1H, 13C, 19Fand 11B NMR spectral reference data of some potassium organotrifluoroborates

Article abstract of DOI:10.1002/mrc.2467

Complete ¹H, ¹³C, ¹⁹Fand ¹¹B NMR spectral data for 28 potassium organotrifluoroborates are described. The resonance for the carbon bearing the boron atom is described for most of the studied compounds. A modifie

Full text of DOI:10.1002/mrc.2467

Spectral Assignments and Reference Data
Received: 25 November 2008
Revised: 25 May 2009
Accepted: 25 May 2009
Published online in Wiley Interscience: 17 June 2009
(www.interscience.com) DOI 10.1002/mrc.2467
1H, 13C, 19F and 11B NMR spectral reference data
of some potassium organotrifluoroborates
Roberta A. Oliveira,a Ricardo O. Silva,b Gary A. Molanderc
and Paulo H. Menezesb∗
Complete 1H, 13C, 19F and 11B NMR spectral data for 28 potassium organotrifluoroborates are described. The resonance for the
carbon bearing the boron atom is described for most of the studied compounds. A modified 11B NMR pulse sequence was used
and better resolution was observed allowing the observation of 11B–19F coupling constants for some of the studied compounds.
c
Copyright ꢀ 2009 John Wiley & Sons, Ltd.
Keywords: 1D NMR; 19F NMR; 11B NMR; potassium organotrifluoroborates
Introduction
acids using KHF2 in MeOH : H2O in good yields[19] and submitted
to 1H, 13C, 11B, and 19F NMR analyses.
Since the discovery of the Suzuki–Miyaura reaction,[1]
organoboron have become important reagents in transition-
metal-catalyzed reactions, particularly in palladium-catalyzed re-
actions, producing new carbon–carbon bonds. The large number
of applications of tricoordinate boron compounds, particularly
boronic acids and esters, can also be explained by the fact that
these compounds are easily synthesized via transmetalation or
hydroboration reactions.[2]
Organotrifluoroborates have proven to be a good option to
replace boronic acids and boronate esters providing advantages
over the latter reagents in many Suzuki type coupling reactions,[3]
1,2-[4] and 1,4-additons[5] to carbonyl compounds, Mannich type
reactions,[6] synthesis of alcohols,[7] amines,[8] and iodides,[9]
and Heck type reactions,[10] among other transformations.[11]
(For an extensive review about synthesis and applications of
organotrifluoroborate salts see Ref. [11].)
One of the major benefits is the ability to elaborate upon the
structure of a simple, functionalized organotrifluoroborate, in-
creasing its molecular complexity while maintaining the valuable
carbon–boron bond for subsequent transformation. Organotri-
fluoroborates may also act as serine protease inhibitors[12] and,
more recently, the pharmacological and toxicological properties
of potassium thiophene-3-trifluoroborate were investigated.[13]
This paper describes the complete spectral reference data of 28
potassium organotrifluoroborates, including hetero-nuclei anal-
ysis of 11B and 19F. The selected list of organotrifluoroborates
includes compounds with different functional groups and struc-
tures that allowed an analysis of the neighboring influence in
the hetero-nuclei shifts. The structural and spectroscopic assign-
ments were also made through the combined use of 1D and
heteronuclear nuclear magnetic resonance (NMR) experiments.
In some of the studied compounds the J (11B–19F) in the 11B
NMR spectra and J (19F–11B) in the 19F NMR spectra were observed
(Fig. 1a and b). The relative rapid 11B relaxation often hinders or
excludes the observation of 11B coupling constants J (11B–X) in
spectra of both 11B and other nuclei by line broadening.[20]
A
modified 11B NMR pulse sequence was used and better resolution
was observed, allowing the observation of 11B–19F coupling
constants for some compounds. A comparison between the
spectrumobtainedusingstandardacquisitionparameters(Fig. 2a)
and the spectrum obtained using a different pulse sequence
(Fig. 2b) is shown in Fig. 2. Because of the better resolution on the
spectrum, it was possible to observe the coupling constant more
clearly.
