2400
Organometallics 2010, 29, 2400–2402 DOI: 10.1021/om100290h
(Selenocarbamoyl)silanes and -germanes: Their Synthesis Using (Selenocarbamoyl)lithium and Characterization Toshiaki Murai,* Rumi Hori, Toshifumi Maruyama, and Fumitoshi Shibahara Department of Chemistry, Faculty of Engineering, Gifu University, Yanagido, Gifu 501-1193, Japan Received April 10, 2010 Summary: Deprotonation of the selenoformyl group in N,Ndibenzyl selenoformamide with LDA, followed by silylation and germylation of the resulting anion with Me3SiCl and Me3GeCl, gives (selenocarbamoyl)silane and -germane in moderate to good yields. The molecular structures of these products and the starting selenoformamide were characterized by using X-ray analyses. Studies of selenocarbonyl compounds have provided fruitful results for over 40 years.1 Owing to their lability, selenoaldehydes and -ketones2 have been generated in situ and trapped by their reactions with dienes. In order to stabilize these substances, bulky substituents are typically incorporated at the selenocarbonyl group.3 Although being dependent on their exact nature, heteroatom-containing functional groups, such as amino, alkoxy, sulfenyl, and selenenyl groups, introduced at the selenocarbonyl carbon also bring about stabilization of these compounds.4 As a result, selenoamides,5 selenoic acid O-esters,6 and their *To whom correspondence should be addressed. Tel: 81-58-293-2614. Fax: 81-58-293-2614. E-mail:
[email protected]. (1) For reviews: (a) Murai, T.; Kato, S. In Topics in Current Chemistry; Wirth, T., Ed.; Springer-Verlag: Berlin, 2000; Vol. 208, p 177. (b) Grobe, J.; Le Van, D. J. Fluorine Chem. 2004, 125, 801. (2) For reviews and recent examples of the generation and reaction of selenoaldehydes and -ketones: (a) Guziec, F. S., Jr.; Guziec, L. J. In Organoselenium Chemistry: A Practical Approach; Back, T. G., Ed.; Oxford University Press: Oxford, U.K., 1999; p 193. (b) Guziec, L. J.; Guziec, F. S., Jr. In Comprehensive Organic Functional Group Transformations, Katritzky, A. R., Taylor, R. J. K., Eds.; Elsevier: Oxford, U.K., 2005; Vol. 3, p 397. (c) Okuma, K; Izaki, T.; Kubo, K.; Shioji, K.; Yokomori, Y. Bull. Chem. Soc. Jpn. 2005, 78, 1121. (d) Shioji, K.; Matsumoto, A.; Takao, M.; Kurauchi, Y.; Shigetomi, T.; Yokomori, Y.; Okuma, K. Bull. Chem. Soc. Jpn. 2007, 80, 743. (e) Okuma, K.; Mori, Y.; Shigetomi, T.; Tabuchi, M.; Shioji, K.; Yokomori, Y. Tetrahedron Lett. 2007, 48, 8311. (f) Okuma, K.; Koda, M.; Shigetomi, T. Phosphorus, Sulfur Silicon Relat. Elem. 2008, 183, 1057. (3) Tokitoh, N.; Okazaki, R. Pol. J. Chem. 1998, 72, 971. (4) (a) Wu, R.; Barr, M. E.; Hernandez, G. O.; Charles, C. C.; Silks, L. A. Recent Res. Dev. Org. Bioorg. Chem. 1998, 2, 29. (b) Wu, R.; Hernandez, G.; Dunlap, R. B.; Odom, J. D.; Martinez, R. A.; Silks, L. A. Trends Org. Chem. 1998, 7, 105. (c) Bricklebank, N. Recent Res. Dev. Inorg. Organomet. Chem. 2001, 1, 25. (d) Guziec, L. J.; Guziec, F. S., Jr. In Comprehensive Organic Functional Group Transformations; Katritzky, A. R., Taylor, R. J. K., Eds.; Elsevier: Oxford, U.K., 2005; Vol. 6, p 573. (5) For reviews: (a) Moore, A. J. In Comprehensive Organic Functional Group Transformations; Katritzky, A. R., Taylor, R. J. K., Eds.; Elsevier: Oxford, U.K., 2005; Vol. 5, p 519. (b) Flynn, C.; Haughton, L. In Comprehensive Organic Functional Group Transformations; Katritzky, A. R., Taylor, R. J. K., Eds.; Elsevier: Oxford, U.K., 2005; Vol. 5, p 571. (c) Murai, T. In Topics in Current Chemistry; Kato, S., Ed.; SpringerVerlag: Heidelberg, Germany, 2005; Vol. 251, p 247. (d) Koketsu, M.; Ishihara, H. Curr. Org. Synth. 