Mercury(II) complexes of stabilized phosphine-phosphonium ylide derived from bis(diphenylphosphino)methane: Synthesis, spectra and crystal structures

Article abstract of DOI:10.1016/j.jorganchem.2008.11.051

The reaction of a mixed phosphine-phosphonium ylide, PPh₂CH₂PPh₂{double bond, long}C(H)C(O)Ph with mercury(II) halides in methanol under mild conditions yielded the P, C-chelated complexes, [HgX₂(PPh₂

Full text of DOI:10.1016/j.jorganchem.2008.11.051

Journal of Organometallic Chemistry 694 (2009) 643–648
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Mercury(II) complexes of stabilized phosphine–phosphonium ylide derived
from bis(diphenylphosphino)methane: Synthesis, spectra and crystal structures
b
Mothi Mohamed Ebrahim a,b, Krishnaswamy Panchanatheswaran a, , Antonia Neels ,
*
Helen Stoeckli-Evans b,
*
a School of Chemistry, Bharathidasan University, Tiruchirappalli, India
b Institute of Microtechnology, University of Neuchâtel, Neuchâtel, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of a mixed phosphine–phosphonium ylide, PPh2CH2PPh2@C(H)C(O)Ph with mercury(II)
halides in methanol under mild conditions yielded the P, C-chelated complexes,
[HgX2(PPh2CH2PPh2C(H)C(O)Ph)] where X = Cl (2), Br (3), I (4). Single crystal X-ray diffraction studies
reveal the presence of mononuclear complexes containing Hg atom in a distorted tetrahedral environ-
ment and long Hg–Cylide bond. The five-membered chelate rings in the two independent molecules pres-
ent in the asymmetric unit of 4 adopt ‘envelope’ and ‘twist’ conformations. Spectroscopic studies also
indicate the weaker Hg–C bonding. Additionally, the molecular structure of the free ylide (1) is also
discussed.
Received 1 September 2008
Received in revised form 8 November 2008
Accepted 18 November 2008
Available online 30 November 2008
Keywords:
Phosphorus ylides
Resonance stabilization
Mecury(II) complexes
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
mode. However, HgBr2 and HgI2 react with the same ylide giving
polymeric halogen bridged phosphine complexes with dangling
Phosphorus ylides with their numerous modifications have
been widely employed as reagents in synthetic organic chemistry
[1,2]. Much of the interest in the coordination properties of reso-
nance stabilized phosphorus ylides stems from their ligating versa-
tility due to the presence of different functional groups in their
molecular skeleton [3]. The monoketo ylides derived from bisphos-
ylide [10]. Such a versatile reactivity has prompted us to expand
our studies to related mixed phosphine–phosphonium ylide with
mercuric halides. Furthermore, coordination of ligands towards
Hg(II) has assumed importance since, in nature’s mercury detoxifi-
cation process, the initial Hg–C bond cleavage involves the increase
in the coordination number around Hg [11]. In addition, evidence
for new classes of metal-binding motifs in enzymes, transcription
factors, and regulatory proteins emphasize the need for structural
insights about local Hg(II) coordination environments [12]. In this
paper, we report the reactivity of Ph2PCH2PPh2@C(H)C(O)Ph, ben-
phines,
viz.,
Ph2PCH2PPh2@C(H)C(O)R,
Ph2PCH2CH2PPh2@
C(H)C(O)R (R = Me, Ph or OMe) [4] contain a P donor site in addi-
tion to C donor (the ylidic C) or O donor (the carbonyl O) sites
for coordination, and therefore can engage in different kinds of
bonding with metal ions. We have been interested in studying
the coordination modes adopted by the resonance stabilized ylides
when ligated to Hg(II) and U(VI) [5]. Hg(II) forms C-coordinated
complexes with Ph3P@C(H)C(O)Ph [6,7] and Ph3P@C(H)CO(OCH2-
CH3) [8], whereas, regiospecific O-coordination of the acetyl oxy-
gen had been observed with Ph3P@C(COPh)(COMe) [9]. The
remarkable change in reactivity arises from a subtle variation in
the molecular–electronic structure of the ylide due to the presence
of additional keto stabilization.