Considering that nuclear spins of 11B and 19F nuclei are equal
to 3/2 and 1/2, respectively and that the lines number on the
spectrum is determined by the term 2nI + 1, where I is the nuclear
spin value and n is number of neighbor nucleus, the spectra
show different lines due to scalar coupling. 19F NMR spectrum
of compound 1 (Fig. 1a) shows four lines of approximately the
same intensity (1 : 1 : 1 : 1) because there is only one nucleus of
11B coupling with the 19F nucleus; in the Fig. 1b, it is possible to
observe a quartet (1 : 3 : 3 : 1) due to scalar coupling with three 19F
nucleus. The resonances corresponding to the carbon bearing the
boron atom were observed to be broad due to the quadrupolar
relaxation mechanism of 11B nucleus. This effect can be observed
in Fig. 1c where the 13C spectrum shows two signals being the
∗
Correspondence to: Paulo H. Menezes, Depto.Química Fundamental, CCEN,
Universidade Federal de Pernambuco, Recife, PE, 50.740-540, Brazil.
E-mail: pmenezes@ufpe.br
˜
a
b
c
Universidade Federal do Vale do Sao Francisco, Rodovia BR 407, 12 Lote 543,
S/N C, Petrolina, PE 56300-000, Brazil
Results and Discussion
Depto.Química Fundamental, CCEN, Universidade Federal de Pernambuco,
Recife, PE, 50.740-540, Brazil
Compounds 1,[14] 2,[15] 3–4,[16] 27,[17] and 28[18] were prepared
according to literature procedures. The potassium organotrifluo-
roborates 5–26 were prepared from the corresponding boronic
Roy and Diana Vagelos Laboratories, Dept. of Chemistry, University of
Pennsylvania, 231 South 34th Street, Philadelphia, PA, 19104-6323, USA
c
Magn. Reson. Chem. 2009, 47, 873–878
Copyright ꢀ 2009 John Wiley & Sons, Ltd.

R. A. Oliveira et al.
(a)
(b)
(c)
Figure 1. NMR spectra of compound 1, parts (a) 19F NMR spectrum (282 MHz, DMSO-d6) showing the 19F–11B coupling; (b) 11B NMR spectrum (96 MHz,
DMSO-d6) showing the 11B–19F coupling; (c) 13C NMR spectrum (75 MHz, DMSO-d6) showing the resonance from the carbon bearing the boron nuclei
(broad).
(a)
(b)
Figure 2. (a) 11B NMR (128 MHz, DMSO-d6) spectra of 28 using standard acquisition parameters and; (b) 11B NMR (96 MHz, DMSO-d6) using a different
pulse sequence.
signal at δ96.98 ppm broad because of the quadrupole moment of
11B nuclei. Notably, this resonance is not described for potassium
organotrifluoroborates.[21]
The chemical shifts in the 19F spectrum generally decrease from
a neutral molecule to an anion. In this way, it would be expected
the more fluorines attached to any given atom, the less shielded
would be the 19F nucleus.[23] This effect was also observed for the
studied organotrifluoroborates where the fluorines attached to
the boron atom presented chemical shifts in the range of −129 to
−141 ppm (Table 2).
By using line-narrowing techniques or less viscous solvents
and/orhighertemperaturesitispossibletoimprovetheresolution.
As predicted, different coupling constants values were observed
in both 11B and 19F spectra of potassium ethynyltrifluoroborate at
25 ◦C when the solvent was changed (Table 1). In the expectation
that the relation between the variation of magnitude of J
with temperature, we also obtained the spectra of potassium
ethynyltrifluoroborate at 25 ◦C, and 50 ◦C in different solvents.
The temperature dependence of the coupling constants is also
given in Table 1. The chemical shifts practically do not change with
temperature.
