Boron coordination compounds derived from 2-phenyl-benzimidazole and 2-phenyl-benzotriazole bidentate ligands

Article abstract of DOI:10.1016/j.jorganchem.2009.07.029

The syntheses and structural analyses of a series of boron heterocycles derived from 2-(1H-benzimidazol-2-yl)-phenylamine (1), 2-(1H-benzimidazol-2-yl)-phenol (2), 2-(1H-benzimidazol-2-yl)-benzenedisulfide (3), 2-[3-(1,1,1,3,-tetramethyl-butyl)-phenyl]-2H

Full text of DOI:10.1016/j.jorganchem.2009.07.029

Journal of Organometallic Chemistry 694 (2009) 3814–3822
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Boron coordination compounds derived from 2-phenyl-benzimidazole
and 2-phenyl-benzotriazole bidentate ligands
Adriana Esparza-Ruiz a, Adrián Peña-Hueso a, Heinrich Nöth b, Angelina Flores-Parra a,
,
*
Rosalinda Contreras a,
*
a Department of Chemistry, Cinvestav, AP 14-740, CP 07000, México DF, Mexico
b Department Chemie, Ludwig-Maximiliams Universität, Butenandt-Strasse 5-13 (Haus D), D-81377 Munich, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
The syntheses and structural analyses of a series of boron heterocycles derived from 2-(1H-benzimidazol-
2-yl)-phenylamine (1), 2-(1H-benzimidazol-2-yl)-phenol (2), 2-(1H-benzimidazol-2-yl)-benzenedisulfide
(3), 2-[3-(1,1,1,3,-tetramethyl-butyl)-phenyl]-2H-benzotriazole (4), 2-[3,5-bis-(1-methyl-1-phenylethyl)-
phenyl]-2H-benzotriazole (5) and (C6H5)2BOH or BF3ꢀOEt2 are reported. The new boron compounds:
Received 12 June 2009
Received in revised form 8 July 2009
Accepted 9 July 2009
Available online 18 July 2009
diphenyl-[2-(1H-benzimidazol-2-yl-
yl- N)-phenolate- O]-boron (7), diphenyl-[2-(1H-benzimidazol-2-yl-
(8), diphenyl-[2-(2H-benzotriazol-2-yl- N)-4-(1,1,3,3-tetramethyl-butyl)-phenolate-
diphenyl-[2-(2H-benzotriazol-2-yl- N)-4,6-(1-methyl-1-phenylethyl)-phenolate- O]-boron (10), difluoro-
[2-(1H-benzimidazol-2-yl- N)-phenolate- O]-boron (11), difluoro-[2-(2H-benzotriazol-2-yl- N)-4-
(1,1,3,3-tetramethylbutyl)-phenolate- O]-boron (12) and difluoro-[2-(2H-benzotriazol-2-yl- N)-4,
6-(1-methyl-1-phenylethyl)-phenolate- O]-boron (13) have four fused rings, with boron included in a
j
N)-phenylamide-
j
N]-boron (6), diphenyl-[2-(1H-benzimidazol-2-
N)-benzenethiolate- S]-boron
O]-boron (9),
j
j
j
j
Keywords:
Organoboron
2-Phenyl-benzimidazole
2-Phenyl-benzotriazole
Coordination compounds
11B and 19F NMR
j
j
j
j
j
j
j
j
j
j
six-membered ring and bound to N, O or S atoms and strongly coordinated by a nitrogen atom from
the imidazole or triazole rings. Their structures are zwitterionic, with a negative charge on the boron
and a delocalized positive charge on the ligand. Compounds 6–12 were studied by NMR, IR, mass spec-
trometry, and 6–10 and 12 by X-ray diffraction analyses.
