Synthesis and structure of dinuclear silver complexes of N,N-bis(2-(diphenylphosphanyl)ethyl)phenylamine

Article abstract of DOI:10.1016/j.poly.2017.01.048

N,N-Bis(2-(diphenylphosphanyl)ethyl)phenylamine, (PN^PhP), and AgX compounds (X?=?OTf, Cl, Br, I) form dimeric complexes of general formula [Ag₂X₂(PN^PhP)₂], 1–4, in which, as revealed by crystallographic investigations, the two phosphorus donors are bound to different metal centers but the central N-donor remains unbound. NMR studies performed on solutions of any 1:1 mixtures of 2–4 demonstrated that these complexes retain their dimeric structure in solution. To the contrary, a monomer/dimer equilibrium strongly shifted toward dimerization was observed in the solutions of 1. The distribution of the dimeric species in the halide¹/halide²mixtures compared to that in the OTf/halide systems is remarkably different and reflects the preference of the Ag/halide interaction over the Ag/OTf coordination. Based on the interplay of the AgP₂planes, the known [Ag₂(μ-X)₂(μ-Ph₂PYPPh₂)₂] complexes can be arranged into four well-discernible groups (Y stands for a 4–6-membered linkage).

Full text of DOI:10.1016/j.poly.2017.01.048

Accepted Manuscript
Synthesis and structure of dinuclear silver complexes of N,N-bis(2-(diphenyl-
phosphanyl)ethyl)phenylamine (REVISED)
Gábor Besenyei, Gábor Szalontai, László Párkányi
PII:
S0277-5387(17)30085-2
DOI:
http://dx.doi.org/10.1016/j.poly.2017.01.048
POLY 12452
Reference:
Polyhedron
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Revised Date:
Accepted Date:
9 December 2016
27 January 2017
28 January 2017
Please cite this article as: G. Besenyei, G. Szalontai, L. Párkányi, Synthesis and structure of dinuclear silver
complexes of N,N-bis(2-(diphenylphosphanyl)ethyl)phenylamine (REVISED), Polyhedron (2017), doi: http://
dx.doi.org/10.1016/j.poly.2017.01.048
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Synthesis and structure of dinuclear silver complexes of N,N-bis(2-
(diphenylphosphanyl)ethyl)phenylamine (REVISED)
Gábor Besenyeia, Gábor Szalontaib, László Párkányia,*
a Research Centre for Natural Sciences, Hungarian Academy of Sciences, P.O.Box 286,
Budapest 1519, Hungary,
bUniversity of Pannonia, NMR Laboratory, 8200 Veszprém, Egyetem u. 10, Hungary
Abstract
N,N-bis(2-(diphenylphosphanyl)ethyl)phenylamine, (PNPhP), and AgX compounds (X = OTf,
Cl, Br, I) form dimeric complexes of general formula [Ag2X2(PNPhP)2], 1-4, in which, as
revealed by crystallographic investigations, the two phosphorus donors are bound to different
metal centers but the central N-donor remains unbound. NMR studies performed on solutions
of any 1:1 mixtures of 2-4 demonstrated that these complexes retain their dimeric structure in
solution. To the contrary, a monomer/dimer equilibrium strongly shifted toward dimerization
was observed in the solutions of 1. The distribution of the dimeric species in the
halide1/halide2 mixtures compared to that in the OTf/halide systems is remarkably different
and reflects the preference of the Ag/halide interaction over the Ag/OTf coordination. Based
on the interplay of the AgP2 planes, the known [Ag2(µ-X)2(µ-Ph2PYPPh2)2] complexes can be
arranged into four well-discernible groups (Y stands for a 4-6-membered linkage).
Keywords
PNP ligand, silver complexes, dimers, X-ray structure, Ag-P coupling
1

1. Introduction
Nitrogen-containing polyphospines cover a wide range of chemical compounds whose
complexes, due to their exceptional balance of stability versus reactivity, have found
application in many fields of coordination chemistry [1]. Within this class of compounds,
tridentate ligands in which two phosphorus donor groups are connected to the central nitrogen
atom by 1,2-ethylene bridges (I in Scheme 1) have been intensively studied over the past two
decades. The combination of soft and hard donor atoms furnishes a hemilabile nature to these
ligands, of which numerous representatives have been successfully applied to stabilize
complexes possessing outstanding catalytic activity [2].
Scheme 1. General formula of compounds I
Complexes of aminodiphosphanes I excel not only by their remarkable catalytic properties
but by their structural variety as well. In cationic square planar complexes, compounds I
typically act as tridentate ligands [3-5] (structure A in Scheme 2) but strong metal-halogen
bonds like the Pt-Cl interaction [4, 6] or reduced electron density at the nitrogen atom induced
by an acyl moiety [3, 7] result in P,P-coordination mode (structures B and C). Interestingly,
the R1 = R2 = phenyl derivative that gives a monomeric complex cation with PdCl2, with
PdBr2 yields the dimeric adduct of type C [8]. Moreover, the 1,4-C6H4{N(CH2CH2PPh2)2}2
ligand possessing two sets of donor atoms shows a two-faced behaviour with PdCl2, as it
binds the metal as a tripodal ligand at one end but establishes only P,P coordination at the
other [9]. From a detailed multinuclear NMR study, the formation of a dimeric species from
[Pd(OTf)(PNP)](OTf) was inferred in which the PNP ligand acts both as a chelating and as a
bridging agent (Scheme 2, structure D) [10].
2

