NCO-chelated organoantimony(III) and organobismuth(III) dichlorides: Syntheses and structures

Article abstract of DOI:10.1135/cccc2010051

The novel NCO chelating ligand L, 1-CH₂N(CH₃) ₂-3-CH₂OCH₃-C₆H₄, was prepared in four steps from commercially available m-tolunitrile in a good yield. Successful lithiation of this ligand was achieved by the reaction with n-BuLi in hexane. Using of this in situ prepared organolithium compound LLi in the reactions with MCl₃ (M = Sb, Bi) in 1:1 molar ratio led to isolation of the desired mono-organocompounds MLCl₂ (M = Sb (1), Bi (2)). Their structures were studied both in solution (NMR) and in the solid state (X-ray diffraction), and were compared with those of the NCN- and OCO-chelating analogues.

Full text of DOI:10.1135/cccc2010051

NCO-Chelated Organoantimony(III) and Organobismuth(III) Dichlorides
1041
NCO-CHELATED ORGANOANTIMONY(III) AND ORGANOBISMUTH(III)
DICHLORIDES: SYNTHESES AND STRUCTURES
1
2
3
4
Jan VRÁNA , Roman JAMBOR , Aleš RŮŽIČKA , Jaroslav HOLEČEK and
5,
Libor DOSTÁL *
Department of General and Inorganic Chemistry, Faculty of Chemical Technology,
University of Pardubice, Studentská 573, 532 10 Pardubice, Czech Republic;
1
2
3
e-mail: st20169@student.upce.cz, roman.jambor@upce.cz, ales.ruzicka@upce.cz,
4
5
jaroslav.holecek@upce.cz, libor.dostal@upce.cz
Received May 18, 2010
Accepted July 12, 2010
Published online October 4, 2010
Dedicated to Dr. Bohumil Štíbr on the occasion of his 70th birthday in recognition of his outstanding
contribution to inorganic and organometallic chemistry.
The novel NCO chelating ligand L, 1-CH2N(CH3)2-3-CH2OCH3-C6H4, was prepared in four
steps from commercially available m-tolunitrile in a good yield. Successful lithiation of this
ligand was achieved by the reaction with n-BuLi in hexane. Using of this in situ prepared
organolithium compound LLi in the reactions with MCl3 (M = Sb, Bi) in 1:1 molar ratio led
to isolation of the desired mono-organocompounds MLCl2 (M = Sb (1), Bi (2)). Their struc-
tures were studied both in solution (NMR) and in the solid state (X-ray diffraction), and
were compared with those of the NCN- and OCO-chelating analogues.
Keywords: Antimony; Bismuth; Chelating ligands; X-ray structure.
In 1978, van Koten et al. reported on the first utilization of potentially
NCN terdentate ligand, [2,6-(Me2NCH2)2-C6H3]– (Chart 1A), for stabiliza-
tion of organotin(IV) cations1. Since that time, the chemistry of so-called
pincer2 ligands has developed to a well established branch of organo-
metallic chemistry, with both main group3 and transition metals4.
Jurkschat et al. enriched the pincer chemistry of main groups by intro-
duction of an OCO ligand (Chart 1B) in 1998 5; the chemistry of this ligand
has been extended so far to Li, Si, Sn, Pb compounds6. We have reported
on OCO pincer ligands based on etheral donor groups (Chart 1C) in 2002 7
and developed their chemistry to Li, Al, Si, Sn, P, Sb, Bi as central atoms8.
The utilization of the so-called hybrid pincer ligands containing a non-
equivalent donor atom array, such as PCN, PCO or SCO, has been reported
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© 2010 Institute of Organic Chemistry and Biochemistry
doi:10.1135/cccc2010051

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Vrána, Jambor, Růžička, Holeček, Dostál:
recently as well, and they often exhibit special reactivity and physical prop-
erties9.
