Hydroximato complexes of boron - The X-ray crystal structures of dicyclohexylammonium bis(benzohydroximato)borate chloroform solvate and tetra-n-propylammonium bis(benzohydroximato)borate

Article abstract of DOI:10.1016/S0277-5387(02)01187-7

Four new alkylammonium bis(benzohydroximato)borates have been prepared and characterized by elemental analysis, IR and ¹H NMR spectra. The crystal and molecular structures of dicycohexylammonium bis(benzohydroximato)borate chloroform solvate (1

Full text of DOI:10.1016/S0277-5387(02)01187-7

Polyhedron 21 (2002) 2351ꢁ2356
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www.elsevier.com/locate/poly
Hydroximato complexes of boron*
/
the X-ray crystal structures of
dicyclohexylammonium bis(benzohydroximato)borate chloroform
solvate and tetra-n-propylammonium bis(benzohydroximato)borate
Alberthmeiry T. de Figueiredo a, Victor M. Deflon a,*, Karl E. Bessler a,
Cacilia Maichle-Mossmer b, Ulrich Abram c
¨
¨
a Instituto de Qu´ımica, Universidade de Bras´ılia, BR-70919-970 Bras´ılia, DF, Brazil
b Institut fur Anorganische Chemie der Universitat Tubingen, D-72076 Tubingen, Germany
¨
¨
¨
¨
c Institut fur Chemie, Freie Universitat Berlin, D-14195 Berlin, Germany
¨
¨
Received 11 March 2002; accepted 23 July 2002
Abstract
Four new alkylammonium bis(benzohydroximato)borates have been prepared and characterized by elemental analysis, IR and 1H
NMR spectra. The crystal and molecular structures of dicycohexylammonium bis(benzohydroximato)borate chloroform solvate (1×
/
CHCl3) and tetra-n-propylammonium bis(benzohydroximato)borate (3) have been determined by X-ray diffraction methods. In
both examples the bis(hydroximato)borate anions show the expected spirochelate structure with slightly distorted tetrahedral BO4
coordination. The Cꢀ
and angles of the BONCO heterocyle are in good agreement with those observed in N-methylacetohydroxamatoboron complexes
(Can. J. Chem. 55 (1977) 1, Can. J. Chem. 56 (1978) 1676). In the crystal structure of 1×CHCl3 the bis(benzoydroximato)borate
anions are linked to the dicyclohexylammonium cations by strong NꢀHÁ Á ÁO and NꢀHÁ Á ÁN hydrogen bonds.
# 2002 Elsevier Science Ltd. All rights reserved.
/
N as well as the Cꢀ/O bonds within the chelate rings have considerable double bond character. Bond lengths
/
/
/
Keywords: Boron complexes; Benzohydroximate anion; Synthesis; Crystal structures
1. Introduction
Most of the well characterized metal complexes
contain the hydroxamate(1ꢀ) anions a.
Several molecular boron chelates involving N-sub-
stituted hydoxamate(1ꢀ) anions have been described
[1,2,5ꢁ11]. The crystal and molecular structures of
/
Hydroxamic acids of the general composition
RC(O)NHOH are well known as versatile chelating
agents [3,4]. Their metal chelates are derived from the
/
/
hydroxamate(1ꢀ
anion b as shown below:
/
) anion a or the hydroximate(2ꢀ)
/
difluoro-N-methylacetohydroxamatoboron [1], diphe-
nyl-N-methylacetohydroxamatoboron [2] and diphe-
nyl-N-(1-hydroxycyclohexyl)benzohydroxamatoboron
[11] have been determined. Several anionic boron
chelates involving the hydroximate(2ꢀ
been described: dihydroxohydroximatoborates [12] and
bis(hydroximato)borates [13ꢁ15]. So far, no structural
/) anion have
/
informations are available concerning boron chelates
with N-unsubstituted hydroxamic anions. We consider
the structure investigation of the hydroximatoborates of
some interest, in order to compare bonding parameters
of the chelate with those of boron hydroxamates
[1,2,11].
* Corresponding author. Tel.: ꢂ
4149
E-mail address: deflon@unb.br (V.M. Deflon).