Good resolution was obtained for the 19F spectra of potassium
organotrifluoroborates. The 19F nucleus has a zero quadrupolar
moment, it is only 20% less sensitive than 1H, and has a high
sensitivity because of a high-magnetogyric ratio.[22] These factors
support the idea that 19F nucleus is the appropriate choice to
analyze potassium organotrifluoroborates by NMR.
It was also known that the J (19F–11B) varies by changing
the solvent.[24] In fact, the observed coupling constants for 1 in
protic solvents were significantly smaller than the ones observed
in nonprotic solvents. The coupling constants did not appear to
be dependent on the temperature on the analyzed compound
(Table 1).[25]
In spite of being salts, potassium organotrifluoroborates are
slightly soluble in water, with some exceptions. Generally these
compounds show high solubility in polar solvents such as
methanol, acetonitrile, acetone, dimethylfumarate (DMF), and
dimethyl sulphoxide (DMSO). It is also known from literature
that electron-donating groups enhance the rate of hydrolysis of
these compounds into the corresponding boronic acids.[26] These
c
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Magn. Reson. Chem. 2009, 47, 873–878

Spectral Assignments and Reference Data
The solid was then washed with acetone and with hot acetone.
The resulting organic solution was filtered, and the solvent was
removed to yield a white solid, which was dissolved in hot acetone
and precipitated with diethyl ether to yield 2.20 g (80%) of the title
compound as a white solid.
Table 1. Effect of solvent and temperature on the 11B and 19F
chemical shifts and coupling constants for 1
Temp.
(◦C)
δ
11B
δ
19F
J1(11B–19F)
Compound
Solvent
D2O
(ppm) (ppm)
(Hz)
25
2.62 −144.2
15.1
BF3K
Potassium alkynyltrifluoroborates (3 and 4)
1
D2O
50
25
50
25
50
25
50
25
50
2.86 −143.8
2.96 −135.8
2.97 −136.0
4.00 −155.7
4.03 −155.7
2.89 −135.7
2.92 −135.8
2.20 −132.8
2.23 −132.9
14.6
32.8
36.2
11.6
11.5
35.9
35.9
36.6
36.1
To a solution of the appropriate alkyne (10 mmol, 1 equiv) in
THF (20 ml) at −78 ◦C under argon dropwise n-BuLi (6.25 ml, 1.6
M in hexane, 10 mmol, 1 equiv) was added. The solution was
stirred for 1 h at this temperature, then trimethyl borate (1.56 g,
15 mmol, 1.5 equiv) was added dropwise. The solution was stirred
at −78 ◦C for 1.5 h and allowed to warm to −20 ◦C. A saturated
aqueous solution of KHF2 (4.7 g, 60 mmol, 6.0 equiv) was added to
the vigorously stirred solution. The resulting mixture was stirred
for 1 h at −20 ◦C and at room temperature for 1 h. The solvent
was removed in vacuo, and the resulting white solid was dried
under high vacuum for 2 h. The solid was then washed with
acetone and with hot acetone. The resulting organic solution
was filtered, and the solvent was removed to yield a white solid,
which was dissolved in hot acetone and precipitated with diethyl
ether. Potassium phenylethynyltrifluoroborate (3) 1.41 g (68%);
potassium hex-1-ynyltrifluoroborate (4) 1.39 g (74%).
Acetone-d6
Acetone-d6
CD3OD
CD3OD
CD3CN
CD3CN
DMSO-d6
DMSO-d6
factors together with the small changes in the coupling constants
and chemical shifts (Table 1), make DMSO-d6 the appropriate
choice for the analysis of potassium organotrifluoroborates.
