Synthesis and single crystal structure of a three coordinate complex of mercury(II) with 1-(ethylthio)-2-(diphenylphosphino) ethane (L) prepared by a new simple method

Article abstract of DOI:10.1016/j.poly.2006.04.025

The (P, S) ligand 1-(ethylthio)-2-(diphenylphosphino) ethane (L) is synthesized by reacting Ph₂PLi with CH₃CH₂SCH₂CH₂Cl. The yield is good (～85%) and the method of preparation is simpler than the liqu

Full text of DOI:10.1016/j.poly.2006.04.025

Polyhedron 25 (2006) 2915–2919
www.elsevier.com/locate/poly
Synthesis and single crystal structure of a three coordinate complex
of mercury(II) with 1-(ethylthio)-2-(diphenylphosphino) ethane
(L) prepared by a new simple method
a
a,
b
c
c
Garima Singh , Ajai K. Singh *, John E. Drake , Michael B. Hursthouse , Mark E. Light
a
Department of Chemistry, Indian Institute of Technology, New Delhi 110016, India
Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ont., Canada N9B 3P4
b
c
Department of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, UK
Received 26 March 2006; accepted 18 April 2006
Available online 8 May 2006
Abstract
The (P, S) ligand 1-(ethylthio)-2-(diphenylphosphino) ethane (L) is synthesized by reacting Ph2PLi with CH3CH2SCH2CH2Cl. The
yield is good (ꢀ85%) and the method of preparation is simpler than the liquid ammonia based one reported earlier. Its complexation
with Cu(I), Hg(II) and organometallic species of Ru(II) are explored. All the complexes and the ligand exhibit characteristic proton,
carbon-13 and phosphorus-31 NMR spectra. The single crystal structure of the Hg(II) complex has been determined. It is found to
be a three coordinate complex. The sum of the bond angles at Hg, viz. P(1)–Hg(1)–Br(1), P(1)–Hg(1)–Br(2) and Br(1)–Hg(1)–Br(2),
is ꢁ360ꢀ. Thus the geometry around Hg can best be described as essentially trigonal planar. The Hg(1)–P(1) bond length is
˚
˚
2.415(1) A and the Hg–Br bond lengths are 2.5152(6) and 2.5952(6) A. There exists a weak secondary interaction between Hg and
˚
˚
the S donor site of the ligand [Hg(1)Á Á ÁS(1) bond distance 3.063(1) A < sum of van der Waal’s radii 3.35 A].
ꢁ 2006 Elsevier Ltd. All rights reserved.
Keywords: 1-(Ethylthio)-2-(diphenylphosphino) ethane; Copper; Ruthenium; Mercury; Complex; Three coordinate complex; Single crystal structure
1. Introduction
C2H5SCH2CH2Cl in THF at À78 ꢀC. This also avoids
the handling of obnoxious liquid ammonia.
Hybrid phosphine ligands containing a sulfur donor
atom, viz. 1-(alkyl/arylthio)-2-(diphenylphosphino) ethane,
have been synthesized by reacting sodium diphenylphos-
phide with the appropriate organic halide in liquid ammo-
nia, and their metal complexes with Ni(0), Rh(I), Ir(I),
(CO)2Co(I), Pt(II), (g3-2-Me-allyl)Pd(II), Co(II), Ru(II)
and Co(III) have been explored [1–10]. A sister ligand,
Ph2PCH2SCH3, and its complexes with Pd(II), Pt(II) and
Rh(I) have also been explored [11,12]. We have found
that 1-(ethylthio)-2-(diphenylphosphino) ethane (L) is
obtained easily (yield ꢀ 85%) when PPh2Li reacts with
4
2
1
3
THF
-78oC
THF
CH3CH2SCH2CH2Cl
PPh2CH2CH2SCH2CH3
PPh2Li +
PPh Cl Li
+
2
L
The reactions of L with Cu2Br2, HgBr2 and [Ru(p-cym-
ene)Cl2] have not been previously studied, and therefore
they are investigated in detail and the results are reported
in the present paper. Single crystals of [HgBr2(L)] (2) were
found to be suitable for X-ray diffraction and therefore its
single crystal structure was determined. Mercury in this
complex is three coordinated as L coordinates through
phosphorus only. The distance between Hg and sulfur is
long but less than the sum of the van der Waal’s radii, indi-
cating a weak interaction only. The proton and carbon-13
NMR of L and all its metal complexes are characteristic.
