Arylboron complexes of the acids Ph2C(XH)CO2H (X = O, NH)

Article abstract of DOI:10.1016/j.ica.2008.04.050

The acids Ph₂C(XH)CO₂H (X = O, NH) readily react with the triarylboron reagents BAr₃ (Ar = Ph, C₆F₅) to form the complexes [Ph₂C(O)CO₂BPh] (1) and [Ph₂C(NH₂

Full text of DOI:10.1016/j.ica.2008.04.050

Inorganica Chimica Acta 362 (2009) 509–514
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Arylboron complexes of the acids Ph2C(XH)CO2H (X = O, NH)
a
b
Abdessamad Arbaoui a, Carl Redshaw a, , David L. Hughes , Mark R.J. Elsegood
*
a School of Chemical Sciences and Pharmacy, The University of East Anglia, Norwich, NR4 7TJ, UK
b Chemistry Department, Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
The acids Ph2C(XH)CO2H (X = O, NH) readily react with the triarylboron reagents BAr3 (Ar = Ph, C6F5) to
form the complexes [Ph2C(O)CO2BPh] (1) and [Ph2C(NH2)CO2BPh2] (2), Ph2C(p-CH3C6H4)CO2H (3a) [in
the presence of Et3N the complex HNEt3[Ph2C(OH)CO2B(C6F5)3] (3b) was formed], and
[Ph2C(NH3)CO2B(C6F5)3] (4), respectively. The synthesis and crystal structures of 1–4 (synchrotron radi-
ation was necessary for 2) are reported.
Received 13 March 2008
Received in revised form 27 April 2008
Accepted 28 April 2008
Available online 13 May 2008
Ó 2008 Elsevier B.V. All rights reserved.
Keywords:
Synthesis
Arylboron
Carboxylic acids
Crystal structures
1. Introduction
The work of Baird and Mitu encouraged us to report our related
system in which the highly electrophilic B(C6F5)3 is complexed
Arylboron complexes have enjoyed considerable interest as
cocatalysts for -olefin polymerisation catalysis [1,2]. More re-
with the acids 2,20-diphenylglycine, Ph2C(NH2)CO2H, and benzilic
acid, Ph2C(OH)CO2H (also known as diphenyl glycolic acid), both
of which contain the Ph2C(X) moiety which is renowned for its
ability to produce crystalline materials. [10,11] The reaction chem-
istry of these acids with BPh3 is also reported, together with an
unexpected C–C coupling reaction between benzilic acid and the
toluene solvent.
a
cently, complexes resulting from the interaction of carboxylic acids
and organoboron reagents have attracted attention due to their
ability to act as initiators for the carbocationic polymerisation of
isobutene [3–6]. In both cases, the key feature is the formation of
weakly coordinating counteranions [2,7].
After studying the cationic polymerisation of isobutene initi-
ated by a titanium complex (Cp*TiMe3) activated by either an alco-
hol adduct of the highly electrophilic B(C6F5)3, giving active species
of the form [Cp*TiMe2][(n-CxH(2x+1)O)B(C6F5)3] (x = 18), or its car-
boxylic acid adduct, giving active species of the form [Cp*Ti-
Me2][n-CxH(2x+1)CO2(B(C6F5)3)y] (x = 17 and y = 1 or 2), Baird and
Mitu showed that adducts of B(C6F5)3 and long chain carboxylic
acids (CH3(CH2)nCO2H, n = 2–20) were able to initiate the carbocat-
ionic polymerisation of isobutene. These systems gave poly(isobu-
tene) of high molecular weight (up to 8 ꢀ 105 g molꢁ1); however,
to the best of our knowledge there are no reports concerning the
structural characterisation of such carboxylic acid adducts of
B(C6F5)3. The closest systems described are the trimethylammoni-
um acetate salts, [(CH3)4N][CH3CO2(B(C6F5)3)] and [(CH3)4N]-
[CH3CO2(B(C6F5)3)2], by Baird and Mitu [8] and a related structure
[(C6H2F3)CO2B(C6F5)2]2 reported by Chen and coworkers [9] when
investigating the reaction between B(C6F5)3 and 2,4,6-F3C6H2CO2H.
