An unexpected entry into the silver(I) chemistry of diphosphazane ligands: Crystal and molecular structures of [Ag{Ph2PN(Pri)PPh2}(CF3SO 3)]2, [Ag{Ph2PN(Pri)PPh(OC6H3

Article abstract of DOI:10.1016/j.poly.2006.05.017

Mononuclear, binuclear and trinuclear silver(I) complexes were obtained unexpectedly while probing the reactivity of diphosphazane ligands of the type X₂PN(Prⁱ)PXY towards the ruthenium-based precursor Ru(bipy)₂Cl₂ · 2H₂O, in the presence of a silver salt as a chloride scavenger. Subsequently, the reactions of AgX [X = Cl, NO₃ or CF₃SO₃] with Ph₂PN(R)PPh(Y) [R = H, Y = Ph; R = Prⁱ, Y = Ph or OC₆H₃Me₂-2, 6] in a 1:1 or 1:2 molar ratio have been investigated. Mononuclear or binuclear Ag(I) complexes containing either chelating or bridging diphosphazane ligands are obtained. Trinuclear silver(I) complexes are accessible by the treatment of diphosphazane ligands, Ph₂PN(R)PPh₂ [R = H, Prⁱ] with AgCl using piperidine as the solvent. In the presence of a suitable chloride donor species, the mononuclear and binuclear complexes of Ph₂PN(Prⁱ)PPh₂ are transformed slowly to the trinuclear complex [Ag₃(μ-Cl)₂{Ph₂PN(Prⁱ)PPh ₂}₃]X, over a period 20 h. The structures of representative complexes have been confirmed by X-ray crystallography and the salient structural features are discussed.

Full text of DOI:10.1016/j.poly.2006.05.017

Polyhedron 25 (2006) 3189–3200
www.elsevier.com/locate/poly
An unexpected entry into the silver(I) chemistry of diphosphazane
ligands: Crystal and molecular structures of
[Ag{Ph2PN(Pri)PPh2}(CF3SO3)]2, [Ag{Ph2PN(Pri)PPh(OC6H3-
Me2-2,6)}2]PF6, and [Ag3(l-Cl)2{Ph2PN(R)PPh2}3]PF6 (R = H, Pri)
Heera Krishna, Setharampattu S. Krishnamurthy ,1, Munirathinam Nethaji
*
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, Karnataka, India
Received 16 May 2006; accepted 18 May 2006
Available online 3 June 2006
Abstract
Mononuclear, binuclear and trinuclear silver(I) complexes were obtained unexpectedly while probing the reactivity of diphosphazane
ligands of the type X2PN(Pri)PXY towards the ruthenium-based precursor Ru(bipy)2Cl2 Æ 2H2O, in the presence of a silver salt as a chlo-
ride scavenger. Subsequently, the reactions of AgX [X = Cl,NO3 or CF3SO3] with Ph2PN(R)PPh(Y) [R = H,Y = Ph; R = Pri,Y = Ph or
OC6H3Me2-2,6] in a 1:1 or 1:2 molar ratio have been investigated. Mononuclear or binuclear Ag(I) complexes containing either chelating
or bridging diphosphazane ligands are obtained. Trinuclear silver(I) complexes are accessible by the treatment of diphosphazane ligands,
Ph2PN(R)PPh2 [R = H,Pri] with AgCl using piperidine as the solvent. In the presence of a suitable chloride donor species, the mono-
nuclear and binuclear complexes of Ph2PN(Pri)PPh2 are transformed slowly to the trinuclear complex [Ag3(l-Cl)2{Ph2PN(Pri)PPh2}3]X,
over a period 20 h. The structures of representative complexes have been confirmed by X-ray crystallography and the salient structural
features are discussed.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Keywords: Phosphorus ligands; Silver(I) complexes; NMR spectroscopy; X-ray crystallography
1. Introduction
trolled chirality [3]. Recent efforts have been devoted to
the study of the stereochemistry of these complexes as a
result of the different interactions that may arise when enan-
tiomeric forms (D or K) interact with a variety of substrates
[4]. Despite the wealth of literature on the polypyridyl com-
plexes of Ru(II) [5] and despite the fact that the redox prop-
erty and catalytic activity of the complexes can be
fine-tuned by varying the ligands present, there are only a
few studies on the reactivity of Ru(II) bipyridyl complexes
towards diphosphinoalkanes [6].
Our original objective was to prepare a series of
diphosphazane chelated ruthenium bipyridyl complexes
of the type [Ru(bipy)2{L–L}2]X2, where {L–L} is a biden-
tate phosphorus ligand of the type X2PN(R)PXY. For this
purpose, we adopted a method which is a slight modifica-
tion of what is already reported in the literature [7]. The
During the past decade, there has been considerable
interest in ruthenium bipyridyl complexes owing to their
exceptional photo physical properties when incorporated
into light-activated devices [1]. Octahedral hexacoordinated
Ru(II) complexes bearing 2,20-bipyridine has attracted con-
siderable attention because of their potential use as chiral
building blocks for supramolecular assemblies or as chiral
probes for biological molecules [2]. In addition, they have
also been used extensively in diastereomerically controlled
synthesis and in the generation of atropisomerically con-
*
Corresponding author. Tel.: +91 80 2293 2401.
E-mail address: sskrish@ipc.iisc.ernet.in (S.S. Krishnamurthy).
INSA Senior Scientist.
1
0277-5387/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2006.05.017

3190
H. Krishna et al. / Polyhedron 25 (2006) 3189–3200
Nomenclature
dppa bis(diphenylphosphino)amine
dppm bis(diphenylphosphino)methane
dppi-Pr bis(diphenylphosphino)isopropylamine
dppnpr bis(diphenylphosphino)n-propylamine
OTf trifluoromethane sulfonate anion
method adopted by us is outlined in (Scheme 1), in which
silver triflate was used as the halide scavenger. To our sur-
prise, this method did not yield the targeted ruthenium
bipyridyl diphosphazane complexes; instead, silver(I) com-
plexes of diphosphazanes were obtained, thus providing an
unexpected entry into the silver(I) chemistry of diphosp-
hazane ligands. Subsequently, the silver(I) complexes of
the diphosphazanes, Ph2PN(Pri)PPh(OC6H3Me2-2,6) (L1),
Ph2PN(Pri)PPh2 (L2) and Ph2PN(H)PPh2 (L3) have been
synthesized by the reactions of appropriate silver salts with
these ligands. The silver(I) complexes have been character-
ized by 1H, and 31P {1H} NMR spectroscopy, and the struc-
tures of some representative complexes determined by single
crystal X-ray diffraction studies. The results of these studies
are reported in this paper. While the silver(I) complexes of
diphosphinoalkanes have been explored extensively [8,9],
similar studies on ‘‘P–N–P’’ based ligands are limited
mainly to the three ligands, Ph2PN(R)PPh2 (R = H,Me
or n-Pr) [10–15].
2.1. Synthesis of Ph2PN(Pri)PPh(OC6H3Me2-2,6) (L1)
A solution of PPh2Cl (3.6 mL, 0.02 mol) in 20 mL ben-
zene was added drop wise with stirring to a solution of iso-
propyl amine (5.12 mL, 0.06 mol) in 30 mL benzene at 0 ꢁC.
The reaction mixture was stirred at room temperature for
6 h and was filtered to remove the precipitated isopropyl
amine hydrochloride. The filtrate was evaporated to
dryness under vacuum to give the aminophosphane
Ph2PNH(Pri) as a viscous oil. The oily residue was redis-
solved in benzene, and triethylamine (4.16 mL, 0.03 mol)
added. The solution was cooled to 0 ꢁC, and PPhCl2
(2.71 mL, 0.02 mol) in benzene was added drop wise with
stirring. The reaction mixture was stirred for 6 h at room
temperature and filtered. The filtrate was evaporated to dry-
ness and the residue dissolved in THF. This solution was
added drop wise at room temperature to sodium 2,6-dim-
ethylphenoxide, which was prepared by adding sodium
hydride (60% dispersion in paraffin), (0.80 g, 0.016 mol) to
a solution of 2,6-dimethylphenol (1.952 g, 0.016 mol) in
dry THF. The reaction mixture was stirred at 30 ꢁC for
5 h and evaporated to dryness. The residue was chromato-
graphed on silica gel using benzene-petroleum ether (1:1 v/
v) as the eluant. A concentrated solution of the ligand in
CHCl3 when cooled at 0 ꢁC for 24 h gave colorless transpar-
ent crystals. Yield: 5.7 g, 60%. Anal. Calc. for C29H31-
N1O1P2: C, 73.9; H, 6.6; N, 3.0. Found: C, 73.8; H, 6.6;
N, 2.8%. 1H NMR (CDCl3, 293 K): d 0.84, 1.38 (d,
CHMe2), 2.12 (s, C6H3Me2), 3.99 (m, CHMe2), 6.8–7.5
(m, aryl protons). 31P {1H} NMR (CDCl3, 293 K): d 36.5
(s), 121.8 (s). IR (KBr, cmꢀ1): 3443 w, 3202 w, 2960 s,
1600 s, 1260 s, 797 s, 695 s.
2. Experimental
All reactions were carried out under an atmosphere of
dry nitrogen by using standard Schlenk-line techniques.
The ligands Ph2PN(Pri)PPh2 (L2) and Ph2PN(H)PPh2
(L3) were prepared using published procedures [16]. The
syntheses of the silver complexes were carried out under
dark conditions owing to the sensitivity of these com-
pounds to light. Solvents were purified by standard proce-
1
dures and freshly distilled prior to use. The H and 31P
{1H} NMR spectra were recorded in CDCl3 using a Bruker
Avance-400 spectrometer with Me4Si as an internal stan-
1
dard for H NMR measurements and 85% H3PO4 as an
2.2. Synthesis of [Ag3(l-Cl)2{Ph2PN(Pri)PPh2}3]X,
(X = NO3, PF6) (1a, 1b)
external standard for 31P NMR measurements. The vari-
able temperature 31P {1H} NMR experiments were carried
out in CD2Cl2 from 183 to 303 K. Chemical shifts down-
field from the standard were assigned positive values. Infra-
red spectra were recorded using a Perkin–Elmer Model 457
spectrometer. Elemental analyses were carried out using a
Perkin–Elmer 2400 CHN analyzer.
2.2.1. Method A
A
solution of Ru(bipy)2Cl2 Æ 2H2O [7] (0.325 g,
6.25 · 10ꢀ4 mol) and AgNO3 (0.138 g, 8.125 · 10ꢀ4 mol)
in acetonitrile was stirred for 30 min after which Ph2PN-
S
Cis-[Ru(bipy)2 (acetone)2](OTf)2
Cis-[Ru(bipy)2]Cl2
+ 2AgOTf
+ 2AgCl
S
Cis-[Ru(bipy)2(acetone)2](OTf)2 + (L-L)
L-L = Bisphosphine ligand ; S = acetone
Scheme 1. Procedure adopted for the attempted synthesis of diphosphazane-bipyridyl complexes of ruthenium.
Cis-[Ru(bipy)2 (L-L)](OTf)2

H. Krishna et al. / Polyhedron 25 (2006) 3189–3200
3191
1
(Pri)PPh2 (L2) (0.267 g, 6.25 · 10ꢀ4 mol) was added. The
reaction mixture was stirred for 3 h, and passed through
a short plug (7 cm · 2 cm) of celite. The filtrate was concen-
trated under vacuum to ꢁ5 mL. Colorless crystals of (1a)
appeared over a period of 24 h. Yield: 0.85 g, 60%. Anal.
Calc. for (1a): C81H81Ag3Cl2N4P6O3: C, 55.8; H, 4.7; N,
52.5 (d, J (31P, Ag) = 450 Hz). IR (Nujol, cmꢀ1), (2b):
3286 s, 3168 s, 3050 m, 1584 m, 928 m, 900 m, 506 s, 437
s, 421 w, 380 w, 367 m, 319 m.
2.4. Synthesis of [Ag(Ph2PN(Pri)PPh2)X]2 (X = NO3,
OTf) (3a, 3b)
1
3.2. Found: C, 55.7; H, 4.6; N, 3.2%. H NMR (CDCl3,
293 K): d 0.32 (d, 18H, CHMe2), 3.82 (s br, 3H, CHMe2),
7–7.5 (m, 60H, C6H5). 31P {1H} NMR (CDCl3, 293 K): d
72.0 (s br). IR (Nujol, cmꢀ1): 3428 m, 3049 s, 2978 s,
1481 s, 1322 s, 1127 s, 1316 s, 967 s, 887 s, 855 s, 696 s,
424 m, 385 m, 342 m, 312 w.
The complex (1b) could be obtained from (1a) by a
metathesis reaction, using a twofold excess of NH4PF6 in
acetone. Yield (1b): 0.86 g, 58% (see below for characteriza-
tion data).
The ligand Ph2PN(Pri)PPh2 (L2) (0.267 g, 6.25 · 10ꢀ4
mol) was added to a solution of AgOTf (0.160 g,
6.25 · 10ꢀ4 mol) in acetonitrile at room temperature and
the reaction mixture stirred for 4 h. Solvent was removed
from the reaction mixture and the resulting colorless solid
was redissolved in dichloromethane. The solution was
passed through a short plug of celite (7 cm · 2 cm) and
concentrated to ꢁ5 mL. Colorless micro-crystals of (3b)
appeared over a period of 24 h. Yield: 0.53 g, 62%. Anal.
Calc. for (3b): C56H54Ag2F6N2O6P4S2: C, 49.0; H, 3.9; N,
1
2.0. Found: C, 49.2; H, 3.9; N, 2.2%. H NMR (CDCl3,
2.2.2. Method B for (1b)
A solution of AgCl (0.117 g, 8.125 · 10ꢀ4 mol) and
Ph2PN(Pri)PPh2 (0.521 g, 1.22 · 10ꢀ3 mol) in piperidine
(20 mL) was stirred at room temperature for 12 h. Solvent
was evaporated from the reaction mixture and freshly dis-
tilled acetone (20 mL) was added followed by the addition
of a twofold excess of NH4PF6. The reaction mixture was
stirred for a further period of 1 h; solvent was evaporated
and the residue redissolved in the minimum quantity of
dichloromethane (2 mL). The addition of diethyl ether gave
a precipitate of the title complex (1b) in 40% yield (0.60 g).
Anal. Calc. for (1b): C81H81Ag3Cl2F6N3P7: C, 53.3; H, 4.4;
N, 2.3. Found: C, 53.5; H, 4.5; N, 2.3%. 1H NMR (CDCl3,
293 K): d 0.30 (d, 18H, CHMe2), 3.76 (s br, 3H, CHMe2),
7.0–7.7 (m, 60H, C6H5). 31P{1H} NMR (CDCl3, 293 K):
d 73.5 (s, br). IR (Nujol, cmꢀ1): 3422 m, 3053 s, 2989 s,
1481 s,1127 s, 959 s, 887 s, 851 s, 695 s, 420 m, 382 m,
348 m, 322 w.
293 K): d 0.59 (s br, 12H, CHMe2), 3.94 (s br, 2H,
CHMe2), 7.2–7.6 (m, 40H, C6H5). 31P{1H}NMR (CDCl3,
293 K): d 81.8 (t, br). IR (Nujol, cmꢀ1), (3b): 3468 s,
3050 m, 2584 m, 1611 m, 1263 w, 1226 s, 1170 s, 968 m,
506 s, 421 w, 367 m, 305 m.
Complex (3a) was prepared by following the same pro-
cedure as above for (3b) using AgNO3 in place of AgOTf.
Yield (3a): 0.41 g, 55%. Anal. Calc. for (3a): C54H54Ag2-
N4O6P4: C, 54.2; H, 4.5; N, 4.7. Found: C, 54.0; H, 4.6;
1
N, 4.7%. H NMR (CDCl3, 293 K): d 0.61 (s br, 12H,
CHMe2), 3.90 (s br, 2H, CHMe2), 7.1–7.6 (m, 40H,
C6H5). 31P{1H}NMR (CDCl3, 293 K): d 82.0 (s, br). IR
(Nujol, cmꢀ1), (3a): 3478 w, 3059 m, 2979 m, 1609 w,
1474 m, 1315 s, 1261 s, 964 m, 695 s, 570 s, 515 m, 411 s,
332 m, 307 w.
2.5. Synthesis of [Ag{Ph2PN(Pri)PPh(OC6H3Me2-2,6)}2]-
(PF6) (4)
2.3. Synthesis of [Ag3(l-Cl)2{Ph2PN(H)PPh2}3]X,
(X = NO3, PF6) (2a, 2b)
The ligand Ph2PN(Pri)PPh(OC6H3Me2-2,6) (L1)
(0.589 g, 12.5 · 10ꢀ4 mol) was added to a solution of
AgNO3 (0.106 g, 6.25 · 10ꢀ4 mol) in acetonitrile at room
temperature and the reaction mixture stirred for 24 h fol-
lowed by the addition of a twofold excess of NH4PF6.
The reaction mixture was stirred for a further period
of 1 h; the colorless precipitate was filtered off using a
Whatman No. 42 filter paper. The filtrate was concen-
trated to 5 mL, 5–6 drops of CHCl3 were added, and
the solution kept at 0 ꢁC for 2 days to obtain colorless
micro-crystals of the title compound. Yield: 0.52 g,
70%. Anal. Calc. for (4): C58H62AgF6N2O2P5: C, 58.2;
H, 5.2; N, 2.3. Found: C, 58.4; H, 5.3; N, 2.2%. 1H
NMR (CDCl3, 293 K): d 1.41, (s br, 12H, CHMe2),
2.19 (s, 12H, C6H3Me2), 4.2 (m, 2H, CHMe2), 7.5–6.8
(m, 36H, C6H5).
Complexes (2a, 2b) were prepared by the same proce-
dures (method A for (2a), (2b); method B for (2b)) as
described above for complexes (1a, 1b) except that the
ligand Ph2PN(H)PPh2 (L3) was used instead of (L2). Yield
(2a): 0.56 g, 40% (method A). Anal. Calc. for (2a):
Ag3C72H63N4O3P6Cl2: C, 52.5; H, 3.9; N, 3.5. Found: C,
52.4; H, 4.0; N, 3.4%.
1H NMR (CDCl3, 293 K): d 4.52 (s, 3H, NH), 6.9–7.4
(m, 60H, C6H5). 31P {1H} NMR (CDCl3, 293 K): d 53.0
1
(d, J (31P, Ag) = 452 Hz). IR (Nujol, cmꢀ1), (2a): 3289 s,
3160 s, 3058 m, 1574 m, 1312 s, 982 m, 897 m, 501 s, 432
s, 423 w, 385 w, 360 m, 330 m.
Yield (2b): 0.58 g, 40% (method A); 0.48 g, 33% (method
B). Anal. Calc. for (2b) C78H75Ag3Cl2F6N3O2P7: C, 51.6;
H, 4.1; N, 2.3. Found: C, 52.0; H, 4.0; N, 2.2%. 1H
NMR (2b) (CDCl3, 293 K): d 4.44 (s, 3H, NH), 7.0–7.6
(m, 60H, C6H5). 31P {1H} NMR (2b) (CDCl3, 293 K): d
31P {1H} NMR (CDCl3, 293 K): dPA 136.0 ppm (s, br),
dPB 83.0 ppm (s, br). IR (Nujol, cmꢀ1): 3413 w, 3122 s,
2966 s, 1650 s, 1240 s, 798 s, 692 s, 615 m.

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H. Krishna et al. / Polyhedron 25 (2006) 3189–3200
Table 1
Summary of X-ray diffraction data for the ligand (L1) and complexes (1b), (2b), (3b) and (4)
Compound
Ligand (L1)
Complex (1b)
Complex (2b)
Complex (3b)
Complex (4)
Formula
M
C
471.5
29H31N1O1P2
C81H81Ag3Cl2N3P7F6
1821.79
orthorhombic
P21 21 21
10.760(2)
23.088(5)
32.684(6)
90.00
90.00
90.00
8120(3)
4
C78H75Ag3Cl2F6N3O2P7
1811.71
monoclinic
P2(1)/c
12.051(12)
29.39(3)
22.40(2)
90.00
97.01(2)
90.00
7877(14)
4
C56H54Ag2F6N2O6P4S2
1368.75
monoclinic
P2(1)/n
10.739(7)
21.078(4)
12.679(2)
90.00
93.940(3)
90.00
2863.4(9)
2
C58H62Ag1F6N2O2P5
1195.82
orthorhombic
Pbca
Crystal system
Space group
monoclinic
P2(1)
10.682(1)
8.233(9)
14.798(3)
90.00
91.56(5)
90.00
1301(4)
2
˚
a (A)
22.345(3)
22.025(3)
23.716(4)
90.00
90.00
90.00
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
U (A )
11672(3)
8
Z
M (Mo Ka) (mmꢀ1
Total reflections
Unique reflections
Rint
)
0.188
11487
5946
0.978
67055
16612
0.051
1.010
47742
11313
0.321
0.939
19964
4879
0.055
0.543
90729
11926
0.082
0.057
R1 (all data)
R1 (I0 > 2r(I0))
wR2 (I0 > 2r(I0))
2h max (ꢁ)
0.145
0.088
0.156
28.0
0.066
0.052
0.104
26.4
0.151
0.081
0.202
23.3
0.041
0.032
0.093
24.7
0.108
0.072
0.181
26.4
wR2 (all data)
0.185
0.113
0.257
0.081
0.215
2.6. Synthesis of [Ag{Ph2PN(Pri)PPh2}2](PF6) (5)
refined with anisotropic displacement parameters and
hydrogen atoms were placed in their calculated positions.
Attempts to improve the data quality of (2b) were unsuc-
cessful due to the poor stability of the compound when
subjected to X-rays. The details of the structure solution
and refinement are given in Table 1.
The ligand Ph2PN(Pri)PPh2 (L2) (0.534 g, 12.5 · 10ꢀ4
mol) was added to a solution of AgNO3 (0.160 g,
6.25 · 10ꢀ4 mol) in acetonitrile. The reaction mixture was
stirred for 5 h at room temperature followed by the addi-
tion of a twofold excess of NH4PF6. The reaction mixture
was stirred for a further period of 1 h; solvent was evapo-
rated to dryness. The colorless solid residue was redissolved
in CH2Cl2–CHCl3 mixture (1:1 v/v), and the solution
passed through a plug of celite and concentrated to
ꢁ15 mL. This solution was added drop wise to 30 mL of
diethyl ether with rapid stirring. The colorless fluffy solid
that precipitated was filtered, washed with diethyl ether
(2 · 20 mL) and dried in air. Yield: 0.51 g, 73%. Anal. Calc.
for AgC54H54N2P5F6 (5): C, 58.5; H, 4.9; N, 2.5. Found: C,
3. Results and discussion
3.1. Synthesis and NMR spectroscopic studies
When the reaction of Ru(bipy)2Cl2 Æ 2H2O with the
diphosphazane ligand Ph2PN(R)PPh2 (R = Pri, H) is car-
ried out in the presence of a silver salt AgX (X = NO3,
OTf), a trinuclear silver species analogous to (1a) or (2a)
is obtained in modest yield. The ruthenium precursor
merely acts as a source of chloride ions in the formation
of these trinuclear Ag(I) complexes, and no ruthenium
bipyridyl complexes of diphosphazanes are formed.2 Sub-
sequently, the reactions of AgX salts with diphosphazane
ligands (L1–L3) were carried out and the reaction condi-
tions were optimized to obtain best yields of monuclear,
binuclear and trinuclear silver complexes as outlined in
Schemes 2–4 (see Section 2).
1
58.1; H, 4.9; N, 2.6%. H NMR (CDCl3, 293 K): d 0.60 (s
br, 12H, CHMe2), 3.78 (m, 2H, CHMe2), 7.2–7.4 (m, 40H,
C6H5). 31P {1H} NMR (CDCl3, 293 K): d 89.9 (s br). IR
(Nujol, cmꢀ1): 3245 w, 3049 s, 2873 s, 1712 s, 1435 s, 965
s, 696 s, 516 s, 367 s, 319 s.
2.7. X-ray crystallography
Crystal data for the ligand (L1) and the complexes (1b),
(2b), (3b) and (4) were collected on a BRUKER SMART
APEX CCD diffractometer with a D8 goniometer (graph-
The reaction of the unsymmetrical ligand (L1) with
AgNO3 in the presence of NH4PF6 gives the bischelate
complex (4) in good yield (Scheme 2). The structure of
(4) has been established by single crystal X-ray analysis
˚
ite-monochromated Mo Ka radiation, k = 0.71073 A)
using the SMART software [17a]. The data was integrated
with SAINT [17b] and an empirical absorption correction
was applied using SADABS [17c]. The structure was solved
by SIR 92 [18a] or by Patterson method using SHELXS-97
[18b] and refined by full-matrix least-squares methods
against F2 (SHELXL-97) [18c]. All non-hydrogen atoms were
2
A direct reaction of [Ru(bipy)2(MeCN)2](PF6) with the diphosphazane
(L2) in boiling MeCN was very sluggish and gave a PIII product with dP
79.0 (s) over a period of 48 h, along with a PV species (dP ꢂ 30); the two
products could not be separated. Only a PV species was formed if harsh
conditions (DMSO, 120 ꢁC) were employed.

H. Krishna et al. / Polyhedron 25 (2006) 3189–3200
3193
iPr
of AgCl with (L2) in a 1:1.5 molar ratio in piperidine for
12 h, followed by counter ion metathesis using NH4PF6.
The analogous complexes (2a, 2b) of the ligand
Ph2PNHPPh2 (L3) were obtained by following the same
procedure (Scheme 4). Ellerman et al. have reported the
synthesis of complex (2b) by the reaction of AgCl and
(L3) in methanol [10a]. Structural assignment for this
complex was based on analytical and spectroscopic data.
The structures of (1b) and (2b) have been established by
X-ray crystallography. The 31P {1H} NMR spectra of
the trinuclear complexes [Ag3(l-Cl)2{Ph2PN(Pri)PPh2}3]X
(X = NO3, PF6) (1a, 1b) show a broad singlet (d
72.0 ppm, br) at 293 K which is shifted downfield from
the free ligand value (d = 48.8 ppm). The spectra of (2a)
or (2b) show a doublet at 53.0 d (d free ligand = 43.1 ppm).
The silver salt AgX (X = NO3, OTf) reacts with (L2) in
a 1:1 molar ratio to form the binuclear complexes (3a) or
(3b), respectively. The reaction of AgNO3 with two molar
equivalents of (L2) in acetonitrile in the presence of
NH4PF6 gives the bischelate complex [Ag{Ph2PN(Pri)-
PPh2}2](PF6) (5) (Scheme 3). The molecular structure of
(3b) has been established by X-ray crystallography (see
Section 3). The 31P NMR spectrum of [Ag{Ph2PN(Pri)-
PPh2}(NO3)]2 (3a) shows a broad singlet at ꢁ81.0 ppm,
whereas that of [Ag{Ph2PN(Pri)PPh2}(OTf)]2 (3b) displays
a broad unresolved triplet at 81.8 ppm at 293 K with a Dd
value of ꢁ33 ppm compared to the free ligand. This differ-
ence in the spectral pattern can be attributed to the
effect of the counter ion on the Ag–P bond strength, which
in turn would affect the Ag–P coupling constant [19b].
Complex (3b) contains a weakly coordinating anion such
as triflate and probably exists essentially as an ionic species
PF6
iPr
N
Ph
Ph
Ph
(i)
N
AgNO3
+
P
P
P
P
Ph2
P
Ph
Ph
OAr
OAr
Ph
Ag
N
L1
(Ar = OC6H3Me2-2,6)
(i) CH CN, 25 0C, 24 h, NH4PF6
P
ArO
Ph
iPr
3
(4)
Scheme 2. Synthesis of mononuclear bischelate complex (4) using the
unsymmetrical ligand (L1).
(see Section 3). The 31P NMR spectrum of complex (4) at
293 K shows two broad peaks at 136.0 ppm and
83.0 ppm, which are assigned to the –PPh2(OAr) and the
–PPh2 phosphorus nuclei, respectively. These are shifted
downfield compared to the 31P chemical shifts for the free
ligand. (dP = 121.8 and 36.5 ppm, respectively). The 31P
NMR spectrum recorded at 183 K shows two symmetrical
quartets, which constitute the AA0XX0 part of an
AA0XX0M spin system. (A and X = P, M = Ag). Thus,
complex (4) shows fluxional behavior in solution which is
typical of the coordination chemistry of silver [8b,19].
The reaction of ligand (L1) with AgX (X = OTf, Cl) in a
1:1 or 1:2 molar ratio did not give products analogous to
complex (4) when monitored by 31P NMR spectroscopy,
but instead formed a white intractable solid which could
not be characterized any further.
The reaction of the symmetrical diphosphazane (L2)
with AgNO3 in a 1:1.3 ratio using Ru(bipy)2Cl2 Æ 2H2O as
the halide donor source gives the trinuclear complex (1a)
(Scheme 3). Complex (1b) is prepared by the direct reaction
iPr
Ph
Ph
N
P
iPr
P
Ph
X
Ph
X
(i)
Ph
N
Ph
Ag
P
Ag
P
P
Ph
P
Ph
Ph
Ph
N
Ph
Ph
L2
iPr
(v)
(iii)
X = NO3 (3a),
= OTf (3b)
X
(ii)
Cl
P
P
Ag
Ag
(1a), X = NO3
(1b), X = PF6
P
P
Ag
Cl
P
iPr
P
PF6
N
Ph
Ph
P
P
P
Ph
Ph
(iv)
Ph
Ph
Ag
N
(i) AgX, CH3CN, 25 0C, 4h
P
(ii) 0.5AgNO3, 25 0C, 5h,CH3CN, NH4PF6,1h
(iii) Ru(bipy)2Cl2, 80 0C, 8h,CH3CN, NH4PF6,1h
(iv) Ru(bipy)2Cl2, 80 0C, 8h,CH3CN, NH4PF6,1h
(v) AgCl, Piperidine, 25 0C, 12h, CH3CN, NH4PF6,1h
Ph
Ph
iPr
(5)
Scheme 3. Synthesis of Ag(I) diphosphazane complexes of ligand (L2).

3194
H. Krishna et al. / Polyhedron 25 (2006) 3189–3200
NO3
P
Cl
P
P
(i)
Ag
Ag
P
Ag
Cl
P
P
H
N
Ph
Ph
P
P
(2a)
Ph
Ph
L3
PF6
P
(ii)
Cl
P
P
Ag
Ag
P
Ag
Cl
P
P
(i) Ru(bipy)2Cl2, AgNO3, 3h
(ii) AgCl, piperidine,12 h, NH4PF6, 1h
(2b)
Scheme 4. Synthesis of trinuclear Ag(I) complexes (2a) and (2b) of the ligand (L3).
[Ag2(L2)2]2+[(OTf)2]2ꢀ. By contrast, in complex (3a), the
counter ion nitrate is strongly bound to the metal. The
impact of the counter ion on the Ag–P bond has been well
The isolation and X-ray crystallographic characterization
of Ag(I) complexes [Ag(CH2Cl2)(g1-P3N3Cl6)2]X [20a] and
[Ag(CH2Cl2)3]X [20b], in which dichloromethane is chelated
to silver through its chlorine atoms lends credence to the
above assumption. The 31P {1H} NMR spectrum of (5)
shows a broad resonance at 90.0 ppm at 293 K; the down-
field shift compared to the free ligand value (Dd = 41 ppm)
is maximum for this complex.
1
documented in the literature; larger J (31P, Ag) coupling
constants are observed for silver(I) phosphine complexes
containing the triflate ion [8d,19b]. The 31P {1H} NMR
spectrum of (3b) at 183 K appears as four distinct sets
(1:1:1:1) centered at d 98.4, 98.3, 71.7 and 68.1 ppm,
respectively (Fig. 1). This result can be explained by
assuming an exchange between two species (3b) and (3b0)
at low temperature in CD2Cl2, as illustrated in (Scheme 5).
The reaction of AgOTf with (L2) in a 1:1 molar ratio
was monitored by 31P {1H} NMR spectroscopy (Fig. 2).
The free-ligand resonance (d = 48.8 ppm, br) disappeared
(a)
(b)
Fig. 1. The 31P {1H} NMR spectrum of complex (3b) at 293 K (a) and 183 K (b) in CD2Cl2 solvent.

H. Krishna et al. / Polyhedron 25 (2006) 3189–3200
3195
2+
iPr
(Fig. 2). This observation indicates that the intermediate
species (I) is involved in the formation of both the com-
plexes (3b) and (5). It is noteworthy that none of these com-
plexes revert to the intermediate (I) under the given
experimental conditions. It was further noted that, in the
presence of a suitable chloride source in solution, the com-
plexes (3b) and (5) transformed slowly to the trinuclear spe-
cies at room temperature over a period of 20 h. The
reaction occurred faster (within a period of 8 h) when the
solution was heated under reflux. The ratio of free ligand
to the silver salt appears to be the key factor that decides
the nature of the complex formed, as noted previously
[19,21]. The broad unresolved pattern at d 52–55 ppm
(293 K) attributed to intermediate species (I) splits into
two doublets of equal intensity centered at d 57.1 and
37.0 ppm at 183 K, with large Ag–P coupling constants
of 812 Hz and 795 Hz (Fig. 3). The temperature depen-
dence of the 31P NMR spectra of the intermediate species
(I) indicates that a dynamic chemical exchange process
occurs in solution. We tentatively propose that the interme-
diate (I) consists of two species (Ia) and (Ib) in equilibrium
(Scheme 6). Attempts to isolate and characterize the inter-
mediate have been unsuccessful to date.
iPr
(X)2
Ph
Ph
Ph
N
Ph
N
P
P
P
P
Ph
X
Ph
S
Ph
Ph
Ag
P
Ag
X
Ag
P
Ag
S
Ph
Ph
P
Ph
P
Ph
N
N
Ph
Ph
Ph
Ph
iPr
(3b)
S = coordinating solvent
Scheme 5. Proposed structures for (3b) … (3b0) at 183 K.
iPr
(3b')
completely within 15 min and two broad resonances at d
52–55 ppm and 80 ppm appeared. The latter peak was
assigned to complex (3b). The peak at d 52–55 ppm which
is attributed to an intermediate (I) disappeared over a per-
iod of 3 h at the expense of the resonance at 81 ppm (3b).
When two more equivalents of the ligand Ph2PN(Pri)PPh2
(L2) were added to the reaction mixture of (3b) and (I) in
the NMR tube, a single broad resonance at d 90.0 ppm
appeared immediately and the resonance at 80 ppm slowly
disappeared. The resonance at d 90.0 ppm was assigned to
a mononuclear bischelate core as present in (5). Complex
(5) could be isolated by adding NH4PF6 to the reaction
mixture. Similarly, when an excess of (L2) was added to a
mixture of the intermediate (I) (d 52–55 ppm) and complex
(3b), both the resonances disappeared completely and the
resonances at d 90 ppm due to (5) and the resonance at d
48.8 ppm arising from unreacted ligand were observed
3.2. X-ray diffraction analyses
3.2.1. The crystal structure analysis of the ligand (L1)
The solid-state structure of ligand (L1) has been deter-
mined by X-ray diffraction. A perspective view of the
t = 5 min; (1:1)
t = 15 min; (1:1)
t = 1 h, 30 min; (1:3)
t = 2 h; (1:4)
Fig. 2. 31P NMR monitoring of the reaction of AgOTf with Ph2PN(Pri)PPh2 (L2) at 293 K in CD2Cl2 solvent. The ratios shown on each spectrum
represents the relative proportions of AgOTf and ligand (L2).

3196
H. Krishna et al. / Polyhedron 25 (2006) 3189–3200
Fig. 3. The 31P {1H} NMR spectrum of complex (3b) and the intermediate (I) at 183 K in CD2Cl2 solvent.
molecule is shown in Fig. 4. Selected bond distances and
bond angles are listed in Table 2. The geometry around
the nitrogen atom is trigonal planar with a P–N–P angle
of 122ꢁ. The ligand adopts a conformation wherein the lone
pair on the PPh2 phosphorus is oriented trans to the isopro-
pyl group on the nitrogen atom whereas the lone pair on the
PPh(OAr) fragment is cis to it. This is in contrast to
the previous observation that the lone pair on the PPh2
phosphorus in Ph2PN(Pri)P(O2C6H4) [22a] and Ph2PN-
(CHMePh)PPh(N2C3HMe2-3,5) [22b] lies cis to the isopro-
pyl group on nitrogen. The two phenyl rings subtend an
angle of 101.5ꢁ at the PPh2 phosphorus atom, but substitu-
ents on the PYY0 phosphorus subtend an angle of 94.7ꢁ.