As a part of our ongoing investigation of pincer type ligands bound to
main group metals, we report here on the synthesis of a novel NCO chelat-
ing ligand [2-Me2NCH2-6-MeOCH2-C6H3]– denoted as L hereinafter. This
type of ligand enables us to compare the chemical properties of organo-
metallic compounds based on this skeleton with compounds containing
pure N- (Chart 1A) or O-donor (Chart 1B, C) ligands. The syntheses and
structures of organoantimony(III) and organobismuth(III) dichlorides
MLCl2 (M = Sb (1) and Bi (2)) are described here as the first derivatives of
this new ligand system.
CHART 1
RESULTS AND DISCUSSION
The starting NCO chelating ligand L was prepared by a four step procedure
according to Scheme 1. The ligand L was obtained as colorless, distillable
liquid in a reasonable yield, see Experimental.
Successful lithiation of the ligand was achieved by using one molar
equivalent of n-BuLi in hexane at room temperature. The organolithium
compound was not isolated but used in an orange hexane solution for in
situ reactions with metallic chlorides (Scheme 2).
Thus, the reaction of the organolithium compound LLi with SbCl3 or
BiCl3 in 1:1 molar ratios gave, after workup, the corresponding dichlorides
1 and 2 (Scheme 2) as air-stable white solids. Both compounds melt with
decomposition at 175 (1) and 180 °C (2). Their identity was established by
satisfactory elemental analyses.
The molecular structures of 1 and 2 were unambiguously determined by
single crystal X-ray diffraction (Figs 1 and 2). As a result of the rigid
tridentate coordination of the NCO ligand L in both compounds, the coor-
dination polyhedron around the central metal, Sb1 (1) and Bi1 (2), can be
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NCO-Chelated Organoantimony(III) and Organobismuth(III) Dichlorides
1043
SCHEME 1
SCHEME 2
best described as a distorted tetragonal pyramid with the apical position oc-
cupied by the ipso-carbon atom C1. The bond distances between donor and
the central atoms, i.e., Sb1–O1 2.469(4), Sb1–N1 2.315(5) Å and Bi1–O1
2.515(12) , Bi1–N1 2.482(17) Å, indicate strong intramolecular interactions,
all these values are close to those observed in organoantimony and bismuth
cations containing OCO or NCN ligands10. The donor atoms O1 and N1 as
well as both chlorido ligands Cl1 and Cl2 are placed in mutual trans-posi-
tions in the basal plane of the tetragonal pyramid, as demonstrated by the
bond angles Cl1–Sb1–Cl2 174.44(5), O1–Sb1–N1 148.05(15)° for 1 and
Cl1–Bi1–Cl2 178.92(13), O1–Bi1–N1 143.8(4)° for 2. The significant devia-
tion of the of O–M–N angles from the ideal value (180°) is a consequence of
the chelating-ring strain.
The comparison of 1 and 2 with analogous compounds containing OCO
or NCN ligands reveals some significant differences, especially in the case
of the OCO ligand (Chart 2). Both oxygen atoms and chlorido ligands are
placed in a cis-fashion (with the angles O–Sb–O 116.68°, Cl–Sb–Cl 84.54°)8a
in the case of the OCO-chelated organoantimony dichloride (Chart 2A).
Thus, the coordination of the OCO pincer type ligand may be described as
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Vrána, Jambor, Růžička, Holeček, Dostál:
pseudofacial, and the resulting polyhedron around the antimony atom is
a trigonal pyramid SbCCl2 (the sum of angles describing the SbCCl2 girdle
reaching 279.7°), which is bicapped by two oxygen donor atoms. The
donor (N, O) atoms as well as the chloride ligands are trans-arranged in
compound 1 (Fig. 1) and the coordination of the NCO ligand is pseudo-
meridional, leading to a distorted tetragonal pyramidal array around the
antimony atom. This bonding situation in 1 is closely related to that in the
NCN analogue11a (Chart 2C) where the ligand shows meridional coordina-
tion and the central antimony atom is located in a distorted tetragonal
pyramidal environment with trans-positioned chlorido and nitrogen donor
atoms (cf. the Cl–Sb–Cl angles of 174.0° and 174.08° (the mean value for
the two independent molecules in 1), and the N–Sb–N angle of 147.3° with
the N–Sb–O angle of 148.4° (the mean value for the two independent mole-
cules in 1)).
