energies for highest occupied eV, whereas is 10.3-13.0 eV. For carboni - PDF document

J. Am. Chem. Sot. 1981, 103, 1375-1380 1375 energies for highest occupied eV, whereas is 10.3-13.0 eV. For carbonium the empty be questioned whether minimal set calculations underestimate mixings between occupied virtual orbitals. Actually, they tend this point, may be cautious in this in mind some proposals analyses. Tilting much faster increases stabilizing in- (28) Umeyama, H.; Morokuma, K. J. Am. Chem. SOC. 1977, 99, 1316. between occupied Conclusion finding in initio calculations, structurally similar present results made to the American Chemical Mayr, H.; Chandrasekhar, J.; Schleyer, this issue. Anionic Systems: Bicyclo[ 3.2.1 ]octa-3,6-dien-2-yl Jayaraman Chandrasekhar, der Friedrich-Alexander Erlangen, Federal anion (6), considered to prototype bishomoaromatic Applequist and Roberts recognized the unusual stability of the cyclobutenylium ion (l).I 1 2 3 4 cilitates substantial 1,3-~-bonding; an cyclopropenyl cation electronically, (1) Applequist, D. E.; Roberts, J. D. J. Am. Chem. SOC. 1956, 78, 4012. 0002-7863/81/1503-1375$01.25/0 systems with destroyed completely one or more intervening groupsS2 This rapid accept- 81, 6524. reviews see: theoretical treatments, 1972, 94, 8908; 5807; 1974, Haddon, R. C. (d) Jorgensen, American Chemical 1376 J. Am. Chem. SOC., Vol. 103, No. 6, 1981 aromatic), and 48 (trishomoaromatic) are well-established exam- ples. Chemists were and homoantiaromaticity interacting frag- “homoconjugative interactions between neutral are destabilizing” homoaromaticity. Experimental According to Win~tein~~ and to Goldstein and Hoffmann: stabilizing I interactions should be observable in appropriately constituted anions as well as in cations. However, we have already demonstrated that the potentially homoaromatic cyclohexadienyl anion 5 does not show homoconjugative 1,5-intera~tion.’@~ We Kaufmann et al. suggested that, in general, monohomoaromaticity should be less significant in anions than in cations. The bicyclo[3.2.l]octa-3,6-dien-2-yl anion (6), with 6 I elec- trons, is the most widely cited example of alleged anionic ho- moaromaticity; the experimental data seem to provide particularly convincing support of the predictions of qualitative I-MO theory. We have examined the degree of .rr interaction in 6 and related anions by means of quantitative semiempirical and ab initio MO calculations. The corresponding potentially antiaromatic 41 cationic system, 7, and its relatives have also been included in our study. Experimental Data was first suggested account for rapid base-catalyzed benzo[6,7]bicyclo[3.2. l]octa-2,6-diene13 l]octa-2,6-diene13 ’The 2.3-ppm high-field evidence for 6a 6b 7 Liang, G. 1975, 97, 5489. G.; Friedrich, (b) Warner, (c) Winstein, M.; Prange, Angew. Chem., Int. Paquette, L. Broadhurst, M. Olah, G. J. Am. Norton, C.; (b) Winstein, Shatavsky, M. (c) Winstein, Hansen, R. Gassman, P. G.; R. K.; Brookhart, M.; Winstein, G.; Patton, G., Jr.; Vries, L. (b) Winstein, 1961, 83, 3235, 3244. C.; Baker, R.; Lin, Y. (d) Masamune, (e) Coates, Olah, G. A,; Surya Prakash, G. Goldstein, M. Hoffmann, R. Radom, L. (b) Houk, N.; Gandour, W.; Strozier, R. W.; Rondan, L. A. 1979, 101, 6797. (c) Olah, A.; Asensio, G.; Mayr, (d) Christoph, G. G.; Muthard, further theoretical W.; Avramides, Birch, A. A. L.; Radom, L. T.; Simmons, 1976, 98, 8401. (1 1) Goebel, P.; Sass, R. Turner, R. Yii, A. J. Am. (c) Jorgensen, W. Borden, W. Jorgensen, W. L. (e) Roth, W. R.; Lennartz, H.-W. 1980, 113, Andrews, G. D.; Baldwin, Gilbert, K. Chim. Acta J. Am. C.; Heilbronner, 1974, 96, 7662. P.; Gleiter, R.; H.; Ruge, Herbst, P. 1976, 109, Hill, R. Morton, G. W.; Choi, a 9 They demonstrated only 3.3 times faster eph Ph H bPh Ph H &qPh Ph 10 11 12 the other “homoaromatic” anion other than homoconjugation might be responsible corresponding cation for interaction was 235 times slower b““’ / / 13 14 Winstein considered be “in that the inductive effect be analyzed more directly in anions proton coupling Chem. Commun. 