Synthesis and characterisation of some new boron compounds containing the 2,4,6-(CF3)3C6 H2 (fluoromes = Ar), 2,6-(CF3)2C6H3 (fluoroxyl = Ar′), or 2,4-(CF3)2 C6H3 (Ar″) ligands

Article abstract of DOI:10.1039/b309820f

Several new boron compounds containing the 2,4,6- (CF₃)₃C₆H₂ (fluoromes = Ar), 2,6-(CF₃)₂C₆H₃ (fluoroxyl = Ar′) or 2,4-(CF₃)₂C₆H₃ (Ar″) ligands have been synthesised from reactions of ArLi, Ar′Li or Ar″Li with BCl₃, and characterised by ¹⁹F and ¹¹B NMR spectroscopy. Chlorine/fluorine exchanges are evident in these reactions. The crystal and molecular structures of Ar₂BF, Ar″₃B, Ar₂B(OH), Ar′B(OH)₂ and Mes₂BF (Mes = 2,4,6-Me₃C₆H₂) have been determined by single crystal X-ray diffraction. Ar″₃B represents the first example of a compound containing three Ar″ ligands to be structurally characterised. Molecular geometries and GIAO-NMR shifts for several new boron compounds have been calculated at the HF/6-31G* level of theory, and compared with the available experimental results.

Full text of DOI:10.1039/b309820f

View Article Online / Journal Homepage / Table of Contents for this issue
Synthesis and characterisation of some new boron compounds
containing the 2,4,6-(CF3)3C6H2 (fluoromes ؍ Ar), 2,6-(CF3)2C6H3
(fluoroxyl ؍ ArЈ), or 2,4-(CF3)2C6H3 (ArЉ) ligands†
Stéphanie M. Cornet, Keith B. Dillon,* Christopher D. Entwistle, Mark A. Fox,*
Andrés E. Goeta, Helen P. Goodwin, Todd B. Marder and Amber L. Thompson
Chemistry Department, University of Durham, South Road, Durham, UK DH1 3LE.
E-mail: k.b.dillon@durham.ac.uk
Received 14th August 2003, Accepted 4th September 2003
First published as an Advance Article on the web 26th September 2003
Several new boron compounds containing the 2,4,6-(CF3)3C6H2 (fluoromes = Ar), 2,6-(CF3)2C6H3 (fluoroxyl = ArЈ)
or 2,4-(CF3)2C6H3 (ArЉ) ligands have been synthesised from reactions of ArLi, ArЈLi or ArЉLi with BCl3, and
characterised by 19F and 11B NMR spectroscopy. Chlorine/fluorine exchanges are evident in these reactions. The
crystal and molecular structures of Ar2BF, ArЉ3B, Ar2B(OH), ArЈB(OH)2 and Mes2BF (Mes = 2,4,6-Me3C6H2) have
been determined by single crystal X-ray diffraction. ArЉ3B represents the first example of a compound containing
three ArЉ ligands to be structurally characterised. Molecular geometries and GIAO-NMR shifts for several new
boron compounds have been calculated at the HF/6-31G* level of theory, and compared with the available
experimental results.
2, ArЉ3B 16 and ArЈB(OH)2 17 have also been determined by
Introduction
low-temperature X-ray crystallography. In addition, molecular
geometries and GIAO-NMR shifts for several boron com-
pounds have been calculated at the HF/6-31G* level of theory,
and compared with the experimental results, where available.
Although the chemistry of 2,4,6-(CF3)3C6H2 (fluoromes = Ar),
2,6-(CF3)2C6H3 (fluoroxyl = ArЈ) and 2,4-(CF3)2C6H3 (ArЉ)
has been well-developed over the last 15 years,1–6 little has been
published about the ability of these ligands to stabilise group 13
elements. Schluter et al. described the syntheses of indium
and gallium derivatives containing the 2,4,6-(CF3)3C6H2 (Ar)
ligand.6,7 Bardají et al. reported the formation of a thallium
derivative, Ar3Tl.8 No syntheses of aluminium derivatives of
these ligands have been reported to date.
Results and discussion
Synthesis and solution-state NMR spectroscopy
Slow addition of ArLi to a BCl3ؒOEt2 solution in diethyl ether,
keeping the boron reagent in excess (Scheme 2), gave rise to a
mixture of ArBCl2 7 and Ar2BF 8, identified from their 19F and
11B NMR spectroscopic data (Table 1). Ar2BF 8 was isolated
and fully characterised by X-ray crystallography. In addition,
boron trihalide–diethyl etherate adducts were observed in solu-
tion (BFCl2ؒOEt2 9, BF2ClؒOEt2 10 and BF3ؒOEt2 11, Table 1).
Their NMR data are very similar to literature results.14
However, the most studied group 13 element involving the
ligands Ar, ArЈ or ArЉ is boron. A preliminary conference
report mentioned the formation of ArBCl2 7 and Ar2BCl 1
from reaction of ArLi with BCl3, and the occurrence of
Cl/F exchange.2 Ishihara et al. explored the arylboronic acid
ArB(OH)2 12 as a catalyst for amidination of carboxylic acids,
and the acid ArЉB(OH)2 21 as a catalyst precursor in the asym-
metric allylation of aldehydes with allyltrimethylsilanes.9,10
Gibson et al. reported the preparation of Ar2BCl 1 from the
reaction of ArLi with boron trichloride, and its hydrolysis to
When the reaction was carried out by addition of BCl3ؒOEt2
to excess ArLi, the products observed were ArBF2ؒOEt2 13 and
Ar2BF 8 (Scheme 3). 19F and 11B NMR data for 13 are included
in Table 1. Adducts 9–11 were not detected in this instance.
Fluorine-19 NMR spectroscopy shows for the three com-
pounds 7, 8 and 13 the characteristic signals of the Ar ligand:
a resonance at around Ϫ57 ppm for the ortho-CF3 groups,
and a singlet at about Ϫ64 ppm corresponding to the para-CF3
groups. (Table 1) The couplings in the 19F NMR spectra of a
give the boronic acid Ar2B(OH) 2, as shown in Scheme 1.11
A
lithium complex of type [LiOBAr2] 3 and a molybdenum com-
plex 4 were synthesised from this acid 2. The synthesis of
Ar2BN3 5 from Ar2BCl and Me3SiN3 was described by Fraenk
et al., and an X-ray structure of the partially hydrolysed
product, a 1 : 1 Ar2BN3ؒAr2B(OH) complex 6, was obtained.12
Here we report in detail the separate reactions of ArLi and
an ArЈLi/ArЉLi mixture with BCl3. The numerous boron species
formed have been characterised by 19F and 11B NMR solution-
state spectroscopy. These reactions clearly involve intriguing
fluorine/chlorine exchanges. We show that compound Ar2BCl 1,
reported as the major product11,12 from the reaction of ArLi
and BCl3, is in fact the boron–fluorine compound Ar2BF 8.
This has been confirmed by single crystal X-ray diffraction. The
molecular structure of the known13 dimesitylfluoroborane
Mes2BF 22 (Mes = 2,4,6-Me3C6H2) has been similarly ascer-
tained, to compare with that of 8. The structures of Ar2B(OH)
5
triplet (Ϫ56.2 ppm, JF–F 15.4 Hz) and a doublet (Ϫ57.4 ppm,
5JF–F 14.3 Hz) for ArBF2ؒOEt2 13 and Ar2BF 8, respectively
arise from the fluorines attached to the boron atoms. The latter
signal has been confirmed as a doublet by recording the 19F
spectrum at two frequencies (188.18 and 376.35 MHz). In both
sets of 19F NMR data reported in the literature11,12 for the
incorrectly characterised compound 1, the two peaks assigned
to the ortho-CF3 groups are in fact a doublet, and this com-
pound is really Ar2BF 8.