zoylmethylenediphenyldiphenylphosphino
(BDEP), towards mercury(II) halides.
methylphosphorane
2. Experimental
All reactions were carried out under nitrogen atmosphere. Reac-
tants and reagents were obtained from Aldrich Chemical Company
and used without further purification. The solvents were dried and
distilled using standard methods [13]. The 1H and 31P–{1H}NMR
spectra were recorded on a Bruker DPX400 spectrometer at
400.13 and 161.98 MHz, referenced relative to residual solvent
and external 85% H3PO4, respectively. The chemical shifts (d) and
the coupling constants (J) were expressed in ppm and Hz, respec-
tively. The IR spectra in the interval of 4000–400 cmꢀ1 were re-
corded on a Perkin–Elmer 1720X FT-IR spectrophotometer using
KBr pellets. Positive mode ESI-Mass spectra were measured on a
Recently, we have observed that the phosphine–phosphonium
ylide with an ethylenic spacer, Ph2PCH2CH2PPh2@C(H)C(O)Ph
forms polymeric Hg(II) complexes with HgCl2 via P, C-bridging
* Corresponding authors. Address: School of Chemistry, Bharathidasan Univer-
sity, Tiruchirappalli, India. Tel.: +91 431 2407053; fax: +91 431 2407045 (K.
Panchanatheswaran).
E-mail address: panch_45@yahoo.co.in (K. Panchanatheswaran).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.11.051

644
M.M. Ebrahim et al. / Journal of Organometallic Chemistry 694 (2009) 643–648
Bruker FTMS 4.7T BioAPEX II instrument using the solution of the
complexes in acetonitrile. Elemental analyses were performed at
the Ecole d’ingénieurs de Fribourg, Switzerland.
C33H28Br2HgOP2: C, 45.93; H, 3.27. Found: C, 44.84; H, 3.01%. IR
(cmꢀ1): 3054, 1598, 1568 (
C@O), 1483, 1436, 1326, 1299, 1203,
m
1188, 1107, 1038, 1022, 998, 872, 833, 772, 742, 688, 531, 498,
2
469. 1H NMR (CDCl3): d 4.13 (t, 2H, PCH2P, JPꢀH = 11.8), 4.79 (d,
2
2.1. Preparation of compounds
1H, PCHCOPh, JPꢀH = 9.8), 7.34–8.04 (m, 25H, Ph). 31P NMR
2
(CDCl3):
d
2.83 (d, PPh2, JPꢀP = 37.4), 25.44 (d, PCHCOPh,
2.1.1. Ph2PCH2PPh2@C(H)C(O)Ph (1)
2JPꢀP = 42.8). Mass spectrum: ESI + [m/z, ion, (%)]: 783.0 [M–Br]+
The ylide was prepared by the treatment of triethylamine on
the monophosphonium bromide derived from bis(diphenylphos-
phino)methane as reported previously [4]. X-ray quality crystals
were obtained by recrystallization from a toluene-petroleum ether
(77).
2.1.4. [HgI2(PPh2CH2PPh2C(H)C(O)Ph)] (4)
This complex was prepared in the same way as used for 2 and 3
using HgI2 (0.13 g, 0.29 mmol). Yield: 0.25 g, 88%. M.p. 166–168 °C.
Anal. Calc. for C33H28I2HgOP2: C, 41.42; H, 2.95. Found. C, 41.16; H,
mixture. IR (cmꢀ1): 3054, 2887, 1581, 1523 (
mC@O), 1482, 1433,
1385, 1348, 1191, 1102, 1063, 1024, 997, 927, 887, 783, 751,
742, 734, 719, 709, 693, 650, 587, 518, 504, 491, 471. 1H NMR
2.71%. IR (cmꢀ1): 3051, 2953, 2893, 1600, 1564 (
mC@O), 1482,
2
(CDCl3): d 3.67 (d, 2H, PCH2P, JPꢀH = 14.4), 4.31 (d, 1H, PCHCOPh,
1437, 1325, 1298, 1197, 1183, 1104, 1033, 1023, 997, 873, 832,
2JPꢀH = 24.4), 7.23–7.87 (m, 25H, Ph). 31P NMR (CDCl3): d ꢀ26.64
771, 760, 740, 722, 688, 649, 528, 492, 472. 1H NMR (CDCl3): d
2
2
2
(d, PPh2, JPꢀP = 62.1), 14.47 (d, PCHCOPh, JPꢀP = 62.1).
