Synthesis of tetramethylammonium phenyltrialkylborate salts by the addition of alkyllithium reagents to a triorganylborane or organoboranylhalides

Article abstract of DOI:10.1016/j.jorganchem.2010.11.019

Several new tetraorganylborate salts have been synthesized by the addition of alkyl or phenyllithium reagents to a triorganylborane or organoboranylhalides. The chemical structure of the borates was confirmed by ¹H, ¹³C NMR and IR spectroscopic measurements and elemental analysis. Solubility, spectroscopic and electrochemical properties of these salts have been investigated as well. The structures of the phenyltrialkylborates were varied systematically to control their oxidation potential. These compounds are the trimethyl-, triethyl-, n-tributyl- and sec-tributylborate derivatives and form a series of substituted phenyltrialkylborates containing either electron-withdrawing or electron-donating substituents in the para position of phenyl ring. The oxidation potential of these borates has been found to be a function of Hammett constant.

Full text of DOI:10.1016/j.jorganchem.2010.11.019

Journal of Organometallic Chemistry 696 (2011) 2135e2141
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis of tetramethylammonium phenyltrialkylborate salts by the addition
of alkyllithium reagents to a triorganylborane or organoboranylhalidesq
*
Marek Pietrzak , Beata Je˛drzejewska
Faculty of Chemical Technology and Engineering, University of Technology and Life Sciences, Seminaryjna 3, 85-326 Bydgoszcz, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Several new tetraorganylborate salts have been synthesized by the addition of alkyl or phenyllithium
reagents to a triorganylborane or organoboranylhalides. The chemical structure of the borates was
confirmed by 1H, 13C NMR and IR spectroscopic measurements and elemental analysis. Solubility,
spectroscopic and electrochemical properties of these salts have been investigated as well. The structures
of the phenyltrialkylborates were varied systematically to control their oxidation potential. These
compounds are the trimethyl-, triethyl-, n-tributyl- and sec-tributylborate derivatives and form a series
of substituted phenyltrialkylborates containing either electron-withdrawing or electron-donating
substituents in the para position of phenyl ring. The oxidation potential of these borates has been found
to be a function of Hammett constant.
Received 8 October 2010
Received in revised form
5 November 2010
Accepted 14 November 2010
Keywords:
Borate salts
Synthesis
Spectroscopic and electrochemical
properties
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
co-workers [25]. Photoinitiated one-electron oxidation of alkyl-
triphenylborates [ReB(Ph)3]ꢀ starts a reaction sequence which
Interest in the chemistry of boron-containing substances has
recently been boosted [1]. Boranes such as BX3, RBX2, and R2BX,
where X is halide, are important Lewis acids used in organic
synthesis, though their high-moisture sensitivity and instability
make them difficult to handle. Recently, these compounds have
been used in various synthetic transformations such as the
hydrosilation of alcohols [2], enones [3], carbonyl compounds [4],
and imines [5,6] the stereoselective transformation of epoxides
[7,8], the allylation of secondary benzyl acetates [9], the cleavage of
aryl and alkyl ethers with hydrosilanes [10,11] and aldol reactions
[12]. Organoboranes react readily with a variety of nucleophiles to
form the corresponding tetravalent tetrahedral borate complexes
[13]. Borates are tetravalent, tetracoordinate anionic boron-con-
taining species [14]. Torssell verified the tetrahedral structure of
borates by synthesizing a chiral example and recording its optical
activity [15].
ultimately leads to the formation of free alkyl radical [16e18]. The
alkyl radical formed initiates the chain polymerization of the
acrylate monomer.
Although studies on borate salts have appeared in the literature
over the past few years, they are mostly focused on the use of
tetraphenyl or alkyltriphenylborate salts [16e24]. There are only
a few examples of synthesis and application of other tetravalent
borates [26]. This prompted the synthesis and the systematic study
of phenyltrialkylborate salts in an attempt to understand the pho-
tophysical properties and structureeproperty relationships in
these compounds. We have developed a new series of borate salts
that exhibit good spectroscopic and electrochemical properties for
application in polymer chemistry.
2. Results and discussion
Tetraalkylammonium butyltriphenylborate salts have been used
extensively as co-initiators for acrylate polymerization [16e24].