2007, 4, 15. (e) Koketsu, M.; Ishihara, H. In Handbook of Chalcogen Chemistry: New Perspectives in Sulfur, Selenium, Tellurium; Devillanova, F. A., Ed.; Royal Society of Chemistry: Cambridge, U.K., 2007; p 145. (e) Hua, G.; Woollins, J. D. Angew. Chem., Int. Ed. 2009, 48, 1368. (6) For a review: Wirth, T. Sci. Synth. 2005, 22, 181. pubs.acs.org/Organometallics
Published on Web 05/04/2010
Scheme 1
sulfur and selenium counterparts6,7 have been widely studied. In contrast, investigations probing the effects of silyl and germyl groups on the properties of selenocarbonyl compounds have not been conducted,8 owing in part to the lack of methods for the introduction of these functional groups. One of the most promising ways to introduce these groups is via the generation of selenocarbonyl anions and their reaction with silyl and germyl halides. However, only a limited number of examples of compounds bearing a selenoformyl group are known. As part of a long-range program to study selenocarbonyl compounds,9 we recently developed a convenient method for the synthesis of selenoformamides by the reaction of formamides, elemental selenium, trichlorosilane, and amines.10 Below, we describe the results of an effort that takes advantage of this methodology in routes for the synthesis of the first examples of (selenocarbamoyl)silanes and -germanes via (selenocarbamoyl)lithium. In addition, we have structurally characterized the (selenocarbamoyl)silanes and -germanes by using X-ray crystallographic and theoretical methods. In exploratory studies we observed that treatment of N,Ndibenzyl selenoformamide (1) with LDA at -78 °C for 2 h generates (selenocarbamoyl)lithium 2 (Scheme 1). Addition of chlorotrimethylsilane to the reaction mixture followed by stirring at -78 °C for 24 h and chromatographic purification (7) For reviews: (a) Murai, T. Synlett 2005, 1509. (b) Ishii, A.; Nakayama, J. In Topics in Current Chemistry; Kato, S., Ed.; Springer-Verlag: Heidelberg, Germany, 2005; Vol. 251, p 227. (8) In situ generation of selenoacylsilane and its trapping by a diene has been reported: Segi, M.; Koyama, T.; Nakajima, T.; Suga, S.; Murai, S.; Sonoda, N. Tetrahedron Lett. 1989, 30, 2095. (9) For recent examples, see: (a) Murai, T.; Aso, H.; Kato, S. Org. Lett. 2002, 4, 1407. (b) Tani, Y.; Murai, T.; Kato, S. J. Am. Chem. Soc. 2002, 124, 5960. (c) Murai, T.; Ishizuka, M.; Suzuki, A.; Kato, S. Tetrahedron Lett. 2003, 44, 1343. (d) Mutoh, Y.; Murai, T. Org. Lett. 2003, 5, 1361. (e) Murai, T.; Fujishima, A.; Iwamoto, C.; Kato, S. J. Org. Chem. 2003, 68, 7979. (f) Mutoh, Y.; Murai, T. Organometallics 2004, 23, 3907. (g) Mutoh, Y.; Murai, T.; Yamago, S. J. Organomet. Chem. 2007, 692, 129. (h) Murai, T.; Nogawa, S.; Mutoh, Y. Bull. Chem. Soc. Jpn. 2007, 80, 2220. (10) Shibahara, F.; Sugiura, R.; Murai, T. Org. Lett. 2009, 11, 3064. r 2010 American Chemical Society
Communication
Organometallics, Vol. 29, No. 11, 2010
2401
Figure 1. ORTEP drawings of selenoformamide 1 (left), (selenocarbamoyl)silane 3 (center), and (selenocarbamoyl)germane 4 (right).
