Synthesis and characterization of allylic dihaloboranes

Article abstract of DOI:10.1021/om9706471

Volatile allylic dihaloboranes have been prepared and characterized by ¹H, ¹¹B, ¹³C, and ¹⁹F NMR spectroscopy and mass spectrometry. The stability (τ_1/2) of such compounds in dilute CDCl₃ solutions depends on the substituents and the halides and ranges from a few minutes (allylic dibromoboranes) to several days (allylic difluoroboranes). Allyldihaloborane etherates were obtained by addition of diethyl ether to the corresponding free allyldihaloborane.

Full text of DOI:10.1021/om9706471

5844
Organometallics 1997, 16, 5844-5848
Syn th esis a n d Ch a r a cter iza tion of Allylic Dih a lobor a n es
Ste´phanie Le Serre and J ean-Claude Guillemin*
Laboratoire de Synthe`ses et Activations de Biomole´cules, ESA CNRS 6052, ENSCR,
35700 Rennes, France
Received J uly 28, 1997X
1
Volatile allylic dihaloboranes have been prepared and characterized by H, 11B, 13C, and
19F NMR spectroscopy and mass spectrometry. The stability (τ1/2) of such compounds in
dilute CDCl3 solutions depends on the substituents and the halides and ranges from a few
minutes (allylic dibromoboranes) to several days (allylic difluoroboranes). Allyldihaloborane
etherates were obtained by addition of diethyl ether to the corresponding free allyldiha-
loborane.
In 1961, Coyle et al. prepared by reaction of BF3 with
with PCl3 or PBr3, AsCl3, or SbCl3 respectively.14
Although the low reactivity of the phosphorus and
arsenic derivatives permitted their isolation and char-
acterization, highly reactive allylation reagents are of
a great interest in organic synthesis. We report here a
general study devoted to volatile allylic dihaloboranes
prepared by reaction of allylic stannanes with boron
trihalides.
tetraallylstannane the first allylic dihaloborane,
CH2dCHCH2BF2, which was characterized by 19F NMR
spectroscopy.1 Fourteen years later, on the basis of the
1H and 11B NMR spectra of the crude mixture, Mikhailov
et al. reported CH2dCHCH(Me)BCl2 as the product
formed by redistribution of tricrotylborane with BCl3.2
In 1979, Haubold et al. described the preparation of 1,4-
bis(dichloroboryl)-2-butene and 1,4-bis(difluoroboryl)-2-
butene by reaction of 1,3-butadiene with B2Cl4 and B2F4,
respectively.3 Recently, allylic dichloroboranes formed
by reaction of allylic tributylstannanes with BCl3 were
Resu lts a n d Discu ssion
We have prepared the allylic difluoroboranes 2a -d
by slow addition of gaseous (≈400 mbar) BF3 to a
degassed solution of allylic tributylstannanes 1a -d ,
respectively, in 1,1,2,2-tetrachloroethane (Scheme 1).
The 2-propenyl- (2a 1) and methallyldifluoroborane (2b)
were separated from the solvent and excess BF3 by trap-
to-trap distillation and obtained in nearly quantitative
yield based on the stannane 1a ,b. The versatility of the
substitution is dependent on the substituents. From the
crotylstannane 1c,c′ and BF3, only the crotyldifluorobo-
rane 2c,c′ was obtained, while (3-methyl-2-butenyl)-
tributylstannane 1d and BF3 gave (3-methyl-2-butenyl)-
difluoroborane 2d (41% yield) and 3-methyl-1-butene
(10% yield). Products 2c,c′ and 2d probably were
formed by a rearrangement of the primary γ-prod-
ucts,15,16 (1-methyl-2-propenyl)- (2e) and (1,1-dimethyl-
2-propenyl)difluoroborane (2f), respectively (Scheme 1).
Attempts to characterize the postulated primary prod-
ucts by low-temperature (-80 °C) NMR spectroscopy
were unsuccessful, even when the reaction was per-
formed at -80 °C in an NMR tube with toluene-d8 as
solvent and BF3 and stannane 1c or 1d as reagents.
The allylic difluoroboranes 2a -d were characterized
1
observed in the reaction mixture by H NMR spectro-
scopy.4 For allylic monohaloboranes, the presence of an
amino5 or phenyl6 substituent led to kinetically stable
(but also less reactive) allylic boranes. Allylic dichloro-
or dibromoboranes were postulated as intermediates,7-9
and the efficacy in carbometalation reactions of allylic
dichloroboranes generated in situ has recently been
described.4
During the last four years, we have reported the
alkenylation, allenylation, or alkynylation of GeCl4,10
13
SnCl4,11 AsCl3,12 or SbCl3 by vinylic, allenyl, and
alkynyltri-n-butylstannane. We have recently described
the formation of allylic dihalophosphines, -arsines, and
-stibines by reaction of an allylic tri-n-butylstannane
X Abstract published in Advance ACS Abstracts, December 1, 1997.
(1) Coyle, T. D.; Stafford, S. L.; Stone, F. G. A. J . Chem. Soc.
(London) 1961, 3103.
(2) Mikhailov, B. M.; Bubnov, Yu. N.; Bogdanov, V. S. J . Gen. Chim.
USSR 1975, 319. Zh. Obshch.Khim. 1975, 45, 333.
(3) Haubold, W.; Stanzl, K. J . Organomet. Chem. 1979, 174, 141.