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
Some of the starting ligands have been used before to prepare
coordination compounds. Ligand 1 has been widely used for the
There is considerable structural and biological interest in the
study of aromatic six-membered ring compounds containing
boron [1–4]. We have studied this kind of boron heterocycles
derived from guanidinobenzimidazole [5], uroylbenzimidazole
[6] and imidazole [7]. Herein, we report the syntheses and
structural analyses of heterocyclic compounds derived from
[BPh2]+ or [BF2]+ groups and 2-phenyl-benzimidazole and
2-phenyl-benzotriazole derivatives. The high Lewis acidity of
these boron groups make them excellent models for transition
metal coordination, with the advantage that they form diamag-
netic molecules easily analyzed by NMR techniques. The chosen
bidentate ligands were compounds 1–5, Scheme 1. Comparison
of benzimidazole and benzotriazole derivatives as coordinating
molecules is interesting because the presence of a third nitro-
gen in the triazole, rather than a carbon in the imidazole, affects
the resonance contributors and has an impact in the stability of
the new heterocycles.
preparation of a series of transition metal coordination compounds
[8,9], whereas, compound 2 has been employed as a ligand for
transition [10–13] and lanthanides metals [14]. The structural
analysis of disulfide 3 has been recently reported [15]. Compound
4 has been used in the synthesis of Re(I) compounds [16]. Deriva-
tives of compound 5 and elements of group 4 have been employed
as catalysing agents [17]. Compounds 1 and 2 have been used to
prepare phosphorus heterocycles [18,19]. Haloboron heterocycles
derived from compound 2 are known. It was proposed that two
benzimidazole ligands were coordinated to a BBrþ2 , through the
imidazole nitrogen atom, however their structural characterization
was not completed [20]. Planar diaminoboranes from ligand 1 have
been prepared [21].
2. Results and discussion
The reactions of compounds 1–5 with BPh2OH and BF3ꢀOEt
afforded the new boron compounds 6–13, which were analyzed
by NMR, IR, mass spectrometry, and 6–10 and 12 by X-ray diffrac-
tion. The reactions of 1 and 3 with BF3ꢀOEt gave a mixture of com-
pounds that were not isolated neither properly assigned, Scheme 1.
* Corresponding authors.
E-mail address: aflores@cinvestav.mx (R. Contreras).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.07.029

A. Esparza-Ruiz et al. / Journal of Organometallic Chemistry 694 (2009) 3814–3822
3815
H
N1
H
7
4
8
N
6
5
10
16
9
2
3 N
N
11
B
X
X
X
B
1
2
X = NH2
X = OH
6
7
11
NH BPh2
O
O
BPh2
BF2
H
N
H
N
N
S
S
N
B
X
N
N
8
X = S B = BPh2
H
3
R1
R2
R1
R2
N
N
N
N
N
N
B
O
HO
4
5
R1 = 1,1,3,3-tetramethyl-butyl, R2 = H
R1 = R2 = 1-methyl-1-phenylethyl
9
B = BPh2
12 B = BF2
13 B = BF2
10 B = BPh2
Scheme 1. Synthesis of boron esters 6–13 from benzimidazole 1–3 and benzotriazole ligands 4–5.
The 11B NMR analysis of compounds 6–13 indicated that (a)
the [BPh2]+ or [BF2]+ groups have substituted the labile O–H
protons of 1, 4 and 5 and the anilinic N–H of 2 and (b) that in
compound 3 the S–S bond was cleaved in order to form an RS–
B bond and probably an RS–F derivative which was not identified,
Table 1. 11B resonances of compounds 6–10 appear at lower fre-
quencies with respect to ROBPh2 (+45 ppm), RNBPh2 (+41 ppm)
or RSBPh2 (+66–67 ppm) characteristic signals [22] indicating
strong N ? B bonds. A triplet was expected in the 11B spectra
of compounds 11–13 due to the 19F coupling, however only 11
showed this coupling (d = +0.8 ppm, 1J(11B,19F) = 14.0 Hz), due to
a stronger N ? B coordination bonding in benzimidazole than
in benzotriazole. The 19F spectra of compounds 11–13 showed
two broad signals, in a 80–20 ratio, which corresponds to the
11BF2 and 10BF2 isotopic groups respectively. The 19F chemical
shifts of the benzimidazole compounds are similar to those found
for
a
BF2 derivative of 2-aminoguanidine benzimidazole
(ꢁ135.2 ppm), Scheme
2 [5]. The benzotriazole compounds
12–13 present a shift in the 19F signals to lower frequencies
(ꢁ142.0 to ꢁ144.5 ppm) with respect to the benzimidazole
derivative (ꢁ136.4 ppm) which denotes that 19F is sensitive to
the nature of the azole ring, Table 1.
