Influence of anion on the solution and solid-state structures of some 1:2 adducts of silver(I) salts with 1,3-bis(diphenylphosphino)propane

Article abstract of DOI:10.1039/a607692k

Crystallization of 1:2 silver(I) halide/pseudo halide:1,3-bis(diphenylphosphino)propane (dppp) mixtures from acetonitrile have resulted in the isolation of a novel series of neutral complexes, [AgX(dppp-P,P′)(dppp-P)] (X = Cl, Br, I or CN) containing co-ordinated anion and uni- and bi-dentate dppp ligands. In contrast, the thiocyanate and nitrate complexes precipitate as ionic [Ag(dppp-P,P′)₂]X with unco-ordinated anion and bidentate phosphine ligands, a structural type previously found for other 1:2 silver(I):diphosphine complexes. The complexes have been characterized by single-crystal X-ray structure determinations and solid-state ³¹P cross-polarization magic angle spinning (CP MAS) NMR spectroscopy. The salt [Ag(dppp-P,P′)₂]SCN is obtained as crystals suitable for X-ray studies from pyridine, crystallizing as a sesqui-pyridine solvate in the monoclinic space group P2₁/c with a = 10.691(2), b = 24.75(2), c = 22.360(4) A, β = 108.38(1)°. The neutral AgXP₃ complexes (X = Cl, Br, I or CN) are isomorphous, crystallizing in the monoclinic space group C₂/c, with a ≈ 21.8, b ≈ 10.3, c ≈ 45 A, β ≈ 95°. The solid-state ³¹P CP MAS spectra are consistent with the structural results; the tetrahedral SCN and NO₃ complexes give a similar broad complex multiplet centred at δ -6, whereas the spectra of the neutral AgXP₃ complexes are interpretable as A₂BMX spin systems with signals assignable to the non-co-ordinated (δ -23), bidentate (δ ca. 13) and unidentate (δ ca. 3) phosphorus atoms. For the latter ¹J(P-Ag) couplings are in the range 288 Hz (CN) to 367 Hz (Br). Solution ³¹P NMR studies on these complexes show that both neutral and ionic complexes exist in equilibrium in solution, with the position of the equilibrium dependent on the nature of the anion X. The potential significance to the antitumour activity of bis-chelated 1:2 silver(I)-diphosphine complexes is discussed.

Full text of DOI:10.1039/a607692k

View Article Online / Journal Homepage / Table of Contents for this issue
Influence of anion on the solution and solid-state structures of some
1:2 adducts of silver(I) salts with 1,3-bis(diphenylphosphino)propane
Dermawan Affandi,a Susan J. Berners-Price,*,†,b Effendy,a Peta J. Harvey,b Peter C. Healy,b
Beate E. Ruchb and Allan H. Whitec
a
Jurusam Pendidikan Kimia, FPMIPA IKIP Malang, Jalan Surabaya 6, Malang 65145, Indonesia
b Faculty of Science and Technology, Griffith University, Nathan, Brisbane, Queensland 4111,
Australia
c Department of Chemistry, University of Western Australia, Nedlands, Western Australia 6907,
Australia
Crystallization of 1:2 silver() halide/pseudo halide:1,3-bis(diphenylphosphino)propane (dppp) mixtures from
acetonitrile have resulted in the isolation of a novel series of neutral complexes, [AgX(dppp-P,PЈ)(dppp-P)]
(X = Cl, Br, I or CN) containing co-ordinated anion and uni- and bi-dentate dppp ligands. In contrast, the
thiocyanate and nitrate complexes precipitate as ionic [Ag(dppp-P,PЈ)2]X with unco-ordinated anion and
bidentate phosphine ligands, a structural type previously found for other 1:2 silver():diphosphine complexes.
The complexes have been characterized by single-crystal X-ray structure determinations and solid-state 31P cross-
polarization magic angle spinning (CP MAS) NMR spectroscopy. The salt [Ag(dppp-P,PЈ)2]SCN is obtained as
crystals suitable for X-ray studies from pyridine, crystallizing as a sesqui-pyridine solvate in the monoclinic space
group P21/c with a = 10.691(2), b = 24.75(2), c = 22.360(4) Å, β = 108.38(1)Њ. The neutral AgXP3 complexes
(X = Cl, Br, I or CN) are isomorphous, crystallizing in the monoclinic space group C2/c, with a ≈ 21.8, b ≈ 10.3,
c ≈ 45 Å, β ≈ 95Њ. The solid-state 31P CP MAS spectra are consistent with the structural results; the tetrahedral SCN
and NO3 complexes give a similar broad complex multiplet centred at δ Ϫ6, whereas the spectra of the neutral
AgXP3 complexes are interpretable as A2BMX spin systems with signals assignable to the non-co-ordinated
1
(δ Ϫ23), bidentate (δ ca. 13) and unidentate (δ ca. 3) phosphorus atoms. For the latter J(P᎐Ag) couplings are in
the range 288 Hz (CN) to 367 Hz (Br). Solution 31P NMR studies on these complexes show that both neutral and
ionic complexes exist in equilibrium in solution, with the position of the equilibrium dependent on the nature of
the anion X. The potential significance to the antitumour activity of bis-chelated 1:2 silver()–diphosphine
complexes is discussed.
Ϫ
Ϫ
Like their gold() counterparts, certain tetrahedral bis-chelated
1:2 silver()–diphosphine complexes of the type [Ag(P᎐P)2]NO3
Both ClO4 and NO3 are non-co-ordinating anions; more
relevant to biological systems are complexes of the type that
exist in the presence of co-ordinating anions, particularly chlor-
ide. Both [Ag(dppe)2]ϩ and [Ag(eppe)2]ϩ cations (as nitrate salts)
are stable in the presence of an excess of ClϪ ions,1,4 indicating
that chloride does not readily displace phosphorus from the AgI
co-ordination sphere. Of great interest therefore is a novel class
of compounds that we have isolated for 1:2 adducts of a num-
ber of silver() compounds, AgX, with dppp in the context of
systematic studies of AgX :dppx type adducts.8 For X = Cl, Br,
I or CN in the solid state the compounds exist as neutral com-
plexes of type [AgX(dppp-P,PЈ)(dppp-P)] with both uni- and
bi-dentate dppp ligands and co-ordinated anion. In contrast,
the thiocyanate complex is not of this type but, rather, ionic
[Ag(dppp)2]SCN.
[where P᎐P is Ph2P(CH2)2PPh2 (dppe), cis-Ph PCH᎐CHPPh
᎐
2
2
(dppey) or Et2P(CH2)2PEt2 (depe)] have been shown to exhibit
antitumour activity against i.p P388 leukaemia in mice, as well
as antifungal and modest antibacterial properties.1,2 Although
the mechanism for the cytotoxicity is not known, tumour cell
mitochondria are likely targets for these lipophilic cations3 and
indeed, the complex [Ag(eppe)2]NO3 [where eppe is Ph2P-
(CH2)2PEt2] exhibits selective primary antimitochondrial activ-
ity in yeast.4
An understanding of the mechanisms responsible for the bio-
logical activity depends on a detailed knowledge of the different
structural types that exist for silver() complexes of bidentate
phosphines in the solid state and in solution. Tolazzi and co-
workers have studied the thermodynamics of complexation of
AgIClO4 with the bidentate phosphines Ph2P(CH2)nPPh2 (n = 1–
3) in dimethyl sulfoxide5 and propylene carbonate.6 For n = 2
(dppe) and 3 (dppp) at 1:2 Ag:P᎐P ratios the only species
present were ionic [Ag(P᎐P)2]ϩ complexes involving chelated
diphosphine ligands. Similarly, in previous 31P NMR studies7 in
chloroform solutions, only the bis-chelated ionic complexes
[Ag(P᎐P)2]NO3 were observed for the bidentate phosphines
dppe, dppp, depe, eppe and dppey; these had greatly enhanced
kinetic and thermodynamic stabilities with respect to similar
AgP4 complexes containing monodentate phosphines, so that
109,107Ag–31P couplings were resolved in the 31P NMR spectra
at ambient temperatures.