on silica gel led to production of the (selenocarbamoyl)silane 3 as an air-stable solid.11 Similar treatment of the in situ generated (selenocarbamoyl)lithium 2 with chlorotrimethylgermane results in the production of (selenocarbamoyl)germane 4.12 It is important to note that 2 does not react in a similar fashion with chlorotrimethylstannane; rather, the starting selenoformamide 1 is recovered along with several unidentified products after aqueous workup. To determine the structural properties of 1, 3, and 4, X-ray crystallographic analyses were performed. ORTEP plots of the data are shown in Figure 1, and selected bond lengths and (11) To a solution of the diisopropylamine (0.29 mL, 2.1 mmol) in THF (5 mL) was added n-butyllithium (1.6 M solution in hexane, 1.3 mL, 2.1 mmol) at -78 °C under an Ar atmosphere followed by stirring for 30 min. To the mixture was added a solution of N,N-dibenzylselenoformamide (1; 0.29 g, 1.0 mmol) in THF (1 mL) at -78 °C followed by stirring for 2 h. To the mixture was added chlorotrimethylsilane (0.27 mL, 2.1 mmol) at -78 °C. The resulting mixture was stirred for 24 h, poured into water, and extracted with Et2O. The organic layer was dried over MgSO4, filtered, and concentrated in vacuo, giving a residue which was subjected to column chromatography on silica gel (hexane/EtOAc 8/1) to give N,N- bis(phenylmethyl)trimethylsilanecarboselenoamide (3; 0.23 g, 0.62 mmol, 63%, Rf = 0.56) as an orange solid. Mp: 71-73 °C. IR (KBr): 2958, 2927, 1450, 1422, 1351, 1240, 1210, 873, 839, 743, 697 cm-1. 1H NMR (CDCl3): δ 0.00 (s, 9H, SiCH3), 4.40 (s, 2H, CH2), 5.01 (s, 2H, CH2), 6.69 (d, J = 7.0 Hz, 2H, Ar), 6.78 (d, J = 6.0 Hz, 2H, Ar), 6.85-6.98 (m, 6H, Ar). 13C NMR (CDCl3): δ 2.00, 56.4, 58.8, 126.6, 127.5, 127.8, 128.1, 128.6, 129.0, 134.3, 134.5, 230.9. 77Se NMR (CDCl3): δ 827.1. MS (EI): m/z 361 [Mþ]. Anal. Calcd for C18H23NSeSi: C, 59.98; H, 6.43; N, 3.89. Found: C, 59.79; H, 6.48; N, 3.90. (12) To a solution of the diisopropylamine (0.15 mL, 1.1 mmol) in THF (5 mL) was added n-butyllithium (1.6 M solution in hexane, 0.66 mL, 1.1 mmol) at -78 °C under an Ar atmosphere followed by stirring for 30 min. To the mixture was added a solution of N,N-dibenzylselenoformamide (1; 0.14 g, 0.5 mmol) in THF (1 mL) at -78 °C followed by stirring for 10 min. To the reaction mixture was added chlorotrimethylgermane (0.13 mL, 1.1 mmol) at -78 °C. The resulting mixture was stirred for 24 h, poured into water, and extracted with Et2O. The organic layer was dried over MgSO4, filtered, and concentrated in vacuo, giving a residue which was subjected to column chromatography on silica gel (hexane/EtOAc 20/1) to give N,Nbis(phenylmethyl)trimethylgermanecarboselenoamide (4; 0.086 g, 0.21 mmol, 42%, Rf = 0.43) as a yellow solid. Mp: 76-78 °C. IR (KBr): 2960, 1601, 1494, 1422, 1350, 1199, 989, 834, 742, 696, 597, 567 cm-1. 1H NMR (CDCl3): δ 0.08 (s, 9H, GeCH3), 4.33 (s, 2H, CH2), 4.98 (s, 2H, CH2), 6.66 (d, J = 7.4 Hz, 2H, Ar), 6.77 (d, J = 6.4 Hz, 2H, Ar), 6.83-6.96 (m, 6H, Ar). 13C NMR (CDCl3): δ 2.54, 56.4, 59.3, 126.7, 127.7, 128.0, 128.2, 128.7, 129.1, 134.3, 134.6, 231.4. 77Se NMR (CDCl3): δ 785.1 (SedC). MS (EI): m/z 405 [Mþ]. Anal. Calcd for C18H23GeNSe: C, 53.38; H, 5.72; N, 3.46. Found: C, 53.62; H, 5.87; N, 3.39. (13) The computations were done using Gaussian 03. The hybrid density functional B3LYP along with the 6-311þG(d) basis set was used for the structure optimization and energy calculations. Further technical details are provided in the Supporting Information.
Figure 2. Representative bond lengths and angles of 1 and 3-5. Table 1. Representative Spectroscopic Properties of 1 and 3-5
a
Measured in CDCl3. b Measured in CHCl3.
angles are given in Figure 2. Bond lengths and angles derived from the theoretical calculations at the B3LYP level with a 6-311G(d) basis set13 are shown in parentheses in Figure 2. The results of a theoretical treatment of selenoamide 5,9 in which a tert-butyl group is present on the CdSe carbon, are also included in Figure 2. Analysis of the results shows that 1 and 3-5 are isostructural, but elongation of the CdSe bond length occurs in a similar manner when the hydrogen atom in 1 is replaced by tert-butyl, silyl, and germyl groups. No striking differences are observed in the CdSe bond lengths in 3-5. Finally, the Se-C-N bond angles were also found to decrease on going from 1 to 3-5. The spectroscopic properties of 1 and 3-5 were also determined (Table 1). Analysis of 13C NMR spectra shows that tert-butyl, silyl, and germyl groups deshield the CdSe carbon, exemplified by the greater than 35 ppm downfield shift for the carbons in 3 and 4 as compared with that of 1. The introduction of silyl and germyl groups to the carbonyl carbons of formamides is known to cause a slight shift to
2402
Organometallics, Vol. 29, No. 11, 2010
Figure 3. Energy levels of the HOMO and LUMO of compounds 1 and 3-5 at the B3LYP/6-311þG(d) level.
