Comparative structural and thermodynamic studies of fluoride and cyanide binding by PhBMes2 and related triarylborane Lewis acids

Article abstract of DOI:10.1039/c0nj00120a

Lewis acidic boranes containing the -BMes₂ unit (Mes = 2,4,6-Me₃C₆H₂) have been widely exploited in molecular sensors for the fluoride ion reflecting, at least in part, the stability to air and moisture of derivatives of the type ArBMes₂. In the current study, the fluoride binding capabilities of the simplest such system, PhBMes₂ (1), have been investigated by spectroscopic and crystallographic methods, with a view to experimentally determining the fundamental thermodynamic and structural parameters associated with this host/guest interaction. A binding constant, K_F, of 8.9(1.9) × 10⁴ M^-1 in dichloromethane solution and a B-F bond length of 1.481(2) for the salt [ⁿBu₄N]⁺[PhMes ₂BF]^- have thus been elucidated and provide a baseline for the analysis of more complex systems. Competitive binding of the cyanide ion is implied by a similar binding constant, K_CN, of 1.9(0.5) × 10⁵ M^-1; structurally, similar degrees of pyramidalization of the BC₃ framework are observed on coordination of each anion {Σ(C-B-C) = 339.8, 340.1°for [ⁿBu₄N] ⁺[PhMes₂BF]^- and [K(18-crown-6)] ⁺[PhMes₂BCN]^-, respectively}. Linking of two ArBMes₂ units via an alkyne spacer results in a 2,2′- bis(dimesitylboryl)tolan system, which is characterized by independent binding of two equivalents of the CN^- anion, rather than cyanide chelation.

Full text of DOI:10.1039/c0nj00120a

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PAPER
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Comparative structural and thermodynamic studies of fluoride and
cyanide binding by PhBMes2 and related triarylborane Lewis acidswz
Christopher Bresner,ab Cally J. E. Haynes,a David A. Addy,a
Alexander E. J. Broomsgrove,a Philip Fitzpatrick,a Dragoslav Vidovic,a
Amber L. Thompson,a Ian A. Fallisb and Simon Aldridge*a
Received (in Gainesville, FL, USA) 15th February 2010, Accepted 2nd April 2010
DOI: 10.1039/c0nj00120a
Lewis acidic boranes containing the –BMes2 unit (Mes = 2,4,6-Me3C6H2) have been widely
exploited in molecular sensors for the fluoride ion reflecting, at least in part, the stability to air
and moisture of derivatives of the type ArBMes2. In the current study, the fluoride binding
capabilities of the simplest such system, PhBMes2 (1), have been investigated by spectroscopic and
crystallographic methods, with a view to experimentally determining the fundamental
thermodynamic and structural parameters associated with this host/guest interaction. A binding
constant, KF, of 8.9(1.9) ꢀ 104 Mꢁ1 in dichloromethane solution and a B–F bond length of
1.481(2) A for the salt [nBu4N]+[PhMes2BF]ꢁ have thus been elucidated and provide a baseline
for the analysis of more complex systems. Competitive binding of the cyanide ion is implied by a
similar binding constant, KCN, of 1.9(0.5) ꢀ 105 Mꢁ1; structurally, similar degrees of
pyramidalization of the BC3 framework are observed on coordination of each anion
{S(C–B–C) = 339.8, 340.11 for [nBu4N]+[PhMes2BF]ꢁ and [K(18-crown-6)]+[PhMes2BCN]ꢁ,
respectively}. Linking of two ArBMes2 units via an alkyne spacer results in a
2,20-bis(dimesitylboryl)tolan system, which is characterized by independent binding of two
equivalents of the CNꢁ anion, rather than cyanide chelation.
Given that boranes of the type ArBMes2 are typically air-
Introduction
and moisture-stable and that under appropriate conditions a
number are known to bind fluoride and/or cyanide,7 these
The selective detection of CNꢁ and Fꢁ (and of their conjugate
acids HCN and HF) constitute significant chemical challenges
compounds are potential components of sensor systems
which have attracted attention not only from a fundamental
designed to generate a macroscopic reporter response on
supramolecular perspective, but also with a view to potential
exposure to these anions. Central to such applications is an
applications in healthcare and environmental monitoring.1,2
in-depth understanding of the anion recognition event; never-
Thus, for example, the necessity to monitor fluoride concen-
theless comparative experimental data relating to the inter-
action of Fꢁ/CNꢁ with simple triarylboranes are surprisingly
trations in domestic water supplies has led to considerable
scarce.7c With this in mind, we have sought to address
research effort being expended on the development of sensors
for fluoride, encompassing a range of host/guest strategies to
bind the target analyte.3–6 Cyanide detection, on the other
geometric consequences of Fꢁ/CNꢁ binding at ArBMes2
fundamental questions relating to the thermodynamic and
hand, has received less attention,7–11 although the affinity of
systems, utilizing the simplest possible archetype (i.e.
CNꢁ for three-coordinate boranes (even in the presence of
PhBMes2) for these studies. Of particular interest at the outset
water) has been known for almost 50 years.12 More recently, a
was a comparison of the relative binding strengths of Fꢁ vs.
CNꢁ, given their potential for competitive binding at borane
number of cyanide receptors have been reported incorporating
an array of Lewis acidic centers,10a,b including systems
Lewis acids, and the fact that their relative basicities are
featuring the –BMes2 (Mes = 2,4,6-Me3C6H2) function,7
known to be very strongly solvent dependent [HF: pKa 3 (in
H2O), 15 (in DMSO); HCN: pKa 9 (in H2O), 13 (in DMSO)].13
and in certain cases offering remarkably selective binding in
aqueous media.7c,g
Experimental
a Inorganic Chemistry Laboratory, University of Oxford,
South Parks Road, Oxford, UK OX1 3QR.
(a) General
E-mail: simon.aldridge@chem.ox.ac.uk; Fax: +44 (0)1865 272690;
Tel: +44 (0)1865 285201
Manipulations of air-sensitive reagents were carried out under
b Cardiff School of Chemistry, Main Building, Park Place, Cardiff,
UK CF10 3AT
a nitrogen or argon atmosphere using standard Schlenk line or
dry box techniques. Non-deuterated solvents were dried using
a commercially available Braun Solvent Purification System;
[D]chloroform (Goss) was degassed and dried over molecular
sieves prior to use. The tetra-n-butylammonium salts of fluoride
and cyanide were dried to constant weight in vacuo, analysed
w This article is part of a themed issue on Main Group chemistry.
z CCDC 765939 ([nBu4N]+[1ꢂF]ꢁ), 765940 ([K(18-crown-6)]+
[1ꢂCN]ꢁ) and 765941 ([K(18-crown-6)]+2[2ꢂ(CN)2]2ꢁ). For crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/
c0nj00120a
ꢃc
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for composition (i.e. for state of hydration),14a and stored
under an atmosphere of dry argon until use. The known
compounds phenyldimesitylborane and 2,20-dibromotolan
were prepared by literature protocols.14b,c All other reagents
were used as received from commercial sources.
