(Phosphine)silver(I) sulfonate complexes

Article abstract of DOI:10.1515/znb-2003-0126

(Phosphine)silver(I) organosulfonate complexes of the type (R₃P)AgOS(O)₂R' have been prepared in good yields from the corresponding silver sulfonates and tertiary phosphines in dichloromethane solution [R₃ = Ph₃, Ph₂(2-Py), Me₂Ph, with R' = 4-Me-C₆H₄; R = Ph, R' = Et and 2,5-Me₂-C₆H₄]. If ethanol is present in the reaction mixture, the products contain one equivalent of ethanol. The crystal structures of (Ph₃P)AgOS(O)₂(C₆H₄-4-Me)(EtOH) (1), and (Me₂PhP)AgOS(O)₂(C₆H₄-4-Me) (5) have been determined. Complex 1 is present as a dimer in which the monomeric units feature intermolecular Ag-O donor/acceptor bonding in a four-membered ring. The coordination sphere of the silver atoms is further complemented by an ethanol molecule which is also engaged in hydrogen bonding with one of the sulfonate oxygen atoms. The solvent-free complex 5 is associated into helical chains via Ag-O coordinative bonds which provide the silver atoms with a distorted planar T-shaped coordination.

Full text of DOI:10.1515/znb-2003-0126

(Phosphine)silver(I) Sulfonate Complexes
Patric Ro¨mbke, Annette Schier, and Hubert Schmidbaur
Anorganisch-chemisches Institut der Technischen Universita¨t Mu¨nchen,
Lichtenbergstraße 4, 85747 Garching, Germany
Reprint requests to Prof. H. Schmidbaur. E-mail: H.Schmidbaur@lrz.tum.de
Z. Naturforsch. 58b, 168 – 172 (2003); received December 6, 2002
(Phosphine)silver(I) organosulfonate complexes of the type (R3P)AgOS(O)2R’ have been prepared
in good yields from the corresponding silver sulfonates and tertiary phosphines in dichloromethane
solution [R3 = Ph3, Ph2(2-Py), Me2Ph, with R’ = 4-Me-C6H4; R = Ph, R’ = Et and 2,5-Me2-C6H4].
If ethanol is present in the reaction mixture, the products contain one equivalent of ethanol. The
crystal structures of (Ph3P)AgOS(O)2(C6H4-4-Me)(EtOH) (1), and (Me2PhP)AgOS(O)2(C6H4-4-
Me) (5) have been determined. Complex 1 is present as a dimer in which the monomeric units feature
intermolecular Ag-O donor/acceptor bonding in a four-membered ring. The coordination sphere of
the silver atoms is further complemented by an ethanol molecule which is also engaged in hydrogen
bonding with one of the sulfonate oxygen atoms. The solvent-free complex 5 is associated into helical
chains via Ag-O coordinative bonds which provide the silver atoms with a distorted planar T-shaped
coordination.
Key words: Silver Complexes, Sulfonate Complexes, Phosphine Complexes, Ethanol Adduct
Introduction
tered information on the composition and structure of
these compounds, some of which are commercially
available [4 – 12].
(Phosphine)gold(I) alkyl- and arylsulfonate com-
plexes of the type (R3P)Au-OS(O)2R’ recently have
attracted considerable interest owing to their potential
as homogeneous catalysts in alkyne and alkene addi-
tion reactions [1]. Extensive studies have suggested
that the poorly solvated [(R3P)Au]+ units present in
solution as components of dissociation equilibria can
be regarded as the active species. Structural investiga-
tions have shown that in the solid state the complexes
are present as monomers with only weak intermolec-
ular aurophilic interactions depending largely on the
bulk of the phosphine ligands employed [2].
An extension of the studies of the catalytic ac-
tivity to include the corresponding silver(I) com-
plexes revealed that these analogues of the type
(R3P)AgOS(O)2R’ have a strongly reduced efficiency
as catalysts for alkyne addition reactions [3]. This ob-
servation suggested that under comparable experimen-
tal conditions the corresponding dissociation equilib-
ria do not involve significant concentrations of active
[(R3P)Ag]+ species. In order to investigate the struc-
tural chemistry of this type of complexes we have pre-
pared a small series of representative examples and
studied their general properties.