For the diaryl compound 8, a weak broad multiplet (arising
from both spin–spin coupling and the quadrupolar nature of
boron) is observed at Ϫ9.1 ppm, assigned to the boron-bound
fluorine. A similar value of Ϫ14.5 ppm is found for the related
dimesitylfluoroborane 22. The 19F signal for the fluorines
bound to boron in ArBF2ؒOEt2 occurs at Ϫ145.9 ppm, at
significantly lower frequency than those reported for other
arylboron difluorides.15 This difference probably arises from the
† Electronic supplementary information (ESI) available: rotatable 3-D
molecular structure diagrams of experimental structures of 2, 8, 16, 17
and 22 and of HF/6-31G* optimised geometries in CHIME format and
tables of data for the HF/6-31G* optimized geometries. See http://
www.rsc.org/suppdata/dt/b3/b309820f/
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 4 3 9 5 – 4 4 0 5
4395

View Article Online
Scheme 1
electron-withdrawing nature of the Ar group, resulting in
thus energetically favourable for exchange to occur, by Ϫ34 kJ
stronger coordination of Et2O, as confirmed by the 11B NMR
shift of Ϫ2.4 ppm. For the similar compound (C6F5)2BFؒOEt2,
a 19F signal at Ϫ150.0 ppm for the fluorine bound to boron and
an 11B shift of 12.4 ppm have been reported.16 Very recently,
dimethyl[8-(difluoroborolyl)naphthalen-1-yl]amine was found
to show clear evidence for formation of an intramolecular ‘ate’-
molϪ1. A similar explanation has been proposed for the observ-
ation of F/Cl exchange in Ar, ArЈ and ArЉ silicon derivatives,
but not in their germanium or tin analogues.18 This cannot be
the full explanation, however, since similar thermodynamic
considerations would apply to a reaction between ArH and
BCl3, where no exchange was detected. It seems probable that a
two-stage process is involved. Coordination of the aromatic
group to boron brings at least one fluorine from a CF3 group
into close proximity to B, as noted in the crystal structures
described below, thus facilitating an intramolecular exchange
between F on C and Cl on B. This exchange would generate a
species with a –CF2Cl group in the ortho-position of the
aromatic moiety, which is not observed in the isolated product.
An intermolecular exchange is now possible, however, between
Ar2BCl and the intramolecular exchange product, similar to
that seen between BCl3ؒOEt2 and BF3ؒOEt2, which is known to
be facile,14 thus allowing the formation of Ar2BF.
complex by donation from N to B of the BF2 group, with an 11
B
NMR shift of 10 ppm, and a 19F shift of Ϫ149 ppm.17
The presence of ArBF2ؒOEt2 13 and Ar2BF 8 (and also the
adducts 9–11) can be explained by chlorine/fluorine exchange
while the reaction is taking place. This phenomenon has also
been observed in the reaction of ArLi with SiCl4.4,18 The only
source of fluorine atoms in the solution is the CF3 groups in the
ArLi compound. No F/Cl exchange between ArH and BCl3 was
found, even after refluxing for 2 h, indicating that exchange
does not take place until the aryl group is attached to Li or B.
The driving force for this exchange may arise from the relative
bond energies. The sum of a C–F and a B–Cl bond energy term
(taken from data for the halides19) is Ϫ929 kJ molϪ1, while that
for a B–F and a C–Cl bond energy term is Ϫ963 kJ molϪ1. It is
The known11,12 boronic acid Ar2B(OH) 2 was obtained by
slow hydrolysis of Ar2BF 8. The structure of the hydroxy-
compound 2 was ascertained by single-crystal X-ray diffrac-
D a l t o n T r a n s . , 2 0 0 3 , 4 3 9 5 – 4 4 0 5
4396

View Article Online
Scheme 2
Scheme 3
tion. Facile hydrolysis of ArBCl2 7 to ArB(OH)2 12 was
observed. 19F and 11B NMR data for these Ar derivatives are
included in Table 1. The 11B resonance becomes more shielded
on replacing an aryl group with a chlorine atom, and even more
so with hydroxy or fluorine substituents, due to increasing π
back donation into the vacant orbital on the three-coordinate
boron atom.20
Reaction of ArЈLi/ArЉLi with BCl3. A solution containing a
mixture of ArЈLi/ArЉLi, obtained from lithiation of 1,3-bis-
(trifluoromethyl)benzene ArЈH, was added to excess of a BCl3
solution in diethyl ether. The 19F and 11B NMR spectra (Table
1) indicated new compounds in solution ArЈBCl2 14 and
ArЈ2BF 15, identified by comparison with the closely related
D a l t o n T r a n s . , 2 0 0 3 , 4 3 9 5 – 4 4 0 5
4397

View Article Online
Scheme 4
compounds ArBCl2 7 and Ar2BF 8, respectively. Another new
compound ArЉ3B 16 and the known species BFCl2ؒOEt2 9,
BF2ClؒOEt2 10 and BF3ؒOEt2 11 (Table 1) were also observed
(Scheme 4). The new compounds 14–16 were separated by
distillation under reduced pressure.
With an excess of ArЈLi/ArЉLi, products 14, 15 and 16 were
again identified in solution, together with the adduct ArЉ2BFؒ
OEt2 20 (Scheme 5, Table 1). The halogen-exchanged derivatives
of BCl3ؒOEt2 were not detected. Hydrolysis of ArЈBCl2 14 in
air gave rise to the formation of ArЈB(OH)2 17 crystals, which
were studied by single-crystal X-ray diffraction. Hydrolysis of
ArЈ2BF with H2O in ether led eventually to ArЈ2B(OH) 19, via
an intermediate 18 retaining a B–F bond according to the
NMR spectra. Comparison of the 19F and 11B NMR shifts with
theoretical calculations, as discussed below, suggests that this
intermediate 18 is probably ArЈ2BFؒ(OH2), although the
anionic species [ArЈ2BF(OH)]Ϫ cannot be entirely discounted
on the basis of the results.
