Chlorination of p-substituted triarylpnictogens by sulfuryl chloride: Difference in the reactivity and spectroscopic characteristics between bismuth and antimony

Article abstract of DOI:10.1016/j.jorganchem.2005.06.040

Competitive oxidative chlorination of p-substituted triarylstibines 3 [(p-XC₆H₄)₃Sb; a: X = OMe, c: Cl, d: CO ₂Et, e: CF₃, f: CN, g: NO₂] by sulfuryl chloride was carried out against 3b (X = H) and the electronic effect of these substituents on the chlorination of 3 was compared with that of homologous triarylbismuthanes 1. The relative ratios 4/4b (Ar₃SbCl ₂/Ph₃SbCl₂) decreased with increasing electron-withdrawing ability of the substituents (a: 53/47, c: 49/51, d: 46/54, e: 44/56, f: 40/60, g: 37/63), but the tendency was not so pronounced as observed in the chlorination of 1. A Hammett plot of the 4/4b ratios against the σ_p constants exhibited a good linear relationship with a negative slope, the value of which was almost half of that deduced from the 2/ 2b (Ar₃BiCl₂/Ph₃BiCl₂) ratios. The difference in the reactivity between 1 and 3 may be explained by the effect of the electron-withdrawing substituents in the aromatic rings, which affects the p-character of the lone pair on the pnictogen atoms by increasing the positive metal charge and appears more remarkably in 1 than in 3. The ¹³C NMR study of 3 revealed that the chemical shifts of the ipso carbons (C1) attached to the antimony show a linear relationship against the σ_p constants with a positive slope (14.5). The value was smaller than that deduced from 1 (17.0), suggesting that the antimony center of 3 is less sensitive to the substituent effect. This is in accord with the tendency of the chlorination.

Full text of DOI:10.1016/j.jorganchem.2005.06.040

Journal of Organometallic Chemistry 690 (2005) 4280–4284
www.elsevier.com/locate/jorganchem
Chlorination of p-substituted triarylpnictogens by sulfuryl
chloride: Difference in the reactivity and spectroscopic
characteristics between bismuth and antimony
*
A.F.M. Mustafizur Rahman, Toshihiro Murafuji , Motoko Ishibashi,
1
Youhei Miyoshi, Yoshikazu Sugihara
Department of Chemistry, Faculty of Science, Yamaguchi University, Yamaguchi 753-8512, Japan
Received 18 March 2005; received in revised form 9 June 2005; accepted 21 June 2005
Available online 11 August 2005
Abstract
Competitive oxidative chlorination of p-substituted triarylstibines 3 [(p-XC6H4)3Sb; a: X = OMe, c: Cl, d: CO2Et, e: CF3, f: CN,
g: NO2] by sulfuryl chloride was carried out against 3b (X = H) and the electronic effect of these substituents on the chlorination of 3
was compared with that of homologous triarylbismuthanes 1. The relative ratios 4/4b (Ar3SbCl2/Ph3SbCl2) decreased with increas-
ing electron-withdrawing ability of the substituents (a: 53/47, c: 49/51, d: 46/54, e: 44/56, f: 40/60, g: 37/63), but the tendency was not
so pronounced as observed in the chlorination of 1. A Hammett plot of the 4/4b ratios against the rp constants exhibited a good
linear relationship with a negative slope, the value of which was almost half of that deduced from the 2/2b (Ar3BiCl2/Ph3BiCl2)
ratios. The difference in the reactivity between 1 and 3 may be explained by the effect of the electron-withdrawing substituents in
the aromatic rings, which affects the p-character of the lone pair on the pnictogen atoms by increasing the positive metal charge
and appears more remarkably in 1 than in 3. The 13C NMR study of 3 revealed that the chemical shifts of the ipso carbons
(C1) attached to the antimony show a linear relationship against the rp constants with a positive slope (14.5). The value was smaller
than that deduced from 1 (17.0), suggesting that the antimony center of 3 is less sensitive to the substituent effect. This is in accord
with the tendency of the chlorination.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Antimony; Bismuth; Oxidative chlorination; 13C NMR study; Hammett plot
1. Introduction
1g bearing a nitro group does not show any reactivity
in the chlorination (2g/2b = 0/100). Such a marked
electronic effect should be stressed since the lone pair
of the bismuth atom is inherently an s-character and
cannot efficiently overlap with the 2p orbitals of the
aromatic ring carbons. To know how the electronic ef-
fect affects the reactivity of triarylpnictogen more
clearly, homologous antimony system was chosen for
comparison [2]. We describe here the oxidative chlori-
nation of p-substituted triarylstibines 3 together with
the spectroscopic characteristics of 3 and their dichlo-
rides 4, in comparison with the bismuth congeners (see
Chart 1).
Recently, we have reported the effect of substituents
on the reactivity and spectroscopic characteristics of
triarylbismuthanes 1 and their dichlorides 2 [1]. Com-
petitive chlorination of 1 against 1b by sulfuryl chlo-
ride revealed that the reactivity of 1 is dramatically
lowered by the electron-accepting substituents. Thus,
*
Corresponding author. Fax: +81 83 933 5738.
E-mail addresses: murafuji@yamaguchi-u.ac.jp (T. Murafuji),
sugihara@yamaguchi-u.ac.jp (Y. Sugihara).
1
Fax: +81 83 933 5730.
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.06.040

A.F.M.M. Rahman et al. / Journal of Organometallic Chemistry 690 (2005) 4280–4284
4281
of the ring carbons used in p interaction and that changes
in the r and p network are competitive [5]. The effect of
electron-withdrawing substituents on the structure and
stabilities of compounds containing heavier main group
elements has been studied from the viewpoint of sp-
hybridization [6]. In substituted lead compounds, an
increasing positive metal charge due to electronegative
substituents increases the size differences between the 6s
and 6p orbitals by greater contraction of the 6s orbital
and makes the efficient sp-hybridization less favorable
[6a]. This destabilizes electronegatively substituted
Pb(IV) compounds. Thus, such an effect of the electron-
withdrawing substituents may reduce the p-character of
the lone pair on the pnictogen atoms, lowering the reactiv-
ity of 1 and 3. It is known that configurational inversion at
the trivalent antimony and bismuth centers can take place
via the edge inversion process [6b] when these central
atoms are substituted by electron-withdrawing substitu-
ents [6c,6d], although the inversion at the pnictogen cen-
ters is a slow process except for the classical vertex
inversion typified by nitrogen. The trigonal transition
state of the classical vertex inversion is destabilized by
the similar electronic effect while the T-shaped transition
state of the edge inversion is rather favorable [6e]. The
pronounced substituent effect in 1 compared to that in 3
seems to be due to the larger orbital size and more electro-
positive nature of bismuth atom than antimony atom. We
have observed the predominant chlorination of 3b over 1b
(4b/2b = 62/38) in the competitive chlorination and as-
cribed this result to the higher p-character of the lone pair
on the antimony atom [1]. This is reflected in the C–Sb–C
bond angles of 3b [98.0(3)ꢁ, 96.0(3)ꢁ, 95.7(3)ꢁ and
97.5(3)ꢁ, 95.5(4)ꢁ, 95.1(3)ꢁ for the two independent mole-
cules in the asymmetric unit] [7], which are larger than the
C–Bi–C bond angles of 1b [96(1)ꢁ, 94(1)ꢁ and 92(1)ꢁ] [8].
X
M
3
X
MCl2
3
1: M = Bi
3: M = Sb
2: M = Bi
4: M = Sb
X = a: MeO, b: H, c: Cl, d: CO2Et,
e: CF3, f: CN, g: NO2
Chart 1.
2. Results and discussion
Substituted triarylstibines 3 were synthesized from the
corresponding aryllithium or aryl-magnesium in accor-
dance with the method for the synthesis of 1 [3]. Compet-
itive chlorination of 3 was carried out against 3b (Eq. (1))
and the result is summarized in Table 1. The relative ratios
1
4/4b (estimated by H NMR) decreased with increasing
electron-withdrawing nature of the p-substituent, but
the tendency was not so pronounced as that of 2/2b. As
shown in Fig. 1, a Hammett plot of 4/4b against rp con-
stants [4] showed a good linear relationship (n = 6,
r = 0.95) with a negative slope (ꢀ0.51), which is almost
half of the 2/2b value (ꢀ0.97). The nuclear quadrupole
resonance study of certain substituted triarylstibines has
suggested that the efficient means of transmission of the
substituent effect to the antimony atom is through the
Sb–C r bonds owing to the mismatch with the p orbitals
Table 1
Relative ratios in the competitive reaction
(a)
(c)
(d)
(e)
(f)
(g)
2/2b
4/4b
53/47
53/47
33/67
49/51
29/71
46/54
35/65
44/56
16/84
40/60
0/100
37/63
1.4
1.2
1
MeO
/
4 4b
Cl
Cl
/
2 2b
CO2Et
CF3
0.8
0.6
0.4
0.2
0
CN
NO2
CF3
CO2Et
CN
NO2
-0.3 -0.2 -0.1
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
1
σ p
Fig. 1. Hammett plots.

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A.F.M.M. Rahman et al. / Journal of Organometallic Chemistry 690 (2005) 4280–4284
SO2Cl2 (1.0 mmol)
C2
C3
+
+
Ar3Sb (Ar ≠ Ph)
3
(1.0 mmol)
Ph3Sb
3b
Ar3SbCl2
Ph3SbCl2
CH2Cl2, r.t.
4
4b
C4
C1
(1.0 mmol)
(+ recovery of 3 and 3b)
C5
Sb
ð1Þ
Chart 2.
The chemical shifts (dC) of the aromatic ring carbons
of 3 and 4 are shown in Table 2. The signals due to the
ipso carbons (C1) attached to the antimony shifted
downfield from about 9 to 12 ppm relative to those of
the parent monosubstituted benzenes 5 [9], but the ten-
dency was not so pronounced as observed in 1 and 2
(25–30 ppm). The signals due to the C2 atoms were ob-
served downfield from about 6 to 8 ppm relative to those
of 5 but the C3 and C4 signals appeared at the region
close to the corresponding signals of 5. With respect to
the C2, C3 and C4 atoms, the chemical shifts of 3 and
4 were approximately comparable to those of 1 and 2,
respectively. An outstanding spectroscopic feature is in
the chemical shifts of the C1 atoms. The C1 signals
shifted downfield with increasing electron-withdrawing
nature of the p-substituents and the chemical shifts of
these signals showed linear relationships against the
Hammett rp constants (n = 7) with positive slopes (3:
14.5, r = 0.86, 4: 12.7, r = 0.83) as well as those of 1, 2
and 5 (1: 17.0, r = 0.89, 2: 11.7, r = 0.81, 5: 12.0,
r = 0.88). It is known that the chemical shifts of the
C1 atoms of 5 are correlated with the rp constants and
total charge density on these carbons [10]. The smaller
value of 3 than that of 1, therefore, implies that the anti-
mony center of 3 is less sensitive to the electronic effect.
This is in accord with the tendency of the chlorination.
Furthermore, the small difference in the slope values be-
tween 3 and 4 compared to that of the bismuth congen-
ers shows that the bismuth system is more sensitive to
the electronic effect with change in the geometry of the
metal center (see Chart 2).
Table 3
The difference in the chemical shifts between 3 and 4 (D4)
(C1)
(C2)
(C3)
(C4)
a
b
c
d
e
f
1.32
1.52
1.53
0.14
0.88
0.24
ꢀ0.66
ꢀ1.54
ꢀ2.13
ꢀ1.89
ꢀ2.10
ꢀ1.76
ꢀ1.77
ꢀ1.59
0.30
0.72
0.54
0.76
0.82
1.26
0.62
2.05
3.15
3.34
2.65
2.77
2.98
1.24
g
Table 3 shows the difference in the chemical shift be-
tween 3 and 4 (D4 = d4 ꢀ d3), which is suggestive of the
tendency of polarization on the aromatic rings of 4 when
the geometry of the antimony center changes from trico-
ordinate to pentacoordinate. p-Polarization is found to
arise in the aromatic rings of 2 on the basis of the chemical
shifts of 1 and 2 (D2 = d2 ꢀ d1), where the charge distribu-
tion of the C1 and C2 atoms are negative while that of the
C3 and C4 atoms positive [1]. Furthermore, dependence
of the electronic effect on the p-polarization is marked
in the C1 atoms. In contrast to the D2(C1) values which
dramatically increase negatively from 1.67 (a) to ꢀ4.08
(g), the D4(C1) values did not show such pronounced
changes, although gradually increased negatively like
the D2(C1) values. The D4 values of the C2, C3 and C4
atoms were also not so large as the D2 values. These find-
ings indicate that the charge distribution ofthe C1, C3 and
C4 is positive while that of the C2 negative, thus similar p-
polarization taking place. The ipso carbons attached to
the silicon of the pentacoordinate silicates are known to
appear more downfield compared to those of the parent
tetracoordinate silanes due to the p-polarization induced
by the electronic fields of the charged substituents [11].
This may be applicable to the bismuth and antimony sys-
tem [12]. Thus, the upfield shift of the C1 signals of 2 rel-
ative to those of 1 is attributed to the positively polarized
bismuth center of 2 due to the electron-withdrawing chlo-
rine atoms. In contrast, the downfield shift of the C1 sig-
nals of 4 compared to those of 3 is considered to show that
the antimony center of 4 is not so polarized as the bismuth
center of 2 with increasing electron-withdrawing nature of
the p-substituents.
Table 2
13C NMR spectral data (d) of 3 and 4 in CDCl3
C1
C2
C3
C4
C5
CH2
CH3
3
a
b
c
129.07
138.40
135.83
143.99
142.21
143.61
145.81
137.32
136.24
137.29
136.11
136.41
136.57
136.92
114.65
128.87
129.31
129.69
125.73
132.39
123.83
160.07
128.59
135.54
131.08
131.44
113.49
148.91
55.06
d
e1
f
166.43
123.94
118.20
61.10
14.30
g
4
a
b
c
130.39
139.92
137.36
144.13
143.09
143.85
145.15
135.78
134.11
135.40
134.01
134.65
134.80
135.33
114.95
129.59
129.85
130.45
126.55
133.65
124.45
162.12
131.74
138.88
133.73
134.21
116.47
150.15
55.44
14.26
3. Experimental
d
e1
f
165.38
123.25
117.18
61.61
Dichloromethane and THF were distilled from calcium
hydride under nitrogen before use. 1H and 13C NMR spec-
tra were recorded in CDCl3 on a BRUKER AVANCE
400S spectrometer with TMS as an internal standard. IR
g
1
Quartet, JCF = around 3.6, 33.0 and 271.3 Hz for C3, C4 and C5,
respectively.

A.F.M.M. Rahman et al. / Journal of Organometallic Chemistry 690 (2005) 4280–4284
4283
spectra were observed as KBr pellets on a Nicolet Impact
410 spectrophotometer. Triphenylstibine (3b) was pur-
chased from Tokyo Kasei Kogyo Co., Ltd. Triarylstibines
3a, 3c and 3e were synthesized from the corresponding
Grignard reagents and antimony(III) chloride.
Tris(4-methoxyphenyl)stibine (3a): yield 52%; m.p.
182–185 ꢁC; 1H NMR d 3.80 (s, 9H), 6.88 (d, 6H,
J = 8.6 Hz), 7.33 (d, 6H, J = 8.6 Hz).
acetate (3 · 10 ml). The combined extracts were dried
(Na2SO4) and concentrated to leave a residue, which
was crystallized from methanol to give a pure product.
Tris(4-nitrophenyl)stibine (3g): yield 34%; m.p. 214–
1
216 ꢁC; H NMR d 7.61 (d, 6H, J = 8.6 Hz), 8.22 (d,
6H, J = 8.6 Hz); IR (cmꢀ1): 1593, 1570, 1519, 1345,
851, 736, 702. Anal. Calc. for C18H12N3O6Sb: C,
44.30; H, 2.48; N, 8.61. Found: C, 44.10; H, 2.20; N,
8.80%.
Tris(4-chlorophenyl)stibine (3c): yield 42%; m.p. 112–
112.5 ꢁC (lit. [5], 110–111 ꢁC); 1H NMR d 7.26 (s, 12H).
Tris(4-trifluoromethylphenyl)stibine (3e): yield 48%;
3.3. Reaction of 3 with sulfuryl chloride: general
procedure
1
m.p. 130–132 ꢁC (lit. [5], 130–132 ꢁC); H NMR d 7.54
(d, 6H, J = 7.8 Hz), 7.61 (d, 6H, J = 7.8 Hz).
To a solution of triarylstibine 3 (1 mmol) in dichloro-
methane (5 ml) was added at room temperature a 1.0 M
solution of sulfuryl chloride in the same solvent (1 ml).
After completion of the reaction (checked by TLC),
the resulting mixture was concentrated to leave a resi-
due, which was crystallized by an addition of hexane
to give a pure product.
Tris(4-methoxyphenyl)antimony dichloride(4a): yield
89%; m.p. 108–110 ꢁC; 1H NMR d 3.86 (s, 9H), 7.05 (d,
6H, J = 9.0 Hz), 8.16 (d, 6H, J = 9.0 Hz); Anal. Calc.
for C21H21Cl2O3Sb: C, 49.07; H, 4.12. Found: C,
48.89; H, 3.90%.
3.1. Synthesis of triarylstibines 3d and 3f: general
procedure
To a solution of 4-iodoarene (3 mmol) in THF
(10 ml) was added dropwise at ꢀ40 ꢁC a solution of iso-
propylmagnesium bromide (3.6 mmol) in the same sol-
vent (6 ml) and the mixture was stirred for 30 min,
during which time the temperature was raised to
ꢀ20 ꢁC. The aryl-Grignard reagent thus generated
in situ was cooled to ꢀ40 ꢁC, a solution of antimony(III)
chloride (1 mmol) in THF (5 ml) was added dropwise,
and the resulting mixture was gradually raised to ambi-
ent. The reaction was quenched with brine and insoluble
substances were filtered off. The mixture was extracted
with ethyl acetate (3 · 10 ml). The combined extracts
were dried (Na2SO4) and concentrated to leave an oily
residue, which was crystallized from methanol to give
a pure product.
Triphenylantimony dichloride (4b): yield 92%; m.p.
1
139–141 ꢁC (lit. [13], 139–142 ꢁC); H NMR d 7.56 (m,
9H), 8.24 (m, 6H).
Tris(4-chlorophenyl)antimony dichloride (4c): yield
91%; m.p. 193–194 ꢁC; 1H NMR d 7.54 (d, 6H,
J = 8.6 Hz), 8.56 (d, 6H, J = 8.6 Hz). Anal. Calc. for
C18H12Cl5Sb: C, 41.00; H, 2.29. Found: C, 41.22; H, 2.50%.
Tris(4-ethoxycarbonylphenyl)stibine (3d): yield 48%;
m.p. 74–76 ꢁC; 1H NMR d 1.38 (t, 9H, J = 7.2 Hz), 4.37
(q, 6H, J = 7.2 Hz), 7.48 (d, 6H, J = 8.2 Hz), 7.99 (d,
6H, J = 8.2 Hz); IR (cmꢀ1): 2986, 1730, 1589, 1386,
1280, 1121, 1056, 1013, 747, 694. Anal. Calc. for
C27H27O6Sb: C, 56.97; H, 4.78. Found: C, 56.77; H, 4.91%.
Tris(4-cyanophenyl)stibine (3f): yield 22%; m.p. 202–
205 ꢁC; 1H NMR d 7.50 (d, 6H, J = 8.2 Hz), 7.64 (d, 6H,
J = 8.2 Hz); IR (cmꢀ1): 2228, 1586, 1483, 1385, 1056,
1013, 828, 550. Anal. Calc. for C21H12N3Sb: C, 58.92;
H, 2.83; N, 9.82. Found: C, 59.15; H, 2.98; N, 9.97%.
Tris(4-ethoxycarbonylphenyl)antimony
dichloride
1
(4d): yield 72%; m.p. 128–130 ꢁC; H NMR d 1.41 (t,
9H, J = 7.1 Hz), 4.42 (q, 6H, J = 7.1 Hz), 8.22 (d, 6H,
J = 8.6 Hz), 8.30 (d, 6H, J = 8.6 Hz); IR (cmꢀ1): 2986,
1733, 1587, 1390, 1301, 1184, 1125, 1053, 1010, 851,
754, 689. Anal. Calc. for C27H27Cl2O6Sb: C, 50.66; H,
4.25. Found: C, 50.38; H, 4.41%.
Tris(4-trifluoromethylphenyl)antimony
dichloride
1
(4e): yield 89%; m.p. 127–129 ꢁC; H NMR d 7.85 (d,
6H, J = 8.1 Hz), 8.38 (d, 6H, J = 8.1 Hz). Anal. Calc.
for C21H12Cl2F9Sb: C, 40.17; H, 1.93. Found: C,
40.34; H, 1.88%.
3.2. Synthesis of triarylstibine 3g
Tris(4-cyanophenyl)antimony dichloride (4f): yield
86%; m.p. 176–178 ꢁC; 1H NMR d 7.87 (d, 6H,
J = 8.5 Hz), 8.37 (d, 6H, J = 8.5 Hz); IR (cmꢀ1): 2231,
1483, 1390, 1010, 828, 547. Anal. Calc. for
C21H12Cl2N3Sb: C, 50.55; H, 2.42; N, 8.42. Found: C,
50.30; H, 2.22; N, 8.18%.
To a solution of 4-iodonitrobenzene (3 mmol) in
THF (20 ml) was added dropwise at ꢀ100 ꢁC a solution
of phenyllithium (3.8 mmol) in cyclohexane–Et2O solu-
tion (3.8 ml). A solution of antimony(III) chloride
(1 mmol) in THF (5 ml) cooled to ꢀ100 ꢁC was then
transferred immediately into the dark purple solution
of 4-nitrophenyllithium obtained above, and the result-
ing mixture was gradually raised to ambient. The reac-
tion was quenched with brine and insoluble substances
were filtered off. The mixture was extracted with ethyl
Tris(4-nitrophenyl)antimony dichloride (4g): yield
1
89%; m.p. 230–233 ꢁC (decomp.); H NMR d 8.44 (d,
6H, J = 9.1 Hz), 8.47 (d, 6H, J = 9.1 Hz); IR (cmꢀ1):
1599, 1531, 1390, 1356, 850, 735. Anal. Calc. for
C18H12Cl2N3O6Sb: C, 38.68; H, 2.16; N, 7.52. Found:
C, 38.40; H, 2.06; N. 7.43%.

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