Direct Ag-Pt2 Interactions in Pentafluorophenyl A-Frame Complexes Containing Halide or OH- and Bis(diphenylphosphino)methane (dppm) as Bridging Ligands. Crystal Structures of [(C6F5)2Pt(μ-OH)(μ-dppm)A

Article abstract of DOI:10.1021/ic9605332

Complexes [NBu₄][(C₆F₅) ₂Pt(μ-X)(μ-dppm)Pt(C₆F₅)₂] (X = Cl, Br) react with AgClO₄ and [Ag(OClO₃)L] (L = PPh₃, SC₄H₈), yield

Full text of DOI:10.1021/ic9605332

Inorg. Chem. 1996, 35, 7867-7872
7867
Direct Ag-Pt2 Interactions in Pentafluorophenyl A-Frame Complexes Containing Halide or
OH- and Bis(diphenylphosphino)methane (dppm) as Bridging Ligands. Crystal Structures
of [(C6F5)2Pt(µ-OH)(µ-dppm){Ag(PPh3)}Pt(C6F5)2]‚C7H8 and
[(C6F5)2Pt(µ-SC4H8)(µ-dppm)Pt(C6F5)2]‚1/2C6H14
Jose´ Mar´ıa Casas, Larry R. Falvello, Juan Fornie´s,* and Antonio Mart´ın
Departamento de Qu´ımica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n,
Universidad de ZaragozasCSIC, Facultad de Ciencias, E-50009 Zaragoza, Spain
ReceiVed May 16, 1996X
Complexes [NBu4][(C6F5)2Pt(µ-X)(µ-dppm)Pt(C6F5)2] (X ) Cl, Br) react with AgClO4 and [Ag(OClO3)L] (L )
PPh3, SC4H8), yielding different compounds depending on the silver reagent used. The reactions with AgClO4
in wet solvents lead to the syntheses of the complexes [(C6F5)2Pt(µ-X)(µ-dppm){Ag(H2O)}Pt(C6F5)2] [X ) Cl
(1), Br (2)] in which the existence of two Pt-Ag bonds is postulated. The reactions with [Ag(OClO3)(PPh3)]
give similar complexes [(C6F5)2Pt(µ-X)(µ-dppm){Ag(PPh3)}Pt(C6F5)2] [X ) Cl (3), Br (4)]. The presence of
silver coordinated to the platinum atoms activates the substitution of the halogen bridge; thus, 3 reacts with
water, yielding the complex [(C6F5)2Pt(µ-OH)(µ-dppm){Ag(PPh3)}Pt(C6F5)2] (5). Complex 5 can be prepared
as well by reaction of [NBu4][(C6F5)2Pt(µ-OH)(µ-dppm)Pt(C6F5)2] (6) with [Ag(OClO3)(PPh3)]. Nevertheless,
the reaction of [NBu4][(C6F5)2Pt(µ-Cl)(µ-dppm)Pt(C6F5)2] with the complex [Ag(OClO3)(SC4H8)] does not render
the analogous complex to 3, but AgCl precipitates and [(C6F5)2Pt(µ-SC4H8)(µ-dppm)Pt(C6F5)2] (7) is formed.
This different behavior depending on the ligand present in the silver complex is probably due to the ability of the
tetrahydrothiophene ligand to act as a bridge. Single-crystal X-ray studies of 5 and 7 have been carried out. For
5, the existence of two Pt-Ag bonds with distances 2.791(1) and 2.832(1) Å has been confirmed. Complex 7
shows a distorted six-membered ring skeleton formed by the metal atoms, dppm ligand, and sulfur atom of the
SC4H8 group. Compound 5‚C7H8 (C74H46AgF20OP3Pt2) crystallizes in the monoclinic system, space group P21/
n: a ) 14.360(1) Å, b ) 21.590(1) Å, c ) 21.585(2) Å, â ) 90.85(1)°, V ) 6691.3(8) Å3, Z ) 4. Compound
7‚1/2C6H14 (C56H37F20P2Pt2S) crystallizes in the monoclinic system, space group P21/n: a ) 22.258(6) Å, b )
11.351(3) Å, c ) 22.268(5) Å, â ) 106.21(3)°, V ) 5402.6(16) Å3, Z ) 4.
Introduction
(dppm ) Ph2PCH2PPh2) and a halide ligand.3 This is not a
common situation since most of the complexes containing dppm
acting as an exodidentate ligand are formed by two metal centers
which are joined by two dppm ligands; and in many cases
metal-metal bonds are present as well.4 In addition, dinuclear
derivatives with such different ligands bridging the metal centers
at the same time are also rather unusual.4
These dinuclear systems (A-C) are inert toward Lewis bases
such as X-, NCMe, SC4H8, and PPh3, which are not even able
to produce the cleavage of the Pt(µ-X)Pt bridging system.
The X-ray structure of the iodo derivative (C) indicates that
the large space requirements of the phenyl rings of the dppm
ligand and the pentafluorophenyl rings seem to produce steric
overcrowding, which results in long Pt‚‚‚Pt distances [4.446(1)
Å]3 and probably in the lack of reactivity due to the difficulties
of the reactants (Lewis bases in all cases) in reaching the Pt-
(µ-X)(µ-dppm)Pt bridging system.
All these facts prompted us to study the reactivity of this
type of complex toward Lewis acids such as AgClO4 or [Ag-
(OClO3)(L)] (L ) PPh3, SC4H8) in order to explore the ability
Anionic perhalophenyl platinate complexes act as Lewis bases
toward metal (M) complexes or metal salts forming polynuclear
derivatives with donor-acceptor PtfM bonds.1 When the
platinate substrates are dinuclear in character, their reactions
with silver salts usually render trinuclear complexes with two
PtfAg bonds and in which the platinate substrate acts as a
didentate chelating ligand.2 The resulting trinuclear complexes
are rather stable, and not only do the PtfAg bonds seem to be
preserved in solutions of donor solvents but in some cases the
complexes react with neutral ligands producing displacement
reactions at the silver center without cleavage of the PtfAg
bonds. For instance, [NBu4][(µ-C6F5)2(C6F5)4Pt2Ag(OEt2)]
reacts with ligands L, yielding [NBu4][(µ-C6F5)2(C6F5)4Pt2Ag-
(L)] [L ) PPh3, SC4H8 (tetrahydrothiophene), C6H11CN].2b
However, there are few such dinuclear platinate substrates, and
hence this type of trinuclear complex with chelating platinate
ligands is rather scarce as well.
In the course of our current research, we have recently
described the syntheses and structural characterization of the
anionic dinuclear platinum(II) complexes {[NBu4][(C6F5)2Pt-
(µ-X)(µ-dppm)Pt(C6F5)2] [X ) Cl (A), Br (B), I (C)]} with two
very different bridging ligands: bis(diphenylphosphino)methane
(3) Casas, J. M.; Falvello, L. R.; Fornie´s, J.; Mart´ın, A.; Toma´s. M. J.
Chem. Soc., Dalton Trans. 1993, 1107.
(4) Puddephat, R. J. Chem. Soc. ReV. 1983, 12, 99 and references cited
therein. Puddephat, R. J.; Thomson, M. A. J. Organomet. Chem. 1982,
238, 231. Langride, C. R.; McEwan, D. M.; Pringle, P. G.; Shaw, B.
L. J. Chem. Soc., Dalton Trans. 1983, 2487. Langride, C. R.; Pringle,
P. G.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1985, 1015. Uso´n,
R.; Fornie´s, J.; Espinet, P.; Fortun˜o, C. J. Chem. Soc., Dalton Trans.
1986, 1849. Fornie´s, J.; Mart´ınez, F.; Navarro, R.; Redondo, A.;
Toma´s, M.; Welch, A. J. J. Organomet. Chem. 1986, 316, 351. Uso´n,
R.; Fornie´s, J.; Espinet, P.; Navarro, R.; Fortun˜o, C. J. Chem. Soc.,
Dalton Trans. 1987, 2077.
X Abstract published in AdVance ACS Abstracts, November 15, 1996.
(1) Uso´n, R.; Fornie´s, J. Inorg. Chim. Acta 1992, 198-200, 165 and
references cited therein.
(2) (a) Uso´n, R.; Fornie´s, J.; Toma´s, M.; Casas, J. M.; Cotton, F. A.;
Falvello, L. R. Inorg. Chem. 1987, 26, 3482. (b) Uso´n, R.; Fornie´s,
J.; Toma´s, M.; Casas, J. M.; Cotton, F. A.; Falvello, L. R.; Llusar, R.
Organometallics 1988, 7, 2279. (c) Casas, J. M.; Fornie´s, J.; Mart´ın,
A.; Menjo´n, B.; Toma´s, M. Polyhedron 1996, 15, 3599.
S0020-1669(96)00533-2 CCC: $12.00 © 1996 American Chemical Society