The 19F NMR spectrum of ArЉ3B 16 consisted of a singlet at
Ϫ56.6 ppm (9F, o-CF3) and a singlet at Ϫ63.8 ppm (9F, p-CF3)
ppm. In order to investigate the rotation of the ring with respect
to the B–C bond, 19F NMR spectra of ArЉ3B were recorded in
toluene-d8 between 90 and Ϫ80 ЊC (Fig. 1). No changes were
observed until Ϫ40 ЊC, where a new set of signals started to
appear. The spectrum at Ϫ80 ЊC showed signals corresponding
to two conformations of ArЉ3B (Fig. 2), i.e. two singlets at Ϫ56.6
and Ϫ63.8 ppm, and two singlets at Ϫ56.2 and Ϫ62.2 ppm, in
an overall 5.5 : 1 ratio. At this temperature, by comparison with
the variable temperature 19F NMR results for (2-CF3C6H5)3B,21
where two signals were only detected at Ϫ100 ЊC in a 0.7 : 1
ratio, it is clear that both conformations A and B exist in solu-
tion, although one of these is dominant. The crystal structure
Fig. 1 Variable-temperature 19F NMR spectra of ArЉ3B 16
determined at Ϫ153 ЊC, discussed in more detail below, shows
that the molecule is in conformation B, unlike (2-CF3C6H4)3B
which is in conformation A from single-crystal X-ray diffrac-
tion at Ϫ80 ЊC.21 It is thus probable that B is the preferred
conformation of 16 at Ϫ80 ЊC. Theoretical calculations
described below indicate that there is only a very small energy
difference between conformations A and B, with B being
slightly more stable in each case, thus providing a reasonable
D a l t o n T r a n s . , 2 0 0 3 , 4 3 9 5 – 4 4 0 5
4398

View Article Online
Scheme 5
Fig. 2 Different conformations for ArЉ3B 16
explanation for the low-temperature results. Unfortunately,
because of solvent limitations, we were unable to extend these
studies to lower temperatures, where further restriction of
rotation would be expected, giving rise to two sets of signals in
a 2 : 1 ratio from conformation B.
Fig. 4 Molecular geometry of Ar2BF 8.
X-Ray crystallography
Single-crystal X-ray diffraction studies were carried out at
120 K for compounds Ar2B(OH) 2, Ar2BF 8, ArЉ3B 16, and
Mes2BF 22, and at 100 K for ArЈB(OH)2 17. Their molecular
structures are illustrated sequentially in Figs. 3–7, respectively.
Selected bond distances and angles are listed in Table 2.
Rotational disorder was found for the para-CF3 group in Ar2BF
Fig. 5 Molecular geometry of ArЉ3B 16.
and Ar2B(OH), as is often observed in compounds containing
these ligands.3,5,18,22
The structure of Ar2B(OH) 2 at 200 K has been determined
previously by Fraenk et al in the 1 : 1 complex of Ar2BN3 and
Ar2BOH 6.12 Their results are very similar to those obtained at
120 K for 2 in the present work. The O(1)–B(1)–C(21) angle is
112.65(13)Њ at 120 K, whereas O(1)–B(1)–C(11) is 121.62(14)Њ.
Fig. 3 Molecular geometry of Ar2B(OH) 2 (atomic displacement
ellipsoids in this and the following Figures are drawn at the 50%
probability level).
D a l t o n T r a n s . , 2 0 0 3 , 4 3 9 5 – 4 4 0 5
4399

View Article Online
Fig. 6 Molecular geometry of ArЈB(OH)2 17. The hydrogens of the
–OH groups are disordered over two positions with ca. 50% occupancy.
Fig. 7 Molecular geometry of Mes2BF 22
An intramolecular OH ؒ ؒ ؒ F bridge is found between the
hydrogen atom of the OH group and one fluorine atom of a
CF3 group (Fig. 3). The OH distance is 0.78(2) Å, while the
H(1) ؒ ؒ ؒ F(13) and H(1) ؒ ؒ ؒ F(12) distances are 2.184(24) and
2.731(23) Å, respectively. The B–C distances in 2 and 8 are
similar to those in the 1 : 1 Ar2BN3ؒAr2B(OH) complex
(1.620(6) and 1.599(7) Å for the two Ar2B components).12 C–B–
C angles in 2 and 8 (125.73(13) and 128.5(2)Њ, respectively) are
similar to that found in Mes2B(OH),23 and larger than the ones
of 123.1(2)Њ in 2,6-(F2C6H3)2BCl12 and of 123.3(4)Њ in
(C6F5)2BCl.24 This is due to the presence of a bulky group such
as CF3 or CH3 in the ortho position.
Comparison between Ar2BF 8 (Fig. 4) and Mes2BF 22
(Fig. 7) shows that the C–B–C angles are similar, reflecting
similar steric bulk for Ar and Mes groups. The B–C distances,
however, are approximately 0.02 Å longer and the B–F distance
is ca. 0.03 Å shorter in Ar2BF than the corresponding bond
lengths in Mes2BF. This is presumably due to reduction of the
electron density on the boron atom by the electron-withdraw-
ing Ar groups, thus increasing the π back-donation from the
fluorine atom.
A compound containing three ArЉ ligands, ArЉ3B 16, has
been structurally characterised for the first time (Fig. 5). Like
(2-CF3C6H4)3B,21 the triaryl compound ArЉ3B exists in a propel-
ler-like geometry, with the three aryl groups twisted out of the
plane defined by the three carbons attached to boron. The three
rings are twisted by 46.7, 53.7 and 68.9Њ towards the reference
plane made by the three carbons bonded to the boron atom,
C(11), C(21) and C(31). These angles are larger than those
observed in triphenylborane (28.3Њ)25 and [(3,5-CF3)2C6H3]3B
(33.3–38.3Њ),26 but are similar to those in (2-CF3C6H4)3B (40Њ–
55Њ)21 and trimesitylborane Mes3B (40–60Њ),27 reflecting the
steric size of the ortho-substituents. The molecular structure of
16 (Fig. 5) shows that it is in the more stable conformation B
(Fig. 2), unlike (2-CF3C6H4)3B which has conformation A. The
C–B–C angles in 16 are 117.6(2), 117.0(2) and 124.7(2)Њ,
respectively, for C(11)–B(1)–C(21), C(21)–B(1)–C(31) and
D a l t o n T r a n s . , 2 0 0 3 , 4 3 9 5 – 4 4 0 5
4400

View Article Online
Table 3 Short B ؒ ؒ ؒ F contacts (Å)
Ar2B(OH) 2
Ar2BF 8
ArЉ3B 16
ArЈB(OH)2 17
B–F
No. of contacts
No. of ortho-fluorines
2.829–2.914
4
12
2.763–2.796
4
12
2.800–2.815
3
9
2.622–2.634
2
6
C(1)–B(1)–C(31), a distorted trigonal planar geometry of the
boron atom. The bond angles at C(11), C(21), and C(31) reveal
a significant bending deformation, for example C(12)–C(11)–
B(1) 126.7(2)Њ and C(16)–C(11)–B(1) 116.8(2)Њ. These signifi-
cant values are due to close packing between two molecules of
16 in the crystal. There is no such distortion in the reported
X-ray structure of (2-CF3C6H4)3B.21
depends on the number of trifluoromethyl groups in the ortho
position. B ؒ ؒ ؒ F contacts are shorter in compounds contain-
ing only one aryl ring (Table 3). In Ar2B(OH) the range of
values is somewhat broader, probably because of the F ؒ ؒ ؒ H
interaction mentioned above.