/
55-61-307-2181; fax: ꢂ55-61-273-
/
0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 1 1 8 7 - 7

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A.T. de Figueiredo et al. / Polyhedron 21 (2002) 2351ꢁ2356
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2. Experimental
CH2) 7.49 (m, 6H, C6H5), 7.91 (m, 4H, C6H5). FTIR
(KBr): 3122m (n NH), 2956ms (n CH2/CH3), 1594ms
(C6H5), 1563s (C6H5), 1498m, 1470m, 1446m (d CH2),
1380s (n OCN), 1124s (nas 10BO4), 1086vs (nas 11BO4),
993s, 942m (das BO4), 773m (n ONC), 738m (n ONC),
703m (C6H5), 690m (C6H5).
2.1. Instrumental
IR spectra were recorded on a BOMEM FT-IR model
1
BM 100 spectrometer. H NMR spectra were measured
on a BRUKER AC250 instrument with TMS as internal
standard. Elemental analyses (CHN) were determined
2.2.3. Tetra-n-propylammonium
bis(benzohydroximato)borate (3)
with a FISONS EA-1108 equipment. Enrafꢁ
/
Nonius
CAD4 diffractometers were used for the diffraction
measurements. Routine FABꢀ mass spectra have been
recorded on a TSQ spectrometer (Finnigan) with
nitrobenzylalcohol as matrix.
A mixture of 0.031 g H3BO3 (0.50 mmol), 0.058 g Ag2O
(0.25 mmol), 0.137 g benzohydroxamic acid (1.00 mmol),
0.133 g tetra-n-propylammonium bromide (0.50 mmol)
in 25 ml C6H6 was heated to reflux for 8 h as described
above. The solid was filtered off and extracted with 15 ml
CH2Cl2. After vacuum evaporation 0.201 g of 3 (yield
86%) were obtained as colorless crystals (m.p. 136 8C).
Anal. Found: C, 66.41; H, 8.10; N, 8.88. Calc. for
C26H38BN3O4: C, 66.81; H, 8.19; N, 8.99%. NMR
2.2. Preparation of the boron complexes
The hydroximatoborates were prepared as described
previously [14], with slight modifications. Solvents and
commercially available chemicals (H3BO3, benzohy-
droxamic acid, di-n-butylamine, dicyclohexylamine, tet-
ra-n-butylammonium bromide, tetra-n-propylammon-
ium bromide and silver oxide) were used as purchased.
1
(25 8C): H (250 MHz, CDCl3): d 0.84 (t, 12H, CH3),
1.50 (m, 8H, CH2ꢀ
/
CH3), 3.03 (t, 8H, CH2ꢀ
/
N), 7.32 (m,
6H, C6H5), 7.86 (m, 4H, C6H5). FTIR (KBr): 2975ms (n
CH2/CH3), 2945m (n CH2/CH3), 1592ms (C6H5), 1558ms
(C6H5), 1488ms, 1461m, 1447m (d CH2), 1377vs (n
OCN/dCH3), 1114s (nas 10BO4), 1078s (nas 11BO4), 981s,
944m (das BO4), 780m (n ONC), 736m (n ONC), 701ms
(C6H5), 674m. FABꢀ MS; m/z: 281.2, 162.1.
2.2.1. Dicyclohexylammonium
bis(benzohydroximato)borate (1)
A mixture of 0.068 g H3BO3 (1.10 mmol), 0.302 g
benzohydroxamic acid (2.20 mmol) and 0.200 g dicyclo-
hexylamine (1.1 mmol) in 25 ml C6H6 was heated under
reflux for 8 h, using a Dean-Stark trap for azeotropic
elimination of water. After evaporation of the C6H6, the
solid residue was dissolved in 15 ml CH2Cl2, 15 ml n-
2.2.4. Tetra-n-butylammonium
bis(benzohydroximato)borate (4)
Compound 4 has been prepared from 0.062 g H3BO3
(1.00 mmol), 0.274 g benzohydroxamic acid (2.00
mmol), 0.240 g tetra-n-butylammonium bromide (1.00
mmol) and 0.116 g Ag2O (0.50 mmol) as described for 3,
yielding 0.470 g (90%). M.p. 165 8C. Anal. Found: C,
67.64; H, 8.79; N, 8.07. Calc. for C30H46BN3O4: C,
68.83; H, 8.86; N, 8.03%. NMR (25 8C): 1H (250 MHz,
C6H14 was added and the mixture was kept at ꢀ
After 48 h the crystals were filtered off and washed with
n-C6H14 yielding 0.474 g of 1 (yield: 91%). M.p. 226ꢁ
/
15 8C.