B
A
R1 = H, R2 = phenyl, M = Pd, X = Cl, Br, NO3
R1 = phenyl, t-butyl, R2 = phenyl, M = Pd, X = Cl
R1 = 1-phenylethyl, R2 = phenyl, M = Pt, X = Cl, I, CN
R1 = 1-phenylethyl, R2 = phenyl
R1 = benzyl, R2 = phenyl
D
C
R1 = 4-methoxybenzoyl, R2 = phenyl, X = Cl
R1 = phosphoryl, R2 = phenyl, X = Cl
R1 = R2 = phenyl, X = Br
R1 = 1-phenylethyl, R2 = phenyl,
Scheme 2. Representative structures of square planar complexes with ligands I
In octahedral aminocarbene ruthenium complexes, the PNP ligand was found to occupy three
facial coordination sites [11] but meridional arrangement of the aminodiphosphane was
observed in the phosphane derivative, [RuCl2(PNP)PPh3] [12]. The five-coordinate
[FeCl2(PNP)] complex (PNP denotes HN(CH2CH2PiPr2)2) could be isolated in two different
geometries. In the square pyramidal species, the PNP ligand coordinates in the expected
meridional fashion whereas the phosphorus and nitrogen donor atoms occupy facial
coordination sites in the trigonal bipyramidal isomer [13]. A rare example for the structural
flexibility of the PNP ligands has been demonstrated recently with the [CoI2(PNP)] complex
(R1 = benzyl, R2 = phenyl group) that shows up as a P,P-coordinated tetrahedral adduct and a
P,N,P-coordinated square pyramidal variant within a single crystal structure [14].
The structural variety observed with most of the late transition metals can certainly be
attributed to the highly flexible ethylenic chains, to the donor set that combines two soft (P)
and one hard (N) donor atoms making the PNP ligands inherently hemilabile, and to the
3

substituents of the phosphorus and nitrogen atoms that can finely tune both the steric and the
electronic properties of these ligands.
Most of the studies performed with ligands I so far have focused on metals of catalytic
importance leaving the chemistry of Group 11 metals largely unexplored [15]. To our
knowledge, the only crystallographically characterized silver complex incorporating an N-aryl
PNP ligand was published by Puddephatt and coworkers [9] who reported a weak Ag···N
interaction in the silver complex of the bis(PNP)-donor pincer ligand 1,4-
C6H4{N(CH2CH2PPh2)2}2. In this paper, we report on the synthesis and solution and solid
state structural features of four novel dimeric silver complexes incorporating
PhN(CH2CH2PPh2)2} as bridging ligand. In order to gain information on the nuclearity of the
complexes in solution, special attention was paid to the 31P NMR spectra of mixtures
containing different anions.
2. Experimental
General comments: All chemicals were purchased from Aldrich and used without further
purification. THF was dried over sodium/benzophenone and distilled before use. Preparation
of ligand I was carried out under a nitrogen atmosphere by using standard Schlenk techniques.
NMR spectra were recorded on a Bruker-Avance II 400 (9.38 T) and Varian 500 (11.75 T)
using tetramethylsilane (1H) as internal standard and 85% H3PO4 (31P) as external standard, in
CDCl3 or CD2Cl2 solutions. Pulse sequences used for the EXSY [16] and DOSY [17]
experiments were the standard Bruker sequences without modifications. Abbreviations used
in the description of the NMR spectra: s, singlet; d, doublet; m, multiplet; br, broad.
2.1. X-ray structure determination
Intensity data collections were performed on a Rigaku Rapid diffractometer using MoKα
radiation (λ = 0.71075 Å). Absorption corrections were applied to each data set (numerical for
1, 3, 4, 1/3, multi-scan for 2). The structures were solved by direct methods using SHELXS
[18] (SHELXT [19] for 1/3) and were refined by anisotropic full matrix least-squares using
the SHELXL [18] program. The maximum and average shift/error after the final cycle was
0.0 in all cases. Crystal data and structure determination details are given in Table 1.
4

Table 1.
Crystal data and details of the structure determination.
Compound
1
C70H66Ag2F6N2O6P4S2
1549.01
2
C68H66Ag2Cl2N2P4, 2·CHCl3
1560.48
3
C68H66Ag2Br2N2P4, 2·CHCl3
824.70
Formula
Formula weight
Crystal system
Space group
Triclinic
Monoclinic
Monoclinic
P-1 (no. 2)
P2 /n (no. 14)
C2/c (no. 15)
1
a, b, c [Å]
10.5844(3), 13.0926(5), 13.4142(4)
14.3385(3), 14.2883(3), 17.5684(4) 19.8975(4), 15.4236(2), 25.2582(5)
α, β, γ [º]
67.9124(9), 82.8519(9), 70.8218(9)
90, 103.9587(7), 90
90, 113.7450(9), 90
V [Å3]
1626.88(9)
3493.00(13)
7095.3(2)
Z
1
4
8
D(calc) [g/cm3]
µ(MoKα) [mm−1]
F(000)
1.581
1.484
1.544
0.837
1.000
2.036
788
1584
3312
Crystal size [mm]
Temperature [K]
0.40x0.54x0.66
93
0.23x0.48x0.66
93
0.38x0.40x0.45
295
5

θ min, max [º], comleteness
Dataset
3.1, 29.6, 0.979
-14:13; -18:18 ; -18:18
33563, 8929, 0.028
8541
3.1, 25.3, 0.996
-17:17; -17:17 ; -21:21
97976, 6369, 0.037
5895
2.8, 26.4, 0.991
-24:24; -19:19; -31:31
78027, 7217, 0.043
6700
Total, unique data, R(int)
Observed data [I > 2.0 σ(I)]
Nref, Npar
8929, 415
6369, 388
7217, 388
0.0234, 0.0588
0.0251, 0.0594, 1.12
-0.33, 0.57
0.0593, 0.1663
0.0626, 0.1689, 1.06
-1.56, 2.71
0.0443, 0.1090
0.0491, 0.1118, 1.07
-0.70, 0.53
R, wR2 [I >2
R, wR2, S
σ
(I)]
Min. and max.
resd. dens. [e/Å3]
6