We report here the characterization of these compounds by
single-crystal X-ray structure determinations and compare the
structures that exist in the solid state to those in solution by
comparison of results from solid state 31P cross-polarization
magic angle spinning (CP MAS) and solution 31P NMR spectro-
scopy. We show that the extent of dissociation of the complexes
in solution to form cationic [Ag(dppp)2]ϩ and/or other species
depends critically on the nature of the anion X.
Experimental
Preparation of compounds
[AgX(dppp-P,PЈ)(dppp-P)] (X = Cl, Br, I or CN). All com-
pounds were prepared similarly. The compounds AgX (1.0
mmol) and dppp (0.85 g, 2.1 mmol) were dissolved with warm-
† E-Mail: S.Berners-Price@sct.gu.edu.au
J. Chem. Soc., Dalton Trans., 1997, Pages 1411–1420
1411

View Article Online
ing in acetonitrile (ca. 20 cm3). After filtration, the solutions
were allowed to stand and cool, depositing colourless crystals
of the product. X = Cl: m.p. 124–126 ЊC (Found: C, 66.8; H,
5.5. C54H52AgClP4 requires C, 67.0; H, 5.4%). X = Br: m.p.
147–149 ЊC (Found: C, 63.9; H, 5.2. C54H52AgBrP4 requires C,
64.05; H, 5.2%). X = I: m.p. 159–161 ЊC (Found: C, 61.4; H,
5.1. C54H52AgIP4 requires C, 61.2; H, 4.95%). X = CN: m.p.
115–117 ЊC (Found: C, 68.9; H, 5.4; N, 1.6. C55H52AgNP4
requires C, 68.9; H, 5.45; N, 1.45%).
0.42 × 0.10 mm, Å*min,max = 1.05, 1.19, N = 7443, No = 3334,
R = 0.065, RЈ = 0.072.
Variata. All compounds presented common problems associ-
ated with (a) the long c axis (possibly introducing some system-
atic error by way of uncompensated reflection overlap, despite
the use of an extended counter arm), (b) rather weak data and
(c) disorder in the terminal phosphorus of the unidentate dppp
ligand, and, less well defined and unresolved, its neighbouring
atoms; phosphorus populations x, (1 Ϫ x) refined to x = 0.77(1),
0.84(1), 0.899(5), 0.85(1) for the four compounds. Inter-
component P ؒ ؒ ؒ P distances are 1.74(3), 1.76(4), 1.67(2) and
1.76(3) Å, respectively; the location of the second component
(Fig. 2) corresponds more plausibly to that expected for inver-
sion of the phosphorus [as in one of the phases of trimesityl-
phosphine10 in which the two sites are 1.725(6) Å apart] rather
than, for example, the full or partial occupancy of an associated
oxygen site of any oxide impurity should it be present. No
resonances for phosphine oxide were discernible in the solid-
state CP MAS 31P NMR spectra of these complexes. ω Scans
were used for data measurement.
[Ag(dppp)2]SCNؒ1.5py (py = pyridine). With AgSCN the same
procedure as for the halide and CN compounds yielded a white
precipitate. This was dissolved in warm pyridine (ca. 5 cm3)
giving a clear solution, which on cooling deposited colourless
crystals, m.p. 95–97 ЊC (Found: C, 67.8; H, 5.3; N, 3.0; S, 3.0.
C62.5H59.5AgN2.5P4S requires C, 67.65; H, 5.4; N, 3.2; S, 2.9%).
[Ag(dppp)2]NO3. This was prepared essentially according to
the literature method,7 by addition of AgNO3 (0.085 g, 0.5
mmol) in water (10 cm3) to a solution of dppp (0.42 g, 1 mmol)
in acetone (20 cm3). Colourless microcrystalline material
formed from the clear solution on standing.
[Ag(dppp)2]SCNؒ1.5py. C55H52AgNP4Sؒ1.5C5H5N, M =
1109.5. Monoclinic, space group P21/c (C 25h, no. 14), a =
10.691(2), b = 24.75(2), c = 22.360(4) Å, β = 108.38(1)Њ, U =
5614 Å3, Dc (Z = 4) = 1.31 g cmϪ3, F(000) = 2300, µM o = 5.5 cmϪ1
,
Crystallography
crystal size 0.51 × 0.28 × 0.16 mm, Å*min,max = 1.09, 1.16, N =
9087, No = 5083, R = 0.052, RЈ = 0.051.
Variata. 2θ/θ Scan mode. Pyridine thermal motion is high;
solvent(2) is disposed about an inversion centre with modelling
of the nitrogen, tentatively assigned, as disordered.
Structure determinations. Unique room temperature diffract-
ometer data sets (Enraf-Nonius CAD-4 instrument, T ≈ 295 K,
monochromatic Mo-Kα radiation λ = 0.710 73 Å) were meas-
ured to 2θmax = 50Њ yielding N independent reflections, No with
I > 3σ(I) being considered ‘observed’ and used in the full-
matrix least-squares refinements after Gaussian absorption cor-
rections. Anisotropic thermal parameters were refined for the
NMR Spectroscopy
non-hydrogen atoms, (x,y,z,Uiso
) being included constrained
Solid-state CP MAS 31P NMR spectra were obtained at ambi-
ent temperature on a Varian UNITY-400 spectrometer at
161.92 MHz. Single contact times of 2 ms were used with a
proton pulse width of 7.0 µs, a proton decoupling field of 62 kHz
and a recycle delay time of 30 s. The samples were packed in
Kel-F inserts within silicon nitride rotors and spun at a speed of
5 kHz at the magic angle. Between 60 and 200 free induction
decays were collected and transformed with experimental
line broadening values of 10–20 Hz. The 31P CP MAS two-
dimensional correlation (COSY) experiment was recorded
using the pulse sequence11 available in the Varian Solids User
Library, and use of the Haberkorn–Ruben (hypercomplex)
method for pure-phase quadrature detection in the F1 dimen-
H
at estimated values. Conventional residuals (on |F |), R and RЈ
are quoted, statistical reflection weights being derivative of
σ2(I) = σ2(Idiff) ϩ 0.0004σ4(Idiff). Neutral-atom complex scatter-
ing factors were employed, computation using the XTAL 3.2
program system implemented by S. R. Hall.9 Pertinent results
are given in the figures and tables. Abnormal features/variations
in procedures/comments for individual samples are recorded
below (‘Variata’). In all figures 20% thermal ellipsoids are
shown for the non-hydrogen atoms; hydrogen atoms, where
included, have arbitrary radii of 0.1 Å.
Atomic co-ordinates, thermal parameters, and bond lengths
and angles have been deposited at the Cambridge Crystallo-
graphic Data Centre (CCDC). See Instructions for Authors,
J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the
CCDC for this material should quote the full literature citation
and the reference number 186/412.
1
sion. The contact time, H 90Њ pulse length and spin-rate were
the same as those implemented in the one-dimensional experi-
ment. Typically a total of 200–256 time increments were used in
each of which 64 transients were added, with a 5 s recycle delay.
Both dimensions were zero-filled to 1 K words and weighted
with sine-bell apodization prior to Fourier transformation.
Chemical shift data are referenced to 85% H3PO4 via an
external sample of solid PPh3 (δ Ϫ9.9). Solution 31P NMR
spectra were recorded on the same instrument on samples
dissolved in CDCl3 or CH2Cl2–10% CD2Cl2 (3 cm3) in 10 mm
NMR tubes at variable temperatures (297–183 K). Spectra
consisting of 8000 data points were acquired using an 8 µs
(45Њ) pulse, proton Waltz decoupling and a 1 s relaxation
delay. A total of 256 scans were collected and the spectra
processed with a 1–5 Hz line broadening. The chemical shifts
were referenced to external 85% H3PO4 (δ 0) measured at
295 K.
Crystal data. The compounds [AgX(dppp)2] (X = Cl, Br, I or
CN) are isomorphous, monoclinic, space group C2/c (C 26h, no.