0.47 g, 50%. 1H NMR ([D]chloroform, 20 1C), d 1.98 [s, 12H,
o-CH3 of Mes], 2.19 [s, 6H, o-CH3 of Mes], 3.54 [s, 24H, CH2
of 18-crown-6], 6.61 [s, 4H, aromatic CH of Mes], 6.95–7.04
[m, 2H, o-CH of Ph], 7.08–7.15 [m, 2H, m-CH of Ph],
8.07–8.14 [m, 1H, p-CH of Ph]. 13C NMR ([D]chloroform,
20 1C), d 20.8 [p-CH3 of Mes], 25.3 [o-CH3 of Mes], 69.9
[18-crown-6], 123.1, 125.6, 128.5, 131.9, 135.8, 142.2 [aromatic
CH of Ph and Mes], boron-bound aromatic quaternary
carbons not observed. 11B NMR ([D]chloroform, 20 1C),
d ꢁ13. IR (KBr disk, cmꢁ1), 2165 (nCN). MS(ESꢁ): 352
(100%) [1ꢂCN]ꢁ; exact mass (calc. for 10B isotopomer) m/z
351.2278, (meas.) 351.2270. Elemental microanalysis: calc. C
67.74, H 7.84, N 2.14%; meas. C 67.81, H 7.75, N 2.13%.
Crystal data: [K(18-crown-6)]+[1ꢂCN]ꢁ, C37H51BKNO6,
orthorhombic, Pbca, a = 18.0486(2), b = 15.7241(1),
c = 25.8240(2) A, V = 7328.80(11) A3, Z = 8, Dx = 1.189
Mg mꢁ3, Mr = 655.72, T = 150(2) K. 131 038 reflections
collected, 8134 independent [Rint = 0.099], 5181 observed
[I > 2s(I)]. R1 = 0.0459, wR2 = 0.0468 for observed unique
reflections [I > 2s(I)]; R1 = 0.0884, wR2 = 0.0880 for all
unique reflections. Goodness of fit = 1.095. Max. and min.
residual electron densities: 0.23 and ꢁ0.24 e Aꢁ3. CCDC
765940.
NMR spectra were measured on a Varian Mercury VX-300
or Bruker AVII 500 FT-NMR spectrometer. Residual signals
of solvent were used as reference for 1H and 13C NMR spectra;
11B and 19F NMR spectra were referenced with respect
to Et2OꢂBF3 and CFCl3, respectively. The 13C signals of
boron-bound Ph, Mes or CN carbon atoms were typically
broad or not observed. Infrared spectra were measured for
each compound pressed into a disk with an excess of dried
KBr or as a solution in an appropriate solvent on a Nicolet
500 FT-IR spectrometer. Mass spectra were measured by the
EPSRC National Mass Spectrometry Service Centre, Swansea
University, or by the departmental service. Perfluorotributyl-
amine was used as a standard for high resolution measurements.
Elemental microanalyses were carried out at London
Metropolitan University. Abbreviations: s = singlet, t = triplet,
m = multiplet.
(b) Syntheses
[nBu4N]+[1ꢂF]ꢁ. To a solution of 1 (0.10 g, 0.31 mmol) in
chloroform (2 mL) was added [nBu4N]+Fꢁ (2.0 equiv.) and
the reaction mixture stirred at 20 1C for 4 h. Filtration and
layering with hexanes at 20 1C led to the formation of single
crystals of [nBu4N]+[1ꢂF]ꢁ suitable for X-ray diffraction. Yield
0.13 g, 72%. 1H NMR ([D]chloroform, 20 1C), d 1.00 [t, 12H,
CH3 of nBu4N+], 1.38–1.47 [m, 8H, CH2 of nBu4N+],
1.53–1.62 [m, 8H, CH2 of nBu4N+], 1.97 [s, 12H, o-CH3 of
Mes], 2.18 [s, 6H, o-CH3 of Mes], 3.12–3.22 [m, 8H, CH2 of
nBu4N+], 6.55 [s, 4H, aromatic CH of Mes], 7.02–7.52
[overlapping m, 5H, aromatic CH of Ph]. 13C NMR
([D]chloroform, 20 1C), d 22.7 [p-CH3 of Mes], 24.1 [o-CH3
of Mes], 14.1, 19.7, 31.6, 58.7 [nBu4N+], 127.9, 128.1, 128.2,
136.3, 138.6, 140.8 [aromatic CH of Ph and Mes], boron-
bound aromatic quaternary carbons not observed. 11B NMR
([D]chloroform, 20 1C), d 5. 19F NMR ([D]chloroform, 20 1C),
d ꢁ171.2. MS(ESꢁ): 345 (42%) [1ꢂF]ꢁ; exact mass (calc.) m/z
344.2232, (meas.) 344.2233. Elemental microanalysis: calc. C
81.70, H 10.81, N 2.38%; meas. C 82.07, H 10.99, N 2.21%.
Crystal data: [nBu4N]+[1ꢂF]ꢁ, C40H63BFN, monoclinic, P21/c,
2. To a stirred solution of 2,20-dibromotolan (0.50 g,
1.49 mmol) in diethyl ether (40 mL) at ꢁ78 1C was added
dropwise n-butyllithium (2.0 equiv., 1.86 mL of a 1.6 M
solution in hexanes) and the stirred reaction mixture allowed
to warm to 20 1C. After 12 h a solution of dimesitylboron
fluoride (2.0 equiv., 0.80 g, 2.98 mmol) in diethyl ether (30 mL)
was added and stirring continued for a further 6 h at 20 1C.
Filtration and removal of volatiles in vacuo afforded a yellow
solid, which was recrystallized from hexanes (ca. 25 mL) at
ꢁ30 1C as a spectroscopically pure colourless solid in 43%
yield. 1H NMR ([D]chloroform, 20 1C), d 1.85 [s, 24H, o-CH3
of Mes], 2.18 [s, 12H, p-CH3 of Mes], 6.45–6.55 [m, 2H,
aromatic CH of tolan], 6.65 [s, 8H, aromatic CH of Mes],
7.06–7.12 [overlapping m, 6H, aromatic CH of tolan]. 13C
NMR ([D]chloroform, 20 1C), d 21.3 [p-CH3 of Mes], 23.2
[o-CH3 of Mes], 93.5 [alkyne quaternary carbon], 127.3
[aromatic quaternary carbon of tolan], 127.4 [aromatic CH
of tolan], 128.3 [aromatic CH of Mes], 129.6 [aromatic CH of
tolan], 133.2 [aromatic CH of tolan], 133.9 [aromatic CH of
tolan], 138.8 [aromatic quaternary of Mes], 140.8 [aromatic
quaternary of Mes], 142.9, 149.8 [boron-bound aromatic
quaternary carbons]. 11B NMR ([D]chloroform, 20 1C),
d 73. MS(EI): 674 (5%) M+; exact mass (calc.) m/z 674.4250
(meas.), 674.4252.
a
=
10.3016(2),
b = 19.4960(3), c = 18.7092(4) A,
b = 94.422(1)1, V = 3746.37(12) A3, Z = 4, Dx
=
1.041 Mg mꢁ3, Mr = 587.76, T = 150(2) K. 48 778 reflections
collected, 8185 independent [Rint = 0.063], 4301 observed
[I > 2s(I)]. R1 = 0.0407, wR2 = 0.0926 for observed unique
reflections [I > 2s(I)]; R1 = 0.0590, wR2 = 0.0994 for all
unique reflections. Goodness of fit = 1.000. Max. and min.
residual electron densities: 0.28 and ꢁ0.27 e Aꢁ3. CCDC
765939.