4.14 (dd, 2H, PCH2P, JPꢀH = 10.1), 4.79 (d, 1H, PCHCOPh,
2JPꢀH = 11.0), 7.31–8.02 (m, 25H, Ph). 31P NMR (CDCl3): d ꢀ9.20
2
2.1.2. [HgCl2(PPh2CH2PPh2C(H)C(O)Ph)] (2)
(br, PPh2), 25.53 (d, PCHCOPh, JPꢀP = 46.4). Mass spectrum:
A
methanolic solution containing PPh2CH2PPh2@CHCOPh
ESI + [m/z, ion, (%)]: 831.0 [MꢀI]+ (100).
(0.15 g, 0.29 mmol) and HgCl2 (0.08 g, 0.29 mmol) was mixed
gently for homogenization. The resulting clear colourless solution
was allowed to stand at ꢀ5° C. The complex was isolated as colour-
less crystals after two days, washed with ice-cold methanol and
dried in vacuo. Yield: 0.18 g, 80%. M.p. > 158 °C (decomposes). Anal.
Calc. for C33H28Cl2HgOP2: C, 51.21; H, 3.65. Found: C, 51.62; H,
2.2. X-ray crystallography
Single crystals were grown as described above and were re-
moved directly from the mother liquor and mounted in an inert
oil using a cryoloop. The intensity data were collected at 173 K
(ꢀ100 °C) on a Stoe Mark II-Image Plate Diffraction System [14]
3.67%. IR (cmꢀ1): 3053, 2901, 1596, 1566 (
mC@O), 1483, 1437,
1329, 1300, 1192, 1157, 1107, 1022, 997, 832, 771, 742, 689,
equipped with a two-circle goniometer and using Mo Ka graphite
2
532, 496, 474. 1H NMR (CDCl3): d 4.15 (t, 2H, PCH2P, JPꢀH = 12.3),
monochromated radiation. The structures were solved by direct
methods using the program SHELXS-97 [15]. The refinement and all
further calculations were carried out using SHELXL-97 [15]. The H-
atoms were included in calculated positions and treated as riding
atoms using SHELXL default parameters. The non-H atoms were re-
fined anisotropically, using weighted full-matrix least-squares on
F2. In complex 2, the phenyl ring atoms C9–C14 were constrained
to have thermal parameters equal to that of the ipso carbon atom
and the C–O distance in the two solvent methanol molecules was
restrained to the theoretical value. Complex 3 crystallized in
monoclinic space group P21/c and was refined as a twin [final BASF
value = 0.115]. The C–O distances in the co-crystallized methanol
molecules were restrained to the theoretical values. In complex
2
4.81 (d, 1H, PCHCOPh, JPꢀH = 10.0), 7.34–8.05 (m, 25H, Ph). 31P
2
NMR (CDCl3): d 8.65 (d, PPh2, JPꢀP = 36.1), 25.09 (d, PCH2COPh,
2JPꢀP = 38.8). Mass spectrum: ESI + [m/z, ion, (%)]: 739.1 [MꢀCl]+
(72).
2.1.3. [HgBr2(PPh2CH2PPh2C(H)C(O)Ph)] (3)
The same procedure as used for the preparation of 2 was fol-
lowed using the ylide (0.15 g, 0.29 mmol) and HgBr2 (0.10 g,
0.29 mmol). The resulting clear colourless solution was allowed
to stand at room temperature. Colourless crystals were obtained
after a day. They were washed with ice-cold methanol and vacuum
dried. Yield: 0.22 g, 85%. M.p. > 156 °C (decomposes). Anal. Calc. for
Table 1
Crystal data and refinement details for compounds 1–4.