The long Hg–S bond (weak interaction) is a surprising
*
Corresponding author. Tel.: +91 11 26591379; fax: +91 11 26581102.
E-mail addresses: aksingh@chemistry.iitd.ac.in, ajai57@hotmail.com
(A.K. Singh).
0277-5387/$ - see front matter ꢁ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2006.04.025

2916
G. Singh et al. / Polyhedron 25 (2006) 2915–2919
result, as the biological chemistry of mercury is dominated
by coordination to cysteine [13]. The preference of Hg for
sulfur donor sites, due to its soft nature, is well known.
In mercury thiolates, apart from the Hg–S bond, the possi-
bility of a secondary mercury(II)–sulfur interaction has
also been reported [14–16], which makes it difficult to antic-
ipate the structures of such complexes.
solved in 10 cm3 of nitromethane under nitrogen atmo-
sphere. The resulting mixture was stirred under an inert
nitrogen atmosphere for 2 h at room temperature. There-
after, the solution was filtered through celite. The clear
filtrate was concentrated to ꢀ10 cm3 on a rotary evapora-
tor and mixed with hexane (20 cm3). The resulting white
solid was filtered, washed with hexane (3 · 20 cm3) and
dried in vacuo and stored under inert conditions. Complex
1 was recrystallized from chloroform–hexane mixture (1:1).
Yield: 75%; m.p.: 78 ꢀC (d). Anal. Calc.: C, 38.79, H, 3.81.
2. Experimental
1
The C and H analyses were carried out with a Perkin–
Elmer elemental analyzer 240 C. The 1H and 13C{1H}
NMR spectra were recorded on a Bruker Spectrospin
DPX-300 NMR spectrometer at 300.13 and 75.47 MHz,
respectively. 31P{1H} NMR spectra were recorded at
121.49 MHz using H3PO4 as an external indicator. IR spec-
tra in the range 4000–250 cmÀ1 were recorded on a Nicolet
Found: C, 38.72, H, 3.01%. Km: 6.50 XÀ1 cm2 molÀ1; H
NMR (d vs TMS, CDCl3, 25 ꢀC) 1.21–1.26 (t, 3H, H1),
2.58–2.60 (m, 2H, H4), 2.69–2.76 (m, 2H, H2), 2.83–2.88
(m, 2H, H3), 7.30–7.47 (m, 10H, Ar-H of –PPh2);
13C{1H} NMR (d vs TMS, 25 ꢀC), 13.5 (C1), 26.5, 26.7
(C4), 29.5, 29.7 (C2), 30.1 (C3), 128.7, 128.8, 130.8, 131.2,
132.5, 133.1, 133.3 (Ar-C of PPh2).
´
Protege 460 FT-IR spectrometer as KBr pellets. The con-
ductance measurements were made in acetonitrile (concen-
tration ꢀ1 mM) using an ORION conductivity meter
model 162. The molecular weights (concentration
ꢀ5 mM) in chloroform were determined with a Knauer
vapour pressure osmometer model A0280. The melting
points determined in open capillary are reported as such.
The Ph2PCl and 2-chloroethyl ethyl sulfide were obtained
from Aldrich (USA). [RuCl2(p-cymene)]2 was synthesized
by the reported method [17].
2.3. Synthesis of [HgBr2(L)] (2)
HgBr2 (0.20 g, 0.55 mmol) was dissolved in acetone
(20 cm3) and mixed with a solution of L (0.15 g,
0.55 mmol) in chloroform (20 cm3). The resulting mixture
was stirred at room temperature until the ligand L was con-
sumed (as monitored by TLC). The solvent was removed
from the mixture on a rotary evaporator. The resulting res-
idue was dissolved in 20 cm3 of chloroform and filtered
through celite. The filtrate was concentrated to 10 cm3 on
a rotary evaporator and mixed with 20 cm3 of hexane.