[K(18-crown-6)]+2[2ꢂ(CN)2]2ꢁ. To a slurry of 2 (0.02 g,
0.03 mmol) in acetonitrile (15 mL) was added 18-crown-6
(2.0 equiv., 0.16 g, 0.06 mmol) and potassium cyanide
(2.0 equiv., 0.04 g, 0.06 mmol), and the reaction mixture
stirred for 12 h at 20 1C. The 11B NMR spectrum of
the reaction mixture at this point revealed a single resonance
at dB ꢁ15 ppm characteristic of a triarylborane/cyanide
adduct. Concentration of the acetonitrile solution and
layering with diethyl ether yielded single crystals of
[K(18-crown-6)+]2[2ꢂ(CN)2]2ꢁ (as the acetonitrile bis-solvate)
[K(18-crown-6)]+[1ꢂCN]ꢁ. To a solution of 1 (0.47 g,
1.43 mmol) in chloroform (5 mL) was added KCN and
18-crown-6 (1.0 equiv. of each) and the reaction mixture
stirred at 20 1C for 12 h. Filtration and layering with
hexanes at 20 1C led to the formation of single crystals of
[K(18-crown-6)]+[1ꢂCN]ꢁ suitable for X-ray diffraction. Yield
ꢃc
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suitable for X-ray diffraction. Larger scale preparative
reactions (ca. 0.1 g) typically yielded [K(18-crown-6)]+
Results and discussion
-
2
[2ꢂ(CN)2]2ꢁꢂ2CH3CN as a spectroscopically pure colourless
A report by Yamaguchi et al. in 2001 of colorimetric sensors
for the fluoride ion based around derivatives of tris(9-anthryl)-
borane represented a conceptually simple, but significant
advance in the use of triarylboranes in sensing.5a Sterically
encumbered systems of this type typically show selectivity for
small, highly nucleophilic anions which give rise to strong
B–X bonds on coordination (e.g. Fꢁ).3s Moreover, several
strategies have subsequently been reported which give rise to
enhanced binding constants for the fluoride ion at borane
Lewis acids, using, for example, peripheral cationic substituents,
chelating binding domains, secondary hydrogen bonding etc.3s
Such systems offer the potential for binding the highly solvated
fluoride ion in more polar media (and ultimately water). In a
number of cases, however, the use of such boranes in practical
fluoride sensing applications is limited by a competing sensor
response for the cyanide ion.5gg With this in mind it is
perhaps surprising that comparative experimental studies of
the fundamental thermodynamic and structural consequences
of Fꢁ/CNꢁ binding at simple triarylboranes have yet to be
reported.
1
material in 60–70% isolated yield. H NMR ([D]chloroform,
20 1C), d 1.94 [s, 24H, o-CH3 of Mes], 2.10 [s, 12H, p-CH3 of
Mes], 3.42 [s, 48H, 18-crown-6], 6.46–6.54 [m, 2H, aromatic
CH of tolan], 6.53 [s, 8H, aromatic CH of mesityl], 6.59–6.83
[overlapping m, 6H, aromatic CH of tolan]. 13C NMR
([D]chloroform, 20 1C), d 20.9 [p-CH3 of Mes], 25.7 [o-CH3
of mesityl], 70.0 [18-crown-6], 128.4 [aromatic CH of Mes],
128.9, 132.0, 136.4, 143.2 [aromatic CH of tolan], quaternary
carbons not observed due to very low solubility. 11B NMR
([D]chloroform, 20 1C), d ꢁ15. IR (KBr disk, cmꢁ1), 2167
(nCN). MS(ES+): 303 (100%) [K(18-crown-6)]+; exact mass
(calc.) m/z 303.1204, (meas.) 303.1203. MS(ESꢁ): 363 (80%)
[2ꢂ(CN)2]2ꢁ, exact mass (calc.) m/z 363.2164, (meas.) 363.2168.
Crystal
data:
[K(18-crown-6)]+2[2ꢂ(CN)2]2ꢁꢂ2CH3CN,
ꢀ
C80H106B2K2N4O12, triclinic, P1, a = 12.5667(2), b =
13.3168(3), c = 13.9064(3) A, a = 102.277(1)1, b =
110.042(1)1, g = 109.954(1)1, V = 1906.52(7) A3, Z = 1,
Dx = 1.233 Mg mꢁ3, Mr = 1415.51, T = 293(2) K. 28 042
reflections collected, 7775 independent [Rint = 0.122], 5459
observed [I > 2s(I)]. R1 = 0.0609, wR2 = 0.1453 for observed
unique reflections [I > 2s(I)]; R1 = 0.0926, wR2 = 0.1604 for
all unique reflections. Goodness of fit = 1.051. Max. and min.
residual electron densities: 0.46 and ꢁ0.57 e Aꢁ3. CCDC
765941.
In seeking to rectify this situation we ruled out the use of the
simplest such derivative, Ph3B, on the grounds of its air- and
moisture-sensitivity, and the related compound Mes3B on
the basis that the much increased steric loading renders it
incapable of binding Fꢁ in moderately competitive solvents
such as dichloromethane (AN
=
20.8).16 PhBMes2
(1; Chart 1), by contrast, appears to fulfill both criteria,
displaying aerobic stability and the ability to bind Fꢁ/CNꢁ
(c) Crystallography
Data for [nBu4N]+[1ꢂF]ꢁ, [K(18-crown-6)]+[1ꢂCN]ꢁ and
[K(18-crown-6)]+2[2ꢂ(CN)2]2ꢁ were collected on a Nonius
KappaCCD diffractometer (Mo-Ka radiation; l = 0.71073 A)
with an Oxford Cryosystems Cryostream N2 open-flow cooling
device.15a Data were processed using the DENZO-SMN package,
including inter-frame scaling (which was carried out using
Scalepack within DENZO-SMN).15b Structures were solved
using SIR92 (for [nBu4N]+[1ꢂF]ꢁ and [K(18-crown-6)]+
[1ꢂCN]ꢁ) or SHELXS (for [K(18-crown-6)]+2[2ꢂ(CN)2]2ꢁ).15c,d
Refinement was carried out using full-matrix least-squares
within the CRYSTALS suite,15e on either F2 ([nBu4N]+
in dichloromethane or chloroform. In addition, Gabbaı and
¨
co-workers have reported quantum chemical studies of
fluoride binding by PhBMes2 in the gas phase,6x thereby
offering for illustrative comparisons with solution and/or
solid state data. Hence we have examined the interaction of
PhBMes2 with fluoride and cyanide in dichloromethane
solution by UV-vis titration methods, and in the solid state
by X-ray crystallography. In addition, given the similar
binding affinities determined for the two anions (vide infra),
we report on attempts to link two aryldimesitylborane units
via an alkyne bridge (as in 2, Chart 1) to give a bifunctional
receptor offering the possibility for size-based selectivity for
cyanide (over fluoride).
[1ꢂF]ꢁ and [K(18-crown-6)]+2[2ꢂ(CN)2]2ꢁ
)
or
F
(for
[K(18-crown-6)]+[1ꢂCN]ꢁ). All non-hydrogen atoms were
refined with anisotropic displacement parameters. For all
three compounds, the majority of hydrogen atoms were visible
in the difference map, while the rest were added geometrically;
refinement of positions and isotropic displacement parameters
using restraints was carried out prior to inclusion into the
model with riding constants.z
Qualitatively, interaction of fluoride with 1 in dichloro-
methane or chloroform can be demonstrated by 11B NMR,
as evidenced by an upfield shift from dB 78 to 5 ppm and by the
presence in the mass spectrum (ESꢁ) of a single feature
corresponding to the adduct [1ꢂF]ꢁ; similar spectroscopic
evidence points to the formation of the corresponding cyanide
adduct under analogous conditions. Thus, on cyanide binding,
signals are detected at dB ꢁ13 (by 11B NMR) and at 2167 cmꢁ1
(d) Binding constant determinations
Binding constants were evaluated for 1 in dichloromethane
with fluoride and cyanide using the UV titration method
´
reported by Sole
and Gabbaı;6r the program LabFit
¨
(www.labfit.net) was used to fit the experimentally determined
data of A/Ao vs. anion concentration. Related efforts aimed at
the determination of binding constants for 2 were frustrated
by precipitation during the titration experiments.
Chart 1
ꢃc
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in the IR spectrum, the latter showing the expected shift
to higher wavenumber (cf. 2080 cmꢁ1 for ‘free’ cyanide).