Compound
1
2 ꢁ 2MeOH
3 ꢁ 2MeOH
4 ꢁ CH2Cl2
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C33H28OP2
502.49
223(2)
C33H28Cl2HgOP2, 2(CH3OH)
838.07
173(2)
C33H28Br2HgOP2, 2(CH3OH)
926.99
173(2)
C33H28HgI2OP2, CH2Cl2
1041.81
173(2)
0.71073
Monoclinic
P21/c
17.3598(11)
21.5815(9)
19.8451(12)
90
109.451(5)
90
0.71073
Triclinic
0.71073
Monoclinic
P21/n
11.1951(9)
16.9989(11)
17.7694(17)
90
93.297(11)
90
3376.0(5)
4
0.71073
Monoclinic
P21/c
11.2610(6)
17.1507(7)
20.5164(11)
90
119.908(4)
90
3434.7(3)
4
ꢀ
P1
10.0742(12)
10.5950(12)
13.7296(16)
81.723(14)
89.236(14)
63.240(12)
1292.7(3)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
Volume (Å3)
7010.6(7)
8
Z
Absorption coefficient (mmꢀ1
Crystal size (mm)
Reflections collected
Independent reflections
Goodness-of-fit on F2
)
0.193
4.846
6.934
6.422
0.38 ꢂ 0.19 ꢂ 0.12
0.25 ꢂ 0.25 ꢂ 0.20
0.33 ꢂ 0.23 ꢂ 0.14
0.40 ꢂ 0.20 ꢂ 0.10
10195
26103
33393
61806
4712
0.815
6572
0.784
12653
1.128
12496
0.909
R1 (I > 2
r
(I))
0.0318
0.0415
0.0547
0.0421
wR2 (All data)
0.0698
0.0870
0.1677
0.0959

M.M. Ebrahim et al. / Journal of Organometallic Chemistry 694 (2009) 643–648
645
Fig. 1. Molecular structure of Ph2PCH2PPh2@CHCOPh (1) at 50% probability
ellipsoids. Selected bond lengths (Å) and angles (°): C(1)–P(1) 1.705(2), C(1)–
C(2)1.404(3), C(2)–O(1)1.249(2), C(2)–C(3) 1.506(3), C(2)–C(1)–P(1) 124.41(15),
O(1)–C(2)–C(1) 124.93(18), O(1)–C(2)–C(3) 117.90(17), P(1)–C(1)–C(2)–O(1)
ꢀ2.5(3).
Fig. 3. Molecular structure of [HgBr2(PPh2CH2PPh2C(H)C(O)Ph)] (3) with 30%
probability ellipsoids. The two methanol solvent molecules have been omitted for
clarity.
Fig. 4. Molecular structure of the two independent molecules of complex 4. The
figure shows ‘envelope’ (4) and ‘twist’ (40) conformation of the five-membered
chelate rings.
3. Results and discussion
3.1. Synthesis
Fig. 2. Molecular structure of [HgCl2(PPh2CH2PPh2C(H)C(O)Ph)] (2) with 30%
probability ellipsoids. The two methanol solvent molecules have been omitted for
clarity.
Complexes 2–4, in crystalline form, were obtained in good
yields (80–88%) by gentle mixing of methanolic solutions of the
ylide and mercuric halide and allowing to stand at room tempera-
ture or at ꢀ5° C. However, when stirred, the same reaction in
methanol gave a grey solid, due to metallic mercury, together with
a mixture of unidentified products. In this case, lowering the reac-
tion temperature, protection from light and change in solvent to
dichloromethane, did not prevent the decomposition. That no such
reduction has been reported for the complexes of this ylide with
4, the co-crystallized dichloromethane molecule was found to be
disordered over two positions (C68/C68A). The refinement of the
site occupancy factor leads to 55.2% occupancy for the major com-
ponent. Further crystallographic data are given in Table 1. The
molecular structure and crystallographic numbering schemes are
illustrated in ORTEP [16] drawings, Figs. 1–4.