Computations
The B–O distances in ArЈB(OH)2 17 (Fig. 6) are similar to
those in the crystal structure of 2,6-F2C6H3B(OH)2, with values
of 1.355(2) and 1.360(2) Å in 17, 1.341(4) and 1.351(4) Å in the
difluoro compound,27 and 1.34(3) and 1.35(3) Å in 3,5-(CF3)2-
C6H3B(OH)2, H-bonded in a complex with a carboxylate
anion.28 The angles around boron are close to trigonal in both
ArЈB(OH)2, ranging from 118.15(14) to 121.03(14)Њ, and
2,6-F2C6H3B(OH)2 (118.1(2) to 122.5(2)Њ),27 showing that the
presence of just one ArЈ group has little effect on the stereo-
chemistry. The B–C distance of 1.597(2) Å in ArЈB(OH)2 17 is
slightly longer than the B–C bond length of 1.578(4) Å reported
in 2,6-F2C6H3B(OH)2,27 and that of 1.56(2) Å in the 3,5-
(CF3)2C6H3B(OH)2 complex.28 The hydrogens of the –OH
groups appear to be disordered over two positions (Fig. 6), with
approximately 50% occupancy of each site. Intermolecular
hydrogen bonding in the crystal of ArЈB(OH)2 17 implies
that, if a particular hydrogen occupies one such position, this
fixes the positions of the three hydroxyl hydrogens forming a
repeating unit, as shown by the dotted lines in Fig. 8. While
the pattern is not necessarily the same in the next dotted rect-
angle, there will be a preference for the same orientation,
resulting from electrostatics, and giving a symmetrical repeating
unit. The O(1) ؒ ؒ ؒ H ؒ ؒ ؒ O(1Ј), O(2) ؒ ؒ ؒ H ؒ ؒ ؒ O(2Ј) and
O(1) ؒ ؒ ؒ H ؒ ؒ ؒ O(2) (intermolecular) distances are 2.7508(25),
2.7532(25) and 2.6801(16) Å, respectively. Similar hydrogen
bonding has been reported for the complex containing the
boronic acid 3,5-(CF3)2C6H3B(OH)2 and a carboxylate anion,
with O ؒ ؒ ؒ H ؒ ؒ ؒ O distances of 2.67(2) and 2.64(2) Å.28
A series of ab initio calculations has been performed to provide
optimised gas-phase structures and NMR shift data for the
boron compounds made here. Use of the computationally
intensive MP2/6-31G* level of theory gave excellent agreements
between observed and optimised geometries for Mes2BF (see
Table S1, ESI† for details). Removal of the para-methyl group
did not significantly affect the geometry around the boron atom
or the calculated boron shifts. The lower level of theory, HF/
6-31G*, gave reasonable agreements between observed and
computational data for Mes2BF. Since there is little justification
in using the MP2/6-31G* level of theory here, calculations were
carried out at the HF/6-31G* level of theory for the com-
pounds described. Selected parameters for the optimised and
experimental geometries of the compounds structurally charac-
terised in this work are also listed in the ESI. The agreement
between computed and optimised geometries is very good. As
shown from X-ray crystallography, short B ؒ ؒ ؒ F contacts are
found. The optimised geometry of ArЈB(OH)2 also shows the
presence of an intramolecular F ؒ ؒ ؒ H bridge.
Both conformations (A and B) of ArЉ3B were optimised at
HF/6-31G*, with B found to be lower in energy than A by ca. 4
kJ molϪ1. This energy difference is substantially less than 15.5
kJ molϪ1 reported21 for the closely related (2-CF3C6H4)3B using
the AM1 level of theory. The latter borane – a model for ArЉ3B
– was computed at the HF/6-31G* level of theory here to give
more realistic energy values. Conformation B is 2 kJ molϪ1
lower in energy than A in (2-CF3C6H4)3B and the rotational
barrier between A and B is 28.9 kJ molϪ1 with respect to B. The
rotational barrier between the two enantiomers of B is 16.8 kJ
molϪ1. All these calculated values at the ab initio level are in
good agreement with the observed 19F NMR data at low tem-
peratures for (2-CF3C6H4)3B and ArЉ3B. It is therefore not
surprising to find either conformation (A or B) in the solid-state
for (2-CF3C6H4)3B and ArЉ3B, considering the very similar
energies computed for both conformations.
Since good agreement is found between computed and
experimental geometries, geometries for compounds not struc-
turally determined in this work were also optimised at the HF/
6-31G* level of theory. The boron environments in optimised
geometries for ArB(OH)2, ArЈ2BF and ArЈ2BOH are virtually
identical to those in ArЈB(OH)2, Ar2BF and Ar2BOH, respect-
ively, showing the para-CF3 group to have little effect on the
environment surrounding the boron atom. The neutral chlor-
ides, ArBCl2 and ArЈBCl2, have similar parameters to those
found in ArB(OH)2 and ArЈB(OH)2.
Selected parameters from optimised geometries of the
adducts, ArBF2ؒOEt2, ArЈ2BFؒOH2, ArЉ2BFؒOEt2 and BFx-
Cl3-xؒOEt2 are shown in the ESI.† The adducts all have four-
coordinate boron with similar boron environments. There are
only two reported examples of arylborane ether adducts struc-
turally characteried, namely Ph3BؒTHF29 and Ph2BClؒTHF.30
Since they are four-coordinate boron compounds, the accuracy
of the HF/6-31G* level of theory was examined by comparing
the optimised geometry with the X-ray data for Ph2BClؒTHF. It
is clear from the results that the agreement is poor with respect
Fig. 8 Repeating pattern via hydrogen bonds in crystal of ArЈB-
(OH)2 17
As often described for compounds containing Ar, ArЈ or ArЉ
groups,18,21,22 short contacts between the central atom and some
fluorine atoms of the o-CF3 substituents are apparent (Table 3).
These compare well with B ؒ ؒ ؒ F contact distances of 2.845(3),
2.816(4) and 2.763(3) Å in (2-CF3C6H4)3B, even with different
conformations of the compounds.21 The number of contacts
D a l t o n T r a n s . , 2 0 0 3 , 4 3 9 5 – 4 4 0 5
4401

View Article Online
to the B–O bond length. It is known that the geometries of
boron adducts in the gas phase differ considerably from geom-
etries in the solid state, particularly for the bond distances
between the boron atom and the Lewis base.31 The optimised
geometries for the adducts made here are therefore expected
in the gas-phase and in solution. A different level of theory
such as the self-consistent reaction field would be needed for
probable solid-state geometries of these adducts.32 Reported
optimised geometries of BF3ؒOMe2 and BCl3ؒOMe2 at ab initio
levels are in good agreement with BF3ؒOEt2 and BCl3ؒOEt2
geometries here.33 The B–O bond distances shorten on going
from BF3ؒOEt2, BF2ClؒOEt2, BFCl2ؒOEt2 to BCl3ؒOEt2 as
expected from the ligand close-packing theory.34 Fig. 9 shows
an optimised geometry for the adduct ArBF2ؒOEt2 at the HF/
6-31G* level of theory.
Chemical shifts were measured relative to external CFCl3 (19F)
or BF3ؒEt2O (11B), with the higher frequency direction taken as
positive. Mass spectra for isolated samples were recorded on a
VG Micromass 7070E instrument under EI conditions at 70 eV
and for impure samples on a Fisons VG Trio 1000 mass
spectrometer coupled directly to a Hewlett Packard 5890 Series
II gas chromatograph (Column: HP-1; 25 m; 0.25 mm I.D.; 0.32
µm film thickness). Mes2BF was synthesised according to the
literature.13
Synthesis of ArBCl2 7 and Ar2BF 8. A solution of ArLi was
prepared by adding BuLi (28 ml, 1.6 M in hexanes, 44.8 mmol)
dropwise to a stirred solution of ArH (12.8 g, 45.4 mmol) in 100
ml of Et2O at Ϫ78 ЊC and leaving the mixture to warm to room
temperature for 5 h. Fluorine NMR spectroscopy on a sample
of the solution revealed two peaks corresponding to ArLi at
Ϫ62.6 (o-CF3) and Ϫ62.8 (p-CF3) ppm, and a small peak at
Ϫ63.7 ppm assigned to ArH. To the yellow ArLi solution was
added dropwise via cannula a BCl3 solution (100 ml, 1 M in
heptane, 100 mmol) in diethyl ether (50 ml) at Ϫ78 ЊC. The
reaction mixture was allowed to warm to room temperature for
6 h with stirring, leaving a yellow solution and a white precipi-
tate. The solution was then filtered and solvents were removed
in vacuo, leaving a yellow oil and a white solid. This mixture was
vacuum distilled at 60 ЊC/0.05 Torr to give a fraction containing
ArBCl2 7 (0.8 g, 5% yield) and the adducts BFxCl3ϪxؒOEt2
(2.6 g). The residue was then sublimed at 95 ЊC under vacuum
to give a white solid identified as Ar2BF 8 (3.2 g, 24% yield).
