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Org. Synth. 1992, 70, 169
DOI: 10.15227/orgsyn.070.0169
9-BORABICYCLO[3.3.1]NONANE DIMER
[9-Borabicyclo[3.3.1]nonane, dimer]
Submitted by John A. Soderquist1 and Alvin Negron.
Checked by Daniel M. Berger and Larry E. Overman.
1. Procedure
CAUTION! The manipulation and handling of air-sensitive compounds requires the use of special techniques. While no difficulties have been encountered with the present procedures, the preparer should consult References 3 and 2 prior to carrying out these syntheses.
A 2-L, three-necked, round-bottomed flask containing a magnetic stirring bar is fitted with a 250-mL addition funnel and a distillation assembly set for downward distillation to a 500-mL receiver flask. Rubber septa are used to isolate the system from atmospheric contact. Under a nitrogen purge, vented to an exhaust hood through a mercury bubbler, the entire system is thoroughly flame-dried (Note 1). After the 2-L flask is cooled to room temperature, it is charged with 500 mL of pure, dry 1,2-dimethoxyethane (Note 2) and 153 mL (1.53 mol) of borane-methyl sulfide complex (Note 3) employing a double-ended needle to effect the transfer. With a similar technique, 164 g (1.52 mol) of 1,5-cyclooctadiene (Note 4) is transferred to the addition funnel. To the stirred borane solution, 1,5-cyclooctadiene is added dropwise over ca. 1 hr to maintain a reaction temperature of 50–60°C during which time a small amount of dimethyl sulfide (bp 38°C) distills slowly from the reaction mixture. After the addition is completed, the addition funnel is replaced with a glass stopper and approximately 300 mL of the solution is distilled to reach a final distillation temperature of 85°C, indicating the complete removal of dimethyl sulfide from the reaction mixture (Note 5). If the distillate temperature does not reach 85°C, 150 mL of additional 1,2-dimethoxyethane is added and the distillation is continued until the distillate temperature reaches 85°C. The distillation assembly is replaced with a rubber septum and 1,2-dimethoxyethane is added to the reaction flask to bring the total liquid volume to 1 L. The mixture is warmed to effect the dissolution of the solid and allowed to cool very slowly to 0°C, which results in the formation of crystalline 9-borabicyclo[3.3.1]nonane (9-BBN) dimer. The supernatant liquid is decanted from the product using a double-ended needle and the 9-BBN dimer is dissolved in 1 L of fresh 1,2-dimethoxyethane. After the flask is cooled to 0°C, the supernatant liquid is removed as above and the large needles are dried under reduced pressure for 12 hr at 0.1 mm to give 158–165 g (85–89%) of product (mp 152–154°C, sealed capillary) (Note 6),(Note 7),(Note 8).
2. Notes
1. Alternatively, the apparatus can be dried for 4 hr at 150°C, assembled hot and purged with dry nitrogen.
2. 1,2-Dimethoxyethane, available from the Aldrich Chemical Company, Inc., was predried over calcium hydride and distilled from sodium/benzophenone prior to use. The solvent was used directly after purification or stored in an ampule bottle, available from the Aldrich Chemical Company, Inc., under a nitrogen atmosphere.
3. Borane-methyl sulfide complex, obtained from the Aldrich Chemical Company, Inc., was used directly without additional purification. However, titration of the reagent was carried out with glycerol as described3 to determine its actual molarity. Older samples of this reagent can be distilled under aspirator vacuum to obtain pure reagent.
4. 1,5-Cyclooctadiene, obtained from the Aldrich Chemical Company, Inc., was distilled under aspirator pressure from lithium aluminum hydride prior to use.
5. Failure to remove the dimethyl sulfide from the reaction mixture increases the solubility of the 9-BBN dimer and lowers the overall yield to ca. 65%.
6. The spectra of the product are as follows: 1H NMR (300 MHz, C6D6) δ: 1.44–1.57 (m, 4 H), 1.58–1.74 (m, 12 H), 1.83–2.07 (m, 12 H). A standard HETCOR experiment revealed that protons on each of the methylene carbons were superimposed upon one another to give rise to these downfield multiplets; 13C NMR (75 MHz, C6D6) δ: 20.2 (br, C-1,5), 24.3 (C-3,7), 33.6 (C-2,4,6,8); 11B NMR (96 MHz, C6D6) δ: 28.
