Structural, theoretical and multinuclear NMR study of mercury(II) and silver(I) complexes with two new ambidentate phosphorus ylides

Article abstract of DOI:10.1016/j.poly.2012.02.034

Reactions of new α-ketostabilized phosphorus ylides of the type Ph₃P = CHC(O)R (R = 2,4-dichlorophenyl (L¹) and 4-isopropylphenyl (L²)) with AgNO₃and Hg(NO ₃)₂.H₂O, using methanol as a solvent, are reported. The crystal structures of L² and [Ag(L²) ₂(NO₃)] (2) have been determined. Characterization of the obtained compounds was also performed by elemental analysis, IR, ¹H, ³¹P and ¹³C NMR. Theoretical studies were carried out on the silver(I) complexes. It was shown that the nitrate ion shows a bonding interaction with the silver ion.

Full text of DOI:10.1016/j.poly.2012.02.034

Polyhedron 38 (2012) 131–136
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Structural, theoretical and multinuclear NMR study of mercury(II) and silver(I)
complexes with two new ambidentate phosphorus ylides
a
a
Seyyed Javad Sabounchei a, , Mehdi Sarlakifar , Sadegh Salehzadeh , Mehdi Bayat a,b, Mahbubeh
⇑
Pourshahbaz a, Hamid Reza Khavasi c
a Faculty of Chemistry, Bu-Ali Sina University, Hamedan 65174, Iran
b Department of Chemistry, Faculty of Science, Malayer University, Malayer 65174, Iran
c Department of Chemistry, Shahid Beheshti University, G.C., Evin, Tehran 1983963113, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Reactions of new a-ketostabilized phosphorus ylides of the type Ph3P = CHC(O)R (R = 2,4-dichlorophenyl
(L1) and 4-isopropylphenyl (L2)) with AgNO3and Hg(NO3)2.H2O, using methanol as a solvent, are reported.
The crystal structures of L2 and [Ag(L2)2(NO3)] (2) have been determined. Characterization of the obtained
compounds was also performed by elemental analysis, IR, 1H, 31P and 13C NMR. Theoretical studies were
carried out on the silver(I) complexes. It was shown that the nitrate ion shows a bonding interaction with
the silver ion.
Received 20 December 2011
Accepted 23 February 2012
Available online 20 March 2012
Keywords:
Phosphorus ylide
Mercury(II) complexes
Silver(I) complexes
X-ray crystal structure
Theoretical studies
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
2. Experimental
The utility of metallated phosphorus ylides in synthetic chemis-
try has been well documented [1,2]. The synthesis of complexes
derived from ylides and Ag(I) began in 1975 by Yamamoto et al.
[3]. Other types of ylide complexes of silver(I) have been reported
[4–9]. In 1987 and 1983, Vicente et al. [10,11] reported the crystal
structures of Ag(I) complexes of phosphorus ylides. The synthesis
of complexes derived from phosphorus ylides and Hg(II) salts
was limited to Hg(II) halides and was started in 1965 by Nesmeya-
nov et al. [12]. Weleski et al. [13] in 1975 proposed a symmetric
halide-bridged dimeric structure for Hg(II) halide complexes, while
Kalyanasundari et al. [14] in 1995 reported an asymmetric halide-
bridged structure. In 2007 we reported the first Hg(II) nitrate poly-
meric complexes with these ylides [15], wherein the nitrate anions
are bridging, confirming the general belief that seven-coordinated
complexes would be formed. In this study, we describe the prepa-
ration and spectroscopic characterization of Ag(I) and Hg(II) com-
plexes with the title ylides. The single crystal X-ray diffraction
study of L2 and 2 demonstrates the C-coordination of the ylides
to the metals (Scheme 1).