Crystals of Ar2BF were obtained by recrystallisation from
dichloromethane.
Fig. 9 Optimised molecular geometry for the adduct ArBF2ؒOEt2 13.
1
2
ArBCl2: H NMR: 8.07 (s) ppm. 13C NMR: 134.6 (q, JC–F
2
3
Computed boron and fluorine NMR shifts generated from
the optimized geometries for all compounds synthesised here
are listed in Table 1. These values are in acceptable agree-
ment with observed shifts, apart from the B–F fluorine shifts
for ArЈ2BFؒOH2 and ArЉ2BFؒOEt2. A related derivative (C6F5)2-
BFؒOEt2 was subjected to computations, in order to see
whether the presence of two aryl groups in an adduct would
give poor computed 19F shifts. The calculated shifts were Ϫ149
(o-CF), Ϫ154 (BF), Ϫ170 (p-CF), Ϫ186 ppm (m-CF) for 19F
and 13.0 ppm for 11B, in good agreement with reported data
(Ϫ134 (o-CF), Ϫ150 (BF), Ϫ155 (p-CF), Ϫ163 ppm (m-CF) for
19F and 12.4 ppm for 11B).16 Selected parameters for the opti-
mized geometry of (C6F5)2BFؒOEt2 are also shown in Table S2
(ESI†). Possible alternatives to ArЈ2BFؒOH2 and ArЉ2BFؒOEt2
such as ArЈ2BFOHϪ anion and ArЉBClFؒOEt2, respectively,
were also examined by computations, and neither gave signifi-
cantly better agreement in the NMR shifts. At present, identifi-
cation of ArЈ2BFؒOH2 and ArЉ2BFؒOEt2, with the four groups
attached to boron in these adducts collectively very bulky, is
tentative.
35.1 Hz), 132.7 (q, JC–F 32.7 Hz), 125.6 (septet, JC–F 3.0 Hz,
1
1
CH), 123.0 (q, JC–F 273.8 Hz), 122.7 (q, JC–F 274.2 Hz) ppm.
GC-MS: m/z 362 (M, calc. for C9H2F9BCl2: 362, with expected
pattern at 361–364 from 10B, 11B, 35Cl and 37Cl isotopes), 327
(M Ϫ Cl).
Ar2BF: 1H NMR: 8.17 (s) ppm. 13C NMR: 137.2 (q,
2JC–F 38.0 Hz), 134.5 (q, JC–F 34.4 Hz), 134.1 (CB), 126.6
2
3
1
(septet, JC–F 3.0 Hz, CH), 122.8 (q, JC–F 275.2 Hz), 122.3 (q,
1JC–F 273.0 Hz) ppm. EI-MS: m/z – (M, calc. for C18H4F19B
592), 573 (M–F, pattern at 572–574 from 10B, 11B and 13C), 505
(M Ϫ CF4 ϩ H).
Synthesis of ArЈBCl2 14, ArЈ2BF 15 and ArЉ3B 16. A solution
of ArЈ/ArЉLi was generated by adding BuLi (28 ml, 1.6 M in
hexanes, 44.8 mmol) dropwise to a stirred solution of ArЈH
(10.5 g, 49.1 mmol) in 100 ml of Et2O at Ϫ78 ЊC and left to
warm to room temperature for 4 h. Fluorine NMR spectro-
scopy on a sample of the solution revealed two peaks corre-
sponding to ArЉLi at Ϫ61.9 (o-CF3) and Ϫ62.8 (p-CF3) ppm, a
peak corresponding to ArЈLi at Ϫ62.1 ppm and a small peak at
Ϫ63.7 ppm assigned to ArЈH. The 19F peak integrals indicate
the solution to contain a ArЈLi : ArЉLi ratio of 3 : 4. To the dark
brown solution of ArЈ/ArЉLi was added dropwise via cannula, a
solution of BCl3 (100 ml, 1 M in heptane, 100 mmol) in Et2O
(50 ml) at Ϫ78 ЊC. The reaction mixture was allowed to warm to
room temperature for 3 h, leaving a brown solution and a white
precipitate. The solution was filtered and the solvents removed
in vacuo, leaving a brown oil, which was distilled under reduced
pressure (0.05 Torr). A fraction containing ArЈBCl2 14 (1.8 g,
14% yield) and the adducts BFxCl3ϪxؒOEt2 (3.2 g) was collected
at 48 ЊC. A second colourless fraction was collected at 92 ЊC and
identified as ArЈ2BF 15 (0.5 g, 5% yield). The white solid
remained in the flask was sublimed under vacuum at 120 ЊC,
affording ArЉ3B 16 as a white crystalline solid (1.6 g, 17% yield).
A crystal of ArЉ3B suitable for X-ray study was obtained by
recrystallization from hexane.
Experimental
All manipulations, including NMR sample preparation, were
carried out either under an inert atmosphere of dry nitrogen or
in vacuo, using standard Schlenk procedures or in a glovebox.
Chemicals of the best available commercial grades were used, in
general without further purification. 19F NMR spectra were
recorded on Varian Mercury 200, Varian VXR 400, or Varian
Inova 500 Fourier-transform spectrometers at 188.18, 376.35,
and 470.26 MHz, respectively. 11B NMR spectra were recorded
on the Varian Mercury 300 or Varian Inova 500 spectrometers
at 96.22 and 160.35 MHz, respectively. 1H and 13C NMR
spectra were recorded on the Varian VXR 400 instrument at
400 and 100.57 MHz, respectively, for ArЉ3B only. Ambient-
temperature NMR spectra were obtained using CDCl3 as sol-
vent for isolated compounds; the NMR spectra of reaction
mixtures were recorded in the solvent(s) used for the reac-
tion, with a little CDCl3 added to provide the deuterium lock.
1
ArЈBCl2: H NMR: 7.88 (d, JHH 7.8 Hz, 2H), 7.73 (t, JHH
7.8 Hz, 1H) ppm. 13C NMR: 132.7 (q, 2JC–F 33.0 Hz), 130.8 (s,
CH), 129.5 (q, 3JC–F 2.9 Hz, CH), 123.7 (q, 1JC–F 272.7 Hz) ppm.
