A well feasible and general route to (organoethynyl)difluoroboranes, RHC{triple bond, long}CBF2, and their perfluorinated analogues, RFC{triple bond, long}CBF2

Article abstract of DOI:10.1016/j.jfluchem.2006.12.012

A representative series of (organoethynyl)difluoroboranes RC{triple bond, long}CBF₂ (R{double bond, long}C₄H₉, (CH₃)₃C, CF₃, C₃F₇, (CF₃)₂CF, CF

Full text of DOI:10.1016/j.jfluchem.2006.12.012

Journal of Fluorine Chemistry 128 (2007) 699–702
www.elsevier.com/locate/fluor
A well feasible and general route to (organoethynyl)difluoroboranes,
§
RHCBBCBF2, and their perfluorinated analogues, RFCBBCBF2
Vadim V. Bardin a, Nicolay Yu. Adonin a, Hermann-Josef Frohn b,
*
a N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, SB RAS, Acad. Lavrentjev Ave. 9, 630090 Novosibirsk, Russia
b Department of Chemistry, Inorganic Chemistry, University of Duisburg-Essen, Lotharstr. 1, D-47048 Duisburg, Germany
Received 28 November 2006; received in revised form 21 December 2006; accepted 21 December 2006
Available online 3 January 2007
Dedicated to the 100th Anniversary of Professor I.L. Knunyants.
Abstract
A representative series of (organoethynyl)difluoroboranes RCBB CBF2 (R C4H9, (CH3)3C, CF3, C3F7, (CF3)2CF, CF3CF CF, C4F9CF CF,
C6F5) was prepared by abstraction of fluoride from the corresponding K[RCBB CBF3] salts with BF3 in appropriate solvents (1,1,1,3,3-
pentafluoropropane, 1,1,1,3,3-pentafluorobutane, or dichloromethane).
# 2007 Elsevier B.V. All rights reserved.
Keywords: Fluoroboranes; Fluoroborates; Alk-1-ynylboron compounds; NMR spectroscopy
1. Introduction
Prop-1-ynyldifluoroborane was obtained in low yield from
bis(prop-1-ynyl)mercury and BF2Cl or from prop-1-ynyldi-
chloroborane by the Swarts reaction [8] (Schemes 3 and 4).
Both routes are not convenient and the products are obtained
only in low yields. We were interested in alkylethynyldifluoro-
boranes, RHCBB CBF2, and their perfluorinated analogues,
RFCBBCBF2, as starting materials for alk-1-ynylxenonium salts
[9,10]. Therefore, we studied an alternative pathway to alk-1-
ynyldifluoroboranes. Our approach is based on the abstraction
of fluoride from K[RBF3] salts with an appropriate fluoride
anion acceptor. This procedure was successfully employed in
the preparation of alkyldifluoroboranes, alkenyldifluorobor-
anes, aryldifluoroboranes [11], and their partially fluorinated
and perfluorinated analogues [12]. In order to demonstrate the
general character of this method, a representative series of
(organoethynyl)difluoroboranes, RCBBCBF2, containing differ-
ent types of alkyl and perfluoroorgano groups R was prepared in
solutions and characterised by multi-NMR spectroscopy.
Despite the important progress in organoboron chemistry
during the last 50 years, some classes of organoboron
compounds remained unknown or less investigated. For
instance, the first communication on ethynyltrifluoroborate
salts, K[RCBBCBF3] (R Bu, Et3Si), was published recently in
1999 [2]. Subsequently the related salts with hydrocarbon
groups RH alkyl, alkenyl, and aryl were prepared [2–5]. Very
recently, the syntheses of potassium (perfluoroorganoethynyl)-
trifluoroborates, K[RFCBBCBF3] (RF represents perfluorinated
alkyl, alkenyl, and aryl groups) were reported [1]. However,
only two examples of hydrocarbon and no fluoro-containing
alk-1-ynyldifluoroboranes were reported. To our knowledge,
ethynyldifluoroborane, HCBB CBF2, and propynyldifluorobor-
ane, CH3CBBCBF2, are the only known representatives of this
class. The former borane was prepared by photochemical
dehydroborylation of cis-Cl2BCH CHBCl2 and subsequent
substitution of chlorine by fluorine in ethynyldichloroborane
with antimony trifluoride [6] (Scheme 1) or by the reaction of
ethynyltrimethyltin with BF3 [7] (Scheme 2).
