Molecular Addition Compounds. 16. New, Highly Reactive Borane Adducts with N,N-Dialkyl-tert-alkylamines for Hydroboration

Article abstract of DOI:10.1021/jo0002745

Several N,N-diethyl-tert-alkylamines, such as N,N-diethyl-2-methyl-2-butylamine (1, t-PentNEt₂), N,N-diethyl-2,3-dimethyl-2-butylamine (2, t-HexNEt₂), N,N-diethyl-2,3,3-trimethyl-2-butylamine (3, t-HeptNEt₂), and N,N-diethyl-1,1,3,3-tetramethylbutylamine (4, t-OctNEt₂) with varying steric bulk around nitrogen (by changing the ter-alkyl group) have been prepared and examined as borane carriers. The complexing ability of these N,N-diethyl-tert-alkylamines with borane decreases in the order: t-BuNEt₂ > t-PentNEt₂ > t-HeptNEt₂ > t-HexNEt₂ ≥ t-OctNEt₂. From these preliminary studies, the more promising tert-octyldialkylamines were selected for detailed studies. The optimum steric bulk around the nitrogen atom was established by comparing various tert-octyldialkylamines containing variable steric requirements for both the alkyl groups. The complexing ability of these amines with borane decreases in the order shown: t-OctNMe₂ (5) > t-OctNEtMe (6) > t-OctN-(CH₂CH₂)₂O (7) > t-OctNEt₂ (4) > t-OctNBuⁱMe (8) > t-OctNPrⁿ2 (9). The reactivity of the corresponding borane adducts toward 1-octene increases in the reverse order. Among the various tert-octyldialkylamine-boranes prepared and examined, only t-OctNEt₂ (4) forms a highly reactive liquid borane adduct, which hydroborates 1-octene in tetrahydrofuran rapidly at room temperature. Accordingly, detailed hydroboration studies with this new, highly reactive amine-borane adduct, t-OctEt₂N:BH₃ (10) and representative mono-, di-, tri-, and tetra-substituted olefins were carried out at room temperature (22 ± 3°C) in selected solvents, tetrahydrofuran, dioxane, tert-butyl methyl ether, n-pentane and dichloromethane. Simple unhindered olefins were hydroborated to the trialkylborane stage, whereas hindered olefins were partially hydroborated to the mono or dialkylborane stage. The hydroborations can be carried out conveniently in a variety of solvents. The amine-borane adduct showed enhanced reactivity in dioxane but low reactivity in dichloromethane. The alkylboranes obtained after hydroboration were oxidized with hydrogen peroxide/ sodium hydroxide and the product alcohols were obtained in quantitative yields, as established by GC analysis. The carrier amine was recovered by simple acid-base manipulations in good yield and can be readily recycled back to the borane adduct.

Full text of DOI:10.1021/jo0002745

J . Org. Chem. 2000, 65, 4655-4661
4655
Molecu la r Ad d ition Com p ou n d s. 16. New , High ly Rea ctive Bor a n e
Ad d u cts w ith N,N-Dia lk yl-ter t-a lk yla m in es for Hyd r obor a tion
Herbert C. Brown,*,† J osyula V. B. Kanth,†,‡,1 Pramod V. Dalvi,†,2 and Marek Zaidlewicz*,‡
H. C. Brown and R. B. Wetherill Laboratories of Chemistry, Purdue University,
West Lafayette, Indiana 47907, and Faculty of Chemistry, Nicolaus Copernicus University,
Torun 87-100, Poland
hcbrown@purdue.edu
Received February 26, 2000
Several N,N-diethyl-tert-alkylamines, such as N,N-diethyl-2-methyl-2-butylamine (1, t-PentNEt2),
N,N-diethyl-2,3-dimethyl-2-butylamine (2, t-HexNEt2), N,N-diethyl-2,3,3-trimethyl-2-butylamine
(3, t-HeptNEt2), and N,N-diethyl-1,1,3,3-tetramethylbutylamine (4, t-OctNEt2) with varying steric
bulk around nitrogen (by changing the tert-alkyl group) have been prepared and examined as borane
carriers. The complexing ability of these N,N-diethyl-tert-alkylamines with borane decreases in
the order: t-BuNEt2 > t-PentNEt2 > t-HeptNEt2 > t-HexNEt2 g t-OctNEt2. From these preliminary
studies, the more promising tert-octyldialkylamines were selected for detailed studies. The optimum
steric bulk around the nitrogen atom was established by comparing various tert-octyldialkylamines
containing variable steric requirements for both the alkyl groups. The complexing ability of these
amines with borane decreases in the order shown: t-OctNMe2 (5) > t-OctNEtMe (6) > t-OctN-
(CH2CH2)2O (7) > t-OctNEt2 (4) > t-OctNBuiMe (8) > t-OctNPrn (9). The reactivity of the
2
corresponding borane adducts toward 1-octene increases in the reverse order. Among the various
tert-octyldialkylamine-boranes prepared and examined, only t-OctNEt2 (4) forms a highly reactive
liquid borane adduct, which hydroborates 1-octene in tetrahydrofuran rapidly at room temperature.
Accordingly, detailed hydroboration studies with this new, highly reactive amine-borane adduct,
t-OctEt2N:BH3 (10) and representative mono-, di-, tri-, and tetra-substituted olefins were carried
out at room temperature (22 ( 3 °C) in selected solvents, tetrahydrofuran, dioxane, tert-butyl methyl
ether, n-pentane and dichloromethane. Simple unhindered olefins were hydroborated to the
trialkylborane stage, whereas hindered olefins were partially hydroborated to the mono or
dialkylborane stage. The hydroborations can be carried out conveniently in a variety of solvents.
The amine-borane adduct showed enhanced reactivity in dioxane but low reactivity in dichlo-
romethane. The alkylboranes obtained after hydroboration were oxidized with hydrogen peroxide/
sodium hydroxide and the product alcohols were obtained in quantitative yields, as established by
GC analysis. The carrier amine was recovered by simple acid-base manipulations in good yield
and can be readily recycled back to the borane adduct.
Borane-amine adducts are important reducing agents
with a multitude of applications in organic synthesis and
industrial processes.3 They have a wide range of reac-
tivities, are soluble in various solvents including hydro-
carbons, and often show low sensitivity to moisture and
air. In contrast, their use as hydroborating agents is of
limited scope due to the formation of strong borane
complexes, rendering the reactivity toward olefins lower
than that of the adducts with ethers and sulfides. On the
other hand, the growing importance of diborane for the
synthesis of pharmaceuticals and other compounds3 and
certain inconveniences of well-established reagents, e.g.,
the low concentration and stability of borane-tetrahy-
drofuran (BH3‚THF), and the high volatility, flammabil-
ity and unpleasant odor of dimethyl sulfide from borane-
dimethyl sulfide (BMS) create a need for easy-to-handle,
stable and environmentally benign hydroborating agents.