2. Results and discussion
Interaction of benzilic acid, Ph2C(OH)CO2H, with triphenylboron
afforded, following work up, a highly crystalline white solid, 1, in
good yield (ca. 60%). Rather than the formation of a Lewis adduct,
this reaction afforded a five membered ring derivative (Scheme
1.i). The synthesis of 1 was first described by Pailer and Huemer
[12]; 1 was later obtained by Paetzold et al. by reacting phenylbo-
ron dihalide and benzilic acid [13]. Single crystals of 1 suitable for a
single crystal X-ray diffraction study were grown from a saturated
solution of acetonitrile at ꢁ25 °C. The structure of 2,5,5-triphenyl-
[1,3,2]dioxaborolan-4-one 1 is given in Fig. 1, with bond lengths
and angles given in the caption.
The five membered ring formed by C(2), O(3), B(1), O(1) and
C(1) is planar within 0.03 Å; the latter also incorporates C(15)
and O(2). Unsurprisingly, 1 exhibits a trigonal planar boron with
the angle involved in the ring slightly distorted (O(3)–B(1)–O(1)
111.99(9)°).
Similar reaction of 2,20-diphenylglycine, Ph2C(NH2)CO2H, with
triphenyl boron (Scheme 1.ii) afforded a colourless crystalline solid
* Corresponding author. Tel.: +44 1603 593137; fax: +44 1603 592003.
E-mail address: Carl.Redshaw@uea.ac.uk (C. Redshaw).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.04.050

510
A. Arbaoui et al. / Inorganica Chimica Acta 362 (2009) 509–514
1715 cmꢁ1, which is comparable to resonances found for other
boroxazolidones (1716 cmꢁ1) [16].
O
In an attempt to synthesise the tris(pentafluorophenyl)boron
adduct of benzilic acid, these two reagents were refluxed in tolu-
ene in a 1:1 ratio (Scheme 2). Following work-up, crystals suitable
for X-ray determination were grown from a saturated chloroform
solution on prolonged standing at ambient temperature.
Surprisingly, instead of the expected adduct, a C–C coupling
reaction occurred to afford the product 3a almost in a quantitative
yield (>90%). Compound 3a is the result of an electrophilic aro-
matic substitution occurring regioselectively at the para position
of the toluene solvent molecule. The overall reaction involves the
loss of water.
The first step may involve the reaction between the benzilic
acid moiety and the boron reagent (or its water adduct, H3O+
[OHB(C6F5)3]ꢁ) leading to the formation of a non-isolable carbocat-
ionic species of the type [(C6F5)3(OH)B][CPh2CO2H] able to react
with the molecule of solvent at the para position selectively. Com-
pound 3a was identified spectroscopically and crystallographically
(see Supplementary material, Fig. 1).
HO
B
O
O
i) BPh3
OH
2PhH
O
1
O
H2N
B
H2N
O
ii) BPh3
OH
PhH
O
2
The synthesis of 3a was first described by Bistrzycki and Wehr-
bein [17] whereby it was obtained by refluxing benzilic acid in tol-
uene in the presence of tin tetrachloride.
Scheme 1. Conditions: toluene, reflux, 12 h; extraction in acetonitrile.
To the best of our knowledge, this is the first reported example
of Friedel/Crafts alkylation catalysed by B(C6F5)3. However, Erker
and coworkers have reported an electrophilic aromatic substitu-
tion involving B(C6F5)3 in which the triarylboron reacts with
Ph3P@CHPh to give, upon heating, [Ph3P][CH2(p-C6H4)B(C6F5)3]
[18].
To prevent this reaction and to obtain the desired addition
product, benzilic acid was initially treated with triethylamine to
form the triethyl ammonium salt, [Ph2C(OH)COO][HNEt3], which
is soluble in toluene. Further treatment with 1 equiv. of B(C6F5)3
readily afforded the desired adduct 3b in a good yield (ca. 70%).
Crystals suitable for X-ray determination were grown from aceto-
nitrile at ambient temperature. The crystal structure of 3b is pre-
sented in Fig. 3, with selected bond lengths and angles given in
the caption. The cation is disordered in two different conforma-
tions in
a ratio of ca. 82.0:18.0; the outer carbon atoms
(+HN(CH2CH3)3) are common to both conformations. The cation is
linked to the anion through an N–Hꢂ ꢂ ꢂO hydrogen bond, and the
hydroxyl group in the anion forms an intramolecular O–Hꢂ ꢂ ꢂO–C
hydrogen bond.
