Möbius bis and tris-Spiro-aromatic Systems

David Hall and Henry S. Rzepa*

Department of Chemistry, Imperial College, London, SW7 2AY

Summary: We propose that a general class of bis and tris-spiro 7-membered ring systems with a common atom X, of which there are a number of examples characterised crystallographically, can in fact be considered as spiroaromatic molecules in which each ring exhibits some degree of Möbius 4np-electron aromaticity. The aromaticity is probed as a function of the spiro-atom using ab initio calculations of the NICS(0) values, which indicate that the Möbius-aromaticity increases as the spiro-atom is changed e.g. from Al to P, and from e.g. P to As.

Graphical Abstract

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Table 1. Representative examples in the Cambridge Database exhibiting structural features of 2 - 5.a

yetreu/B(III)b perjeb/Al(III)c zohvib/Al(III)d ubiqur/In(III)e
kezqah/Ga(III)f gukdiz/Si(IV)g gukdul/Ge(IV)g gajfus/Sn(IV)h
mspaps/P(V)i paqwuz/P(V)j eapdop10/P(V)k doxlor/As(V)l
hegday/Sb(V)m yegduj/Bi(III)n tpcate/Te(IV)o tectcl/Te(IV)p
qirpuc/La(III)q qazreo/Y(III)r govsoz/Ti(IV)s cigtuh/Ti(IV)t
bzdtzr10/Zr(IV)u HOVTUH/V(IV)v rilhoj/Nb(V)w bzdtnb10/Nb(V)x
cuqgea/Cr(III)y doxqai/Cr(V)z sixwif/Mo(V)z gefkor/W(IV)aa
aCambridge reference code and oxidation state of X as determined from the charge on the counter ions (not shown). b K. Ishihara, M. Miyata ,K. Hattori, T. Tada and H. Yamamoto J. Am. Chem. Soc., 1994, 116, 10520. cT. Arai, H. Sasai, K. Yamaguchi and M.S Hibasaki J. Am. Chem. Soc., 1998, 120, 441. dT. Arai, H. Sasai, K. Aoe, K. Okamura, T.Date, M. Shibasaki Angew.Chem.,Int.Ed.Engl., 1996, 35, 104. eS. Chitsaz and B. Neumuller Organometallics, 2001, 20, 2338. fS. Matsunaga, J. Das, J. Roels, E. M. Vogl, N. Amamoto, T. Iida, K.Yamaguchi and M.Shibasaki J. Am. Chem. Soc., 2000, 122, 2252. g R. Tacke, A. Stewart, J. Becht, C. Burschka and I.Richter, Can.J.Chem., 2000, 78, 1380. h R. R. Holmes, S. Shafieezad, V. Chandrasekhar, A. C. Sau, J. M. Holmes, R. A. Day J. Am. Chem. Soc., 1998, 110, 1168. iH. Wunderlich Acta Crystallogr.,Sect.B, 1981, 37, 995. jD. J. Sherlock, A. Chandrasekaran, T. K. Prakasha, R.O.Day, R. R. Holmes Inorg. Chem., 37, 93. kH. R. Allcock, E. C. Bissell J. Am. Chem. Soc., 1973, 95, 3154. lB. A. Borgias, G. G. Hardin, K. N. Raymond Inorg. Chem., 1986, 25, 1057. mJ. Wegener, K. Kirschbaum and D. M. Giolando J. Chem. Soc., Dalton Trans., 1994, 1213. nG. Smith, A. N. Reddy, K. A. Byriel and C. H. L. Kennard Aust. J. Chem., 1994, 47, 1413. oK. von Deuten, W. Schnabel, G. Klar Cryst. Struct. Commun., 1980, 9, 161. pO. Lindqvist Acta Chem.Scand., 1967, 21, 1473. qT. Nemoto, T. Ohshima, K. Yamaguchi and M. Shibasaki J.Am.Chem.Soc., 2001, 123, 2725. rH. C. Aspinall, J. F. Bickley, J. L. M. Dwyer, N. Greeves, R. V. Kelly and A. Steiner Organometallics, 2000, 19, 5416. sTing-Bin Wen, Bei-Sheng Kang, Cheng-Yong Su, Da-Xu Wu, Li-Ge Wang, Sen Liao and Han-Qin Liu Bull.Chem.Soc.Jpn., 1998, 71, 2339. tB. A. Borgias, S. R. Cooper,Y. B. Koh and K. N. Raymond Inorg. Chem., 1984, 23, 1009. uM. Cowie and M. J. Bennett Inorg.Chem., 1976, 15, 1595. vBei-Sheng Kang, Xiu-Jian Wang, Cheng-Yong Su ,Han-Qin Liu, Ting-Bin Wen and Qiu-Tian Liu Transition Met.Chem., 1999, 24, 712. wP. R. Challen, D. H. Peapus and K. A. Magnus, Polyhedron, 1997, 16, 1447. xM. Cowie and M. J. Bennett, Inorg. Chem., 1976, 15, 1589. yR. J. Cross, L. J. Farrugia, D. R. McArthur, R. D. Peacock and D. S. C. Taylor, Inorg.Chem., 1999, 38, 5698. zHo-Chol Chang, S. Kitagawa, M. Kondo and T. Ishii, Mol. Cryst. Liq. Cryst. Sci. Technol.,Sect.A, 1999, 335, 183. aaC. Lorber, J. P. Donahue, C. A. Goddard, E. Nordlander and R. H. Holm, J. Am. Chem. Soc., 1998, 120, 8102.
Table 2. B3LYP/6-31G(d) Calculated energies (Hartree) and NICSa Values (ppm) for 1-5
Substituentsb Energy, Y=O NICS (angle)a Energy, Y=NR NICS (angle)a
1, X=N, R=H -359.53314 17.4 (45.7) -319.93038
 26.7 (34.9)
1, X=N, R=F -756.39305 (365.7i)c 11.1 (54.0) -915.07525 (189.9i)c
 -1.0 (59.0)
1, X=P, R=H -646.31012 18.6 (23.7) -606.60521
 19.4 (38.0)
1, X=P, R=F -1043.17777 (167.6i)c 14.3 (41.2) -1201.76006 (112.6i)c
 -2.0 (54.6)
2, RR, X=N, R=H -664.72355 -1.3 (76.6) -585.371678
 -2.8 (73.8)
2, RR, X=N, R=F d d -1775.73438
 -9.0 (84.3)
2, RR, X=P, R=H -951.62957 -0.2 (56.6) -872.17703
 -0.7 (55.4)
2, RS, X=P, R=H 0.2e -0.3 (57.4) 4.8e
 -0.7 (54.2)
2, RR, X=P, R=F -1745.37896 -4.5 (63.2) -2062.50669
 -9.3 (64.7)
2, RS, X=P, R=F 0.9e -4.5 (62.9) -0.6e
 -8.8 (60.0)
4, X=P, R=H -796.78568 -7.4 (0.0) -717.36303
 -9.8 (0.0)
3, RRS, X=Al, R=H -1158.153405 0.2, 0.3 (33.5, 34.4) -1038.79166
 0.0, 0.1 (39.0, 39.1)
3, RRS, X=Si, R=H -1205.36111 -1.0, -0.4 (43.0, 53.0) -1086.03770
 -1.4, -1.6 (42.5, 42.3)
3, RRS, X=Ge, R=H -2990.82401 -2.5,-2.3 (57.7, 58.9) -2871.52125
 -2.2,-2.9 (44.5, 53.9)
3, RRS, X=P, R=H -1257.16780 -2.6, -2.7 (67.2, 66.9) -1137.8865
-3.4,-3.4 (42.0, 53.9)
3, RRR, X=P, R=H 1.7e -2.2 (66.5) -4.7e
 -4.2 (55.0)
3, RRS, X=P, R=F -2447.98997 -6.7, -6.9 (69.2, 69.0) -2923.62738
 -9.4, -10.0 (69.2, 69.0)
3, RRR, X=P, R=F 0.8e -6.6 (69.3) 5.0e
 -10.2 (62.8)
3, RRS, X=As, R=H -3149.58333 -3.7,-3.4 (67.3, 68.3) -3030.31362
 -4.3, -4.4 (56.7, 58.8)
5, X=P, R=H -1024.96531 -6.3 (0.0) -905.65126
 -3.0 (0.0)

aNICS(0) value, ppm (dihedral angle a-b-c-d). b The designation RR/RS or RRR/RRS indicates relative rather than absolute chiral configurations for the 7-membered rings. c Wavenumber for imaginary normal mode corresponding to distortion to 6. d Dissociates to C4F4O2 and C4F4NO2+. e Energy (kcal/mol) relative to chiral diastereomer.

Figure 1. B3LYP/6-31G* computed molecular orbitals, contoured at 0.01 Hartree for (a) HOMO of 1, X=N, Y=NF, (b) HOMO of 1, X=P, Y=NF, (c) HOMO of 2, X=N, Y=NF, (d) HOMO-1 of 2, X=N, Y=NF, (e) HOMO of 2, X=P, Y=N, (f) HOMO-1 of 2, X=P, Y=NF, (g) HOMO of 3, X=P, Y=NF, (h) HOMO-1 of 2, X=P, Y=NF

(a) (b)
Orbital 49 Orbital 53
(c) (d)
Orbital 94 Orbital 94
(e) (f)
Orbital 99 Orbital 98
(g) (j)
Orbital 53 Orbital 53