2.1. Physical measurements and materials
All reactions were performed in air. Methanol was distilled over
magnesium powder and diethyl ether over a mixture of sodium
and benzophenone just before use. All other solvents were reagent
grade and were used without further purification. The ligands were
synthesized by the reaction of triphenylphosphine with 2- chloro
and 2-bromoactophenones to produce the related phosphonium
salts. Further treatment with aqueous NaOH solution led to elimi-
nation of HCl and HBr, giving the free ligands [16]. Melting points
were measured on a Stuart SMP3 apparatus. Elemental analysis for
C, H and N were performed using a Perkin-Elmer 2400 series ana-
lyzer. Fourier transform IR spectra were recorded on a Shimadzu
435-U-04 spectrophotometer and samples were prepared as KBr
pellets. 1H, 31P and 13C NMR spectra were recorded on 90 MHz Jeol
and 300 MHz Bruker spectrometers in CDCl3 or DMSO-d6 as the
solvent at 25 °C. Chemical shifts (ppm) are reported according to
internal TMS and external 85% phosphoric acid.
2.2. X-ray crystallography
The single crystal X-ray diffraction data of suitable crystals of L2
and 2 were collected on a STOE IPDS-II diffractometer at 298 K,
using graphite monochromated Mo Ka radiation (k = 0.71073 Å).
⇑
Corresponding author. Tel.: +98 8118272072; fax: +98 8118380709.
E-mail address: jsabounchei@yahoo.co.uk (S.J. Sabounchei).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.02.034

132
S.J. Sabounchei et al. / Polyhedron 38 (2012) 131–136
Table 1
IR (cmꢀ1), 1H and 31P NMR [d (ppm), J (Hz)] spectral data.
a
m(C@O)
dPCH
2JPH(y)
2JPH(Ps)
d
2JHgP
PPh3
L1,b
L2,b
1b
1576
1579
1609
1600
1667
1652
4.0(d)
23.66
24.37
14.06
9.67
12.09
5.55
12.36
11.92
–
–
–
–
12.40(s)
14.05(s)
19.96(s)
23.11(s)
27.13(s)
28.48(s)
–
–
–
–
4.38(d)
4.42 (d)
4.92(d)
6.28(d)
6.45(d)
2c
3c
285.31
287.19
4c
y, ylide; Ps, phosphonium salt; s, singlet; d, doublet; br, broad.
a
T = 298 K; TMS d = 0.00 ppm; shifts relative to internal TMS and external 85%
phosphoric acid.
b
Recorded in CDCl3.
Recorded in DMSO-d6.
c
Turbomole 5 [24] energies and gradients. Single-point energies of
both [Ag(Ylide)2]+ and NO3 fragments in the complexes at the
ꢀ
BP86/SVP optimized geometries were calculated with BP86 and
the def 2-SVP[21] basis set. The geometry of the metal complex
2, as determined by the X-ray crystal structure analysis (see
Fig. 1), was fully optimized at above mentioned level of theory.
The observed geometry of compound 2 was used as a basis for
the DFT calculations of compound 1.
2.4. Sample preparation
2.4.1. Synthesis of [2,4-Cl2C6H3C(O)CHPPh3] (L1)
To an acetone solution (10 mL) of triphenylphosphine (0.262 g,
1 mmol) was added 2,20,40-trichloroacetophenone (0.223 g,
1 mmol), and the mixture was stirred for 24 h. The solid product
(phosphonium salt) was filtered off, washed with Et2O and dried.
Further treatment with aqueous NaOH solution led to elimination
of HCl, giving the free ligand. Yield: 84%, M.p. 114–116 °C. Anal.
Calc. for C26H19OPCl2: C, 69.50; H, 4.26. Found: C, 69.61; H, 4.34%.
Scheme 1. Schematic illustration of the complexes under study.
The data collection was performed using the
x-scan technique and
using the STOE X-AREA software package [17], while data reduc-
tion was carried out using the program X-RED [17]. The crystal
structures were solved by direct methods and refined by full-ma-
trix least-squares on F2 using the programs SHELX and SHELXL,
respectively [18], and using the X-STEP32 crystallographic soft-
ware package [19]. The H atoms were included in calculated posi-
tions and treated as riding atoms using SHELXL [18] default
parameters. Numerical absorption corrections were applied for
both L2 and 2.
IR (KBr disk, cmꢀ1 : 1576 (CO), 878 (P+-Cꢀ). 1H NMR (CDCl3,
) m
2
ppm) dH: 3.98 (d, JPH = 23.21 Hz, 1H, CHP), 7.12–7.34 (m, 18H,
arom.). 31P NMR (CDCl3, ppm) dP: 12.43. 13C{1H} NMR (CDCl3,
1
ppm) dC: 53.44 (d, JPC = 94.05 Hz, CHP), [122.72 (d), 125.43 (s),
127.68 (d), 129.26 (s), 130.71 (s), 131.70 (d), 139.98 (s), 140.61
(d) (Ph)], 182.31 (s, CO).
2.4.2. Synthesis of [4-(CH3)2CHC6H4C(O)CHPPh3] (L2)
To
a chloroform solution (10 mL) of triphenylphosphine
2.3. Computational methods
(0.262 g, 1 mmol) was added 2-bromo-4-isopropylacetophenone
(0.241 g, 1 mmol), and the mixture was stirred for 24 h. The solid
product (phosphonium salt) was filtered off, washed with Et2O
and dried under reduced pressure. Further treatment with aqueous
NaOH solution led to elimination of HBr, giving the free ligand.
Yield: 81%, M.p. 217–219 °C. Anal. Calc. for C29H27OP: C, 82.44; H,
The geometries of the compounds have been optimized without
symmetry constraints at the BP86 [20]/def2-SVP [21] level of the-
ory using the Gaussian 03 [22] optimizer [23] in conjunction with
6.44. Found: C, 82.71; H, 6.57%. IR (KBr disk, cmꢀ1
)
m
: 1579 (CO),
3
887 (P+–Cꢀ). 1H NMR (CDCl3, ppm) dH: 1.23 (d, JHH = 6.76 Hz, 6H,
2
CH3), 2.90 (m, 1H, CH(CH3)2), 4.38 (d, JPH = 24.37, 1H, CHP), 7.23–
7.92 (m, 19H, arom.). 31P NMR (CDCl3, ppm) dP: 14.05. 13C{1H}
NMR (CDCl3, ppm) dC: 23.23 (s, CH3), 33.15 (s, CH(CH3)2), 47.03
1
(d, JPC = 112.39 Hz, CHP), [124.62 (d), 125.03 (s), 126.38 (s),
127.89 (d), 131.31 (s), 132.18 (d), 138.18 (d), 149.44 (s) (Ph)],
184.13 (s, CO).
2.4.3. Synthesis of the Ag(I) complexes
2.4.3.1. General procedure. To AgNO3 (0.5 mmol) dissolved in 10 mL
of dried methanol was added the ylide L1 (0.450 g, 1 mmol). The
mixture was stirred for ꢁ4 h, during which time it was protected
from light. The white solid product was filtered, washed with
Et2O and dried under reduced pressure.
Fig. 1. X-ray crystal structure of L2.

S.J. Sabounchei et al. / Polyhedron 38 (2012) 131–136
133
Table 2
Crystal data and refinement details for L2 and 2.
Empirical formula
Formula weight
T (K)
C29H27O1P1
422.48
298(2)
C58H54Ag1N1O5P2
1014.83
298(2)
Wavelength (Å)
Crystal system
space group
Unit cell dimensions
a (Å)
0.71073
monoclinic
P21/n
0.71073
triclinic
ꢀ
P1
12.2435(15)
14.4144(14)
14.3923(18)
90.00
107.280(10)
90.00
10.8914(5)
13.5866(7)
17.7670(8)
79.417(4)
79.940(4)
81.634(4)
2527.1(2)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
2425.3(5)
4
Z
Calculated density (mg/ 1.157
1.334
m3)
Absorption coefficient
(mmꢀ1
F(000)
Crystal size (mm)
h Range for data
collection (°)
0.131
0.511
1052
)
896
Fig. 2. X-ray crystal structure of 2. Hydrogen atoms are omitted for clarity.
0.45 ꢂ 0.38 ꢂ 0.32
0.45 ꢂ 0.30 ꢂ 0.23
2.05–29.20
2.08–29.19
Limiting indices
ꢀ16 6 h 6 16,
ꢀ14 6 h 6 14,
ꢀ19 6 k 6 17,
ꢀ18 6 k 6 18,
ꢀ19 6 l 6 17
ꢀ21 6 l 6 24
Reflections collected/
16705/6510 (0.0805)
2889/13559 (0.0777)
unique (Rint
)
Completeness (%)
Absorption correction
Maximum and
minimum
99.3
Numerical
0.960 and 0.940
99.1
Numerical
0.890 and 0.830
transmission
Refinement method
Full-matrix least-
squares on F2
6510/0/280
Full-matrix least-
squares on F2
13559/0/604
Data/restraints/
parameters
Goodness-of-fit (GOF)
1.065
1.103
on F2
Final R indices [I > 2
R indices (all data)
r
(I)] R1 = 0.0700,
R1 = 0.0794,
wR2 = 0.1250
R1 = 0.1487,
wR2 = 0.1793
R1 = 0.1076,
wR2 = 0.2107
0.688 and ꢀ0.323
wR2 = 0.1446
0.534 and ꢀ0.394
Largest difference in
peak and hole (e Åꢀ3
)
Table 3
Selected bond lengths (Å) and bond angles (°) for L2.
Fig. 3. A representation of part of the unit cell contents of L2 showing the head-to-
tail dimeric C–Hꢃ ꢃ ꢃpphen interactions and non-classical C–Hmethylꢃ ꢃ ꢃO@C hydrogen
bonds.
Bonds
Angles
C7–C10
C10–C11
C10–O1
C11–P1
C12–P1
C18–P1
C24–P1
1.501(3)
1.399(3)
1.257(3)
1.715(2)
1.808(3)
1.803(2)
1.814(2)
O1–C10–C7
118.1(2)
121.3(2)
117.84(18)
106.41(11)
113.80(12)
115.53(12)
O1–C10–C11
C10–C11–P1
C11–P1–C12
C11–P1–C18
C11–P1–C24
Table 4
Selected bond lengths (Å) and bond angles (°) for 2.
Bonds
Angles
Ag1–C11
Ag1–C40
P1–C11
P2–C40
O1–C10
O2–C39
P1–C12
C10–C11
P2–C41
C7–C10
C36–C39
C39–C40
2.207(4)
2.199(4)
1.757(4)
1.742(4)
1.235(7)
1.299(6)
1.808(5)
1.4.57(6)
1.814(4)
1.505(6)
1.515(6)
1.466(6)
Ag1–C11–P1
Ag1–C11–C10
Ag1–C40–P2
Ag1–C40–C39
C11–P1–C12
C11–Ag1–C40
C7–C10–C11
C36–C39–C40
P1–C11–C10
P2–C40–C39
C40–P2–C41
C41–P2–C53
109.2(2)
100.6(3)
111.7(2)
100.2(3)
114.4(2)
171.3(1)
118.9(4)
118.3(3)
114.8(3)
117.2(3)
113.5(2)
108.3(2)
2.4.3.2. Data for [Ag(2,4-Cl2C6H3C(O)CHPPh3)2]NO3 (1). Yield: 77%,
M.p. 204–206 °C. Anal. Calc. for C52H38NO5P2Cl4Ag: C, 58.45; H,
3.58; N, 1.31. Found: C, 58.74; H, 3.69; N, 1.47%. IR (KBr disk,
cmꢀ1
)
m
: 1609 (CO), 861 (P+–Cꢀ). 1H NMR (CDCl3, ppm) dH: 4.42
2
(d, JPH = 14.06 Hz, 1H, CH), 7.15–7.34 (m, 18H, arom.). 31P NMR
(CDCl3, ppm) dp: 19.96. 13C{1H} NMR (CDCl3, ppm) dC: 45.33 (d,
1JPC = 80.67 Hz, CHP), [122.09 (d), 126.12 (s), 128.65 (d), 130.09
(s), 130.79 (s), 132.48 (d), 138.50 (s), 138.75 (d) (Ph)], 188.37 (s,
CO).
5.36; N, 1.38. Found: C, 68.93; H, 5.42; N, 1.47%. IR (KBr disk,
cmꢀ1
)
m
: 1600 (CO), 860 (P+–Cꢀ). 1H NMR (DMSO-d6, ppm) dH:
2.4.3.3. Data for [Ag(4-(CH3)2CHC6H4C(O)CHPPh3)2]NO3 (2). Yield:
68%, M.p. 185–187 °C. Anal. Calc. for C58H54AgNO5P2: C, 68.64; H,
3
1.15 (d, JHH = 6.72 Hz, 6H, CH3), 2.89 (m, 1H, CH), 4.92 (d,

134
S.J. Sabounchei et al. / Polyhedron 38 (2012) 131–136
Table 6
A comparison between the selected calculated bond lengths (Å) and bond angles (°)
for compounds 1 and 2, and the corresponding experimental values for complex 2.
2
1
2
calculated
calculated
X-ray
Bond lengths
Ag–C(40)
Ag–C(11)
2.21866
2.20279
2.55419
2.22160
2.20762
2.55928
2.19932
2.20655
2.72571
Ag–O(3)
Bond angles
P(2)–C(40)–Ag
P(1)–C(11)–Ag
C(40)–Ag–O(3)
C(40)–Ag–O(3)
C(39)–C(40)–Ag
C(10)–C(11)–Ag
C(11)–Ag–C(40)
109.795
111.881
81.057
108.823
111.483
81.302
111.730
109.242
84.780
102.766
100.151
100.618
171.293
99.635
99.796
106.871
103.765
178.759
107.871
103.188
178.017
Fig. 4. A representation of complex 2 packing showing the association of the
adjacent molecules through C-Hphenylꢃ ꢃ ꢃpphenyl, C–Hmethylꢃ ꢃ ꢃp, C–Hphenylꢃ ꢃ ꢃOnitrate
and C–Hmethylꢃ ꢃ ꢃOnitrate interactions. Different colours show different adjacent
molecules.
2.4.4.2. Data for [2,4-Cl2C6H3C(O)CHPPh3.Hg(NO3)2](3). Yield: 74%,
M.p. 162–164 °C. Anal. Calc. for C26H19Cl2HgN2O7P: C, 40.35; H,
2.47; N, 3.62. Found: C, 40.78; H, 2.56; N, 3.73%. IR (KBr disk,
2JPH = 9.67, 1H, CH), 7.14–7.60 (m, 19H, arom.). 31P NMR (DMSO-d6,
ppm) dP: 23.11. 13C{1H} NMR (DMSO-d6, ppm) dC: 23.35 (s, CH3),
33.31 (s, CH(CH3)2), 35.48 (d, JPC = 69.38 Hz, CHP), [122.67 (d),
125.83 (s), 127.17 (s), 128.67 (d), 131.55 (s), 132.54 (d), 135.15
(d), 152.03(s) (Ph)], 189.82 (s, CO).
cmꢀ1
)
m
: 1667 (CO), 818 (P+–Cꢀ). 1H NMR (DMSO-d6, ppm) dH:
2
6.28 (d, 1H, JPH = 5.12 Hz, CH), 7.13–8.42 (m, 18H, arom.). 31P
NMR (DMSO-d6, ppm) dp: 27.13 (s with satellites,
2JHgP = 285.31 Hz). 13C{1H} NMR (DMSO-d6, ppm) dC: 43.64 (d,
1JPC = 52.63 Hz, CHP), [119.06 (d), 127.29 (s), 129.52 (d), 132.18
(s), 132.57 (s), 133.52 (s), 133.97 (s), 137.24 (s) (Ph)], 192.89 (s, CO).
1
2.4.4. Synthesis of the Hg(II) complexes
2.4.4.1. General procedure. To a magnetically stirred solution of
Hg(NO3)2.H2O (0.344 g, 1 mmol) in methanol (10 mL), was added
a methanolic solution (5 mL) of ylide L1 (0.450 g, 1 mmol). After
30 min the solvent was removed under reduced pressure to 3 mL.
Addition of diethylether (30 mL) gave the white solid product that
was separated by filtration.
2.4.4.3. Data for [4-(CH3)2CHC6H4C(O)CHPPh3.Hg(NO3)2](4). Yield:
71%, M.p. 160–162 °C. Anal. Calc. for C29H27HgN2O7P: C, 46.62; H,
3.64; N, 3.75. Found: C, 46.95; H, 3.72; N, 3.81%. IR (KBr disk,
cmꢀ1
)
m
: 1652 (CO), 819 (P+–Cꢀ). 1H NMR (DMSO-d6, ppm) dH:
3
1.15 (d, JHH = 6.04 Hz, 6H, CH3), 2.96 (m, 1H, CH), 5.45 (d, 1H,
2JPH = 4.57 Hz, CH), 7.44–8.15 (m, 19H, arom.). 31P NMR (DMSO-
Table 5
Significant C–H. . .O non-classical hydrogen bonds (interatomic distance (Å) and bond angles (°)) found in the structures of L2 and complex 2.
D–Hꢃ ꢃ ꢃA
L2
D–H
Hꢃ ꢃ ꢃA
Dꢃ ꢃ ꢃA
D–Hꢃ ꢃ ꢃA
Symmetry code
C5–H5ꢃ ꢃ ꢃO1
0.9300
2.4400
3.358(3)
169.00
1/2 + x, 1/2 ꢀ y, 1/2 + z
Complex 2
C6–H6ꢃ ꢃ ꢃO1
C8–H8ꢃ ꢃ ꢃO4
C15–H15ꢃ ꢃ ꢃO4
C29–H29ꢃ ꢃ ꢃO1
C32–H32Cꢃ ꢃ ꢃO5
C54–H54ꢃ ꢃ ꢃO2
0.9300
0.9300
0.9300
0.9300
0.9600
0.9300
2.4400
2.5500
2.5900
2.3000
2.4700
2.5200
2.768(6)
3.464(7)
3.338(8)
3.038(6)
3.430(13)
3.269(7)
100.00
169.00
138.00
135.00
174.00
138.00
–
–
2 ꢀ x, 2 ꢀ y, 1 ꢀ z
–
1 ꢀ x, 2 ꢀ y, 2 ꢀ z
–
Fig. 5. Optimized geometries of both complexes 1 and 2.

S.J. Sabounchei et al. / Polyhedron 38 (2012) 131–136
135
mers. The 31P NMR spectra of the Hg(II) complexes at room
temperature clearly exhibit satellites (8% intensity each,
2JPHg ꢁ 290 Hz), while these satellites for ylidic complexes of Hg(II)
halides are only observed at low temperature or in solid state 31P
NMR spectra [10].
The most interesting aspect of the 13C NMR spectra of the com-
plexes is the upfield shift of the signals due to the ylidic carbon.
Such an upfield shift observed in PdCl(g
3-2-XC3H4) (C6H5)3PCH-
COR (X = H, CH3; R = CH3, C6H5) was attributed to the change in
hybridization of the ylidic carbon [28]. Similar upfield shifts of d
2–3 ppm with reference to the parent ylide were also observed
in the case of [(C6H5)3PC5H4HgI2]2 [29] and our synthesized com-
plexes [15]. The 13C shifts of the CO group in the complexes are
around 190 ppm, relative to 182 ppm noted for the same carbon
in the parent ylide, indicating much lower shielding of the carbon
of the CO group in these complexes.
3.2. X-ray crystallography
Crystals of L2 were obtained by slow evaporation of a CHCl3 solu-
tion at room temperature. Significant bond distances and angles are
collected in Table 3 and crystallographic details in Table 2. An ORTEP
plot (Fig. 1) shows that in the molecule of L2, the geometry around
the P atom is nearly tetrahedral, and the O atom is oriented cis to
the P atom. The aromatic ring of the benzoyl group is twisted with
respect to the plane of the carbonyl group through an angle of
ꢀ8.3(4)°. The P–C(11) (1.715 (2) Å) and C(11)–C(10, sp2)
(1.399(4) Å) bond lengths are shorter than the P+–C(sp3) and C–C
normal values, 1.800 and 1.511 Å, respectively. This is due to the yli-
dic resonance and the values are intermediate between common
values for single and double bonds (for example P–C = 1.80 and
P = C = 1.66 Å). The CO bond also is longer (1.256(3) Å) than the nor-
mal value (1.210 Å). This bond distance suggests resonance delocal-
ization in these molecules [30]. In L2, there are head-to-tail C–
Fig. 6. Shape of the energetically highest-lying orbitals HOMO-1, HOMO-4, HOMO-
11 and HOMO-12 for complex 2.
2
d6, ppm) dp: 28.48 (s with satellites, JHgP = 287.19 Hz). 13C{1H}
NMR (DMSO-d6, ppm) dC: 23.45 (s, CH3), 33.97 (s, CH(CH3)2),
1
40.44 (d, JPC = 62.74 Hz, CHP), [119.62 (d), 128.29 (s), 129.50 (d),
131.56 (s), 133.45 (d), 138.71 (d), 155.30 (s) (Ph)], 193.15 (s, CO).
3. Results and discussion
3.1. Spectroscopy
The
m
(CO) values, which are sensitive to complexation, occur at
Hphenyl. . .pphenyl (2.694 Å) interactions between adjacent molecules,
1576 and 1579 cmꢀ1 in the parent ylides, and these values increase
for all complexes (Table 1), indicative of coordination of the ylide
forming dimeric rings. These dimeric rings are further linked to adja-
cent molecules by C–Hphenylꢃ ꢃ ꢃO@C non-classical hydrogen bonds to
generate three dimensional packing (Fig. 3, Table 5).
through carbon. The m
(P+–Cꢀ), which is also diagnostic for coordina-
tion, occurs at 878 and 887 cmꢀ1 in L1 and L2, respectively, and
these values are shifted to lower frequencies for the complexes,
suggesting removal of electron density in the P–C bond [25].
The 1H NMR data for the complexes and the parent ylides are
listed in Table 1. The methine proton was a doublet in all cases.
Compounds wherein the ylide is C-coordinated exhibit a 2JPH value
of 10 Hz or less [11]. The 31P NMR resonances of the complexes oc-
cur at a lower field with respect to the free ylide. The expected
downfield shifts of the 1H and 31P signals for the PCH group upon
complexation were observed. The appearance of single signals for
the PCH group in both the 31P and 1H spectra at ambient temper-
ature indicates the presence of only one molecule for all the com-
plexes, as expected for C-coordination; O-coordination of the ylide
sometimes leads to formation of cis- and trans-isomers, giving rise
to two different signals in the 31P and 1H NMR spectra [26].
Although two diastereoisomers (RR/SS and RS) are possible for
the silver complexes (because the methane carbons are chiral),
NMR spectroscopy does not distinguish them at room temperature.
Methine resonances are intermediate between those in the free
ylides and phosphonium salts (Table 1), and 2JPH values are smaller,
as observed for other C-coordinated carbonyl-stabilized phospho-
rus ylide complexes, due to the hybridization change in the ylidic
carbon (sp2–sp3) upon C coordination [6,11,26]. Much larger values
Crystals of 2 were obtained by slow diffusion of n-hexane into a
CHCl3 solution at room temperature. The complex is shown in
Fig. 2, crystallographic details in Table 2 and significant bond dis-
tances and angles are collected in Table 4. The Ag(I) atom is located
in a slightly distorted linear environment, surrounded by C atoms
of the methine of the ylide.
The relative configuration at the chiral carbon atoms are RR. The
configuration about the molecular axis C(11). . .C(40) is almost
eclipsed (Fig. 2). The coordination geometry at silver is essentially
linear, although the bond lengths and angles at silver are slightly
distorted (C(11)–Ag–C(40), 171.3(1)°). The P(1)-C(11) (methine)
distance is 1.757(4) Å, shorter than the average P-C (Ph) single
bond distance (1.807 Å), indicating some multiple bond character
[33]. For comparison, the P-C bond distance in Ph3PCH2 is 1.66 Å,
which corresponds to a bond order of 1.33 [31–33]. The C(10)-
C(11) distance is 1.457(6) Å, indicating single bond character. The
C(10)-O(1) distance is 1.235(7) Å, similar to C–O bond distances
found in C-bonded ylides [13,34,35]. Complex 2 is an example of
an ylide C-bonded to a soft metal center. In complex 2, a combina-
tion of several weak and medium intermolecular interactions,
including C-Hphenylꢃ ꢃ ꢃpphenyl (3.332 Å), C-Hmethylꢃ ꢃ ꢃpphenyl (3.548
Å), C–Hphenylꢃ ꢃ ꢃOnitrate and C–Hmethylꢃ ꢃ ꢃOnitrate, determine the struc-
tural assembly in this compound (Fig 4, Table 5).
2
of JPH (ca 20 Hz) have been observed in complexes where coordi-
nation is through the oxygen [27]. Neither H–Ag nor P–Ag coupling
was observed at room temperature in the spectra; possibly a fast
equilibrium between the complexes and the free ylides is respon-
sible for the failure to observe NMR coupling or two diastereoiso-
3.3. Theoretical studies
We carried out DFT calculations at the BP86 [20]/def2-SVP [21]
level of theory using the GAUSSIAN 03 [22] optimizer [23] in

136
S.J. Sabounchei et al. / Polyhedron 38 (2012) 131–136
conjunction with Turbomole 5 [24] energies and gradients. The
geometry of the metal complex 2, as determined by X-ray crystal
structure analysis (see Fig. 2), was fully optimized at above men-
tioned level of theory. The observed geometry of compound 2
was used as a basis for DFT calculations of compound 1. Fig. 5
shows the optimized geometries of both complexes 1 and 2. The
calculated bond lengths and bond angles of 2 are in good agree-
ment with the experimental values (see Table 6). The computed
Ag–C distances are 0.2–0.3 Å longer than the X-ray values. The
computed values for the Ag–O distance are about 0.17 Å shorter
than the X-ray value. The calculated bond lengths of these com-
pounds are also gathered in Table 6. As it can be seen in this Table,
there is good agreement between the calculated bond lengths for
this compound with those derived from the X-ray crystal structure.
Fig. 6 shows the shape of the energetically highest-lying orbitals,
HOMO-1, HOMO-4, HOMO-11 and HOMO-12. HOMO-1 and
HOMO-4 are localized at the Ag–C(Ylide). The shape of HOMO-11
Appendix A. Supplementary data
CCDC 837049 and 837048 contain the supplementary crystal-
lographic data for compounds L2 and 2, respectively. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary
data associated with this article can be found, in the online
version, at http://dx.doi.org/10.1016/j.poly.2012.02.034.
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Acknowledgements
We are grateful to the Bu-AliSina University for a grant and Mr.
Zebarjadian for recording the NMR spectra.