka University. 'The Institute of Physical and Chemical Research.
0002-7863/86/1508-7032$01.50/0
X=H
(z): X=SnBun3 graph-theoretical and a modified Pariser-Parr-Pople-type SCF MO methods ("the variable integrals method I") and elucidated the cause of stabilization. In addition, acyclic bicalicene has been synthesized as a reference K system for cyclic bicalicene. Since the electronic spectrum of cyclic bicalicene is very characteristic, the character of electronic transition is interpreted by using the (1) (a) Johns, W. M.; Pyron, P. S . J. Am. Chem. SOC.1965,87, 1608. (b) Ueno, M.; Murata, I.; Kitahara, Y. Tetrahedron Letf. 1965, 6, 2967. (c) Kende, A. S.; Izzo, P. T. J . Am. Chem. SOC.1965.87, 4162. (d) Prinzbach, H.; Fischer, U. Angew. Chem. 1965, 77, 258. (e) Bergmann, E. D.; Agranat, I. Tefrahedron 1966, 22, 1275. (f) Prinzbach, H.; Fischer, U. Helu. Chim. Acta 1967, SO, 1669. (8) Prinzbach, H.; Woischnik, E. Helu. Chim. Acta 1969, 52, 2472. (h) Prinzbach, H. Pure Appl. Chem. 1971, 28, 281. (i) Yoshida, 2.Pure Appl. Chem. 1982, 54, 1059. (2) (a) Dewar, M. J. S.; Gmeidner, G. J. Tetrahedron 1965.21, 3423. (b) Nakajima, T.; Kohda, S.; Tajiri, A,; Karasawa, S. Tetrahedron 1957, 23, 2189. (3) Yoneda, S.; Shibata, M.; Kida, S. Yoshida, Z . , Kai, Y . ; Kasai, N. Angew. Chem. 1984, 96, 75; Angew. Chem., I n f . Ed. Engl. 1984, 23, 63.
0 1986 American Chemical Society
J . Am. Chem. SOC., Vol. 108, No. 22, 1986 7033
Electronic Structure of Cyclic Bicalicenes Scheme I
S'
2_5
?_b
configuration interaction method combined with the S C F MO method mentioned above.
Results and Discussion Synthesis of 2a, 2b, 3, and 4 and X-ray Structure Analysis of 2a and 2b. When 1,2-bis(tert-butylthio)-3,3-dichlorocyclopropene,
A
obtained by the thionyl chloride treatment of bis(tert-butylthio)cycl~propenethione,~ was reacted with 2 equiv of lithium cyclopentadienide in THF a t -70 'C, h was isolated as a reddish purple solid in 10% yield. The reaction of 2a with tri-n-butylstannyl hydride in the presence of AIBN gave 3,1l-bis(tri-n-butylstannyl) cyclic bicalicene (2c) (orange crystals, 42% yield). Conversion of 2c into 2b was unsuccessful by the usual acids or bases. It was, however, readily achieved by standing 2c on silica gel for 0.5 h at r m m temperature (yield 40%) (Scheme I). Silica gel is considered to act as a mild acid catalyst for the S n - C bond fission. Acyclic bicalicene 4 was formed by the reaction of 1,2bis[bis(tert-butylthio)cyclopropenylio]cycl~pentadienide~ with tetramethylammonium 1,2-dicyano~yclopentadienide~ in dichloromethane a t 0 'C as an unstable yellow solid in 5% yield along with 3 (13% yield). When 4 was allowed to stand in dichloromethane at room temperature, 3 was obtained as reddish purple crystals in 73% yield.
\
\
(b)
(3)
(4)
The single crystals of 2a and 2b were obtained by recrystallization from dimethoxyethane and chloroform, respectively. X-ray crystallographic analysis of 2a determined the centrosymmetric molecular structure shown in Figure 1 along with the selected bond distances and angles. No bond alternation is observed in the outer sixteen-membered and inner eight-membered ring systems. The outer sixteen-membered ring is nearly planar, the mean atomic deviation from the least-squares plane (A) bein 0.026 A. The inner eight-membered ring is planar ( A = 0.006 The diheral angles between the eight- and five-membered rings ( A = 0.003 A) and between the eight- and three-membered rings a r e 1.6' and 4.5', respectively. Thus, the molecular structure excluding the tert-butylthio substituent has approximate Du symmetry. The chemically equivalent but significantly different structural parameters in a crystal structure are as follows: C,-C2 (1.388 %.) and C4-C5 (1.401 A), CI-C2-C3 (151.6') and C3-C4-C5 (1 56.4'),
1).
(4) Miki, S . Ph.D. Thesis, Kyoto University, 1978. This compound was synthesized by the reaction of tris(rerr-butylthio)cyclopropenium perchlorate with sodium bicarbonate in refluxing ethyl acetate in 90% yield. ( 5 ) Yoshida, Z.; Shibata, M.; Kida, S.; Miki, S.; Sugimoto, T.; Yoneda, S . Tetrahedron Lett. 1984, 345. (6) Webster, 0. W. J . Am. Chem. Soe. 1966, 88, 3046.
Figure 1. (a) Molecular structure of 2s shown by the ORTEP-II drawing. Thermal ellipsoids for non-hydrogen atoms are drawn at the 30% probability level. The hydrogen atoms are shown as the spheres with radii of 0.1 A. (b) Selected bond distances and angles in the molecular structure of 2a. The estimated standard deviations are 0.002 .& for C-S and 0.003-0.004 A for C-C bonds, O.Io for C-S-C and 0.1-0.2° for S-C-C and C-C-C angles. Distances and angles omitted in the figure are as follows: C I 7 C l 8= 1.522 A, C I 7 C l 9= 1.524 A, CI7-C,, = 1.534 A,S-€,,-Cls = 109.5", S-CI7-Cl9 = 109.9O, and S-CI7-C2, = 103.4O.
C2-C3-S (143.1') and S-C3-C4 (155.6'), and C8.C,-C, (127.5') and C4-C5-C6 (130.8'). All the bond angles along the S-C3C4-C5system are larger than those along the S-C3€&1 system with the same trend of a slight elongation in C4-C5bond compared with the C1-C2 bond, indicating that the sixteen-membered ring deforms significantly from the DZhsymmetry. This deformation can be attributed mainly to the steric effect of the tert-butylthio substituent. The nonbonded distance between C I 8and H, is 3.23 A, which represents a normal van der Waals contact in considering the van der Waals radii of methyl carbon (2.0 A) and hydrogen (1.2 A). The preliminary X-ray structure analysis of 2b has already been r e p ~ r t e d . The ~ planarity of 2b is greater than that of 2a. The A values of the sixteen-, eight-, and five-membered rings are 0.023, 0.003, and 0.010 A, respectively. The dihedral angles between the eight- and five-membered ring planes and between the eightand three-membered ring planes are 0.6' and 0.8', respectively. In addition to the high planarity of the molecule, the bond dis-
7034 J. Am. Chem. SOC.,Vol. 108, No. 22, 1986
Sugimoto et al. -0.10-
(a)
b lQi
124.7-130.5
+0.02
t.8"