(Table 1, continued)
Compound
4
1/3
C142H142Ag4Br2F6N4O7P8S2
Formula
C68H66Ag2I2N2P4, 2·CHCl3
3033.78
Formula weight
Crystal system
Space group
a, b, c [Å]
871.69
Monoclinic
Monoclinic
C2/c (no. 15)
P21/n (no. 14)
12.646(5), 38.650(2), 14.192(5)
20.2010(4), 15.1698(2), 24.6049(4)
90.00, 93.45(1), 90.00
α, β, γ [º]
90, 111.6267(7), 90
V [Å3]
7009.3(2)
6924(4)
Z
8
2
D(calc) [g/cm3]
µ(MoKα) [mm−1]
F(000)
1.652
1.455
1.321
1.802
3084
3456
0.38 x 0.25 x 0.13
103
Crystal size [mm]
Temperature [K]
θ min, max [º], completeness
0.46 x 0.55 x 0.60
93
2.2, 33.1, 0.996
3.00 25.4, 0.830
,
7

Dataset
-31:29 ; -23:23 ; -37:37
67907, 13315, 0.064
12138
-15:15;-46 46;-16:16
:
67598, 10520, 0.1502
6099
Total, unique data, R(int)
Observed data [I > 2.0 σ(I)]
Nref, Npar
10520, 813
13315, 388
0.0724, 0.1404
0.1400, 0.1695, 1.026
0.55, -0.68
0.0406, 0.1148
0.0472, 0.1203, 1.02
-1.722, 2.413
R indices [I >2 (I)]
σ
R, wR2, S (all data)
Min. and max. resd. dens. [e/Å3]
8

Several attempts were made to obtain suitable crystals for the mixed ligand 1/2, 1/3, 1/4
complexes. The structure of 1/4 could be solved but was not refinable. The structure
determination and refinement of compond 1/3 was carried out with limited success. The
crystal lattice seemed to deteriorate during experiment resulting in high R for the agreement
between equivalent reflections, low observed/unobserved reflection ratio, low completeness
value. Though the experiment was carried out at low temperature, the ADP values look more
characteristic for a room temperature measurement, indicating disorder for some phenyl ring
atoms and for F2, F3, O2. However, this structure clearly proves that the mixed ligand
complex is formed.
Similar unit cell data and identical space group for compounds 3 and 4 indicates possible
isostructurality, but no such relationship exists. 3 and 4 form different hydrogen bonding
schemes (Table 6). The centroid of the molecule of 4 is shifted by a non-crystallographic
operation ¼, ¼, -½ with respect to that of 3.
2.2 Syntheses
Preparation of N,N-bis(2-(diphenylphosphanyl)ethyl)phenylamine, PNPhP
Of the various routes suggested for the preparation of N-phenyl PNP type ligands, that
suggested in [3] was followed with some modifications. Into an oven-dried (120 °C) Schlenk-
tube, 40 mL of dry THF, 370 mg (9.46 mmol) K and 0.85mL (1.04 g, 4.73 mmol) of Ph2PCl
were charged under N2. The reaction mixture was gently refluxed and stirred under N2 for 90
min. The reaction vessel was immersed into melting ice and 1.15 g (2.35 mmol) of
PhN(CH2CH2OTs)2 was added under N2 in small portions. The cooling bath was removed and
the viscous reaction mixture was stirred at RT for 2 hours. After addition of 5 mL of
deaerated MeOH and 40 mL of dry THF, the slurry was filtered under N2 and the filtrate was
concentrated to an oil under vacuum. The crude product was redissolved in a deaerated
mixture of 5 mL CH2Cl2 and 15 mL EtOH. Slow evaporation of the more volatile solvent
under vacuum resulted in the formation of a white precipitate that was filtered out, washed
with chilled etanol and dried. Yield: 1.01 g (83%). 1H NMR (500 MHz, CDCl3) δ (ppm):
2.24-2.30 (4H, m, CH2P), 3.30-3.38 (4H, m, CH2N), 6.33-6.38 (2H, m), 6.60-6.65 (1H, m),
7.06-7.12 (2H, m) (resonances of the orto, para and meta protons of the N-phenyl group),
7.29-7.35 (12H, m, PPh), 7.37-7.43 (8H, m, PPh); 31P NMR (CDCl3), δ (ppm): −21.1 (s).
Preparation of [Ag2(OTf)2(PNPhP)2], 1
9