1H and 13C spectra of compounds 6–9, 11–13 showed that all
atoms have different resonances indicating that the N ? B coordi-
nation bond partially stopped the tautomeric N–H or conforma-
tional equilibria characteristic of free benzimidazole or
Table 1
F
H
11B and 19F NMR data of compounds 6–13.
F
B
N
N
Compd, solvent
d
11B[1J(11B,19F)]
d(11B)-19F d(10B)-19F [isotopic effect, Hz]
NH2
N
N
+
6, CDCl3
ꢁ0.8
+3.5
ꢁ1.6
+6.7
+5.5
7, DMSO-d6
8, DMSO-d6
9, CDCl3
10, CDCl3
11, DMSO-d6
12, CDCl3
13, CDCl3
H
+0.8 triplet [14.0 Hz] ꢁ136.4 and ꢁ136.5 [16.9]
+1.0 broad
+0.6 broad
ꢁ142.0 and ꢁ141.9 [25.3]
ꢁ144.5 and ꢁ144.4 [19.8]
Scheme 2. BF2 heterocycle derived from 2-aminoguanidine benzimidazole,
d
19F = ꢁ135.2 ppm [5].

3816
A. Esparza-Ruiz et al. / Journal of Organometallic Chemistry 694 (2009) 3814–3822
Table 2
Selected 13C data for 6–9, 11.
Compounds
C8
C9
C11
6
7
8
132.6
133.5
134.9
143.2
132.3
143.0
135.7
135.3
136.1
136.8
135.0
135.2
151.6
160.8
145.5
150.0
156.6
145.0
146.6
9 (ꢁ20 °C)
11
12
13
benzotriazole. These equilibria in free ligands make the N1–N3,
CH8–CH9, CH4–CH7, and CH5–CH6 pairs equivalent, Table 2. C11
signals are shifted to higher frequencies due to the boron bonding,
(Dd from +2.7 to +9.1 ppm in 6–8). In compounds 12 and 13, the
Fig. 1. The calculated minimum energy structure for the [MꢁPh]+ fragment of
compound 7.
C11 resonance is
a triplet by the fluorine atoms coupling
[3J(13C,19F) = 2.5 (12) and 2.0 Hz (13)]. In 11 the triplet was not
completely resolved due to a small value of the coupling constant.
In the benzotriazole compounds 9, and 13, N ? B coordination
bond shifted to lower frequencies the C9 signal, whereas the C8
out of it. Fig. 6 shows the six-membered ring conformation for
compounds 6 and 8.
resonance remains characteristic of
a C–N–lone pair group,
Analysis of the bond lengths in compounds 6–10 and 12 shows
that the B–N3 bonds are in the range: 1.597(4)–1.641(3) Å, shorter
than the N–B coordination bond (1.685 Å) found in a six-mem-
bered BPh2 heterocycle, Scheme 5 [26]. The B–N16 bond length
in 6 (1.535(4) Å) is shorter than a B–N covalent bond (1.61 Å)
and the B–O16 bond length in compounds 7, 9, 10–12 varies from
1.436(4) to 1.506(3) Å whereas a reported B–O covalent bond is
(ꢂ143 ppm) [23,24]. 1H and 13C spectra of 10–12 were complex
and difficult to assign.
In order to study the dynamic behavior of 9 induced by a weak
N ? B bond, (Scheme 3) 1H, 13C and 11B NMR spectra in CDCl3 were
recorded at different temperatures between +20 and ꢁ60 °C. The
N ? B bond energy was calculated as being 55.3 kJ molꢁ1 [25].
Mass spectra of compounds 6–13 showed in all cases the molec-
ular ion. The fragmentation is interesting because each compound
lost a phenyl group or a fluorine atom to give, in almost all cases,
the base peak. The trigonal boron atom contributes to the planarity
of the fused tetracyclic planar framework. The calculated mini-
mum energy structure for the sp2 boron heterocycle in 7 is in Fig. 1.
Of interest in the reported heterocycles is the analysis of the
electronic delocalization of the fused tetracyclic system. A reso-
nance structure [coordination bond M covalent bond] could aver-
age the B–N and B–Y (Y = NH, O or S) bond lengths, Scheme 4.
The resonance contributors for the benzimidazole derivatives sug-
gest a zwitterionic structure with the borate bearing the negative
charge and a positive charge delocalized in the boron and the
phenyl rings, whereas the benzotriazole compounds delocalize
the positive charge in the benzotriazole rings. The structural data
from X-ray diffraction analyses are of interest as they may be
related to the electronic delocalization in the ligands and the
nature of the boron coordination.