Preparative Results
Silver(I) organosulfonates are readily prepared from
the corresponding organosulfonic acids and silver ox-
ide in water. The compounds are obtained as color-
less precipitates which can be reacted further as a sus-
pension in polar solvents like dichloromethane, chlo-
roform or ethanol, in which they are very sparingly
soluble.
The silver organosulfonates dissolve slowly in a
dichloromethane/ethanol mixed solvent as a tertiary
phosphine is added to the slurry at room temperature.
Colorless solutions are obtained from which the prod-
ucts can be precipitated in satisfactory yield upon ad-
dition of pentane. The products were found to con-
tain tightly bound ethanol which cannot be removed
by washing with excess pentane or diethylether or in a
vacuum at room temperature. According to eq. (1) the
following products have been isolated and character-
ized by analytical and spectroscopic data:
R3P + R’SO3Ag + EtOH → (R3P)AgOS(O)2R’(EtOH) (1)
The literature on silver sulfonates and their com-
plexes generally is very limited and gives only scat-
1: R = Ph, R’ = 4-MeC6H4; 2: R = Ph, R’ = 2,5-Me2C6H4;
3: R = Ph2(2-Py), R’ = 4-MeC6H4
c
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P. Ro¨ mbke et al. · (Phosphine)silver(I) Sulfonate Complexes
169
The same reaction carried out in the absence of
ethanol requires longer reaction times and yields an
alcohol-free product (eqs. 2a, b).
Ph3P + EtSO3Ag → (Ph3P)AgOS(O)2Et
(2a)
4
Me2PhP + 4-Me-C6H4SO3Ag
(2b)
→ (Me2PhP)AgOS(O)2-C6H4-4-Me
5
The complexes are colorless, crystalline solids
which melt with decomposition at temperatures most
of well above 100 ◦C. Decomposition of both the solids
and their solutions is observed upon exposure to in-
candescent light. All compounds gave satisfactory ele-
mental analysis data, and their NMR spectra have con-
firmed the proposed composition. In solution (CD2Cl2)
there appears to be rapid ligand exchange on the NMR
time scale. As demonstrated for compound 2, the 31P-
Fig. 1. Molecular structure of [(Ph3P)AgOS(O)2-p-
Tol(EtOH)]2, (1). The two monomers are related by a cen-
◦
˚
ter of inversion. Selected bond lengths [A] and angles [ ]:
Ag-O1 2.5568(17), Ag-O1A 2.3085(17), Ag-P 2.3483(6),
S-O1 1.4804(17), S-O2 1.449(2), S-O3 1.437(2); P-Ag-
O1 112.83(4), P-Ag-O1’ 146.48(4), O1-Ag-O1’ 78.83(6),
Ag-O1-Ag’ 101.17(6), S-O1-Ag 122.90(10), S-O1-Ag’
112.73(9). Hydrogen bond: O4-H4 0.776, O2-H4 1.949,
O4-O2 2.716, O2-H4-O4 169.18.
◦
107/109Ag coupling is absent at◦25 C but appears as
the samples are cooled to −63 C. The coupling con-
stants determined at the low-temperature limit [J =
466/536 Hz] are in agreement with literature data for
low-coordinate silver atoms.
The mass spectra (FAB) show dinuclear cations of
the general formula [(LAg)2Y]+ as the cations of high-
est mass which indicate association of the complexes
in the solid state (L = tertiary phosphine, Y = R’SO3).
Ligand-bridged dinuclear cations are among the most
common fragments in the mass spectra of LAuY and
LAgY complexes, the halogen-bridgedexamples being
particularly prominent [13]. As expected, the cations
[L2Ag]+ and [LAg]+ are the most abundant species.