233 mg (0.450 mmol) of PNPhP ligand was added to 118 mg (0.459 mmol) of [Ag(OTf)]
suspended in a mixture of 10 mL of CH2Cl2 and 6 mL of diethyl ether. The colourless
homogeneous solution was protected from light and was stirred for 30 min under N2.
Evaporation to ca. 3 mL and addition of diethyl ether resulted in a white precipitate that was
filtered, washed with Et2O and dried under vacuum. Yield: 293 mg (84%)
1H NMR (500 MHz, CDCl3) δ (ppm) (major component): 2.75-2.85 (4H, br, CH2P), 3.66-
3.76(4H, br, CH2N), 6.11-6.18 (2H, m), 6.49-6.55 (1H, m), 6.97-7.04 (2H, m) (resonances of
the orto, para and meta protons of the N-phenyl group), 7.27-7.34 (8H, m, PPh), 7.35-7.41
(4H, m, PPh) 7.49-7.56 (8H, m, PPh); 31P NMR (CDCl3, 161.8 MHz), δ (ppm): 0.46 (two
doublets, 1J(107Ag-31P) = 491 Hz, 1J(109Ag-31P) = 568 Hz. The resonances of the minor isomer
(ca. 9 %) can be observed in the 1H NMR spectrum at 2.34-2.44, 3.13-3.23 and 7.58-7.71 ppm
and in the 31P NMR spectrum at −2.1 and −6.4 ppm as broad signals.
Preparation of [Ag2Cl2(PNPhP)2], 2
85.0 mg (0.109 mmol) of [Ag2(OTf)2(PNPhP)2] was suspended in 10 mL of CH2Cl2 and 41.7
mg (0.107 mmol) of benzyltriphenylphosphonium chloride in 3 mL of CH2Cl2 was added
dropwise at ambient temperature. A homogeneous solution is formed that was stirred for 15
min. Evaporation to ca. 3 mL and addition of 10 mL of methanol yielded a white precipitate
that was filtered out, washed with methanol and dried (63 mg, 89 %). 1H NMR (400 MHz,
CDCl3) δ (ppm): 2.53-2.81 (4H, br), 3.69-3.96 (4H, br), 6.09-6.29 (2H, m), 6.44-6.59 (1H,
m), 6.96-7.09 (2H, m) (resonances of the orto, para and meta protons of the N-phenyl group),
7.09-7.79 (20H, multiplets of the PPh hydrogen atoms). 31P NMR (300 K, CDCl3), δ (ppm):
−4.42 (two doublets, 1J(107Ag-31P) = 386 Hz, 1J(109Ag-31P) = 444 Hz.
Preparation of [Ag2Br2(PNPhP)2], 3 and [Ag2I2(PNPhP)2], 4
By using MePh3PBr and MePh3PI in the metathetical reaction, the bromide and iodide
analogs of compound 2, [Ag2Br2(PNPhP)2], 3 and [Ag2I2(PNPhP)2], 4 could be prepared
identically on 0.1 mmol scale delivering 3 in 94% and 4 in 92 % yield. We note that it is
advisable to use methanol as precipitating agent in the anion exchange reactions because
diethyl ether renders the product contaminated with the phosphonium salt.
[Ag2Br2(PNPhP)2], 3. 1H NMR (400 MHz, CDCl3) δ (ppm): 2.68-2.84 (4H, br), 3.73-3.89 (4H,
br), 6.17-6.31 (2H, m), 6.46-6.57 (1H, m), 6.99-7.09 (2H, m) (resonances of the orto, para
and meta protons of the N-phenyl group), 7.15-7.50 (20H, multiplets of the PPh hydrogen
atoms). 31P NMR (300 K, CDCl3), δ (ppm): −8.55 (two doublets 1J(107Ag-31P) = 377 Hz,
1J(109Ag-31P) = 435 Hz.
10

[Ag2I2(PNPhP)2], 4. 1H NMR (400 MHz, CD2Cl2) δ (ppm): 2.76-2.91 (4H, br), 3.74-3.89 (4H,
br), 6.30-6.34 (2H, m), 6.48-6.56 (1H, m), 7.01-7.11 (2H, m) (resonances of the orto, para
and meta protons of the N-phenyl group), 7.17-7.28 (8H), 7.29-7.46 (12H) (multiplets of the
PPh hydrogen atoms). 31P NMR (CD2Cl2), δ (ppm): −14.2 (two doublets, 1J(107Ag-31P) = 346
Hz, 1J(109Ag-31P) = 400 Hz.
Mixed-ligand complexes were prepared for NMR investigations by charging 0.004 mmol (ca.
2.8-3.1 mg) of the appropriate complexes into the NMR-tube. These compounds were not
isolated after the NMR measurements unless our attempt to grow crystals from these solutions
suitable for X-ray studies was successful.
3. Results and Discussions
3.1 Syntheses and solution NMR studies
For the synthesis of N,N-bis(2-(diphenylphosphanyl)ethyl)phenylamine, PNPhP, the route
suggested in [3] was followed with some modifications. The 1H and 31P NMR spectra are
presented in Figures S1 and S2 (see Supplementary Material).
The direct reaction of silver trifluoromethanesulfonate with PNPhP ligand in a mixture of
CH2Cl2 and diethyl ether resulted in the dinuclear complex [Ag2(OTf)2(PNPhP)2], as found by
crystallographic studies. The halogen containing species, [Ag2X2(PNPhP)2] (X = Cl, Br or I),
could be easily prepared via metathetical reactions using benzyl- or
methyltriphenylphosphonium halides as sources of halide ions (Scheme 3).
R4PX stands for BzPh3PCl, MePh3PBr or MePh3PI
Scheme 3. Synthesis of complexes 1-4
The isolated white, crystalline solids are soluble in CH2Cl2 and CHCl3 and can be stored in a
refrigerator for years without noticeable decomposition.
The 1H NMR spectrum of 1 in CD2Cl2 (Fig. S3) shows the expected, well separated
resonances of the aliphatic hydrogen atoms at 3.71 (CH2N) and 2.79 ppm (CH2P). The
multiplets at 6.20, 6.56 and 7.02 ppm can be ascribed to the ortho, para and meta hydrogen
atoms of the isolated N-phenyl group, while the intense resonances between 7.33 and 7.60
11