Experimental
General procedure for preparation of potassium organotriflu-
oroborates (5–26)
Standard bench top techniques were employed for handling
air-sensitive reagents. tetrahydrofuran (THF) was distilled from
Na/benzophenone ketyl. Methanol was distilled from magnesium
methoxide. Distilled H2O was degassed by sparging with Ar(g)
for >30 min. All other solvents were high-performance liquid
chromatographic(HPLC)gradeandusedasreceived. Boronicacids
5 and 6 were purchased from Aldrich Chemical Company. Boronic
acids 7–26 were purchased from Frontier Chemicals and used as
received. Deuterated solvents were purchased from Cambridge
Isotope Laboratories, Inc. (CIL).
To the boronic acid (5 mmol) in MeOH (10 ml) a solution of KHF2
was added dropwise (1.56 g, 20 mmol) in H2O (8 ml) using an
addition funnel. The mixture was stirred for 30 min and concen-
trated under high vacuum. The residual solids were extracted with
four portions of 20% MeOH in acetone. The combined extracts
were concentrated close to the saturation point and Et2O was
added until no more precipitation was observed. The solids were
collected, washed with two portions of Et2O, and dried under high
vacuum to give the corresponding products. Potassium phenyltri-
fluoroborate (5) 0.73 g, 80%; potassium perfluorotrifluoroborate
(6) 0.82 g (60%); potassium 4-methoxyphenyltrifluoroborate (7)
0.92 g (82%); potassium 4-(trifluoromethyl)phenyltrifluoroborate
(8) 1.00 g (80%); potassium 4-formyl-phenyltrifluoroborate (9)
0.97 g (92%); potassium 3-formyl-phenyltrifluoroborate (10)
0.95 g (90%); potassium 2-formyl-phenyltrifluoroborate (11)
0.90 g (85%); potassium o-tolyl-trifluoroborate (12) 0.84 g (85%);
potassium 2,6-dimethyltrifluoroborate (13) 0.84 g (80%); potas-
sium 4-fluoro-phenyltrifluoroborate (14) 0.80 g (80%); potas-
sium 3-nitro-phenyltrifluoroborate (15) 0.93 g (82%); potassium
2,6-difluorophenyltrifluoroborate (16) 0.93 g (85%); potassium
phenylethyltrifluoroborate (17) 0.85 g (81%); potassium 5-formyl-
2-methoxyphenyltrifluoroborate (18) 1.08 g (90%); potassium
3,5-bis(trifluoromethyl)phenyltrifluoroborate (19) 1.36 g (85%);
potassium p-tolyl-trifluoroborate (20) 0.79 g (80%); potassium
5-formylthiophen-2-yl-trifluoroborate (21) 0.89 g (82%); potas-
sium 5-formylthiophen-3-yl-trifluoroborate (22) 0.87 g (80%);
potassium pyridin-3-yltrifluoroborate (23) 0.76 g (83%); potas-
sium 2-thienyltrifluoroborate (24) 0.77 g (82%); potassium 3-
thienyltrifluoroborate (25) 0.80 g (85%); potassium cyclopropyl
trifloroborate (26) 0.59 g (80%);
Potassium ethynyltrifluoroborate (1)
To a solution of ethynylmagnesium bromide in THF (10.0 mmol,
20 ml of a 0.5 M THF solution) trimethyl borate was added (1.59 g,
15.3 mmol) at −78 ◦C. The solution was stirred for 1 h at this
temperature, and then warmed up to −20 ◦C and stirred for an
additional hour. To the resultant white suspension a solution
of KHF2 was added (4.71 g, 60.3 mmol) in water (15 ml) and
the solution was stirred at this temperature for 1 h and at
room temperature for 1 h. The obtained reaction mixture was
concentrated in vacuo and the residue was dissolved in hot
acetone. The residue was removed by filtration and the filtrate
was concentrated to yield 1.05 g (80%) of the title compound as a
white solid (mp 210–212 ◦C decomp.).
