Molecular addition compounds. 10. Borane adducts with N,N-dialkylanilines for hydroboration

Article abstract of DOI:10.1021/om980418u

Borane adducts with selected N,N-dialkylanilines have been prepared and examined as hydroborating agents. The adduct H₃B:NPhPrⁱ₂ is a solid, considered less desirable than liquid adducts as hydroborating agents. Fortunately, the adducts H₃B:NPhBuⁱMe, H₃B: NPhPrⁱMe, H₃B:NPhPrⁱEt, and H₃B:NPhPrⁱPrⁿ are liquids above 0 °C, hydroborating 1-octene in tetrahydrofuran in less than 1 h at room temperature. Convenient procedures are described for generating gaseous diborane quantitatively, either by thermal dissociation of the borane-N,N-diisopropylaniline adduct or by the reaction of a 2.00 M solution of sodium borohydride in triglyme with a 5.40 M solution of boron trifluoride in triglyme.

Full text of DOI:10.1021/om980418u

4202
Organometallics 1998, 17, 4202-4205
Molecu la r Ad d ition Com p ou n d s. 10. Bor a n e Ad d u cts
w ith N,N-Dia lk yla n ilin es for Hyd r obor a tion
Herbert C. Brown,* Marek Zaidlewicz,1a and Pramod V. Dalvi1b
H. C. Brown and R. B. Wetherill Laboratories of Chemistry, Purdue University,
West Lafayette, Indiana 47907
Received May 26, 1998
Borane adducts with selected N,N-dialkylanilines have been prepared and examined as
hydroborating agents. The adduct H3B:NPhPri is a solid, considered less desirable than
2
liquid adducts as hydroborating agents. Fortunately, the adducts H3B:NPhBuiMe, H3B:
NPhPriMe, H3B:NPhPriEt, and H3B:NPhPriPrn are liquids above 0 °C, hydroborating 1-octene
in tetrahydrofuran in less than 1 h at room temperature. Convenient procedures are
described for generating gaseous diborane quantitatively, either by thermal dissociation of
the borane-N,N-diisopropylaniline adduct or by the reaction of a 2.00 M solution of sodium
borohydride in triglyme with a 5.40 M solution of boron trifluoride in triglyme.
In tr od u ction
for hydroborations and other reactions.7a Very recently
the adduct was successfully applied for stoichiometric
reductions of representative functional groups such as
aldehydes, ketones, carboxylic acids, tertiary amides,
lactams, and Schiff bases, as well as for the oxazaboro-
lidine-catalyzed enantioselective reduction of prochiral
ketones.7b,c
Borane adducts with N-phenylmorpholine and N-
phenylaniline are still more reactive,6,8 hydroborating
1-octene in tetrahydrofuran in less than 1 h at room
temperature. However, they are solids, considered to
be less convenient to handle than liquids for large-scale
applications. Nevertheless, these examples clearly sug-
gest the potential of suitable borane adducts with N,N-
dialkylanilines for hydroboration.
On the other side, the growing importance of diborane
for the synthesis of pharmaceuticals and other com-
pounds9,10 and certain inconveniences of well-estab-
lished reagents, e.g., the low concentration and stability
of borane-tetrahydrofuran (BH3‚THF) and the high
volatility, flammability, and unpleasant odor of dimethyl
sulfide from borane-dimethyl sulfide (BMS), create a
need for easy-to-handle, stable, and environmentally
benign hydroborating agents.
Considering these factors, borane-amine adducts
offer the advantages of lower sensitivity to moisture and
air, the easy recovery of amines from nonbasic reaction
products, and the environmentally important possibility
of recycling the borane carrier easily. Consequently, we
decided to prepare a series of N,N-dialkylanilines and
examine their complexing ability toward borane with
the objective of developing adducts meeting the follow-
ing requirements: economic amine synthesis, liquid
adduct of high hydride content, relatively stable over
long periods, readily soluble in various solvents, and
Borane adducts with amines are versatile reagents
exhibiting many different properties as compared to the
metal borohydrides.3 For example, they are soluble in
a variety of solvents, including hydrocarbons or even
water, and in some cases can be used in an acidic
medium. Many adducts have been synthesized,4,5 and
several are commercially available. They find various
uses, e.g., as fuel additives, polymerization catalysts,
polymer stabilizers, and stain removers, in metal plat-
ing, and in the dye and pharmaceutical industries.3
Most of these applications are based on their reducing
properties. In contrast, the use of borane-amine ad-
ducts for hydroboration has been rather limited due to
strong complexation in the available derivatives, ren-
dering their reactivity relatively low, as compared to the
far weaker borane adducts with ethers and sulfides. A
systematic study of the hydroborating and reducing
properties of borane adducts with various amines car-
ried out several years ago in this laboratory revealed
that in contrast to simple, unhindered alkylamines the
less basic aniline derivatives form weaker and hence
more reactive adducts with borane.6 For example,
borane-triethylamine does not hydroborate 1-octene in
tetrahydrofuran at room temperature, whereas borane-
N,N-diethylaniline reacts in 2 h under these conditions.
Later, the borane-N,N-diethylaniline adduct was used
(1) (a)Visiting Professor from Nicolaus Copernicus University,
Torun, supported by the Purdue Borane Research Fund. (b) Postdoc-
toral research associate supported by the Purdue Borane Research
Fund.
(2) In the papers describing our studies in this area, we have found
it convenient to represent the groups n-propyl, isopropyl, tert-butyl,
and isobutyl by the symbols n-Pr, i-Pr, t-Bu, and i-Bu when they appear
before the nitrogen atom of the amine and by the more compact
representation Prn, Pri, But, Bui when they appear after the nitrogen
atom of the amine.
(3) Lane, C. F. Aldrichim. Acta 1973, 6, 51.
(7) (a) Narayana, C.; Periasamy, M. J . Organomet. Chem. 1987, 323,
145. (b) Salunkhe, A. M.; Burkhardt, E. R. Tetrahedron Lett. 1997,
38, 1519. (c) Salunkhe, A. M.; Burkhardt, E. R. Tetrahedron Lett. 1997,
38, 1523.
(4) Long, L. H. In A Comprehensive Treatise on Inorganic and
Theoretical Chemistry; Mellor, W. J ., Ed.; Longman: London, 1981;
Suppl. Vol. 5, Part B1, p 1.
(5) Meller, A. In Gmelin Handbook of Inorganic and Organometallic
Chemistry; Springer: Berlin, 1992; 4th Suppl. Vol. 3, p 1.
(6) Brown, H. C.; Murray, L. T. Inorg. Chem. 1984, 23, 2746.
(8) Camacho, C.; Uribe, G.; Contreras, R. Synthesis 1982, 1027.
(9) Follet, M. Chem. Ind. 1986, 123.
(10) Ren, O.; Meatres, C. F. Bioconjugate Chem. 1992, 3, 563.
S0276-7333(98)00418-X CCC: $15.00 © 1998 American Chemical Society
Publication on Web 08/22/1998

Borane Adducts with N,N-Dialkylanilines
Organometallics, Vol. 17, No. 19, 1998 4203
Ta ble 1. Bor a n e-N,N-Dia lk yla n ilin e Ad d u cts P r ep a r ed
amine‚BH3
exchange,a
%
hydroboration of 1-octene,f rt
BH3‚
SMe2
BH3‚
THF
stateb
(mp, °C)
11B NMRd
amine
[BH3]c
4.8
de
in THFg
neat
PhNEt2
66
30
19
0
50
36
25
0
94
80
61
10
85
79
70
36
liquid
liquid
liquid
liquid
liquid
liquid
liquid
solid
-11.55
-3.26
2 hh
12 h
PhNBuiMe (1a )
PhNBuiEt (1b)
4.5
30 min
15 min
15 min
30 min
15 min
15 min
15 min
2 h
1 h
4.0 ® 3.2i
0.9 ® 0.6j
4.9
-9.17
PhNBui (1c)
-9.68k
-8.77
2
PhNPriMe (2a )
PhNPriEt (2b)
PhNPriPrn (2c)
12 h
2 h
4.7
4.1
-14.68
-14.21
-16.49k
2 h
PhNPri (2d )
45 minl
2
(36-38)
a
b
Amine mixed with BMS or BH3‚THF in 1:1 molar ratio and analyzed by 11B NMR. At 0 °C. c Estimated by hydrolysis in 2 M HCl-
glycerol-water (2:1:1) and measuring hydrogen evolved. Recorded on a Varian Gemini 300 multinuclear spectrometer. e From the exchange
d
with BMS. f 5% excess of 1-octene. 3 M solution in 1-octene. Ref 6. Loss of borane in 4 days at room temperature. Loss of borane in
g
h
i
j
k
l
24 h at room temperature. From the exchange with BH3‚THF. 3 M solution of the adduct in 2d .
reasonably rapid hydroboration (such as quantitatively
hydroborating 1-octene in THF in less than 1 h at room
temperature).
Resu lts a n d Discu ssion
The alkylation of N-isobutylaniline with isobutyl
The reactivity of borane-N,N-diethylaniline toward
1-octene is considerably higher than that of borane-
N,N-dimethylaniline6 and only slightly too low to meet
our requirements. This observation suggested that an
increase in the steric requirements of the alkyl groups
attached to the nitrogen atom in the N,N-dialkylanilines
should further lower their complexing ability, providing
adducts with the desired properties. Consequently, two
series of amines, N-alkyl-N-isobutylanilines 1a -c and
N-alkyl-N-isopropylanilines 2a -d , have been synthe-
sized and compared for borane complexing ability with
the commercially available N,N-diethylaniline.
bromide is very slow.11 Only 52% of PhNBui was
2
obtained after 40 h reflux, followed by 5 h heating at
150 °C in an autoclave. Fortunately, the reaction rate
is accelerated in the presence of tetrabutylammonium
iodide, so that the product can be obtained in a shorter
time and higher yield. Similarly, PhNPri can be
2
prepared by stepwise alkylation of aniline with isopropyl
bromide. Other reported procedures for the preparation
of 1c and 2d are less convenient for scaling up.12-15
The complexing ability of the amines prepared was
tested by examining the exchange with BMS and BH3‚
THF. The amount of borane taken up by the amine in
the equilibrium is shown in Table 1. It should be noted
that only for BMS, which is a neat adduct, is the molar
ratio of borane, amine and dimethyl sulfide precisely
1:1:1, whereas for BH3‚THF, which is a 1.00 M solution
the values can be considered only as qualitative, involv-
ing the presence of THF in large excess. The exchange
experiments reveal an interesting picture. The N-alkyl-
N-isobutylanilines, despite the two alkyl groups being
both primary, show lower complexing ability compared
to the corresponding isopropyl derivatives. This is
observed even for N,N-diisobutyl- and N,N-diisopropyl-
anilines. Although neither PhNBui2 nor PhNPri2 takes
borane from BMS, PhNPri takes more than PhNBui
2
2
from BH3‚THF. Apparently, the isobutyl group exerts
a slightly greater steric influence than that of the
isopropyl group in diminishing the donor properties of
the alkylated aniline base in these equilibria. The trend
revealed by the exchange experiments is reflected in the
neat adducts (Table 1). Thus, PhNBuiMe and PhN-
BuiEt form adducts 4.5 and 4.0 M in BH3, respectively,
with PhNBuiEt complexing more weakly, the molarity
dropping to 3.7 in 24 h and to 3.2 in 4 days at room
temperature. Both adducts hydroborate 1-octene in
The mixed amines 1a ,b and 2a ,b were prepared from
low-cost N-methyl- and N-ethylaniline, respectively, and
isolated by fractional distillation (eq 1).
An improved synthesis of 2b based on the alkylation
of N-ethylaniline by diisopropyl sulfate was developed.
The other amines were prepared from aniline 2c by
reductive alkylation of an intermediate N-isopropyl-
aniline, 1c and 2d , by stepwise alkylation (eq 2).
(11) Hickinbottom, W. J .; Lambert, E. W. J . Chem. Soc. 1939, 1383.
(12) Katritzky, A. R.; Rechwal, S.; Wu, J . Can. J . Chem. 1990, 68,
456.
(13) Caube`re, P.; Derozier, N. Bull. Soc. Chim. Fr. 1969, 1737.
(14) Bunnett, J . F.; Brotherton, T. K. J . Org. Chem. 1957, 22, 832.
(15) Kanth, J . V. B.; Periasamy, M. J . Org. Chem. 1993, 58, 3156.

4204 Organometallics, Vol. 17, No. 19, 1998
Brown et al.
N-Eth yl-N-isop r op yla n ilin e (2b). P r oced u r e A, Typ i-
ca l for 1a ,b a n d 2a ,b. A mixture of N-ethylaniline (12.12 g,
0.10 mol) and 2-bromopropane (13.53 g, 0.11 mol) was refluxed
with stirring until the temperature of the reaction mixture
rose to 120 °C. The mixture was cooled to 80 °C, and 5.0 M
aqueous potassium hydroxide (30.0 mL) was added. The
organic layer was separated and dried with magnesium
sulfate. Excess 2-bromopropane was removed by distillation,
and the crude product containing N-ethyl-N-isopropylaniline
(83.5%), N-ethylaniline (16%), and N,N-diethylaniline (0.5%)
was obtained. N-Ethyl-N-isopropylaniline was isolated by
fractional distillation under vacuum, treated with 2.5 M
n-butyllithium solution in hexanes (2.0 mL) and distilled, 10.03
g (61%), bp 50-51 °C/1 mmHg, n2D0 ) 1.5310, 98.5% pure by
GC (30 m SPB-5 capillary column).
P r oced u r e B. Diisopropyl sulfate (21.88 g, 0.12 mol) was
added dropwise with stirring to N-ethylaniline (12.12 g 0.10
mol) at 60-80 °C. After 2 h at 100 °C, 5.0 M aqueous
potassium hydroxide (60.0 mL, 0.30 mol) was added. The
organic layer was separated, washed with 5.0 M potassium
hydroxide (10.0 mL, 50.0 mmol), and dried with magnesium
sulfate. Distillation gave 14.69 g of N-ethyl-N-isopropyl-
aniline, 2b (90%), bp 50-51 °C/1 mmHg.
THF at room temperature in less than 1 h and under
neat conditions in less than 2 h. The corresponding
N-alkyl-N-isopropylanilines, 2a -c, complex borane
slightly more strongly. Although both 1a ‚BH3 and 2a ‚
BH3 hydroborate 1-octene in THF in 30 min, under neat
conditions the isobutyl derivative, 1a ‚BH3, reacts in 2
h, whereas the isopropyl derivative, 2a ‚BH3, requires
12 h. The borane adducts of 1a and 2a -c are liquids
above 0 °C, stable at room temperature, and readily
soluble in typical hydroboration solvents, such as diethyl
ether, tetrahydrofuran, and dichloromethane.
The complexing ability of PhNBui is much lower as
2
compared to the other amines studied. Only a 0.9 M
solution of the adduct is formed at 0 °C, losing almost
half of its borane content in 24 h at room temperature.
Interestingly PhNPri2 forms a weak solid highly reactive
adduct, hydroborating 1-octene under neat conditions
in less than 1 h at room temperature. It loses borane
above its melting point (36-38 °C), so that diborane can
be quantitatively generated by heating the adduct. The
gas is readily reabsorbed upon cooling (eq 3).
N,N-Diisobu tyla n ilin e (1c). A mixture of aniline (14.90
g, 0.16 mol), 1-bromo-2-methylpropane (21.92 g, 0.16 mol), and
tetrabutylammonium iodide (2.95 g, 8.0 mmol) was refluxed
for 2.5 h. Aqueous 5.0 M potassium hydroxide solution (60.0
mL, 0.30 mol) was added, and the organic layer was separated
and dried over magnesium sulfate. The crude product was
further treated with 1-bromo-2-methylpropane (21.92 g) and
tetrabutylammonium iodide (2.95 g) and refluxed for 5.5 h.
The mixture was worked up as described above. GC analysis
showed N-isobutylaniline (63%) and N,N-diisobutylaniline
(37%). The mixture was treated with the same amounts of
1-bromo-2-methylpropane and tetrabutylammonium iodide as
above and refluxed for 8 h. The basic workup as described
above and fractional distillation gave 1c, 20.90 g (64%), bp
86-87 °C/1.5 mmHg (lit.11 bp 142-144 °C/21 mmHg).
N-P r op yl-N-isop r op yla n ilin e (2c). Sodium borohydride
(12.86 g, 0.34 mol) was added in portions to a mixture of
propionic acid (16.23 g, 0.22 mol) and N-isopropylaniline (10.00
g, 74.0 mmol) at room temperature under nitrogen, and the
mixture was kept at 55 °C for 1 h. Aqueous 5.0 M potassium
hydroxide solution (50.0 mL, 0.25 mol) was added, the organic
layer was separated, and the aqueous layer was extracted with
diethyl ether. The extracts were combined with the organic
layer and dried over magnesium sulfate. The product was
isolated by distillation, 9.73 g (74%), bp 88-89 °C/5 mmHg.
N,N-Diisop r op yla n ilin e (2d ). A mixture of aniline (18.63
g, 0.20 mol) and 2-bromopropane (24.60 g, 0.20 mol) was
refluxed until the temperature increased to 130 °C (5 h). After
cooling to room temperature, aqueous 5.0 M potassium hy-
droxide solution (50.0 mL, 0.25 mol) was added, the organic
layer was separated, and the aqueous layer was extracted with
diethyl ether. The extracts were combined with the organic
layer and dried over magnesium sulfate. Ether was removed
to give 25.15 g of a crude product. GC analysis on a 12 ft ×
0.125 in. column packed with 10% SE-30 on Chromosorb W
100-120 mesh showed aniline (7%), N-isopropylaniline (89%)
and N,N-diisopropylaniline (4%). 2-Bromopropane (24.60 g,
0.20 mol) was added, and the mixture was refluxed until the
temperature increased to 130 °C (∼40 h). The same workup
as described above and fractional distillation gave 31.15 g
(88%) of product containing ∼2% of N-isopropylaniline, which
was removed by the addition of 2.5 M n-butyllithium in hexane
(5.0 mL) and distillation. There was obtained 28.67 g of 2d
(81%), bp 50-52 °C/1 mmHg, >99% GC pure (lit.18 bp 98-
100 °C/13 mmHg).
Con clu sion
This study has demonstrated that N-alkyl-N-isobutyl-
and N-alkyl-N-isopropylanilines 1a and 2a -c are new
promising borane carriers, forming liquid borane ad-
ducts, stable at room temperature, soluble in various
solvents, hydroborating 1-octene in THF in less than 1
h at room temperature. Borane-N,N-diisopropylaniline
is a convenient source of diborane, liberating the gas
quantitatively by heating the adduct above its melting
point, 36-38 °C.
Exp er im en ta l Section
Gen er a l Meth od s. Techniques for handling air-sensitive
compounds described elsewhere were followed.19 Glassware
was oven dried for several hours, assembled while hot, and
cooled in a stream of dry nitrogen gas. 1H, 13C, and 11B NMR
spectra were recorded at 300, 75, and 96 MHz, respectively.
The 11B NMR shifts are in δ relative to BF3‚Et2O. GC analyses
were performed on a chromatograph (katharometer) equipped
with a 12 ft x 0.125 in column packed with 10% SE-30 on
Chromosorb W 100-120 mesh. Microanalyses were performed
at the Microanalytical Laboratory, Purdue University.
Ma ter ia ls. Tetrahydrofuran was freshly distilled from
benzophenone ketyl prior to use. Borane trifluoride-diethyl
etherate was distilled under vacuum from calcium hydride.
Diglyme and triglyme were distilled under vacuum from a
small amount of lithium aluminum hydride. Diisopropyl
sulfate was prepared by absorbing propene in concentrated
sulfuric acid at -10 to 0 °C according to the literature
procedure.20 Borane-methyl sulfide (BMS), borane-THF,
aniline, N-methylaniline, and N-ethylaniline were commercial
products (Aldrich).
(16) van Hoek, T. C.; Verkade, P. E.; Wepster, B. M. Rec. Trav. Chim.
Pays-Bas 1958, 77, 559.
(17) Fro¨chlich, E. Ber. 1909, 42, 1561.
(18) Rosser, M.; Ritter, J . J . J . Am. Chem. Soc. 1937, 59, 2179.
(19) Brown, H. C. Organic Syntheses via Boranes; Wiley: New York,
1975; p 18. A reprinted edition, Organic Syntheses via Boranes, Vol 1;
Aldrich Chemical Co., Inc.: Milwaukee, 1997, is currently available.
(20) Kranzfelder, A. L.; Sowa, F. J . J . Am. Chem. Soc. 1937, 59,
1491.
P r oced u r e B. Diisopropyl sulfate (21.88 g, 0.12 mol) was
added dropwise with stirring to aniline (9.31 g, 0.10 mol) at
60-80 °C. After 2 h at 100 °C, 5.0 M aqueous potassium

Borane Adducts with N,N-Dialkylanilines
Organometallics, Vol. 17, No. 19, 1998 4205
hydroxide (60.0 mL, 0.30 mol) was added. The organic layer
was separated, washed with 5.0 M potassium hydroxide (10.0
mL, 50.0 mmol), and dried with magnesium sulfate. GC
analysis showed the presence of aniline (5%) and N,N-
diisopropylaniline (10%) in addition to N-isopropylaniline
(85%). To this mixture was added diisopropyl sulfate (21.88
g, 0.12 mol) at 60-80 °C, and the mixture was maintained at
100 °C for 2 h. After the same workup as described above
and fractional distillation N,N-diisopropylaniline was obtained
in 92% yield.