Fig. 1. Molecular structure of 1, indicating the atom numbering scheme. Selected
dimensions, (Å, °): B(1)–O(3) 1.3626(13), B(1)–O(1) 1.4069(14), B(1)–C(15)
1.5326(15), O(3)–B(1)–O(1) 111.99(9), O(3)–B(1)–C(15) 124.91(10), O(1)–B(1)–
C(15) 123.09 (9).
Reaction of tris(pentafluorophenyl)boron with 1 equiv. of 2,20-
diphenylglycine in refluxing toluene afforded, after work up, a
white solid in ca. 35% yield (Scheme 2). Small crystals suitable
for X-ray determination were grown from a saturated acetonitrile
solution on prolonged standing at ambient temperature. The struc-
ture of the zwitterionic species (4) obtained (Fig. 4) is similar to
that of 3b. The length of the B–O bond in 3b (1.5381(15) Å) is com-
parable to the one found in 4 (1.5308(18) Å) and in 2 (1.517(2) Å),
but significantly longer than those found in 1 (1.3630(13) and
1.4066(14) Å). The B–O bond length in 3b and 4 is also similar to
that found in [(CH3)4N][CH3CO2B(C6F5)3] (1.512(2) Å) [6] but short-
er than the one reported for C2H5CO2CH3B(C6F5)3 (1.579(2) Å) [19].
In both 3b and 4, the boron adopts a four-coordinate distorted tet-
rahedral geometry.
Zwitterion 4 exhibits intermolecular hydrogen bonds between
the ammonium moiety and the free oxygen of a neighbouring mol-
ecule. These pairs of head-to-tail N–Hꢂ ꢂ ꢂO@C hydrogen bonds give
rise to hydrogen-bonded dimers over inversion centres. There are
three acetonitrile molecules of crystallisation, two of which are
bonded to 4 through N–Hꢂ ꢂ ꢂNCCH3 hydrogen bonds. As observed
for [(CH3)4N][CH3CO2(B(C6F5)3)], the boron in 3b and 4 coordinates
the carboxylic acid moiety through the C–O oxygen rather than
through the C@O oxygen [19].
in good yield (ca. 60%). Crystals suitable for an X-ray determination
using synchrotron radiation [14,15] were obtained from a satu-
rated acetonitrile solution at ambient temperature. The structure
of 2 is presented in Fig. 2, with selected bond length and angles gi-
ven in the caption. There are two molecules of the complex and
two acetonitriles of crystallisation in the asymmetric unit.
Again, rather than a carboxylic acid adduct, the product ob-
tained is a five membered ring derivative. The boroxazolidone
derivative 2 exhibits a distorted tetrahedral geometry at the boron
centre. The B(1)–O(1) bond length is significantly longer in 2 than
in 1 (1.517(2) and 1.4069(14) Å, respectively), but this bond is
somewhat shorter than those for other reported boroxazolidones
[13] (1.528(6)–1.540(4) Å). The structure of 2 also exhibits inter-
molecular hydrogen bonding occurring between a hydrogen of
the ammonium moiety and the oxygen of the carbonyl group of
a neighbouring molecule. The second hydrogen of the ammonium
is engaged in hydrogen bonding to a molecule of acetonitrile,
resulting in an up, down, up, down pattern relative to the c axis
(see Fig. 2b). The IR spectrum of 2 displays a mC@O resonance at

A. Arbaoui et al. / Inorganica Chimica Acta 362 (2009) 509–514
511
a
b
Fig. 2. (a) Molecular structure of [Ph2C(NH2)CO2BPh2]. (b) Unit cell showing the intermolecular hydrogen bonding in 2. Selected dimensions, (Å, °): B(1)–N(1) 1.630(2), B(1)–
O(1) 1.517(2), B(1)–C(21) 1.597(2), B(1)–C(15) 1.607(2), N(1)–B(1)–O(1) 98.33(11), N(1)–B(1)–C(15) 111.38(13), O(1)–B(1)–C(21) 110.32(13), C(15)–B(1)–C(21) 116.65(13),
N(1)–C(2)–C(1) 102.25(12).