The white complex 2 was filtered, dried in vacuo and
recrystallized from chloroform–hexane (1:1) mixture.
Yield: 80%; m.p.: 135 ꢀC. Anal. Calc.: C, 30.26, H, 2.29.
Found: C, 30.04, H, 2.66%. Molecular weight; found:
2.1. Synthesis of 1-(ethylthio)-2-(diphenylphosphino)
ethane (L)
Chlorodiphenylphosphine solution (5.0 cm3 of 1.0 M
solution in THF) was added to lithium (0.63 g, 5.0 mmol)
in dry THF (25 cm3) at room temperature in a Schlenk
flask. The mixture was stirred until the solution became
dark red in colour, which indicated the formation of lith-
ium diphenylphosphide. The PPh2Li was then filtered and
transferred to a Schlenk tube under nitrogen atmosphere
and cooled to À78 ꢀC. 2-Chloroethyl ethyl sulfide (0.62 g,
5.0 mmol) was added to it with constant stirring. The mix-
ture was allowed to come to room temperature over ꢀ12 h,
after which all the THF was evaporated off from the mix-
ture on a rotary evaporator and the residue was dissolved
in deoxygenated dichloromethane (30 cm3). The solution
was again concentrated to ꢀ10 cm3on a rotary evaporator
and mixed with hexane (30 cm3). The resulting solid was
then recrystallized with a dichloromethane–methanol mix-
ture (1:1) to obtain L as a white crystalline solid. Yield
ꢀ85%; m.p. 45 ꢀC. Anal. Calc.: C, 70.04, H, 6.98. Found:
659.0, calculated: 634.39; Km: 4.60 XÀ1 cm2 molÀ1 1H
;
NMR (d vs TMS, CDCl3, 25 ꢀC), 1.27–1.32 (t, 3H, H1),
2.66–3.11 (m, 6H, H4, H3 and H2), 7.59–7.80 (m, 10H,
Ar-H of –PPh2); 13C{1H} NMR (d vs TMS, 25 ꢀC), 13.8
(C1), 26.3 (C4), 27.4 (C2), 30.1 (C3), 129.9, 130.00, 132.9,
33.26, 134.00 (Ar-C of PPh2).
2.4. Synthesis of [Ru(p-cymene)Cl2(L)] (3)
[RuCl2(p-cymene)]2 (0.61 g, 1.0 mmol) was taken in
20 cm3 of dichloromethane and a solution of L (0.54 g,
2.0 mmol) in 10 cm3 of dichloromethane was added to it.
The mixture was stirred for 2 h at room temperature. The
solvent was completely removed on a rotary evaporator
under reduced pressure. The residue obtained was dis-
solved in dichloromethane (5 cm3) and mixed with hexane
(30 cm3). The resulting red precipitate (3) was filtered,
washed with hexane (3 · 20 cm3) and dried in vacuo. It
was recrystallized from dichloromethane–hexane (1:1) mix-
ture. Yield: 80%; m.p.: 89 ꢀC (d). Anal. Calc.: C, 53.78, H,
5.68. Found: C, 52.71, H, 5.25%. Molecular weight; found:
1
C, 70.01; H, 6.30%. H NMR (d vs TMS, CDCl3, 25 ꢀC):
1.17–1.22 (t, 3H, H1), 2.30–2.35 (m, 2H, H4), 2.49–2.62
(m, 4H, H3 and H2), 7.32–7.47 (m, 10H, Ar-H of PPh2).