When paired with a reactive light absorber such as a cyanine dye,
butyltriphenylborates undergo photoinduced single-electron
transfer reaction. The first systematic investigation of the photo-
chemistry of organic borate salts was carried out by Williams and
2.1. Synthesis
The method of borate salts synthesis using alkyllithium reagents
is similar to that published by Neckers and co-workers [26,27].
Tetramethylammonium phenyltrimethylborate (B5) and tetrame-
thylammonium phenyltriisopentylborate (B9) were prepared from
the reaction of dichlorophenylborane with methyllithium followed
by cation exchange. The other phenyltrialkylborate salts were
obtained by the addition of phenyllithium to the appropriate tri-
alkylborane. The tetramethylammonium phenyltrialkylborate salts
q
In memory to Professor Jerzy Pa˛czkowski.
* Corresponding author. Tel.: þ48 52 374 9034; fax: þ48 52 374 9009.
E-mail address: marek@utp.edu.pl (M. Pietrzak).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.11.019

2136
M. Pietrzak, B. Je˛drzejewska / Journal of Organometallic Chemistry 696 (2011) 2135e2141
Fig. 1. Electronic absorption spectra of selected borate salts in methanol.
Fig. 3. Electronic absorption spectra of selected borate salts in methanol.
were synthesized in reasonable yields of about 35e65%. The
alternative method of the borate synthesis by the addition of
Grignard reagents to the triorganylborane or organoboranylhalides
gives products in lower yields of about 10%.
important from the point of view their practical applications.
Figs. 1e3 show the illustrative electronic absorption spectra for the
tested borate salts in methanol.
All compounds were purified by recrystalization and charac-
terized on the basis of analytical results and spectral evidences. The
1H and 13C NMR analyses confirm that the borate salts have
designed structures. The details of all of the borates’ protons
chemical shifts and the coupling constants as well elemental
analysis data are presented in Experimental section. The inspection
of the data presented in Experimental section also shows that the
melting points for all compounds are rather sharp. This indicates
the high purity of the synthesized borates.
Generally, prepared borate salts are water insoluble white
solids, relatively stable to air and moisture. Only in the case of
phenyltri-sec-butylborate salts (B8), phenylisopentylborate (B9)
and phenyltriethylbotate salts possessing strong electron donor
substituent in para position of the phenyl ring (B62) one can
observe decomposition after three weeks of keeping in room
temperature (decomposition degree of about 10%).
UVevis spectroscopic measurements of tested compounds
show characteristic absorption bands at about 205 nm and 230 nm
and broad absorption bands above 250 nm. Methanol solutions of
these borates show no absorbance in the near ultraviolet region.
In order to evaluate the reactivity of synthesized borates as
photocoinitiators for photopolymerization of standard acrylic
formulations, electrochemical measurements are needed. The
oxidation potentials of the borate salts were determined from the
cyclovoltameric measurements. The typical cyclic voltammpero-
grams for examined phenyltrialkylborates in acetonitrile are pre-
sented in Figs. 4 and 5.
Analysis of the curves presented in Figs. 4 and 5 indicates that
the electrochemical oxidation of the tetramethylammonium phe-
nyltrialkylborates is irreversible. This is a result of a very short
lifetime of phenyltrialkylboranyl radical. This causes that the
oxidation potential of borates could not be precisely measured by
electrochemical techniques [17]. However, the peak potential
2.2. Spectroscopic and electrochemical properties
The characterization of the spectroscopic and electrochemical
properties of the phenyltrialkylborate salts under the study is very
Fig. 4. Cyclic voltammperograms for selected tetramethylammonium phenyltrialkyl-
borates under the study in acetonitrile. Solution contained tetra-n-butylammonium
perchlorate as the supporting electrolyte and was deoxygenated prior to analysis by
purging with argon for 15 min.
Fig. 2. Electronic absorption spectra of selected borate salts in methanol.

M. Pietrzak, B. Je˛drzejewska / Journal of Organometallic Chemistry 696 (2011) 2135e2141
2137
Fig. 6. Relationship between the Hammett constant and the oxidation potential of the
phenyltriethylborate series.