ppm are attributed to P-phenyl moieties. Interestingly, a second set of resonances attributed to
both aliphatic (2.44 and 3.19 ppm) and aromatic (7.07-7.32 and 7.60-7.71 ppm) hydrogen
atoms can also be recognized, indicating the presence of a minor constituent in solution phase.
As the proportion of the minor component was dependent on the solvent and the
concentration, it could be concluded that it is not a contamination but several molecular
entities are formed upon dissolution of the solid 1. The multicomponent nature of the
silver/phosphane complexes in solution is known and has been repeatedly observed by
various experimental techniques [20, 21]. In contrast to the pure PNP ligand (Fig. S1), the
resonances of the aliphatic hydrogen atoms of 1 are unresolved both at RT and at low
temperatures, hampering a deeper analysis of the NMR spectra.
The room temperature 31P NMR spectrum of 1 (major constituent) (Fig. S4) displays two well
resolved doublets centered at 0.98 ppm, due to 1J(107Ag-31P) and 1J(109Ag-31P) coupling. The
1
magnitude of the coupling constants (1J(107Ag-31P) = 491, J(109Ag-31P) = 568) are in the
range typical for silver complexes coordinating two tertier phosphane ligands and an oxo
anion with strong electron withdrawing properties [20, 22, 23]. The broad resonances of the
minor component show up at −3.66 and −6.85 ppm and the average coupling constant (517
Hz) suggests that the environment around the silver atom is similar to that in the main
constituent. The striking feature of the 31P NMR spectrum is that the resonances are sharp not
only at low temperatures which is characteristic for silver/phosphane complexes but at
ambient temperature as well. In contrast to the well resolved 31P NMR spectrum of 1, the
silver complex of the earlier mentioned 1,4-C6H4{N(CH2CH2PPh2)2}2 ligand showed only a
broad resonance with no resolved coupling to the metal center [9].
The 1H and 31P NMR spectra of the halide complexes 2-4 are presented in Figures S5-S10, the
31P NMR spectral data are summarized in Table 2. The spectra show that replacement of the
OTf ion by halide ions eliminates the minor constituent. The methylene resonances invariably
appear as broad signals at 2.7-2.8 ppm and around 3.8 ppm and the N-phenyl and P-phenyl
hydrogen atoms are also insensitive to the nature of the halide ion. To the contrary, both the
chemical shifts and the 1J(Ag-P) coupling constants show a systematic decrease on going
from chloride to iodide, in line with the increasing nucleophilicity of the halide anions (I > Br
> Cl). The trends observed in the 31P NMR features are in coincidence with the behavior of
other AgX/phosphane complexes [24-26].
12

Table 2.
31P NMR data of the isolated (1-4) and the mixed ligand complexes in CDCl3 at the indicated
temperatures.
Anion
Comp.
1J(107Ag-31P)/
1J(109Ag-31P)
(absolute values)
491/568
T/K
δ/ppm
OTf
0.46
300
300
296
298
298
218
218
223
298
298
218
1
Cl
386/444
377/435
350/404
381/439
385/445
368/425
370/426
432/498
427/491
416/480
2
−4.42
−8.55
−13.70
−5.41
−4.95
−8.07
−9.30
−1.04
−1.90
−4.12
Br
3
I
4
Cl/Br
Cl/Br
Cl/I
2/3
2/3
2/4
3/4
1/2
1/3
1/4
Br/I
OTf/Cl
OTf/Br
OTf/I
Scheme 4. General formula of dimeric and monomeric [AgX(µ-PPh2YPPh2)] complexes.
The kinetic lability of silver/phosphane complexes, especially of those incorporating
monophosphane ligands, is known and they readily form multicomponent systems in solution
[20]. Although bisphosphane ligands may give chelate complexes with enhanced kinetic
stability [27] and, due to their double bridged feature (structure A in Scheme 4) as determined
by X-ray diffraction (see later), one can expect increased stability for 1-4 as well, it is not
evident that the dimeric structure is preserved in solution. Surveying our spectra we may say
that they are in line with structure A but the broad signals of the methylene protons provide no
13

unequivocal evidence to confirm this hypothesis. Moreover, a search of literature data have
shown that coupling constants reported for mononuclear complexes of type B may have very
close values (Table 3, right column) that reduces the strength of our data to prove the dimeric
nature of 1-4 in solution. In order to gain a deeper insight into the solution structure of these
complexes, we set up various experiments.
If we assume that the prevailing form of the complexes in solution is dimeric, observation of
3J(Ag-P) coupling transmitted by the bridging halide ions may provide us a direct proof for
the binuclear nature of the complexes. Our attemps to detect such couplings was unsuccessful
even at −60 °C demonstrating that the halide ions exchange rapidly in the coordination sphere
and cannot transfer magnetic information from one silver center to the other. To our
knowledge, 3J(Ag-P) couplings have been observed at low temperatures for dinuclear silver
complexes only if the P-donors are separated by a single methylene bridge (dppm) [29-32].
The lability of the halide complexes excluded the possibility to detect the heteronuclear 107Ag-
109Ag coupling as well.
14

Table 3
A compilation of 1J(31P-107Ag) and 1J(31P-109Ag) coupling constants (absolute values) regarding structures A and B in Scheme 4.
A
A
B
X
1J(Ag-P)
T/K X
1J(Ag-P)
T/K X
1J(Ag-P)
Y =
Cl
[24]
Y =
[23, 25]
390/450 263-273
Y =
[23,26]
382/441
377/434
337/388
457/525
RT Cl
RT Br
RT Y =
RT Cl
Y =
Br
383/442
381/438
372/420
218 Cl
[23] I
411/474
378/437
507/585
I
NO3
263-273 ClO4
[23]
Y =
[28]
Br
218
Cl
377/435
15

As a further attempt to obtain direct experimental evidence for the dimeric nature of our
compounds in solution, we studied the NMR spectra of complexes with mixed
(halide1/halide2) anions. It was anticipated that an exchange of halide ions occurring between
monomeric [AgX1(PNPhP)] and [AgX2(PNPhP)] complexes will not modify the spectra. In
case of dimeric complexes, however, a distribution of the halide ions should result and
complexes with compositions [Ag2X1 (PNPhP)2], [Ag2X1X2(PNPhP)2] and [Ag2X2 (PNPhP)2]
2
2
will be formed. The 31P NMR spectrum of a 1:1 molar mixture of [Ag2Cl2(PNPhP)2] and
[Ag2Br2(PNPhP)2] is presented in Fig. 1, the δ(P) and 1J(Ag-P) data for the possible 2/3, 2/4
and 3/4 pairs are summarized in Table 2.
Fig. 1. 31P NMR spektrum of a 1:1 molar mixture of [Ag2Cl2(PNPhP)2] and [Ag2Br2(PNPhP)2]
in CDCl3 at 298 K. (Cl and Cl’, and all analogous designations here and in the Supplement,
mark the high- and low-frequency parts of the spin systems ascribed to pure [Ag2X2(PNPhP)2]
complexes.)
The spectrum in Fig. 1 can be described as a threefold repetition of the pair of doublets
characteristic for Ag/P interaction. The sections Cl and Cl’ have been ascribed to the
bischloro complex, the resonances labeled as Br, Br’ to the bisbromo complex while the most
intense peaks have been attributed to the mixed ligand chlorobromo derivative, 2/3. The
bischloro and bisbromo constituents of the mixture could be identified by compairing their
NMR data with the corresponding values of the pure complexes. The δ(P) and 1J(Ag-P) data
of the mixed ligand dimer take intermediate positions between those of the parent complexes.
Because a better separation of the peaks was achieved at 218 K, the integration was carried
out on a spectrum recorded at low temperature (Fig. S12). The 1:1.71:0.95 ratio of the
components is close to a simple statistical distribution of 1:2:1 and proves directly that the
16