The OCO-chelated bismuth compound (Chart 2B) forms a tightly bound
dimer in the solid state via two chlorido bridges. The OCO ligand again pre-
FIG. 1
The ORTEP plot of the molecular structure of compound 1 showing both independent mole-
cules. Selected bond lengths (in Å) and angles (in °)]: Sb1–O1 2.469(4), Sb1–N1 2.315(5),
Sb1–C1 2.118(8), Sb1–Cl1 2.5560(18), Sb1–Cl2 2.6569(16); Cl1–Sb1–Cl2 174.44(5), O1–Sb1–N1
148.05(15), C1–Sb1–Cl1 88.94(19), C1–Sb1–Cl2 85.54(19), C1–Sb1–O1 71.69(18), C1–Sb1–N1
76.5(2); Sb2–O2 2.481(4), Sb2–N2 2.312(4), Sb2–C12 2.099(7), Sb2–Cl3 2.6567(16), Sb2–Cl4
2.5612(16), Cl3–Sb2–Cl4 173.71(5), O2–Sb2–N2 148.73(14), C12–Sb2–Cl3 85.23(19),
C12–Sb2–Cl4 88.50(19), C12–Sb2–O2 71.31(18), C12–Sb2–N2 77.46(19)
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NCO-Chelated Organoantimony(III) and Organobismuth(III) Dichlorides
1045
fers pseudofacial coordination, as demonstrated by the O–Bi–O bond angle
of 127.50°. Compound 2 remains essentially mononuclear in the solid state
and the meridional coordination of the NCO ligand (Fig. 2) resembles the
situation in the NCN-chelated compound11b (Chart 2C; cf. the Cl–Bi–Cl
CHART 2
FIG. 2
The ORTEP plot of the molecular structure of compound 2. Selected bond lengths (in Å) and
angles (in °): Bi1–O1 2.521(12), Bi1–N1 2.483(17), Bi1–C1 2.189(14), Bi1–Cl1 2.643(4), Bi1–Cl2
2.704(4); Cl1–Bi1–Cl2 178.88(13), O1–Bi1–N1 143.5(4), C1–Bi1–Cl1 89.9(4), C1–Bi1–Cl2
89.1(4), C1–Bi1–O1 69.5(5), C1–Bi1–N1 74.2(5)
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Vrána, Jambor, Růžička, Holeček, Dostál:
angles of 173.73 and 178.88° in 2, and the N–Bi–N angle of 144.18° with
the N–Bi–O angle of 143.5° in 2). In summary, these data indicate that the
NCO ligand L, in this limited series of compounds, prefers meridional coor-
dination, thereby resembling analogous NCN-chelated compounds rather
than the OCO derivatives. The preference of the NCO ligand to behave as
an NCN analogue may be ascribed to the presence of the nitrogen donor
atom in 1 and 2, which is in general a better donor than the etheral
oxygen, leading to a stronger donor atom–metal interaction. The latter may
compel the ligand coordination geometry to change from pseudofacial
(OCO type) to meridional (NCN and NCO types).
1
The H and 13C NMR spectra of 1 and 2 have revealed one set of sharp
signals for both CH2OMe and CH2NMe2 groups, indicating rigid tridenate
(meridional) coordination of the ligand L, which is consistent with the mo-
lecular structures determined in the solid state (vide supra). The proton sig-
nals of CH2O (δ 4.98 and 5.08 ppm for 1 and 2, respectively) and CH2N
(δ 4.41 and 4.83 ppm for 1 and 2, respectively) are shifted to a lower field
in comparison with the non-substituted ligand (δ 4.46 ppm for CH2O and
3.43 ppm for CH2N), proving the metal–O(N) donor–acceptor interactions.