D a l t o n T r a n s . , 2 0 0 3 , 4 3 9 5 – 4 4 0 5
4402

View Article Online
Table 4 Crystal data and structure refinement parameters
ArЈ2B(OH) 2
Ar2BF 8
ArЉ3B 16
ArЈB(OH)2 17
Mes2BF 22
Empirical formula
Mr
Crystal system
Space group
Crystal size/mm
T/K
C18H5BF18O
590.03
C18H4BF19
592.02
Monoclinic
P21/n
0.20 × 0.20 × 0.05
120(2)
C24H9BF18
650.12
C8H5BF6O2
257.93
Orthorhombic
P21212
0.43 × 0.20 × 0.10
100(2)
C18H22BF
268.17
Monoclinic
P21/c
0.30 × 0.22 × 0.20
120(2)
Triclinic
Triclinic
¯
¯
P1
P1
0.38 × 0.24 × 0.18
120(2)
0.50 × 0.20 × 0.10
120(2)
a/Å
b/Å
c/Å
α/Њ
9.1587(3)
10.1298(3)
12.5200(4)
112.5700(10)
99.9530(10)
102.5760(10)
1003.60(5)
2
8.9564(6)
9.4751(6)
23.6514(15)
90
98.494(1)
90
1985.1(2)
4
1.981
10.1795(7)
11.0533(8)
11.4719(8)
94.9440(10)
108.3620(10)
94.5490(10)
1212.75(15)
2
14.0859(14)
14.4620(14)
5.0028(5)
90
90
90
1019.12(17)
4
1.681
8.2080(5)
7.8003(5)
24.0891(16)
90
90.3380(10)
90
1542.27(17)
4
1.155
β/Њ
γ/Њ
V/Å3
Z
Dc/g cmϪ3
1.953
0.234
1.78
0.200
µ/mmϪ1
0.241
0.187
0.072
Rint
0.0274
3844
0.0359
0.0447
0.0914
0.0981
1.022
386
0.0736
2748
0.0469
0.0982
0.0924
0.1113
1.026
0.0365
3840
0.0528
0.0741
0.1255
0.1362
1.057
388
0.0283
2209
0.0305
0.0333
0.0717
0.0735
1.122
169
0.0388
2719
0.0528
0.0795
0.1274
0.1418
1.025
269
Observed data [I > 2σ(I )]
R1 index [I > 2σ(I )]
R1 index (all data)
wR2 index [I > 2σ(I )]
wR2 index (all data)
Goodness of fit (S)
No. of variables
381
GC-MS: m/z 294 (M, calc. for C8H3F6BCl2 294), 259 (M Ϫ Cl,
isotope pattern at 258–261).
Reaction of BCl3 with excess ArLi. A solution of ArLi was
made by adding BuLi (28 ml, 1.6 M in hexanes, 44.8 mmol)
dropwise to a stirred solution of ArH (12.8 g, 45.4 mmol) in 100
ml of Et2O at Ϫ78 ЊC and left to warm to room temperature
overnight. The light brown solution was slowly treated with
BCl3 (6 ml, 1 M in heptane, 6 mmol) at Ϫ78 ЊC, and left to
warm to room temperature for 1 h. Fluorine and boron NMR
spectra were obtained from a sample of the reaction mixture
which showed ArBF2ؒOEt2 to be the major product. Ar2BF and
a substantial amount of unreacted ArLi were also present. To
the reaction mixture was then added a further 6 ml of BCl3
(1 M in heptane, 6 mmol) at Ϫ78 ЊC. After warming the mixture
to room temperature, 19F and 11B NMR data on an aliquot of
the solution gave Ar2BF as the major component and ArBF2ؒ
OEt2 as the only other significant compound. On removing the
ether and heptane in vacuo, the residue contained a yellow oil
and a white solid. NMR data on the yellow oil revealed Ar2BF
but no ArBF2ؒOEt2. It is presumed the latter adduct dissociated
into ArBF2 and Et2O on removing the ether in vacuo. Vacuum
sublimation of the residue at 93 ЊC gave a white solid identified
as Ar2BF (3.3 g, 46% yield).
ArЈ2BF: 1H NMR: 7.97 (d, JHH 8.0 Hz, 2H), 7.78 (t, JHH 8.0
Hz, 1H) ppm. 13C NMR: 133.7 (q, 2JC–F 34.5 Hz), 131.5 (s, CH),
3
1
129.2 (q, JC–F 3.0 Hz, CH), 123.3 (q, JC–F 275.2 Hz) ppm.
EI-MS: m/z 456 (M, calc. for C16H6F13B 456), 369 (M–CF4 ϩ
H, isotope pattern at 368–370).
ArЉ3B: 1H NMR: 8.00 (s, 1H), 7.80 (d, JHH 7.6 Hz, 1H), 7.41
(d, JHH 7.6 Hz, 1H) ppm. 13C NMR: 143.7 (CB), 135.4 (s, CH),
133.6 (q, 2JC–F 34.3 Hz), 133.5 (q, 2JC–F 33.7 Hz), 127.3 (q, 3JC–F
3
1
3.6 Hz, CH) 123.1 (septet, JC–F 3.0 Hz, CH), 123.1 (q, JC–F
1
274.5 Hz), 122.9 (q, JC–F 273.0 Hz) ppm. EI-MS: m/z 650
(M, calc. for C24H9F18B 650), 631 (M Ϫ F, isotope pattern at
630–632), 436 (M Ϫ ArЉ Ϫ H).
Synthesis of Ar2BOH 2. Distilled water (5 ml) was added
dropwise to a stirred solution of Ar2BF (0.5g, 0.85 mmol) in
ether (30 ml). The ether layer was separated and dried in vacuo
to yield a white solid Ar2BOH 2 (0.4 g, 80%). This solid was
recrystallized from dichloromethane to yield crystals suitable
for X-ray crystallography.
Ar2BOH: 1H NMR: 8.15 (CH, 4H, s), 7.87 (OH, 1H, s) ppm.
2
2
13C NMR: 138.5 (CB), 136.8 (q, JC–F 35.2 Hz), 133.4 (q, JC–F
34.4 Hz), 126.6 (septet, 3JC–F 3.0 Hz, CH), 123.0 (q, 1JC–F 275.2
Hz), 122.4 (q, 1JC–F 273.1 Hz) ppm.
Reaction of BCl3 with excess ArЈLi. A solution of ArЈ/ArЉLi
was generated by adding BuLi (28 ml, 1.6 M in hexanes, 44.8
mmol) dropwise to a stirred solution of ArЈH (10.5 g, 49.1
mmol) in 100 ml of Et2O at Ϫ78 ЊC and left to warm to room
temperature overnight. The brown solution was slowly treated
with BCl3 (6 ml, 1 M in heptane, 6 mmol) at Ϫ78 ЊC and left to
warm to room temperature for 1 h. Fluorine and boron NMR
spectra obtained from a sample of the reaction mixture
revealed ArЉ3B to be the major product. ArЉ2BFؒOEt2 and un-
reacted ArЈLi were also present. The reaction mixture was then
treated with a further 6 ml of BCl3 (1 M in heptane, 6 mmol)
at Ϫ78 ЊC. After warming the mixture to room temperature,
19F and 11B NMR data on an aliquot of the solution gave ArЉ3B
and ArЈ2BF as the major components. ArЉ2BFؒOEt2 and
ArЈBCl2 were also observed. On removing the ether and hepta-
ne in vacuo, the residue contained a yellow oil and a white solid.
NMR data on the yellow oil revealed only ArЉ3B and ArЈ2BF.
The fates of ArЉ2BFؒOEt2 and ArЈBCl2 are not clear.