(4) Singleton, D. A.; Waller, S. C.; Zhang, Z.; Frantz, D. E.; Leung,
S.-W. J . Am. Chem. Soc. 1996, 118, 9986.
(5) Hancock, K. G.; K., J ames D. J . Organomet. Chem. 1974, 64,
C29.
(6) Rolland, H.; Potin, P.; Majoral, J .-P.; Bertrand, G. Tetrahedron
Lett. 1992, 33, 8095.
(7) Hancock, K. G.; Kramer, J . D. J . Am. Chem. Soc. 1973, 95, 3425.
(8) J oy, F.; Lappert, M. F.; Prokai, B. J . Organomet. Chem. 1966,
5, 506.
(9) Depew, K. M.; Danishefsky, S. J .; Rosen, N.; Sepp-Lorenzino, L.
J . Am. Chem. Soc. 1996, 118, 12463.
(10) Guillemin, J .-C.; Lassalle, L.; J anati, T. Planet., & Space Sci.
1995, 43, 75.
(11) (a) J anati, T.; Guillemin, J .-C.; Soufiaoui, M. J . Organomet.
Chem. 1995, 486, 57. (b) Lassale, L.; J anati, T.; Guillemin, J .-C. J .
Chem. Soc. Chem. Commun. 1995, 699.
1
by H, 13C, 11B, and 19F NMR spectroscopy and high-
resolution mass spectrometry (HRMS). Typical of the
presence of a boron atom, broad signals were observed
for the allylic hydrogens (1H NMR) and carbon (13C
NMR). The 11B NMR signal of each compound was
observed near 27.7 ppm ((0.1 ppm). The quadruplet
1
(intensity 1:1:1:1, J BF ≈ 80 Hz) observed by 19F NMR
(14) Le Serre, S.; Guillemin, J .-C.; Karpati, T.; Soos, L.; Nyula´szi,
L.; Veszpre´mi, T. J . Org. Chem. In press.
(15) (a) Yamamoto, Y.; Asao, N. Chem. Rev. 1993, 93, 2207-2293.
(b) Nishigaichi, Y.; Takuwa, A.; Naruta, Y.; Maruyama, K. Tetrahedron
Rep. Number 337 1993, 49, 7395.
(12) (a) Guillemin, J . C.; Lassalle, L. Organometallics 1994, 13, 1525.
(b) Guillemin, J .-C.; Lassalle, L.; Dre´an, P.; Wlodarczak, G; Demaison,
J . J . Am. Chem. Soc. 1994, 116, 8930. (c) Lassalle, L.; Legoupy, S.;
Guillemin, J .-C. Inorg. Chem. 1995, 35, 5694.
(13) (a) Legoupy, S.; Lassalle, L.; Guillemin, J .-C.; Me´tail, V.; Senio,
A.; Pfister-Guillouzo, G. Inorg. Chem. 1995, 35, 1466. (b) Lassalle, L.;
Legoupy, S.; Guillemin, J .-C. Organometallics 1996, 15, 3466.
(16) Similar observations have already been reported in the prepa-
ration of substituted allylic chlorostannanes: Naruta, Y.; Nishigaichi,
Y.; Maruyama, K. Tetrahedron 1989, 45, 1067.
S0276-7333(97)00647-X CCC: $14.00 © 1997 American Chemical Society

Allylic Dihaloboranes
Organometallics, Vol. 16, No. 26, 1997 5845
Sch em e 1
Sch em e 3
attempts to condense and then revaporize the pure
allylic dichloroboranes 3a -d were unsuccessful. Dichlo-
roboranes 3a -d were analyzed by 1H, 13C, and 11B NMR
spectroscopy. They exhibit typical NMR spectra: broad
signals were observed for the allylic carbon and hydro-
gens. The 11B NMR signals were observed near 61 ppm,
an area characteristic of alkyldichloroboranes.18 The
presence of 3a was confirmed by HRMS; in the ioniza-
tion chamber of the mass spectrometer, the volatile
borane 3a was selectively vaporized from a mixture
containing 3a and the high-boiling solvent (C2H2Cl4)
(M+• for C3H5BCl2 (3a ) calcd 121.986, found 121.986).
Such dichloro derivatives are less stable than the
corresponding difluoroboranes 2a -d . The half-life of
boranes 3a ,c-d in dilute (≈5%) solutions of CDCl3 is
about several hours at room temperature. Only the
methallyldichloroborane 3b was too unstable to be
characterized at room temperature and its NMR spectra
were recorded at -60 °C in toluene-d8.
Sch em e 2
spectroscopy is characteristic of the presence of a “BF”
group.17 The half-life of boranes 2a -d in dilute (≈5%)
solutions of CDCl3 ranges from 4 h (2b) to several days
(2c,c′) at room temperature; the methallyldifluorobo-
rane (2b), in particular, is less stable than the other
derivatives. Compounds 2a -d could be condensed in
pure form at low temperature and then revaporized.