Fig. 5. Cyclic voltammperograms for selected tetramethylammonium phenyltrialkyl-
borates under the study in acetonitrile. Solution contained tetra-n-butylammonium
perchlorate as the supporting electrolyte and was deoxygenated prior to analysis by
purging with argon for 15 min.
Fig. 6. indicates that the experimental results follow linear
relationship for all Hammett constants with expect of eOC6H5
substituent. The correlation coefficient being larger than 0.96
(besides the B63 compound), indicate a good linearity. This indi-
cates that the oxidation potential of the phenyltriethylborate series
increases as the Hammett constant increases.
obtained by either cyclic or square wave voltammetry usually
follow the same trend as those measured by kinetic methods
[17,31]. Therefore, the obtained electrochemical values for borates
tested can be used for the comparison of their oxidative properties.
The measured oxidation potential of the tetramethylammonium
borate salts under the study are summarized in Table 1.
The difference in the oxidation potentials is indicative of the
relative ease of electron removal from each borate anion. The
results indicate that increasing the number of alkyl groups on
boron leads to easier oxidation of the borate, thus, the phenyltri-n-
butylborate (B7) has a less electropositive peak potential than the
n-butyltriphenylborate (B2) (see data in Table 1). The type of an
alkyl group attached to the boron atom has also a crucial role in the
ease of oxidation. The replacement of methyl ligands on boron by
butyl ones makes the borate easier to oxidize, e.g. the oxidation
potentials change from 888 mV to 708 mV for B5 and B7, respec-
tively. Generally, the tendency is that the more stable radical can be
formed, the easier it is to oxidize the borate. Secondary alkyl
radicals are more stable than primary, thus phenyltri-sec-butylbo-
rate (B8) has lower oxidation potential than phenyltri-n-butylbo-
rate (B7). It is necessary to emphasize that a less electropositive
peak potential of the borate causes it to be more reactive in the
other physicochemical processes, e.g. initiation of polymerization
reaction.
The ease of electron removal from each phenyltrialkylborate
anion can also be modified by an appropriate functional group
substitution on the phenyl ring. For example, introduction of
a cyano group to the benzene ring causes the increase of the
oxidation potential compared with non-substituted phenyl-
triethylborate (B6). Relationship between the Hammett constant
and the oxidation potential of the phenyltriethylborate series is
good example illustrating this behavior (Fig. 6).
3. Conclusion
In view of the borates potential for general use, we undertook
synthesis and evaluation of
a number of several phenyl-
trialkylborate salts and studied their spectral and electrochemical
properties. These compounds are easily prepared by straightfor-
ward synthesis, and most display good solubility in moderate
polarity solvents. The borates are crystalline white compounds and
most of them are stable and insensitive to air and moisture. Their
structures were easily modified by the introduction of different
substituent in para position in phenyl ring. This causes that the
oxidation potentials of the borates differ significantly. It can be said
that the measured oxidation potential of the borate salts varies as
a function of the substituents on the phenyl ring. Generally, the
more stable radical can be formed, the easier it is to oxidize the
borate.
The described methods of synthesis of tetramethylammno-
nium phenyltrialkylborate salts in the paper are important from
the point of practical application. The phenyltrialkylborate salts
under the study appear to be very promising candidates as elec-
tron donors for acrylic polymerization formulations instead of
alkyltriphenylborates.
4. Experimental
4.1. Measurements
Table 1
All starting reagents and solvents (reagent grade) were
purchased from Aldrich Chemical Co. and Lancaster Chemical Co.
and were used without further purification.
The measured oxidation potential of the tetramethylammonium borate salts under
the study.
No
Eox [mV]
No
Eox [mV]
No
Eox [mV]
No
Eox [mV]
Melting points (uncorrected) were determined on the Boëthius
apparatus.
The elemental analysis was made with a Vario Macro 11.45-
0000 (Elementar Analysesysteme GmbH, Germany) operating with
the software VARIOEL (version 5.14.4.22).
B5
B7
B71
888
708
618
B8
B81
B9
664
468
748
B6
B61
B62
764
706
632
B63
B64
B65
684
890
954
For tetramethylammonium n-butyltriphenylborate (B2) Eox ¼ 1244 mV.