2.2. Synthesis of [CuBr(L)]2 (1)
620.0, calculated: 580.07; Km: 3.80 XÀ1 cm2 molÀ1 1H
;
NMR (d vs TMS, CDCl3, 25 ꢀC), 1.22–1.33 (m, 9H,
H1 + CH3 of i-Pr), 2.15 (s, 3H, CH3 of p-cymene), 2.29
To a solution of L (0.13 g, 0.50 mmol) made in 10 cm3 of
chloroform was added Cu2Br2 (0.07 g, 0.50 mmol) dis-

G. Singh et al. / Polyhedron 25 (2006) 2915–2919
2917
(m, 1H, CH of p-cymene), 2.81–3.06 (m, 6H, H4, H3 and
H2), 7.37–7.72 (m, 10H, Ar-H of –PPh2); 13C{1H} NMR
(d vs TMS, 25 ꢀC), 12.09 (C1), 17.11 (CH3 of i-Pr), 20.1
(C4), 22.3 (CH3 of p-cymene), 28.8 (C2), 32.5 (CH of p-
cymene), 33.1 (C3), 87.9, 91.0 (Ar-C of p-cymene), 127.0,
128.3 129.9, 130.3, 132.2, 137.0 (Ar-C of PPh2).
2.5. X-ray crystallography
The X-ray data for 2 were collected (at 120 K) on an
Enraf Nonius Kappa CCD area detector diffractometer,
with / and x scans chosen to give a complete asymmetric
unit. Cell refinement [18,19] corresponds to an orthorhom-
bic cell whose dimensions are given in Table 1, along with
other experimental parameters. An absorption correction
was applied [18,19]. The structure was solved by direct
methods [20] and refined using the WinGX version [21]
of SHELX-97 [22]. Hydrogen atoms were included in ideal-
ized positions with isotropic thermal parameters set at 1.2
times that of the carbon atom to which they were attached.
Non-hydrogen atoms were treated anisotropically. The
final cycle of full-matrix least-squares refinement for 2
was based on 4199 observed reflections (3243 for
F2 > 4r(F2)) and 191 variable parameters and converged
(largest parameter shift was 0.001 times its esd). The molec-
ular structure of 2 is displayed as an ORTEP diagram in
Fig. 1. Its selected bond lengths and bond angles are given
in Table 2.
Fig. 1. Molecular structure of [HgBr2(L)] (2).
Table 2
˚
Selected bond lengths (A) and angles (ꢀ) for 2
Hg(1)–Br(1)
Hg(1)–P(1)
S(1)–C(14)
P(1)–C(1)
2.5152(6)
2.415(1)
1.811(5)
1.809(5)
1.825(5)
Hg(1)–Br(2)
Hg(1)–S(1)
S(1)–C(15)
P(1)–C(7)
2.5952(6)
3.063(1)
1.811(6)
1.810(5)
Table 1
Crystal data and structure refinement for 2
Empirical formula
Formula weight
Temperature (K)
C16H19PSBr2Hg
634.75
120(2)
0.71073
orthorhombic
Pbca
P(1)–C(13)
Br(1)–Hg(1)–P(1)
Br(1)–Hg(1)–Br(2)
Br(1)–Hg(1)–S(1)
Hg (1)–P(1)–C(1)
Hg(1)–P(1)–C(13)
C(1)–P(1)–C(7)
C(7)–P(1)–C(13)
C(7)–C(8)–C(9)
C(9)–C(10)–C(11)
C(11)–C(12)–C(7)
135.52(4)
Br(2)–Hg(1)–P(1)
P(1)–Hg(1)–S(1)
Br(2)–Hg(1)–S(1)
Hg(1)–P(1)–C(7)
C(14)–S(1)–C(15)
C(1)–P(1)–C(13)
119.48(4)
104.98(2)
92.22(3)
112.6(2)
108.5(2)
107.3(2)
105.3(2)
120.0(5)
120.0(5)
119.6(5)
78.78(4)
101.23(3)
115.3(2)
100.6(3)
107.4(2)
˚
Wavelength (A)
Crystal system
Space group
˚
a (A)
13.567(1)
14.859(1)
18.095(1)
3647.6(6)
8
2.312
13.014
2368
0.15 · 0.08 · 0.02
3.30–27.53.
À17 6 h 6 17,
À19 6 k 6 19,
À23 6 l 6 23
29610
˚
b (A)
˚
c (A)
3
C(8)–C(9)–C(10)
C(10)–C(11)–C(12)
C(12)–C(7)–C(8)
120.4(5)
120.6(5)
119.3(4)
˚
V (A )
Z
Dcalc (g/cm3)
Absorption coefficient (mmÀ1
F(000)
)
Crystal size (mm3)
3. Results and discussion
h Range for data collection (ꢀ)
Index ranges
The ligand L, obtained as white crystalline solid, is
unstable and is moisture and air sensitive. It can be stored
at low temperature ꢀ5 ꢀC in dry nitrogen atmosphere with-
out appreciable decomposition for 2–3 months easily. It is
soluble in common organic solvents such as chloroform,
dichloromethane and acetone, but is insoluble in hexane.
The crystals of 2 are not air and moisture sensitive, but 1
and 3 require storing in a refrigerator to avoid their decay.
The complexes are soluble in common organic solvents
such as chloroform, dichloromethane and acetone,
but are insoluble in hexane. The molar conductance
values Km of the complexes 1–3 in acetonitrile at ꢀ1 mM
Reflections collected
Independent reflections (Rint
Maximum and minimum
transmission
)
4199 (0.0602)
0.7808 and 0.2456
Refinement method
full-matrix least-squares
on F2
4199/0/191
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [F2 > 4r(F2)]
R indices (all data)
1.036
R1 = 0.0331, wR2 = 0.0649
R1 = 0.0526, wR2 = 0.0711
1.001 and À1.162
À3
˚
Largest difference in peak and hole (e A
)

2918
G. Singh et al. / Polyhedron 25 (2006) 2915–2919
concentration have been found to be between 3.8 and
6.5 XÀ1 cm2 molÀ1, which are much lower than the values
expected for a 1:1 electrolyte. The molecular weights of
complexes 2–3, determined in chloroform by the vapour
pressure osmometric method, were found to be very close
to the values calculated from their molecular formulae.
This indicates that there is no appreciable dissociation of
these complexes in solution. In the IR spectrum of 1, the
band at 248 cmÀ1 suggests the presence of bridging Cu–
Br unit. The IR spectrum of 3 has msym(Ru–Cl) and
[25–28] and such examples include Hg arsine complexes
[25]. The chemistry of Hg–phosphine complexes has been
extensively studied by Bell et al. [30], including three coor-
dinate Hg species containing phosphine ligands. However,
2 is the first example of a Hg–(P, S) ligand complex where
Hg is three coordinated. The Hg(1)–P(1) bond length of
˚
2.415(1) A is consistent with the earlier reported values of
˚
2.513(2) and 2.408(2)–2.437(2) A [29,30]. The Hg(1)Á Á ÁS(1)
bond distance [3.063(1)] is shorter than the sum of the van
˚
der Waal’s radii (3.35 A). The Hg(1)–Br(1) and Hg(1)–
m
asym(Ru–Cl) at 326 and 294 cmÀ1, respectively [23,24]. In
Br(2) bond lengths are 2.5152(6) and 2.5952(6) A and these
˚
the 1H NMR spectrum of L, signals of H2 and H3 protons
are merged together and appear as a multiplet, whereas the
signal of H4 appears shielded in comparison to those of H2
are consistent with our earlier observations [31] of
˚
˚
2.505(2)–2.700(2) A, and 2.528(3) and 2.637(3) A reported
by Bell et al. [30]. The bond angles around Hg are in the
range of 78.78(4)–135.52(4)ꢀ, with a Br(1)–Hg(1)–Br(2)
angle of 104.98(2)ꢀ and P(1)–Hg(1)–S(1) angle of
78.78(4)ꢀ. However, the sum of the bond angles P(1)–
Hg(1)–Br(1), P(1)–Hg(1)–Br(2) and Br(1)–Hg(1)–Br(2) is
ꢁ360ꢀ. Therefore, the Hg, two Br and P atoms are copla-
nar and the geometry around Hg can be best described
as essentially trigonal planar. There is a HgÁ Á ÁS secondary
interaction in 2 and the S atom is nearly perpendicular to
the plane of the three coordinate Hg-complex. In 2, the
C–C bond lengths and bond angles of all the phosphine
rings were found to be normal.