/
229 8C. Anal. Found: C, 67.12; H, 6.93; N, 9.12. Calc.
for C26H34BN3O4: C, 67.39; H, 7.40; N, 9.07%. NMR
1
(25 8C): H (250 MHz, CDCl3): d 1.02 (m, 6H, CH2),
CDCl3): d 0.84 (t, 12H, CH3), 1.40 (m, 16H, CH2ꢀ
/
1.47 (m, 4H, CH2), 1.56 (m, 6H, CH2), 1.95 (m, 4H, CH2),
3.10 (m, 2H, CH), 7.26 (m, 6H, C6H5), 7.78 (m, 4H,
C6H5). FTIR (KBr): 3035m (n NH), 2934s (n CH2),
2856s (n CH2), 1597ms (C6H5), 1562ms (C6H5), 1499m,
1447m (d CH2), 1388vs (n OCN), 1125s (nas 10BO4),
1085vs (nas 11BO4), 987s, 942m (das BO4), 792m (n ONC),
742m (n ONC), 691m (C6H5) (IR data: vs, very strong; s,
strong; ms, medium strong; m, medium).
CH3), 3.14 (t, 8H, NꢀCH2), 7.32 (m, 6H, C6H5), 7.86
/
(m, 4H, C6H5). FTIR (KBr): 2966ms (n CH2/CH3),
2929m (n CH2/CH3), 1594m (C6H5), 1558m (C6H5),
1490m, 1382vs (n OCN), 1118s (nas 10BO4), 1083vs (nas
11BO4), 981 s, 944m (das BO4), 770m (n ONC), 737m (n
ONC), 695s (C6H5), 670m (C6H5).
2.3. X-ray crystal structure determinations
2.2.2. Di-n-butylammonium
bis(benzohydroximato)borate (2)
Compound 2 was prepared from 0.080 g H3BO3 (1.30
mmol), 0.357 g benzohydroxamic acid (2.60 mmol) and
0.170 g di-n-butylamine (1.31 mmol) as described above.
Crystals of the chloroform solvate 1×
suitable for structure analysis were obtained from
CHCl3ꢁn-C6H14 solutions (1:1) of the complexes. The
cell constants were calculated from 25 reflexes with a
wide range of 2u. The program HELENA [16] was used
for the data reduction. Both complexes crystallize
monoclinic. The space groups were assigned using the
criterion of choosing the setting which corresponds to
the lowest monoclinic b angle. The structures were
solved by direct methods with SHELXS-97 [17] and
/
CHCl3 and of 3
/
Yield: 0.450 g (84%). M.p. 113ꢁ114 8C. Anal. Found:
/
C, 64.06; H, 6.45; N, 10.28. Calc. for C22H30BN3O4: C,
64.24; H, 7.35; N, 10.22%. NMR (25 8C): 1H (250
MHz, CDCl3): d 0.80 (t, 6H, CH3), 1.3 (m, 4H, CH2ꢀ
/
CH3), 1.79 (m, 4H, CH2ꢀCH2ꢀCH2), 3.10 (t, 4H, Nꢀ
/
/
/

A.T. de Figueiredo et al. / Polyhedron 21 (2002) 2351ꢁ
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2356
2353
H3BO3 ꢂ2C6H5CONHOHꢂR2NH
0 [R2NH2][B(C6H5CONO)2]ꢂ3H2O
refined with SHELXL-97 [18]. A c-scans [16] absorption
correction was performed and all non-hydrogen atoms
were refined with anisotropic displacement parameters
in both structures. The hydrogen atoms were found in
for 1 and 2, or:
the Fourier-map in 1×
/
CHCl3 and calculated at idealized
2H3BO3 ꢂ4C6H5CONHOHꢂ2[R4N]BrꢂAg2O
0 2[R4N][B(C6H5CONO)2]ꢂ2AgBrꢂ7H2O
positions and refined using the riding model in 3.