7. The 9-BBN dimer so prepared is reasonably air-stable so that exposure to the atmosphere for 1 month lowered the mp to ca. 146–151°C.
8. Purification of commercial 9-BBN and other samples can be effected by recrystallization from 1,2-dimethoxyethane. Insoluble impurities can be removed from hot 1,2-dimethoxyethane solutions of 9-BBN by decantation of the solution to a second dry flask. To prevent clogging of the double-ended needle during the transfer process it is important to keep the ends of needle below the liquid surfaces. We have found that the receiver vessel should be charged with a small quantity of fresh, hot 1,2-dimethoxyethane prior to decantation and that a portion of this material should be transferred under a positive pressure of nitrogen to the 9-BBN solution to warm initially the transfer needle. Subsequently, the hot 9-BBN solution can be transferred without difficulty.
Handling and Disposal of Hazardous Chemicals
The procedures in this article are intended for use only by persons with prior training in experimental organic chemistry. All hazardous materials should be handled using the standard procedures for work with chemicals described in references such as "Prudent Practices in the Laboratory" (The National Academies Press, Washington, D.C., 2011 www.nap.edu). All chemical waste should be disposed of in accordance with local regulations. For general guidelines for the management of chemical waste, see Chapter 8 of Prudent Practices.
These procedures must be conducted at one's own risk. Organic Syntheses, Inc., its Editors, and its Board of Directors do not warrant or guarantee the safety of individuals using these procedures and hereby disclaim any liability for any injuries or damages claimed to have resulted from or related in any way to the procedures herein.
3. Discussion
9-Borabicyclo[3.3.1]nonane (9-BBN) has been prepared by the thermal redistribution of 9-n-propyl-9-BBN,4 and the hydroboration of 1,5-cyclooctadiene with borane-tetrahydrofuran complex followed by thermal isomerization of the mixture of dialkylboranes at 65°C.5 Solutions of 9-BBN have been prepared from the hydroboration of 1,5-cyclooctadiene with borane-methyl sulfide in solvents other than THF.6 The present procedure involves the cyclic hydroboration of 1,5-cyclooctadiene with borane-methyl sulfide in 1,2-dimethoxyethane.7 Distillative removal of the dimethyl sulfide in this special solvent system provides a medium that gives high purity, large needles of crystalline 9-BBN dimer in excellent yield. The material can be handled in air for brief periods without measurable decomposition.
As a dialkylborane, 9-borabicyclo[3.3.1]nonane (9-BBN) is unrivaled in both stability and selectivity.8 It has been distilled (bp 195°C, 12 mm) and exhibits a strong characteristic IR absorption band at 1560 cm−1 (B-H-B) for the bridged dimeric structure.5 The crystal structure of 9-BBN dimer has been determined9 and the drawing above approximates the conformational features of this compound. The 13C NMR properties of 9-BBN adducts have been studied extensively.10
Since the 9-methoxy derivative of 9-BBN is a common by-product of several reactions of 9-BBN,11 its efficient conversion back to 9-BBN has been described.12 Such a process enables one to recycle 9-BBN in reactions which require its high regioselectivity in hydroboration reactions and the related organoborane conversions.
The selective transformations of 9-BBN are numerous and varied, with derivatives being readily prepared through both hydroboration and organometallic methodology.8 It has been used for the preparation of isomerically-pure boracycles,11,13 the highly enantioselective reduction of aldehydes and ketones,14 the preparation of new selective borohydride reducing agents,15 C-C bond-forming transformations,16 and radiopharmaceutical labeling.17 Its reactivity has made it the reagent of choice for many organoborane conversions.18 The stability and distinctive spectral properties of 9-BBN have provided the initial key information to unravel the details of hydroboration reactions.8,19
This preparation is referenced from:

References and Notes
  1. Department of Chemistry, University of Puerto Rico, Rio Piedras, PR 00931.
  2. "Handling of Air-Sensitive Reagents"; Aldrich Technical Product Bulletin No. AL-134, 1983.
  3. Brown, H. C.; Kramer, G. W; Levy, A. B.; Midland, M. M. "Organic Syntheses Via Boranes"; Wiley-Interscience: New York, 1975.
  4. Köster, R. Angew. Chem. 1960, 72, 626.
  5. Knights, E. F.; Brown, H. C. J. Am. Chem. Soc. 1968, 90, 5280; Brown, H. C.; Knights, E. F.; Scouten, C. G. J. Am. Chem. Soc. 1974, 96, 7765.
  6. Brown, H. C.; Mandal, A. K.; Kulkarni, S. U. J. Org. Chem. 1977, 42, 1392.
  7. Soderquist, J. A.; Brown, H. C. J. Org. Chem. 1981, 46, 4599.
  8. Brown, H. C.; Lane, C. F. Heterocycles 1977, 7, 453; Rao, V. V. R.; Mehrotra, I.; Devaprabhakara, D. J. Sci. Ind. Res. 1979, 38, 368; Zaidlewicz, M. In "Comprehensive Organometallic Chemistry"; Wilkinson, G.; Stone, F. G. A.; Abel, E. W., Eds.; Pergamon Press: Oxford, 1982; Vol. 7, pp 161 and 199; Pelter, A.; Smith, K.; Brown, H. C. "Borane Reagents"; Academic Press: London, 1988.
  9. Brauer, D. J.; Krueger, C. Acta Crystallogr., Sect. B 1973, 29, 1684.
  10. Brown, H. C.; Soderquist, J. A. J. Org. Chem. 1980, 45, 846; Blue, C. D.; Nelson, D. J. J. Org. Chem. 1983, 48, 4538; Soderquist, J. A.; Colberg, J. C.; Del Valle, L. J. Am. Chem. Soc. 1989, 111, 4873; Soderquist, J. A.; Rivera, I.; Negron, A. J. Org. Chem. 1989, 54, 4051.
  11. Soderquist, J. A.; Shiau, F.-Y.; Lemesh, R. A. J. Org. Chem. 1984, 49, 2565; Soderquist, J. A.; Negron, A. J. Org. Chem. 1989, 54, 2462 and references cited therein.
  12. Soderquist, J. A.; Negron, A. J. Org. Chem. 1987, 52, 3441; Brown, H. C.; Kulkarni, S. U. J. Organomet. Chem. 1979, 168, 281.
  13. Brown, H. C.; Pai, G. G. J. Organomet. Chem. 1983, 250, 13; Soderquist, J. A.; Najafi, M. R. J. Org. Chem. 1986, 51, 1330.
  14. Midland, M. M.; Graham, R. S. Org. Synth., Coll. Vol. VII 1990, 402; Brown, H. C.; Jadhav, P. K. In "Asymmetric Synthesis"; Morrison, J. D., Ed.; Academic Press: New York, 1983; Vol. 2, Chapter 1; Midland, M. M. In "Asymmetric Synthesis"; Morrison, J. D., Ed.; Academic Press: New York, 1983; Vol. 2, Chapter 2; Midland, M. M.; McLoughlin, J. I.; Gabriel, J. J. Org. Chem. 1989, 54, 159.
  15. Brown, H. C.; Park, W. S.; Cho, B. T. J. Org. Chem. 1986, 51, 1934; Brown, H. C.; Cho, B. T.; Park, W. S. J. Org. Chem. 1988, 53, 1231; Narasimhan, S. Indian J. Chem., Sect. B 1986, 25B, 847; Cha, J. S.; Yoon, M. S.; Kim, Y. S.; Lee, K. W. Tetrahedron Lett. 1988, 29, 1069; Soderquist, J. A.; Rivera, I. Tetrahedron Lett. 1988, 29, 3195; Cha, J. S.; Lee, K. W.; Yoon, M. S.; Lee, J. C.; Yoon, N. M. Heterocycles 1988, 27, 1713.