The slow addition of gaseous BCl3 to stannane 1a in
dilute solution gave the allyldichloroborane (3a ) in only
low yield with propene as the major product of the
reaction. However, good yields were obtained by addi-
tion of the stannane 1a ,c-d to a cooled (-40 °C), dilute
solution of an excess of BCl3 (Scheme 1). The formation
of BuBCl2 was not observed when the reaction and the
distillation of the allylic boranes 3a ,c-d with CDCl3
were performed at low temperature (< -10 °C). Only
small amounts of 1-butene were detected in the prepa-
ration of crotylborane 3c,c′, but 3-methyl-1-butene was
formed in 20% yield in the synthesis of the (3-methyl-
2-butenyl)dichloroborane (3d ). Compound 3a can also
be prepared starting from BCl3 and tetrallylstannane
(4a ), with the redistribution giving the allyltrichlo-
rostannane as the organotin product (eq 1). The crotyl-
The reaction of 2-propenyltri-n-butylstannane with
BBr3 has been reported,19 but the sole NMR signal (δ
11B
39 ppm) is not consistent with a dibromoborane.18
However, this approach effectively leads to the expected
product as shown by its recently described chemical
trapping.4 We found that allylic dibromoboranes 5a,c-d
can be prepared by addition of a tetraallylic stannane
4a ,c,20d , respectively, to a cooled (-50 °C) solution
containing boron tribromide in excess (Scheme 3). The
four allylic groups of the stannane 4a were replaced by
bromine, and the sole stannane observed at the end of
119Sn
this reaction was tin tetrabromide (δ
-635 ppm).
From stannanes 4c,d , the corresponding allylic dibro-
moboranes 5c,d and allylic tribromostannanes were
obtained (Scheme 3). Starting with BBr3 and stannanes
1b or 4b, attempts to detect by low-temperature 11B and
1H NMR spectroscopy the methallyldibromoborane 5b
were unsuccessful even in toluene-d8 at -90 °C. This
result is in line with the high instability of the other
methallyldihaloboranes (2b, 3b) while the crotylboranes
(2c,c′, 3c,c′, and 5c,c′) are, in each case, the most stable
compounds. Allyldibromoboranes 5a ,c,c′ were sepa-
rated from stannanes by codistillation with a solvent
dichloroboranes 3c,c′ were obtained from BCl3 and
crotylstannanes 1c,c′ or from BCl3 and (1-methyl-2-
propenyl)triphenylstannane (1e). These results indicate
that only the thermodynamic product (the isomer less
substituted on the R-carbon) can be isolated (Scheme
2). Methallyldichloroborane (3b) exhibited a particular
instability and was prepared from BCl3 and stannane
1b in a cooled (-80 °C) solution of C7D8.
(18) No¨th, H.; Wrackmeyer, B. NMR Spectroscopy of Boron Com-
pounds, Vol. 14. NMR Grundlagen und Forschritte; Springer-Verlag,
Heidelsberg, Berlin, 1978.
(19) Harston, P. Wardell, J . L.; Marton, D.; Tagliavini, G.; Smith,
P. J . Inorg. Chim. Acta 1989, 162, 245.
(20) Compound 4c has been obtained by reaction of crotyl magne-
sium chloride with SnCl4. A mixture of tetraallylic stannanes with Z-
and E-crotyl- and 1-methyl-2-propenyl groups as substituents was
obtained.
Boranes 3a -d were purified by trap-to-trap distilla-
tion. They must be trapped with a cosolvent since
(17) Cowley, A. H.; Furtsch, T. A. J . Am. Chem. Soc. 1969, 91, 39.

5846 Organometallics, Vol. 16, No. 26, 1997
Le Serre and Guillemin
Sch em e 4
(C7D8 or Cl2CHCHCl2) but an important loss of product
is observed and the presence of numerous decomposition
products cannot be avoided. The half-life of boranes
5a ,c-d in dilute (≈5%) solutions of CDCl3 is only of few
minutes at room temperature. The 11B NMR signals
were observed near 63 ppm.
The distinctive NMR data are characteristic of the
halogen substituents: the presence of the two fluorine
atoms in compound 2a shifted the signals of the allylic
hydrogens (δ ≈ 1.98 ppm) upfield with respect to those
of the chloro 3a (δ ≈ 2.45 ppm) and bromo derivatives
5a (δ ≈ 2.55 ppm). A similar effect was observed for
the R-carbon signals in the 13C NMR spectra: δ2a 18-
21, δ3a 34-36, δ5a 48.0-48.2. The 11B NMR signals
were observed at 27.6 (2a ), 61.4 (3a ), and 63.0 ppm (5a ),
respectively.
reaction of free boranes 2a , 3a , and 5a 23 or borane
etherates 7a -c with the benzaldehyde. The addition
of benzaldehyde to allyldichloroboranes 3a and 7b or
allyldibromoboranes 5a and 7c gave, after hydrolysis,
the expected homoallyl alcohol 6a (Scheme 4). With
allyldifluoroboranes 2a and 7a , the alcohol 6a was not
observed. Hence, the reaction of an allylic stannane
with an aldehyde in the presence of BF3 or BF3-Et2O
cannot proceed via a transmetalated intermediate,
because this species does not react with an aldehyde to
give the corresponding homoallylic alcohol. From our
experiments, the mechanism is more difficult to eluci-
date with chloro- and bromoboranes and such reactions
could be dependent on the strength of the borane-
electrophile complexes, the experimental conditions, and
the boron trihalide/electrophile ratio.15a
In conclusion, the volatile allylic difluoro-, dichloro-,
and dibromoboranes were easily prepared and charac-
terized by spectroscopy. Most of them can now be
considered as isolable compounds. The allylborane
etherates are synthesized by the addition of diethyl
ether to the corresponding free boranes. Extension of
this approach to the preparation of other highly reactive
boron derivatives and the study of their chemistry
currently are in progress.