halide complexes are dimeric in solution. 31P NMR spectra of mixtures 2/4 and 3/4 have an
identical appearance and have been assigned according the above considerations.
By recording 2D 31P-31P exchange spectra using different mixing times we could prove
unambigously that halogen scrambling, slow on the 31P time scale at 9.4 T, is going on
between the complexes. As an illustrative example the 31P-31P exchange spectrum of an
[Ag2Cl2(PNPhP)2]: [Ag2Br2(PNPhP)2] = 1:1 molar mixture is shown in Figure 2. The off-
diagonal cross peaks identify the exchanging sites clearly already at 50 ms exchange (mixing)
time. As expected, the first-order cross-peaks (highlighted in red) connecting the mixed ligand
complex (the strongest doublets) with the peaks of 2 or 3 are much stronger than those linking
the homogeneous complexes 2 and 3 (highlighted in blue).
Fig. 2. 31P-31P exchange (EXSY) spectrum of an [Ag2Cl2(PNPhP)2]:[Ag2Br2(PNPhP)2] = 1:1
molar mixture (2/3, exchange time = 50 ms, CDCl3, 298 K).
Although the chloride, bromide and iodide ions all form stabile complexes with Ag(I), their
hard/soft properties are characteristically different and they are classified as hard (Cl−),
intermediate (Br−) and soft (I−) bases [33]. In the light of their dissimilar softness, one may
expect characteristically different distributions for the Cl/Br, Cl/I and Br/I cases. Therefore it
surprised us that the distribution of the dimeric species found for the Cl/Br (1:1.71:0.95), Cl/I
(1:1.69:0.84) and Br/I pairs (1:1.83:1.18) practically shows no variance (all measured at 218
K). It should be stressed, however, that these measurements are not suitable (and they were
not planned to be) to deliver any kind of thermodynamic data.
17

The dominance of the halide ions over the OTf ion became visible, however, when we
extended our study to OTf/Cl, 1/2, OTf/Br, 1/3 and OTf/I, 1/4 pairs. Fig. 3 shows the room
temperature 31P NMR spectrum of a 1:1 mixture of 1 and 3. NMR spectra for all of the
combinations are added to the Supplementary Material, Table 2 includes the respective δ(P)
and 1J(Ag-P) data.
Fig. 3. 31P NMR spectrum of a 1:1 mixture of [Ag2Br2(PNPhP)2] and [Ag2(OTf)2(PNPhP)2] in
CDCl3 at 298 K.
The spectrum in Fig. 3 clearly demonstrates that formation of silver-bromide bonds is much
more advantageous than the silver-OTf interaction. The approximate ratio of 1:21:1 witnesses
about the dominance of the bromide over the OTf ion in the competition for the available
coordination sites. As we have found for the halide pairs, the chemical shifts and the coupling
constants of the OTf/halide derivatives occupy intermediate values between those of the
parent compounds.
Having strong evidence from the experiments with mixed ligand complexes for the dimeric
nature of compounds 1-4 in solution, we turned our attention to the minor constituent of the
dissolved [Ag2(OTf)2(PNPhP)2] complex, which has not been identified. The section of a 1H
DOSY [17] spectrum recorded on a CD2Cl2 solution of 1 (Fig. S21) shows that the resonances
of the conventional (1D) spectrum are separated according to the diffusion rate of the
constituents. As the major component is characterized by the smaller diffusion coefficient,
and, consequently, by the larger hydrodynamic radius, this species can be identified as a
dimeric aggregate, while resonances of the minor constituent have been ascribed to a
monomeric complex.
Based on our investigations carried out with mixed ligand complexes we conclude that
compounds 2-4 are dimeric in solution. The different diffusion coefficients detected for the
18

two constituents in the solutions of 1, as observed by 1H DOSY experiments, make a
monomer/dimer equilibrium highly probable for the silver triflate/PNPhP complex which is,
however, strongly shifted toward the dimeric species. The dimeric nature of 1-4 is further
supported by the magnitude of the 1J(Ag-P) coupling constants which are in good agreement
with couplings found for other dinuclear double bridged diphosphine silver complexes.
3.2 Crystal Structures
Molecular diagrams are shown in Figs. 5 and 6. Atomic displacement parameters are depicted
at the 50% probability level (except for 1/3, where the 40 % probability value is used). As the
conformation of 3 and 4 is rather similar as shown in the overlap diagram Fig. 4, only 2 and
the low-temperature structure of 4 is presented in the figures. The atomic numbering schemes
are identical. Hydrogen atoms and solvent molecules have been omitted for clarity.
Phosphane phenyl ring atoms are drawn as circles with arbitrary radii. Selected parameters are
summarized in Tables 4-6 (more detailed description is presented in Tables S1 and S2 (see
Supplementary Material).
Fig. 4. Least-squares fit of Ag, P and N atoms (solid lines: 2, dashes: 3 and 4).
19