Potassium vinyltrifluoroborate (2)
To a solution of trimethyl borate (3.4 ml, 30 mmol) in THF (20 ml)
at −78 ◦C under argon was added dropwise vinyl magnesium
bromide (20 ml, 20 mmol of a 1 M solution in THF). The mixture
was stirred for 0.5 h at this temperature and at room temperature
for 0.5 h. KHF2 (9.4 g, 120 mmol) was added in one portion at 0 ◦C
followed by water (20 ml). The resulting suspension was stirred for
0.5 h at room temperature, and the solvents were removed and
the resulting white solid was dried under high vacuum for 2 h.
Potassium 4-oxopentyltrifluoroborate (27)
To a solution of potassium 4-methylpent-4-enyltrifluoroborate
[H2C C(CH3)CH2CH2CH2BF3K] (0.202 g, 1.28 mmol) in an
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Magn. Reson. Chem. 2009, 47, 873–878
Copyright ꢀ 2009 John Wiley & Sons, Ltd.
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R. A. Oliveira et al.
Table 2. 1H, 13C, 11B, and 19F chemical shifts of selected potassium organotrifluoroborates
Compound
BF3K
δ(1H) (ppm)
1.93 (s, 1H)
δ (13C) (ppm)
97.6 (br); 79.1
δ (11B (ppm)
δ (19F (ppm)
1
2
2.20 (J = 36.6 Hz) −132.8
5.84–5.69 (m, 1H); 5.22–2.13 146.2(br); 121.6
(m, 2H)
6.87 (J = 51 Hz)
−139.5
BF3K
3
4
7.28–7.25 (m, 5H)
130.9; 128.3; 126.9; 125.4;
104.3 (br); 89.5
2.92 (J = 19 Hz)
−132.0
BF3K
BF3K
1.97 (t, J = 5.1 Hz, 2H);
1.34–1.29 (m, 4H); 0.83 (t,
J = 7.2 Hz, 3H)
90.8; 56.9; 31.5; 22.0; 18.7;
14.0
2.65
−131.5
−139.3
Bu
5
6
7.43 (d, J = 6.6 Hz, 2H);
149.1(br); 131.6; 126.8; 125.8
7.94
BF3K
BF3K
7.19–7.10 (m, 3H)
–
147.9 (d, J = 247 Hz); 139.0
(d, J = 240 Hz); 136.6 (d,
J = 247 Hz); 119.1 (br)
6.01 (J = 42 Hz)
−132.8; (−135.0)–(−135.1)
(m); −160.7 (t, J = 19 Hz);
(−165.3)–(−165.7) (m)
F
F
F
F
F
7
7.73 (d, J = 7.8Hz, 2H); 7.49
(d, J = 7.8Hz, 2H); 2.51 (s,
3H)
157.9; 141.5(br); 132.8; 112.6;
55.1
7.39
7.44
7.12
7.44
−140.1
MeO
F3C
BF3K
BF3K
BF3K
8
7.58–7.50 (m, 2H); 7.43–7.35 155.9 (br); 132.0; 126.2 (qua,
(m, 2H)
−135.4; −140.2
−140.2
J = 30 Hz); 125.2 (qua,
J = 272 Hz); 122.8
9
9.90 (s, 1H); 7.66 (d,
J = 7.5Hz, 2H); 7.55 (d,
J = 7.5Hz, 2H)
193.3; 159.5(br); 133.8; 131.6;
127.7
OHC
OHC
10
9.95 (s, 1H); 7.89 (s, 1H); 7,68
195.0; 150.3 (br); 138.4;
135.1; 133.4; 127.7; 127.2
−139.9
(ddd, J3 = 7.5Hz, Hz,