2. Results and discussion
Alk-1-ynyldifluoroboranes are very moisture sensitive
molecules and strong Lewis acids. Due to these properties,
anhydrous and weak-coordinating solvents (dichloromethane,
1,1,1,3,3-pentafluoropropane (PFP), or 1,1,1,3,3-pentafluoro-
butane (PFB)) were used as reaction media. RCBBCBF2 boranes
§
Part 15 in the series ‘‘(Fluoroorgano)fluoroboranes and -borates’’ [1].
* Corresponding author. Tel.: +49 203 379 3310; fax: +49 203 379 2231.
E-mail address: h-j.frohn@uni-due.de (H.-J. Frohn).
0022-1139/$ – see front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2006.12.012

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V.V. Bardin et al. / Journal of Fluorine Chemistry 128 (2007) 699–702
the mother liquor by 19F NMR spectroscopy. Detailed
investigations of the reactivity of RCBB CBF2 and the factors
which influence the instability of (organoethynyl)difluorobor-
anes are in progress.
Scheme 1.
3. Experimental details
The NMR spectra were recorded on a Bruker AVANCE 300
spectrometer (1H at 300.13 MHz, 11B at 96.29 MHz, 19F at
282.40 MHz). The chemical shifts are referenced to TMS (1H),
BF3ÁOEt2/CDCl3 (15%, v/v) (11B), and CCl3F (19F) [with C6F6
as a secondary reference (À162.9 ppm)]. The composition of
the reaction mixtures and the yield of products were determined
by 19F NMR spectroscopy using 1,1,2-trichlorotrifluoroethane
as an internal quantitative standard.
Scheme 2.
Scheme 3.
1,1,1,3,3-Pentafluorobutane (PFB) (Solvay), 1,1,1,3,3-pen-
tafluoropropane (PFP) (Honeywell), 1,1,2-trichlorotrifluor-
oethane (Solvay K113), boron trifluoride (Messer Griesheim)
were used as supplied. Dichloromethane (Baker) was purified
by a standard procedure [14] (treatment in sequence by H2SO4,
Na2CO3 (aq), H2O, P4O10) and stored over molecular sieves
Scheme 4.
were obtained by bubbling of BF3 gas (excess) into an
intensively stirred suspension of the corresponding potassium
(organoethynyl)trifluoroborate at À25 to À40 8C, and sub-
sequent separation of the alk-1-ynyldifluoroborane-containing
solution from insoluble K[BF4] (Scheme 5). The acidities of
RCBBCBF2 can be determined in the gas phase by their fluoride
affinities. Thus, for CF3CBB CBF2 the fluoride affinity was
calculated (B3LYP/6-31 + G*) to 89.0 kcal molÀ1 [13]. This
value exceeds that of BF3 (78.8 kcal molÀ1) remarkably [13].
Consequently, the driving force for the formation of RCBBCBF2
is the gain of lattice energy of K[BF4].
˚
3 A before use. Potassium (organoethynyl)trifluoroborates
K[RCBBCBF3] (R C4H9 [3], (CH3)3C [4], CF3, C3F7,
(CF3)2CF, CF3CF CF, C4F9CF CF, C6F5 [1] were prepared
by literature procedures. All manipulations with (organoethy-
nyl)difluoroboranes were performed in FEP (block copolymer
of tetrafluoroethylene and hexafluoropropylene) equipment
under an atmosphere of dry argon.