Synthesis of ArЈ2BOH 19. The method for the synthesis of
Ar2BOH was also used to convert ArЈ2BF into ArЈ2BOH in a
similar yield. Fluorine and boron NMR spectra on an aliquot
of the ether layer after 30 min stirring revealed an intermediate,
presumed to be ArЈ2BFؒOH2. The NMR data for the inter-
mediate were recorded from a CDCl3 solution of ArЈ2BF with a
drop of water and two drops of ether added.
1
ArЈ2BOH: H NMR: 7.94 (d, JHH 8.0 Hz, 2H), 7.69 (t, JHH
2
8.0 Hz, 1H) ppm. 13C NMR 132.5 (q, JC–F 34.2 Hz), 130.5 (s,
CH), 129.6 (q, 3JC–F 3.7 Hz, CH), 123.6 (q, 1JC–F 275.2 Hz) ppm.
Syntheses of ArЈB(OH)2 17 and ArB(OH)2 12. A portion of
the distilled fraction containing ArЈBCl2 and the adducts
BFxCl3ϪxؒOEt2 in ether was left exposed to air. After two days,
white crystals were formed and identified by X-ray crystallo-
graphy as ArЈB(OH)2. A solid was obtained from slow exposure
to air of a sample of ArBCl2 and the adducts BFxCl3ϪxؒOEt2,
and tentatively identified by NMR as ArB(OH)2.
Crystallography. Single crystal structure determinations were
carried out from data collected at 100 or 120 K, using graphite
monochromated Mo-Kα radiation (λ = 0.71073 Å) on a Bruker
D a l t o n T r a n s . , 2 0 0 3 , 4 3 9 5 – 4 4 0 5
4403

View Article Online
J. Organomet. Chem., 1998, 550, 481; P. Espinet, S. Martín-Barrios,
SMART-CCD detector diffractometer equipped with
a
Cryostream N2 flow cooling device.35 In each case, series of
narrow ω-scans (0.3Њ) were performed at several ꢀ-settings in
such a way as to cover a sphere of data to a maximum reso-
lution between 0.70 and 0.77 Å. Cell parameters were deter-
mined and refined using the SMART software,36 and raw frame
data were integrated using the SAINT program.37 The struc-
tures were solved using direct methods and refined by full-
matrix least squares on F 2 using SHELXTL.38 Relevant param-
eters for data collection and structure solution are given in
Table 4
F. Villafañe, P. G. Jones and A. K. Fisher, Organometallics, 2000, 19,
290; A. S. Batsanov, K. B. Dillon, V. C. Gibson, J. A. K. Howard,
L. J. Sequeira and J. W. Yao, J. Organomet. Chem., 2001, 631, 18;
A. S. Batsanov, S. M. Cornet, L. A. Crowe, K. B. Dillon, R. K.
Harris, P. Hazendonk and M. D. Roden, Eur. J. Inorg. Chem., 2001,
1729.
2 K. B. Dillon, H. P. Goodwin, T. A. Straw and R. D. Chambers,
Euchem. Conf. Phosphorus, Silicon, Boron and Related Elements in
Low Coordinated States, Paris-Palaiseau, 1988.
3 K. H. Whitmire, D. Labahn, H. W. Roesky, M. Noltemeyer and
G. M. Sheldrick, J. Organomet. Chem., 1991, 402, 55.
4 J. K. Buijink, M. Noltemeyer and F. T. Edelmann, J. Fluorine Chem.,
1993, 61, 51.
CCDC reference numbers 217588–217592.
5 N. Burford, C. L. B. Macdonald, D. J. LeBlanc and T. S. Cameron,
Organometallics, 2000, 19, 152.
6 R. D. Schluter, H. S. Isom, A. H. Cowley, D. A. Atwood, R. A.
Jones, F. Olbritch, S. Corbelin and R. J. Lagow, Organometallics,
1994, 13, 4058.
See http://www.rsc.org/suppdata/dt/b3/b309820f/ for crystal-
lographic data in CIF or other electronic format.
Computational methods. All ab initio computations were
carried out with the Gaussian 98 package.39 All geometries dis-
cussed here were optimised at the HF/6-31G* level with no
symmetry constraints. Frequency calculations were computed
on these optimised geometries at the HF/6-31G* level for
imaginary frequencies; none was found for geometries where
the para CF3 group is absent. Theoretical 11B chemical shifts at
the GIAO-HF/6-31G*//HF/6-31G* level have been referenced
to B2H6 (16.6 ppm)40 and converted to the usual BF3ؒOEt2
scale: δ(11B) = 123.4 Ϫ σ(11B). For Mes2BF, the HF/6-31G*
optimised geometry in Table 4 was then optimised at the MP2/
6-31G* level of theory, and the 11B shift of 55.4 ppm was com-
puted from the MP2 optimised geometry at the GIAO-B3LYP/
6-311G* level of theory with the scale: δ(11B) = 102.84 Ϫ σ(11B).
Unlike the excellent agreements between observed and com-
puted 11B NMR shifts of fluoroboranes, computed 19F NMR
shifts have not been shown to be as accurate.41,42 Here, calcu-
lated 19F chemical shifts at the GIAO-HF/6-31G*//HF/6-31G*
level have been referenced to HF and converted to the usual
CFCl3 scale: δ(19F) = (237.7 Ϫ σ(19F))/0.911. Computed NMR
shifts (GIAO-HF/6-31G*//HF/6-31G*) for ArЉBFClؒOEt2: 11B
12.0 ppm; 19F Ϫ84 (o-CF3), Ϫ86 (p-CF3), Ϫ135 (BF) ppm; for
ArЈ2BFOHϪ: 11B 3.8 ppm; 19F Ϫ78 (CF3), Ϫ158 (BF) ppm; for
dimethyl[8-(difluoroborolyl)naphthalen-1-yl]amine: 11B 9.9
ppm; 19F Ϫ146 ppm.17 Cartesian coordinates for the optimised
geometries obtained are available in the ESI.†
7 R. D. Schluter, A. H. Cowley, D. A. Atwood, R. A. Jones, M. R.
Bond and C. J. Carrano, J. Am. Chem. Soc., 1993, 115, 2070.
8 M. Bardají, P. G. Jones, A. Laguna, A. Moracho and A. K. Fischer,
J. Organomet. Chem., 2002, 648, 1.
9 K. Ishihara, S. Ohara and H. Yamamoto, J. Org. Chem., 1996, 61,
4196.
10 K. Ishihara, M. Mouri, Q. Gao, T. Maruyama, K. Furuta and
H. Yamamoto, J. Am. Chem. Soc., 1993, 115, 11490.
11 V. C. Gibson, C. Redshaw, W. Clegg and M. R. J. Elsegood,
Polyhedron, 1997, 16, 2637.
12 W. Fraenk, T. M. Klapötke, B. Brumm, P. Mayer, H. Nöth,
H. Piotrowski and M. Suter, J. Fluorine Chem., 2001, 112, 73.
13 A. Pelter, K. Smith and H. C. Brown, Borane Reagents: Best
Synthetic Methods, Academic Press, London, 1988, p. 428.
14 K. Sasakura, Y. Terui and T. Sugasawa, Chem. Pharm. Bull., 1985,
33, 1836.
15 H. J. Frohn, H. Franke, P. Fritzen and V. V. Bardin, J. Organomet.
Chem., 2000, 598, 127.