This could probably be due to the oxygen spacer, which
relieves the steric strain arising from the 2,6- disubstituted
aryl rings to some extent. Both the P–N bond lengths are
1
˚
nearly equal (1.71 A) in the ligand (L ) and are close to
the bond lengths observed for the diphosphazane ligands
i
˚
Ph2PN(Pr )PPh2 (1.71 A) [23a] and Ph2PN((S)-CHMePh)-
˚
PPh2 (1.72 A) [23b]. Two different P–N bond lengths are
observed for the unsymmetrically substituted diphospha-
Fig. 4. ORTEP plot and atom labeling scheme for ligand [Ph2PN(Pri)-
PPh(OC6H3Me2-2,6)] (L1).
+
Ph
Ph
Ph
Ph
N
P
P
zanes, Ph2PN(Pri)P(O2C6H4) [22a] and Ph2PN((S)-CH-
X¯
Ag
X
+
Pri
N
Ag
S
Pri
MePh)PPh(N2C3HMe2-3,5) [22b]; the P–N bond connected
P
P
˚
˚
to the P(O2C6H4) or PPh(N2C3HMe2-3,5) (1.65 A, 1.69 A,
respectively) is shorter than the other P–N bond connected
Ph
Ph
Ph
Ph
˚
˚
to the PPh2 center (1.74 A, 1.73 A, respectively). These dif-
ferences are best explained in terms of the negative hyper-
conjugative interaction between the nitrogen lone pair and
the adjacent P-X r* orbitals [24]. The near equality of the
X = CF3SO3 , S = coordinating solvent
(Ib)
(Ia)
Scheme 6. Tentative structures for (Ia) … (Ib) at 183 K.

H. Krishna et al. / Polyhedron 25 (2006) 3189–3200
3197
Table 2
1
˚
Selected bond distances (A) and angles (ꢁ) for (1b), (2b), (3b), (4) and (L )
[Ag3(dppi-Pr)3(Cl)2]PF6 (1b)
Ag–Cl–Ag (ave)
P(3)–N(2)–P(4)
P(5)–N(3)–P(6)
P(1)–N(1)–P(2)
Cl–Ag–Cl (ave)
69.46(7)
117.8(3)
117.2(2)
114.9(2)
98.89(8)
Ag–P (ave)
2.460(3)
2.716 (5)
3.096(6)
2.968(9)
3.102(1)
Cl–Ag (ave)
Ag(1)ꢃ ꢃ ꢃAg(2)
Ag(1)ꢃ ꢃ ꢃAg(3)
Ag(2)ꢃ ꢃ ꢃAg(3)
[Ag3(dppa)3(Cl)2]PF6 (2b)
Ag–Cl–Ag (ave)
P(1)–N(1)–P(2)
P(3)–N (2)–P(4)
P(5)–N(3)–P(6)
Cl–Ag–Cl (ave)
72.803(8)
Ag–P (ave)
2.450(2)
2.719(8)
3.153(3)
3.244(3)
3.288(2)
126.0(6)
124.4(6)
126.9(6)
93.80(3)
Cl–Ag (ave)
Ag(1)ꢃ ꢃ ꢃAg(2)
Ag(1)ꢃ ꢃ ꢃAg(3)
Ag(2)ꢃ ꢃ ꢃAg(3)
[Ag2(dppi-Pr)2(OTf)2] (3b)
O(1)–Ag(1)–Ag(1)0
O(1)–Ag(1)–P(2)
P(2)–Ag(1)–Ag(1)0
P(2)–Ag(1)–P(1)
O(1)–Ag(1)–P(1)
P(2)–Ag(1)–Ag(1)0
114.56(9)
Ag(1)–O(1)
Ag(1)–P(1)
Ag(1)–P(2)
Ag(1)–Ag(1)0
2.398(3)
2.442(9)
2.417(9)
2.868(6)
113.84(9)
78.97(2)
143.37(3)
102.18(9)
91.48(2)
Ag(Ph2PN(Pri)PPhOC6H3Me2-2,6)2PF6 (4)
Ag–P (ave)
2.52(4)
66.93(5)
66.97(5)
131.76(5)
P–N–P (ave)
109.9(2)
P(1)–Ag(1)–P(2)
P(3)–Ag(1)–P(4)
P(1)–Ag(1)–P(4)
P(2)–Ag(1)–P(4)
P(2)–Ag(1)–P(3)
P(1)–Ag(1)–P(3)
118.27(5)
141.54(5)
141.26(5)
Fig. 5. ORTEP plot and atom labeling scheme for [Ag3(l-Cl)2{Ph2PN-
(Pri)PPh2}3](PF6) (1b). (The hydrogen atoms and PF6 ion have been
omitted for clarity.)
Ph2PN(Pri)PPh(OC6H3Me2-2,6) (L1)
P(2)–O (1)–C(22)
P(2)–N (1)–C(13)
P(1)–N (1)–P(2)
P(1)–N (1)–C(13)
C(1)–P (1)–C(7)
121.2(4)
114.9(4)
122.0(3)
121.8(3)
101.5(2)
P(2)–O(1)
N(1)–C(13)
P(1)ꢃ ꢃ ꢃP(2)
O(1)–C(22)
P–N (ave)
1.662(4)
1.492(7)
2.986
1.405(7)
1.713(5)
3.2.3. The crystal structure analysis of
{Ag(Ph2PN(Pri)PPh2)OTf}2 (3b)
The molecular structure of [Ag(L2)(OTf)]2 which has a
crystallographic inversion symmetry is depicted in Fig. 7.
The selected bond distances and angles are given in Table
2. The solid-state structure consists of a neutral dimeric
molecular unit, in which the two silver atoms are bridged
by a pair of diphosphazane ligands. In addition, each silver
atom is bonded to a single triflate anion in a monodentate
two P–N bonds in ligand (L1) arises because the electron
withdrawing effect of the oxygen spacer is compensated
by the electron donating methyl substituents on the phenyl
rings.
˚
˚
fashion. The Ag–P distances of 2.442 A and 2.417 A are in
good agreement with those found for analogous dppm
complexes reported earlier [25a]. The observed Ag–O dis-
3.2.2. The crystal structure analyses of [Ag3(l-Cl)2-
{Ph2PN(R)PPh2}3]PF6 (R = Pri, (1b) and R = H (2b))
X-ray crystallographic studies reveal that the central
core in both complexes (1b) and (2b) comprises a pair of
halogen atoms, each of which is bonded to three Ag atoms
which form an approximately equilateral triangular plane.