Our results led us to reanalyze some previous reports.
2
The reaction of tricrotylborane with BCl3 cannot lead
to the γ-product CH2dCHCH(Me)BCl2, since this com-
pound rearranges to the crotyl derivatives 3c,c′ even
1
at low temperature. The reported H and 11B NMR data
clearly show that crotyldichloroborane 3c,c′ and 1-butene
were formed. The 1H NMR chemical shifts and coupling
constants reported for 1,4-bis(difluoroboryl)-2-butene
and 1,4-bis(dichloroboryl)-2-butene3 are not consistent
with those of boranes 2a -d and 3a -d , respectively, and
especially not with those of the crotyl derivatives 2c,c′
and 3c,c′, which have a comparable structure.
The preparation of an allylic dihaloborane complex
has never been reported. The addition of stannane 1a
or 4a on BF3-Et2O21 or BCl3-Et2O did not give the
expected product and only traces of allyldibromoborane
etherate were observed by reaction of 1a with BBr3-
Et2O. We synthesized allylic difluoro- (7a ), dichloro-
(7b), and dibromoborane etherates (7c) by addition of
diethyl ether to the corresponding free allylic dihalobo-
rane (eq 2). The yields range from 83 (7a ) to 63% (7c).
Exp er im en ta l Section
Ma ter ia ls. Boron trifluoride was prepared as described;24
boron trichloride in p-xylene, boron tribromide, and 1,1,2,2-
tetrachloroethane were purchased from Aldrich. All chemicals
were used without further purification except BCl3, which was
separated from p-xylene by trap-to-trap distillation. Allylic
tributylstannanes 1a -d 25 and tetraallylic stannanes 4a -d 26
were prepared as previously reported. A mixture of (1-methyl-
2-propenyl)triphenylstannane (1e) and crotyltriphenylstan-
nane was prepared as previously reported.25b Fractional
crystallization in pentane yielded compound 1e (33% yield)
with a purity higher than 90%. 1-Phenyl-3-buten-1-ol (6a ) was
identified by comparison with an authentic sample.27
The 1H and 13C NMR data of compounds 7a -c are
similar to those of the corresponding free derivatives.
Only the 11B NMR signals are shifted upfield (7a , 15.6
ppm; 7b, 14.6 ppm; and 7c, 0.0 ppm). The correspond-
ing free and complexed allyldihaloboranes exhibited a
similar stability.
The mechanism of the reaction of an allylic stannane
with an electrophile in the presence of a free or com-
plexed boron halide can now be partially elucidate.15,21
No transmetalation occurs between an allylic stannane
and BF3-Et2O since no fluorostannane was observed
in the reaction mixture.21 However it is generally
accepted that the allylation of an electrophile by an
allylic stannane in the presence of BCl3 or BBr3 probably
proceeds via a transmetalation.4,9,21,22 We studied the
Gen er a l. 1H (400 MHz), 19F (376 MHz), and 13C (100 MHz)
NMR spectra were recorded on a Bruker spectrometer ARX400
and 11B (96.3 MHz) NMR on a Bruker spectrometer AC 300C.
Chemical shifts are given in ppm on the scale δ relative to
tetramethylsilane (1H NMR), solvent (13C NMR, δ ) 77.7 ppm),
(23) The contamination of borane 5a with BBr3 cannot be completely
avoided.
(24) Booth, H. S.; Willson, K. S. Inorganic Syntheses; McGraw-Hill,
New York, 1939; Vol. 1, 21.
(25) (a) Seyferth, D.; Weiner, M. A. J . Org. Chem. 1961, 26, 4797.
(b) Matarasso-Tchiroukine, E.; Cadiot, P. J . Organomet. Chem. 1976,
121, 169-176. (c) Naruta, Y. J . Am. Chem. Soc. 1980, 102, 3774.
(26) (a) Fishwick, M.; Wallbridge, M. G. H. J . Organomet. Chem.
1970, 25, 69. (b) Seyferth, D.; J ula, T. F. J . Organomet. Chem. 1974,
66, 195.
(21) Denmark, S. E.; Wilson, T.; Willson, T. M. J . Am. Chem. Soc.
1988, 110, 984-986.
(22) Marton, D.; Tagliavini, G.; Zordan, M.; Wardell, J . L. J .
Organomet. Chem. 1990, 390, 127.
(27) Gerard, F.; Miginiac, P. J . Organomet. Chem. 1976, 111, 17.

Allylic Dihaloboranes
Organometallics, Vol. 16, No. 26, 1997 5847
1
1
1J CH ) 126.2 Hz), 112.3 (dd, J CH ) 150.9 Hz, J CH ) 159.6
•
Hz), 138.7 (s). HRMS: calcd for (C4H7BF2 )+ 104.0608, found
104.061; m/ z (%) 104 (48.6), 103 (10.7), 89 (22.1), 88 (5.3), 87
(5.4), 69 (31.8), 68 (6.3), 57 (6.0), 55 (13.6), 49 (13.0), 41 (100),
39 (34.7).