Fig. 2. Monomeric unit (Me2PhP)AgOS(O)2-p-Tol, (5),
˚
with atomic numbering. Selected bond lengths [A] and
angles [◦]: Ag1-O1 2.2333(16), Ag1-P1 2.3590(6), S1-O1
1.4719(17), S1-O2 1.4604(17), S1-O3 1.4450(17); P1-Ag1-
O1 157.59(5), Ag1-O1-S1 122.54(9).
Structural Studies
and should therefore not be rated as only a weak solva-
tion. The silver atoms are tetracoordinated with largely
equidistant oxygen and phosphorus donor atoms, but
with strongly distorted X-Ag-Y angles when referred
to a standard tetrahedral geometry. Two of these are
constrained by the chelate rings. The bridgehead oxy-
gen atoms (O1 and O4) are in a pyramidal configura-
tion.
Two representative examples were selected from the
above series of complexes 1 – 5 for structure investiga-
tion.
Compound 1 crystallizes in the triclinic space group
¯
P1 with Z = 2 formula units in the unit cell. The
molecules have been found to be associated into cen-
trosymmetrical dimers as shown in Figure 1. The
core unit is a parallelogram (AgO1)2 – planar by
symmetry – with edges Ag-O1 2.5568(17) / Ag-O1’
The ethanol molecule is engaged in hydrogen bond-
◦
˚
2.3085(17) A and angles O1-Ag-O1‘ 78.83(6) / Ag- ing with one of the two terminal sulfonate oxygen
O1-Ag’ 111.7(6)◦. The silver atoms are further coor- atoms [O4-H4 0.776 A, O4-O2 2.716 A, O4-H4-
˚
˚
dinated by the phosphine [Ag-P 2.3483(6) A] and by O2 169.18◦] and are thus supporting the solvation of
˚
˚
the ethanol molecule [Ag-O4 2.405(2) A]. It should be the dimer. As expected, the remaining of the three
noted that this Ag-O4 distance is intermediate in its sulfonate oxygen atoms O3 is most tightly bound
length between the Ag-O1 / Ag-O1’ distances (above) to the sulfur atom: S-O3 1.437(2) vs. S-O2 (hydro-
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170
P. Ro¨mbke et al. · (Phosphine)silver(I) Sulfonate Complexes
no solvent is accepted in the coordination sphere of the
metal atoms [2b].
For compounds 2 and 3 a similar structure as that
found for 1 is to be proposed.
Crystals of the ethanol-free compound 5 are or-
thorhombic, space group P212121, with Z = 2 for-
mula units in the unit cell. The monomers are aggre-
gated into an unidimensional polymer through inter-
molecular Ag-O coordination. The silver atom of a
monomeric unit (Fig. 2) accepts a dative bond from
one of the two terminal oxygen atoms (O2) of a neigh-
bouring molecule to become three-coordinate in a dis-
torted T-shaped geometry. The distance to the incom-
˚
ing atom O2 is much larger [Ag1-O2’ 2.5283(7) A]
than the internal distance of the monomer [Ag1-O1
˚
2.2333(16) A], making this difference larger than ob-
served for complex 1 above (Figs 3a,b).
The large angle of the P1-Ag1-O1 unit [157.59(5) ◦]
(the horizontal bar of the T) shows that the bending
away from linearity induced by the incoming O2 is
not very pronounced. With the remaining angles O1-
Ag1-O2’ at 82.32(6)◦ and P1-Ag1-O2’ at 116.48(4)◦
the sum of the angles of 356.4◦ indicates only a small
deviation of the T from planarity.
In the absence of ethanol the silver atom in com-
plex 5 thus clearly adopts the standard trigonal planar
configuration while in the ethanol adduct 1 the silver
atoms become tetrahedrally tetracoordinate.
The chain of molecules present in the crystals of
compound 5 is helical. Fig. 3a shows a projection
parallel to the helical axis. As judged from the dis-
tances and orientations of the substituents there is no
significant π-stacking or phenyl / tolyl embracing in
the structure which could influence the packing of the
molecules.
Fig. 3. Projections parallel (top, along a-axis) and per-
pendicular to (bottom, along c-axis) a helical chain of
molecules (Me2PhP)AgOS(O)2-p-Tol, 5, in the crystal as-
˚
sociated via Ag-O2’ contacts. Ag-O2’ 2.5283(17) A; O1-
Ag-O2’ 82.32(6), P-Ag-O2’ 116.48(4)◦.
Conclusions
gen bonded) 1.449(2) and S-O1(silver coordinated)
1.4804(17) A.
The results of the present study show very clearly
the fundamental differences in the coordination chem-
istry of silver and gold. The structural chemistry of the
organosulfonate complexes is an example where these
variations become immediately obvious.
The gold compounds appear as monomers or
loosely aggregated oligomers in which weak, but sig-
nificant aurophilic bonding is determining the associ-
ation of the molecules. The linear two-coordination of
the metal atoms is largely retained.
˚
The structure of complex 1 is remarkable for two
reasons. The mode of dimerization reflects the high ac-
ceptor character of the silver atoms in these sulfonate
complexes which leads not only to strong binding of
an extra oxygen atom of a neighbouring molecule but
also to a fixation of an ethanol molecule. For the corre-
sponding gold complexes no such acceptor properties
regarding oxygen donors are discernible. In crystals of
(Ph3P)Au-OS(O)2-C6H4-4-Me the monomers are only
By contrast, the silver compounds feature standard
weakly associated via aurophilic contacts (Au–Au) and intermolecular donor-acceptor interactions which lead
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P. Ro¨ mbke et al. · (Phosphine)silver(I) Sulfonate Complexes
171
to an increase in the coordination number beyond two.
In the absence of additional, external donor ligands
the silver atoms are found three-coordinate, but there
is still acceptor capacity to accommodate other lig-
ands. Ethanol was found to be a suitable component
which is not only accepted as an oxygen donor, but
also as a partner for chelating hydrogen bonding. The
observations made with the gold and silver sulfonate
complexes have parallels in the chemistry of phos-
phate/phosphonate [14] as well as of carboxylate com-
pounds [15], where oxygen donor and hydrogen bond-
ing capacities are also available.
The low catalytic reactivity of LAgX as compared
to LAuX complexes, e.g. in the addition of alcohols
or water to alkynes, is readily explained by the much
stronger ligand binding at the silver atoms. The pro-
posed active [LAg]+ species are therefore much less
abundant in the corresponding dissociation equilibria
than the [LAu]+ species [1,2]. High [LAg]+ activity
is to be expected only in cases with counterions X−
devoid of any donor capacity and in the complete ab-
sence of donor solvent molecules. The corresponding
m/z 910 (5.4%), [(Ph3P)2Ag2SO3C6H4Me]+; 631 (16.3)
[(Ph3P)2Ag]+; 369 (100) [Ph3PAg]+; 262 (26.4) [Ph3P]+.
C27H28AgO4PS (587.40): calcd. C 55.2, H 4.8, S 5.5; found
C 55.4, H 4.6, S 5.7.
(Triphenylphosphine)silver(I) 2,5-dimethylphenylsulfonate
(ethanol) (2)
As described for 1, 2,5-Me2C6H4SO3Ag (200 mg,
0.61 mmol) was treated with Ph3P (160 mg, 0.61 mmol)
to give 330 mg of colorless, microcrystalline product (92%
yield), m.p. 131 ◦C with decomposition. NMR (CD2Cl2,
1
20 ◦C), 31P{ H}: 11.3, s; 9.45, d [J(Ag/P) 466 and 536 Hz]
◦
at −63 C;. 1H: 7.00-7.77, m, 18 H, Ph and C6H3; 3.59,
q, 2 H, J = 7.3 Hz, CH2; 2.50 and 2.12, s, 3 H each,
1
Me(xylene); 1.11, t, 3 H, Me. 13C{ H}: 135.1, 133.6, 131.5,
130.7 for xylene; 134.3 (d, J = 10.4), 131.1 (d, J = 84.0),
129.4 (d, J = 5.2 Hz), 128.3 (s) for Ph; 54.3 and 18.7 for
EtOH; 20.95 and 20.3 for Me(xylene). MS(FAB): 631 (100)
[(Ph3P)2Ag]+; 369 (91.5) [Ph3PAg]+; 262 (20.2) [Ph3P]+.