Crystal data and more detailed information about the
structure determinations are given in Table 1. Labeled
for 3 and 4.
The use of silver oxide and a quaternary ammonium
bromide, which resulted in the formation of insoluble
silver bromide and easily removable water as bypro-
ducts, proved to be a favorable synthetic route for
tetraalkylammonium bis(benzohydroximato)borates.
These quaternary ammonium cations acted effi-
ciently, as expected due to their favorable size, as
counter ions for the crystallographic study also in
diagrams of the structures of 1×
in Figs. 1 and 2, respectively. Selected bond lengths and
angles are given in Table 2.
/
CHCl3 and 3 are shown
3. Results and discussion
3.1. Synthesis of the bis(benzohydroximato)borates
absence of the Nꢀ
/
HÁ Á ÁO and NꢀHÁ Á ÁN hydrogen bonds
/
between the anionic complex and the counter ion,
normally present in the lower alkylammonium salts, as
Bis(benzohydroximato)borates were obtained in high
yield in simple one-step reactions according to:
in 1×
/
CHCl3. Good quality crystals of 3, additionally
Table 1
Crystal data and structure refinement for 1 CHCl3 and 3
Compound
1×CHCl3
3
Empirical formula
Formula weight
Temperature (8C)
Wavelength (pm)
Radiation
C27H35BCl3N3O4
582.74
C26H38BN3O4
467.40
20(2)
ꢀ65(2)
154.056
71.073
Cu Ka
monoclinic
P21/c
Mo Ka
monoclinic
Pn
Crystal system
Space group
Unit cell parameters
a (pm)
b (pm)
1302.88(9)
1127.18(17)
1987.55(10)
91.484(8)
2917.9(5)ꢃ106
4
1118.7(3)
967.64(8)
1278.8(3)
108.89(2)
1309.7(5)ꢃ106
2
c (pm)
b (8)
V (pm3)
Z
Absorption coefficient (mmꢀ1
Crystal size (mm)
Method
)
3.146
0.5ꢃ0.4ꢃ0.1
v scans
0.079
0.40ꢃ0.20ꢃ0.20
v scans
u range (8)
5ꢁ/
65
3ꢁ/25
Index ranges (h, k, l)
Collected reflections
Unique reflections
Rint
ꢀ1015, 0013, ꢀ23020
5511
ꢀ13013, 0011, ꢀ15015
4606
4843
0.0930
4606
0.0000
Observed data [I ꢀ2s(I)]
Absorption correction
Min/max transmission
Structure refinement
Weighting scheme
2774
c-scans [16]
2518
c-scans [16]
0.76443/0.95645
full-matrix least-squares on F2
0.84812/0.94824
full-matrix least-squares on F2
wꢄ1/[s2(Fo2)ꢂ(0.0810P)2ꢂ1.8367P],
wꢄ1/[s2(Fo2)ꢂ(0.1097P)2ꢂ0.0139P],
Pꢄ(Fo2ꢂ2Fc2)/3
Fourier-map
483
Pꢄ(Fo2ꢂ2Fc2)/3
riding model
308
Hydrogen treatment
Refined parameters
Structure factors [I ꢀ2s(I)]
Goodness-of-fit, S
R1ꢄ0.0647, wR2ꢄ0.1583
1.039
R1ꢄ0.0758, wR2ꢄ0.1712