Accordingly, we have undertaken an extensive study
in the hope of developing some highly reactive amine-
borane adducts for hydroboration and reduction. In the
preceding papers of this series, we reported highly
reactive borane adducts with N,N-dialkylanilines, alkyl-
diisopropylamines and tert-butyldialkylamines as dem-
onstrated by their success in hydroborating 1-octene in
tetrahydrofuran at room temperature in less than 1 h.4
Recently it was shown that borane adducts of N-silyl-
amines also show similar high reactivity in hydrobora-
tions.5 All these studies show for the first time that
aliphatic amines are useful borane carriers for hydrobo-
(4) (a) Brown, H. C.; Zaidlewicz, M.; Dalvi, P. V. Organometallics
1998, 17, 4202. (b) Brown, H. C.; Kanth, J . V. B.; Zaidlewicz, M. J .
Org. Chem. 1998, 63, 5154. (c) Brown, H. C.; Kanth, J . V. B.;
Zaidlewicz, M. Tetrahedron 1999, 55, 5991. (d) Brown, H. C.; Zaid-
lewicz, M.; Dalvi, P. V.; Narasimhan, S.; Mukhopadhyay, A. Organo-
metallics 1999, 18, 1305. (e) Brown, H. C.; Kanth, J . V. B.; Zaidlewicz,
M. Organometallics 1999, 18, 1310. (f) Brown, H. C.; Kanth, J . V. B.;
Dalvi, P. V.; Zaidlewicz, M.; J . Org. Chem. 1999, 64, 6263.
(5) (a) Soderquist, J . A.; Medina, J . R.; Huertas, R. Tetrahedron Lett.
1998, 39, 6119. (b) Soderquist, J . A.; Huertas, R.; Medina, J . R.
Tetrahedron Lett. 1998, 39, 6123.
† Purdue University.
‡ Νicolaus Copernicus University.
(1) Postdoctoral Associate with support from Aldrich Chemical Co.
and Borane Research Fund.
(2) Postdoctoral Associate with support from the Borane Research
Fund.
(3) (a) Lane, C. F. Aldrichim. Acta 1973, 6, 51. (b) Follet, M. Chem.
Ind. 1986, 123. (c) Ren, O.; Meatres, C. F. Bioconjugate Chem. 1992,
3, 563. (c) Carboni, B.; Monnier, L. Tetrahedron 1999, 55, 1197.
10.1021/jo0002745 CCC: $19.00 © 2000 American Chemical Society
Published on Web 07/06/2000

4656 J . Org. Chem., Vol. 65, No. 15, 2000
Brown et al.
Sch em e 1
ration. Their potential advantages over traditional car-
riers, such as tetrahydrofuran or dimethyl sulfide for
large-scale applications have been pointed out. We, in our
several earlier papers, demonstrated that borane com-
plexation depends strongly on the steric requirements of
the amine.4 The results obtained with alkylisopropyl-
amines and tert-butyldialkylamines prompted us to
examine N,N-dialkyl-tert-alkylamines, with the objective
of developing useful borane adducts meeting the following
requirements: (1) hydroboration of 1-octene in tetrahy-
drofuran at room temperature in less than 1 h; (2) liquid
adduct (for easy transfer, miscibility and convenience in
neat reactions) of high borane concentration, stable at
room temperature, soluble in various solvents.
Ta ble 1. Bor a n e Ad d u cts w ith N,N-Dieth yl Der iva tives
of ter t-Alk yla m in es
exchange,a
BH3‚THF BMS 11B NMRb
%
hydroboration
of 1-octenec,d
amine
e
t-BuNEt2
100
100
87
100
88
85
83
40
80
38
-14.89
-14.86
-19.23
-16.77
-15.14
6 h
4 h
30 min
3.5 h
20 min
t-PentNEt2 (1)
t-HexNEt2 (2)
t-HeptNEt2 (3)
t-OctNEt2 (4)
Resu lts a n d Discu ssion
In our earlier studies with various N,N-dialkyl deriva-
tives of tert-butylamine, the corresponding N,N-diethyl
derivative takes 85% of borane from BMS and its adduct
is relatively unreactive in hydroboration and requires 6
h for the hydroboration of 1-octene.4f However, the
corresponding N-methyl-N-isopropyl or N-ethyl-N-isobu-
tyl derivatives form stable, highly reactive borane ad-
ducts and the hydroboration of 1-octene is complete
within 30 min. On the other hand, tert-butyl-N-ethyl-N-
isopropylamine forms an unstable borane adduct and
N,N-diisobutyl-tert-butylamine completely fails to com-
plex with borane. These observations clearly show the
dramatic effect of steric bulk around nitrogen on its
complexing abilities with borane. Though our earlier
studies provided highly reactive trialkylamine-boranes
for hydroboration, the synthesis of amines containing
three different alkyl groups is not an economical process.
Accordingly, the introduction of two identical alkyl groups
on a primary amine is more practical. It was therefore
decided to prepare various tert-alkyl derivatives keeping
the N,N-diethyl groups common, to obtain a better
understanding of the steric effect, leading to the develop-
ment of a new generation of hydroborating agents.
Consequently, the syntheses of the following N,N-diethyl-
2-methyl-2-butylamine (1, t-PentNEt2), N,N-diethyl-2,3-
dimethyl-2-butylamine (2, t-HexNEt2), N,N-diethyl-2,3,3-
trimethyl-2-butylamine (3, t-HeptNEt2) and N,N-diethyl-
1,1,3,3-tetramethylbutylamine (4, t-OctNEt2) were under-
taken.
a
Amine mixed with BH3‚THF or BH3‚SMe2 in 1:1 molar ratio
at room temperature and analyzed by 11B NMR at equilibrium.
b From the exchange with BH3‚SMe2. c 5% excess of 1-octene, room
d
temperature in THF. 3 M solution of 1-octene and 1 M in BH3.
e Values taken from ref 4f.
corresponding tert-alcohols was thought to be one that
could be used conveniently for large-scale synthesis. The
N-acetyl derivatives were prepared following the reported
procedure.7b
Reduction of the N-acetyl derivative with BMS pro-
vides the corresponding N-ethyl derivative in very good
yields. N,N-Diethyl-tert-alkylamines can be prepared by
treatment with diethyl sulfate. However, in the case of
the tert-hexylamine, the diethyl derivative carried some
sulfur derivative contamination even after the purifica-
tion, interfering with the preparation of the borane
adduct. Fortunately, preparation of the acetyl derivative
of the secondary amine followed by the reduction gave a
highly pure sample (Scheme 1).