3.1. Hex-1-ynyldifluoroborane
The preparative yield of RCBB CBF2 was determined by 19
F
The stirred suspension of K[C4H9CBBCBF3] (84 mg,
0.45 mmol) in PFP (1 mL) in a 8 mm i. d. FEP trap was
cooled to À40 8C and boron trifluoride was bubbled over a
period of 15 min. The suspension was centrifuged at À78 8C,
and the cold mother liquor was transferred to a cold (À78 8C)
trap via a Teflon tube using a pressure of dry argon. The
solution contained 0.44 mmol (98%) of C4H9CBB CBF2 (19F
NMR). 1H NMR (PFP, À40 8C): d 2.28 (t, 3J (H3, H4) = 7 Hz, t,
4J(H3, H5) = 2 Hz, 2H, H3), 1.57–1.36 (m, 4H, H4,5), 0.92 (t,
3J(H6, H5) = 7 Hz, 3H, H6). 19F NMR (PFP, À40 8C): d À77.3
(br s, t1/2 = 60 Hz, BF2). 11B NMR (PFP, À40 8C): d 16.1
(br s, t1/2 = 180 Hz).
NMR spectroscopy using the quantitative internal reference
(1,1,2-trichlorotrifluoroethane). When the reaction (not opti-
mised) was performed in CH2Cl2, the yield of (organoethy-
nyl)difluoroboranes diminished to 30–40%.
We found a remarkable dependence of the stability of
RCBBCBF2 in solution on the nature of R. Thus, no
decomposition of alk-1-ynyl- and perfluoroalk-1-ynyldifluor-
oboranes (R C4H9, (CH3)3C, CF3, C3F7, (CF3)2CF) in PFP was
detected at 20–22 8C over days under an atmosphere of dry
argon (19F NMR). For distinction, brown coloration of solutions
of CF3CF CFCBBCBF2 and C4F9CF CFCBBCBF2 appeared
within a few minutes at 22 8C. After 1 h, the degree of
decomposition was 40 and 70%, respectively (19F NMR).
When a solution of C6F5CBB CBF2 in PFP was kept at 22 8C for
5–10 min, a white precipitate was formed and only traces of
pentafluorophenyl-containing products were still detected in
3.2. 3,3-Dimethylbut-1-ynyldifluoroborane
(A) Boron trifluoride was bubbled into a stirred suspension of
K[(CH3)3CCBB CBF3] (81 mg, 0.43 mmol) in PFP (1 mL)
Scheme 5.

V.V. Bardin et al. / Journal of Fluorine Chemistry 128 (2007) 699–702
701
at À40 8C over a period of 15 min. After centrifugation at
À78 8C, the solution of (CH3)3CCBB CBF2 in PFP was
transferred to a cold (À78 8C) trap via a Teflon tube using a
(PFP, À40 8C): d 1.24 (s, 3CH3). 19F NMR (PFP, À40 8C):
d À77.2 (br s, t1/2 = 65 Hz, BF2). 11B NMR (PFP, À40 8C):
d 19.7 (br s, t1/2 = 168 Hz).
(d, 3J(CF3, F3) = 10 Hz, 6F, 2CF3), À169.0 (septet, 3J(F3,
5
CF3) = 11 Hz, t, J(F3, BF2) = 3 Hz, 1F, F3). 11B NMR
(PFP, À10 8C): d 15.7 (br s, t1/2 = 101 Hz).
1
pressure of dry argon (95% yield, 19F NMR). H NMR
(B) Boron trifluoride was bubbled into a stirred suspension of
K[(CF3)2CFCBBCBF3] (155 mg, 0.51 mmol) in CH2Cl2
(2 mL) at À40 8C for 40 min. After centrifugation at 0 8C,
the solution of (CF3)2CFCBB CBF2 was transferred to a cold
(0 8C) trap via a Teflon tube using a pressure of dry argon
and the residue was washed with cold (0 8C) CH2Cl2
(1 mL). The combined extracts contained 0.17 mmol
(30%) of borane (CF3)2CFCBBCBF2 (19F NMR) in CH2Cl2.
(B) Boron trifluoride was bubbled into a stirred suspension of
K[(CH3)3CCBBCBF3] (300 mg, 1.51 mmol) in CH2Cl2
(2 mL) at À40 8C for 30 min. The solution of
(CH3)3CCBBCBF2 (30% yield, 19F NMR) in CH2Cl2 was
separated after centrifugation at 0 8C.