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M. Pietrzak, B. Je˛drzejewska / Journal of Organometallic Chemistry 696 (2011) 2135e2141
4.1.1. Spectral measurements
747, 711. Elemental analysis: anal. calc. for C13H26NB (207.22 g/
mol): C, 75.4%; H, 12.6%; N, 6.8%. Found: C, 75.1%; H, 12.3%; N, 6.5%.
The 1H (200 MHz) and 13C (50 MHz) NMR spectra were recorded
with the use of a Varian spectrometer Gemini 200. Dimethylsulf-
oxide (DMSO-d6) was used as the solvent and tetramethylsilane as
the internal standard.
The UVevis absorption spectra were recorded with a Shimadzu
UVevis Multispec-1501 spectrophotometer. For the measurements
of the electronic absorption spectra the borate solutions in meth-
anol were prepared.
The IR spectra of the synthesized salts were recorded using
a
Bruker spectrophotometer Vector 22, in the range 400e
4.2.2. Tetramethylammonium phenyltriisopentylborate (B9)
This compound was prepared applying the procedure described
above using isopentyllithium (27 mmol, 24 mL, 1.13 M). Yield 57%.
Isopentyllithium was synthesized based on the method described
by Gilman and co-workers [28].
4500 cmꢀ1, by KBr pellet technique.
4.1.2. Electrochemical measurements
The oxidation potential of the borates were measured by cyclic
voltammetry using an Electroanalytical Cypress System Model CS-
1090. The typical three-electrode setup was employed for electro-
chemical measurements. The electrolyte was 0.1 M tetrabuty-
lammonium perchlorate in dry acetonitrile, which was purged with
argon prior to a measurement. Platinum 1 mm electrode was
applied as working electrode and platinum and Ag/AgCl were used
as auxiliary and reference electrodes, respectively.
M.p. 134 ꢁC. 1H NMR (DMSO-d6)
d
(ppm): 7.20 (d, J ¼ 6.2, 2H),
6.83 (t, J ¼ 7.4 Hz, 2H), 6.62 (t, J ¼ 6.8 Hz, 1H), 3.08 (s, 12H), 1.20 (m,
3H), 0.78 (m, 6H), 0.75 (d, J ¼ 6.6 Hz, 18H), 0.08 (m, 6H). 13C NMR
4.2. Synthesis
(DMSO-d6)
d
(ppm): 170.9 (q, J ¼ 45.5 Hz, C PheB), 132.6 (CH), 124.8
(CH), 119.8 (CH), 54.4 (t, J ¼ 4.1 Hz, Nþ(CH3)4), 37.3 (CH2), 31.8 (CH),
24.3 (q, J ¼ 40.5 Hz, BeCH2), 23.3 (CH3). IR (KBr): 3051, 2944, 2882,
2831, 2791, 1483, 1466, 948, 758, 715. Elemental analysis: anal. calc.
for C25H50NB (375.40 g/mol); C, 80.0%; H, 13.4%; N, 3.7%. Found: C,
79.9%; H, 13.0%; N 3.9%. The other borate salts under the study were
prepared according to the route shown in Scheme 2.
Simple synthetic procedures have been developed to prepare
suitably substituted stable phenyltrialkylborate tetramethylammo-
nium salts [26,27]. The synthetic approaches that have been applied
are outlined below and are based on the addition of alkyl or phe-
nyllithium reagents to a triorganylborane or organoboranylhalides.
A general route for the synthesis of tetramethylammonium
phenyltrimethylborate and tetramethylammonium phenyltrii-
sopentylborate is shown in Scheme 1.
4.2.3. Tetramethylammonium phenyltriethylborate (B6)
To a solution of triethylborane in hexane (15 mmol, 15 mL, 1 M)
anhydrous diethyl ether (25 mL) was added. To the vigorous stirred
solution under nitrogen phenyllithium (16.6 mmol, 17.5 mL, 0.95 M
in diethyl ether) was added dropwise at ꢀ85 ꢁC over 10 min. The
mixture was allowed to warm slowly to room temperature and
stirred for further 2 h. Solvent was removed under reduced pres-
sure, the residue was dissolved in 10 mL of water and poured into
100 mL saturated aqueous N(CH3)4Cl. White precipitate formed was
filtered, washed with water, dried and recrystallized from ethanol.
Yield 63%. Phenyllithium was synthesized with lithium and bro-
mobenzene, based on the method described in literature [29].