Quantitative assessment of the host/guest interaction in each
case was undertaken by spectroscopic titration methods. In
Given the extensive use of arylboranes in the sensing of
fluoride, and the particularly widespread exploitation of
–BMes2 functionalized systems, the data determined in
the current study (i.e. KF and KCN) provide a convenient
baseline against which to judge the effects of peripheral
substituents on the strength of anion binding (Table 1). Thus
ferrocene-functionalized systems show little divergence in
1
this respect standard H NMR measurements have proved to
be ineffective—the binding of cyanide to 1, for example, being
characterized by slow exchange (on the NMR timescale)
between the free receptor and the cyanide adduct. Alternative
UV-vis titration experiments were therefore carried out; the
intensity of the absorption due to 1 at 351 nm was monitored
as a function of anion (Fꢁ or CNꢁ) concentration and the
resulting graph of A/Ao fitted using LabFit (Fig. 1).
their binding affinities from
1 (except in the case of
[1,2-fc(BMes2)CH2NMe3]+ which exhibits borane/H-bond
cooperativity in its interaction with fluoride), but increased
affinities of between three and four orders of magnitude are
observed for systems featuring extended aromatic conjugation,
cationic substituents and/or peripheral coordination to metal
centres.3s,5bb,ff,gg,n,r,u,17
The binding constants of 1 for Fꢁ and CNꢁ are calculated
to be 8.9(1.9) ꢀ 104 Mꢁ1 and 1.9(0.5) ꢀ 105 Mꢁ1, respectively—
values which are not statistically different, given the associated
standard deviations. More definitive evidence that the binding
of cyanide by 1 is stronger than that of fluoride comes from
competition experiments. Thus, addition of excess cyanide
to a solution of [1ꢂF]ꢁ in dichloromethane can be shown by
multinuclear NMR experiments to result in the formation of
[1ꢂCN]ꢁ, while the reverse reaction, i.e. the displacement of
CNꢁ from [1ꢂCN]ꢁ by excess fluoride does not appear to be
spontaneous under any of the sets of reaction conditions
studied (Scheme 1). The competitive binding of Fꢁ and CNꢁ
by 1 is perhaps unsurprising given the small steric demands of
both anions, and the similar pKas reported for HF/HCN in
non-aqueous media (15 and 13, respectively, in dimethyl
sulfoxide);13 a similar lack of differentiation has also been
reported for ferrocenyl derivatized systems.5gg
Table 1 BMes2 substituted arenes: compound 1 as a baseline for
comparative fluoride binding data
Compound
KFa/Mꢁ1
References
This work
1
8.9(1.9) ꢀ 104
6 ꢀ 107
3s
>108
(in chloroform)
5ff
>108 (K1)
B106 (K2)
5r
>109 (K1)
B106 (K2)
5r, 5bb
Fig. 1 Calculated fit (line) to experimental data (points) showing the
response at 351 nm to the addition of (a) fluoride or (b) cyanide to 1
(R2 = 0.9991, 0.9987, respectively). The initial concentrations of 1
were 2.28 and 0.79 mM, respectively.
2.1(0.3) ꢀ 104
5n
5u
5.0(0.2) ꢀ 105
(in chloroform)
7.8(1.2) ꢀ 104
9.4(3.6) ꢀ 105
5.6(2.3) ꢀ 109
5gg
5gg
5gg
a
In dichloromethane unless otherwise stated (the acceptor numbers as
defined by Gutmann et al. for dichloromethane and chloroform are
20.4 and 23.1, respectively).16
Scheme 1 Comparative binding of fluoride and cyanide by the
archetypal triarylborane Lewis acid 1.
ꢃc
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for [K(18-crown-6)]+[FcB(2,6-Xyl)2ꢂCN]ꢁ).
A
secondary
interaction between the cyanide nitrogen and the potassium
centre of the [K(18-crown-6)]+ cation augments the coordination
geometry at the metal centre, with a Kꢂ ꢂ ꢂN separation of
2.758(2) A having been determined. The potassium centre also
interacts with one of the phenyl m-CH bonds of an adjacent
[1ꢂCN]ꢁ anion, with this additional contact occurring at the
distal face of the [K(18-crown-6)]+ unit. The Kꢂ ꢂ ꢂH and
Kꢂ ꢂ ꢂC distances associated with this interaction (2.913 and
3.357 A) fall comfortably within the sums of the respective van
der Waals radii (3.51 and 4.16 A, respectively).19
Given the lack of discrimination for the binding of Fꢁ/CNꢁ
revealed for 1 by UV-vis titration experiments, we have
targeted related derivatives which offer selective binding
of either anion, based on potentially chelating Lewis acid
receptors tailored to the specific sizes/geometries of the two
anions. While systems based on ortho-disubstituted benzene or
ferrocene backbones offer chelating binding of simple monatomic
anions bearing >1 lone pair (e.g. halides), and the crystal
structure of [C6F4-1,2-(BF2)2(m-F)]ꢁ, for example, has been
reported by Piers and co-workers (Chart 2),6y,20 receptors
targeting the bifunctional binding of cyanide require a
significantly larger binding cavity. Given that strongly Lewis
acidic boranes have previously been shown to be capable of
binding to both the C- and N-based lone pairs of the cyanide
anion,21 and reasoning that a CRC triple bond should offer a
reasonable templating backbone for cyanide chelation, we
have synthesized and examined the binding capabilities of
the 2,20-diborylated tolan system 2.
Fig. 2 Crystal structures of [nBu4N]+[1ꢂF]ꢁ (left) and [K(18-crown-
6)]+[1ꢂCN]ꢁ (right); hydrogen atoms omitted for clarity and thermal
ellipsoids set at the 50% probability level. Key bond lengths (A) and
angles (1): (for [nBu4N]+[1ꢂF]ꢁ) F(1)–B(2) 1.481(2), C(3)–B(2)–C(12)
115.9(1), C(3)–B(2)–C(21) 117.5(1), C(12)–B(2)–C(21) 106.4(1); (for
[K(18-crown-6)]+[1ꢂCN]ꢁ) K(1)–N(20) 2.758(2), N(20)–C(21) 1.156(3),
C(21)–B(22) 1.631(3), N(20)–C(21)–B(22) 173.4(2), C(23)–B(22)–C(32)
108.1(2), C(23)–B(22)–C(38) 113.7(2), C(32)–B(22)–C(38) 118.4(2).
The structures of [nBu4N]+[1ꢂF]ꢁ and [K(18-crown-6)]+[1ꢂCN]ꢁ
have been determined by single crystal X-ray diffraction
(Fig. 2). The former is made up of [nBu4N]+ and [1ꢂF]ꢁ ions,
with the closest secondary contacts consisting of three
B–Fꢂ ꢂ ꢂH–C hydrogen bonds involving the a-carbon bound
hydrogens H(281) and H(402), together with H(332) which is
bound to one of the b carbons of the same [nBu4N]+ cation.
Similar hydrogen bonds between B–F and C–H linkages
(in which the latter is positioned a to a quaternary ammonium
function) have been reported recently, with a somewhat
shorter Cꢂ ꢂ ꢂF distance of 2.826(4) A having been determined
in one case for a related intramolecular ArMes2BFꢂ ꢂ ꢂHC
The synthesis of 2 is readily accomplished from the known
compound 2,20-dibromotolan (Scheme 2) in isolated yields of
40–50% via a single step simple lithiation/electrophilic quench
procedure, utilizing the commercially available borane
Mes2BF. 2 has been characterized by standard spectroscopic
procedures and is competent for the binding of cyanide, as
evidenced by the growth of a signal at dB ꢁ15 on addition
of either [nBu4N]+[CN]ꢁꢂ2H2O or KCN/18-crown-6 in
acetonitrile. That said, no evidence has been found for a
bridging mode of interaction of a single cyanide ion between
the two borane centres. On the contrary, mass spectrometry
and crystallographic studies are consistent with the formation
of the bis(cyanide) adduct [2ꢂ(CN)2]2ꢁ both in solution and in
the solid state. In the presence of ca. one equivalent of cyanide,
the reaction mixture contains both uncomplexed –BMes2 and
cyanide bound –BMes2CNꢁ functionalities (by multinuclear
NMR spectroscopy), thus arguing against cyanide chelation.