In conclusion, four arylboron complexes of the acids 2,20-
3. Experimental
diphenylglycine and benzilic acid have been synthesised and
crystallographically characterised. While BPh3 leads to borolane
and boroxazolane-type products when reacted with benzilic acid
and 2,20-diphenylglycine, respectively, the use of the highly elec-
trophilic B(C6F5)3 yields the expected carboxylic adducts. In the
case of benzilic acid, an unexpected electrophilic aromatic substi-
tution of toluene occurs. Initial deprotonation of the carboxylic
moiety of benzilic acid by triethylamine prevents this reaction.
3.1. General
All manipulations, unless otherwise stated, were carried out un-
der an atmosphere of dry nitrogen using conventional Schlenk and
cannula techniques or in a conventional nitrogen-filled glove box.
All solvents were refluxed over the appropriate drying agent, dis-
tilled and degassed prior to use. BPh3 and B(C6F5)3 were synthes-
ised using slight variations of reported literature procedures [20].
Benzilic acid and diphenylglycine were obtained commercially
Complex
4
was found to be inactive for isobutene
polymerisation.

512
A. Arbaoui et al. / Inorganica Chimica Acta 362 (2009) 509–514
a
O
OH
O
i)
HO
3a
B(C6F5)3
OH
N(C2H5)3
H
ii)
O
O
HO
B(C6F5)3
3b
O
O
O
H2N
H3N
i)
B(C6F5)3
OH
B(C6F5)3
b
4
Scheme 2. Conditions: (i) toluene, reflux, 12 h; extraction in acetonitrile; (ii)
triethylamine (1 equiv.), reflux in toluene, 12 h; extraction in acetonitrile.
Fig. 4. (a) Molecular structure of
4 indicating the atom numbering scheme.
Hydrogen atoms (except those involved in hydrogen bonds) have been omitted for
clarity. (b) Intermolecular hydrogen bonds in 4. Selected geom. (Å, °): O(1)–B(1)
1.5381(15), B(1)–C(15) 1.6463(19), B(1)–C(21) 1.6396(18), B(1)–C(27) 1.6453(18),
O(2)–H(1C0) 2.00, O(1)–B(1)–C(15) 103.13(9), O(1)–B(1)–C(21) 114.64(9), O(1)–
B(1)–C(27) 104.64(9).
400 MHz (1H), a Gemini at 300 MHz (1H) or a Bruker Avance
DPX-300 spectrometer at 300 MHz (1H) (for 11B (96 MHz) and 19F
(282 MHz) NMR). The 1H NMR spectra were calibrated against
the residual protio impurity of the deuterated solvent. Elemental
analyses were performed by the elemental analysis service of the
London Metropolitan University.
3.2. Synthesis of 2,5,5-triphenyl-[1,3,2]dioxaborolan-4-one (1)
Fig. 3. Molecular structure of 3b indicating the atom numbering scheme. Hydrogen
atoms (except those involved in hydrogen bonds) have been omitted for clarity.
Selected geom. (Å, °): B(1)–O(1) 1.5307(18), B(1)–C(15) 1.638(2), B(1)–C(21)
1.636(2), B(1)–C(27) 1.640(2), O(1)ꢂ ꢂ ꢂH(3) 1.970(18), O(3)–H(3) 0.875(18),
O(3)–H(3)ꢂ ꢂ ꢂO(1) 122.2(15), H(1)ꢂ ꢂ ꢂO(3) 2.003(19), N(1)–H(1) 0.905(19),
N(1)–H(1)ꢂ ꢂ ꢂO(3) 171.5(17), O(1)–B(1)–C(15) 113.72(11), O(1)–B(1)–C(21)
104.14(11), O(1)–B(1)–C(27) 103.01(11).