4.2.1. Tetramethylammonium phenyltrimethylborate (B5)
To
a stirred solution of dichlorophenylborane (1.35 g,
8.5 mmol) in 25 mL of anhydrous diethyl ether cooled to ꢀ60 ꢁC
methyllithium (17 mL, 27 mmol, 1.6 M in diethyl ether) was
added dropwise under nitrogen. Mixture was allowed to warm
slowly to room temperature and was stirred for further 2 h.
Solvent was removed under reduced pressure, the residue was
dissolved in 10 mL of water and poured into 100 mL saturated
aqueous N(CH3)4Cl. White precipitate formed was filtered,
washed with water, dried and recrystallized from ethanol.
Yield 35%.
M.p. 138e144 ꢁC. 1H NMR (DMSO-d6)
d (ppm): 7.25 (br, s, 2H),
6.85 (t, J ¼ 7.4 Hz, 2H), 6.65 (t, 7.2 Hz, 1H), 3.07 (s, 12H, Nþ(CH3)4),
ꢀ0.47 (q, J ¼ 3.8 Hz, 9H). 13C NMR (DMSO-d6)
d (ppm): 131.7 (CH),
125.1 (CH), 120.2 (CH), 54.4 (t, J ¼ 4.1 Hz, Nþ(CH3)4), 17.5 (q,
J ¼ 41.4 Hz, BeCH3). IR (KBr): 3049, 3013, 2889, 2796, 1487, 949,
Scheme 1. A general route for the synthesis of tetramethylammonium phenyltrimethylborate and tetramethylammonium phenyltriisopentylborate.

M. Pietrzak, B. Je˛drzejewska / Journal of Organometallic Chemistry 696 (2011) 2135e2141
2139
Scheme 2. A general route for the synthesis of B6, B7 and B8 borate series.
M.p. 230e236 ꢁC. 1H NMR (DMSO-d6)
d
(ppm): 7.20 (br, s, 2H),
M.p. 135e140 ꢁC. 1H NMR (DMSO-d6)
d
(ppm): 7.03 (d, J ¼ 7.4 Hz,
6.85 (t, J ¼ 7.4 Hz, 2H), 6.65 (t, J ¼ 7 Hz, 1H), 3.08 (s, 12H, Nþ(CH3)4),
2H), 6.47 (d, J ¼ 8 Hz, 2H), 3.59 (s, 3H), 3.08 (s, 12H), 0.45 (m, 9H).
0.49 (m, 9H), 0.09 (m, 6H). 13C NMR (DMSO-d6)
d
(ppm): 169.8 (q,
13C NMR (DMSO-d6)
d (ppm): 154.3 (C), 133.6 (CH), 111.0 (CH), 55.3
J ¼ 46 Hz, C PheB), 132.7 (CH), 124.9 (CH), 120.1 (CH), 54.4 (t,
J ¼ 4.1 Hz, Nþ(CH3)4), 16.9 (q, J ¼ 41.4 Hz, BeCH2), 11.8 (CH3). IR
(KBr): 3049, 3028, 2934, 2890, 2843, 1480, 948, 801. Elemental
analysis: anal. calc. for C16H32NB (249.26 g/mol); C, 77.1%; H, 12.9%;
N, 5.6%. Found: C, 77.3%; H, 12.7%; N, 5.8%.
(OeCH3), 54.4 (t, J ¼ 4.1 Hz, Nþ(CH3)4), 16.7 (q, J ¼ 42.4 Hz, BeCH2),
11.8 (CH3). IR (KBr): 3030, 3008, 2935, 2894, 2847, 1585, 1485, 1228
(AreO), 1029 (OeCH3), 949, 811. Elemental analysis: anal. calc. for
C17H34NOB (279.27 g/mol); C, 73.1%; H, 12.3%; N, 5.0%. Found: C,
72.8%; H, 12.0%; N 4.6%.
4.2.4. Tetramethylammonium p-methylphenyltriethylborate (B61)
This compound was prepared applying the procedure described
above using p-methylphenyllithium (16.6 mmol, 18.3 mL, 0.91 M).
Yield 67%. p-Methylphenyllithiumwas synthesized with lithium and
p-bromotoluene, based on the method described in literature [29].