Fig. 5. Molecular diagrams of compounds 1, (left), and 1/3, (right).
Fig. 6. Molecular diagrams of compounds 2, (left), and 4, (right).
The asymmetric unit is half a molecule for complexes 1-4. The inversion centre generates the
whole molecules: 1: 2-x, -y, 1-z; 2: -x, -y, 1-z; 3: 1-x, 1-y, -z; 4: 1/2-x, 1/2-y, -z.
The Ag atoms display distorted tetrahedral configuration. The bulky PPh2 moieties make wide
P-Ag-P angles of 120-135º.
20

Table 5.
Selected bond distances (Å) and angles (º) for 2-4.
2
3
4
X = Cl; a = -x, -y, -z
X = Br; a = -x, -y, 1-z
X = I; a = 1/2-x, 1/2-y, -z
2.9342(2)
Ag1-X1
2.748(1)
2.8292(5)
Ag1-P1
2.483(1)
2.459(1)
2.727(1)
1.389(7)
93.10(3)
116.9(4)
120.7(4)
122.3(4)
2.471(1)
2.474(1)
2.7318(5)
1.391(4)
87.88(1)
114.0(3)
121.7(3)
120.9(3)
2.4634(6)
2.4635(7)
2.8707(2)
1.384(3)
82.62(1)
114.1(2)
121.7(2)
121.1(2)
Ag1-P2
Ag1-X1_a
N1-C5
Ag1-X1-Ag1_a
C2-N1-C3
C2-N1-C5
C3-N1-C5
21

Table 6.
Hydrogen bonds (Å, º) for compounds 1-4 and 1/3.
D-H···A
d(D-H)
1
d(H···A) d(D···A)
<(D-H···A)
C3-H3a···F2[2-x,-y,1-z]
C3-H3b···O2
0.97
0.97
0.93
1/3
2.540
2.440
2.550
3.493(2)
3.283(2)
3.380(2)
166.0
146.0
148.0
C10-H10···O3[1-x,-y,1-z]
C14-H14b···O3
0.97
0.93
0.93
2
2.420
2.490
2.340
3.32(1)
3.36(1)
2.91(3)
154.0
155.0
119.0
C18-H18···F3[x,y,-1+z]
C39p-H39p···O1s
C1s-H1s···Cl1[-x,-y,-z]
C2-H2b···Cl1
1.00
0.93
0.95
0.95
3
2.40
2.78
2.79
2.80
3.382(11)
3.582(6)
3.724(6)
3.742(6)
168.0
146.0
169.0
169.0
C2p-H2p···Cl1
C18p-H18p···Cl1[-x,-y,-z]
C1s-H1s···Br1[-x,y,1/2-z]
0.98
0.93
0.93
4
2.81
2.77
2.83
3.645(6)
3.614(8)
3.568(8)
144.0
151.0
137.0
C21p-H21p···Cl2s[-1/2+x,-1/2+y,z]
C23p-H23p···Cl3s[[-x,y,1/2-z]
C1s-H1s···I1[-x,-y,-z]
1.00
0.95
2.93
2.75
3.744(3)
3.676(4)
139.0
166.0
C23p-H23p···Cl1s[1/2+x,-1/2-y,1/2+z]
The Ag···Ag distances across the macrocycle is dependent on the bridging atoms/moieties.
The longest separation (5.12 Å) is in 1 where the three-membered O-S-O linkage connects the
two Ag atoms. A considerably longer (5.72 Å) Ag···Ag distance is reported for bis(µ2-
trifluoromethanesulfonato-O,O')-tetrakis(triphenylphosphane)-disilver(I), where the constraint
22

by the chain linking the pairs of phosphorous atoms is missing [34]. The distance of 4.64 Å in
1/3 indicates that the presence of Br influences the positions of the Ag atoms resulting in an
intermediate value. Halogen bridging forces shorter separations that sligthly decreases with
the atomic number of the halogens (2: 3.98, 3: 3.86 and 4: 3.83 Å). The Ag-X-Ag bond angles
(X = Cl, Br, I) are getting smaller accordingly: 93.1, 87.9 and 82.6º in contrast to the 117º
angle of 1/3. These findings corroborate the similar and more prominent tendency as shown
by the series of bis((µ2-X)-(µ2-4R,5R-trans-4,5-bis((diphenylphosphanyl)methyl)-2,2-
dimethyl-1,3-dioxolane-P,P')-silver(I)), (X = Cl, Br, I) where the corresponding Ag···Ag
distances and Ag-X-Ag angles are 3.72, 3.59(5)(mean), and 3.07 Å and 88.2(1), 80.3(9).
63.1(4)º [35].
In complexes 1-4, both the Ag-O and Ag-halogen bond distances (linking to the same Ag
atom) are of different length, forming a rhomboid shape. The nitrogen atoms in all structures
are planar (sp2) showing a considerable interaction with the π electron system of the phenyl
ring and contributing to the reduced ability of the nitrogen to form coordinative bonds.
All crystal structures, except 1, contain solvent molecules that maintain non-classical C-H···A
hydrogen bonds (Table 6). 1/3 crystallizes with diethyl-ether and the ether oxygen interacts
with a C(sp2)-H atom only.
A search for structures of type A Scheme 4 in CCDC revealed that disilver complexes
incorporating two bridging diphosphine and two bridging halide ligands may have four-, five-
and six-membered linkages between the phosphorus atoms. An overview of their structural
properties showed that these complexes can be classified according to the relative positions of
their AgP2 planes. In three cases (CPESAG, IPESAG, YAKMON), all the phosphorus atoms
and the silver ions lay in the same plane, i.e. the two AgP2 planes are coplanar. In another
group of compounds, the two silver atoms are located at the same distance but on the opposite
sides of the plane defined by the four phosphorus atoms. This means that the two AgP2 planes
are parallel in these complexes. This structural feature can be observed with a variety of
chains linking the donor phosphorus atoms like tetramethylene, hexamethylene and nitrogen-
containing five-membered linkages such as that in compounds 1-4. In the three compounds
having 4,5-bis((diphenylphosphino)methyl)-2,2-dimethyl-1,3-dioxolane as bridging
diphosphane ligand (XIDZAL, XIDZEP, XIDZIT), the dispositions of the silver centers from
the P4-plane are different causing thereby the two planes to form a small angle. Finally, the
two AgP2 planes may be twisted around the Ag-Ag axis forming a large (ca. 20-40°) angle.
Table 7 summarizes the respective ψ((AgP2)1/(AgP2)2) and d(P4-plane/Ag) data.
23

