Silver(I) complexes of bis[2-(diphenylphosphino)phenyl] ether

Article abstract of DOI:10.1016/j.poly.2007.11.019

The reaction of AgOTf in dichloromethane with bis(2-(diphenylphosphino)phenyl) ether (DPEphos) in an equimolar ratio afforded a dinuclear complex [Ag₂(κ²-P,P′-DPEphos)₂(μ-OTf)₂] (1), whereas the similar reaction in a 1:2 molar ratio resulted in the formation of a bis-chelating complex [Ag(κ²-P,P′-DPEphos)₂][OTf] (2). The silver(I) complex 1 was obtained as a dimer, in which two silver atoms are bridged by two triflate groups to form three adjacent eight-membered spirocyclic rings. The mixed-ligand complex [Ag(κ²-P,P′-DPEphos)(2,2′-bpy)][OTf] (3) was obtained in the reaction of 1 in dichloromethane with 2,2′-bipyridine. The crystal structures of complexes 1-3 were determined by single crystal X-ray analyses.

Full text of DOI:10.1016/j.poly.2007.11.019

Available online at www.sciencedirect.com
Polyhedron 27 (2008) 899–904
www.elsevier.com/locate/poly
Silver(I) complexes of bis[2-(diphenylphosphino)phenyl] ether
a,
a
b
*
Maravanji S. Balakrishna , Ramalingam Venkateswaran , Shaikh M. Mobin
a Phosphorus Laboratory, Department of Chemistry, Indian Institute of Technology, Bombay, Mumbai 400 076, India
b National Single Crystal X-ray Diffraction Facility, Indian Institute of Technology, Bombay, Mumbai 400 076, India
Received 31 July 2007; accepted 4 November 2007
Available online 31 December 2007
Abstract
The reaction of AgOTf in dichloromethane with bis(2-(diphenylphosphino)phenyl) ether (DPEphos) in an equimolar ratio afforded
a dinuclear complex [Ag2(j2-P,P0-DPEphos)2(l-OTf)2] (1), whereas the similar reaction in a 1:2 molar ratio resulted in the formation of
a bis-chelating complex [Ag(j2-P,P0-DPEphos)2][OTf] (2). The silver(I) complex 1 was obtained as a dimer, in which two silver atoms are
bridged by two triflate groups to form three adjacent eight-membered spirocyclic rings. The mixed-ligand complex [Ag(j2-P,P0-DPE-
phos)(2,20-bpy)][OTf] (3) was obtained in the reaction of 1 in dichloromethane with 2,20-bipyridine. The crystal structures of complexes
1–3 were determined by single crystal X-ray analyses.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Mixed-ligand silver complexes; DPEphos; 2,20-Bipyridine; Chelating complexes; Crystal structures
1. Introduction
2. Results and discussion
The coordination chemistry of bis(2-(diphenylphos-
phino)phenyl) ether (DPEphos) is interesting due to its ver-
satile coordination behavior and its catalytic utility in a
variety of organic transformations. The tridentate nature
of this ligand produces interesting coordination architec-
tures, often the ether-O donor being hemilabile in nature.
van Leeuwan and co-workers [1] and others [2] have exten-
sively studied the transition metal chemistry and catalytic
utility of DPEphos [3]. We recently reported the synthesis
of RuII [4] and CuI [5] complexes of DPEphos and their
application in catalytic hydrogenation of styrenes. As a
part of our interest [6] herein we report for the first time,
the synthesis, reactivity and crystal structures of AgI com-
plexes containing DPEphos.
Treatment of AgOTf with DPEphos in 1:1 and 1:2
molar ratios at room temperature afford colorless crystalline
solids [Ag2(j2-P,P0-DPEphos)2(l-OTf)2] (1) and [Ag-
(j2-P,P0-DPEphos)2][OTf] (2), respectively, in good yield.
Complex 2 can be prepared by treating complex 1 with DPE-
phos in 0.5:1 stoichiometry as shown in Scheme 1.
The 31P{1H} NMR spectrum of complex 1 shows a
broad doublet at ꢀ10.0 ppm with JAgP coupling of 486.8
Hz at room temperature, whereas at ꢀ50 °C, the peaks
resolve into two doublets centered at ꢀ10.4 ppm with
109
AgP
107
J
and J
couplings of 526.8 and 456.7 Hz, respec-
AgP
tively. This clearly indicates that both the phosphorus
atoms in the DPEphos ligand are attached to silver(I) in
a chelating fashion and are equivalent. The coordination
chemical shift is 7.0 ppm. The 31P{1H} NMR spectrum
of complex 2 consists of two doublets centered at
109
AgP
107
ꢀ10.5 ppm with J
and J
couplings of 269.7 and
AgP
233.8 Hz, respectively. The JAgP values are comparable
with those reported in the literature for analogous com-
plexes [7,8]. The EI mass spectrum of complex 2 shows a
*
Corresponding author. Tel.: +91 22 2576 7181; fax: +91 22 2576 7152/
2572 3480.
E-mail address: krishna@chem.iitb.ac.in (M.S. Balakrishna).
0277-5387/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.11.019