4.2.6. Tetramethylammonium p-phenoxyphenyltriethylborate (B63)
This compound was prepared based on the procedure described
above using p-phenoxyphenyllithium (16.2 mmol, 35 mL, 0.46 M).
Yield 52%. p-Phenoxyphenyllithium was synthesized with
n-butyllithium and p-bromodiphenyl ether. The stirred solution of
4.93 g (19.8 mmol) p-bromodiphenyl ether in 30 mL of anhydrous
diethyl ether was cooled in an ice-bath under nitrogen. To this
solution n-butyllithium (17.5 mmol, 7 mL, 2.5 M solution in hexane)
was added dropwise. The reaction mixture was stirred at 0 ꢁC for
10 min and 20 min in room temperature.
M.p. 120e124 ꢁC. 1H NMR (DMSO-d6)
2H), 6.70 (d, J ¼ 7.4 Hz, 2H), 3.07 (s, 12H), 2.14 (s, 3H), 0.52 (m, 9H),
d
(ppm): 7.11 (d, J ¼ 6 Hz,
0.08 (m, 6H). 13C NMR (DMSO-d6)
d (ppm): 132.6 (CH), 127.6 (C),
125.8 (CH), 54.4 (t, J ¼ 4.1 Hz, Nþ(CH3)4), 20.9 (ArCH3), 17.0
(q, J ¼ 41.2 Hz, BeCH2), 11.8 (CH3). IR (KBr): 3020, 2998, 2934, 2893,
2847, 1482, 949, 802. Elemental analysis: anal. calc. for C17H34NB
(263.28 g/mol); C, 77.6%; H, 13.0%; N, 5.3%. Found: C, 77.1%; H,
12.5%; N, 5.3%.
M.p.128e130 ꢁC. 1H NMR (DMSO-d6)
6.95 (t, J ¼ 7.2 Hz, 1H), 6.84 (d, J ¼ 7.6 Hz, 2H), 6.60 (d, J ¼ 8.4 Hz, 2H),
3.08 (s,12H), 0.54 (m, 9H), 0.11 (m, 6H). 13C NMR (DMSO-d6)
(ppm):
d (ppm): 7.31e7.20 (m, 4H),
d
158.9 (C),149.8 (C),133.5 (CH),129.4 (CH),121.2 (CH),116.8 (CH),116.6
(CH), 54.4 (t, J ¼ 4.1 Hz, Nþ(CH3)4), 17.0 (q, J ¼ 42.4 Hz, BeCH2), 11.8
(CH3). IR (KBr):3019, 2931, 2890, 2843, 2794,1589,1487,1230 (AreO),
948, 867. Elemental analysis: anal. calc. for C22H36NOB (341.29 g/
mol); C, 77.4%; H, 10.6%; N, 4.1%. Found: C, 77.1%; H, 10.3%; N, 4.3%.
4.2.5. Tetramethylammonium p-methoxyphenyltriethylborate (B62)
This compound was prepared adopting the procedure described
above using p-methoxyphenyllithium (16.5 mmol, 29 mL, 0.57 M).
Yield 34%. p-Methoxyphenyllithium was synthesized using
n-butyllithium and p-bromoanisole. The solution of 3.70 g (19.8
mmol) p-bromoanisole in 25 mL of anhydrous diethyl ether was
cooled in an ice-bath under nitrogen with stirring. To this solution
n-butyllithium (17.5 mmol, 7 mL, 2.5 M solution in hexane) was
added dropwise. The reaction mixture was stirred at 0 ꢁC for 10 min
and 20 min in room temperature.
4.2.7. Tetramethylammonium p-chlorophenyltriethylborate (B64)
This compound was prepared according to the procedure
described above using p-chlorophenyllithium (15.3 mmol, 30 mL,
0.51 M). Yield 41%. p-Chlorophenyllithium was synthesized with
n-butyllithium and p-bromochlorobenzene, based on the method
described in literature [30]. The solution of 3.80 g (19.8 mmol)
p-bromochlorobenzene in 25 mL of anhydrous diethyl ether was
cooled in an ice-bath under nitrogen with stirring. To this solution
n-butyllithium (17.5 mmol, 7 mL, 2.5 M solution in hexane) was
added dropwise. The reaction mixture was stirred at 0 ꢁC for 10 min
and 20 min in room temperature.