646
M.M. Ebrahim et al. / Journal of Organometallic Chemistry 694 (2009) 643–648
Pd(II) [4], Pt(II) [4] and Rh(I) [17] suggests that Hg(II) brings about
a special reactivity causing the formation of metal. It is likely that
Hg(0) is produced following the oxidation of phosphine by trace
amount of water leading to the formation of phosphonium salt
as shown below.
nify the halogen dependence of the chemical shifts which agrees
well with the situation encountered in mercury(II)-phosphine
complexes [19]. However, 199Hg satellites could not be observed
in CDCl3 solution due to exchange decoupling caused by presum-
able fast exchange, as noted previously in the case of some
Hg(II)–phosphine complexes [20,21]. The spectral data thus indi-
cate the bidentate coordination of the ligand through both P and
C atoms.
ꢄ
ꢅ
H2
O
2Ph2PCH2PPh2@CHCOPh ! 2O@PPh2CH2 P Ph2CH2COPh X þHg:
HgX2
½Oꢃ
It is interesting to note that, in addition to the major resonances
discussed above, the 31P NMR spectra in CDCl3 show the presence
of two other minor species. One set of two doublets in the region of
26.06 ppm and 21.75 ppm in the 31P NMR spectra can be attributed
to [O@PPh2CH2P+Ph2CH2COPh]Xꢀ (where X = anion concerned).
The assignment has been confirmed by comparison of the spectral
properties with that of [O@PPh2CH2P+Ph2CH2COPh]Brꢀ which dis-
plays essentially the same features (see Supplementary informa-
tion). The origin of another set of minor doublets (35.18 and
The 31P NMR of the product gives some evidence for the formation
of the phosphine oxide-phosphonium salt (vide infra). In fact, cata-
lytic oxidation of bis(diphenylphosphino)methane (dppm) by Hg2+
to dppmO and dppmO2 has been noted previously [18].
3.2. Spectroscopy
2
The upward frequency shift of the m(CO) absorption in com-
8.36 ppm, JPꢀP = 24 Hz), is not immediately apparent. However,
plexes 2, 3 and 4 at 1566, 1568 and 1564 cmꢀ1, respectively, with
reference to the free ylide (1523 cmꢀ1), strongly suggests coordina-
tion of the ylidic carbon to form an Hg–Cylide bond. Significantly, the
if one considers the cleavage of the ylide to form Ph2PCH2PPh2,
the subsequent mono oxidation and coordination to Hg2+ could
possibly explain the observed additional signals.
coordination shifts [
D
m
=
m
(CO)complex
–m
(CO)free ylide] of ꢆ40 cmꢀ1
Interestingly, the 31P NMR spectra when measured in CD3CN are
are much lower than the corresponding shifts (88–110 cmꢀ1
)
clean
and
show
only
a
negligible
amount
of
O@PPh2CH2P+Ph2CH2COPhꢁXꢀ in the spectrum of 3 and an almost
complete absence in 2 and 4, indicating the stability of the com-
plexes in the above solvent. The 1H and 31P NMR spectra in CD3CN
(data provided as Supplementary information) are consistent with
the P, C-mode of coordination of ylide and show the expected sol-
vent dependent differences in chemical shifts. The most important
aspect in the 31P NMR spectra is the observation of Hg–P coupling
observed in the other C-bonded Hg(II) complexes containing
Ph3PC(H)C(O)Ph [6] and Ph3P@C(H)CO(OCH2CH3) [8]. This perhaps
signals a weaker Hg–C bonding in these complexes.
The initial NMR measurement of the complexes in DMSO-d6
solution showed extensive dissociation and decomposition, which
is in contrast to the stability of [Ph3PCHCOPh.HgX2]2 (X = Cl, Br, I)
[6] complexes in the same solvent. The 1H NMR spectra of all com-
plexes in CDCl3 exhibit a doublet in the region of 4.80 ppm due to
the methine protons. The observed downfield shifts and decrease
1
for complex 4. The JPꢀHg coupling constant of 1881 Hz is in the
range similar to that of the reported Hg(II)–phosphine complexes
[18]. The P, C-chelated monomeric structure is also supported by
+ESI-mass spectra, the fragmentation pattern of the peaks at m/z
739.1, 783.0 and 831.0, respectively, for complexes 2, 3, and 4, fits
the calculated isotopic pattern of the pseudomolecular ion,
[HgX2LꢀX]+ (X = Cl, Br, I).