900
M.S. Balakrishna et al. / Polyhedron 27 (2008) 899–904
CF3
O
S
S
Ph2
P
Ph2
P
Ph2
P
O
O
N
N
2,2'-Bipyridine
DCM
Ag
Ag
O
O
Ag
O
OTf
O
O
P
O
P
P
Ph2
Ph2
Ph2
F3C
3
1
2 AgOTf
DPEphos
DCM
Ph2
P
Ph2
P
PPh2
PPh2
AgOTf
DCM
Ag
O
OTf
O
2
O
P
P
Ph2
Ph2
2
Scheme 1.
molecular ion peak corresponding to the cationic complex
part at m/z 1185.46 [M]+ with the appropriate isotopic
pattern. This evidences that the AgI metal center is bis-che-
lated by DPEphos ligands to form a spirocyclic compound
(Fig. 2). The microanalysis supports the structural compo-
sition of complex 2, which is further confirmed by single
crystal X-ray data.
The solid state structure of complex 1 shows the pres-
ence of a AgI complex as a dimer, in which DPEphos
binds in a chelating mode whereas the two triflate ions
are bridging the two silver atoms via O@S–Oꢀ units, thus
making a three eight-membered spirocyclic ring structure
as shown in Fig. 1. The counter ion plays an important
role in coordination with silver atoms, providing stability
to complex 1. Similarly, counter ions such as nitrate, ace-
tate and perchlorate are also known to bridge silver atoms
[9–11]. Although the triflate units anchor the silver(I) cen-
ters to stabilize complex 1, they are labile and can be easily
substituted with P- and N-donors. The mixed-ligand
complex [Ag(j2-P,P0-DPEphos)(2,20-bpy)][OTf] (3) was
synthesized in good yield by the reaction of 1 with 2,20-
bipyridine in a 1:2 molar ratio at room temperature. The
31P{1H} NMR spectrum of complex 3 at room tempera-
ture exhibits a pair of doublets centered at ꢀ8.8 ppm with
1H NMR spectrum confirms the presence of 2,20-bipyri-
dine, which presents peaks at 8.04 and 8.35 ppm. The JAgP
values are in the range 370–430 Hz, which is in agreement
with those values reported for analogous complexes
[10,12].
109
AgP
107
J
and J
values of 426 and 374 Hz, respectively. The
AgP
Fig. 1. Molecular structure of complex 1. Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms, phenyl rings attached to
phosphorus and uncoordinated solvent molecules have been omitted for clarity.

M.S. Balakrishna et al. / Polyhedron 27 (2008) 899–904
901
2.1. Crystal structures of complexes 1–3
Complex 1 crystallizes in the monoclinic crystal system
with a center of symmetry and it is dimeric in nature.
The AgI center possesses a distorted tetrahedral geometry,
whose edges are shared by two phosphorus atoms of a
DPEphos ligand and two oxygen atoms of triflate ions.
Each silver atom is anchored to a chelating DPEphos
and bridged by triflate units. The Ag1–O1, Ag1–O2,
Ag1–P1 and Ag1–P2 bond distances are 2.553(2),
Complexes 1 and 2 were recrystallized from a mixture of
CH2Cl2/Et2O, and complex 3 was recrystallized from a
CHCl3/Et2O mixture. The molecular structures of com-
plexes 1–3 are shown in Figs. 1–3, respectively, and selected
bond parameters are displayed in Tables 1 and 2. The crys-
tallographic information is given in Table 3.
Fig. 2. Molecular structure of complex 2. Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms have been omitted for clarity.
Fig. 3. Molecular structure of complex 3. Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms and uncoordinated solvent
molecules have been omitted for clarity.