Benzilic acid (0.29 g, 1.3 mmol) and Ph3B (0.31 g, 1.3 mmol)
were refluxed in toluene (30 ml) for 12 h. Following removal of
volatiles in vacuo, the residue was extracted into acetonitrile
(30 ml) affording on prolonged standing at ꢁ25 °C colourless
prisms of 1 (0.24 g, 59%). 1H NMR (300 MHz, CDCl3) d 8.06 (d,
J = 7.5 Hz, 2H, B-oC6H5), 7.62 (m, 5H, B-pC6H5 + C(oC6H5)2), 7.50
(m, 2H, C(pC6H5)2), 7.39 ppm (m, 6H, B-mC6H5 + C(mC6H5)2); 11B
NMR (96 MHz, CDCl3) d 37.8 ppm; elemental Anal. Calc. for
C20H15BO3: C, 76.47; H, 4.81. Found: C, 76.52; H, 4.85%. MS (ES):
314.2 [M+]; IR (nujol): 1810(w), 1604(w), 1408(w), 1261(w),
1144(w), 1076(s), 1025(w), 966(w), 803(m), 766(w), 728(w),
696(w), 665(w), 650(w) cmꢁ1; m.p. 191–194 °C (decomposition).
and dried in vacuo overnight prior to use. All other chemicals were
obtained commercially and used as received. IR spectra (nujol
mulls, KBr windows) were recorded on Perkin–Elmer 577 and
457 grating spectrophotometers. NMR spectra were recorded at
room temperature on
a Varian VXR 400 S spectrometer at

A. Arbaoui et al. / Inorganica Chimica Acta 362 (2009) 509–514
513
Table 1
Crystallographic data
Compound
1
2 ꢂ MeCN
3a
3b
4 ꢂ 3MeCN
Formula
C20H15BO3
314.1
triclinic
C26H22BNO2 ꢂ C2H3N
C21H18O2
302.4
monoclinic
P21/c
C32H11BF15O3, C6H16
841.4
monoclinic
P21/n
N
C32H13BF15NO2 ꢂ 3C2H3N
Formula weight
Crystal system
Space group
Unit cell dimensions
a (Å)
432.3
862.4
triclinic
ꢀ
Pı
triclinic
ꢀ
Pı
ꢀ
Pı
8.0939(6)
10.2082(9)
10.7171(9)
108.876(8)
103.640(7)
92.182(7)
807.92(12)
2
10.4814(6)
11.6604(6)
20.4798(11)
91.2266(7)
101.0119(7)
105.8538(7)
2356.3(2)
4
12.5651(10)
7.3221(8)
17.228(3)
90
90.469(10)
90
12.1191(10)
14.0120(5)
21.6833(16)
90
104.234(7)
90
11.5724(7)
12.0663(7)
14.5752(9)
78.5139(10)
69.3732(9)
81.0457(10)
1858.48(19)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
1585.0(3)
4
3569.1(4)
4
Z
T (K)
140(1)
150(2)
140(1)
140(1)
150(2)
Radiation, k (Å)
Mo K
1.291
0.085
0.968–0.977
0.38 ꢀ 0.31 ꢀ 0.27
30
a
, 0.71073
synchrotron, 0.6911
1.219
0.076
0.977–0.999
0.31 ꢀ 0.04 ꢀ 0.02
27.5
Mo K
1.267
0.080
0.949–0.993
0.66 ꢀ 0.21 ꢀ 0.09
25
a
, 0.71073
Mo K
1.566
0.151
0.921–0.959
0.55 ꢀ 0.35 ꢀ0.28
30
a
, 0.71073
Mo Ka, 0.71073
1.541
0.148
0.852–0.983
1.12 ꢀ 0.58 ꢀ 0.12
31
Dcalc (g cmꢁ3
)
Absorption coefficient (mmꢁ1
Transmission factors
Crystal size (mm)
)
h (max) (°)
Reflections measured
13438
23713
16353
52767
22317
Unique reflections
4610
3569
11608
8006
2779
1523
10339
6547
11293
8293
Reflections with F2 > 2
r
(F2)
Rint