(Z)- a n d (E)-2-Bu ten yld iflu or obor a n es (2c,c′). Yield:
92% (Z:E ratio 27:73), τ1/2 (5% in CDCl3) ) 2-3 days. E. 1H
1
NMR (CDCl3, RT): δ 1.69 (d, 3H, J HH ) 5.8 Hz), 1.88 (br s,
2H), 5.40-5.55 (m, 2H). 11B NMR (CDCl3, RT): δ 27.7 (t, 1J BF
) 80.6 Hz). 19F NMR (CDCl3, RT): δ -74.2 (q). 13C NMR
1
(CDCl3, RT): δ 16-19 (very broad), 19.0 (q, J CH ) 125.6 Hz),
1
1
1
121.9 (d, J CH ) 149.2 Hz), 127.6 (d, J CH ) 151.6 Hz). Z. H
1
NMR (CDCl3, RT): δ 1.63 (d, 3H, J HH ) 6.1 Hz), 1.88 (br s,
2H), 5.40-5.60 (m, 2H). 11B NMR (CDCl3, RT): δ 27.7. 19F
NMR (CDCl3, RT): δ -74.2 (q, J BF ) 83 Hz). 13C NMR
1
1
(CDCl3, RT): δ 13.7 (q, J CH ) 125.6 Hz), 16-19 (very broad),
1
1
120.9 (d, J CH ) 158.2 Hz), 125.9 (d, J CH ) 162.8 Hz).
•
HRMS: calcd for (C4H7BF2 )+ 104.0608, found 104.060; m/ z
(%) 104 (48.5), 103 (12.9), 89 (18.1), 81 (7.1), 69 (6.7), 68 (7.5),
56 (6.6), 56 (6.6), 55 (24.6), 54 (6.1), 49 (14.7), 41 (100), 39
(24.9).
(3-Meth yl-2-bu ten yl)d iflu or obor a n e (2d ). Yield: 41%,
τ1/2 (5% in CDCl3) ≈ 18 h. 1H NMR (CDCl3, RT): δ 1.62 (s,
F igu r e 1.
3
3H), 1.73 (s, 3H), 1.85 (br s, 2H), 5.18 (t, 1H, J HH ) 7.3 Hz).
1
11B NMR (CDCl3, RT): δ 27.8 (t, J BF ) 79.7 Hz). 19F NMR
external CCl3F, (19F NMR) or external BF3-Et2O (11B NMR).
The NMR spectra were recorded using CDCl3 as solvent.
High-resolution mass spectrometry experiments (HRMS) were
performed on a Varian MAT 311 instrument. To record the
mass spectra, the allylic difluoroboranes 1a -d were directly
introduced from a cooled cell into the ionization chamber of
the spectrometer. The yields and half-lives (τ1/2) of the
unstabilized derivatives were determined by 1H NMR with an
internal reference.
(CDCl3, RT): δ -74.2 (q). 13C NMR (CDCl3, RT): δ 13-15
1
1
(very broad), 18.6 (q, J CH ) 125.1 Hz), 26.4 (q, J CH ) 125.6
1
Hz), 114.7 (d, J CH ) 155.1 Hz), 133.6 (s). HRMS: calcd for
•
(C5H9BF2 )+ 118.0765, found 118.077; m/ z (%) 118 (39.0), 117
(9.9), 103 (38.7), 102 (9.8), 81 (21.9), 77 (6.0), 70 (7.8), 69 (12.5),
55 (100), 42 (20.7), 41 (30.6).
Allyld ich lor obor a n es 3a -d . Gen er a l P r oced u r e. In a
two-necked flask equipped with a nitrogen inlet and a stirring
bar were introduced BCl3 (1.3 mmol) and a solvent (1 mL of
chloroform, toluene, 1,1,2,2-tetrachloroethane, etc.). The flask
was cooled to -40 °C and the stannane 1a ,c-d (1.0 mmol)
was added in about 1 min. with a microsyringe. At the end of
the addition, the solution was stirred for 10 min at -40 °C
and the flask then was fitted on a vacuum line. The product
was purified by trap-to-trap distillation. For NMR experi-
ments, the solvent (CDCl3, C7D8, C2Cl4D2, etc.) and the boranes
3a ,c-d were separated from chlorotributylstannane by distil-
lation in vacuo (10-1 mbar) and condensation at -100 °C to
remove excess BCl3.
Pure borane 3a ,c-d can be obtained using 1,1,2,2-tetra-
chloroethane as solvent. The purification was performed by
trap-to-trap distillation. The solvent was selectively condensed
in a trap cooled at -50 °C and the pure boranes 3a ,c-d were
condensed at -80 °C; a cosolvent was added at this step before
revaporization to inhibit any decomposition.
Allyld iflu or obor a n es 1. Gen er a l P r oced u r e. Into a 50
mL one-necked flask equipped with a magnetic stir bar and a
stopcock was introduced the allylic tri-n-butylstannane 1a -d
(3.0 mmol) and 1,1,2,2-tetrachloroethane (6 mL). The flask
was fitted to a vacuum line and degassed (Figure 1). The
vacuum line was disconnected from the vacuum pump and
filled with BF3 at a pressure of 400 mbar. The flask was
allowed to warm to room temperature and briefly opened to
the BF3 atmosphere at 5 min intervals until the pressure was
unchanged. The flask then was placed on another vacuum
line to perform the purification by trap-to-trap distillation. The
solvent was selectively condensed in a trap cooled at -60 °C.