EXPERIMENTAL
All air sensitive operations were carried out under an argon atmosphere, using a standard
Schlenk technique. Solvents were dried by standard procedures and distilled prior to use. 1H
and 13C NMR spectra were measured on a Bruker 400 spectrometer. Chemical shifts (δ, ppm)
have been referenced to residual signals of CDCl3 (δH 7.27, δC 77.23). The starting com-
pounds m-tolunitrile (98%), antimony chloride (99.99%) and bismuth chloride (99.999%)
were obtained from commercial suppliers and used as received.
Synthesis of 1-CN-3-CH2Br-C6H4
A mixture of m-tolunitrile (32 g, 0.27 mol) with N-bromosuccinimide (48.6 g, 0.27 mol)
and benzoyl peroxide (1.1 g, 4.54 mmol) was heated in benzene (250 ml) to reflux for 3 h.
The mixture was cooled to room temperature and the insoluble material was filtered off
and discarded. The filtrate was evaporated, giving a cream solid that was washed twice with
hexane (2 × 50 ml). The product was crystallized from ethanol and dried in vacuo to give
28.1 g (53%) of 1-CN-3-CH2Br-C6H4, m.p. 97 °C. The sample was sufficiently pure for the
next step. 1H NMR (CDCl3, 293 K): 4.47 s, 2 H (CH2Br); 7.47 dd, 1 H (Ar-H5); 7.61 m, 2 H
(Ar-H4,6); 7.69 s, 1 H (Ar-H2). 13C NMR (CDCl3, 293 K): 31.4 (CH2Br); 113.1, 118.4, 129.9,
132.1, 132.6, 133.5 (Ar-C); 139.4 (CN). For C8H6BrN (196.1) calculated: 49.0% C, 3.1% H;
found: 49.2% C, 3.3% H.
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NCO-Chelated Organoantimony(III) and Organobismuth(III) Dichlorides
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Synthesis of 1-CN-3-CH2OCH3-C6H4
1-CN-3-CH2Br-C6H4 (13.5 g, 0.069 mol) was added as a THF solution (60 ml) to a solution of
sodium methoxide (130 ml) prepared from the sodium metal (1.9 g, 0.083 mol). The reac-
tion mixture was stirred for 5 h. The reaction mixture was evaporated to dryness and the
residue was divided between diethyl ether (50 ml) and water (50 ml). The organic layer was
separated and the water phase extracted with additional 50 ml of diethyl ether. Combined
organic layers were dried over MgSO4 and evaporated to give the product as a yellowish oil.
The product was obtained after distillation at 90 °C (130 Pa) as colorless liquid 9.3 g (92%).
It was used for next step without further purification. 1H NMR (CDCl3, 293 K): 3.42 s, 3 H
(CH3O); 4.48 s, 2 H (CH2O); 7.46 dd, 1 H (Ar-H5); 7.57 m, 2 H (Ar-H4,6); 7.64 s, 1 H
(Ar-H2). 13C NMR (CDCl3, 293 K): 58.6 (CH3O); 73.5 (CH2O); 112.6, 118.9, 129.3, 130.9,
131.3, 131.8 (Ar-C); 140.0 (CN). For C9H9NO (147.2) calculated: 73.5% C, 6.2% H; found:
73.4% C, 6.1% H.
Synthesis of 1-CH2NH2-3-CH2OCH3-C6H4
1-CN-3-CH2OCH3-C6H4 (9.1 g, 0.062 mol) was carefully added as a neat oil via syringe to a
THF suspension (150 ml) of LiAlH4 (2.5 g, 0.066 mol) under stirring at 0 °C. The reaction
mixture was allowed to reach room temperature and remained stirred for additional 12 h.
Subsequently, the reaction mixture was heated to reflux for 5 h. After cooling back to room
tempearture, the remaining LiAlH4 was quenched with water (20 ml) and 2 M KOH (20 ml).