Attempts to isolate a 1 : 1 adduct under such conditions
for structural characterization have been frustrated by
crystallization of the much less soluble bis(cyanide) adduct
[K(18-crown-6)]+2[2ꢂ(CN)2]2ꢁ, despite the fact that it is
interaction (cf. 3.165–3.370
A
for [nBu4N]+[1ꢂF]ꢁ).5k
Nonetheless, the Cꢂ ꢂ ꢂF distances for [nBu4N]+[1ꢂF]ꢁ are
comfortably shorter than those reported for an analogous
intermolecular BFꢂ ꢂ ꢂHC system by Gale and co-workers
[3.442(4) and 3.447(3) A].18
The B–F distance determined for the anionic component
[1.481(2) A] agrees well with that derived from quantum
chemical calculations (1.491 A), and is somewhat greater than
that calculated for [Ph3BF]ꢁ (1.465 A) as expected on the basis
of the relative steric demands of the aryl substituent manifold.
It is also marginally longer than that found in the fluoride
adduct of the more strongly Lewis acidic cationic system
[1-Me3NC6H4BMes2]+ [1.465(3) A].7c Consistent with these
observations, the extent of pyramidalization of the boron
centre on fluoride binding (as manifested by the sum of
the three BC2 angles, 339.81) is similar to that predicted
computationally (340.51) and smaller than that associated
with the less hindered borane Ph3B [S(C–B–C) = 3331]. A
similar degree of pyramidalization at the boron centre is
observed on cyanide binding, as manifested by the structure
of [K(18-crown-6)]+[1ꢂCN]ꢁ [S(C–B–C)
= 340.91]. In
this case, and in common with related cyanide adducts of
ferrocenyl boranes,5gg the C-bound cyanide ligand features an
essentially linear B–C–N framework (+B–C–N = 173.4(2)1,
cf. 170.2(2)1 for [K(18-crown-6)]+[FcB(2,6-Xyl)2ꢂCN]ꢁ). The
B–CN bond length [1.631(3) A] is also similar to those
found for related ferrocene-derived systems (e.g. 1.624(3)1
Chart 2
ꢃc
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1656 | New J. Chem., 2010, 34, 1652–1659

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of pyramidalization at B(22) [S(C–B–C) = 339.91] is also
essentially identical to that measured for the corresponding
cyanide adduct of 1 (340.91).
The solid state structure shown in Fig. 3 implies that the
[K(18-crown-6)]+ cation can function as a competing Lewis
acid centre for the coordination of the N-based lone pair, in
the solid state at least. The identification of [2ꢂ(CN)2]2ꢁ in
acetonitrile solution by ESI-MS, however, implies that even in
the absence of an intimately bound counter-cation, the use of
systems featuring greater conformational rigidity and/or
borane Lewis acidity may be required in order to bring about
cyanide chelation.
Conclusions
In summary we have shown that in dichloromethane solution
fluoride and cyanide bind with very similar affinities to the
archetypal triarylborane PhBMes2, with similar degrees of
pyramidalization at the boron centre also being observed in
the solid state for the adducts [PhBMes2X]ꢁ. Competition
experiments are consistent with marginally stronger binding
of CNꢁ. A related bifunctional system based on a tolan
backbone, while similarly competent for the capture of one
equivalent of cyanide at each binding domain, does not appear
to function as a chelating Lewis acid.
Scheme 2 Synthesis and cyanide binding properties of 2,20-bis-
(dimesitylboryl)tolan, 2.
presumably present in relatively low concentrations at
equilibrium.
Evidence for the formation of [2ꢂ(CN)2]2ꢁ in acetonitrile
solution comes from in situ electrospray mass spectrometry
experiments, which give ‘flagpole’ spectra containing an
isotopic envelope centred at m/z = 363 (with half-integral
spacings) at low cone voltages (ca. 20 V). Evidence for the
mono(cyanide) adduct [2ꢂCN]ꢁ (m/z = 701) only becomes
apparent at much higher cone voltages, and this species is
presumably an artifact of fragmentation during the mass
spectrometry experiment. Confirmation of the structure of
[2ꢂ(CN)2]2ꢁ in the solid state was obtained from crystallo-
graphic studies of [K(18-crown-6)]+2[2ꢂ(CN)2]2ꢁꢂ2MeCN
(Fig. 3). The [K(18-crown-6)]+2[2ꢂ(CN)2]2ꢁ unit features two
[ArBMes2CN]ꢁ groups related by a centre of inversion, with
B–CN and K–NC distances of 1.632(3) and 2.842(2) A,
respectively. The near linear B–C–N and significantly more
bent K–N–C angles [177.2(2)1 and 143.5(2)1, respectively]
are similar to those found for the corresponding unit in
[K(18-crown-6)]+[1ꢂCN] [173.4(2)1 and 141.8(2)1]; the degree
Acknowledgements
We thank the EPSRC for funding (GR/S98771 and
EP/G006156) and for access to the National Mass Spectro-
metry Service Centre (Swansea University).
Notes and references
1 (a) Y.-C. Yang, J. A. Baker and J. R. Ward, Chem. Rev., 1992, 92,
1729; (b) S. I. Baskin and T. G. Brewer, Medical Aspects of
Chemical and Biological Warfare, ed. F. R. Sidell, E. T. Takafuji
and D. R. Franz, TMM Publications, New York, NY, 1997,
pp. 271–286; (c) H. Sohn, S. Letant, M. J. Sailor and
´
W. C. Trogler, J. Am. Chem. Soc., 2000, 122, 5399;
(d) C. Bresner, S. Aldridge, I. A. Fallis, C. Jones and L.-L. Ooi,
Angew. Chem., Int. Ed., 2005, 44, 3606; (e) J. Colquhoun, Perspect.
Biol. Med., 1997, 41, 29; (f) R. J. Carton, Fluoride, 2006, 39, 163.
2 (a) M. A. Holland and L. M. Kozlowski, Clin. Pharm., 1986, 5,
737; (b) F. Baud, Hum. Exp. Toxicol., 2007, 26, 191.
3 For recent reviews of anion binding, see, for example: (a) A. P. de
Silva, H. Q. N. Gunaratne, T. Gunnlaugsson, A. J. M. Huxley,
C. P. McCoy, J. T. Rademacher and T. E. Rice, Chem. Rev., 1997,
97, 1515; (b) F. P. Schmidtchen and M. Berger, Chem. Rev., 1997,
97, 1609; (c) P. A. Gale, J. A. Sessler and V. Kral, Chem. Commun.,
1998, 1; (d) P. D. Beer and P. A. Gale, Angew. Chem., Int. Ed.,
2001, 40, 486; (e) J. J. Lavigne and E. V. Anslyn, Angew. Chem.,
Int. Ed., 2001, 40, 3118; (f) R. Martınez-Manez and F. Sancernon,
´ ´ ´
Chem. Rev., 2003, 102, 4419; (g) M. D. Best, S. L. Tobey and
E. V. Anslyn, Coord. Chem. Rev., 2003, 240, 3; (h) J. A. Sessler,
S. Camiolo and P. A. Gale, Coord. Chem. Rev., 2003, 240, 17;
(i) J. M. Llinares, D. Powell and K. Bowman-James, Coord. Chem.