The borane 2a -d was separated from residual BF3 by con-
densation at -120 °C, then revaporized and frozen on a cold
finger (-196 °C) connected at the bottom to a Schlenk flask
or NMR tube. If necessary, a solvent was added. The cold
finger was disconnected from the vacuum line by stopcocks,
the apparatus was filled with dry nitrogen, and liquid nitrogen
was subsequently removed. The product was collected in the
Schlenk flask or NMR tube and kept at low temperature (< -
80 °C) before analysis (NMR spectroscopy). For HRMS experi-
ments, the cold finger containing pure boranes 2a -d under
vacuum was directly fitted on the mass spectrometer.
The methallyldichloroborane 3b was prepared from BCl3
and stannane 1b in a cooled (-80 °C) solution of C7D8.
2-P r op en yld ich lor obor a n e (3a ).4 Yield: 62%. τ1/2 (5%
in CDCl3 or C7D8 at RT) ≈ 4 h. 1H NMR (CDCl3, -40 °C): δ
3
3
2.45 (br d, 2H, J HH ) 7.3 Hz), 5.04 (dd, 1H, J HHtrans ) 17.0
Hz, 2J HH ) 1.5 Hz), 5.08 (dd, 1H, 3J HHcis ) 10.3 Hz, 2J HH ) 1.5
3
3
3
Hz), 5.89 (ddt, 1H, J HHtrans ) 17.0 Hz, J HHcis ) 10.3 Hz, J HH
2-P r op en yld iflu or obor a n e (2a ).1 Yield: 98%. τ1/2 (5%
in CDCl3) ≈ 18 h. 1H NMR (CDCl3, RT): δ 1.98 (br s, 2H),
5.07 (d, 1H, 3J HHcis ) 9.9 Hz), 5.11 (d, 1H, 3J HHtrans ) 17.1 Hz),
) 7.3 Hz). 11B NMR (CDCl3, -50 °C): δ 61.4. 13C NMR
1
(CDCl3, -40 °C): δ 34.5-36.5 (very broad), 117.2 (t, J CH
)
1
155.0 Hz), 131.4 (d, J CH ) 152.3 Hz). HRMS: calcd for
3
3
3
•
(C3H5BCl2 )+: 121.9861, found 121.986.
5.82 (ddt, 1H, J HHtrans ) 17.1 Hz, J HHcis ) 9.9 Hz, J HH ) 7.3
Hz). 11B NMR (CDCl3, RT): δ 27.6 (t, J BF ) 78.8 Hz). 19F
1
(2-Meth yl-2-p r op en yl)d ich lor obor a n e (3b). Yield: 58%.
NMR (CDCl3, RT): δ -73.4 (q). 13C NMR (CDCl3, RT): δ 18-
τ
1/2 (5% in CDCl3 or C7D8) decomposed before allowed to warm
1
1
to room temperature; 2 h (-60 °C). 1H (C7D8, -60 °C): δ 1.52
(s, 3H), 1.87 (br s, 2H), 4.55 (s, 1H), 4.79 (s, 1H). 11B NMR
(C7H8-C6D6, -50 °C): δ 62.0. 13C NMR (C7D8, -60 °C): δ
24.1 (q, 1J CH ) 125.7 Hz), 38-40 (br t, 1J CH ) 133.0 Hz), 113.2
21 (very broad), 117.2 (t, J CH ) 160.1 Hz), 129.8 (d, J CH
)
•
153.9 Hz). HRMS: calcd for (C3H5BF2 )+ 90.04523, found
90.0453; m/ z (%) 90 (62.4), 89 (15.5), 70 (36.4), 69 (20.8), 68
(5.5), 49 (33.7), 48 (6.4), 45 (12.3), 42 (35.3), 41 (100).
1
(t, J CH ) 160.0 Hz), 139.7 (s).
(2-Meth yl-2-p r op en yl)d iflu or obor a n e (2b). Yield: 96%.
τ
1/2 (5% in CDCl3) ≈ 6 h. 1H NMR (CDCl3, RT): δ 1.82 (s, 3H),
(Z)- a n d (E)-2-Bu ten yld ich lor obor a n es (3c,c′).4 (Z:E
ratio 1:1) The E-isomer is less stable than the Z. Yield: 60%.
τ1/2 (5% in CDCl3 or C7D8 at RT) ≈ 16 h. Z. 1H (CDCl3, -40
1.96 (br s, 2H), 4.73 (s, 1H), 4.81 (s, 1H). 11B NMR (CDCl3,
RT): δ 27.6. 19F NMR (CDCl3, RT): δ -72.8 (q, J BF ) 80.0
1
Hz). 13C NMR (CDCl3, RT): δ 22-24 (very broad), 25.1 (q,
°C): δ 1.66 (d, 3H, J HH ) 6.7 Hz), 2.46 (br d, 2H, J HH ) 6.2
1
3

5848 Organometallics, Vol. 16, No. 26, 1997
Le Serre and Guillemin
Hz), 5.45-5.67 (m, 2H). 11B NMR (CDCl3, -50 °C): δ 61.0.
stoichiometric amount of diethyl ether to a cooled (-40 °C)
solution of allyldifluoroborane (2a ), allyldichloroborane (3a ),
or allyldibromoborane (5a ) (1 mmol) in CDCl3 (900 µL) led to
a solution containing, respectively, the allyldifluoroborane
diethyl etherate (7a ), allyldichloroborane diethyl etherare (7b),
or allyldibromoborane diethyl etherate (7c). This solution then
was quickly transferred with a flexible needle into a cooled
(-50 °C) NMR tube.