92, 3821. M.; Cain, Moncur, M. J. Am. (b) Goldstein, M. 1973, 95, 6451. M.; Sakai, M.; Nicholson, A. F.; Sakai, M.; Winstein, Sustmann, R.; Gellert, R. W. Kawamura, T.; Takeichi, Sakamoto, M.; Yonezawa, Sustmann and J. Am. Chem. SOC., Vol. 103, No. 6, 1981 1377 15 16 that the allylic hyperfine coupling with protons H-2, H-3, and not reduced bond in showed only couplings in excluding significant delocalization conclusion was Gellert reported display homoconjugative suggested a distortion Discussion is based a comparison geometric, electronic, energetic properties and the 4~ cation Cations 17 19 22 Anions 18 21 24 from the triene orbital symmetry enforces a different interaction pattern than antisymmetric (Figure antisymmetric orbital, butadiene fragment bond in either cation from symmetry procedures were these interactions. Complete geometry opti- carried out etries were then initio calculations with one change: were set also with complete geometry optimizations, and singlepoint initio calculations Since the results were identical (deviations previously been systems considered here. This stabilization energies based structures and (19) Dewar, 236, Indiana University, University, Bloomington, Indiana. (21) Hehre, W. J.; Stewart, R. F.; Pople, J. A. J. Chem. Phys. 1969, 51, 2657. (22) Complete optimization without symmetry restrictions level showed energy minimum correspond to L., preceding paper this issue. (23) Bingham, R. C.; Dewar, M. J. S.; Lo, D. H. J. Am. Chem. Soc. 1975, 97, 1285. drawings were the STO-3G In homoaromatic ions like place which increase not provide evidence for allylic bond virtually unchanged 18, 21, double bonds. almost identical allylic bond calculated for 7, 17, 19, cyclic conjugation might be a reduction to that the C-2-C-7 4~ system other cations insignificantly different from corresponding anions. Homoaromatic interaction occurs in the appropriate negligible in the STO-3G (Figure 2) this clearly. two systems recognized in primarily localized also shown the HOMO'S revealing: they virtually identical. in these additional double and Bond population analyses shown in carbons C-2 the other only 0.026 also found 7, 17, in which nearly identical and C-7 those in observed in partially reflected a net increase and C-7 However, a similar is seen in 7, and 9 in more electrons, their neutral counterparts. appears to be relatively insensitive additional double increased shielding does not necessarily imply cyclic delocalization. all small antibonding interaction In particular, overlap population corresponding cation (-0.043 vs. energetic impact eq 1 Anlon 18 6 -4.2 (t0.6) (1) 9 7 12.9 (t1.0) (2) 8 Cation 17 obtained from almost thermoneutral, initio calculations a stabilization (4 kcal/mol) saturated counterpart 1318 J. Am. Chem. Soc.. Vol. 103, No. 6, 1981 Kaufmann et al. n &- , ‘-\ \ \ \ n I I I . -- I-- I --H A $2 WTt Tt 22 24 -I- SI L 1% 21 with ethylene different orientations. Hydrocarbons and C-14-2 C-243 C-5-C-6 C-14-8 C-24-7 C-2C-8 X species (C-44-5) (C-3-C-4) (C-14-7) C-6-C-7 ((2-54-8) C=CH, (C-44-6) (C4-C-8) 1.511 1.406 1.573 1.563 2.543 2.488 9 1.519 1.351 1.557 2.529 2.481 1.514 1.561 1.502 1.394 1.567 1.551 1.562 X 7 1.513 1.573 2.483 1.351 1.531 1.354 1.567 2.484 2.486 1.558 1.517 1.565 2.543 2.540 X 1.513 1.404 1.487 1.565 2.470 2.497 1.535 1.495 1.560 2.492 2.498 1.558 1.342 1.500 1.394 1.545 1.497 1.563 1.344 2.503 4 2.549 2.439 23 1.518 1.560 1.550 1.531 1.337 2.542 1.512 1.562 1.529 2.609 2.498 1.502 1.394 1.567 2.552 2.449 X Table IL Charges on Carbon and Overlap Populations (STO-3G) in Hydrocarbons and Ions (C-4) C-3 ~(4-6) ~(4-8) -0.099 -0.100 -0.065 -0.107 -0.105 -0.057 -0.050 X -0.044 -0.078 -0.094 -0.048 -0.050 -0.044 -0.045 -0.043 -0.053 -0.032 -0.242 -0.068 -0.093 X -0.063 +0.004 -0.102 -0.136 -0.047 -0.048 -0.111 +0.008 -0.105 -0.174 X +0.134 -0.098 -0.104 -0.034 23 -0.048 -0.064 -0.064 -0.106 +0.020 -0.153 -0.110 -0.102 -0.039 -0.048 -0.036 -0.251 -0.060 -0.104 +0.037 -0.199 -0.056 9 9* X in Anionic J. Am. Chem. Soc., Vol. 103, No. 6, 1981 1379 HOMO 5 anions and Hydrocarbons and species AH*' (MNDO) E+,+ 6TO-3G) 17 9 18 7 8 6 19 20 21 24 202.4 0.2 7.7 236.8 33.6 41.7 243.6 44.2 49.4 222.0 21.9 27.7 -305.461 72 - 306.260 70 -305.445 42 -304.225 57 -305.029 16 -304.220 64 -380.18377 -380.981 86 -380.179 30 -342.817 40 -343.616 29 -342.808 67 bond is thus regard and the not find actions? Homoconjugative interactions may too small be seen functions. Alternatively, inductive effect additional double be used these two Anion 18 21 -8.0 (-2.3) (31 Catton 17 19 -0.6 (-2Bl (41 20 9 24 -48 1-17] (5) 23 9 Anion 18 cation 17 22 00(-21) (6) additional double interactions with inhibited. Nevertheless, defer detailed effects in alleged homoaromatic cations next paper this series where systems better constituted for favorable interactions Conclusions anion (6) is clearly not a bishomoaromatic system, same may which have 25 26 27 28 ph example, probably not have gested delocalized electron system this series. parallel work, Grutzner and Jorgensen concluded that the due to 29 30 31 general rule not observable anionic systems. not consider not sufficient predicting stabilizations is likely fragment orbitals their interactions9 do because both and the energy difference between combination with similar-in magnitude to that with two exo the owration inductive effect. Unlike (24) Anastassiou, A. G.; Kasmai, H. J. Chem. SOC., Chem. Commun. 107s mi 11,_.( ,&"I. Homoconjugative interactions small magnitude, be involved. for sp3- (25) Trimitsis, G. B.; Crowe, E. W.; Slomp, G.; Helle, T. L. J. Am. Chem. (26) Paquette, L. A,; Kukla, M. J.; Ley, S. V.; Traynor, S. G. J. Am. 1271 Goldstein. M. J.: Nomura. Y.: Takeuchi. Y.: Tomoda. S. J. Am. Sot. 1973,95,4333. Chem, sot. 19,7, 99, 4756. sp2-hybridized carbons, Chem.'Soc. 1978,' 100, 4899. 1380 previous conclusions homoaromaticity does not is not effect in anions,lk this homoaromaticity may systems which can distort interacting orbitals. J. Am. Chem. SOC. 1981, 103, 1380-1383 thank R. Gleiter for informing their work prior Chemischen Industrie for financial and the Rechenzentrum Erlangen with Acyclic Organique et Belgium. Received interesting finding the considerable difference complexation enthalpies and entropies: sodium complex (2+Na), the This difference reflects pyridine 1-Na (but formation. When the used, solvent coordination to the cation significant for the Introduction complexes with ushered in a routinely used many industrial also for their cation- binding selectivity.s Crown ethers those present many antibiotic ionophore antibiotics include monensin, nigericin, grisorixin, A (lasalocid), alborixin, in a cyclic speciese6 Acyclic synthetic analogues should behave and thus to the oligoethers, called no need for high-dilution effects in their preparation.* group has numerous such potential utility for studying cation binding a preliminary communication complexing properties report here results obtained also have selected these ligands, synthesized in Professor Vogtle in Chimie Organique et de Biochimie, Universitd Sart-Tilman par Chemistry, Florida University, Tallahassee, Florida R. M. Ace. Chem. In “Synthetic Multi- Macrocyclic Compounds”; Vogtle, F.; Rest, A. Inorg. Chem. Tech. Lab. Laszlo, P.; 351-384. Chart I 4&R 3\ 2 ‘a: 2’ 1, n = 1, R = -NHCOCH, 2, n = 3, R = -NHCOCH, 3, n = 1, R = -CONHCH, ~,~=~,R=-NH--co 9 NO? w R p-R R NA -0 0- 6, R = -CO- NH L/ 7 (())3,6,9-trioxaundecane; 5, 1,ll-bis[o-[ [o-(10-(0-nitrophenyl) 1,4,7,10-tetraoxadecyl)phenyl] amido] phenoxy]-3,6,9- include pentaethers two nitrogen available for coordination to the ((2.2.1)~~)~3 0002-7863/81/1503-1380$01.25/0 American Chemical