lower fields of CdO carbon resonances.14,15 A series of sulfur isologues of 3 and 4 display downfield shifts similar to those with HC(S)Bn2 (6),16 but the carbon resonances of 3 and 4 are more greatly shifted to lower fields. Likewise, downfield shifts are observed in the 77Se NMR spectra for 3-5 as compared to 1. The chemical shifts of 77Se in 3 and 4 occur at greater than 210 ppm lower fields compared with that of 1. The absorption band ascribed to an n-π* transition in the UV-visible spectrum of 1 occurs at a maximum at 408.5 nm. The corresponding n-π* absorptions of 3-5 are red-shifted, with that of 3 occurring at the longest wavelength. (14) For recent examples of carbamoylsilanes: (a) Cunico, R. F.; Motta, A. R. Org. Lett. 2005, 7, 771. (b) Chen, J.; Pandey, R. K.; Cunico, R. F. Tetrahedron: Asymmetry 2005, 16, 941. (c) Cunico, R. F.; Pandey, R. K. J. Org. Chem. 2005, 70, 5344. (d) Cunico, R. F.; Pandey, R. K. J. Org. Chem. 2005, 70, 9048. (e) Cunico, R. F.; Pandey, R. K.; Chen, J.; Motta, A. R. Synlett 2005, 3157. (f) Cunico, R. F.; Motta, A. R. J. Organomet. Chem. 2006, 691, 3109. (g) Canac, Y.; Aniol, G. E.; Conejero, S.; Donnadieu, B.; Bertrand, G. Eur. J. Inorg. Chem. 2006, 5076. (15) For examples of carbamoylgermanes: (a) Bravo-Zhivotovskii, D. A.; Pigarev, S. D.; Kalikhman, I. D.; Vyazankina, O. A.; Vyazankin, N. S. J. Organomet. Chem. 1983, 248, 51. (b) Seleznev, A. V.; BravoZhivotovskii, D. A.; Vakul'skaya, T. I.; Voronkov, G. Polyhedron 1990, 9, 227. (16) For comparison of the properties of 3 and 4 with those of their sulfur isologues, Me3SiC(S)NBn2 (7) and Me3GeC(S)NBn2 (8) were prepared from HC(S)NBn2 (6) in a procedure that is similar to that used to prepare 3 and 4. The CdS carbons of 6-8 resonate at δ 189.5, 224.2, and 225.1, respectively (see the Supporting Information).
Murai et al.
The HOMO and LUMO energy levels of 1 and 3-5 are shown in Figure 3. In all cases, the HOMO corresponds to the orbital containing the lone pair of the CdSe selenium atom, while π* orbitals of CdSe double bonds serve as LUMOs. In contrast to 1, introduction of silyl and germyl groups increases the energy of the HOMO and lowers that of the LUMO. The HOMO and LUMO energy differences decrease on going from 1 to 5, 4, and 3, a finding that is in accord with the trend observed in the UV-visible spectra. In summary, in this effort the first examples of silicon- and germanium-substituted selenocarbonyl compounds have been synthesized and structurally and spectroscopically characterized. Elongation of the CdSe bonds and red shifts of n-π* transitions in UV-visible spectra were observed to take place by the introduction of the silicon and germanium substituents. Particularly interesting is the fact that the effect of the silyl group on the spectroscopic properties is greater than that of the germyl group. Further studies probing applications of (selenocarbamoyl)silanes and -germanes as well as (selenocarbamoyl)lithium17 are in progress.
Acknowledgment. This work was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan. Supporting Information Available: Text and tables giving experimental procedures and spectral data for new compounds and a CIF file giving crystallographic data for 1, 3, and 4. This material is available free of charge via the Internet at http://pubs.acs.org. (17) In contrast to the generation of carbamoyllithiums18 and thiocarbamoyllithiums,19 no studies of their selenium isologues have been reported. (18) (a) Banhidai, B.; Schollkopf, U. Angew. Chem., Int. Ed. Engl. 1973, 12, 836. (b) Schollkopf, U.; Beckhaus, H. Angew. Chem., Int. Ed. Engl. 1976, 15, 293. (c) Fletcher, A. S.; Smith, K.; Swaminathan, K. J. Chem. Soc., Perkin Trans. 1 1977, 1881. (d) Hiiro, T.; Mogami, T.; Kambe, N.; Fujiwara, S.; Sonoda, N. Synth. Commun. 1990, 20, 703. (19) Seebach, D.; Luboch, W.; Enders, D. Chem. Ber. 1976, 109, 1309.