The complexing ability of these amines toward borane
was tested by the exchange with BMS and BH3‚THF
mixed in 1:1 molar ratio. The amount of borane taken
by the amine in the equilibrium was determined by 11B
NMR and is shown in Table 1. As expected, tert-pentyl-
N,N-diethylamine shows reactivities similar to those of
the corresponding tert-butyl derivative, with only mar-
ginal improvement of the rate. Also, the tert-heptyl-N,N-
diethylamine forms a relatively strong borane adduct and
the hydroboration of 1-octene takes 2.5 h. However, the
tert-hexyl-N,N-diethylamine (2) and tert-octyl-N,N-di-
ethylamine (4) show much improved reactivity. The tert-
hexyl derivative (2) takes 87% borane from BH3‚THF and
40% from BMS (Table 1) and its hydroboration of 1-octene
is complete within 30 min. Similarly, the tert-octyl-N,N-
diethylamine takes up only 38% of the borane from BMS
and 88% from BH3‚THF and its borane adduct hydro-
borates 1-octene within 20 min (Table 1).
Syn th esis of Am in es a n d th e Cor r esp on d in g Bo-
r a n e Ad d u cts. The tert-pentyl-N,N-diethylamine and
tert-octyl-N,N-diethylamine were prepared from the com-
mercially available tert-pentylamine and tert-octylamines,
respectively. The diethyl derivatives were prepared by
treatment of the amines with diethyl sulfate, following
the procedure reported for tert-butylamine.4f
Unlike tert-pentylamine, the corresponding tert-hexyl
and heptylamines are not commercially available. Out
of several possible syntheses,6,7 the preparation from the
(6) Gasc, M. B.; Lattes, A.; Perie, J . J . Tetrahedron 1983, 39, 703
and the references therein.
(7) (a) Hennion, G. F.; Hangel, S. J . Am. Chem. Soc. 1960, 82, 4908.
(b) Timberlake, J . W.; Hodges, M. L.; Betterton, K. Synthesis 1972,
632. (c) Wagner, B. D.; Ruel, G.; Lusztyk, J . J . Am. Chem. Soc. 1996,
118, 13.
It is quite evident from these preliminary studies that
the amines 2 and 4 show the qualities of a good hydrobo-
rating agent. However, the starting material for the
preparation of 4, namely tert-octylamine is commercially

Molecular Addition Compounds
J . Org. Chem., Vol. 65, No. 15, 2000 4657
Ta ble 2. Bor a n e Ad d u cts w ith t-OctNR2 a n d t-OctNR1R2
amine‚ BH3
hydroboration
of 1-octenee
exchange,a
%
amine
BH3‚SMe2
BH3‚THF
stateb (mp, °C)
[BH3]c M
11B NMRd (δ)
in THFf
neat
t-OctNMe2
t-OctNEtMe 6
t-OctN(CH2CH2)2O 7
5
85
77
50
38
35
25
94
100
87
88
88
-11.40
-15.60
-16.42
-15.14
-14.29
-14.32
no
24 h
96-97
liquid
48-50
43-45
20 min
3 h
t-OctNEt2
4
4.0
20 min
1.5 h
20 min
t-OctNBuiMe, 8
t-OctNPrn
9
81
2
a
b
Amine mixed with BH3:SMe2 or 1 M BH3:THF in 1:1 molar ratio at room temperature and analyzed by 11B NMR at equilibrium. At
0 °C. c Estimated by hydrolysis in 2 M HCl-glycerol-water (2:1:1) and measuring the hydrogen evolved. From the exchange with BH3:
d
SMe2. e 5% excess of 1-octene, room temperature. f 3 M solution of 1-octene and 1 M in BH3.
available and is less expensive. Accordingly we selected
this derivative for our detailed studies.
9 are both solids of similar reactivity in THF. In general,
the adducts of 4, 7, 8, and 9 are more reactive, however,
the adduct 4 meets our requirements to be a good
hydroborating agent, liquid at room temperature, high
borane concentration and hydroborates 1-octene rapidly
at room temperature. Accordingly, the borane adduct of
this amine was selected for detailed hydroboration stud-
ies.
Hyd r obor a tion Stu d ies Usin g ter t-Octyld ieth yl-
a m in e-Bor a n e. The borane adduct of tert-octyldiethyl-
amine (4) was prepared by passing a slight excess of
diborane gas into the neat amine at 0-5 °C (eq 5). The
concentration of the adsorbed borane was established to
be 4.0 M by hydrolysis of an aliquot, using a 2 M HCl-
glycerol-water mixture, measuring the hydrogen evolved.
To make sure that we were not sacrificing the pos-
sibility of obtaining an even better hydroborating agent
by confining ourselves to N,N-diethyl groups on tert-
octylamine, it was decided to examine more fully the
steric factors around the nitrogen atom. Accordingly, we
prepared several N,N-dialkyl substituted tert-octylamines
(4-9), with increasing steric bulk of the alkyl groups
within the series keeping the tert-octyl group common.
The amines 4, 5, 7, and 9 having two primary un-
branched alkyl groups, were prepared by the repetitive
alkylation of tert-octylamine, following routine procedures
(eq 3).
The adduct thus obtained, maintained under nitrogen,
is stable at room-temperature indefinitely. The 11B NMR
examination reveals a peak at -14.9 (q, CCl4). The
stability of this adduct in THF was also studied. Thus a
solution of the adduct in THF (2.0 M in BH3) was sealed
in an NMR tube and monitored over several months
using 11B NMR at appropriate intervals. No new peaks
in the 11B NMR spectra other than that given by the
adduct appeared during the 6 months of observation.
H yd r ob or a t ion of Olefin s in Tet r a h yd r ofu r a n .