1
13C NMR (CDCl3, -40 °C): δ 13.0 (q, J CH ) 126.2 Hz), 33.5-
1
1
35.5 (very broad), 122.6 (d, J CH ) 159.5 Hz), 126.2 (d, J CH
)
154.7 Hz). (E): 1H (CDCl3, -40 °C): δ 1.73 (d, 3H, 3J HH ) 4.5
Hz), 2.41 (br, 2H), 5.45-5.67 (m, 2H). 11B NMR (CDCl3, -50
°C): δ 61.0. 13C NMR (CDCl3, -40 °C): δ 18.0 (q, 1J CH ) 125.9
Hz), 28.5-30.5 (very broad), 123.5 (d, 1J CH ) 158.1 Hz), 127.9
1
(d, J CH ) 158.4 Hz).
3-Meth yl-2-bu ten yld ich lor obor a n e 3d . Yield: 32%. τ1/2
(5% in CDCl3 or C7D8 at RT) ≈ 8 h. 1H NMR (CDCl3, -40 °C):
δ 1.63 (s, 3H), 1.76 (s, 3H), 2.38 (br d, 2H, 3J HH ) 7.6 Hz), 5.26
(t. hept, 1H, 3J HH ) 7.6 Hz, 4J HH ) 1.3 Hz). 11B NMR (CDCl3,
Allyld iflu or obor a n e Dieth yl Eth er a te (7a ). Yield: 83%.
τ
1/2 (5% in CDCl3 at RT) ≈ 20 h. 1H NMR (CDCl3, RT): δ 1.28
3
3
(t, 6H, J HH ) 7.0 Hz), 1.70 (br d, 2H, J HH ) 7.6 Hz), 3.77 (br
3
3
q, 4H, J HH ) 7.0 Hz), 4.94 (d, 1H, J HHtrans ) 19.6 Hz), 4.96
-40 °C): δ 60.7. 13C NMR (CDCl3, -40 °C): δ 18.1 (q, 1J CH
)
3
3
(d, 1H, J HHcis ) 10.2 Hz), 5.84 (ddt, 1H, J HHtrans ) 19.6 Hz,
126.6 Hz), 26.1 (q, 1J CH ) 128.7 Hz), 29-31 (very broad), 116.2
3J HHcis ) 10.2 Hz, J HH ) 7.6 Hz). 11B NMR (CDCl3, -45 °C):
3
1
δ 15.6 (t, J BF ≈ 70 Hz). 19F NMR (CDCl3, RT): δ -89.0 (br
1
(d, J CH ) 154.4 Hz), 134.6 (s).
q). 13C NMR (CDCl3, RT): δ 15.2 (q, 1J CH ) 126.5 Hz), 21 (br),
Allyld ibr om obor a n es 5a ,c-d . Into a two-necked flask (or
an NMR tube) were introduced BBr3 (1.3 mmol) and a solvent
(CD2Cl2, CDCl3, C7D8, C2D2Cl4, 0.8 mL). The solution was
cooled to -50 °C and the tetraallylic stannane 4a ,c,d (0.25
mmol) was added slowly with stirring. At the end of the
addition, the solution was stirred for 3 min at -50 °C. To
remove respectively SnBr4 or (Z)- + (E)-crotyltribromostan-
nanes from the reaction mixture, borane 5a ,c,c′ and the
solvent (toluene or 1,1,2,2-tetrachloroethane) were distilled in
vacuo (10-1 mbar). However, this separation led to an
important loss of borane, and the presence of decomposition
products in the tin-free solution cannot be avoided. Attempts
to distill the borane 5d were unsuccessful.
1
1
68.0 (br t, J CH ) 145.1 Hz), 114.6 (t, J CH ) 151.5 Hz), 134.2
(d, J CH ) 151.5 Hz).
1
Allyld ich lor obor a n e Dieth yl Eth er a te (7b). Yield: 75%.
τ1/2 (5% in CDCl3 at RT) ≈ 5 h. 1H NMR (CDCl3, -40 °C): δ
3
3
1.46 (t, 6H, J HH ) 7.1 Hz), 1.82 (br d, 2H, J HH ) 7.1 Hz),
3
3
4.38 (br s, 4H, J HH ) 7.1 Hz), 4.92 (d, 1H, J HHtrans ) 19.3
3
3
Hz), 4.94 (d, 1H, J HHcis ) 10.1 Hz), 5.91 (ddt, 1H, J HHtrans
)
19.3 Hz, J HHcis ) 10.1 Hz, J HH ) 7.1 Hz). 11B NMR (CDCl3,
3
3
-40 °C): δ 15.0. 13C NMR (CDCl3, -40 °C): δ 14.7 (q, 1J CH
)
1
125.7 Hz), 33-34 (br), 74.6 (br t, J CH ) 144.1 Hz), 114.3 (t,
1J CH ) 153.5 Hz), 136.8 (d, J CH ) 152.8 Hz).
1
Allyld ibr om obor a n e Dieth yl Eth er a te (7c). Yield: 63%.