1.452 Å, Scheme
5 [26] or 1.367 Å [27]. B–S bond lengths
(1.947(5) and 1.958(5) Å) in compound 8 are slightly longer than
the bond length for a tetracoordinated B–S (ꢂ1.896 Å) [27]. There-
fore we can conclude that the coordination bonds are shorter than
expected and covalent bonds are longer (with exception of 6), indi-
cating an electronic resonance in the six-membered ring, shown in
Scheme 4.
On the other hand, the lengths of C(N)2–N3, C11–Y16, with
exception of sulfur compound, and C(N)2–C10 and C10–C11 indi-
cate the positive charge delocalization in the six-membered ring,
Table 3.
The diphenylboron molecules 6–10 showed cooperative intra-
molecular interactions of C–H with
p electrons and lone pairs that
contribute to a rigid molecular framework. These interactions are
shown for compound 6, Fig. 7.
Intermolecular interactions such as N–Hꢀ ꢀ ꢀO, Hꢀ ꢀ ꢀS, C–Hꢀ ꢀ ꢀO
hydrogen bonds and p-stacking were found. In compound 6 which
cocrystallized with DMSO, a water molecule is bound to the N–H
(1.87 Å) and in turn two DMSO are linked to it, Fig. 8 (left). Com-
pound 7 which crystallized from DMSO, presents an intermolecular
hydrogen bond with the solvent, Fig. 8 (right).
The molecular structures of compounds 6–10 and 12 were
determined by X-ray diffraction analyses, Figs. 2–5. Selected bond
lengths and angles are given in Table 3.
The study showed that the boron coordination forms a six-
membered ring in a fused planar tetracycle. For compounds 6, 7,
9, 10 and 12, the boron is out of a plane formed by the other five
atoms and has one substituent in axial position. In compound 8,
there are four atoms in a plane [B–N3–C–C] with the sulfur atom
One of the two molecules found in the asymmetric unit of 8 has
a hydrogen bond between the sulfur atom and a CHCl3 molecule
(2.52 Å), which gives more sp3 character to the sulfur (C–S–B angle
103.8(3)°), Fig. 9 (left). Compound 8 presented
p-stacking interac-
tions, Fig. 9 (right) and 12 Fꢀ ꢀ ꢀH–C and C–Hꢀ ꢀ ꢀN interactions, Fig. 10.
R1
R2
R1
R2
R1
R2
R1
1
3
1
3
N
N
N
N
N
N
N
N
N
N
N
N
R
3
3
1
1
B
R
O
B
O
B
R
O
R2
B
R
O
R
R
R
R
R = Ph or F
Scheme 3. Conformational equilibrium in compound 9, produced by the opening of the N3 ? B bond, followed by N2–C10 bond rotation and N1 ? B bond formation.

A. Esparza-Ruiz et al. / Journal of Organometallic Chemistry 694 (2009) 3814–3822
3817
H
H
N
N
N
N
B
R
Y
B
R
Y
R
R
R = Ph or F
Y = N, O or S
Scheme 4. [Coordination bond M covalent bond] resonance in benzimidazole derivatives.
Fig. 2. ORTEP diagrams for 6 (left) and 7 (right).
Fig. 3. The crystal of 8 presented two enantiomeric conformations, 8a and 8b, in the asymmetric unit.
boron in BF2 being more acidic than in BPh2, produces the shortest
B ? N and B–O bonds. Mass spectra have shown that the mole-
cules lost a boron substituent in order to give a planar tetracyclic
system where the boron can obtain a sp2 hybridisation.
3. Conclusion
Compounds 1–5 act as bidentate ligands when they react with
(C6H5)2BOH or BF3. Their boron derivatives 6–13 are stable to air
and moisture due to the BPh2 and BF2 groups strong coordination.
NMR in solution and X-ray diffraction in the solid state allowed a
structural analysis of the boron heterocycles. The resulting com-
pounds are zwitterions. The boron atoms have a borate nature,
whereas the positive charge is delocalized in part of the molecule.