1
and H3. In the H NMR spectrum of 1, the signals corre-
sponding to H2 and H3 get separated and deshielding of
the order of 0.2–0.3 ppm is found with respect to the corre-
sponding signals of ligand L. The signal of H4 appears
deshielded by ꢀ0.25 ppm in comparison to the correspond-
ing signal of L. Signals for aromatic protons remain
1
unchanged on the formation of 1. In the H NMR spec-
trum of 2, signals corresponding to all –CH2 protons merge
at 2.66–3.11 ppm, showing deshielding of ꢀ0.35–0.45 ppm.
In the proton NMR spectrum of 3 also, signals of all the
CH2 protons are merged and the average deshielding was
found to be ꢀ0.5 ppm. The CH3 signal of the ligand (L)
appears to be merged with the CH3 signal of the isopropyl
group of the p-cymene ring in the 1H NMR spectrum of 3.
No significant shift occurs in the aromatic protons.
4. Conclusion
A relatively simple method is reported for the synthesis
of the (P, S) ligand 1-(ethylthio)-2-(diphenylphosphino)
ethane (L). Its complexation with Cu(I), Hg(II) and orga-
nometallic species of Ru(II) have been explored. The single
crystal structure of the Hg(II) complex has been deter-
mined. It is found to be a three coordinate species. The
sum of the bond angles at Hg, viz. P(1)–Hg(1)–Br(1),
P(1)–Hg(1)–Br(2) and Br(1)–Hg(1)–Br(2), is ꢁ360ꢀ, and
consequently the geometry of Hg can be best described as
trigonal planar. There exists a weak secondary interaction
between Hg and the S donor site of the ligand [Hg(1)Á Á ÁS(1)
In the carbon-13 NMR spectrum of 1, the C4 signal is
deshielded by ꢀ0.8 ppm as compared to that of free L.
The signals for C2 and C1 appear to be deshielded by 1.9
and 1.6 ppm, respectively, with respect to the correspond-
ing signals of free L. In the carbon-13 NMR spectrum of
2, the C4 signal appears deshielded by 0.68 ppm and the
C3 signal by 1.68 ppm in comparison to those of free L,
whereas in the spectrum of 3, the deshielding of the C2 sig-
nal is ꢀ1.2 ppm and the other signals do not undergo any
significant change in their chemical shifts. The 31P {1H}
NMR spectra of L, 1, 2 and 3 all have a single peak at
À17.0, 31.3, 20.16 and 28.9 ppm, respectively. The signals
in the spectra of the complexes are deshielded with respect
to that of the ligand. All these NMR data indicate that the
interaction of L with Cu(I), Hg(II) and Ru(II) is through
both phosphorous and sulfur. With sulfur it may be weak
(secondary type), as found out in the case of 2 when its sin-
gle crystal structure was determined. However, in the case
of 1 and 3, which did not give crystals suitable for X-ray
diffraction, it could not be ascertained unequivocally.
˚
bond distance 3.063(1) A; sum of van der Waal’s radii
˚
3.35 A].
5. Supplementary data
The CCDC No. 602402 contains the supplementary
crystallographic data for 2. These data can be obtained free
of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or
from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (internat.)
+44 1223 336 033; e-mail: deposit@ccdc.cam.ac.uk].
3.1. Crystal structure
The molecular structure of 2 is shown in Fig. 1 and
selected bond lengths and angles are given in Table 2.
The ligand L coordinates through phosphorus only, result-
ing in a coordination number of three for Hg. The three
coordination number for mercury is already known
Acknowledgements
A.K.S. and G.S. thank the Department of Science and
Technology (India) and Council of Scientific and Industrial
Research, New Delhi (India) for financial support.

G. Singh et al. / Polyhedron 25 (2006) 2915–2919
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