902
M.S. Balakrishna et al. / Polyhedron 27 (2008) 899–904
Table 1
Selected bond distances and bond angles for complexes 1 and 2
Complex 1
Complex 2
Bond distances (A)
˚
˚
Bond distances (A)
Bond angles (°)
Bond angles (°)
Ag1–O2
Ag1–P2
Ag1–P1
Ag1–O1
S1–O3
S1–O1
S1–C1
F1–C1
2.411(2)
2.4383(9)
2.4521(8)
2.553(2)
1.426(2)
1.436(3)
1.815(3)
1.327(4)
O2–Ag1–P2
O2–Ag1–P1
P2–Ag1–P1
O2–Ag1–O1
P2–Ag1–O1
P1–Ag1–O1
O3–S1–O1
111.52(6)
113.49(6)
117.40(3)
99.12(8)
104.07(6)
109.13(6)
115.41(15)
112.58(13)
Ag1–P3
Ag1–P4
Ag1–P1
Ag1–P2
S1–O3
2.5385(7)
P3–Ag1–P4
P3–Ag1–P1
P4–Ag1–P1
P3–Ag1–P2
P4–Ag1–P2
P1–Ag1–P2
106.37(2)
107.47(2)
115.38(2)
107.77(2)
110.56(2)
108.96(2)
2.5461(7)
2.6119(7)
2.6232(7)
1.450(3)
1.786(5)
1.338(5)
S1–C73
F1–C73
S1–O1–Ag1
monoclinic crystal system and AgI exists in a distorted tet-
rahedral geometry. The silver(I) atom is attached to four
phosphorus atoms of two DPEphos ligands. The Ag–P
bond distances are 2.5385(7), 2.5460(7), 2.6118(7) and
2.6232(7) A and are approximately 0.1–0.19 A longer than
the same distances in complex 1. The bite angles of the two
DPEphos ligands are 106.37(2)° and 108.96(2)°, which are
10.73° and 8.44° less when compared with the same angles
in complex 1.
Table 2
Selected bond distances and bond angles for complex 3
Complex 3
˚
Bond distances (A)
Bond angles (°)
˚
˚
Ag1–N2
Ag1–N1
Ag1–P2
Ag1–P1
S1–O2
2.305(6)
2.355(6)
2.405(2)
2.488(2)
1.439(6)
1.317(11)
1.853(11)
N2–Ag1–N1
N2–Ag1–P2
N1–Ag1–P2
N2–Ag1–P1
N1–Ag1–P1
P2–Ag1–P1
70.4(2)
126.98(16)
119.60(17)
110.69(15)
107.77(15)
113.51(7)
F3–C47
S1–C49
In complex 3, the AgI atom possesses a distorted tetra-
hedral geometry containing two phosphorus and two nitro-
gen atoms. The pyridyl units of the 2,20-bipyridine ligand
are not in a plane and are twisted by an angle of 14.50°.
˚
˚
2.411(2), 2.453(3) and 2.438(2) A, respectively. The Ag1–
O2 bond distances of 0.142(2) A is shorter than Ag1–O1,
which indicates that the former one is an ionic bond and
the latter one is a covalent bond. The bite angle of the
DPEphos ligand is 117.40(3)°, which is 15.4° larger than
its natural bite angle (bn). Complex 2 crystallizes in the
˚
˚
The Ag1–P1 bond (2.488(2) A) is considerably longer than
the Ag1–P2 bond (2.405(2) A). The Ag1–N1 and Ag1–N2
˚
bond distances are 2.305(6) and 2.355(6) A, respectively.
One set of diagonally opposite Ag–N and Ag–P bonds
are longer than the other set of Ag–N and Ag–P bonds.
Table 3
Crystallographic data for complexes 1–3
1
2
3
Formula
Fw
C
880.39
38H30AgCl2F3O4P2S
C73H56AgF3O5P4S
1333.99
monoclinic
P21/c
14.04760(10)
19.0664(2)
23.1718
90
91.6160(10)
90
6203.80(10)
4
C48H37AgCl3F3N2O4P2S
1071.02
triclinic
Crystal system
Space group
monoclinic
P21/a
12.2506(15)
26.477(5)
12.5255(6)
90
115.035(8)
90
3681.1(8)
4
ꢀ
P1
˚
a (A)
9.547(5)
13.800(5)
19.221(5)
107.804(5)
94.406(5)
92.280(5)
2398.6(17)
2
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
3
˚
V (A )
Z
qcalc (g cmꢀ3
)
1.589
0.892
1776
1.428
0.524
2736
1.483
0.754
1084
l(Mo Ka) (mmꢀ1
F(000)
)
Crystal size (mm)
T (K)
0.33 ꢁ 0.26 ꢁ 0.21
0.26 ꢁ 0.21 ꢁ 0.18
0.08 ꢁ 0.17 ꢁ 0.23
100(2)
150(2)
150(2)
2h Range (°)
Total number reflections
2.92–25.00
20732
2.90–25.00
60904
3.05–30.00
8354
Number of independent reflections [Rint
]
6460 [0.027]
1.074
0.0332
10906 [0.0447]
1.051
0.0358
3817 [0.089]
0.842
0.0678
Goodness-of-fit (F2)
R1a
wRb2
0.0800
0.0850
0.1705
P
P
a
R = jjFoj ꢀ jFcjj/ jFoj.
P
P
2
1=2
2
b
Rw ¼ f½ wðF 2o ꢀ F c2Þ= wðF 2oÞ ꢂg w ¼ 1=½r2ðF o2Þ þ ðxPÞ ꢂ where P ¼ ðF o2 þ 2F 2c Þ=3.