The benzimidazole has the strongest coordination bonds due to a
more basic nitrogen atom. The benzotriazole has a weaker nitrogen
atom due to the electronegativity of the nitrogen in position 2. The
4. Experimental
4.1. General comments
Vacuum line techniques were employed for all manipulations
of air and moisture sensitive compounds. THF was dried by
distillation from sodium-benzophenone under
a
nitrogen

3818
A. Esparza-Ruiz et al. / Journal of Organometallic Chemistry 694 (2009) 3814–3822
Fig. 4. Molecular structure of 9 (left) and 10 (right). For the clarity, hydrogen atoms are not shown.
placed. In compound 6 the other hydrogen atoms were refined,
in 7 the hydrogen atoms were found but nor refined with excep-
tion of the N–H. In compounds 8, 9 and 12 the hydrogen atoms
were found but not refined, with exception of the aromatic
hydrogen atoms that were refined. Selected bond lengths and an-
gles are presented in Table 3.
4.3. Syntheses
4.3.1. Diphenyl-[2-(1H-benzimidazol-2-yl-N)-phenolamide-N]-boron
(6): general procedure for compounds (6–10)
Using a Dean Stark trap, in a dry nitrogen atmosphere, com-
pound
1 (392 mg, 1.9 mmol) was reacted with (C6H5)2BOH
(341 mg, 1.9 mmol) in toluene (30 mL) and p-toluenesulfonic acid
(30 mg). The reaction mixture was refluxed for 6 h, and then cooled
and filtered. The solvent was evaporated in vacuum. The reaction
product is a green crystalline solid (419 mg, 60%). Mp 210 °C. IR
Fig. 5. ORTEP diagram for compound 12.
(KBr),
m
(cmꢁ1): 1626 (C@N), 1554 (C@C), 1397 (B–N). MS m/z
(%): 373(1) [M]+Å, 296(100) [MꢁC6H5]+, 218(5) [Mꢁ2C6H5]+. NMR
(CDCl3), d (ppm): 1H 12.16 (NH), 7.03 (H4), 7.01 (H5), 7.17 (H6),
7.34 (H7), 6.60 (H12), 7.10 (H13), 6.35 (H14), 7.46 (H15). 13C
152.0 (C2), 117.1 (C4), 123.4 (C5), 123.7 (C6), 111.4 (C7), 132.6
(C8), 135.7 (C9), 114.7 (C10), 151.6 (C11), 113.3 (C12), 133.9
atmosphere prior to use. Dry CDCl3, DMSO-d6, THF-d8, and boron
compounds were purchased from Aldrich and used without fur-
ther purification. The melting points were obtained on a Mel-
Temp II apparatus and are uncorrected. IR spectra were taken
in KBr disc using a FT Spectrum GX Perkin Elmer spectrometer.
Mass spectra in the EI mode were recorded at 20 eV on a Hew-
lett–Packard HP 5989 spectrometer. Elemental analyses were
performed on Flash 1112 Thermo Finnigan. 1H, 13C, 11B, and
19F NMR spectra were obtained on a Jeol GSX-270, Jeol Eclipse
400 MHz and Bruker Advance 300 MHz. 1H and 13C chemical
shifts assignments were based on 2D experiment 1H/1H COSY,
1H/13C HETCOR and COLOC.
(C13),
117.1
(C14),
125.8
(C15).
Anal.
Calc.
for
C25H20BN3ꢀ2(CH3)2SOꢀH2O: C, 63.61; H, 6.26; N, 7.67. Exp.: C,
63.60; H, 5.99; N, 7.61%.
4.3.2. Diphenyl-[2-(1H-benzimidazol-2-yl-N)-phenolate-O]-boron (7)
Ligand 2 (284 mg, 1.35 mmol) was reacted with (C6H5)2BOH
(246 mg, 1.35 mmol). Compound 7 is a grey solid (350 mg, 69%).
Mp. 260 °C. IR (KBr),
m
(cmꢁ1): 1629, 1610 (C@N), 1574, 1554
(C'C), 1388 (B–O), 1196, 919 (B-N). MS: m/z (%): 374(2) [M]+Å,
297(100) [MꢁC6H5]+, 220(2) [Mꢁ2(C6H5)]+. NMR (DMSO-d6), d
(ppm): 1H 14.35 (NH), 6.79 (H4), 7.13 (H5), 7.34 (H6), 7.70 (H7),
7.05 (H12), 7.42 (H13), 6.91 (H14), 7.93 (H15). 13C 147.7 (C2),
116.3 (C4), 124.5 (C5), 125.0 (C6), 133.3 (C7), 133.5 (C8), 135.3
(C9), 111.2 (C10), 160.8 (C11), 118.9 (C12), 135.2 (C13), 120.5
(C14), 126.1 (C15). Anal. Calc. for C25H19BN2Oꢀ1/3(CH3)2SO: C,
77.01; H, 5.29; N, 7.00. Exp.: C, 77.12; H, 5.57; N, 7.15%.