2
in JPꢀH coupling constants when compared to the free ylide are
in accordance with the reduction in P–C bond order, a consequence
of the C-coordination of the ylide. In the 31P NMR spectra (CDCl3)
the signal due to phosphonium group appears as a doublet around
25.35 ppm. The significant downfield shift of this signal from that
of the free ylide (d 14.47) is in agreement with the C-bonding of the
ylide. The coordination of phosphine is also clearly evident from
the strong downfield shifts of the signal due to ‘PPh2’ group when
compared to that of same signal in the free ylide (d ꢀ26.64). The
doublet signals at 8.65 ppm and 2.83 ppm, respectively, for 2 and
3, as well as the broad resonance centered at ꢀ9.20 ppm for 4, sig-
3.3. Crystal structures
3.3.1. Molecular structure of Ph2PCH2PPh2@C(H)C(O)Ph (1)
The molecular structure of the ligand is shown in Fig. 1. As shown,
both the phosphine and ylidic components are devoid of steric
Table 2
Selected bond distances (Å) and angles (°) in compounds 2, 3 and 4.
X = Cl (2)
X = Br (3)
X = I
4
40
Hg(1)–C(1)
Hg(1) –P(2)
Hg(1) –X(1)
Hg(1) –X(2)
P(1) –C(1)
P(1) –C(21)
P(2) –C(21)
O(1) –C(2)
2.345(7)
2.569(2)
2.493(2)
2.450(2)
1.766(7)
1.811(7)
1.834(7)
1.248(9)
1.469(10)
123.79(19)
111.70(18)
105.36(7)
90.12(18)
113.03(7)
112.41(7)
112.8(5)
104.4(5)
103.7(3)
21.0(10)
2.415(12)
2.546(3)
2.5612(14)
2.5773(15)
1.769(12)
1.829(13)
1.829(13)
1.244(16)
1.431(18)
119.4(3)
110.8(3)
107.10(5)
89.2(3)
112.62(8)
117.46(9)
113.6(9)
105.6(8)
102.5(5)
18.2(17)
2.418(8)
[Hg(2)–C(34) = 2.616(7)]
[Hg(2)–P(4) = 2.505(2)]
[Hg(2)–I(4) = 2.7113(7)]
[Hg(2)–I(3) = 2.6932(6)]
[P(3)–C(34) = 1.719(8)]
[P(3)–C(54) = 1.811(8)]
[P(4)–C(54) = 1.824(7)]
[O(2)–C(35) = 1.247(9)]
[C(34)–C(35) = 1.435(10)]
[C(34)–Hg(2)–I(4) = 109.07(16)]
[C(34)–Hg(2)–I(3) = 102.41(18)]
[I(3)–Hg(2)–I(4) = 114.64(2)]
[P(4)–Hg(2)–C(34) = 86.65(18)]
[P(4)–Hg(2)–I(4) = 112.94(5)]
[P(4)–Hg(2)–I(3) = 124.89(5)]
[C(35)–C(34)–P(3) = 117.5(6)]
[C(35)–C(34)–Hg(2) = 99.4(5)]
[P(3)–C(34)–Hg(2) = 103.8(3)]
[P(3)–C(34)–C(35) –O(2) = ꢀ25.2(10)]
2.5688(19)
2.7673(6)
2.7436(7)
1.760(8)
1.815(7)
1.823(8)
1.245(9)
C(1) –C(2)
1.454(11)
109.03(18)
111.50(16)
107.20(2)
88.24(18)
120.07(5)
118.92(5)
112.8(5)
104.2(5)
103.2(3)
ꢀ28.1(10)
C(1) –Hg(1) –X(2)
C(1) –Hg(1) –X(1)
X(2) –Hg(1) –X(1)
C(1) –Hg(1) –P(2)
X(2) –Hg(1) –P(2)
X(1) –Hg(1) –P(2)
C(2) –C(1) –P(1)
C(2) –C(1) –Hg(1)
P(1) –C(1) –Hg(1)
P(1) –C(1) –C(2) –O(1)

M.M. Ebrahim et al. / Journal of Organometallic Chemistry 694 (2009) 643–648
647
restrictions and can interact with metal ions and reagents. The P(1)–
C(1) [1.706(2) Å], C(2)–O(1) [1.249(2) Å] and C(1)–C(2) [1.401(3) Å]
bond lengths within the ylidic fragment are comparable to those ob-
served for the other monoketo ylides [22,23]. No steric or electronic
effects due to the presence of –CH2PPh2 is thus anticipated. The 1,4-
P,O intramolecular interaction, indicated by the short contact
[3.107(2) Å] as well as by the cis orientation [P(1)–C(1)–C(2)–O(1)
ꢀ2.5(3)°] of the P+ and Oꢀ centers, is also present in this ylide as ob-
served for other keto-stabilized ylides [24].