Gen er a l P r oced u r e for Bor a n e-Am in e Ad d u cts. Dibo-
rane, generated as described below, was passed into a neat
amine (50.0 mmol) at 0 °C and placed in a bubbler provided
with a sintered glass tip and a magnetic stirring bar. Excess
diborane not absorbed by the amine was absorbed in the next
bubbler containing tetrahydrofuran (10.0 mL) over mercury,
cooled in ice water. A mercury bubbler was connected to the
exit. Diborane was passed into the amine until the concentra-
tion of borane in THF was ∼1 M. The borane-amine adduct
was stirred overnight at room temperature prior to discon-
necting the bubblers and then analyzed for active hydrogen
by a standard procedure, using a 2.0 M hydrochloric acid-
glycerol-water (2:1:1) hydrolysis solution.21
means of a hypodermic syringe. Generation of diborane is
smooth, and the reaction is not exothermic. After the addition
was completed, the flask was heated to 100 °C and kept at
this temperature for 15 min. Diborane was absorbed in
tetrahydrofuran (30.0 mL) at 0 °C. Analysis for active hydride
of the BH3‚THF solution obtained according to the standard
procedure, revealed a 2.41 M concentration of borane (95%);
11B NMR, δ +1.00 ppm.
P r oced u r e B. Crystalline H3B:NPhPri2 (1.15 g, 6.0 mmol)
was placed in a flask (10 mL volume) flushed with nitrogen
and attached to a buret filled with mercury. The flask was
slowly heated from 24 °C to 100 °C. Liberation of diborane
started at 40 °C, and the total amount of diborane evolved was
2.94 mol (98%). Diborane was reabsorbed upon cooling the
flask to room temperature.
Exch a n ge Rea ction of BMS a n d H 3B:THF w ith N,N-
Dia lk yla n ilin es. Gen er a l P r oced u r e. An oven-dried 25
mL RB flask, provided with septum inlet and a stirring bar
was cooled to room temperature under nitrogen. The flask
was charged with N,N-dialkylaniline (4 mmol), and BMS or
H3B:THF (4.0 mmol) was added. The contents were further
stirred at room temperature. The progress of equilibration
was followed by 11B NMR (see Table 1).
Bor a n e Tr iflu or id e Ad d u cts w ith Diglym e or Tr i-
glym e. Typical P r ocedu r e. Boron trifluoride-diethyl ether-
ate (14.19 g, 0.10 mol) was added to diglyme (13.42 g, 0.10
mol), and the mixture was stirred under 100 mmHg and finally
under 12 mmHg at room temperature to constant weight.
Diethyl ether (7.31 g, 98.6% yield) was collected in a cold trap
(liquid nitrogen). A pale yellow liquid adduct, 20.3 g, 11B NMR,
δ 0.00 ppm, was obtained. It darkened slowly when kept at 0
°C and was used within two weeks. The triglyme additive was
prepared similarly. The adducts with diglyme and triglyme
are 5.4 and 4.5 M in BF3, respectively. For preparation on a
large scale, the use of boron trifluoride-triglymate facilitates
recovery and recycle of triglyme.
Hyd r obor a tion of 1-Octen e w ith N,N-Dia lk yla n ilin e-
Bor a n e Ad d u cts in THF . Gen er a l P r oced u r e. An oven-
dried 25 mL RB flask, provided with septum inlet and a
stirring bar, was cooled to room temperature under nitrogen.
The flask was charged with N,N-dialkylaniline-borane in THF
(3.0 mmol), and 1-octene in THF (9.0 mmol) was added. The
solvent THF is taken in such a way that the final solution is
1.0 M in borane and 3.0 M in 1-octene. The contents were
further stirred at room temperature. The progress of hydrobo-
ration was followed by 11B NMR (see Table 1).
Ack n ow led gm en t. Financial support of this study
by the Purdue Borane Research Fund is acknowledged.
The assistance provided by Dr. J . V. B. Kanth with some
of the experiments is appreciated.
Gen er a tion of Dibor a n e. P r oced u r e A. A 50 mL one-
neck, round-bottom flask provided with
magnetic stirring bar, and an adapter with
a
septum inlet,
stopcock,
a
connected to a bubbler containing tetrahydrofuran (30.0 mL),
was charged with boron trifluoride-diglyme or -triglyme
adduct (75.0 mmol). A 2.0 M solution of sodium borohydride
in triglyme (28.5 mL, 57.0 mmol) was added dropwise by
Su p p or tin g In for m a tion Ava ila ble: 1H, 13C NMR, and
mass spectral data for amines 1a -c and 2a -d (2 pages).
Ordering information is given on any current masthead page.
(21) Reference 19, p 241.
OM980418U