Rev., 2003, 240, 57; (j) S. Loeb and C. R. Bondy, Coord. Chem.
Rev., 2003, 240, 77; (k) K. Choi and A. D. Hamilton, Coord.
Chem. Rev., 2003, 240, 101; (l) T. J. Wedge and M. F. Hawthorne,
Coord. Chem. Rev., 2003, 240, 111; (m) P. D. Beer and E. J.
Hayes, Coord. Chem. Rev., 2003, 240, 167; (n) E. J. O’Neill and
B. D. Smith, Coord. Chem. Rev., 2006, 250, 3068; (o) M. H. Filby
and J. W. Steed, Coord. Chem. Rev., 2006, 250, 3200; (p) P. A. Gale
and R. Quesada, Coord. Chem. Rev., 2006, 250, 3219;
Fig. 3 Crystal structure of [K(18-crown-6)]+2[2ꢂ(CN)2]2ꢁꢂ2MeCN;
hydrogen atoms and acetonitrile solvent molecules omitted for clarity
and thermal ellipsoids set at the 50% probability level. Key bond
lengths (A) and angles (1): K(1)–N(20) 2.842(2), N(20)–C(21) 1.154(3),
C(21)–B(22) 1.632(3), N(20)–C(21)–B(22) 177.2(2), K(1)–N(20)–C(21)
143.5(2), C(23)–B(22)–C(32) 109.8(2), C(23)–B(22)–C(41) 111.5(2),
C(32)–B(22)–C(41) 119.7(2).
(q) T. W. Hudnall, C. W. Chiu and F. P. Gabbaı, Acc. Chem.
¨
ꢃc
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View Article Online
Res., 2009, 42, 388; (r) Z. M. Hudson and S. Wang, Acc. Chem.
Res., 2009, 42, 1584; (s) C. R. Wade, A. E. J. Broomsgrove,
K. Venkatasubbaiah, A. Doshi, R. A. Lalancette, L. Kakalis and
F. Jakle, Inorg. Chem., 2007, 46, 10174; (u) C. L. Dorsey,
¨
P. Jewula, T. W. Hudnall, J. D. Hoefelmeyer, T. J. Taylor,
S. Aldridge and F. P. Gabbaı, Chem. Rev., DOI: 10.1021/
cr900401a.
¨
N. R. Honesty, C.-W. Chiu, M. Schulte and F. P. Gabbaı, Dalton
¨
Trans., 2008, 4442; (v) T. W. Hudnall, Y.-K. Kim, M. W.
4 For examples of fluoride binding by boronic acid/esters see, for
example: (a) C. Dusemund, K. R. A. S. Sandanayake and
S. Shinkai, J. Chem. Soc., Chem. Commun., 1995, 333;
(b) H. Yamamoto, A. Ori, K. Ueda, C. Dusemund and
S. Shinkai, Chem. Commun., 1996, 407; (c) C. R. Cooper,
N. Spencer and T. D. James, Chem. Commun., 1998, 1365;
(d) H. Shiratori, T. Ohno, K. Nozaki and A. Osuka, Chem.
Commun., 1999, 2181; (e) A. Yuchi, A. Tatebe, S. Kani and
T. D. James, Bull. Chem. Soc. Jpn., 2001, 74, 509; (f) C. J. Ward,
P. Patel and T. D. James, Chem. Lett., 2001, 406; (g) M. Nicolas,
B. Fabre and J. Simonet, Electrochim. Acta, 2001, 46, 1179;
P. Bebington, D. Bourissou and F. P. Gabbaı, J. Am. Chem.
¨
Soc., 2008, 130, 10890; (w) A. Kawachi, A. Tani, J. Shimada and
Y. Yamamoto, J. Am. Chem. Soc., 2008, 130, 4222; (x) R. Boshra,
A. Doshi and F. Jakle, Organometallics, 2008, 27, 1534;
¨
(y) Q. Zhao, F. Li, S. Liu, M. Yu, Z. Liu, T. Yi and C. Huang,
Inorg. Chem., 2008, 47, 9256; (z) G. Zhou, M. Baumgarten and
K. Mullen, J. Am. Chem. Soc., 2008, 130, 12477; (aa) Y. Kim and
¨
¨
F. P. Gabbaı, J. Am. Chem. Soc., 2009, 131, 3363; (ab) Y. Sun
and S. Wang, Inorg. Chem., 2009, 48, 3755; (ac) Y.-L. Rao and
S. Wang, Inorg. Chem., 2009, 48, 7698; (ad) Z. M. Hudson,
S.-B. Zhao, R.-Y. Wang and S. Wang, Chem.–Eur. J., 2009, 15,
6131; (ae) T. Agou, M. Sekine, J. Kobayashi and T. Kawashima,
(h) B. Fabre, U. Lehmann and A. D. Schluter, Electrochim. Acta,
¨
2001, 46, 2855; (i) N. DiCesare and J. R. Lakowicz, Anal.
Biochem., 2002, 301, 111; (j) S. Arimori, M. G. Davidson,
T. M. Fyles, T. G. Hibbert, T. D. James and G. I. Kociok-Kohn,
Chem. Commun., 2004, 1640; (k) R. Badugu, J. R. Lakowicz and
C. D. Geddes, J. Fluoresc., 2004, 14, 693; (l) Y. Kubo,
A. Kobayashi, T. Ishida, Y. Misawa and T. D. James, Chem.
Commun., 2005, 2846; (m) Y. Kubo, T. Ishida, A. Kobayashi and
T. D. James, J. Mater. Chem., 2005, 15, 2889; (n) R. Badugu,
J. R. Lakowicz and C. D. Geddes, Curr. Anal. Chem., 2005, 1, 157;
(o) R. Badugu, J. R. Lakowicz and C. D. Geddes, Sens. Actuators,
B, 2005, 104, 103; (p) K. M. K. Swamy, Y. J. Lee, H. N. Lee,
J. Chun, Y. Kim, S.-J. Kim and J. Yoon, J. Org. Chem., 2006, 71,
8626; (q) Y. Kubo, T. Ishida, T. Minami and T. D. James, Chem.
Lett., 2006, 35, 996; (r) T. Neumann, Y. Dienes and
T. Baumgartner, Org. Lett., 2006, 8, 495; (s) W. Tan, D. Zhang,
Z. Wang, C. Liu and D. J. Zhu, J. Mater. Chem., 2007, 17, 1964;
(t) A. Oehlke, A. A. Auer, I. Jahre, B. Walfort, T. Rueffer,
P. Zoufala, H. Lang and S. Spange, J. Org. Chem., 2007, 72,
4328; (u) K. Kataoka, T. D. James and Y. Kubo, J. Am. Chem.
Soc., 2007, 129, 15126; (v) T. Agou, J. Kobayashi, Y. Kim,
Chem. Commun., 2009, 1894; (af) C. R. Wade and F. P. Gabbaı,
¨
Dalton Trans., 2009, 9169; (ag) A. E. J. Broomsgrove, D. Addy,
A. Di Paolo, I. R. Morgan, C. Bresner, V. Chislett, I. A. Fallis,
A. L. Thompson, D. Vidovic and S. Aldridge, Inorg. Chem., 2010,
49, 157.