τ1/2 (5% in CDCl3 at RT) ≈ 10 min. 1H NMR (CDCl3, -50 °C):
2-P r op en yld ibr om obor a n e (5a ). Yield ≈ 50%. τ1/2 (5%
in CDCl3) ) 3 min. 1H NMR (CDCl3, -50 °C): δ 2.55 (br d,
3
3
δ 1.52 (t, 6H, J HH ) 6.9 Hz), 2.04 (br d, 2H, J HH ) 7.1 Hz),
3
3
3
3
2H, J HH ) 6.8 Hz), 5.10 (d, 1H, J HHtrans ) 16.8 Hz), 5.14 (d,
1H, 3J HHcis ) 11.0 Hz), 5.94 (ddt, 1H, 3J HHtrans ) 16.8 Hz, 3J HHcis
4.58 (br q, 4H, J HH ) 6.9 Hz), 4.97 (d, 1H, J HHcis ) 10.0 Hz),
5.00 (d, 1H, 3J HHtrans ) 17.2 Hz), 5.97 (ddt, 1H, 3J HHtrans ) 17.2
) 9.7 Hz, J HH ) 6.8 Hz). 11B NMR (CDCl3, -50 °C): δ 62.6.
3
Hz, J HHcis ) 10.0 Hz, J HH ) 7.1 Hz). 11B NMR (CDCl3, -50
3
3
13C NMR (CDCl3, -50 °C): δ 48.1 (br t, 1J CH ) 126.8 Hz), 117.5
°C): δ 0.0. 13C NMR (CDCl3, -50 °C): δ 13.9 (q, 1J CH ) 125.2
1
1
1
1
(t, J CH ) 154.9 Hz), 132.7 (d, J CH ) 157.1 Hz).
Hz), 35.1 (br t, J CH ) 118.8 Hz), 68.0 (br t, J CH ) 141.3 Hz),
1
1
(Z)- a n d (E)-2-Bu ten yld ibr om obor a n es (5c,c′). Yield ≈
115.3 (t, J CH ) 155.5 Hz), 137.7 (d, J CH ) 154.1 Hz).
Rea ction of Allyld ih a lobor a n es w ith Ben za ld eh yd e.
The reactions of benzaldehyde with 2-propenyldihaloboranes
2a , 3a , 5a , or 7a -c were performed under nitrogen by addition
of benzaldehyde (1 mmol) to a cooled solution (-40 °C) of an
allyldihaloborane (1 mmol) in CH2Cl2 (10 mL). After 10 min
of stirring, the mixture was allowed to warm to room temper-
ature and hydrolyzed with a saturated solution of NaHCO3.
The organic phase was dried on MgSO4 and the volatile part
was removed in vacuo. The resulting residue was chromato-
graphed on a silica gel column to give 1-phenyl-3-butenol (6a ).
From benzaldehyde and 2a , 3a , and 5a , 1-phenyl-3-butenol
(6a ) was obtained in a 0, 57, and 53% yield, respectively. The
yields were 0, 67, and 38% in reactions of benzaldehyde with
the corresponding borane etherates 7a , 7b, or 7c.
60%; E:Z 4:1. τ1/2 (5% in CDCl3) ) 7 min. E. 1H NMR (CDCl3,
1
3
-40 °C): δ 1.69 (d, 3H, J HH ) 4.8 Hz), 2.47 (br d, 2H, J HH
)
5.5 Hz), 5.48-5.53 (m, 2H). 11B NMR (CDCl3, -50 °C): δ 62.5.
13C NMR (CDCl3, -40 °C): δ 40.8 (br t, 1J CH ) 123.1 Hz), 19.1
(q, 1J CH ) 126.1 Hz), 124.4 (d, 1J CH ) 156.7 Hz), 128.3 (d, 1J CH
) 151.8 Hz). Z. 1H NMR (CDCl3, -40 °C): δ 1.71 (d, 3H,
1J HH ) 6.1 Hz), 2.52 (br d, 2H, J HH ) 7.4 Hz), 5.48-5.53 (m,
3
2H). 11B NMR (CDCl3, -50 °C): δ 62.5. 13C NMR (CDCl3,
1
1
-40 °C): δ 13.1 (q, J CH ) 127.0 Hz), 46.3 (br t, J CH ) 120.6
1
1
Hz), 123.3 (d, J CH ) 159.5 Hz), 126.8 (d, J CH ) 155.4 Hz).
(3-Meth yl-2-bu ten yl)d ibr om obor a n e (5d ). Yield ≈ 50%.
τ1/2 (5% in CDCl3) ) 3 min. 1H NMR (CDCl3, -50 °C): δ 1.73
(s, 3H), 1.61 (s, 3H), 2.49 (br d, 2H, 3J HH ) 7.5 Hz), 5.21 (tsept,
3J HH ) 7.5 Hz, J HH ) 1.3 Hz). 11B NMR (CDCl3, -50 °C): δ
4
61.6. 13C NMR (CDCl3, -50 °C): δ 18.7 (q, J CH ) 125.4 Hz),
1
1
1
26.5 (q, J CH ) 127.9 Hz), 37.6 (br t, J CH ) 126.8 Hz), 116.4
(d, J CH ) 156.6 Hz), 135.3 (s).
Su p p or tin g In for m a tion Ava ila ble: 1H and 13C NMR
spectra of the allylic difluoro- (2a -d , 7a ) and dichloroboranes
(3a -d , 7b) (20 pages). Ordering information is given on any
current masthead page.
1
Allyld ih a lobor a n e Eth er a tes 7a -c. Gen er a l P r oce-
d u r e. The reactions of 2-propenyldihaloboranes 2a , 3a , or 5a
with diethyl ether were performed in a 25 mL two-necked flask
under nitrogen. Addition with stirring of an approximately
OM9706471