J4 = 1.5, 1H); 7,61 (ddd,
J3 = 7.5 Hz, J4 = 1.5, 1H);
7,34 (dd, J3 = 7.5 Hz, 1H)
BF3K
11
10.45 (s, 1H); 7.69 (d, J = 7.5
Hz, 1H); 7.63 (d, J = 7.2 Hz,
1H); 7.40 (dd, J = 7.5 Hz,
J = 7.2 Hz, 1H); 7.24 (dd,
J = 7.2 Hz, J = 7.5 Hz, 1H)
197.1; 156.0 (br); 139.2;
132.9; 132.1; 126.0; 124.6
7.59 (J = 51 Hz)
−132.5
BF3K
CHO
12
13
7.30 (d, J = 6.0 Hz, 1H);
6.85–6.87 (m, 3H); 2.27 (s,
3H)
148.9 (br); 140.5; 131.6;
128.2; 125.1; 123.4; 21.7
7.74 (J = 52 Hz)
8.23 (J = 53 Hz)
−137.7
−129.6
BF3K
Me
6.81–6.76 (m, 1H); 6.69 (d,
J = 7.2 Hz; 2H); 2.31 (s, 6H)
141.0; 126.6; 126.0 (br);
124.7; 23.4
BF3K
Me
Me
14
15
7.40–7.36 (m, 2H); 6.93–6.87 161.7 (d, J1 = 240Hz); 145.2
7.77
7.24
−118.6; −139.1
−140.5
F
BF3K
BF3K
(m, 2H)
(br); 133.4; 113.5 (d,
J2 = 15 Hz)
8.18 (s, 1H); 7,96 (dd, J3 = 8.1 152.4 (br); 147.4; 138.7;
O2N
Hz, J4 = 2.0 Hz, 1H); 7,80
(dd, J = 7,2 Hz, J4 = 2.0
Hz, 1H); 7,43 (dd, J3 = 7.8
Hz, J3 = 7,2 Hz, 1H)
7.16–7.06 (m, 1H); 6.69 (t,
J = 9.0 Hz, 2H)
128.5; 125.7; 121.1
16
166.1 (dd, J1 = 240 Hz,
J3 = 17 Hz); 128.0; 121.3
(br); 110,3 (d, J2 = 29 Hz)
6.57 (J = 45 Hz)
−103.0; −132.5
BF3K
F
F
c
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Magn. Reson. Chem. 2009, 47, 873–878

Spectral Assignments and Reference Data
Table 2. (Continued)
Compound
δ(1H) (ppm)
δ (13C) (ppm)
δ (11B (ppm)
δ (19F (ppm)
−138.3
17
18
7.21–7.02 (m, 5H); 2.48–2.42
(m, 2H); 0.40–0.28 (m, 2H)
148.0; 127.9; 127.7; 124.5;
32.1; 22.3 (br)
5.19 (J = 18 Hz)
BF3K
9.78 (s, 1H); 7.87 (d, J4 = 2.5
Hz, 1H); 7.66 (dd, J3 = 8.7
Hz, J4 = 2.5 Hz,1H); 6.91
(d, J3 = 8.7 Hz, 1H); 3.74
(s, 3H)
192.2; 168.1; 137.8 (br);
135.1; 131.0; 128.5; 109.6;
55.1
7.23
6.94
7.88
−138.2
−61.7; −141.2
−138.8
BF3K
BF3K
OMe
OHC
F3C
19
20
7.88 (s, 2H); 7.72 (s, 1H)
131.3; 128.2(br); 126.0; 122.4;
118.8
CF3
7.22 (d, J = 7.2 Hz, 2H); 6.91
(d, J = 7.2 Hz, 2H); 2.21 (s,
3H)
146.0 (br); 133.6; 131.5;
127.2; 21.2
BF3K
Me
21
22
9.87 (s, 1H); 7.84 (s, 1H); 7.64
(s, 1H)
185.3; 153.7 (br); 144.0;
143.1; 136.9
6.41
6.60
−136.8
−136.9
S
S
OHC
BF3K
9.86 (s, 1H); 7.85 (s, 1H); 7.65
(s, 1H)
185.1; 153.6 (br); 143.9;
143.0; 136.7
OHC
N
BF3K
23
8.54 (s, 1H); 8.29 (d, J = 4.8
Hz, 1H); 7.67 (d, J = 9.0 Hz,
1H); 7.12 (dd, J3 = 9.0,
J3 = 4.8, 1H)
152.6; 147.0; 142.2 (br);
139.6; 123.2.