  16. Miyaura, N.; Ishiyama, T.; Sasaki, H.; Ishikawa, M.; Satoh, M.; Suzuki, A. J. Am. Chem. Soc. 1989, 111, 314; Hooz, J.; Oudenes, J.; Roberts, J. L.; Benderly, A. J. Org. Chem. 1987, 52, 1347; Soderquist, J. A.; Santiago, B.; Rivera, I. Tetrahedron Lett. 1990, 31, 4981; Soderquist, J. A.; Santiago, B. Tetrahedron Lett. 1990, 31, 5541.
  17. Kothari, P. J.; Finn, R. D.; Vora, M. M.; Boothe, T. E.; Emran, A. M.; Kabalka, G. W. Int. J. Appl. Radiat. Isot. 1985, 36, 412; Kabalka, G. W.; Delgado, M. C.; Kunda, U. S.; Kunda, S. A. J. Org. Chem. 1984, 49, 174.
  18. For example, see: Soderquist, J. A.; Hassner, A. J. Organomet. Chem. 1978, 156, C12; Soderquist, J. A.; Brown, H. C. J. Org. Chem. 1980, 45, 3571; Brown, H. C.; Molander, G. A.; Singh,. S. M.; Racherla, U. S. J. Org. Chem. 1985, 50, 1577; Brown, H. C.; Vara, Prasad, J. V. N.; Zee, S.-H. J. Org. Chem. 1985, 50, 1582; Brown, H. C.; Cha, J. S.; Nazer, B.; Brown, C. A. J. Org. Chem. 1985, 50, 549; Molander, G. A.; Singaram, B.; Brown, H. C. J. Org. Chem. 1984, 49, 5024; Brown, H. C.; Narasimhan, S. J. Org. Chem. 1984, 49, 3891; Brown, H. C.; Mathew, C. P.; Pyun, C.; Son, J. C.; Yoon, N. M. J. Org. Chem. 1984, 49, 3091; Yamataka, H.; Hanafusa, T. J. Org. Chem. 1988, 53, 772; Bubnov, Yu. N.; Zheludeva, V. I. Izv. Akad. Nauk SSSR., Ser. Khim. 1987, 235; Chem. Abst. 1987, 107, 197578b; Brown, H. C.; Midland, M. M.; Kabalka, G. W. Tetrahedron 1986, 42, 5523; Liu, C.; Wang, K. K. J. Org. Chem. 1986, 51, 4733; Fleming, I.; Lawrence, N. J. Tetrahedron Lett. 1988, 29, 2073, 2077; Köster, R.; Schüssler, W.; Yalpani, M. Chem. Ber. 1989, 122, 677.
  19. Brown, H, C.; Wang, K. K.; Scouten, C. G. Proc. Nat. Acad. Sci. USA 1980, 77, 698; Nelson, D. J.; Cooper, P. J.; Coerver, J. M. Tetrahedron Lett. 1987, 28, 943; Nelson, D. J.; Cooper, P. J. Tetrahedron Lett. 1986, 27, 4693.

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

9-BBN

9-Borabicyclo[3.3.1]nonane dimer

9-Borabicyclo[3.3.1]nonane, dimer

9-borabicyclo[3.3.1]nonane (9-BBN) dimer

9-BBN dimer

9-Borabicyclo[3.3.1]nonane (9-BBN)

9-n-propyl-9-BBN

9-BB

glycerol (56-81-5)

nitrogen (7727-37-9)

Benzophenone (119-61-9)

sodium (13966-32-0)

borane (7440-42-8)

dimethyl sulfide (75-18-3)

THF (109-99-9)

lithium aluminum hydride (16853-85-3)

calcium hydride (7789-78-8)

1,2-dimethoxyethane (110-71-4)

1,5-cyclooctadiene

borane-tetrahydrofuran complex (14044-65-6)

borane-methyl sulfide complex,
borane-methyl sulfide (13292-87-0)