4.2. Crystallographic study
Data were measured on a Nonius Kappa CCD instrument with
a CCD area detector using graphite-monochromated MoK
ation. Intensities were measured using / + scans. Crystals
a radi-
x
were obtained from DMSO (6 and 7) and CHCl3 (8–10 and 12).
All structures were solved using direct methods, using SHELX-97
[28] and the refinement (based on F2 of all data) was performed
by full matrix least-squares techniques with Crystals 12.84 [29]
In the asymmetric unit of compound 6, there are two DMSO
and one H2O molecules. Compound 7 cocrystallized with DMSO.
The cell of 8 has two molecules of the compound and one of
CHCl3. The asymmetric unit of 10 has two molecules of CDCl3.
All non-hydrogen atoms were refined anisotropically. In com-
pounds 6 and 7 the DMSO hydrogen atoms were geometrically
4.3.3. Diphenyl-[2-(1H-benzimidazol-2-yl-N)-benzenethiolate-S]-
boron (8)
Compound 3 (440 mg, 1 mmol) was reacted with (C6H5)2BOH
(355 mg, 2 mmol). Compound
8
is
m
a
green crystalline solid
(286 mg, 75%). Mp 166 °C. IR (KBr),
(cmꢁ1): 1601 (C@N), 1559
(C@C), 1345 (B–S). MS: m/z (%): 390(2) [M]+Å, 313(100) [MꢁC6H5]+.
NMR (DMSO-d6), d (ppm): 1H 11.34 (NH), 6.58 (H4), 6.44 (H5), 6.86

A. Esparza-Ruiz et al. / Journal of Organometallic Chemistry 694 (2009) 3814–3822
3819
Table 3
Selected geometric parameters
6
7
8a
8b
9
10
12
Bond lengths (Å)
B–C(F)18
B–C24(F)19
B–N3
1.634(5)
1.625(4)
1.597(4)
1.535(4)
1.355(4)
1.339(4)
1.349(4)
1.438(4)
1.431(4)
1.624(4)
1.606(4)
1.606(3)
1.506(3)
1.339(3)
1.331(3)
1.348(3)
1.445(3)
1.407(4)
1.623(6)
1.601(7)
1.605(6)
1.947(5)
1.754(5)
1.331(5)
1.360(5)
1.457(6)
1.404(6)
1.605(7)
1.606(8)
1.602(5)
1.958(5)
1.772(5)
1.343(5)
1.340(5)
1.449(6)
1.396(6)
1.606(4)
1.607(4)
1.641(3)
1.480(3)
1.353(3)
1.345(3)
1.318(3)
1.426(3)
1.386(3)
1.619(6)
1.612(5)
1.636(4)
1.481(4)
1.332(4)
1.341(4)
1.323(4)
1.422(4)
1.392(5)
1.365(4)
1.372(4)
1.605(4)
1.436(4)
1.358(3)
1.346(3)
1.314(3)
1.416(4)
1.403(4)
B–Y16
C11–Y16
C(N)2–N3
C(N)2–N1
C(N)2–C10
C10–C11
Bond angles (°)
C18–B–C24(F19)
C18–B–N3
C24–B–N3
C18–B–Y16
113.7(2)
108.5(2)
108.8(2)
111.8(3)
110.4(2)
103.1(2)
115.5(2)
108.9(2)
110.5(2)
107.1(2)
109.8(2)
104.5(2)
114.7(4)
108.2(3)
111.3(3)
112.7(3)
104.9(3)
104.8(3)
116.7(4)
112.2(4)
107.6(3)
104.7(3)
111.3(3)
103.6(3)
118.4(2)
108.4(2)
106.4(2)
108.1(2)
111.7(2)
102.7(2)
115.3(3)
107.6(3)
108.9(3)
112.3(3)
108.3(3)
103.7(3)
112.1(3)
107.7(3)
106.1(3)
111.2(3)
112.3(3)
107.1(2)
C24(F19)–BY16
N3–B–Y16
Fig. 6. Conformation of six-membered heterocycles in compounds 6 (left) and 8 (right).
(H6), 7.55 (H7), 7.25 (H12), 7.46 (H13), 6.96 (H14), 8.21 (H15). 13
149.2 (C2), 120.8 (C4), 125.6 (C5), 126.5 (C6), 112.2 (C7), 134.9
C
(C8), 136.1 (C9), 121.8 (C10), 145.5 (C11), 131.5 (C12), 136.0
(C13), 135.7 (C14), 132.6 (C15). Anal. Calc. for C25H19BN2Sꢀ1/
2CHCl3: C, 68.06; H, 4.37; N, 6.23. Exp.: C, 67.69; H, 4.62; N,
6.68%.
4.3.4. Diphenyl-[2-(2H-benzotriazol-2-yl-N)-4-(1,1,3,3-tetramethyl-
butyl)-phenolate-O]-boron (9)
N
O
Compound 4 (1.83 g, 5.65 mmol) was reacted with (C6H5)2BOH
(1.03 g, 5.65 mmol). Compound 9 is a yellow crystalline solid.
o
o
1.452 A
B
1.685 A
(2.01 g, 73%). Mp 230 °C. IR (KBr),
m
(cmꢁ1): 1624 (C@N), 1571
Ph
Ph
(C@C), 1364 (B–O). MS: m/z (%): 487(0.3) [M]+Å, 410(100)
[MꢁC6H5]+. NMR (CDCl3), d (ppm): 1H 6.88 (H4), 7.55 (H5), 7.43
Scheme 5. Bond lengths in diphenyl[2-(2-pyridyl)-ethoxyl-kO,kN]-borane [26].

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A. Esparza-Ruiz et al. / Journal of Organometallic Chemistry 694 (2009) 3814–3822
4.3.6. Difluoro-[2-(1H-benzimidazol-2-yl-N)-phenolate-O]-boron
(11): general procedure for compounds 11–13
Compound 2 (200 mg, 1 mmol) was dissolved in dried tolu-
ene (15 mL). The solution was cooled to ꢁ78 °C in a dry nitrogen
atmosphere and BF3ꢀEt2O (0.12 mL, 1 mmol) was added drop-
wise. The solution was refluxed for 6 h and then cooled and
evaporated under vacuum. Compound 11ꢀis a dark green solid
(350 mg, 69%,). Dec. at 310 °C. IR (KBr),
m
(cmꢁ1): 1631(C@N),
1569 (C@C), 1380 (B–O), 1181 (B–F), 930 (B–N). MS: m/z (%):
258(10) [M]+Å, 238 (100) [MꢁHF]+. NMR (DMSO-d6), d (ppm):
1H 14.2 (NH), 7.80 (H4), 7.50 (H5), 7.53 (H6), 7.79 (H7), 7.12
(H12), 7.59 (H13), 7.17 (H14), 8.11 (H15). 13C 147.3 (C2),
115.0 (C4), 125.0 (C5), 125.5 (C6), 113.2 (C7), 132.3 (C8),
135.0 (C9), 108.6 (C10), 156.6 (C11), 119.2 (C12), 132.1 (C13),
119.9 (C14), 125.6 (C15). Anal. Calc. for C13H9BF2N2Oꢀ1/
3(CH3)2SO: C, 57.78; H, 3.90; N, 9.86. Exp.: C, 57.38; H, 3.71;
N, 9.78%.
4.3.7. Difluoro-[2-(2H-benzotriazol-2-yl-N)-4-(1,1,3,3-tetramethyl-
butyl)-phenolate-O]-boron (12)
Fig. 7. Cooperative intramolecular interactions of C–H with
pairs contribute to a rigid molecular framework, shown here for compound 6
(distances in Å).
p electrons and lone
Compound 4 (200 mg, 0.6 mmol) was reacted with BF3ꢀEt2O
(87 mg, 0.6 mmol, 78 lL). Compound 12 was crystallized from
CHCl3 and, is a yellow solid (184 mg, 80%). Mp 166 °C. IR (KBr),
m
(cmꢁ1): 1618 (C@N), 1576 (C@C), 1364 (B–O), 1175 (B–F),
888 (B–N). MS: m/z (%): 371(6.0) [M]+Å, 323(2.0) [MꢁBF2]+,
300(100) [MꢁC5H11]+. NMR (CDCl3), d (ppm): 1H 8.12 (H4), 7.67
(H5), 7.74 (H6), 8.09 (H7), 7.27 (H12), 7.57 (H13), 8.27 (H15).