6 For bidentate boron-centered Lewis acids see, for example:
(a) H. E. Katz, J. Am. Chem. Soc., 1985, 107, 1420;
(b) H. E. Katz, J. Org. Chem., 1985, 50, 5027; (c) L. Jia,
X. Yang, C. Stern and T. J. Marks, Organometallics, 1994, 13,
3755; (d) K. Kohler, W. E. Piers, X. Sin, Y. Feng, A. M. Bravakis,
¨
A. P. Jarvis, S. Collins, W. Clegg, G. P. A. Yap and T. B. Marder,
Organometallics, 1998, 17, 3557; (e) V. C. Williams, W. E. Piers,
W. Clegg, M. R. J. Elsegood, S. Collins and T. B. Marder, J. Am.
Chem. Soc., 1999, 121, 3244; (f) V. C. Williams, C. Dai, Z. Li,
S. Collins, W. E. Piers, W. Clegg, M. R. J. Elsegood and
T. B. Marder, Angew. Chem., Int. Ed., 1999, 38, 3695;
(g) M. V. Metz, D. J. Schwartz, C. L. Stern, P. N. Nickias and
T. J. Marks, Angew. Chem., Int. Ed., 2000, 39, 1312;
(h) V. C. Williams, G. J. Irvine, W. E. Piers, Z. M. Li,
S. Collins, W. Clegg, M. R. J. Elsegood and T. B. Marder,
Organometallics, 2000, 19, 1619; (i) W. E. Piers, G. Irvine and
V. C. Williams, Eur. J. Inorg. Chem., 2000, 2131;
(j) J. D. Hoefelmeyer, M. Schulte, M. Tschinkl and
F. P. Gabbaı and T. Kawashima, Chem. Lett., 2007, 36, 976;
¨
(w) J. K. Day, C. Bresner, N. D. Coombs, I. A. Fallis, L.-L. Ooi
and S. Aldridge, Inorg. Chem., 2008, 47, 793; (x) E. Galbraith,
T. M. Fyles, F. Marken, M. G. Davidson and T. D. James, Inorg.
Chem., 2008, 47, 6236; (y) R. Ting, C. W. Harwig, J. Lo, Y. Li,
M. J. Adam, T. J. Ruth and D. M. Perrin, J. Org. Chem., 2008, 73,
4662; (z) R. Ting, C. Harwig, U. auf dem Keller, S. McCormick,
P. Austin, C. M. Overall, M. J. Adam, T. J. Ruth and
D. M. Perrin, J. Am. Chem. Soc., 2008, 130, 12045; (aa) Z. Xu,
S. K. Kim, S. J. Han, C. Lee, G. Kociok-Kohn, T. D. James and
J. Yoon, Eur. J. Org. Chem., 2009, 3058.
F. P. Gabbaı, Coord. Chem. Rev., 2002, 235, 93;
¨
(k) L. D. Henderson, W. E. Piers, G. J. Irvine and
R. McDonald, Organometallics, 2002, 21, 340; (l) M. V. Metz,
D. J. Schwartz, C. L. Stern, T. J. Marks and P. N. Nickias,
Organometallics, 2002, 21, 4159; (m) D. J. M. Emslie,
W. E. Piers and M. Parvez, Angew. Chem., Int. Ed., 2003, 42,
1252; (n) F. P. Gabbaı, Angew. Chem., Int. Ed., 2003, 42, 2218;
¨
5 For fluoride binding by other three-coordinate boron-containing
systems see, for example: (a) S. Yamaguchi, S. Akiyama and
K. J. Tamao, J. Am. Chem. Soc., 2001, 123, 11372;
(b) S. Yamaguchi, T. Shirasaka, S. Akiyama and K. Tamao,
J. Am. Chem. Soc., 2002, 124, 8816; (c) M. Miyata and
Y. Chujo, Polym. J., 2002, 34, 967; (d) Y. Kubo, M. Yamamoto,
M. Ikeda, M. Takeuchi, S. Shinkai and K. Tamao, Angew. Chem.,
Int. Ed., 2003, 42, 2036; (e) G. E. Herberich, U. Englert, A. Fischer
and D. Wiebelhaus, Eur. J. Inorg. Chem., 2004, 4011; (f) Z. Q. Liu,
M. Shi, F. Y. Li, Q. Fang, Z. H. Chen, T. Yi and C. H. Chuang,
Org. Lett., 2005, 7, 5481; (g) I. H. A. Badr and M. E. Meyerhoff,
J. Am. Chem. Soc., 2005, 127, 5318; (h) T. Agou, J. Kobayashi and
T. Kawashima, Org. Lett., 2005, 7, 4373; (i) S. Xu, K. Chen and
H. J. Tian, J. Mater. Chem., 2005, 15, 2676; (j) K. Parab,
(o) S. P. Lewis, N. J. Taylor, W. E. Piers and S. Collins, J. Am.
Chem. Soc., 2003, 125, 14686; (p) I. Ghesner, W. E. Piers,
M. Parvez and R. McDonald, Organometallics, 2004, 23, 3085;
(q) D. J. Morrison, W. E. Piers and M. Parvez, Synlett, 2004, 2429;
(r) S. Sole
(s) W. E. Piers, Adv. Organomet. Chem., 2005, 52, 1;
(t) M. Melaımi and F. P. Gabbaı, Adv. Organomet. Chem., 2005,
´
and F. P. Gabbaı, Chem. Commun., 2004, 1284;
¨
¨
¨
52, 61; (u) M. Scheibitz, J. B. Heilmann, R. F. Winter, M. Bolte,
J. W. Bats and M. Wagner, Dalton Trans., 2005, 159;
(v) M. Scheibitz, M. Bolte, J. W. Bats, H.-W. Lerner, I. Nowik,
R. H. Herber, A. Krapp, M. Lein, M. Holthausen and M. Wagner,
Chem.–Eur. J., 2005, 11, 584; (w) F. P. Gabbaı, ACS Symp. Ser.,
¨
F. P. Gabbaı, Inorg. Chem., 2006, 45, 8136; (y) P. A. Chase,
¨
2006, 917, 208; (x) M. Melaımi, S. Sole, C.-W. Chiu, H. Wang and
´
¨
L. D. Henderson, W. E. Piers, M. Parvez, W. Clegg and M. R.
K. Venkatasubbaiah and F. Jakle, J. Am. Chem. Soc., 2006, 128,
¨
¨
12879; (k) C.-W. Chiu and F. P. Gabbaı, J. Am. Chem. Soc., 2006,
J. Elsegood, Organometallics, 2006, 25, 349; (z) M. H. Lee and
F. P. Gabbaı, Inorg. Chem., 2007, 46, 8132.
128, 14248; (l) T. Agou, J. Kobayashi and T. Kawashima, Inorg.
Chem., 2006, 45, 9137; (m) E. Sakuda, A. Funahashi and
N. Kitamura, Inorg. Chem., 2006, 45, 10670; (n) X. Y. Liu,
D. R. Bai and S. Wang, Angew. Chem., Int. Ed., 2006, 45, 5475;
¨
7 For examples of cyanide binding by triarylboranes see for example
ref. 5j and (a) J. Zhou, S. J. Lancaster, D. A. Walker, S. Beck,
M. Thornton-Pett and M. Bochmann, J. Am. Chem. Soc., 2001,
123, 223; (b) I. C. Vei, S. I. Pascu, M. L. H. Green, J. C. Green,
R. E. Schilling, G. D. W. Anderson and L. H. Rees, Dalton Trans.,
2003, 2550; (c) T. W. Hudnall and F. P. Gabbaı, J. Am. Chem.