7.66
−139.4
BF3K
24
25
7.23 (dd, J3 = 3.9, J3 = 3.8,
1H); 6.93 (dd, J3 = 3.8,
J4 = 1.2, 1H); 6.87 (br)
150.6 (br); 127.5; 126.9; 124.4
151.3 (br); 132.0; 124.7; 123.0
6.87 (J = 46 Hz)
−134.1
−135.8
S
BF3K
7.22 (d, J3 = 3.0 Hz, 1H); 7.10
(s, 1H); 7.06 (d, J3 = 3.0
Hz, 1H)
7.20
BF3K
S
26
27
(−0.02)–(−0.151) (m, 4H);
(−0.71)–(−0.84) (m, 1H)
2.28 (t, J = 7.5 Hz, 2H); 2.03
(s, 3H); 1.37 (qui, J = 7.5
Hz, 2H); 1.07 (qui, J = 7.5
Hz, 2H); −0.06 (m, 2H)
1.2; −0,4(br)
8.77
9.36
−141.2
−137.2
BF3K
210.8; 43.9; 30.0; 27.7; 25.5
O
BF3K
( )2
∗
28
1.80 (s, 2H).
6.85 (J = 50 Hz)
−140.7
I
BF3K
∗ No peak was observed for this compound.
acetone/H2O mixture (30% H2O in acetone, 14 ml) at −70 ◦C
was applied a flow of ozone for 14 min. The solution was then de-
gassed with N2 for 15 min followed by the addition of H2O (2 ml).
This was allowed to warm to r.t. while stirring. Following solvent
removal, the resulting white solid was purified by dissolving in hot
acetone and precipitating with Et2O, affording 27 (0.14 g, 70%) as
a white solid.
one portion. After stirring at 25 ◦C for 2 h, the suspension was
filtered through a Celite pad and then the solvent was evaporated
under reduced pressure to give the crude product, which was
purified by dissolving in a minimal amount of dry acetone and
precipitatingwithEt2Otoyielda2.38 g(96%)ofthetitlecompound
as a white solid.
NMR measurements
Potassium iodomethyltrifluoroborate (28)
1H (300 MHz), 13C (75 MHz), 11B (96 MHz), and 19F (282 MHz) NMR
spectra were obtained on a Varian UNITY PLUS 300 spectrometer.
Spectra were recorded in dimethylsulfoxide (DMSO-d6), using
To a solution of potassium bromomethyltrifluoroborate (2.0 g,
10 mmol) in acetone (150 ml) NaI was added (1.5 g, 10 mmol) in
c
Magn. Reson. Chem. 2009, 47, 873–878
Copyright ꢀ 2009 John Wiley & Sons, Ltd.
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R. A. Oliveira et al.
1
DMSO residual peak as the H internal reference (2.5 ppm); and
Organic Syntheses via Boranes, vol. 2, Aldrich Chemical: Milwaukee,
WI, 2001; (c) A. Suzuki, H. C. Brown, Organic Syntheses via Boranes,
vol. 3, Aldrich Chemical: Milwaukee, WI, 2003.
the central peak of DMSO-d6 at 39.5 ppm for 13C NMR. 11B NMR
spectra were calibrated using BF3· Et2O (0.0 ppm) as external
reference. All 19F NMR chemical shifts were referenced to external
CF3CO2H (0.0 ppm).
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Conclusion
Inthisstudy,complete1H,13C,19F,and11BNMRspectraldatafor28
potassium organotrifluoroborates were described. The resonance
for the carbon bearing the boron atom is described for the first
time for most of the studied compounds. In addition, a modified
11B NMR pulse sequence was used and better resolution was
observed, allowing the observation of 11B–19F coupling constants
for some compounds.
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www.interscience.wiley.com/journal/mrc
Copyright ꢀ 2009 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2009, 47, 873–878