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Hypercoordinated Carbon in 2,8,9-Sila- and Thia-Substituted Carbatranes

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Hypercoordinated Carbon in 2,8,9-Sila- and Thia-Substituted Carbatranes Chemistry Publications Chemistry 6-2007 Hypercoordinated Carbon in 2,8,9-Sila- and Thia- Substituted Carbatranes Valerii F. Sidorkin Siberian Branch of the Russian Academy of Sciences Elena F. Belogolova Siberian Branch of the Russian Academy of Sciences Mark S. Gordon Iowa State University, [email protected] Maria I. Lazarevich Siberian Branch of the Russian Academy of Sciences Nataliya F. Lazareva Siberian Branch of the Russian Academy of Sciences Follow this and additional works at: http://lib.dr.iastate.edu/chem_pubs Part of the Chemistry Commons The ompc lete bibliographic information for this item can be found at http://lib.dr.iastate.edu/ chem_pubs/489. For information on how to cite this item, please visit http://lib.dr.iastate.edu/ howtocite.html. This Article is brought to you for free and open access by the Chemistry at Iowa State University Digital Repository. It has been accepted for inclusion in Chemistry Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Hypercoordinated Carbon in 2,8,9-Sila- and Thia-Substituted Carbatranes Abstract Ab initio methods demonstrate that internally protonated forms (a) of the molecules of carbatranes XC(SiH2CH2CH2)3N (X = H, F) are significantly more favorable than their externally protonated forms (b). The quantum-topological AIM approach suggests that the main reason for that is the formation of a medium-strength hydrogen C···H+N bond unknown previously in the silacarbanyl cations a. Disciplines Chemistry Comments Reprinted (adapted) with permission from Organometallics 26 (2007): 4568, doi:10.1021/om700306x. Copyright 2007 American Chemical Society. This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/chem_pubs/489 4568 Organometallics 2007, 26, 4568-4574 Hypercoordinated Carbon in 2,8,9-Sila- and Thia-Substituted Carbatranes Valery F. Sidorkin,*,† Elena F. Belogolova,† Mark S. Gordon,‡ Maria I. Lazarevich,† and Nataliya F. Lazareva† A. E. FaVorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, FaVorsky, 1, Irkutsk 664033, Russian Federation, and Department of Chemistry, Iowa State UniVersity, Ames, Iowa 50011 ReceiVed March 29, 2007 The structures of carbatranes XC(SiH2CH2CH2)3N(8) and XC(SCH2CH2)3N(9), where X ) H, F, and their in and out protonated forms were studied at the MP2 level of theory using the 6-31G*, 6-311G**, and 6-311++G** basis sets. Compounds 8 and 9 are the first representatives of the derivatives of 5-aza- 1-carbabicyclo[3.3.3]undecanes, whose endo-isomer contains a nitrogen lone electron pair directed inside the cage. The geometrical, AIM, and NBO peculiarities of sila- (8) and thiacarbatranes (9) are indicative of the existence of a weak coordination XCrN interaction in these compounds, which is enhanced with the increasing of electronegativity of the axial substituent X. The MP2 and MP4/SDQ(T) (single-point calculations) methods demonstrate that the in protonated forms of compounds 8 are significantly (>6 kcal/mol) more favorable than their out forms. The quantum-topological AIM approach suggests that the main reason for this is the formation of a medium-strength (4-15 kcal/mol) hydrogen C1‚‚‚H+N bond unknown previously in the in silacarbanyl cations. That bond provides a high pentacoordination degree (>60%) of the bridged carbon atom C1 in the compounds. Introduction Chart 1 Regardless of the nature of the substituent X, the molecules of 2,8,9-substituted 5-aza-1-silabicyclo[3.3.3]undecanes, XSi- (YCH2CH2)3N (at Y ) O(1), NR (2), CH2 (3),S(4)), possess geometries with an endo-orientation of the nitrogen lone electron pair (LEP). This orientation is in principle favorable for its donor-acceptor interaction with the orbitals of the XSiY3 fragment.1-8 The possibility of this interaction is excluded for the probable exo-isomers of these molecules. At the same time, according to ab initio calculations, the exo-isomers do not correspond to minima on the corresponding potential energy 1 are often referred to as silatranes. Throughout this paper we surfaces (PES).9-11 use the designation “silatranes” for XSi(YCH2CH2)3N with any 6 Y. An increase in the coordination number of the Si atom in According to the Verkade definition, atranes XSi(YCH2- silatranes to five is observed with milder electronegativity CH2)3N with Y ) O, NR, CH2, and S are the oxa-, aza-, carba-, and thiasilatranes, respectively. Various oxasilatrane derivatives demands on the axial substituent X (for example, X may be H, Alk) as compared with other hypervalent silicon compounds.12-15 * Corresponding author. E-mail: [email protected]. Tel: +7-3952- This can be attributed to the following. In compounds 1-4 the 424871. Fax: +7-3952-419346. connection of three equatorial Y atoms with the N-donor † A. E. Favorsky Irkutsk Institute of Chemistry. ‡ Iowa State University. center ensures a linear structure of the axial XSiN fragment, (1) Voronkov, M. G. Pure Appl. Chem. 1969, 19, 399. and the three five-membered SiYCCN heterocycles formed with (2) Sidorkin, V. F.; Pestunovich, V. A.; Voronkov, M. G. Usp. Khim. Si‚‚‚N interaction are almost unstrained.16,17 1980, 49, 789; Russ. Chem. ReV. (Engl. Transl.) 1980, 49, 414. (3) Hencsei, P.; Pa´rka´nyi, L. In ReViews on Silicon, Germanium, Tin A steric promotion to the trigonal-bipyramidal (TBP) structure and Lead Compounds; Gielen, M., Eds.; Freund Publishing House: Tel- of the coordination center XSiY3N, being characteristic of the Aviv, 1985; Vol. 8, pp 191-218. (4) Tandura, S. N.; Voronkov, M. G.; Alekseev, N. V. Top. Curr. Chem. (12) Chuit, C.; Corriu, R. J. P.; Reye, C.; Young, J. C. Chem. ReV. 1993, 1986, 131, 99. 93, 1371. (5) Greenberg, A.; Wu, G. Struct. Chem. 1990, 1, 79. (13) Voronkov, M. G.; Pestunovich, V. A.; Baukov, Yu. I. Metalloorg. (6) Verkade, J. G. Coord. Chem. ReV. 1994, 137, 233. Khim. 1991, 4, 1210; J. Organomet. Chem. USSR (Engl. Transl.) 1991, 4, (7) Lukevics, E.; Pudova, O. A. Teor. Eksp. Khim. Khim. Geterotsikl. 593. Soedin. 1996, 1605; Chem. Heterocycl. Compd. (Engl. Transl.) 1996, 32, (14) Pestunovich, V. A.; Sidorkin, V. F.; Voronkov, M. G. In Progress 1381. in Organosilicon Chemistry; Marciniec, B., Chojnowski, J., Eds.; Gordon (8) Pestunovich, V.; Kirpichenko, S.; Voronkov, M. In The Chemistry and Breach Science Publishers: New York, 1995; pp 69-82. of Organic Silicon Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley: (15) Kost, D.; Kalikhman, I. In The Chemistry of Organic Silicon Chichester, 1998; Vol. 2, Part 2, pp 1447-1537. Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley: Chichester, 1998; (9) Csonka, G. I.; Hencsei, P. J. Comput. Chem. 1996, 17, 767. pp 1339-1445. (10) Schmidt, M. W.; Windus, T. L.; Gordon, M. S. J. Am. Chem. Soc. (16) Voronkov, M. G.; Keiko, V. V.; Sidorkin, V. F.; Pestunovich, V. 1995, 117, 7480. A.; Zelchan, G. I. Khim. Geterotsikl. Soed. 1974, 5, 613 (Chem. Abstr. 1974, (11) Boggs, J. E.; Chunyang, P.; Pestunovich, V. A.; Sidorkin, V. F. J. 81, 119809h). Mol. Struct (THEOCHEM) 1995, 357, 67. (17) Csonka, G. I.; Hencsei, P. J. Organomet. Chem. 1993, 446, 99. 10.1021/om700306x CCC: $37.00 © 2007 American Chemical Society Publication on Web 07/14/2007 Hypercoordinated Carbon in Sila- and Thia-Substituted Carbatranes Organometallics, Vol. 26, No. 18, 2007 4569 Chart 2 the molecule in question and BH+ designates its protonated form. The ∆E and PA values were estimated using the MP2 method with the geometry and ZPVE obtained at the MP2/6-31G* level of theory and were refined with the single-point MP4(SDQ(T))/6-311G** calculations. The integral equation formalism version of the polarized continuum model (IEF-PCM)22 was employed for the estimation of polar solution (DMSO) effects on the MP2/6-31G* geometry of 8. The calculations were performed using the GAUSSIAN23 program package. The GAMESS24 electronic structure code was employed for performing the resource consuming harmonic fre- 5-aza-1-silabicyclo[3.3.3]undecane derivatives, is a promising quency calculations with the same exponents as have been used reason to obtain their carbon analogues, carbatranes XC(YCH2- for geometry optimizations. 18 CH2)3N. However, numerous efforts to synthesize the oxa- We used the geometrical criterion shown in eq 2 to estimate the (Y ) O(5)) and azacarbatranes (Y ) NR (6)) have failed.2,6 trigonal bipyramidal (TBP) pentacoordination character of the More recently, it has become clear from ab initio and DFT bridged carbon atom, ηe, in carbatranes, where θn are the equatorial - 1- calculations that carbatrane molecules 5, 6, and 7 (Y ) CH2), Y C Y angles. The ηe parameter was suggested by Tamao et regardless of the X nature, exist exclusively in the exo-form; al.25 for determination of the “ideal” TBP structure contribution to - this is their essential distinction from silatranes 1-3.19 21 the geometry of actual hypervalent silicon compounds. The ηe value Minima corresponding to endo-forms have not been found on is equal to 0% at the “ideal” tetrahedral configuration of bonds at 1 ) ° ) ) ° the PES of 5-7. A possible reason for the dramatic change of C (θ 109.5 ) and ηe 100% (θ 120.0 )ataTBP the N atom configuration upon substitution of the silicon atom configuration. - in 1 3 by the carbon is a drastic increase in the strain that 3 occurs when these heterocycles try to retain the atrane structural ) - - - × ηe [1 [(120 1/3∑θn)/(120 109.5)]] 100% (2) arrangement. It is interesting to consider whether this reason is n)1 an insurmountable obstacle for carbatranes to achieve a geom- etry with a nitrogen LEP directed inside the cage. Can carbatrane Analysis of the electron density in terms of the atoms in isomers have a pentacoordinate carbon atom C1? To explore molecules (AIM) theory26 was performed using the MORPHY1.027 this question, we have considered the structures of the molecules program.
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