M.S. Balakrishna et al. / Polyhedron 27 (2008) 899–904
903
107
AgP
A similar trend was observed in the analogous copper com-
plex [Cu(j2-P,P0-DPEphos)(l-4,40-bpy)]n[BF4]n, but to a
lesser extent [5].
CDCl3): ꢀ10.5 ppm (2d, J1A0g9P ¼ 269:7, J
¼ 233:8). MS
(EI): m/z 1185.46 [MꢀOTf]+. Anal. Calc. for C73H56O5-
P4AgF3S: C, 65.72; H, 4.23; S, 2.40. Found: C, 65.74; H,
4.20; S, 2.44%.
3. Conclusion
4.2.3. Synthesis of [Ag(j2-P,P0-DPEphos)(2,20-
bpy)][OTf] (3)
The silver(I) complexes [Ag2(j2-P,P0-DPEphos)2(l-
OTf)2] (1), [Ag(j2-P,P0-DPEphos)2][OTf] (2) and [Ag(j2-
P,P0-DPEphos)(2,20-bpy)][OTf] (3) have been synthesized
and structurally characterized. In all the complexes, the sil-
ver(I) atoms exist in a distorted tetrahedral environment
and the DPEphos ligand binds in a chelating fashion.
The solid state structure of complex 1 evidences the pres-
ence of three adjacent eight-membered spirocyclic rings.
The triflate ions in complex 1 act as bridging units between
the two silver atoms to form a dinuclear complex.
A solution of 2,20-bipyridine (0.010 g, 0.063 mmol) in
CH2Cl2 (5 mL) was added dropwise to a stirring solution
of 1 (0.050 g, 0.031 mmol) also in CH2Cl2 (10 mL) at room
temperature. After 4 h all the solvents were removed under
vacuum and the remaining white solid was recrystallized
from a CHCl3/Et2O mixture as colorless crystals of 3.
1
Yield: 88% (0.053 g), m.p.: >260 °C. H NMR (400 MHz,
CDCl3): 6.79–7.38 (m, 28H, Ph), 7.00 (t, 2H, bpy), 8.04
(dt, 2H, bpy), 8.35 ppm (m, 4H, bpy). 31P NMR
(162 MHz, CDCl3): ꢀ8.8 ppm (2d, J1A0g9P ¼ 425:6, J
¼
107
AgP
4. Experimental
374:3). Anal. Calc. for C47H36O4P2AgF3SN2: C, 59.32; H,
3.81; N, 2.94; S, 3.37. Found: C, 59.25; H, 3.85; N, 2.86;
S, 3.32%.
4.1. General methods
All manipulations were performed under an atmosphere
of dry nitrogen using standard Schlenk techniques. All the
solvents were purified by conventional procedures and dis-
tilled under nitrogen prior to use [13]. The ligand DPEphos
was prepared according to the published procedure [14].
4.3. X-ray crystallography
A single crystal of each compound 1–3 suitable for
X-ray crystal analysis was mounted on a glass fiber with
epoxy resin. Unit cell determination and data collection
of all the compounds were collected on an Oxford Diffrac-
tion XCALIBUR-S CCD system using Mo Ka radiation
4.2. Instrumentation
˚
(k = 0.71073 A). The structures were solved and refined
The 1H and 31P{1H} NMR (d in ppm) spectra were
recorded using a Varian 400 Mercury Plus spectrometer
operating at the appropriate frequencies using TMS and