13C 114.7 (C4), 129.3 (C5), 132.1 (C6), 119.0 (C7), 143.0 (C8),
135.2 (C9), 122.3 (C10), 146.0 (C11) [3J(13C,19F) = 2.5 Hz], 120.7
(C12), 131.7 (C13), 144.0 (C14), 116.0 (C15). Anal. Calc. for
C32H34BN3O: C, 64.71; H, 6.52; N, 11.32. Exp.: C, 64.91; H, 6.70;
N, 11.30%.
(H6), 8.08 (H7), 7.32 (H12), 7.51 (H13), 8.12 (H15). 13C 115.3 (C4),
128.3 (C5), 131.0 (C6), 118.9 (C7), 143.2 (C8), 136.8 (C9), 124.3
(C10), 150.0 (C11), 121.0 (C12), 131.3 (C13), 142.2 (C14), 116.5
(C15). Anal. Calc. for C32H34BN3O: C, 78.85; H, 7.03; N, 8.62. Exp.:
C, 78.90; H, 7.43; N, 8.61%.
4.3.5. Diphenyl-[2-(2H-benzotriazol-2-yl-N)-4,6-(1-methyl-1-phenyl-
ethyl)-phenolate-O]-boron (10)
4.3.8. Difluoro-[2-(2H-benzotriazol-2-yl-N)-4,6-(1-methyl-1-phenyl-
ethyl)-phenolate-O]-boron (13)
Compound 5 (800 mg, 1.8 mmol) was reacted with (C6H5)2BOH
(325 mg, 1.78 mmol). Compound 10 is a yellow solid (820 mg,
Compound 5 (200 mg, 0.45 mmol) was reacted with BF3ꢀEt2O
75%). Mp 150 °C. IR (KBr),
m
(cmꢁ1): 1600 (C@N), 1572 (C@C),
(63 mg, 0.45 mmol, 56 lL). Compound 13 is a yellow solid that
1311 (B–O). MS: m/z (%): 611(0.3) [M]+Å, 534(100) [MꢁC6H5]+. Anal.
Calc. for C42H38BN3O: C, 82.48; H, 6.26; N, 6.87. Exp.: C, 82.45; H,
6.35; N, 6.91%.
was purified by sublimation (197 mg, 89%). Mp. 227 °C. E.M: m/z
(%): 495(65) [M]+Å, 480(91) [MꢁCH3]+, 460(100) [MꢁHFCH3]+.
NMR (CDCl3), d (ppm): 13C 145.0 (C11) [3J(13C,19F) = 2.0 Hz]. Anal.
Fig. 8. Intermolecular H-bonds in compounds 6 (left) and 7 (right).

A. Esparza-Ruiz et al. / Journal of Organometallic Chemistry 694 (2009) 3814–3822
3821
Fig. 9. Solid state structure of compound 8, showing the Sꢀ ꢀ ꢀH bond (left).
p-Stacking in 8 [C7–C12 distance = 3.35 Å] (right).
Fig. 10. Weak Interactions in difluoro compound 12.
ˇ
ˇ
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Calc. for C32H34BN3O: C, 72.74; H, 5.70; N, 8.48. Exp.: C, 73.08; H,
5.33; N, 8.32%. IR (KBr),
(cmꢁ1): 1601 (C@N), 1577 (C@C), 1360
(B–O), 1160 (B–F), 889 (B–N).
m
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Acknowledgments
Financial support from Conacyt-Mexico and Cinvestav is
acknowledged as well as Conacyt-Mexico scholarships for A.E.-R.
and A.P.-H. The authors are grateful to J. Guthrie and E. Mijangos
for valuable comments and discussions.
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Contreras, Cryst. Growth Des. 7 (2007) 2031.
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Appendix A. Supplementary material
CCDC 735744, 735745, 735746, 735747, 735748 and 735749
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif. Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2009.07.029.
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