Hydroboration of representative mono-, di-, tri-, and
tetrasubstituted olefins with 10 was conducted in THF
at room temperature. To establish the rate and stoichi-
ometry, the reactions were carried out in solutions that
were 0.5 M in BH3 and 1.5 M in an olefin. The procedure
followed was to add the THF solution of the olefin (3
equiv) to the amine-borane (1 equiv) in THF at 0 °C,
stirring the mixture further at room temperature (22 (
3 °C). The progress of the hydroboration was conveniently
followed by taking out aliquots at intervals, hydrolyzing
with 3 M HCl-glycerol-THF (2:1:0.2), and measuring
the hydrogen evolved.9 The reactions were also followed
by 11B NMR, monitoring a decreasing amine-borane
signal and an increasing alkylborane signal.
Slow addition of diethyl sulfate at controlled temper-
ature and subsequent methylation gave 6 in a good yield,
while 8 was obtained by routine alkylation with isobutyl
bromide and methylation, according to eq 4.
The complexing ability of these amines toward borane
was tested by the exchange with BMS (borane-methyl
sulfide) and BH3‚THF (borane-tetrahydrofuran) mixed
in 1:1 molar ratio. The amount of borane taken by an
amine in the equilibrium was determined by 11B NMR
and is shown in Table 2. Values for the exchange with
BH3‚THF, a 1 M solution, should be considered qualita-
tive since THF is in considerable excess. As revealed by
the exchange experiments, the dimethyl derivative, 5,
takes 85% of borane from BMS and its adduct is unre-
active in hydroboration. In contrast, 4 takes up only 38%
of the borane and the reactivity of its adduct is dramati-
cally increased (Table 2). It is a liquid, 4.0 M, in borane,
stable at room temperature. The borane adducts of 7 and
Under the conditions indicated, the hydroboration of
1-hexene by tert-octyldiethylamine-borane (10) in THF
is complete in 2 h, forming the trihexylborane. Hydrolysis
(8) Brown, H. C. Organic Syntheses via Boranes; Wiley: New York,
1975. A reprinted edition, Organic Syntheses via Boranes, Vol. 1;
Aldrich Chemical Co., Inc., Milwaukee, 1997, is currently available.
(9) ref 8, p 241.

4658 J . Org. Chem., Vol. 65, No. 15, 2000
Ta ble 3. Hyd r obor a tion of Rep r esen ta tive Olefin s With 10 in Va r iou s Solven ts a t Room Tem p er a tu r ea
dioxane THF tert-butyl methyl ether n-pentane dichloromethane
hydrides
Brown et al.
time,
h
hydrides
utilized
time,
h
time,
h
hydrides
utilized
time,
h
hydrides
utilized
time,
h
hydrides
utilized
olefin
utilized
1-hexene
2.0
1.0
3.0
1.0
3.0
1.0
3.0
1.0
3.0
1.0
24
0.91
24
1.66
24
0.33
24
0.40
3.00
2.76
3.00
2.73
3.00
2.73
3.00
2.54
3.00
2.64
2.95
2.00
2.95
2.00
2.00
1.00
1.76
1.00
2.0
1.0
4.0
1.0
4.0
1.0
4.0
1.0
4.0
1.0
24
0.91
24
2.16
24
0.50
24
0.33
3.00
2.88
3.00
2.52
3.00
2.66
3.00
2.40
3.00
2.36
2.81
2.00
2.85
2.00
1.90
1.00
1.71
1.00
4.0
1.0
4.0
1.0
4.0
1.0
4.0
1.0
4.0
1.0
24
0.91
24
1.66
24
0.66
24
0.75
3.00
2.66
3.00
2.66
3.00
2.66
3.00
2.40
3.00
2.53
2.90
2.00
2.90
2.00
1.85
1.00
1.67
1.00
3.0
1.0
4.0
1.0
4.0
1.0
4.0
1.0
4.0
1.0
24
3.0
24
6.0
24
0.50
24
0.66
3.00
2.05
3.00
2.02
3.00
2.02
3.00
2.12
3.00
2.95
2.92
2.00
2.90
2.00
1.70
1.00
1.66
1.00
48
48
48
48
48
48
48
48
48
2.50
2.51
2.61
2.80
2.88
2.76
2.85
1.64
1.69
styrene
â-pinene
cyclopentene
norbornene
cyclohexene
2-methyl-2-butene
R-pinene
2,3-dimethyl-2-butene
a
Reactions were carried out using amine-borane 10 (5 mmol) and an olefin (15 mmol) in a total volume of 10 mL solution.
of the reaction mixture does not evolve any hydrogen,
indicating the complete utilization of borane. Disubsti-
tuted olefins, such as â-pinene and cyclopentene, are
hydroborated to the trialkylborane stage in 4 h. Moder-
ately hindered 2-methyl-2-butene gave disiamylborane
after 2 h (11B NMR, δ ppm +31.5), with further hydro-
boration proceeding more slowly. Cyclohexene forms
dicyclohexylborane rapidly in 1 h (11B NMR, δ ppm, +51.2
after methanolysis), and 2.81 hydride equivalents are
utilized in 24 h (11B NMR, δ ppm, +81.3 after metha-
nolysis corresponding to the formation of tricyclohexy-
lborane). However, the more hindered R-pinene consumes
one hydride rapidly in 30 min and then the reaction
continues slowly, with the hydride utilization increasing
to 1.9 in 24 h at room temperature, indicating incomplete
formation of Ipc2BH. This is also confirmed by 11B NMR,
which reveals two peaks after methanolysis, at +31.5
(minor, due to IpcB(OMe)2) and +52.6 (major, due to Ipc2-
BOMe). Further substitution on the olefin, i.e., the
tetrasubstituted 2,3-dimethyl-2-butene, results in a fur-
ther lowering of the hydride uptake. Here also, the
addition of the first hydride is very fast, giving thexyl-
borane (11B NMR, δ ppm +24.6) with the olefin/BH3 ratio
then rising to 1.71 after 24 h (11B NMR, δ ppm +23.9
and +80.8, after methanolysis +31.1 and +52.9).
Hyd r obor a tion of Olefin s in Oth er Solven ts. Hy-
droborations with 10 were also conducted in solvents
such as dioxane, tert-butyl methyl ether, n-pentane, and
dichloromethane. In dioxane, 10 show an enhanced
reactivity when compared to solutions of 10 in tetra-
hydrofuran. Thus, in dioxane, 10 hydroborates unhin-
dered mono- and disubstituted olefins to the correspond-
ing trialkylborane stage within 3 h (Table 3). Enhanced
reactivity is also observed for hindered olefins. For
example, R-pinene is cleanly hydroborated to the Ipc2-
BH stage. This is also confirmed by 11B NMR observation,
which reveals the exclusive presence of Ipc2BOMe after
methanolysis (δ ppm +53).
cyclohexene, 2.92 equivalents of hydride were consumed
after 24 h, whereas it is 2.9 for 2-methyl-2-butene. More
hindered R-pinene and 2,3-dimethyl-2-butene were rap-
idly hydroborated to the monoalkyl stage within 30 min,
with further hydroboration proceeding slowly, consuming
only 1.7 and 1.66 hydride equivalents, respectively, after
24 h (see Table 3)
In tert-butyl methyl ether also the reactivity of the
borane-amine adduct 10 is very similar to that observed
in THF and n-pentane. However, in dichloromethane
unusual rate retardation in hydroboration was observed.