85% H3PO4 as internal and external references, respec-
tively. Microanalyses were performed on a Carlo Erba
Model 1112 elemental analyzer. Electro-spray ionization
(EI) mass spectrometry experiments were carried out using
a Waters Q-Tof micro-YA-105.
by full-matrix least-squares techniques on F2 using
SHELX-97 (SHELXL program package) [15]. The absorption
corrections were done by multi-scan and all the data were
corrected for Lorentz and polarization effects. The non-
hydrogen atoms were refined with anisotropic thermal
parameters. All the hydrogen atoms were geometrically
fixed and allowed to refine using a riding model.
Acknowledgements
4.2.1. Synthesis of [Ag2(j2-P,P0-DPEphos)2(l-OTf)2] (1)
A mixture of DPEphos (0.252 g, 0.467 mmol) and
AgOTf (0.120 g, 0.467 mmol) in CH2Cl2 (20 mL) was stir-
red for 4 h at room temperature. All the solvents were dried
under vacuum to obtain a white solid, which was recrystal-
lized from CH2Cl2/Et2O as colorless crystals of 1. Yield:
83% (0.309 g), m.p.: 256–258 °C. 1H NMR (400 MHz,
CDCl3): 6.75–7.46 ppm (m, 56H, Ph). 31P NMR
(162 MHz, CDCl3): ꢀ10.0 ppm (d, JAgP = 486.8 Hz). 31P
We are grateful to The Department of Science and
Technology (DST), New Delhi, for funding. We also
thank The Department of Chemistry Instrumentation
Facilities, IIT Bombay and The National Single Crystal
X-ray Diffraction Facility, IIT Bombay, for instrument
facilities.
Appendix A. Supplementary material
NMR (162 MHz, 223 K, CDCl3): ꢀ10.4 ppm (2d, JA10g9P
¼
107
AgP
526:8, J
¼ 456:7). Anal. Calc. for C74H56O8P4Ag2F6S2:
CCDC 643885, 643886 and 643887 contain the supple-
mentary crystallographic data for 1, 2 and 3. These data
can be obtained free of charge via http://www.ccdc.cam.
ac.uk/conts/retrieving.html, or from the Cambridge Crys-
tallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK, fax: (+44) 1223-336-033, or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with
this article can be found, in the online version, at
doi:10.1016/j.poly.2007.11.019.
C, 55.86; H, 3.55; S, 4.03. Found: C, 55.90; H, 3.56; S,
3.92%.
4.2.2. Synthesis of [Ag(j2-P,P0-DPEphos)2][OTf] (2)
The procedure was similar to that of 1, but using AgOTf
(0.025 g, 0.097 mmol) and DPEphos (0.105 g, 0.194 mmol).
1
Yield: 98% (0.127 g), m.p.: >260 °C. H NMR (400 MHz,
CDCl3): 6.68–7.21 (m, 56H, Ph). 31P NMR (162 MHz,

904
M.S. Balakrishna et al. / Polyhedron 27 (2008) 899–904
[5] R. Venkateswaran, M.S. Balakrishna, S.M. Mobin, H.M. Tuononen,
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