15), Z = 8.
X = Cl. C54H52AgClP4, M = 968.3, a = 21.731(9), b =
10.26(1), c = 44.61(2) Å, β = 94.44(4)Њ, U = 9917 Å3, Dc = 1.30 g
cmϪ3, F(000) = 4000, µM o = 6.2 cmϪ1, crystal size 0.22 × 0.46 ×
0.16 mm, A*min,max = 1.09, 1.13, N = 8718, No = 2911, R = 0.065,
RЈ = 0.069.
X = Br. C54H52AgBrP4. M = 1012.7, a = 21.709(5), b =
10.289(5), c = 44.920(9) Å, β = 94.76(2)Њ, U = 9998 Å3, Dc = 1.35
g cmϪ3, F(000) ≈ 4144, µM o = 13.6 cmϪ1, crystal size 0.23 ×
0.42 × 0.05 mm, Å*min,max = 1.06, 1.32, N = 7628, No = 2697,
R = 0.067, RЈ = 0.071.
X = I. C54H52AgIP4, M = 1059.7, a = 21.77(1), b = 10.341(8),
c = 45.35(2) Å, β = 95.51(4)Њ, U = 10162 Å3, Dc = 1.39 g cmϪ3
,
Results and Discussion
F(000) = 4288, µM o = 10.6 cmϪ1
, crystal size 0.20 × 0.42 ×
Crystal structures
0.16 mm, Å*min,max = 1.17, 1.24, N = 8945, No = 4514, R = 0.041,
RЈ = 0.041.
X = CN. C55H52AgNP4, M = 958.8, a = 21.892(9), b =
10.257(9), c = 44.68(2) Å, β = 94.36(3)Њ, U = 10 003 Å3, Dc = 1.27
g cmϪ3, F(000) = 3968, µM o = 5.7 cmϪ1, crystal size 0.26 ×
The results of the room-temperature single-crystal X-ray stud-
ies are consistent with the formulation of the complexes, in
terms of stoichiometry and connectivity, as 1:2 AgX :dppp
adducts (X = Cl, Br, I, CN or SCN); in all cases, one formula
1412
J. Chem. Soc., Dalton Trans., 1997, Pages 1411–1420

View Article Online
Table 1 Molecular core geometries (angles in Њ) for [Ag(dppp)2]SCNؒ1.5py. Ligand angles (values for ligands a, b respectively)
Ag᎐P(1)᎐C(1)
111.6(3), 110.4(2)
115.8(5), 116.2(5)
114.6(7), 115.6(6)
121.0(3), 121.5(2)
113.0(2), 114.9(2)
103.2(3), 102.4(3)
102.5(3), 101.8(4)
103.6(3), 103.3(3)
Ag᎐P(2)᎐C(2)
P(2)᎐C(2)᎐C(12)
111.8(2), 110.6(2)
113.1(5), 116.4(5)
P(1)᎐C(1)᎐C(12)
C(1)᎐C(12)᎐C(2)
Ag᎐P(1)᎐C(111)
Ag᎐P(1Ј)᎐C(121)
C(1)᎐P(1)᎐C(111)
C(1)᎐P(1)᎐C(121)
C(111)᎐P(1)᎐C(121)
Ag᎐P(2)᎐C(211)
Ag᎐P(2)᎐C(221)
C(2)᎐P(2)᎐C(211)
C(2)᎐P(2)᎐C(221)
C(211)᎐P(2)᎐C(221)
111.5(3), 121.3(2)
120.3(2), 113.5(3)
104.5(8), 103.2(3)
101.5(3), 102.8(3)
105.8(3), 103.3(3)
P(2)᎐Ag᎐P(1)᎐C(1)
Ϫ25.7(2), Ϫ31.7(3)
P(1)᎐Ag᎐P(2)᎐C(2)
Ag᎐P(2)᎐C(2)᎐C(12)
P(2)᎐C(2)᎐C(12)᎐C(1)
P(1)᎐Ag᎐P(2)᎐C(211)
P(1)᎐Ag᎐P(2)᎐C(221)
29.1(3),
Ϫ56.6(5), Ϫ57.2(6)
85.4(6),
145.6(2), 153.4(3)
32.6(3)
Ag᎐P(1)᎐C(1)᎐C(12)
P(1)᎐C(1)᎐C(12)᎐C(2)
P(2)᎐Ag᎐P(1)᎐C(111)
P(2)᎐Ag᎐P(1)᎐C(121)
Ag᎐P(1)᎐C(111)᎐C(112)
Ag᎐P(1)᎐C(121)᎐C(122)
50.3(6),
54.9(6)
Ϫ82.1(7), Ϫ79.7(8)
Ϫ147.4(2), Ϫ151.6(3)
81.3(7)
89.1(3),
82.9(3)
Ϫ89.8(3), Ϫ82.4(3)
81.7(7), Ϫ105.1(6)
17.7(7), Ϫ167.6(6)
Ag᎐P(2)᎐C(211)᎐C(212) Ϫ103.9(6), 160.9(5)
Ag᎐P(2)᎐C(221)᎐C(222) Ϫ11.6(8), 55.5(6)
Fig. 1 Projection of the [Ag(dppp)2]ϩ cation of the thiocyanate complex down its quasi-2 axis
unit comprises the asymmetric unit of the structure, with four-
co-ordinate silver() atoms. The thiocyanate complex obtained
from pyridine solution is ionic, [Ag(dppp)2]ϩ(SCN)Ϫ as a pyri-
dine sesqui-solvate. The [Ag(dppp)2]ϩ cation represents the first
bis[bidentate bis(diphenylphosphino)propane]silver() cation
structurally characterized. The pyridine appears to have no
unusual interactions with cation or anion, but simply occupies
lattice voids, with high thermal motion, also evident on the
anion and rendering insignificant the recorded geometries of
these moieties. The cation has quasi-2, non-crystallographic
symmetry, closely approximated by ring torsions (Table 1) and
phenyl ring dispositions about one pole; about the other, the
relation is more approximate (Fig.1). The bite angles of the two
ligands are similar, while interligand P᎐Ag᎐P angles about the
quasi-symmetry axis are appreciably different: 108.83(7) vs.
120.34(7)Њ reflecting a lowering of the symmetry of the complex
from D2d. A slight asymmetry in the Ag᎐P distances is observed
for each ligand with differences of ≈0.03 and ≈0.01 Å for
ligands a and b, respectively. The structure of this cation can
be compared to the three other reported structures in which
silver() is bis-chelated by two bidentate diphenylphosphine
ligands:12–14 [Ag(dppe)2]NO3, [Ag(dppey)2][Ph3Sn(NO3)2] and
[Ag(dppf)2]ClO4 [where dppf is 1,1Ј-bis(diphenylphosphino)-
ferrocene]. Comparative data are presented in Table 2. For all
of these structures, the [Ag(P᎐P)2] geometry is only slightly dis-
torted from D2d symmetry with the angles15 θx, θy, θz close to the
expected values of 90Њ (Table 2). The mean Ag᎐P distances vary
from 2.473(7) for [Ag(dppey)2][Ph3Sn(NO3)2] to 2.57(2) Å for
[Ag(dppf)2]ClO4, with the value of 2.52(2) Å for the present
dppp complex similar to that recorded for [Ag(dppe)2]NO3.
These results can be compared also with data obtained for
complexes containing the [Ag(PPh3)4]ϩ cation where for
example, for the nitrate complex,16 the Ag᎐P bond lengths are
2.643(3) (×3) and 2.671(4) Å, with P᎐Ag᎐P angles close to the
tetrahedral angle.
In the Cl, Br, I and CN, complexes, the silver atom is also
bonded to two dppp ligands within a discrete mononuclear
species but, unlike the SCN complex, one of these is unidentate
rather than bidentate, the fourth co-ordination site being occu-
pied by the halide or cyanide group to give a neutral AgXP2P
molecule (Fig. 2). The P᎐Ag᎐P angle within the bidentate lig-
and is the smallest angle within the co-ordination sphere,
J. Chem. Soc., Dalton Trans., 1997, Pages 1411–1420
1413

View Article Online
Fig. 2 Projection of [AgCl(dppp-P,PЈ)(dppp-P)] (a) down and (b) normal to the Cl–Ag bond; the disordered P(2b) component is included in both
and not noticeably different from the values observed in those
of the cation arrays; the ring conformation has approximate m
symmetry here, with phosphorus substituents equatorial and
axial, the latter to the same side of the ligands (Table 3). The
Ag᎐P (bidentate) bond lengths are also similar, but Ag᎐P
(unidentate), in a more spacious disposition, is shorter. The
X᎐Ag᎐P angles are similar in magnitude, the P (uniden-
tate)᎐Ag᎐P (bidentate) angles being the largest. In all bidentate
ligands, angles within the rings are quasi-tetrahedral at the
phosphorus and larger at the carbon atoms. About the metal
centre minor geometrical differences only are found between
Cl, Br and I adducts; the geometry of the cyanide adduct
deviates more substantially, Ag᎐P being elongated by ca. 0.02 Å
for the bidentate and 0.035 Å for the unidentate ligand, with
the X᎐Ag᎐P angle also enlarged, all indicative of increased
Ag᎐X interaction in the cyanide (Table 3). The [AgX(PPh3)3]
analogues, considered in comparison, exist in a wide variety of
phases;12,17 Ag᎐P bond lengths in the chloride and bromide
complexes usually lie in the range 2.54–2.60 Å; one of the lig-
ands is incipiently dissociating in the iodide and cyanide, with
one Ag᎐P bond 0.2 (X = I) to 0.5 Å (X = CN) longer than the
other two. The Ag᎐X bond lengths in these complexes are simi-
lar to those found for the present series, differences being of the
order of 2% or less.
1414
J. Chem. Soc., Dalton Trans., 1997, Pages 1411–1420

View Article Online
Table 2 Comparative core geometries (distances in Å, angles in Њ) for
tetrahedral [Ag(P᎐P)2]X complexesa
dppeb
dppeyc
dppp d
dppfe
Ag᎐P(1a)
Ag᎐P(2a)
Ag᎐P(1b)
Ag᎐P(2b)
〈Ag᎐P〉
2.488(3) 2.472(2) 2.527(2) 2.561(2)
2.523(3) 2.476(2) 2.501(3) 2.584(2)
2.527(3) 2.479(2) 2.526(2) 2.549(2)
2.523(3) 2.463(2) 2.516(2) 2.602(2)
2.51(2)
2.473(7) 2.52(2)
2.57(2)
P(1a)᎐Ag᎐P(2a)
P(1a)᎐Ag᎐P(1b)
P(1a)᎐Ag᎐P(2b)
P(2a)᎐Ag᎐P(1b)
P(2a)᎐Ag᎐P(2b)
P(1b)᎐Ag᎐P(2b)
θx
84.5(1)
84.1(1) 93.51(7) 105.71(4)
129.5(1) 123.8(1) 120.34(7) 113.15(4)
128.8(1) 127.8(1) 122.99(6) 117.84(4)
116.0(1) 117.8(1) 120.65(6) 106.81(4)
117.9(1) 124.2(1) 108.83(7) 114.54(4)
83.8(1)
89.8
83.9(1)
85.7
92.39(7) 98.39(4)
86.7
96.2
96.5
86.0
94.6
91.4
θy
θz
100.3
91.3
94.0
91.5
a
θz is generally similar to the dihedral angle between ligand planes
usually reported for this type of structure. For molecules adopting D2d
symmetry, θx = θy = θz = 90.0Њ. Deviation of θz from 90Њ represents a
‘twisting’ of ligand b relative to ligand a and lowers the symmetry to D2.
Values of θx and θy different from 90Њ represent ‘rocking’ or ‘waggling’
displacements of ligand b with respect to ligand a (ref. 15). b Ref. 12,
X = NO3. c Ref. 13, X = Ph3Sn(NO3)2. d This work, X = SCN. In the
anion, C᎐S,N are 1.76(1), 0.68(1) Å; S᎐C᎐N is 164(1) Å. e Ref. 14,
X = ClO4.
Solid-state 31P NMR spectroscopy
The 31P CP MAS solid-state spectra of the complexes [Ag-
(dppp)2]X (X = NO3 or SCN) and [AgX(dppp-P,PЈ)(dppp-P)]
(X = Cl, Br, I or CN) are shown in Fig. 3. The spectrum of the
SCN complex, precipitated from acetonitrile solution, consists
principally of a complex multiplet centred at δ Ϫ6 [Fig. 3(b)];
the 31P chemical shift is in a similar region to that of
[Ag(dppp)2]ϩ in solution (Fig. 5), but in the solid state the four P
atoms are crystallographically distinct, resulting in magnetic
inequivalence and hence a more complex multiplet pattern is
expected. The spectrum of the nitrate complex [Fig. 3(a)] is
almost identical to that of the SCN complex, showing that the
multiplet pattern is independent of the anion. However,
recrystallization of the SCN complex from pyridine resulted
in small changes in the appearance of the 31P CP MAS multi-
plet (not shown), with further distinct peaks observable at δ ca.
Ϫ3 and ϩ1, the intensities of which were dependent on the
conditions of crystallization. This is suggestive of the pres-
ence of different phases of [Ag(dppp)2]ϩ, possibly as a con-
sequence of variation in lattice site occupancy by the pyridine
solvent.
Fig. 3 The 31P CP MAS spectra of [Ag(dppp)2]X, (a) X = NO3, (b)
X = SCN and [AgX(dppp-P,PЈ)(dppp-P)] complexes, (c) X = Cl, (d)
X = Br, (e) X = I and (f) X = CN. The neutral complexes are interpret-
able as A2BMX spin systems (see text). In (a) the peaks at δ 0 to 5 are at
present unassigned
can be assigned unambiguously in the 31P solution spectrum of
[AgBr(dppp-P,PЈ)(dppp-P)] (see below) and the solid-state
spectra have the expected appearance of A2BM multiplets in
which the line widths are too broad (ca. 130 Hz) to resolve the
multiplet splittings. The A2BMX spin system is substantiated
by two-dimensional 31P CP MAS COSY spectra, as shown for
[AgI(dppp-P,PЈ)(dppp-P)] in Fig. 4. The weak cross-peaks
between the multiplets at δ Ϫ15 (PA ) and δ Ϫ4 (PB) confirm
2
that these resonances are part of the same spin system. No
cross-peaks are observed between the high-field singlet (PM )
4
and the PB multiplet, but the JPB᎐PM coupling is expected to
be only very small and was not resolved in the 31P NMR solu-
tion spectrum of [AgBr(dppp-P,PЈ)(dppp-P)] (Table 5). The
chemical shift of the high field singlet (PM ) is insensitive to
the nature of the anion X in the four neutral complexes
(Fig. 3) (and similar to the chemical shift of free dppp), consist-
ent with the expected behaviour for the non-co-ordinated phos-
phorus environment in the unidentate dppp ligand. The relative
broadness of the peak is consistent with the observed struc-
tural disorder about this atom (see above). Although the
A2BMX spin system is second order the 2J(P᎐P) coupling con-
stant is expected to be of the order of 50–80 Hz (cf. ref. 18), as
shown for [AgBr(dppp-P,PЈ)(dpppO-P)] (Table 5). As this value
is smaller than the line widths in the solid-state spectra, the
observed line spacing of the low-field (PB) doublet corresponds
approximately to the value of 1J(Ag᎐PB). These values are
tabulated in Table 4. Little change is observed in passing from
the chloride to the bromide complexes. However, the value for
the iodide decreases by ca. 5% while that of the cyanide
decreases by a further 17%. These trends are consistent with
those observed for the analogous series of complexes [AgX-
{P(C6H11)3}2]19 and reflect the similar donating properties of
the halogens to silver in these complexes and, as expected,
stronger Ag᎐X interactions in the cyanide complex. As for
The solid-state 31P CP MAS spectra of the four neutral
[AgX(dppp-P,PЈ)(dppp-P)] complexes are similar [Fig. 3(c)–
3(f)], and distinct from those of the ionic bis-chelated com-
plexes, consisting of three distinct sets of 31P resonances: a
broad high-field singlet (δ Ϫ23), a broad low-field doublet
(δ ca. Ϫ3) and an intermediate multiplet (δ ca. Ϫ13) whose
appearance is anion dependent. These spectral results are con-
sistent with the structural data with the high-field singlet and
low-field doublet assignable to the terminal and co-ordinated
phosphorus atoms of the unidentate dppp ligand, respectively,
and the complex multiplet at δ Ϫ13 assignable to the phos-
phorus atoms of the chelated ligand. While the two phosphorus
atoms of the chelate ligand are crystallographically distinct,
examination of the AgXP3 core geometries (Table 3, Fig. 2)
suggests that the immediate chemical environment is similar
for both atoms. Making the assumption that the chemical
shifts of both of these atoms are the same, the 31P NMR spec-
trum of each complex would be expected to consist of the
A2BM part of two overlapping A2BMX spin systems which
arise from spin–spin coupling to each of the two Ag spin ¹
¯
²
isotopes (107Ag, 51.82%; 109Ag, 48.18%). This multiplet pattern
J. Chem. Soc., Dalton Trans., 1997, Pages 1411–1420
1415

View Article Online
Table 3 Molecular core geometries (distances in Å, angles in Њ) for [AgX(dppp-P,PЈ)(dppp-P)]
X
Cl
Br
I
CN a
Ag᎐X
2.567(5)
2.508(5)
2.512(4)
2.438(5)
2.696(3)
2.511(5)
2.511(5)
2.445(5)
2.852(1)
2.494(2)
2.514(2)
2.437(3)
2.19(2)
Ag᎐P(1a)
Ag᎐P(2a)
Ag᎐P(1b)
2.532(4)
2.536(4)
2.473(4)
X᎐Ag᎐P(1a)
X᎐Ag᎐P(2a)
X᎐Ag᎐P(1b)
P(1a)᎐Ag᎐P(2a)
P(1a)᎐Ag᎐P(1b)
P(2a)᎐Ag᎐P(1b)
Ag᎐P(1a)᎐C(1a)
Ag᎐P(2a)᎐C(2a)
105.7(2)
103.3(2)
104.9(2)
93.1(1)
123.2(2)
124.1(1)
108.3(5)
106.7(5)
117(1)
107.0(1)
102.7(1)
103.7(1)
93.4(2)
124.5(2)
123.1(2)
107.4(7)
106.5(5)
118(1)
107.66(6)
101.66(5)
103.61(5)
93.68(7)
125.74(7)
121.88(1)
107.7(3)
106.5(2)
117.8(5)
114.3(5)
116.4(6)
116.5(3)
121.2(3)
119.1(2)
122.4(2)
115.0(3)
113.7(2)
105.0(4)
99.9(3)
100.4(3)
104.1(4)
102.4(3)
105.9(3)
103.1(4)
98.9(4)
104.2(4)
101.4(3)
103.4(3)
100.8(5)
109.3(4)
108.5(4)
108.0(4)
91.2(1)
119.1(1)
119.6(1)
106.9(5)
105.5(4)
117.1(9)
114.1(9)
116(1)
121.0(6)
118.9(5)
121.9(4)
122.6(2)
114.5(5)
117.5(5)
104.3(7)
98.6(6)
P(1a)᎐C(1a)᎐C(12a)
P(2a)᎐C(2a)᎐C(12a)
C(1a)᎐C(12a)᎐C(2a)
Ag᎐P(1a)᎐C(111a)
Ag᎐P(1a)᎐C(121a)
Ag᎐P(2a)᎐C(211a)
Ag᎐P(2a)᎐C(221a)
Ag᎐P(1b)᎐C(111b)
Ag᎐P(1b)᎐C(121b)
C(1a)᎐P(1a)᎐C(111a)
C(1a)᎐P(1a)᎐C(121a)
C(2a)᎐P(2a)᎐C(211a)
C(2a)᎐P(2a)᎐C(221a)
C(1b)᎐P(1b)᎐C(111b)
C(1b)᎐P(1b)᎐C(121b)
C(2b)᎐P(2b)᎐C(211b)b
C(2b)᎐P(2b)᎐C(221b)b
C(111a)᎐P(1a)᎐C(121a)
C(211a)᎐P(2a)᎐C(221a)
C(111b)᎐P(1b)᎐C(121b)
C(211b)᎐P(2b)᎐C(221b)b
114(1)
115(1)
114(2)
113(1)
118.0(7)
120.6(7)
117.7(5)
125.2(5)
115.5(6)
113.3(5)
105.8(8)
98.6(8)
98.7(7)
102.6(7)
102.4(7)
104.8(7)
107(1)
117.1(7)
120.1(8)
117.8(6)
123.7(6)
114.8(6)
112.3(6)
105.7(9)
100.1(9)
99.5(8)
103.0(8)
102.1(9)
106.9(9)
106(1)
98.8(6)
103.0(6)
102.1(6)
104.5(6)
104.6(9)
97.9(9)
104.0(7)
101.2(6)
103.2(6)
100(1)
98(1)
97(1)
104(1)
102.8(8)
104.8(9)
98(1)
103.2(9)
101.8(7)
103.6(7)
99(1)
Ag᎐P(1a)᎐C(1a)᎐C(12a)
Ag᎐P(2a)᎐C(2a)᎐C(12a)
P(1a)᎐C(1a)᎐C(12a)᎐C(2a)
P(2a)᎐C(2a)᎐C(12a)᎐C(1a)
P(2a)᎐Ag᎐P(1a)᎐C(1a)
P(1a)᎐Ag᎐P(2a)᎐C(2a)
X᎐Ag᎐P(1a)᎐C(111a)
X᎐Ag᎐P(1a)᎐C(121a)
X᎐Ag᎐P(2a)᎐C(211a)
X᎐Ag᎐P(2a)᎐C(221a)
X᎐Ag᎐P(1b)᎐C(1b)
58(1)
Ϫ64(1)
Ϫ79(2)
82(1)
59(1)
Ϫ64(1)
Ϫ81(2)
83(2)
56.3(6)
Ϫ63.3(5)
Ϫ77.6(8)
81.5(7)
Ϫ37.8(3)
41.4(3)
Ϫ176.7(3)
Ϫ48.2(3)
Ϫ179.9(3)
51.7(3)
60(1)
Ϫ66.7(9)
Ϫ78(1)
82(1)
Ϫ38.6(5)
41.2(5)
Ϫ173.9(6)
Ϫ46.1(8)
Ϫ175.4(5)
53.8(7)
54.3(6)
Ϫ65.4(6)
175.3(6)
45(1)
33(2)
0(1)
Ϫ97(1)
1(2)
60(1)
Ϫ37.7(7)
41.3(6)
Ϫ174.6(6)
Ϫ46.5(8)
Ϫ177.6(6)
51.6(8)
55.5(7)
Ϫ62.5(7)
177.9(7)
44(2)
35(2)
1(2)
Ϫ98(2)
0(2)
62(2)
Ϫ42.6(5)
45.4(5)
Ϫ173.6(7)
Ϫ42.8(7)
Ϫ176.5(7)
51.7(7)
51.8(7)
Ϫ64.7(6)
173.9(7)
45(1)
28(1)
1(1)
Ϫ95(1)
Ϫ2(1)
61(1)
56.9(3)
X᎐Ag᎐P(1b)᎐C(111b)
X᎐Ag᎐P(1b)᎐C(121b)
Ϫ61.8(2)
179.4(3)
43.5(7)
38.5(8)
1.1(7)
Ϫ99.9(6)
2.7(6)
61.1(6)
Ag᎐P(1a)᎐C(111a)᎐C(112a)
Ag᎐P(1a)᎐C(121a)᎐C(122a)
Ag᎐P(2a)᎐C(211a)᎐C(212a)
Ag᎐P(2a)᎐C(221a)᎐C(222a)
Ag᎐P(1b)᎐C(111b)᎐C(112b)
Ag᎐P(1b)᎐C(121b)᎐C(122b)
a
C᎐N 1.12(2) Å, Ag᎐C᎐N 179(1)Њ. b Major component.
Table
4
Solid-state CPMAS 31P NMR parameters for [AgX-
high-field multiplet corresponds to the two phosphorus nuclei
in the chelated dppp ligand. The appearance of this multiplet
is dependent on the nature of X (Fig. 3). For X = I or CN
it consists of a broad, asymmetric doublet while for the
bromide and chloride complex the spectrum devolves to a
pair of overlapping doublets. A possible interpretation is that
for X = I or CN the chemical shifts of the two chelated P
are essentially the same in which case the observed splittings
(ca. 232 and 173 Hz, respectively) will reflect the average
1J(Ag᎐PA) coupling constant. For X = Br or Cl the greater
complexity of the multiplets suggests significant differences
in different chemical shifts for the two phosphorus atoms.
For X = Br the multiplet has the appearance of two over-
lapped doublets with a splitting of ca. 250 Hz. This agrees
well with the estimate of the average value for 1J(Ag᎐PA)
obtained from the 31P solution spectrum of [AgBr-
(dppp-P,PЈ)(dppp-P)] (Table 5). However, for the Cl complex it
(dppp-P,PЈ)(dppp-P)] complexes. Estimated error in coupling con-
stants ±10 Hz
δ PA
δ PB
δ PM 1J(PB᎐Ag)/Hz*
Cl
Br
I
Ϫ12.8 Ϫ1.7
Ϫ13.6 Ϫ2.7
Ϫ15.1 Ϫ4.1
Ϫ12.3 Ϫ3.8
Ϫ23.3
363
367
348
288
Ϫ23.4
Ϫ23.0
Ϫ23.4
CN
1
* Estimate only, based on multiplet splitting (Fig. 3). J(PB᎐Ag) is the
average of the J(109Ag᎐31P) and 1J(107Ag᎐31P) coupling constants, see
1
text.
the tricyclohexylphosphine complexes, the observed changes
in the scalar coupling constants are not reflected in any signifi-
cant changes in the Ag᎐P bond lengths for the halides, other
than the small increase noted for the cyanide complex. The
1416
J. Chem. Soc., Dalton Trans., 1997, Pages 1411–1420

View Article Online
Table 5 Solution 31P NMR parameters for 1:2 Ag:dppp complexes (estimated error in coupling constants ±1 Hz)
Ϫ1J/Hz
Compound
Solvent
T/K
δ PA
δ PB
δ PM
PA–107,109Ag (average) PB–107,109Ag (average)
[Ag(dppp)2]X
X = SCN a
[AgX(dppp-P,PЈ)(dppp-P)]
X = Cl
X = Br
X = I
CDCl3
223
Ϫ4.7
Ϫ7.9
221, 254 (237)
CDCl3
CDCl3
CD2Cl2–CH2Cl2 233
CD2Cl2–CH2Cl2 183
CD2Cl2–CH2Cl2 183
253
223
b
Ϫ18.3
(250)c
b
Ϫ7.4d Ϫ3.3d Ϫ18.4
239, 276 (257)d
(250)c
348, 402 (375)d
Ϫ11.8
Ϫ12.4
b
Ϫ18.6
Ϫ20.8
b
X = CN (species I)
X = CN (species II)
Ϫ3.5
(214)c
(245)c
Ϫ13.0e Ϫ2.7e Ϫ19.6
e
e
[AgBr(dppp-P,PЈ)(dpppO-P)]f CDCl3
223
Ϫ9.1
1.8
35.0
239, 276 (257)
348, 402 (375)
a
The [Ag(dppp)2]ϩ cation is observed also as a dissociation product in solutions of [AgX(dppp-P,PЈ)(dppp-P)] (X = Cl, Br, I or CN) (see text). In
CDCl3 δ has a temperature dependence of Ϫ0.01 ppm KϪ1. In CD2Cl2–CH2Cl2 δ is Ϫ5.3 at 233 K. b Overlapped by major doublet of doublets for
[Ag(dppp)2]ϩ. c Couplings not fully resolved at this temperature. d The PA and PB multiplets are partially obscured by the [Ag(dppp)2]ϩ resonance at
δ Ϫ4.7 and also for PA the [AgBr(dppp-P,PЈ)(dpppO-P)] multiplet at δ Ϫ9.1 [see Fig. 5(e)]. The chemical shifts are estimated based on the assumption
that the coupling constants and the multiplet splitting patterns are identical to the analogous multiplets in [AgBr(dppp-P,PЈ)(dpppO-P)]. The
spectrum simulated with these values gives a reasonable fit to the observed spectrum [Fig. 5(e)]. e Cannot be measured accurately due to overlap with
compound I see Fig. 6. f 2J(Pa᎐PB) = 58 Hz, 4J(PB᎐PM ) = 0 Hz, 6J(PA᎐PM ) = 0 Hz; see simulated spectrum Fig. 5(e).
Scheme 1
couplings are resolved at 295 K. This is consistent with the
relative donor strengths of the two anions, as the more weakly
co-ordinating nitrate group would be less expected to facilitate
rupture of the Ag᎐P bonds than the thiocyanate.
The 31P solution spectra obtained from dissolution of the
neutral [AgX(dppp-P,PЈ)(dppp-P)] complexes were found to
be very dependent on the nature of X. For X = Cl in CDCl3,
the spectra exhibit a similar behaviour to the SCN complex.
₁
A broad (∆ν = 200 Hz) resonance (δ Ϫ6.4) at 297 K resolved
₂
at 253 K into the two overlapping doublets for [Ag(dppp)2]ϩ
[Fig. 5(a)]. However, unlike the SCN spectra, additional very
minor signals were also just visible at this temperature. These
had the expected multiplet pattern for [AgCl(dppp-P,PЈ)-
Fig. 4 The two-dimensional 31P CP MAS COSY solid-state NMR
(dppp-P)], with the assumption that the PB multiplet was
spectrum of [AgI(dppp-P,PЈ)(dppp-P)]
obscured by the major [Ag(dppp)2]ϩ resonance (Table 5). The
total integrated intensity of these minor peaks was ca. 2% of
1
is not possible to obtain an estimate of the value of J(Ag᎐PA)
the intensity of the [Ag(dppp)2]ϩ 31P signals. This result shows
by inspection.
that for the chloride complex in CDCl3 solution, the equi-
librium (Scheme 1) exists, but that the equilibrium constant
lies well to the left, favouring displacement of the anion by
Solution 31P NMR studies
The results of the structural and solid-state NMR studies
described above show that both cationic [Ag(dppp)2]ϩ and neu-
tral [AgX(dppp-P,PЈ)(dppp-P)] complexes can be isolated in
the solid state with the formation of each dependent on the
anion. To investigate which of these structures is favoured in
solution, or whether an equilibrium exists between the two
(Scheme 1), we recorded variable-temperature solution 31P
NMR spectra of the complexes in CDCl3 and/or CD2Cl2–
CH2Cl2 solutions. Representative spectra are shown in Fig. 5.
the phosphine ligand.
An explanation for the exclusive formation of the neutral
species in the solid state is that while the cation is the more
stable species in solution, the neutral species is more stable in
the solid state and preferentially forms under the recrystalliz-
ation conditions necessary for the preparation of X-ray quality
crystals.
For X = Br in CDCl3 the 31P NMR spectrum at 297 K con-
₁
sisted of a broad singlet (δ Ϫ7.5, ∆ν = 200 Hz). At 253 K this
₂
For [Ag(dppp)2]SCN in CDCl3 a broad (∆ν = 350 Hz) 31P
had partially resolved into the pair of doublets indicative of
[Ag(dppp)2]ϩ, together with a range of minor broad peaks
between δ ϩ6 and Ϫ10. All couplings were fully resolved on
cooling the sample to 223 K [Fig. 5(b) and 5(e)]. The minor
peaks arise from two distinct pairs of A2BMX spin systems (for
each of the 109Ag and 107Ag isotopes) which are assignable to
₁
₂

resonance (δ Ϫ5.9) was observed at 297 K which resolved below
273 K into two overlapping doublets (δ Ϫ5.1) characteristic of
1
the [Ag(dppp)2]ϩ cation.7 The J(107,109Ag᎐31P) coupling con-
stants (221 and 254 Hz) are the same as reported previously7 for
[Ag(dppp)2]NO3 although for the nitrate complex the spin–spin
J. Chem. Soc., Dalton Trans., 1997, Pages 1411–1420
1417

View Article Online
Fig. 5 Solution 31P NMR spectra of [Ag(dppp)2X] complexes in CDCl3 at 223 K. (a) X = Cl (253 K), (b) X = Br, (c) X = I and (d) X = CN. (e) An
expansion of spectrum (b) together with the simulated spectrum analysed as two distinct pairs of overlapping A2BMX spin systems for each of the
109Ag and 107Ag isotopes. Peaks labelled PA , PB and PM correspond to [AgBr(dppp-P,PЈ)(dppp-P)] and PЈA and PЈB to the oxidized species
2
2
[AgBr(dppp-P,PЈ)(dpppO-P)]; the PЈM peak (not shown) is at δ ϩ35 (see text). The derived chemical shifts and couplings constants for [AgBr(dppp-
P,PЈ)(dpppO-P)] are given in Table 5. As the PA and PB multiplets for [AgBr(dppp-P,PЈ)(dppp-P)] are partially obscured by the [Ag(dppp)2]ϩ
2
resonance, the simulated spectrum was obtained by estimating the chemical shifts of the two multiplets and assuming all coupling constants were the
same as for the oxidized species. The peak labelled u is unidentified
[AgBr(dppp-P,PЈ)(dppp-P)] and, as well, its oxidation product
[AgBr(dppp-P,PЈ)(dpppO-P)] in which the non-co-ordinated P
in the unidentate dppp ligand has been oxidized. There was no
evidence for oxidized product in the 31P CP MAS spectrum of
[AgBr(dppp-P,PЈ)(dppp-P)], suggesting that oxidation had
occurred in solution in the period between preparation of the
samples and acquisition of the spectra. Fig. 5(e) shows a com-
parison of the observed 31P spectrum at 223 K, together with a
simulated spectrum of two overlapped A2BMX spin systems.
From this we deduced that the well resolved multiplets [labelled
PЈB and PЈA , Fig. 5(e)] are due to the chelated (PA ) and uniden-
tate (PB) phosphorus atoms in the oxidized species since the
intensity of the signal at δ Ϫ18.4 is too low to correspond to the
PM resonance in the same spin system. A signal with the correct
intensity for the oxidized P in [AgBr(dppp-P,PЈ)(dpppO-P)]
was present at δ ϩ35.0. The A2 and B multiplets of [AgBr-
(dppp-P,PЈ)(dppp-P)] are partially obscured by the [Ag-
(dppp)2]ϩ 31P signal, but are just visible in Fig. 5(e). These have
the correct intensity to belong to the same pair of A2BMX spin
systems as the PM signal at δ Ϫ18.4, as shown in the simulated
spectrum. The chemical shifts and coupling constants derived
from the simulated spectra are listed in Table 5. From peak
integrals we estimate that the ring-opened species account for
ca. 7% of the species present {[AgBr(dppp-P,PЈ)(dppp-P)] 2%
and [AgBr(dppp-P,PЈ)(dpppO-P)] 5%}. This is slightly greater
than for the chloride complex, reflecting a relative donor
strength BrϪ > ClϪ. However direct comparison is difficult since
the equilibrium (Scheme 1) becomes irreversible once the
unco-ordinated P is oxidized. When the sample of [AgBr(dppp-
P,PЈ)(dppp-P)] was dissolved in CD2Cl2–CH2Cl2 the bis-
chelated complex was the only species observed in the 31P solu-
tion spectrum at 23 K.
For X = I in CDCl3 the compound was not completely sol-
uble at 297 K. However, a single 31P resonance was observed
₁
which was sharper (∆ν = 130 Hz) and more shielded
₂
(δ Ϫ9.2) than for the SCN,Cl and Br complexes indicating the
occurrence of equilibria between different types of AgI phos-
phine species. As the solution was cooled the resonance broad-
ened and then at 253 K began to resolve into three set of peaks:
two broad doublets at δ Ϫ0.4 and Ϫ11.2, 1J(Ag᎐P) (average) ca.
380 and 243 Hz, respectively and a very broad resonance at
δ Ϫ6.8. At 223 K these resonances had been replaced by a pair of
doublets centred at δ Ϫ10.8 [1J(Ag᎐P) ca. 249 Hz, Fig. 5(c)] and
a broadened doublet at δ Ϫ4.7 characteristic of [Ag(dppp)2]ϩ.
The 107,109Ag᎐31P couplings were not resolved above the freezing
point of the solvent. No peaks were visible that were assignable
to the ring-opened species [AgI(dppp-P,PЈ)(dppp-P)] but
broadened resonances were observed in the region δ 0 to Ϫ4,
indicative of additional species involved in exchange equilibria.
In an attempt to identify the species present in solution we
recorded 31P NMR spectra of [AgI(dppp-P,PЈ)(dppp-P)] in
CH2Cl2–CD2Cl2 since this allowed spectra to be obtained at
lower temperatures. However, different behaviour was ob-
served in this solvent and at 243 K the spectrum resembled
that of the chloride complex with the two overlapping
doublets characteristic of the [Ag(dppp)2]ϩ cation and add-
itional minor signals with the expected multiplet pattern for
[AgI(dppp-P,PЈ)(dppp-P)] (Table 5). There was a significantly
greater proportion of the ring-opened species (ca. 16% of
the total products, based on peak integrals) compared to the Br
2
2
1418
J. Chem. Soc., Dalton Trans., 1997, Pages 1411–1420

View Article Online
and Ϫ19.6) with an intensity ratio of 3:1; multiplets with the
correct intensity ratio for the second A2BMX spin system are
visible, although partially overlapped with the major PA and
2
PB multiplets. The chemical shifts and coupling constants for
the two A2BMX spin systems are listed in Table 5. Although
1
1
the J(PB᎐Ag) and J(PB᎐Ag) coupling constants of the major
species are slightly larger than estimated from the 31P CP
MAS spectrum of [AgCN(dppp-P,PЈ)(dppp-P)] the chemical
shifts for the three non-equivalent P environments are similar
to those observed in the solid state and it seems reasonable
that each of the species observed in solution is [AgCN-
(dppp-P,PЈ)(dppp-P)] with, however, the substituents on the
dppp ligands frozen into two distinct conformational
structures.
Conclusion
Structural dislocation is observed in complexes of 1:2
AgX :dppp stoichiometry which can be isolated in both cat-
ionic [Ag(dppp)2]X and neutral [AgX(dppp-P,PЈ)(dppp-P)]
forms in the solid state, depending on the anion X. To date,
the neutral form only has been isolated from acetonitrile for
X = Cl, Br, I or CN, whereas for SCNϪ and NO3 the cationic
Ϫ
complex only is isolated. In solution, the two forms exist in an
equilibrium involving displacement of the anion by the unco-
ordinated phosphine ligand. For ClϪ the cationic form is
favoured almost exclusively, consistent with the results of pre-
vious studies1,4 on the related complexes [Ag(dppe)2]NO3 and
[Ag(eppe)2]NO3 which showed that ClϪ does not readily dis-
place P from the Ag co-ordination sphere. For the bromide
complex similar behaviour was observed although the obser-
vation of significant amounts of ring-opened phosphine oxide
complex [AgBr(dppp-P,PЈ)(dpppO-P)] in chloroform solution
highlights the ease of opening of the chelated diphosphine, and
subsequent oxidation, in the presence of the co-ordinating
anion. For X = I, a greater proportion of the neutral complex
exists in solution, consistent with the increased donor strength
of IϪ, and competing dissociative equilibria are also evident in
CDCl3 solutions. For X = CN, the neutral complex is favoured,
with little formation of the cationic complex. Since the anti-
tumour properties of metal diphosphine complexes may be
related to the uptake of lipophilic cations into mitochondria,
studies of this type are of fundamental importance to a mean-
ingful interpretation of structure–activity relationships to
establish whether the bis-chelated cationic species [Ag(dppp)2]ϩ
will be the major species present in vivo for the different com-
plexes of 1:2 AgX :dppp stoichiometry.
Fig. 6 Solution 31P NMR spectra of [AgCN(dppp-P,PЈ)(dppp-P)] (4
mmol dmϪ3) in CH2Cl2–30% CD2Cl2 at 297, 233, 203 and 183 K. The
spectrum at 183 K is assignable as two independent A2BMX spin sys-
tems which may arise from two different conformational structures (I
and II) (see text and Table 5)
and Cl complexes consistent with the greater donor strength of
IϪ.
The 31P NMR solution spectrum of the cyanide complex in
CDCl3 at 297 K was similar to the iodide complex with a single
₁
relatively sharp peak (∆ν = 140 Hz) at δ Ϫ10.3. On cooling to
₂
263 K, this resolved intoa minor broad signal (δ Ϫ5.5) and a
major signal (δ Ϫ11.1). At 233 K the former had resolved into
the typical doublet for [Ag(dppp)2]ϩ (δ Ϫ4.9) and a major very
broad peak (δ Ϫ12.1). With further cooling the latter separated
into three broad resonances (δ Ϫ3, Ϫ11 and Ϫ18) [Fig. 5(d)].
The [Ag(dppp)2]ϩ ion accounted for only ca. 9% of the total
products in solution, based on peak integrals. The temperature-
dependent behaviour is consistent with the equilibrium
(Scheme 1), in which there is little dissociation of the anion, so
that the major species is [AgCN(dppp-P,PЈ)(dppp-P)]. How-
ever, the broadness of the peaks at 223 K is indicative of the
occurrence of an additional equilibrium at low temperature. To
investigate this further we recorded 31P solution spectra of the
complex in CH2Cl2–CD2Cl2 (Fig. 6). The rate of exchange was
slower in this solvent so that at ambient temperature two broad
resonances were observed (δ ca. Ϫ6.3 and Ϫ14.5). On cooling
the low-field resonance resolved into the [Ag(dppp)2]ϩ pair
of doublets with spin–spin couplings fully resolved at 233 K.
This species accounted for ca. 38% of the total products at
273 K, but on cooling the intensity gradually decreased until
the resonance disappeared altogether just below 193 K. The
high-field resonance sharpened initially, then below 273 K
broadened and shifted to high frequency. Below 233 K it began
to resolve into three broad resonances (δ ca. Ϫ3, Ϫ13 and Ϫ19)
and as the solution was cooled further these resolved into dis-
tinct sets of multiplets. Although the spin–spin couplings were
not fully resolved above the freezing point of the solvent the
spectrum at 183 K is interpretable as two distinct (but over-
lapped) A2BMX spin systems. This is seen most clearly for
the PM resonance which shows two distinct singlets (δ Ϫ20.8
Acknowledgements
We acknowledge support of this work by the Australian
Research Council and the Australian National Health and
Medical Research Council (R. Douglas Wright Award to
S. J. B.-P.). We thank Dr. David Rice (Varian, Palo Alto) for
assistance with the two-dimensional CP MAS COSY pulse
sequence.
References
1 S. J. Berners-Price, R. K. Johnson, A. J. Giovenella, L. F. Faucette,
C. K. Mirabelli and P. J. Sadler, J. Inorg. Biochem., 1988, 33, 285.
2 S. J. Berners-Price and P. J. Sadler, Struct. Bonding (Berlin), 1988,
70, 28.
3 S. J. Berners-Price and P. J. Sadler, Coord. Chem. Rev., 1996, 151, 1.
4 S. J. Berners-Price, D. C. Collier, M. A. Mazid, P. J. Sadler, R. E. Sue
and D. Wilkie, Metal-Based Drugs, 1995, 2, 111.
5 P. Di Bernardo, G. Dolcetti, R. Portanova, M. Tolazzi, G. Tomat
and P. Zanonato, Inorg. Chem., 1990, 29, 2859.
6 A. Del Zotto, P. Di Bernardo, M. Tolazzi, G. Tomat and P.
Zanonato, J. Chem. Soc., Dalton Trans., 1993, 3009.
J. Chem. Soc., Dalton Trans., 1997, Pages 1411–1420
1419

View Article Online
7 S. J. Berners-Price, C. Brevard, A. Pagelot and P. J. Sadler, Inorg.
Chem., 1985, 24, 4278.
8 Effendy and A. H. White, unpublished work.
9 S. R. Hall, H. D. Flack and J. M. Stewart, The XTAL 3.2 Reference
Manual, Universities of Western Australia, Geneva and Maryland,
1992.
10 F. J. Blount, D. Camp, R. D. Hart, P. C. Healy, B. W. Skelton and
A. H. White, Aust. J. Chem., 1994, 47, 1631.
11 G. Wu and R. E. Wasylishen, Organometallics, 1992, 11, 3242.
12 C. S. W. Harker and E. R. T. Tiekink, J. Coord. Chem., 1990, 21, 287.
13 C. Franzoni, G. Pelizzi, G. Predieri, P. Tarasconi and C. Pelizzi, Inorg.
Chim. Acta, 1988, 150, 279.
15 J. F. Dobson, B. E. Green, P. C. Healy, C. H. L. Kennard,
C. Pakawatchai and A. H. White, Aust. J. Chem., 1984, 37, 649.
16 P. F. Barron, J. C. Dyason, P. C. Healy, L. M. Engelhardt,
B. W. Skelton and A. H. White, J. Chem. Soc., Dalton Trans., 1986,
1965.
17 L. M. Engelhardt, P. C. Healy, V. A. Patrick and A. H. White, Aust.
J. Chem., 1987, 40, 1873.
18 S. Attar, N. W. Alcock, G. A. Bowmaker, J. S. Frye, W. H. Bearden
and J. H. Nelson, Inorg. Chem., 1991, 30, 4166.
19 G. A. Bowmaker, Effendy, P. J. Harvey, P. C. Healy, B. W. Skelton
and A. H. White, J. Chem. Soc., Dalton Trans., 1996, 2449.
14 M. C. Gimeno, P. G. Jones, A. Laguna and C. Sarroca, J. Chem.
Soc., Dalton Trans., 1995, 1473.
Received 12th November 1996; Paper 6/07692K
1420
J. Chem. Soc., Dalton Trans., 1997, Pages 1411–1420