16 R. Duchateau, S. J. Lancaster, M. Thornton-Pett and
M. Bochmann, Organometallics, 1997, 16, 4995.
17 R. L. Giles, J. A. K. Howard, L. G. F. Patrick, M. R. Probert, G. E.
Smith and A. Whiting, J. Organomet. Chem., 2003, 680, 257.
18 A. S. Batsanov, S. M. Cornet, K. B. Dillon, A. E. Goeta, A. L.
Thompson and B. Y. Xue, Dalton Trans., 2003, 2496.
19 Thermodynamical Properties of Individual Substances, ed. I. V.
Gurvich, I. V. Veits and S. B. Alcock, Hemisphere Publ. Corp.,
Washington DC, USA, 4th edn., 1991, vol. 2, pt. 1; Handbook of
Chemistry and Physics, ed. D. R. Lide, CRC Press, Boca Raton, FL,
USA, 76th edn., 1995–1996; S. S. Batsanov, Strukturnaya Khimiya,
Dialog MGU, Moscow, 2000.
20 M. E. Schwarz and L. C. Allen, J. Am. Chem. Soc., 1970, 92, 1466.
21 S. Toyota, M. Asakura, M. Oki and F. Toda, Bull. Chem. Soc. Jpn.,
2000, 73, 2357.
22 A. S. Batsanov, S. M. Cornet, K. B. Dillon, A. E. Goeta,
P. Hazendonk and A. L. Thompson, J. Chem. Soc., Dalton Trans.,
2002, 4622.
23 K. J. Weese, R. A. Bartlett, B. D. Murray, M. M. Olmstead and
P. Power, Inorg. Chem., 1987, 26, 2409.
—
Acknowledgements
We thank the EPSRC for the award of studentships (to
S. M. C., C. D. E., H. P. G., and A. L. T.), for an Advanced
Research Fellowship (to M. A. F.), and C. F. Heffernan, A. M.
Kenwright and I. P. McKeag for assistance in recording some
of the NMR spectra.
24 W. E. Piers, R. E. v. H. Spence, L. R. MacGillivray and M. J.
Zaworotko, Acta Crystallogr., Sect. C, 1995, 51, 1688.
25 W. V. Konze, B. L. Scott and G. J. Kubas, Chem. Commun., 1999,
1807.
26 J. F. Blount, P. Finocchiaro, D. Gust and K. Mislow, J. Am. Chem.
Soc., 1973, 95, 7019.
27 D. C. Bradley, I. S. Harding, A. D. Keefe, M. Motevalli and D. H.
Zheng, J.Chem. Soc., Dalton Trans., 1996, 3931.
28 M. T. Reetz, J. Huff, J. Rudolph, K. Töllner, A. Deeze and
R. Goddard, J. Am. Chem. Soc., 1994, 116, 11588.
29 W. J. Evans, J. L. Shreeve and J. W. Ziller, Acta Crystallogr., Sect. C,
1996, 52, 2571; M. Niehues, G. Erker, O. Meyer and R. Frohlich,
Organometallics, 2000, 19, 2813.
30 W. I. Cross, M. P. Lightfoot, F. S. Mair and R. G. Pritchard,
Inorg. Chem., 2000, 39, 2690.
31 K. R. Leopold, M. Canagaratna and J. A. Phillips, Acc. Chem. Res.,
1997, 30, 57.
32 H. Jiao and P. v. R. Schleyer, J. Am. Chem. Soc., 1994, 116, 7429.
33 V. Jonas, G. Frenking and M. T. Reetz, J. Am. Chem. Soc., 1994, 116,
8741.
34 B. D. Bowsell, R. J. Gillespie and G. L. Heard, Inorg. Chem., 1999,
38, 4659.
References
1 G. E. Carr, R. D. Chambers, T. F. Holmes and D. G. Parker,
J. Organomet. Chem., 1987, 325, 13; M. Scholz, H. W. Roesky,
D. Stalke, K. Keller and F. T. Edelmann, J. Organomet. Chem., 1989,
366, 73; H. Grutzmacher, H. Pritzkow and F. T. Edelmann,
Organometallics, 1991, 10, 23; S. Brooker, J. Buijink and F. T.
Edelmann, Organometallics, 1991, 10, 25; M. Abe, K. Toyota and
M. Yoshifuji, Chem Lett., 1992, 12, 259; K. B. Dillon and H. P.
Goodwin, J. Organomet. Chem., 1992, 429, 169; K. B. Dillon and
H. P. Goodwin, J. Organomet. Chem., 1994, 469, 125; F. T.
Edelmann, Comments Inorg. Chem., 1992, 12, 259; M. Belay and
F. T. Edelmann, J. Organomet. Chem., 1994, 479, C21; J.-T.
Alhemann, H. W. Roesky, M. Noltemeyer, H.-G. Schmidt, L. N.
Markovsky and Y. G. Shermolovich, J. Fluorine Chem., 1998, 87, 87;
C. Bartolomé, P. Espinet, F. Villafañe, S. Giesa, A. Martín and A. G.
Orpen, Organometallics, 1996, 15, 2019; K. B. Dillon, V. C. Gibson,
J. A. K. Howard, L. J. Sequeira and J. W. Yao, Polyhedron, 1996, 15,
4173; V. C. Gibson, C. Redshaw, L. J. Sequeira, K. B. Dillon,
W. Clegg and M. R. J. Elsegood, Chem. Commun., 1996, 2151; K. B.
Dillon, V. C. Gibson, J. A. K. Howard, C. Redshaw, L. Sequeira and
J. W. Yao, J. Organomet. Chem., 1997, 528, 179; M. G. Davidson,
K. B. Dillon, J. A. K. Howard, S. Lamb and M. D. Roden,
35 J. Cosier and A. M. Glazer, J. Appl. Crystallogr., 1986, 19, 105.
36 SMART-NT, Data Collection Software, version 5.0, Bruker
Analytical X-ray Instruments Inc., Madison, WI, 1999.
D a l t o n T r a n s . , 2 0 0 3 , 4 3 9 5 – 4 4 0 5
4404

View Article Online
37 SAINT-NT, Data Reduction Software, version 6.0, Bruker
Analytical X-ray Instruments Inc., Madison, WI, 1999.
38 SHELXTL, version 5.1, Bruker X-ray Analytical Instruments Inc.,
Madison, WI, 1999.
39 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Montgomery, Jr.,
R. E. Stratmann, J. C. Burant, S. Dapprich, J. M. Millam, A. D.
Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J. Tomasi, V. Barone,
M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo,
S. Clifford, J. Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui,
K. Morokuma, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B.
Foresman, J. Cioslowski, J. V. Ortiz, B. B. Stefanov, G. Liu,
A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R. L. Martin,
D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
C. Gonzalez, M. Challacombe, P. M. W. Gill, B. G. Johnson,
W. Chen, M. W. Wong, J. L. Andres, M. Head-Gordon, E. S.
Replogle and J. A. Pople, GAUSSIAN 98 (Revision A.9), Gaussian,
Inc., Pittsburgh, PA, 1998.
40 T. P. Onak, H. L. Landesman and R. E. Williams, J. Phys. Chem.,
1959, 63, 1533.
41 T. Onak, M. Diaz and M. Barfield, J. Am. Chem. Soc., 1995, 117,
1403.
42 M. A. Fox, R. Greatrex and D. L. Ormsby, Chem. Commun., 2002,
2052.
D a l t o n T r a n s . , 2 0 0 3 , 4 3 9 5 – 4 4 0 5
4405