0.047
0.065
0.0784
0.058
0.019
Number of parameters
217
0.041
613
0.060
210
0.052
557
0.042
545
0.042
R1 [F2 > 2 (F2)]
r
R1 (all data)
0.057
0.089
0.127
0.081
0.061
wR2 (all data)
Goodness-of-fit
0.109
1.056
0.35 and ꢁ0.20
0.171
1.001
0.32 and ꢁ0.24
0.122
0.945
0.18 and ꢁ0.22
0.109
0.999
0.65 and ꢁ0.34
0.117
1.048
0.35 and ꢁ0.24
Largest difference peak and hole (e Åꢁ3
)
3.3. Synthesis of [Ph2C(NH2)CO2BPh2] (2)
(30 ml) affording on prolonged standing at room temperature col-
ourless prisms of 3b (0.83 g, 71%). 1H NMR (400 MHz, CDCl3) d 8.48
(br s, 1H, (C2H5)3NH+), 7.22–7.28 (m, 10H, C6H5), 4.26 (br s, 1H,
OH), 2.65 (m, 6H, (CH3CH2)3NH+), 1.00 ppm (m, 9H,
(CH3CH2)3NH+); 11B NMR (96 MHz, CDCl3) d 50.6 ppm; 19F NMR
(282 MHz, CDCl3) d ꢁ134.1 (o-C6F5), ꢁ160.8 (p-C6F5), ꢁ165.7 ppm
(m-C6F5); elemental Anal. Calc. for C38H27BF15NO3: C, 54.39; H,
3.69; N, 1.91. Found: C, 54.55; H, 3.54; N, 1.95%. MS (ES): 739.0
[Ph2C(OH)CO2B(C6F5)3]+; IR (nujol): 3554(m), 3163(w), 2724(m),
2668(w), 2362(w), 2338(w), 1676(m), 1646(w), 1604(w),
1517(m), 1278(w), 1261(m), 1170(w), 1159(w), 1053(w),
As for 1, but using diphenylglycine (0.70 g, 3.1 mmol) and Ph3B
(0.76 g, 3.1 mmol) affording 2 as colourless crystals (0.75 g, 62%).
1H NMR (400 MHz, CDCl3) d 7.43 (d, J = 6.2 Hz, 4H, B(o-(C6H5)2)),
7.35–7.20 (m, 16H, C6H5), 5.51 ppm (br s, 2H, NH2þ); 11B NMR
(96 MHz, CDCl3) d 55.8 ppm; elemental Anal. Calc. for C26H22BNO2:
C, 79.81; H, 5.67; N, 3.58. Found: C, 80.48; H, 5.48; N, 3.88%. MS
(ES): 391.0 [M+]; IR (nujol): 3165(w), 2724(m), 2654(w), 1715(s),
1586(m), 1261(m), 1156(m), 1022(m), 951(w), 803(w), 726(w),
697(w) cmꢁ1; m.p. 248–250 °C.
1017(w), 978(m), 808(s), 773(w), 754(w), 700(m), 665(m) cmꢁ1
;
3.4. Synthesis of Ph2C(pCH3C6H4)CO2H (3a)
m.p. 113–120 °C.
As for 1, but using benzilic acid (0.31 g, 1.4 mmol) and (C6F5)3B
(0.71 g, 1.4 mmol); recrystallisation from chloroform afforded 3a
as colourless crystals, further removal of solvent yielded 3a as a
pale yellow solid (0.38 g, 90%). 1H NMR (400 MHz, C6D6) d 10.96
(br s, 1H, COOH), 7.35 (d, J = 7.5 Hz, 4H, o-C6H5), 7.25 (d,
J = 8.2 Hz, 2H, o-C6H4CH3), 7.02 (m, 6H, m-C6H5 + p-C6H5), 6.88 (d,
J = 8.1 Hz, 2H, m-C6H4CH3), 2.03 ppm (s, 3H, CH3); elemental Anal.
Calc. for 3a ꢂ 0.9 CHCl3, C21H18O2 ꢂ 0.9(CHCl3): C, 64.19; H, 4.65.
Found: C, 64.11; H, 4.37%. MS (ES): 257.0 [MꢁCO2]+, 326.0
[M+Na]+; IR (nujol): 3161(w), 2724(m), 2660(w), 1709(w),
1605(w), 1261(m), 1169(m), 1022(w), 974(w), 813(m), 735(m)
cmꢁ1; m.p. 195–200 °C (lit. 205 °C) [14,15].