P bond, whereas in molecule 40 an opposite trend is observed with
a long Hg–C and a short Hg-P bond (Table 2). The Hg–I distances in
both the molecules are comparable to those of 2.733(1) and
2.763(1) Å found in [HgI2(PPh3)2] [30], and the terminal Hg–I dis-
tances of 2.671(2) and 2.684(2) Å in dimeric [{HgI2(PPh3)}2] [31].
In summary, the ylide, PPh2CH2PPh2@CHCOPh reacts with mer-
cury(II) halides in mild conditions to form P,C-chelated complexes.
The crystal structures of the above complexes reveal the formation
of puckered five-membered chelate rings. The Hg–C bond in these
complexes are longer than normal Hg–Cylide bonds, and consists of
a carbene ligated to Hg(II). This fact underlines the potential of
these complexes in displaying reactivity similar to those exhibited
by organomercurials and metalated ylides.
3.3.2. Molecular structures of chelate complexes 2, 3 and 4
The molecular structures of complexes 2–4 are shown in Figs.
2–4. Selected bond distances and angles are listed in Table 2. The
asymmetric unit in each of the complexes 2 and 3 contains a mol-
ecule of the complex along with two molecules of methanol. The
asymmetric unit of 4 is composed of two symmetry independent
molecules (4 and 40) and a molecule of solvent dichloromethane.
The X-ray analysis reveals the P,C-chelate mode of coordination
of the ligand, Ph2PCH2PPh2@C(H)C(O)Ph to Hg atom in all the three
complexes. The Hg atom is surrounded by one P atom of the PPh2
unit, one ylidic C atom and two halogen atoms leading to a dis-
torted tetrahedral geometry around the metal. In fact, the major
deviation from the ideal geometry is exhibited by the ligand bite
angle, C(1)–Hg(1)–P(2) 88.5(2)° (average). The stereogenic center
formed due to C-bonding adopts same absolute configuration (R
for C1) in the both 2 and 3, whereas in complex 4 it is found to
be inverted (S for C1).
A comparison of the structural features in the present com-
plexes with those of the dinuclear or trinuclear Hg–phosphoylide
compounds [6–8,25] reveal striking dissimilarities, the most
important being the significantly long Hg–C bond whose distances
are 2.345(7), 2.415(12) and [2.418(8) and 2.616(7)] Å in complexes
2, 3 and 4, respectively (Table S1, Supplementary information). In
addition, the P–Cylide distance is found to be shorter (Table 2) than
the corresponding distances in C–coordinated Hg(II)–phosphorus
ylide complexes which lie in the range, 1.786(10)–1.806(10) Å
[6–8]. Surprisingly, the C@O (keto) distances of 1.248(9),
1.244(16) and [1.245(9) and 1.247(9)] Å in 2, 3 and 4, respectively,
are found to be close to that of the same distance in the parent
ylide [1.249(2) Å]. All these data perhaps indicate that the chelat-
ing ylide does not complex well when compared to the non-chelat-
ing ylides.
Acknowledgements
M.M.E thanks the Swiss Federal Commission for a scholarship to
study at the University of Neuchâtel. K.P. thanks Department of
Science and Technology, New Delhi, India for financial assistance
(SERC-SR/S1/IC-29/2003).
Appendix A. Supplementary material
CCDC 662092, 662093, 662094 and 662095 contain the supple-
mentary crystallographic data for 1, 2 ꢁ 2MeOH, 3 ꢁ 2MeOH,
4 ꢁ 2CH2Cl2, respectively. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2008.11.051.
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