¨
Soc., 2007, 127, 11978; (d) C.-W. Chiu and F. P. Gabbaı, Dalton
¨
Trans., 2008, 814; (e) J.-O. Huh, Y. Do and M. H. Lee, Organo-
(o) T. W. Hudnall, M. Melaımi and F. P. Gabbaı, Org. Lett., 2006,
¨
¨
8, 2747; (p) C. Bresner, J. K. Day, N. D. Coombs, I. A. Fallis,
S. Aldridge, S. J. Coles and M. B. Hursthouse, Dalton Trans., 2006,
3660; (q) M. H. Lee, T. Agou, J. Kobayashi, T. Kawashima and
F. P. Gabbaı, Chem. Commun., 2007, 1133; (r) Y. Sun, N. Ross,
¨
S.-B. Zhao, K. Huszarik, W.-L. Jia, R.-Y. Wang, D. Macartney
and S. Wang, J. Am. Chem. Soc., 2007, 129, 7510; (s) Y. Cui,
Z.-H. Lu and S. Wang, Dalton Trans., 2007, 2634; (t) R. Boshra,
metallics, 2008, 27, 1022; (f) C. W. Chiu, Y. Kim and F. P. Gabbaı,
¨
J. Am. Chem. Soc., 2009, 131, 60; (g) Y. Kim, H. Zhao and
¨
F. P. Gabbaı, Angew. Chem., Int. Ed., 2009, 48, 4957;
ꢃc
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(h) T. Agou, M. Sekine, J. Kobayashi and T. Kawashima,
J. Organomet. Chem., 2009, 694, 3833.
8 For examples of boron sub-phthalocyanines in cyanide sensing see,
13 See, for example: http://www2.lsdiv.harvard.edu/labs/evans/pdf/
evans_pKa_table.pdf.
14 (a) The compositions of the tetrabutylammonium fluoride and
cyanide hydrates used in anion binding studies (and prepared by
prolonged drying in vacuo) were determined to be [nBu4N]Fꢂ4H2O
for example: (a) J. V. Ros-Lis, R. Martı
Chem. Commun., 2005, 5260; (b) E. Palomares, M. V. Martı
T. Torres and E. Coronado, Adv. Funct. Mater., 2006, 16, 1166.
´
nez-Ma
´
nez and J. Soto,
´
nez-Dıaz,
´
and
[nBu4N]CNꢂ2H2O
by
elemental
microanalysis;
9 For examples of cyanide sensing using boronic acids in aqueous
solution making use of the equilibriumArB(OH)2 + 3HCN -
[ArB(CN)3]ꢁ + H2O + [H3O]+see, for example: (a) R. Badugu,
J. R. Lakowicz and C. D. Geddes, Anal. Biochem., 2004, 327, 82;
(b) R. Badugu, J. R. Lakowicz and C. D. Geddes, Anal. Chim.
Acta, 2004, 522, 9; (c) R. Badugu, J. R. Lakowicz and
C. D. Geddes, J. Am. Chem. Soc., 2005, 127, 3635;
(d) R. Badugu, J. R. Lakowicz and C. D. Geddes, Dyes Pigm.,
2005, 64, 49.
(b) R. L. Letsinger and J. R. Nazy, J. Am. Chem. Soc., 1959, 81,
3013; (c) N. M. D. Brown, F. Davidson and J. W. Wilson,
J. Organomet. Chem., 1981, 209, 1.
15 (a) J. Cosier and A. M. Glazer, J. Appl. Crystallogr., 1986, 19, 105;
(b) Denzo: Z. Otwinowski and W. Minor, Methods in Enzymology,
ed. C. W. Carter and R. M. Sweet, AcademicPress, New York,
1996, vol. 276, p. 307; (c) Sir-92: A. Altomare, G. Cascarano,
C. Giacovazzo, A. Guagliardi, M. C. Burla, G. Polidori and
M. Camalli, J. Appl. Crystallogr., 1994, 27, 435; (d) SHELX:
G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystallogr.,
2008, 64, 112; (e) CRYSTALS: P. W. Betteridge, J. R. Carruthers,
R. I. Cooper, K. Prout and D. J. Watkin, J. Appl. Crystallogr.,
2003, 36, 1487.
16 As determined by a null response in the UV-vis spectrum of Mes3B
to the addition of fluoride in dichloromethane (AN = 20.8); a
binding constant of 3.3(0.3) ꢀ 105 Mꢁ1 has been determined in the
less competitive solvent thf (AN = 8).6r Definition of AN scale:
U. Mayer, V. Gutmann and W. Gerger, Monatsh. Chem., 1975,
106, 1235.
17 A recent study by Do, Lee and co-workers reports fluoride binding
constants for a series of para-substituted derivatives of the type
4-XC6H4BMes2 (albeit in thf solution) which are in agreement with
the respective Hammett parameters for X: J. O. Huh, H. Kim,
K. M. Lee, Y. S. Lee, Y. Do and M. H. Lee, Chem. Commun.,
2010, 46, 1138.
18 I. E. D. Vega, P. A. Gale, M. E. Light and S. J. Loeb, Chem.
Commun., 2005, 4913.
19 J. Emsley, The Elements, Oxford University Press, Oxford, 1995.
20 I. R. Morgan, A. Di Paolo, D. Vidovic, I. A. Fallis and
S. Aldridge, Chem. Commun., 2009, 7288.
10 For examples of cyanide binding/sensing by transition metal
¨
systems see, for example: (a) S. Warzeska and R. Kramer, Chem.
Commun., 1996, 499; (b) B. Ahlers, K. Cammann, S. Warzeska and
R. Kramer, Angew. Chem., Int. Ed. Engl., 1996, 35, 2141;
¨
(c) Y.-H. Kim and J.-I. Hong, Chem. Commun., 2002, 512;
(d) P. Anzenbacher, Jr., D. S. Tyson, K. Jursıkova and
´ ´
F. N. Castellano, J. Am. Chem. Soc., 2002, 124, 6232;
(e) C.-F. Chow, M. H. W. Lam and W.-Y. Wong, Inorg. Chem.,
2004, 43, 8387; (f) H. Liu, X.-B. Shao, M.-X. Jia, X.-K. Jiang,
Z.-T. Li and G.-J. Chen, Tetrahedron, 2005, 61, 8095;
(g) K. Poland, E. Topoglidis, J. R. Durrant and E. Palomares,
Inorg. Chem. Commun., 2006, 9, 1239.
11 For organic cyanide sensors see, for example: (a) J. V. Ros-Lis,
R. Martı
(b) M. Tomasuloand and F.M. Raymo, Org. Lett., 2005, 7, 4633;
(c) F. Garcıa, J. M. Garcıa, B. Garcıa-Acosta, R. Martınez-Manez,
F. Sanceno and J. Soto, Chem. Commun., 2005, 2790;
nez-Manez and J. Soto, Chem. Commun., 2002, 2248;
´ ´
´
´
´
´
´
´
n
(d) Y. Chung, H. Lee and K. H. Ahn, J. Org. Chem., 2006, 71,
9470; (e) M. Tomasulo, S. Sortino, A. J. P. White and
F. M. Raymo, J. Org. Chem., 2006, 71, 744; (f) Y.-K. Yang and
J. Tae, Org. Lett., 2006, 8, 5721; (g) Y. M. Chung, B. Raman,
D.-S. Kim and K. H. Ahn, Chem. Commun., 2006, 186;
(h) C.-L. Chen, Y.-H. Chen, C.-Y. Chen and S.-S. Sun, Org. Lett.,
2006, 8, 5053.
21 See, for example: (a) J. Zhou, S. J. Lancaster, D. A. Walker,
S. Beck, M. Thornton-Pett and M. Bochmann, J. Am. Chem. Soc.,
2001, 123, 223; (b) N. M. Brunkan, D. M. Brestensky and
W. D. Jones, J. Am. Chem. Soc., 2004, 126, 3627.
12 J. Havir, Collect. Czech. Chem. Commun., 1961, 26, 1775.
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