The three metal atoms are bridged around the periphery of
the triangle by three diphosphazane ligands in such a way
that the coordination environments of the chlorine atoms
are pyramidal three-coordinate ClAg3, and the metal atoms
are four coordinate P2Ag (l-Cl)2. The molecular structures
of (1b) and (2b) are shown in Figs. 5 and 6, respectively.
Selected bond lengths and bond angles for (1b) and (2b)
˚
tance of 2.398 A is comparable to the bonding distance
˚
of 2.439 A for the asymmetrically bound nitrate in
˚
(PPh3)AgNO3 [25b] and the reported value of 2.417 A in
case of the dppm analogue [25a]. The Ag–Ag distance
˚
(2.869 A) is shorter than those observed in complexes
(1b) and (2b), and also the corresponding dppa complex
˚
(2.961 A) [14]. The P–Ag–P units are non-linear and
eclipsed, resulting in a folding of the Ag2P4 core along
the Ag–Ag axis to give rise to a staggered arrangement.
The P (2)–Ag–P (10) angle of 143.4ꢁ is significantly greater
than the corresponding P (1)–Ag–P (20) angle of 138.3 (1)ꢁ
found in the related binuclear dppm complex with the for-
mula [Ag(dppm)(NO3)]2 [25a] but less than that (148.4ꢁ)
found for the dppa analogue [14].
˚
are given in Table 2. The Ag–P distances of ꢁ2.45 A and
˚
Ag–Cl distances of ꢁ2.72 A in complexes (1b) and (2b)
are comparable to those observed for [Ag3(l-Cl)2(dppm)3]-
X complexes reported recently in the literature [8b]. The
˚
˚
Agꢃ ꢃ ꢃAg distances [2.97–3.10 A in (1b) and 3.15–3.29 A
3.2.4. The crystal structure analyses of complex (4)
in (2b)] are shorter than that in the trinuclear Ag complex
The molecular structure of complex (4) as revealed by a
single crystal X-ray study is shown in Fig. 8 and features a
four coordinated tetrahedral silver ion. Selected bond
lengths and bond angles are displayed in Table 2. The
+
˚
[Ag3(dppm)3Cl2] (ꢂ3.42 A) [8b] and comparable to the
bond distance in [Ag3(dppm)3(l3-g1-C„C–C6H4-NO2-
p)2]+ (ꢂ3.01 A) [13b].
˚

3198
H. Krishna et al. / Polyhedron 25 (2006) 3189–3200
Fig. 6. ORTEP plot and atom labeling scheme for [Ag3(l-Cl)2{Ph2PN-
(H)PPh2}3](PF6) (2b). (The hydrogen atoms and PF6 ion have been
omitted for clarity.)
Fig. 8. ORTEP plot and atom labeling scheme for [Ag{Ph2PN(Pri)P-
Ph(OC6H3Me2-2,6)}2](PF6) (4). (The hydrogen atoms and PF6 ion have
been omitted for clarity.)
decreasing trend: (3b) > (1b) > (4). This observation is in
accord with earlier findings that a change in the number
of phosphine ligands around silver leads to difference in
‘s’ contribution to the hybridization at the silver center,
which in turn results in different P–Ag–P angles in the sil-
ver(I)-phosphine complexes [19].
4. Conclusions
Novel silver(I) complexes have been synthesized by the
reaction of AgX (X = NO3, OTf) with diphosphazane
ligands Ph2PN(Pri)PPh(R) [R = Ph or OC6H3Me2-2,6] by
varying the stoichiometry and the reaction conditions.
Symmetrically substituted diphosphazanes (L2 and L3)
bearing a relatively weak p-acceptor phosphorus form sta-
ble Ag(I) complexes with different coordination numbers
and geometries depending on the ratio of the reactants.
On the other hand, the diphosphonite ligand, (RO)2PN
(Me)P(OR)2 (R = C6H5) bearing a strong p-acceptor phos-
phorus does not form stable silver(I) complexes.3 The
unsymmetrical ligand (L1) which has similar p-acceptor
ability as ligands (L2 and L3) forms only the mononuclear
bischelate complex irrespective of the reaction stoichiome-
try, presumably due to steric reasons. It may also be noted
that the sterically bulky [(RO)2PN(Me)P(OR)2, (R = OC6-
Fig. 7. ORTEP plot and atom labeling scheme for [Ag{Ph2PN(Pri)P-
Ph2}(OTf)]2 (3b). (The hydrogen atoms have been omitted for clarity.)
two ‘‘P–N–P’’ ligands are chelated to the metal center with
a P–N–P angle of ꢁ110ꢁ which is considerably less than
that observed in case of the free ligand (122ꢁ). The bite
angles of the two ligands are similar (ꢁ66.95ꢁ), while the
interligand P–Ag–P angles vary approximately from
141.5ꢁ to 118.3ꢁ suggesting a highly distorted tetrahedral
core. The Ag–P distances are in the range observed for
the similar structures reported in the literature [21]. A com-
parison of the structural data for the complexes (1b), (3b)
and (4) shows that the P–Ag–P angle subtended by the
diphosphazane ligands on the metal center follows the
3
The diphosphonite ligands (RO)2PN(Me)P(OR)2 react with one
equivalent of AgNO3 in CH3CN to give unstable Ag(I) complexes as
shown by the 31P NMR spectra of the reaction mixtures [dP 122.0 (d, br)
and 126.0 (s, br) for R = C6H5; dP 126.0 (d, br) for R = C6H3 Me2-2,6];
the complexes could not be isolated.

H. Krishna et al. / Polyhedron 25 (2006) 3189–3200
3199
H3Me2-2,6] does not form stable silver(I) complexes.3
NMR monitoring of the formation of silver(I) complexes
of the diphosphazane ligand (L2) shows the involvement
of an intermediate species in the transformation of bridged
binuclear species to mononuclear bischelate species. In the
presence of a chloride source, the mono and the binuclear
species are converted into dichloro-bridged trinuclear com-
plex. Further investigations are required to gain insights
into the nature of the intermediate species and the mecha-
nism of interconversions of Ag(I) complexes of varying
nuclearity.
´
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Acknowledgements
We thank the Department of Science and Technology,
New Delhi, India for financial support and also for data
collection using the CCD X-ray facility at IISc, Bangalore
set up under IRHPA program.
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Tables of bond distances and angles, atomic aniso-
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with the Cambridge Crystallographic Data Centre, CCDC
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