Table 7
Classification of halogen-bridged bis(diphosphine) disilver complexes (structure A in Scheme 4) according
to the mutual orientation of their AgP2 planes.
Refcode
X
Y
ψ((AgP2)1/(AgP2)2)
Coplanar AgP2 planes
d(P4-plane/Ag) References
CPESAG
IPESAG
Cl
I
Y1
Y1
Y2
0
0
0
0
0
0
[36]
[37]
[25]
YAKMON
Br
Parallel AgP2 planes
KAXKOL
Cl
Cl
Br
I
Y3
Y4
Y5
Y5
Y6
Y6
Y7
Y7
Y7
Y7
0
0
0
0
0
0
0
0
0
0
0.01
1.74
0.06
0.07
0.12
0.11
0.28
0.05
0.17
0.15
[38]
[38]
[25]
[25]
[25]
[25]
t. w.
t. w.
t. w.
t. w.
KAXKUR
YAKLAY
YAKLEC
YAKPEG
Br
I
YAKPIK
OTf
Cl
Br
I
1
2
3
4
Bent AgP2 planes
XIDZAL
Cl
Br
Br
I
Y8
Y8
Y8
Y8
0.69
2.7
[35]
[35]
[35]
[35]
−0.038; 0.040
−0.01; +0.06
0; −0.01
XIDZEP(1)
XIDZEP(2)
XIDZIT
1.0
2.4
−0.05; +0.10
Twisted AgP2 planes
PPENAG
Cl
Y2
Y2
Y9
Y9
Y10
41.8
22.8
22.7
42.5
18.4
25.7
n. a.
n. a.
n. a.
n. a.
n. a.
n. a.
[39]
[25]
[24]
[24]
[41]
t. w.
YAKMUT(1) I
YIYMIC
YIYMOI
OTUGUG
1/3
I
Cl
I
Br/OTf Y7
t. w. = this work; n.a. = not applicable
Y1: -CH2CH2SCH2CH2-; Y2: -(CH2)5-; Y3:
; Y4:
; Y5: -(CH2)4-;
Y6: -(CH2)6-; Y7: PhN(CH2CH2)2; Y8:
; Y9:
; Y10:
24

While searching for explanation why one of the observed conformations is preferred over
another, we supposed that intramolecular non-classical hydrogen bonds may be involved. In
some cases, indeed, we found relatively strong C−H···O, C−H···F (compound 1, see Table 6)
and C−H···Cl (compound 2, see Table 6) interactions. However, this type of bonding in other
complexes of the same group (e.g. KAXKOL, KAXKUR) seems to be much weaker as
almost all the C−H···Cl distances fall outside the limit defined as a criteria for C−H···Cl
bonding interactions (2.95 Å) [40]. The compilation in Table 7 also shows that the nature of
the halogen bridge is not crucial as Cl, Br and I equally appear in all groups. It seems,
however, that the chains linking the phosphorus donor groups have a strong influence on the
structural properties as the chloro, bromo and iodo derivatives of a [Ag2X2(Ph2PYPPh2)2]
complex tend to behave similarly, although an exception can be identified (see YAKMON vs.
PPENAG and YAKMUT). Therefore we believe that intra- and intermolecular steric effects
rather than intramolecular secondary bonds are important in determining the conformation of
these macrocycles.
4. Conclusions
N,N-bis(2-(diphenylphosphanyl)ethyl)phenylamine, (PNPhP), forms dinuclear
[Ag2X2(PNPhP)2] complexes with AgX salts (X = OTf, Cl, Br, I), 1-4, in which both the
diphosphane ligands and the halide ions occupy bridging position. Single crystal X-ray
diffraction studies on 1-4 showed that this diphosphane can span Ag···Ag distances over a
wide range (3.83-5.12 Å), satisfying the requirements of the bridging inorganic ligands, which
testifies the remarkable flexibility of the PNPhP ligand. Solution phase NMR studies on mixed
ligand [Ag2X1X2(PNPhP)2] bishalide complexes proved in a simply and convincing way that
these complexes preserve their dinuclear structure in solution. The analysis of the structural
details of the [Ag2(µ-X)2(µ-PNPhP)2] complexes have shown that the linkages between the
phosphorus donor atoms rather than intramolecular secondary bonding interactions govern the
conformation of the macrocycles.
Acknowledgement
The authors thank the Research Centre for Natural Sciences of HAS and the University of
Pannonia for their support and Dr. D. Csányi for recording spectra on Varian-500 instrument.
25

Appendix A. Supplementary data
Further supplementary data associated with this article are presented in the Supporting
Information (Figs. S1–S21 and Tables S1-S2). CCDC 1517416-1517421 contain the
supplementary crystallographic data for 1-4, 1/3 and the unpublished Pd complex (Ref. 28).
These data can be obtained free of charge via ttp://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.
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28

Table 4
Selected bond lengths (Å) and bond angles (º) for 1 and 1/3.
1
1/3
[a = 2-x, -y, 1-z]
Ag1-Br1
Ag2-Br1
Ag1-O1
Ag1-O2_a
Ag2-O2
S1-O1
2.735(2)
2.710(1)
2.610(7)
2.484(1)
2.663(1)
2.609(9)
1.425(7)
1.409(9)
1.428(8)
116.87(4)
1.450(1)
1.445(1)
1.440(1)
S1-O2
S1-O3
Ag1-Br1-Ag2
29