1.049
0.056(7)
Extinction coefficient
Absolute structure parameter
Programs used
not refined
none
0.00001
HELENA, PLATON [16], SHELXS-97 [17], SHELXL-97 [18] HELENA, PLATON [16], SHELXS-97 [17], SHELXL-97 [18]

2354
A.T. de Figueiredo et al. / Polyhedron 21 (2002) 2351ꢁ2356
/
Table 2
Selected bond lengths (pm) and angles (8) for 1×CHCl3 and 3
1×CHCl3
3
Bond lengths
a
a
BꢀO(1)/BꢀO(3)
BꢀO(2)/BꢀO(4)
147.0(6)/147.3(5) 146.7(8)/147.9(8)
146.8(6)/147.2(5) 146.4(8)/146.9(8)
a
O(1)ꢀC(1)/O(3)ꢀC(2)
C(1)ꢀN(1)/C(2)ꢀN(2)
N(1)ꢀO(2)/N(2)ꢀO(4)
132.6(4)/133.6(5) 133.4(6)/132.7(7)
128.1(5)/128.9(5) 126.5(7)/126.9(7)
a
a
142.0(4)/144.6(4) 141.6(6)/142.6(6)
146.6(6)/147.2(5) 147.2(8)/147.6(8)
a
C(1)ꢀC(11)/C(2)ꢀC(21)
N(3)ꢀH(31)Á Á ÁN(1)
N(3)ꢀH(31)
286.7(6)
88.0(6)
199(6)
H(31)Á Á ÁN(1)
b
(N3)ꢀH(32)Á Á ÁO(4)
283.6(4)
88.0(5)
196(6)
N(3)ꢀH(32)
H(32)Á Á ÁO(4)
Bond angles
b
a
O(1)ꢀBꢀO(2)/O(3)ꢀBꢀO(4)
O(1)ꢀBꢀO(3)
O(1)ꢀBꢀO(4)
O(2)ꢀBꢀO(3)
O(2)ꢀBꢀO(4)
102.3(3)/101.9(3) 102.7(5)/101.6(5)
113.3(3)
113.6(4)
112.6(4)
113.6(3)
113.9(5)
112.8(4)
112.5(4)
113.8(5)
Fig. 1. ORTEP plot (30% probability) of 1 in 1×CHCl3. The H-atoms
/
are omitted for clarity, except H(31) and H(32). The dashed lines
indicate the H-bonds.
O(1)ꢀC(1)ꢀN(1)/
O(3)ꢀC(2)ꢀN(2)
116.0(4)/117.7(3) 117.5(5)/118.5(5)
a
C(1)ꢀN(1)ꢀO(2)/
C(2)ꢀN(2)ꢀO(4)
107.2(3)/104.7(3) 106.5(4)/105.1(4)
a
a
N(1)ꢀO(2)ꢀB/N(2)ꢀO(4)ꢀB
O(1)ꢀC(1)ꢀC(11)/
107.0(3)/109.0(3) 107.8(4)/108.9(4)
120.3(4)/119.9(3) 118.7(4)/118.7(5)
a
O(3)ꢀC(2)ꢀC(21)
N(1)ꢀC(1)ꢀC(11)/
123.7(4)/122.5(4) 123.8(5)/122.8(6)
a
N(2)ꢀC(2)ꢀC(21)
N(3)ꢀH(31)ꢀN(1)
N(3)ꢀH(32)ꢀO(4)
178.0(6)
175.0(5)
b
a
Values for two non equivalent chelate rings, respectively.
Symmetry operation: ꢀxꢂ1, yꢂ1/2, ꢀzꢂ1/2.
b
chelate. The Nꢀ
lammonium salts 1 and 2 appears as multicomponent
absorption pattern in the range 3050ꢁ
2400 cmꢀ1
characteristic for strong hydrogen bonds.
/H stretching vibration of the dialky-
/
,
1
The H NMR spectra of the described hydroximato-
borates in CDCl3 show the expected patterns.
Fig. 2. ORTEP plot (30% probability) of 3. The H-atoms are omitted
for clarity.
The FABꢀ MS-Spectrum of 3 (nitrobenzylalcohol
matrix) shows m/z peaks at 281.2 and 162.1, corre-
without solvent of crystallization, could be obtained for
this purpose.
sponding
to
[B(C6H5CONO)2]ꢀ
(281)
and
[OB(C6H5CONO)]ꢀ (162), respectively.