3.6. Synthesis of [Ph2C(NH3)CO2B(C6F5)3] (4)
As for 1, but using diphenylglycine (0.24 g, 1.1 mmol) and
(C6F5)3B (0.54 g, 1.1 mmol) affording 4.3CH3CN as colourless crys-
tals (0.32 g, 35%). 1H NMR (400 MHz, CDCl3) d 7.46 (t, J = 7.2 Hz, 2H,
pC6H5), 7.34 (m, 4H, mC6H5), 7.19 (d, J = 7.5 Hz, 4H, oC6H5), 7.14 (br
s, 3H, NH3þ), 2.00 ppm (s, 9H, CH3CN); 11B NMR (96 MHz, CDCl3) d
49.3 ppm; 19F NMR (282 MHz, CDCl3) d ꢁ134.3 (o-C6F5), ꢁ159.7 (p-
C6F5), ꢁ165.1 ppm (m-C6F5); elemental Anal. Calc. for 4 ꢂ 2CH3CN,
C36H19BF15N3O2: C, 52.64; H, 2.33; N, 5.12. Found: C, 52.11; H,
1.87; N, 5.33%. MS: m/z: 739.1 [M]+; IR (nujol): 3286(w),
2724(m), 2667(w), 2363(w), 2337(w), 2297(w), 2263(w),
1684(m), 1646(m), 1600(w), 1516(w), 1261(m), 980(m), 870(w),
803(s), 761(w), 731(w), 700(w) cmꢁ1; m.p. 112–116 °C.
3.5. Synthesis of HNEt3[Ph2C(OH)CO2B(C6F5)3] (3b)
Benzilic acid (0.31 g, 1.4 mmol) was dissolved in toluene
(20 ml). Triethylamine (0.19 ml, 1.4 mmol) was added slowly upon
stirring at room temperature. (C6F5)3B (0.71 g, 1.4 mmol) in tolu-
ene (10 ml) was added to the colourless solution. The mixture
was stirred for 12 h at room temperature. Following removal of
volatiles in vacuo, the residue was extracted into acetonitrile
3.7. X-ray crystallography
Measurements for compounds 1, 3a, and 3b were made on an
Oxford Diffraction Xcalibur-3 CCD diffractometer equipped with
Mo K
a
radiation and graphite monochromator. Intensity data were
- and /-scans. Data were processed using
measured by thin-slice
x

514
A. Arbaoui et al. / Inorganica Chimica Acta 362 (2009) 509–514
the CRYSALIS-CCD and -RED [21] programs. Structures were determined
by the direct methods routines in the SHELXS program [22] and re-
fined by full-matrix least-squares methods, on F2, in SHELXL [22].
Data for 2 were collected at Daresbury Laboratory Station 9.8 using
silicon 111 monochromated synchrotron radiation on a Bruker APEX
via www.ccdc.cam.ac.uk/data_request/cif. The X-ray crystal struc-
ture of 3a is described in the Supplementary data which can be
found, in the online version, at doi:10.1016/j.ica.2008.04.050.
References
2
CCD diffractometer. Data for 4 were measured on a Bruker APEX 2
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CCD diffractometer. Bruker AXS APEX 2 and SAINT, and SADABS software
were employed for data collection/processing for 2 and 4 [23,24].
See Ref. [25] for source of scattering factors. Non-H atoms were re-
fined anisotropically. Hydrogen atoms were included in idealised
positions and their Uiso values were set to ride the Ueq values of
the parent atoms except for the NH atoms in 2 and NH and OH
atoms in 3b where the coordinates were freely refined. In 2 there
are two molecules of the boron complex plus two acetonitrile mol-
ecules of crystallisation. In 4 there are three acetonitrile molecules
of crystallisation, two of which H-bond to the boron complex. In
3b, the cation was modelled as disordered with the N-bound C
atoms split over two sets of positions; major occupancy:
82.0(3)%. Crystallographic data for the five compounds examined
are collated in Table 1.
Acknowledgements
We would like to thank the National Mass Spectrometry Service
(Swansea, UK) for mass spectrometry of 1, 3b and 4, the EPSRC for
studentship to A.A. and for the award of beam-time at Daresbury
Laboratory. We also thank Dr. J. Warren at Daresbury Laboratory
for technical support.
[19] S. Mitu, M.C. Baird, Organometallics 25 (2006) 4888.
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[22] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112–122.
[23] APEX 2 and SAINT software for CCD diffractometers, Bruker AXS Inc., Madison, WI,
2006.
Appendix A. Supplementary material
[24] G.M. Sheldrick, SADABS, University of Gottingen, 2004.
[25] International Tables for X-ray Crystallography, Kluwer Academic Publishers,
Dordrecht, Vol. C, 1992.
CCDC 680053, 680054, 680055, 680056 and 680057 contain the
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre