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DOI:10.15227/orgsyn.070.0169

Organic Syntheses, Coll. Vol. 9, p.95 (1998); Vol. 70, p.169 (1992).

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 specialtechniques. While no difficulties have been encountered with the present procedures, the preparershould 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 250mL 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 toan exhaust hood through a mercury bubbler, the entire system is thoroughly flame-dried (Note 1). Afterthe 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 amountof 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 ofadditional 1,2-dimethoxyethane is added and the distillation is continued until the distillate temperaturereaches 85°C. The distillation assembly is replaced with a rubber septum and 1,2-dimethoxyethane isadded to the reaction flask to bring the total liquid volume to 1 L. The mixture is warmed to effect thedissolution 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 theproduct using a double-ended needle and the 9-BBN dimer is dissolved in 1 L of fresh 1,2dimethoxyethane. After the flask is cooled to 0°C, the supernatant liquid is removed as above and thelarge needles are dried under reduced pressure for 12 hr at 0.1 mm to give 158–165 g (85–89%) ofproduct (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 overcalcium 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 useddirectly 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 underaspirator 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 9BBN dimer andlowers the overall yield to ca. 65%.
6. The spectra of the product are as follows: H 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 were13
superimposed upon one another to give rise to these downfield multiplets; C NMR (75 MHz, C D ) δ: 20.2 (br, C-1,5),
166

1124.3 (C-3,7), 33.6 (C-2,4,6,8); B NMR (96 MHz, C D ) δ: 28.
7. The 9-BBN dimer so prepared is reasonably air-stable so that exposure to the atmosphere for 1 month lowered the mpto ca. 146–151°C. Due to the potential for the formation of pyrophoric contaminants, it is recommended that 9-BBN be
stored and handled under an inert atmosphere at all times.
8. Purification of commercial 9-BBN and other samples can be effected by recrystallization from 1,2dimethoxyethane.
Insoluble impurities can be removed from hot 1,2-dimethoxyethane solutions of 9BBN by decantation of the solution toa second dry flask. To prevent clogging of the double-ended needle during the transfer process it is important to keep theends of needle below the liquid surfaces. We have found that the receiver vessel should be charged with a small quantityof fresh, hot 1,2dimethoxyethane prior to decantation and that a portion of this material should be transferred under apositive 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.
66Waste Disposal Information
All toxic materials were disposed of in accordance with "Prudent Practices in the Laboratory"; National Academy Press;
Washington, DC, 1995.

3. Discussion
49-Borabicyclo[3.3.1]nonane (9-BBN) has been prepared by the thermal redistribution of 9-n-propyl9-BBN, and thehydroboration of 1,5-cyclooctadiene with borane-tetrahydrofuran complex followed by thermal isomerization of the5mixture of dialkylboranes at 65°C. Solutions of 9-BBN have been prepared from the hydroboration of
1,5-cyclooctadiene with borane-methyl sulfide in solvents other than THF. The present procedure involves the cyclichydroboration of 1,5-cyclooctadiene with boranemethyl sulfide in 1,2-dimethoxyethane. Distillative removal of thedimethyl 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.
678As a dialkylborane, 9-borabicyclo[3.3.1]nonane (9-BBN) is unrivaled in both stability and selectivity. It has been
distilled (bp 195°C, 12 mm) and exhibits a strong characteristic IR absorption band at 1560 cm (B-H-B) for the bridged
dimeric structure. The crystal structure of 9-BBN dimer has been determined and the drawing above approximates theconformational features of this compound. The C NMR properties of 9-BBN adducts have been studied extensively.
−159131011Since the 9-methoxy derivative of 9-BBN is a common by-product of several reactions of 9-BBN, its efficientconversion back to 9-BBN has been described. Such a process enables one to recycle 9BBN in reactions which require
its high regioselectivity in hydroboration reactions and the related organoborane conversions.
12The selective transformations of 9-BBN are numerous and varied, with derivatives being readily prepared throughboth hydroboration and organometallic methodology. It has been used for the preparation of isomerically-pureboracycles, the highly enantioselective reduction of aldehydes and ketones, the preparation of new selective
borohydride reducing agents, C-C bond-forming transformations, and radiopharmaceutical labeling. Its reactivity has
made it the reagent of choice for many organoborane conversions. The stability and distinctive spectral properties of9-BBN have provided the initial key information to unravel the details of hydroboration reactions.
811,13

14

15

16

17

188,19This preparation is referenced from:• Org. Syn. Coll. Vol. 9, 107

zOrg. Syn. Coll. Vol. 10, 273

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.;
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Chem. Ber. 1989, 122, 677.
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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)
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