Thus, the hydroboration of simple unhindered olefins,
such as 1-hexene, is incomplete even after 48 h at room
temperature, consuming only 2.5 equivalents of hydride
out of the 3.00 available. 11B NMR analysis of the reaction
mixture showed the presence of unreacted amine-borane
(10) (∼15%). The hydride uptake is higher for moderately
hindered cyclohexene and 2-methyl-2-butene, 2.76 and
2.85, respectively. Also, 11B NMR analysis of the reaction
mixture after 48 h did not show the presence of any
starting amine-borane. A similar reactivity was also
observed for the more hindered R-pinene and 2,3-di-
methyl-2-butene. This unusual reactivity is may be due
to the solvent interference in the reaction.
It is well established from our earlier studies4,8 that,
the rate-determining step in the hydroboration of olefins
with BH3:LB, is the formation of free “BH3”. However,
such dissociation is not observed when the borane adduct
10, was taken in dichloromethane. The 11B NMR exami-
nation of the amine-borane in dichloromethane over a
period of time showed only signals due to the amine-
borane and no gas evolution was noted in gasimeter
studies (diborane, after dimerization of dissociated “BH3”).
Whereas, in coordinating solvents such as THF, small
amounts (2%) of BH3:THF (11B NMR, 0.9 ppm, q) were
noted. Also, the amine-borane may be stabilized by the
hydrogen in dichloromethane carrying a positive charge
(eq 6). This could be the reason for initial slower reactiv-
ity of olefins toward the borane adduct 10 in dichlo-
romethane.
In n-pentane, the hydroborations are comparable to
that in THF requiring only 4 h to reach the trialkylborane
stage with simple unhindered olefins. However, the
hydroboration of moderately hindered olefins, such as
cyclohexene and 2-methyl-2-butene, does not give tri-
alkylboranes cleanly, even after 24 h. In the case of
In the case of less bulkier olefins, the RBH2 formed
after first hydroboration may coordinate with the carrier
amine 4 to form RBH2‚NR3, leading to slower further
hydroboration. This is confirmed with 1-hexene by 11B

Molecular Addition Compounds
J . Org. Chem., Vol. 65, No. 15, 2000 4659
hydroborations are carried out in water-immiscible sol-
vents, such as tert-butyl methyl ether and n-pentane,
addition of small amounts of methanol or ethanol is
essential to ensure complete oxidation using NaOH/H2O2.
Con clu sion s
This study has demonstrated that N,N-dialkyl-tert-
alkylamines are convenient borane carriers for hydro-
boration. The complexing ability of amines can be varied
in a predictable manner by a proper choice of alkyl
groups. Among the various tert-alkyl-N,N-dialkylamine-
boranes prepared, the amine 4 formed a stable, highly
reactive liquid adduct. Simple procedures for the syn-
thesis of the majority of amines examined have been
worked out. As a result of this and other previous
studies,4,5 a group of new, highly reactive borane-amine
adducts has become available for the first time. The
present study also demonstrates the synthetic potential
of the new, highly reactive amine-borane adduct tert-
octyldiethylamine-borane (10). Simple unhindered ole-
fins can be hydroborated to the trialkylborane stage,
whereas hindered olefins can be partially hydroborated
to the mono or dialkylborane stage. The hydroborations
can be carried out conveniently in a variety of solvents.
The amine-borane adduct shows enhanced reactivity in
dioxane but low reactivity in dichloromethane. This
unusual reactivity in dichloromethane may be used for
selective hydroborations. The hydroboration products
were oxidized using hydrogen peroxide/sodium hydroxide
to give the corresponding alcohols in quantitative yields,
without any interference by the amine. As the carrier
amine is basic, oxidation in the absence of sodium
hydroxide can also be carried out. However, under these
conditions, the oxidation is incomplete. It can be made
complete by the addition of 20 mol % of the carrier amine
to the reaction mixture before the oxidation. The borane
carrier amine 4 can be readily recovered from the
hydroboration products by simple acid-base manipula-
tions, distillation, or column chromatography, and can
be easily recycled for the preparation of the borane
adduct.
NMR analysis, which showed the formation of major
amounts of RB(OCH3)2 after methanolysis of the reaction
mixture at 24 h. However, such coordination is minimum
or absent in the case of hindered olefins, due to the more
bulky alkyl groups, leading to relatively faster hydrobo-
rations with the second and third equivalents of olefin.
Summarizing the data for all the solvents, the following
order of reactivity with solvent in the hydroboration of
representative olefins with 10 was noted: dioxane >
tetrahydrofuran > n-pentane g tert-butyl methyl ether
. dichloromethane. Table 3 summarizes the results in
various solvents.
Hyd r obor a tion -Oxid a tion of Olefin s. To further
establish the synthetic applicability of this new highly
reactive amine-borane adduct, the hydroboration-oxida-
tion of representative olefins was also studied. Hydrobo-
ration-oxidation of 1-hexene in THF gave a mixture of
1,2-hexanols in quantitative yield, as observed by GC
analysis with an internal standard. The ratio of the boron
addition to the internal vs the terminal positions in
1-hexene was established as 4:96 from the relative ratios
of the corresponding alcohols after oxidation. These
selectivities are similar to that reported for THF‚BH3 or
BMS.8
Hydroboration-oxidation of cyclohexene with 10 in
THF gave cyclohexanol in quantitative yields (∼99% by
GC, 91% isolated, eq 8). The recovered amine, using
acid-base manipulations, can be used again for the
preparation of borane adducts.
Exp er im en ta l Section
Manipulations and reactions with air-sensitive compounds
were carried out under a nitrogen atmosphere. Glassware was
oven-dried for several hours, assembled while hot and cooled
in a stream of dry nitrogen gas. Techniques for handling air-
sensitive compounds, described elsewhere were followed.8 1H,
13C and 11B NMR spectra were recorded on a 300 MHz
multinuclear instrument. The 11B NMR chemical shifts are
in δ relative to BF3:Et2O. Mass spectra were obtained on a
mass spectrometer in both CI and EI modes. GC analyses were
carried out either on a chromatograph equipped with capillary
column (0.25 µm × 30 m) or with a chromatograph provided
with FID and a CI-100A integrator. The following columns
were used, 6 ft × 0.125 in, 15% Carbowax 20M on Chromosorb
W, 9 ft × 0.125 in, 3% OV-17 on Chromosorb-G and 3 ft ×
0.125 in, 10% SE 30 on Chromosorb W. Optical rotations were
measured on a polarimeter. The hydride analysis studies were
carried out using the gasimeter.9 Microanalyses were per-
formed at the Microanalytical Laboratory, Purdue University.
Ma ter ia ls. tert-Hexylamine,7 tert-heptylamine7 N-tert-oct-
ylmorpholine,10 1c, and diisopropyl sulfate11 were prepared
Hydroboration-oxidation studies of various represen-
tative olefins listed in Table 3 and the adduct 10 in THF
were also carried out. The results obtained are similar
to that reported for BH3‚THF and no interference of
carrier amine was noted. However, since the basic amine
4 was present in the reaction mixture after hydrobora-
tion, oxidation of the organoborane with hydrogen per-
oxide was also examined without the usual addition of
sodium hydroxide. The oxidation was instantaneous,
however the yield of cyclohexanol was slightly lower
(∼91% by GC). In the case of 1-hexene, the yield of 1-
and 2-hexanols was even less (80% by GC) and the
isomeric ratio was 89:11. Apparently, the oxidation is not
complete. The complete oxidation can be achieved by the
addition of 20 mol % of carrier amine to the reaction
mixture before oxidation. Also, these preparative scale
experiments can be carried out in other solvents such as
dioxane, tert-butyl methyl ether and n-pentane. When the
(10) Olin, S. M.; Brit. Pat. 742, 298 1955; Chem. Abstr. 1957, 51,
4936.
(11) Kranzfelder, A. L.; Sowa, F. J . J . Am. Chem. Soc. 1937, 59,
1491.

4660 J . Org. Chem., Vol. 65, No. 15, 2000
Brown et al.
according to the literature. tert-Octylamine and tert-pentyl-
amine were commercial products. All solvents were purified
according to literature procedures and stored under nitrogen.
Tetrahydrofuran and dioxane were freshly distilled from
benzophenone ketyl before use. All olefins were distilled from
a small amount of lithium aluminum hydride and stored under
with n-pentane. The pentane solution was dried over anhy-
drous magnesium sulfate and the product, tert-octyldimethyl-
amine, was isolated by distillation: 12.24 g (77%); bp 62-63
1
°C/17 mmHg (lit.12 bp 174-175 °C); H NMR (CDCl3) δ 1.00
(s, 9H, CH3), 1.11 (s, 6H, CH3), 1.39 (s, 2H, CH2), 2.21 (s, 6H,
CH3).
nitrogen. (+)-R-Pinene, [R]22 +45.2° (87.3% ee) was used.
D
ter t-Octyleth ylm eth yla m in e 6. Diethyl sulfate (33.92 g,
0.22 mol) was slowly added to tert-octylamine (25.86 g, 0.2 mol)
keeping the reaction mixture at 60-65 °C and then it was
stirred for 15 min. Aqueous 8 M potassium hydroxide (40 mL,
0.32 mol) was added to the warm mixture. The organic layer
was separated, dried over anhydrous magnesium sulfate and
then again heated at 80 °C for 0.5 h. The two layers formed
were separated. The upper amine layer was dried over
anhydrous magnesium sulfate and the product, tert-octylethyl-
amine, was isolated by distillation: 28 g (89%); bp 64-66 °C/
20 mmHg.
A 37% solution of formaldehyde (7.93 g, 109 mmol) was
added to a mixture of tert-octylethylamine (17.3 g, 100 mmol)
and 88% formic acid (8.31 g, 181 mmol) at 0 °C. The reaction
mixture was kept at 80 °C for 3 h. Aqueous 8 M potassium
hydroxide (33 mL, 211 mmol) was added, the organic layer
was separated and aqueous layer was extracted with n-
pentane. The organic solutions were combined, dried over
anhydrous magnesium sulfate and the product, tert-octyleth-
ylmethylamine, was isolated by distillation: 14.5 g (85%); bp
78-80 °C/20 mmHg; 1H NMR (CDCl3) δ 0.99 (s, 9H, CH3), 1.02
(t, 3H, J ) 6.1, CH3), 1.10 (s, 6H, CH3), 1.39 (s, 2H, CH2), 2.16
(s, 3H, CH3), 2.41 (q, 2H, J ) 6.1, CH2); 13C NMR (CDCl3) δ
14.80 (CH3), 26.21 (CH3), 31.42 (C), 31.96 (CH3), 33.93 (CH2),
44.16 (CH3), 49.20 (CH2), 57.83 (CN); MS (70 eV EI CI) 171
(M+), 100 (100). Anal. Calcd for C11H25N: C, 77.11; H, 14.70;
N, 8.17. Found: C, 76.80; H, 14.63; N, 8.55.
ter t-Octylisobu tylm eth yla m in e 8. A mixture of tert-
octylamine (25.86 g, 0.2 mol) and 2-methyl-1-bromopropane
(13.70 g, 0.1 mol) was heated at 130 °C for 28 h. Aqueous 8 M
potassium hydroxide (40 mL, 0.32 mol) was added. The organic
layer was separated and dried with anhydrous magnesium
sulfate. The organic layer, after distillation gave a pure
fraction of tert-octylisobutylamine, 10.37 g, (56%), bp 92-94
°C/23 mmHg.
A 37% solution of formaldehyde (4.22 g, 58 mmol) was added
to a mixture of tert-octylisobutylamine (10 g, 53 mmol) and
88% formic acid (9.41 g, 96 mmol) at 0 °C. The reaction mixture
was kept at 50-55 °C for 10 h. Aqueous 8 M potassium
hydroxide (17 mL, 143 mmol) was added, the organic layer
was separated and the aqueous layer was extracted with
n-pentane. The organic solutions were combined, dried over
anhydrous magnesium sulfate and the product, tert-octyliso-
butylmethylamine, was isolated by distillation: 9.08 g (86%);
bp 104-106 °C/20 mmHg; 1H NMR (CDCl3) δ 0.86 (d, 6H, J )
6.6, CH3), 0.99 (s, 9H, CH3), 1.07 (s, 6H, CH3), 1.37 (s, 2H,
CH2), 1.64 (nonet, 1H, J ) 6.6, CH), 2.09 (d, 2H, J ) 6.6, CH2),
2.12 (s, 3H, CH3); 13C NMR (CDCl3) δ 21.03 (CH3), 26.54 (CH3),
27.12 (CH), 31.41 (C), 31.98 (CH3), 35.58 (CH2), 49.31 (CH2),
57.41 (C), 59.06 (CH2); MS (70 eV EI CI), 200 (M+ + 1), 128-
(100), 72(39), 57(27). Anal. Calcd for C13H29N: C, 78.31; H,
14.66; N, 7.02. Found: C, 78.21; H, 14.72; N, 7.41.
ter t-Alk yld ieth yla m in es. The procedures followed for tert-
pentyl-, -hexyl-, -heptyl-, and -octyldiethylamine are the same.
The procedure followed for tert-octyldiethylamine (4) is rep-
resentative.
ter t-Octyld ieth yla m in e 4. The diethyl sulfate (18.50 g,
0.12 mol) was added to tert-octylamine (12.93 g, 0.1 mol) at
room temperature. The reaction was exothermic and the
temperature rose to 120 °C. After cooling to 50 °C, aqueous 8
M potassium hydroxide (40 mL, 0.32 mol) was added, the
organic layer was separated when warm, and then dried over
anhydrous magnesium sulfate. This crude product was treated
with diethyl sulfate (18.50 g, 0.12 mol) and heated with stirring
at 100-150 °C for 15 min. After the same workup as described
above, the organic layer was separated, dried over anhydrous
magnesium sulfate and heated at 120 °C for 30 min. Basic
workup and distillation gave the product, tert-octyldiethyl-
amine: 16.66 g (90%); bp 88-89 °C/17 mmHg; 1H NMR
(CDCl3) δ 0.99 (s, 9H, CH3), 1.02 (t, J ) 7.0, 6H, CH3), 1.13 (s,
6H, CH3), 1.40 (s, 2H, CH2), 2.53 (q, J ) 7.0, 4H, CH2); 13C
NMR (CDCl3) δ 17.00 (CH3), 27.56 (CH3), 31. 41 (C), 31.99
(CH3), 43.06 (CH2), 50.04 (CH2), 58.75 (CN); MS (70 eV EI CI)
185 (M+), 114 (100), 58 (14). Anal. Calcd for C12H27N: C, 77.76;
H, 14.68; N, 7.56. Found: C, 77.47; H, 14.71; N, 7.93.
ter t-P en tyld ieth yla m in e 1:7a yield 70%; bp 129-131 °C/
1
760 mmHg; H NMR (CDCl3) δ 0.83 (t, J ) 7.3, 3H), 0.88 (s,
6H), 0.98 (t, J ) 7.3, 6H), 1.82 (m, 1H), 2.49 (t, J ) 7.1, 4H);
13C NMR (CDCl3) δ 17.02 (CH3), 17.42 (CH3), 20.01 (CH3),
34.49 (CH), 35.54 (C), 42.70 (CH2).
ter t-Hep tyld ieth yla m in e 3:7b yield 62%; bp 58-60 °C/20
mmHg; 1H NMR (CDCl3) δ 0.91 (s, 9H), 1.02 (s, 6H), 1.21 (t, J
) 7.0, 6H), 3.47 (t, J ) 7.05, 4H); 13C NMR (CDCl3) δ 16.35
(CH3), 21.07 (CH3), 25.42 (CH3), 36.74 (C), 46.23 (CH2), 56.69
(C).
ter t-Hexyld ieth yla m in e 2.7c Meth od A. Initially this
amine was prepared by the reaction of diethyl sulfate with
tert-hexylamine following the procedure used for tert-octyldi-
1
ethylamine: yield 75%; bp 156-160 °C/760 mmHg; H NMR
(CDCl3) δ 0.83 (t, J ) 7.5, 3H), 0.98 (s, 6H), 1.01 (t, J ) 7.1,
6H), 1.41 (q, J ) 7.4, 2H), 2.51 (q, J ) 7.08, 4H); 13C NMR
(CDCl3) δ 8.74 (CH3), 16.77 (CH3), 24.20 (CH3), 32.74 (CH2),
42.63 (CH2), 57.13 (C).
Meth od B. To a diethyl ether (50 mL) solution of N-acetyl-
tert-hexylamine7b (21.50 g, 150 mmol), borane-dimethyl sul-
fide (30 mL, 10 M, 300 mmol) was added slowly (caution!
hydrogen evolution) during 30 min. After the gas evolution
ceased, the reaction mixture was refluxed for 24 h. The
reaction was quenched with careful addition of water and 6 N
HCl was added. The diethyl ether was removed by rotary
evaporation and the residue was made basic by the addition
of KOH pellets. The amine later was separated and dried over
anhydrous magnesium sulfate. Filtration and simple distilla-
tion provided essentially pure N-ethyl-tert-hexylamine in
92.2% yield (17.49 g): bp 98-100 °C/760 mmHg; 1H NMR
(CDCl3) δ 0.86 (d, J ) 6.0, 6H), 0.98 (s, 6H), 1.07 (t, J ) 7.1,
3H), 1.75 (m, 1H), 2.1 (bs, 1H), 2.54 (q, J ) 7.1, 2H); 13C NMR
(CDCl3) δ 16.01 (CH3), 17.30 (CH3), 23.53 (CH3), 34.51 (CH),
35.41 (CH2), 54.52 (C).