3.6. Perfluoropent-3-en-1-ynyldifluoroborane
3.3. Perfluoroprop-1-ynyldifluoroborane
Boron trifluoride was bubbled into a stirred suspension of
K[CF3CF CFCBBCBF3] (80 mg, 0.30 mmol) (cis:trans =
1:2) in PFP (1 mL) at À40 8C for 15 min. After centrifugation
at À78 8C, the solution of CF3CF CFCBB CBF2 (cis:trans =
1:2) in PFP was separated at À40 8C as described above and
collected in a cold (À40 8C) FEP trap (91% yield, 19F NMR).
(A) Boron trifluoride was bubbled into a stirred suspension of
K[CF3CBBCBF3] (57 mg, 0.28 mmol) in PFP (1.5 mL) at
À40 8C for 10 min. After centrifugation at À78 8C, the
solution of CF3CBBCBF2 in PFP was transferred to a cold
(À40 8C) trap via a Teflon tube using a pressure of dry
argon (93% yield, 19F NMR). 19F NMR (PFP, À30 8C): d
3
19F NMR (PFP, À40 8C): d À67.5 (d, J(F5, F4) = 11 Hz, d,
À52.0 (s, 3F, F3), À72.0 (br s, t1/2 = 82 Hz, 2F, BF2). 11
NMR (PFP, À30 8C): d 15.6 (br s, t1/2 = 98 Hz).
B
4J(F5, F3) = 21 Hz, 3F, F5), À73.6 (br s, t1/2 = 51 Hz, 2F,
BF2), À144.0 (d, 3J(F3, F4) = 139 Hz, q, 4J(F3, F5) = 21 Hz, t,
3
(B) Boron trifluoride was bubbled into a stirred suspension of
K[CF3CBBCBF3] (500 mg, 2.61 mmol) in CH2Cl2 (4 mL)
at À40 8C for 30 min. The suspension was centrifuged at
À78 8C and the mother liquor was decanted at À40 8C into
a cold (À40 8C) FEP trap. The precipitate was washed with
cold (À40 8C) CH2Cl2 (2 mL). The combined extracts
contained 0.80 mmol (30%) of borane CF3CBBCBF2 (19F
NMR) in CH2Cl2.
5J(F3, BF2) = 2 Hz, 1F, F3), À154.5 (d, J(F4, F3) = 139 Hz,
q, 3J(F4, F5) = 11 Hz, 1F, F4) (trans-isomer); À67.6 (d, 3J(F5,
4
F4) = 12 Hz, d, J(F5, F3) = 6 Hz, 3F, F5), À73.9 (br s, t1/2
3
4
= 51 Hz, 2F, BF2), À127.9 (d, J(F3, F4) = 7 Hz, q, J(F3,
3
3
F5) = 6 Hz, 1F, F3), À135.3 (d, J(F4, F3) = 7 Hz, q, J(F4,
F5) = 12 Hz, 1F, F4) (cis-isomer). 11B NMR (PFP, À40 8C):
d 16.1 (br s, t1/2 = 175 Hz).
3.7. Perfluorooct-3-en-1-ynyldifluoroborane
3.4. Perfluoropent-1-ynyldifluoroborane
Boron trifluoride was bubbled into a stirred suspen-
sion of K[C4F9CF CFCBBCBF3] (72 mg, 0.17 mmol)
(cis:trans = 46:54) in PFB (1.5 mL) at À25 8C for 10 min.
The solution of C4F9CF CFCBB CBF2 (cis:trans = 46:54) in
PFB was separated at À40 8C as described above and collected
in a cold (À40 8C) FEP trap (100% yield, 19F NMR). 19F NMR
(PFB, À10 8C): d À73.4 (br s, t1/2 = 42 Hz, 2F, BF2), À80.2 (t,
Boron trifluoride was bubbled into a stirred suspension of
K[C3F7CBBCBF3] (444 mg, 1.48 mmol) in PFP (2 mL) at
À35 8C for 30 min. The suspension was stirred at 0 8C for
5 min and centrifuged at À78 8C. The mother liquor was
separated at À40 8C as described above and the residue was
washed with cold (À40 8C) PFP (1 mL). The combined
solutions of C3F7CBB CBF2 in PFP were collected in a cold
(À40 8C) FEP trap (100% yield, 19F NMR). 19F NMR (PFP,
4
3J(F8, F7) = 2 Hz, t, J(F8, F6) = 10 Hz, 3F, F8), À117.1 (d,
3J(F5, F4) = 12 Hz, t, 4J(F5, F7) = 12 Hz, d, 4J(F5, F3) = 25 Hz,
2F, F5), À123.4 (m, 2F, F6), À125.4 (m, 2F, F7), À141.8 (d,
3J(F3, F4) = 139 Hz, t, 4J(F3, F5) = 25 Hz, t, 5J(F3, BF2) = 6 Hz,
À20 8C): d À72.2 (br s, t1/2 = 153 Hz, BF2), À79.1 (t, J(F5,
4
F3) = 8 Hz, 3F, F5), À100.6 (t, 3J(F3, F4) = 4 Hz, q, 4J(F3,
1F, F3), À150.8 (m, d, J(F4, F3) = 139 Hz, 1F, F4) (trans-
3
3
3
F5) = 8 Hz, 2F, F3), À125.6 (t, J(F4, F3) = 4 Hz, 2F, F4). 11B
isomer); À73.8 (br s, t1/2 = 51 Hz, 2F, BF2), À80.2 (t, J(F8,
4
3
NMR (PFP, À20 8C): d 15.5 (br s, t1/2 = 100 Hz).
F7) = 2 Hz, t, J(F8, F6) = 10 Hz, 3F, F8), À115.5 (d, J(F5,
F4) = 14 Hz, t, 4J(F5, F7) = 14 Hz, 2F, F5), À122.2 (m, 1F, F4),
À122.7 (m, 2F, F6), À125.4 (m, 2F, F7), À131.2 (m, 1F, F3) (cis-
isomer). 11B NMR (PFB, À10 8C): d 16.1 (br s, t1/2 = 138 Hz).
3.5. Perfluoro-3-methylbut-1-ynyldifluoroborane
(A) Boron trifluoride was bubbled into a stirred suspension of
K[(CF3)2CFCBBCBF3] (82 mg, 0.26 mmol) in PFP
(1.5 mL) at À40 8C for 10 min. After centrifugation at
À78 8C, the solution of (CF3)2CFCBBCBF2 in PFP was
transferred to a cold (À40 8C) trap via a Teflon tube using a
pressure of dry argon (92% yield, 19F NMR). 19F NMR
(PFP, À10 8C): d À72.3 (br s, t1/2 = 80 Hz, 2F, BF2), À75.3
3.8. Pentafluorophenylethynyldifluoroborane
Boron trifluoride was bubbled into a stirred suspension of
K[C6F5CBBCBF3] (106 mg, 0.35 mmol) in PFP (1.5 mL) at
À35 8C for 10 min. After centrifugation at À78 8C, the solution
of C6F5CBB CBF2 in PFP was separated at À50 8C as described

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V.V. Bardin et al. / Journal of Fluorine Chemistry 128 (2007) 699–702
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above and collected in a cold (À50 8C) FEP trap (96% yield,
19F NMR). 19F NMR (PFP, À30 8C): d À74.9 (br s,
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8416–8423.
t
1/2 = 45 Hz, 2F, BF2), À134.0 (m, 2F, Fortho), À148.1 (t,
4
3J(Fpara, Fmeta) = 19 Hz, t, J(Fpara, Fortho) = 4 Hz, 1F, Fpara),
À161.2 (m, 2F, Fmeta). 11B NMR (PFP, À30 8C): d 16.4 (br s, t1/
2 = 178 Hz).
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Acknowledgements
We gratefully acknowledge financial support by the
Deutsche Forschungsgemeinschaft, the Russian Foundation
for Basic Research (Grant 04-03-04002-NNIO_a), and the
Fonds der Chemischen Industrie.
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