3.2. Spectroscopic characterization
3.3. Crystal structures
The infrared spectra of the presented compounds
(KBr pellets) exhibit the expected characteristic features
of the bis(hydroximato)borate moiety [14]. The stron-
gest absorption at about 1080 cmꢀ1 corresponds to nas
11BO4, showing the component for nas 10BO4 at about
1120 cmꢀ1. Another strong absorption band at approxi-
mately 985 cmꢀ1 can be attributed to a deformation
mode das BO4. The strong absorption band at about
1380 cmꢀ1 most probably involves a stretching vibra-
tion of the OCN group (n OCN) within the hydroximato
The crystal structures show the expected spirochelate
structure of the bis(benzohydroximato)borate anions
with slightly distorted tetahedral BO4 coordination. The
Bꢀ
/
O distances (mean value 147.0 pm) are in good
agreement with the mean value of 146.8 pm for
ꢀ
compounds containing the BO4 moiety [19]. The
endocyclic Oꢀ
102.78, the exocyclic Oꢀ
are slightly larger compared to the ideal tetrahedral
angle. The CꢀN bond lengths (126.5ꢁ128.9 pm) are
/
Bꢀ
/
O-angles lie between 101.68 and
/
BꢀO-angles (112.58ꢁ113.98)
/
/
/
/

A.T. de Figueiredo et al. / Polyhedron 21 (2002) 2351ꢁ
/
2356
2355
close to the standard value of a double bond. The Cꢀ
bonds (132.6ꢁ133.6 pm) are considerably shortened
with respect to a single bond [19]. The NꢀO bond
lengths (141.6ꢁ144.6 pm) correspond to a single bond
and are longer compared to the mean NꢀO distance of
139.4 pm in oximes [19].
The chelate rings are essentially planar with maximum
atomic displacements from the mean plane between 0.80
and 6.1 pm. The phenyl groups are slightly distorted
with respect to the adjacent chelate rings, showing
torsion angles from 4.808 to 27.188.
/
O
that the presence of an additional negative charge in the
hydroximate anion does not change substantially the
electron density distribution in the chelate ring, as it
could be expected. Thus, the bonds among the rings are
not affected due to the presence of the lone electron pair
at the hydroximate’s nitrogen atom in the bis(benzohy-
droximato)borate complex. Also the involvement of
chelate’s atoms in strong hydrogen bonds between the
complex and the counter ion do not promote any
/
/
/
/
substantial changes in the ring’s bonds in 1×
/
CHCl3, in
comparison with the values found in 3.
Bond lengths and angles of the BONCO heterocyles
in 1 and 3 show only slight variations and are in fairly
good agreement with those observed in difluoro-N-
methylacetohydroxamatoboron (5) [1]. The Bꢀ
tances in 1 and 3 (mean value 147.0 pm) are slightly
shorter compared to 5 (mean value 148.3 pm) while the
/
O dis-
5. Supplementary material
Crystallographic data (excluding structure factors)
have been deposited with the Cambridge Crystallo-
graphic Data Centre, CCDC Nos. 178861 and 178862
Nꢀ
/
O bonds are considerably longer (mean value 142.7
for 1 and 3, and 134.2 pm for 5).
The structural data indicate a considerable delocaliza-
tion of p electrons in the boron chelates 1 and 3, as well
as in the hydroxamatoboron complexes [1,2]. We
propose the following resonance structures having
major contribution to the bonding hybrid in the
benzohydroximatoborates:
for compounds 1×
/
CHCl3 and 3. Copies of the data can
be obtained free of charge on application to The
Director, CCDC, 12 Union Road, Cambridge CB2,
1EZ, UK (fax: ꢂ44-1223-336033; e-mail: deposit@
/
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Strong hydrogen bonds between the dicyclohexylam-
monium nitrogen N(3) and the atoms N(1) and O(4),
Acknowledgements
from different complex molecules, occur in 1×
forming a chain like arrangement, as shown in Fig. 1.
The distances N(3)ꢀH(31)Á Á ÁN(1)ꢄ286.7(6) and N(3)ꢀ
283.6(4) pm are considerably shorter
compared to the mean values for these types of H-bond,
307 and 293 pm [20], respectively. The corresponding
/
CHCl3,
The authors are grateful to Professor J. Strahle
¨
(Tubingen) for the use of the X-ray diffractometer and
¨
acknowledge the Federal District Foundation for the
Support of Research (FAPDF) for financial support and
the National Council for Research and Development
(CNPq) for providing a scholarship to V.M.D.
/
/
/
H(31)Á Á ÁO(4b)ꢄ
/
bond angles are N(3)ꢀ
/
H(31)ꢀ
/
N(1)ꢄ
/
178(6)8 and N(3)ꢀ
/
H(31)ꢀO(4b)ꢄ175(5)8.
/
/
References
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