C28H29AgO4PS (600.42): calcd. C 56.0, H 4.9, S 5.3; found
C 56.1, H 4.7, S 5.4.
[Diphenyl(2-pyridyl)phosphine]silver(I) p-toluenesulfonate
gold systems are much less sensitive to the nature of (ethanol) (3)
X− and of the solvent owing to the strongly reduced
acceptor properties of the metal atom.
As described for 1, 4-MeC6H4SO3Ag (200 mg,
0.72 mmol) was reacted with Ph2(2-Py)P (190 mg,
0.72 mmol) to give 360 mg of colorless microcrystalline
product (92%◦yield), m. p. 126 ◦C with decomposition. NMR
Experimental Section
1
(CD2Cl2, 20 C), 31P{ H}: 16.5, s; 1H: 9.26 and 7.98, m,
The silver(I) organosulfonates were prepared following
literature procedures [16]. All other reagents were commer-
cially available. The reactions were routinely carried out in
an atmosphere of dry and pure nitrogen in standard equip-
ment. Solvents were purified, dried and saturated with ni-
trogen. Glassware was oven-dried and filled with nitrogen.
Reaction vessels were protected against incandescent light.
1 H each, 6.89-7.65, m, 16 H, aryl; 2.24, s, Me; 3.52, q, 2 H,
and 1.04, t, 3 H, J = 7.7 Hz for EtOH. MS (FAB): 913 (5.6)
[Ph2(2-Py)PAg]2SO3C6H4Me+; 633 (23.3) [L2Ag]+, 370
(100) [LAg]+, 263 (3.4) [L]+. C26H27AgNO4PS (588.39):
calcd. C 53.1, H 4.6, N 2.4, S 5.4; found C 53.7, H 4.4, N 2.3,
S 5.4.
(Triphenylphosphine)silver(I) ethylsulfonate (4)
(Triphenylphosphine)silver(I) p-toluenesulfonate
(ethanol) (1)
As described for 1, EtSO3Ag (220 mg, 1.01 mmol) was
treated with Ph3P (265 mg, 1.01 mmol) in dichloromethane
(10 ml) to give 440 mg of colorless, microcrystalline
product (90% yield◦), m.p. 109 ◦C with decomposition.
m, 15 H, Ph; 2.96, q, 2 H, and 1.21, t, 3 H, J =
7.9 Hz, Et. MS (FAB): 848 (8.7) [(Ph3P)2Ag2SO3Et]+;
631 (3.4) [(Ph3P)2Ag]+; 369 (100) [(Ph3P)Ag]+; 262 (12.3)
[Ph3P)]+. C20H20AgO3PS (479.29): calcd. C 50.1, H 4.2,
S 6.7; found C 49.7, H 4.3, S 6.6.
4-MeC6H4SO3Ag (290 mg, 1.04 mmol) was suspended
in a mixture of dichloromethane and ethanol (10 ml each)
at room temperature and treated with Ph3P (270 mg,
1.04 mmol) for 2 h with stirring to give an almost clear
colorless solution. Small amounts of residue were filtered
off and the volume of the filtrate was reduced to a few ml.