The resulting mixture was extracted twice with diethyl ether (2 × 50 ml). The organic layer
was dried over Na2SO4 and evaporated to yield 7.4 g (79%) of the product as a yellow oil
that was used for next step without further purification. 1H NMR (CDCl3, 293 K): 1.88 s, 2 H
(NH2); 3.37 s, 3 H (CH3O); 3.82 s, 2 H (CH2N); 4.43 s, 2 H (CH2O); 7.24 m, 4 H (Ar-H).
13C NMR (CDCl3, 293 K): 46.4 (CH2N); 58.3 (CH3O); 74.7 (CH2O); 126.3, 126.5 overlap of
two signals, 128.7, 131.5, 143.4 (Ar-C). For C9H13NO (151.2) calculated: 71.5% C, 8.7% H;
found: 71.7% C, 8.4% H.
Synthesis of 1-CH2N(CH3)2-3-CH2OCH3-C6H4 (L)
A mixture of 1-CH2NH2-3-CH2OCH3-C6H4 (7.4 g, 0.049 mol) was added to HCOOH (5 ml)
in water (30 ml) at 0 °C, followed by paraformaldehyde (2.94 g, 0.098 mol) used as a water
suspension (100 ml). The resulting mixture was heated to reflux for 5 h. After cooling to
room tempearture, an excess of solid KOH was added. The resulting mixture was extracted
twice with diethyl ether (2 × 50 ml). The organic layer was dried over Na2SO4 and evapo-
rated to give a yellow oil. The product was obtained after distillation at 65 °C (120 Pa) as
a colorless oil, yield 7 g (80%). 1H NMR (CDCl3, 293 K): 2.25 s, 6 H (N(CH3)2); 3.40 s, 3 H
(CH3O); 3.43 s, 2 H (CH2N); 4.46 s, 2 H (CH2O); 7.27 m, 4 H (Ar-H). 13C NMR (CDCl3,
293 K): 45.4 ((CH3)2N); 58.2 (CH3O); 64.5 (CH2N); 74.8 (CH2O); 126.6, 128.4, 128.5, 128.6,
138.3, 139.0 (Ar-C). For C11H17NO (179.3) calculated: 73.7% C, 9.6% H; found: 73.9% C,
9.5% H.
Synthesis of Sb(2-CH2N(CH3)2-6-(CH2OCH3-C6H3)Cl2 (1)
A hexane solution of 1.6 M n-BuLi (2.3 ml, 0.37 mmol) was added to a hexane solution
(20 ml) of the ligand L (0.66 g, 0.37 mmol). The resulting yellow-orange solution was stirred
Collect. Czech. Chem. Commun. 2010, Vol. 75, No. 10, pp. 1041–1050

1048
Vrána, Jambor, Růžička, Holeček, Dostál:
for 12 h. This solution of organolithium compound LLi was added to a pre-cooled (–70 °C)
solution of SbCl3 (0.84 g, 0.37 mmol) in diethyl ether (100 ml). The resulting cream suspen-
sion was stirred for 12 h at room temperature The insoluble material was filtered and
washed with additional hexane (20 ml). The remaining solid was extracted with dichloro-
methane (50 ml). Evaporation of the filtrate gave compound 1 as a yellowish powder, yield
0.75 g (55%). Compound 1 was crystallized from a dichloromethane/hexane solution to give
single crystals suitable for X-ray diffraction technique, m.p. 175 °C (decomp.). 1H NMR
(CDCl3, 293 K): 3.03 s, 6 H (N(CH3)2); 3.87 s, 3 H (CH3O); 4.41 s, 2 H (CH2N); 4.98 s, 2 H
(CH2O); 7.24 m, 2 H (Ar-H3,5); 7.37 t, 1 H (Ar-H4). 13C NMR (CDCl3, 293 K): 48.9
((CH3)2N); 59.9 (CH3O); 67.0 (CH2N); 74.8 (CH2O); 124.3, 125.1, 130.2, 141.8, 143.1, 155.9
(Ar-C). For C11H17NO (370.9) calculated: 35.6% C, 4.4% H; found: 35.7% C, 4.5% H.
Synthesis of Bi(2-CH2N(CH3)2-6-CH2OCH3-C6H3)Cl2 (2)
A hexane solution of 1.6 M n-BuLi (2.9 ml, 0.47 mmol) was added to a hexane solution
(20 ml) of the ligand L (0.83 g, 0.47 mmol). The resulting yellow-orange solution was stirred
for 12 h. The dissolved organolithium product LLi was added to a pre-cooled (–70 °C) solu-
tion of BiCl3 (1.48 g, 0.47 mol) in diethyl ether (100 ml). The resulting cream suspension
was stirred at room temperature for 12 h. The insoluble material was filtered off and washed
with additional hexane (20 ml). The remaining solid was extracted with dichloromethane
(50 ml). Evaporation of the filtrate gave compound 2 as a yellowish powder, yield 1.3 g
(61%). Compound 2 was crystallized by slow evaporation of a saturated dichloromethane
solution to give single crystals suitable for X-ray diffraction analysis, m.p. 180 °C (decomp.).
1H NMR (CDCl3, 293 K): 3.15 s, 6 H (N(CH3)2); 3.86 s, 3 H (CH3O); 4.83 s, 2 H (CH2N);
5.08 s, 2 H (CH2O); 7.49 dd, 1 H (Ar-H4); 7.73 d, 1 H (Ar-H); 7.85 d, 1 H (Ar-H). 13C NMR
(CDCl3, 293 K): 48.9 ((CH3)2N); 60.8 (CH3O); 71.6 (CH2N); 78.8 (CH2O); 127.0, 128.8, 129.5,
148.6, 152.6 (Ar-C); (Ar-C1) not observed. For C11H17NO (458.1) calculated: 28.8% C, 3.5% H;
found: 28.7% C, 3.7% H.
X-ray Crystallography
The details of the crystal structure determination and refinement for studied compounds are
given in Table I. The suitable single crystals were mounted on glass fibre with an oil and
measured on four-circle diffractometer KappaCCD with CCD area detector by mono-
chromatized MoKα radiation (λ = 0.71073 Å) at 150(1) K. The numerical12 absorption correc-
tions from crystal shape were applied for all crystals. The structures were solved by the
direct method (SIR92)13 and refined by a full matrix least squares procedure based on F2
(SHELXL97)14. Hydrogen atoms were fixed into idealized positions (riding model) and as-
signed temperature factors Hiso(H) = 1.2 Ueq (pivot atom) or 1.5 Ueq for the methyl moiety,
with C–H = 0.96, 0.97 and 0.93 Å for methyl, methylene and hydrogen atoms in the aro-
matic ring, respectively. The final difference maps displayed no peaks of chemical signifi-
cance, as the highest peaks and holes are in a close vicinity (~ 1 Å) of heavy atoms. The
non-positive temperature factors of C1, C2 C3 and C7 in structure of 2 were treated by
EADP instructions within the SHELXL97 program package14. CCDC 772343 (for 1) and
772344 (for 2) contain the supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from
the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge, CB2 1EZ, UK;
fax: +44 1223 336033; or deposit@ccdc.cam.ac.uk).
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NCO-Chelated Organoantimony(III) and Organobismuth(III) Dichlorides
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TABLE I
Crystallographic data for compounds 1 and 2
Parameter
1
2
Crystal system
orthorhombic
Pna21
monoclinic
Cc
Space group
a, Å
13.3120(4)
8.8241(16)
22.9329(16)
9.7231(12)
23.1532(14)
6.9678(9)
119.40(2)
1366.59(7)
4
b, Å
c, Å
β, °
V, Å3
2693.9(5)
8
Z
Density, g cm–3
µ, mm–1
1.829
2.425
150(1)
17672
5610; 0.035
4934
2.227
13.272
150(1)
T, K
No. of reflections measured
No. of unique reflections; Rint
No. of observed ref. [I > 2σ(I)]
No. of parameters
Final R indices [I > 2σ(I)]
wR2 indices (all data)
5189
2606; 0.069
2556
289
109
0.029
0.053
0.052
0.132
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