Treatment of N-ethyl-tert-hexylamine with acetic anhydride
provided the corresponding N-acetyl derivative, which was
again reduced using borane-dimethyl sulfide complex to the
corresponding tert-hexyldiethylamine following the above-
mentioned procedure in 83% yield.
ter t-Octyld im eth yla m in e 5. Formic acid, 88% (20.92 g,
0.4 mol) was added to tert-octylamine (12.93 g, 0.1 mol),
followed by a 37% formaldehyde solution (17.83 g, 0.22 mol)
at 0 °C. The mixture was warmed to 50-55 °C and kept at
this temperature for 2 h. Aqueous 8 M potassium hydroxide
(65 mL, 0.52 mol) was added and the mixture was extracted
ter t-Oct yld i-n -p r op yla m in e 9. A mixture of tert-octyl-
amine (25.86 g, 0.2 mol), 1-iodopropane (25.50 g, 0.15 mol) and
glycerol (7.13 g, 77 mmol) was refluxed for 2 h. Aqueous 8 M
potassium hydroxide (40 mL, 0.32 mol) was added, the organic
layer was separated and dried with anhydrous magnesium
sulfate. It was treated with 1-iodopropane (25.50 g, 0.15 mol)
and refluxed for 6 h. Basic workup as described above and
distillation gave the product, tert-octyldi-n-propylamine: 9.90
g (31%); bp 112-113 °C/17 mmHg; 1H NMR (CDCl3) δ 0.82 (t,
J ) 7.0, 6H, CH3), 0.88 (s, 9H, CH3), 1.12 (s, 6H, CH3), 1.39 (s,
2H, CH2), 1.41 (sextet, J ) 7.0, 4H, CH2), 2.37 (m, 4H, CH2);
13C NMR (CDCl3) δ 11.85 (CH3), 25.07 (CH2), 27.78 (CH3),
31.28 (C), 31.99 (CH3), 49.45 (CH2), 52.79 (N-CH3), 58.46 (C);
(12) Bortnick, N. M.; Luskin, L. S.; Hurwitz, M. D.; Craig, W. E.;
Exner, L. J .; Mizra, J . J . Am. Chem. Soc. 1956, 78, 4039.

Molecular Addition Compounds
J . Org. Chem., Vol. 65, No. 15, 2000 4661
MS (70 eV El Cl) 213 (M+), 142 (100), 72 (18), 58 (10), 57 (16).
Anal. Calcd for C14H31N: C, 78.79; H, 14.64; N, 6.56. Found:
C, 78.80; H, 14.49; N, 6.81.
mixture was cooled to 10 °C and 3.0 mL of 3.0 N NaOH was
added, followed by the slow addition of 2.0 mL 30% hydrogen
peroxide during 10 min. The contents were further stirred at
50 °C for 2 h to ensure completion of oxidation. The reaction
mixture was cooled to room temperature and the organic layer
was separated. The aqueous layer was saturated with potas-
sium carbonate and extracted with ether, the combined organic
extract was washed with brine and dried over anhydrous
magnesium sulfate. The combined yield of 1- and 2-hexanols
was 98% (by GC using OV-17 column). The ratio of 1-hexanol/
2-hexanol is 96:4
Hyd r obor a tion -Oxid a tion of Cycloh exen e w ith 10 in
Tetr a h yd r ofu r a n . An oven-dried hydroboration flask was
cooled to 0 °C under a stream of nitrogen gas. In the flask
was placed 10 (1.1 mL, 4.5 M, 5.0 mmol) in freshly distilled
THF (7.4 mL). Cyclohexene (10.0 mmol, 0.82 g) was added
slowly during 5 min at 0 °C. The contents were further stirred
for 1 h at room temperature. The reaction was quenched with
careful addition of water. The reaction mixture was cooled to
10 °C and 3.0 mL of 3.0 N NaOH was added followed by the
slow addition of 1.0 mL 30% hydrogen peroxide. The contents
were further stirred at 50 °C for 2 h. The reaction mixture
was cooled to room temperature and the organic layer was
separated. The aqueous layer was saturated with potassium
carbonate and extracted with ether. The combined organic
layer was washed with 3.0 N HCl, then with brine, and dried
over anhydrous magnesium sulfate. Evaporation of the solvent
gave essentially pure cyclohexanol, which was further purified
by passing through a small silica gel pad, providing a yield of
1.07 g (90.3%).
Bor a n e-Am in e Ad d u cts. Gen er a l P r oced u r e. Diborane
generated as described elsewhere13,14 was passed into a neat
amine (50 mmol) at 0 °C, placed in a bubbler provided with a
sintered glass tip and a magnetic stirring bar. Excess of
diborane not absorbed by the amine was absorbed in a next
bubbler containing tetrahydrofuran over mercury and cooled
in ice water. A mercury bubbler was connected to the exit.
Diborane was passed into the amine until the concentration
of borane in THF was ∼1 M. The borane-amine adduct was
stirred overnight at room temperature prior to disconnecting
the bubblers and then analyzed for active hydride by a
standard procedure,9 using a 2 M hydrochloric acid-glycerol-
water (2:1:1) hydrolysis solution.
Hyd r obor a tion of Rep r esen ta tive Olefin s w ith 10.
Gen er a l P r oced u r e. An oven-dried, 50 mL RB flask, provided
with a septum inlet to introduce and remove compounds, a
stirring bar and a stopper, was cooled to 0 °C under nitrogen.
The flask was charged with an amine-borane adduct 10 (5.0
mmol) and a solvent. A solution of an olefin (15.0 mmol, 6.0
M, 2.5 mL) was added at 0 °C and the contents were further
stirred at room temperature (19-25 °C). The contents of the
reactions were always maintained in the temperature range.
Aliquots (1.0 mL) were taken out at intervals and hydrolyzed
using 3.0 M HCl-glycerol-THF (2:1:0.2) as the hydrolysis
solvent. The hydrogen evolved was measured using a gasim-
eter to establish the presence of active hydride. The reactions
were simultaneously followed by 11B NMR, observing the
relative ratio of an amine-borane signal and the signals due
to the hydroboration product.
The aqueous layer was neutralized with 3.0 N KOH solution
and extracted with ether. The combined organic extract was
washed with brine and dried over anhydrous magnesium
sulfate. GC analysis of the crude showed the presence of
cyclohexanol (2%) in addition to 4 (98%). Amine was recovered
in pure form by column chromatography using hexane/ethyl
acetate (95:5) as eluent in 86% (0.68 g) yield.
H yd r ob or a t ion -Oxid a t ion of 1-H exen e w it h 10 in
Tetr a h yd r ofu r a n . An oven-dried RB flask was cooled to 0
°C under a stream of nitrogen gas. In the flask was placed 10
(1.1 mL, 4.5 M, 5.0 mmol) in freshly distilled THF (7.4 mL)
and undecane (7.5 mmol, GC standard). 1-Hexene (15.0 mmol,
1.26 g) was added slowly during 5 min. at 0 °C. The contents
were further stirred for 2 h at room temperature. The reaction
was quenched with careful addition of water. The reaction
Ack n ow led gm en t. Financial support of this study
by the Borane Research Fund and Aldrich Chemical Co.
is gratefully acknowledged.
(13) ref 8, p 18.
(14) For improved methods for the generation of diborane, see:
Kanth, J . V. B.; Brown, H. C. Inorg. Chem. 2000, 39, 1795.
J O0002745