The product was precipitated by addition of n-pentane, fil-
tered, washed with n-pentane and diethylether, and dried in
a vacuum (430 mg, 76% yield, m.p. 124 ◦C with decomposi-
tion). Single crystals can be grown from n-pentane/ethanol
1
NMR (CD2Cl2, 20 C), 31P{ H}: 16.0, s. 1H: 6.96-7.89,
(Dimethylphenylphosphine)silver(I) p-toluenesulfonate (5)
As described for 1, 4-MeC6H4SO3Ag (160 mg,
◦
◦
1
at −30 C. NMR (CDCl3, 20 C), 31P{ H}: 14.2, s. 1H:
6.87-7.96, m, 19 H, Ph and C6H4; 3.55, q, 2 H, J = 7.4 Hz,
CH2; 2.14, s, 3 H, 4-Me; 1.16, t, 3H, Me. MS(FAB): 0.57 mmol) was reacted with Me2PhP (80 mg, 0.57 mmol)
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172
P. Ro¨mbke et al. · (Phosphine)silver(I) Sulfonate Complexes
in dichloromethane (20 ml). Evaporation of the solvent
Crystal data for C27H28AgO4PS (1): M = 587.39, tri-
˚
from the filtrate left a colorless resinous residue which clinic, a = 10.8837(2), b = 11.0192(2), c = 11.7906(3) A,
could be crystallized from dichloromethane/pentane [1:1] α = 94.890(1), β = 109.465(1), γ = 90.329(1)◦, space
at −30 ◦C to give 190 mg of product (79% yield), m.p. group P1, Z = 2, V = 1327.49(5) A , µ(Mo-Kα ) =
3
¯
˚
1
87 ◦C with decomposition. NMR (CD2Cl2, 20 ◦C), 31P{ H}: 9.28 cm−1, 42437 measured and 5534 unique reflections
−20.2, s. 1H: 7.16-7.73, m, 9 H, Ph and C6H4; 2.35, [Rint = 0.043], wR2 = 0.0742, R = 0.0322 for 5534 reflec-
1
s, 3 H, Me; 1.66, d, 6 H, J = 8.9 Hz, Me2. 13C{ H}: tions [I ≥ 2σ(I)] and 311 parameters.
140.7, 131.6, 128.9, 126.1 (all for p-tolyl). 134.1, d, J =
Crystal data for C15H18AgO3PS (5): M = 417.19,
51; 131.4, d, J = 14.1; 130.6, d, J = 4.1 Hz; 128.5, s; orthorhombic, a = 6.0429(1), b = 13.9308(3), c =
˚
(all for Ph). 21.2, s, 3 H, Me; 14.3, d, J = 21 Hz, Me2. 18.8836(3) A, space group P212121, Z = 4, V =
3
MS (FAB): 663 (2.9) [L2Ag2SO3C6H4Me]+; 417 (2.0) 1589.67(5) A , µ(Mo-Kα ) = 15.06 cm−1, 30910 measured
˚
[M]+; 383 (26.1) [L2Ag]+; 245 (100) [LAg]+; 138 (8.8) and 3692 unique reflections [Rint = 0.031], wR2 = 0.0590,
[L]+. C15H18AgO3PS (417.19): calcd. C 43.2, H 4.4; found R = 0.0225 for 3692 reflections [I ≥ 2σ(I)] and 190 param-
C 42.9, H 4.4.
eters; absolute structure parameter: 0.007(18). – The func-
tion minimized was wR2 = Σ[w(Fo2 − Fc2)2]/Σ[w(Fo2)2]1/2
;
Crystal structure determination
w = 1/[σ2(Fo2)+(ap)2 +bp]; p = (Fo2 +2Fc2)/3; a = 0.0221
(1), 0.0289 (5); b = 1.34 (1), 0.54 (5).
The crystalline samples were placed in inert oil, mounted
on a glass pin, and transferred to the cold gas stream of
the diffractometer. Crystal data were collected and integrated
using a Nonius DIP2020 system with ◦monochromated Mo-
Displacement parameters and complete tables of inter-
atomic distances and angles have been deposited with the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK. The data are available on request
on quoting CCDC-199148 (1), 199149 (5).
˚
Kα(λ = 0.71073 A) radiation at −130 C. The structure was
solved by direct methods using SHELXS-97 and refined by
full matrix least-squares calculations on F2 (SHELXL-97).
Non-hydrogen atoms were refined with anisotropic displace-
ment parameters. All hydrogen atoms, except for the O-H
atom of the solvent ethanol in compound 1 which was lo-
cated and refined isotropically, were placed in idealized po-
sitions and refined using a riding model with fixed isotropic
contributions.
Acknowledgement
This work was supported by Deutsche Forschungsge-
meinschaft, Fonds der Chemischen Industrie, Volkswagen-
stiftung, and Heraeus GmbH.
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