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4.2.10. Tetramethylammonium p-methylphenyltri-n-butylborate
(B71)
Prepared as compound B61, using tri-n-butylborane in diethyl
ether (15 mL, 1 M). Yield 56%.
M.p. 80e82 ꢁC. 1H NMR (DMSO-d6)
2H), 6.88 (d, J ¼ 8.4 Hz, 2H), 3.08 (s, 12H), 0.52 (m, 9H), 0.09 (m, 6H).
d
(ppm): 7.21 (d, J ¼ 7.4 Hz,
13C NMR (DMSO-d6)
d (ppm): 134.3 (CH), 124.6 (CH), 54.4
(t, J ¼ 4.1 Hz, Nþ(CH3)4), 16.8 (q, J ¼ 41.4 Hz, BeCH2), 11.7 (CH3). IR
(KBr): 3025, 2933, 2890, 2842, 2789, 1481, 947, 807. Elemental
analysis: anal. calc. for C16H31NClB (283.22 g/mol); C, 67.7%; H,
11.0%; N 4.9%. Found: C, 67.3%; H, 10.5%; N 5.0%.
M.p. 100e103 ꢁC. 1H NMR (DMSO-d6)
d (ppm): 7.09
(d, J ¼ 7.4 Hz, 2H), 6.66 (d, J ¼ 7.4 Hz, 2H), 3.08 (s, 12H, Nþ(CH3)4),
2.12 (s, 3H, (Ph-CH3)), 1.09 (m, 6H), 0.88 (m, 6H), 0.75 (t, J ¼ 7 Hz,
9H), 0.09 (m, 6H). 13C NMR (DMSO-d6)
d (ppm): 167.0 (q,
4.2.8. Tetramethylammonium p-cyanophenyltriethylborate (B65)
To a solution of p-bromobenzonitrile 3.46 g (19 mmol) in 30 mL
J ¼ 44.9 Hz, C PheB), 133.2 (CH), 125.8 (CH), 54.3 (t, J ¼ 4.1 Hz,
Nþ(CH3)4), 30.3 (CH2), 28.0 (CH2), 27.8 (q, J ¼ 40.7 Hz, BeCH2), 20.9
(ArCH3), 14.8 (CH3). IR (KBr): 3020, 2951, 2898, 2866, 2843, 2784,
1483, 949, 810. Elemental analysis: anal. calc. for C23H46NB
(347.37 g/mol); C, 79.5%; H, 13.3%; N, 4.0%. Found: C, 79.4%; H,
12.9%; N, 4.0%.
of anhydrous THF-hexane (4:1)
a solution of n-butyllithium
(17 mmol, 6.8 mL, 2.5 M solution in hexane) at ꢀ100 ꢁC under
nitrogen was added. The mixture was stirred for 20 min then the
temperature raised to ꢀ85 ꢁC, and a solution of triethylborane in
hexane (15 mL, 1 M) was added dropwise. Mixture was allowed to
rise slowly to ambient temperature and stirred for 2 h. Solvent was
removed in reduced pressure, the residue was dissolved in 10 mL of
water and poured into 100 mL saturated aqueous N(CH3)4Cl. White
precipitate formed was filtered, washed with water, dried and
recrystallized from ethanol. Yield 48%.
4.2.11. Tetramethylammonium phenyltri-sec-butylborate (B8)
Prepared as compound B6, using tri-sec-butylborane in THF
(15 mL, 1 M). Yield 55%.
M.p. 175e177 ꢁC. 1H NMR (DMSO-d6)
d (ppm): 7.22 (d,
J ¼ 7.4 Hz, 2H), 6.85 (t, J ¼ 7.4 Hz, 2H), 6.64 (t, J ¼ 6.8 Hz, 1H), 3.08
M.p. 94e96 ꢁC. 1H NMR (DMSO-d6)
2H), 7.24 (d, J ¼ 9 Hz, 2H), 3.08 (s, 12H), 0.50 (m, 9H), 0.13 (m, 6H).
d
(ppm): 7.40 (d, J ¼ 7.6 Hz,
(s, 12H, Nþ(CH3)4), 1.47 (m, 3H), 0.76 (t, J ¼ 6.6 Hz, 9H), 0.68e0.61
(m, 15H). 13C NMR (DMSO-d6)
d
(ppm): 165.8 (q, J ¼ 45 Hz, C
13C NMR (DMSO-d6)
d (ppm): 133.3 (CH), 128.0 (CH), 121.3 (C),
PheB), 134.1 (CH), 124.3 (CH), 119.7 (CH), 54.4 (t, J ¼ 4.1 Hz,
Nþ(CH3)4), 28.3 (CH2), 18.4 (CH3), 16.1 (CH3). IR (KBr): 3050, 2947,
2846, 1482, 948, 729, 713. Elemental analysis: anal. calc. for
C22H44NB (333.36 g/mol); C, 79.3%; H, 13.3%; N, 4.2%. Found: C,
79.0%; H, 13.0%; N, 4.1%.
54.4 (t, J ¼ 4.1 Hz, Nþ(CH3)4), 15.2 (q, J ¼ 40.1 Hz, BeCH2), 11.6
(CH3). IR (KBr): 3028, 2934, 2889, 2844, 2800, 2210 (CN), 1579,
1481, 945, 813. Elemental analysis: anal. calc. for C17H31N2B
(274.26 g/mol); C, 74.5%; H, 11.4%; N, 10.2%. Found: C, 74.2%; H,
11.4%; N, 10.0%.
4.2.12. Tetramethylammonium p-methylphenyltri-sec-butylborate
(B81)
Prepared as compound B61, using tri-sec-butylborane in THF
(15 mL, 1 M). Yield 58%.
4.2.9. Tetramethylammonium phenyltri-n-butylborate (B7)
Prepared as compound B6, using tri-n-butylborane in diethyl
ether (15 mL, 1 M). Yield 61%.
M.p. 144e145 ꢁC. 1H NMR (DMSO-d6)
d
(ppm): 7.20 (d, J ¼ 7 Hz,
M.p. 180e185 ꢁC. 1H NMR (DMSO-d6)
d
(ppm): 7.10 (d, J ¼ 7 Hz,
2H), 6.83 (t, J ¼ 7.4 Hz, 2H), 6.62 (t, J ¼ 7 Hz, 1H), 3.08 (s, 12H,
Nþ(CH3)4), 1.09 (m, 6H), 0.96 (m, 6H), 0.74 (t, J ¼ 7 Hz, 9H), 0.11 (m,
2H), 6.67 (d, J ¼ 7 Hz, 2H), 3.09 (s, 12H, Nþ(CH3)4), 2.12 (s, 3H,
6H). 13C NMR (DMSO-d6)
d (ppm): 132.5 (CH), 124.8 (CH), 119.8
(CH3)), 1.45 (m, 3H), 0.74 (t, J ¼ 7 Hz, 9H), 0.67e0.62 (m, 15H). 13
C
(CH), 54.4 (t, J ¼ 4.1 Hz, Nþ(CH3)4), 30.2 (CH2), 28.0 (CH2), 27.7 (q,
J ¼ 40.7 Hz, BeCH2), 14.7 (CH3). IR (KBr): 3049, 2950, 2900, 2866,
2836, 2785, 1576, 1481, 948, 715. Elemental analysis: anal. calc. for
C22H44NB (333.36 g/mol); C, 79.3%; H, 13.3%; N, 4.2%. Found: C,
78.9%; H, 13.0%; N, 4.3%.
NMR (DMSO-d6)
d
(ppm): 134.1 (CH), 125.3 (CH), 54.4 (t, J ¼ 4.1 Hz,
Nþ(CH3)4), 28.1 (CH2), 20.8 (ArCH3), 17.8 (CH3), 15.9 (CH3). IR (KBr):
3048, 2941, 2849, 2818, 1481, 948, 813. Elemental analysis: anal.
calc. for C23H46NB (347.37 g/mol); C, 79.5%; H, 13.3%; N, 4.0%.
Found: C, 79.3%; H, 13.0%; N, 4.3%.

M. Pietrzak, B. Je˛drzejewska / Journal of Organometallic Chemistry 696 (2011) 2135e2141
2141
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Acknowledgment
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This work was supported by The Ministry of Science and Higher
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