7868 Inorganic Chemistry, Vol. 35, No. 26, 1996
Casas et al.
Anal. Found (calcd) for [(C6F5)2Pt(µ-Cl)(µ-dppm){Ag(PPh3)}Pt-
(C6F5)2] (3): C, 43.22 (43.54); H, 2.39 (2.02). IR data (cm-1): C6F5
X-sensitive7 809(s), 787(s), C6F5 others 1635(m), 1606(m), 1502(vs),
1060(vs), 960(m); dppm 1099(m), 741(m), 693(m), 522(m), 510(m),
490(m); ν(Pt-Cl) 313(w); PPh3 absorptions not assigned due to overlap
with those of dppm.
Anal. Found (calcd) for [(C6F5)2Pt(µ-Br)(µ-dppm){Ag(PPh3)}Pt-
(C6F5)2] (4): C, 42.38 (42.51); H, 2.11 (1.97). IR data (cm-1): C6F5
X-sensitive7 808(s), 789(s), C6F5 others 1638(m), 1608(m), 1503(vs),
1061(vs), 960(m); dppm 1099(m), 741(m), 693(m), 522(s), 510(m),
489(m); PPh3 absorptions not assigned due to overlap with those of
dppm.
Anal. Found (calcd) for [(C6F5)2Pt(µ-OH)(µ-dppm){Ag(PPh3)}Pt-
(C6F5)2] (5): C, 43.65 (43.98); H, 2.08 (2.09). IR data (cm-1): C6F5
X-sensitive7 806(s), 785(s), C6F5 others 1638(m), 1608(m), 1505(vs),
1062(vs), 960(m); dppm 1100(m), 693(m), 522(m), 491(m); ν(O-H)
3609(m); PPh3 absorptions not assigned due to overlap with those of
dppm.
Preparation of Crystals of 5. Suitable crystals for X-ray purposes
were obtained by slow evaporation of a solution of 5 in CH2Cl2 in a
toluene atmosphere.
Synthesis of [NBu4][(C6F5)2Pt(µ-OH)(µ-dppm)Pt(C6F5)2] (6). To
a solution of 0.15 g (0.09 mmol) of [NBu4][(C6F5)2Pt(µ-Br)(µ-dppm)-
Pt(C6F5)2] in a mixture of 30 mL of MeOH and 10 mL of H2O, was
added KOH in excess, and the mixture was refluxed for about 24 h.
The suspension was concentrated to ca. 10 mL, and the solid precipitate
was filtered off. The resulting solid was washed with 3 mL of iPrOH
and treated with n-hexane, yielding 6, 78% yield.
Anal. Found (calcd) for 6: C, 45.90 (45.86); H, 3.37 (3.49); N,
0.93 (0.82). IR data (cm-1): C6F5 X-sensitive7 809(s), 787(s), C6F5
others 1638(m), 1608(m), 1499(vs), 1058(vs), 956(vs); dppm 1101(s),
772(m), 743(s), 691(m), 678(w), 530(m), 495(m), 482(m); ν(O-H)
3621(m); NBu4+ 884(m).
Synthesis of [(C6F5)2Pt(µ-SC4H8)(µ-dppm)Pt(C6F5)2], (7). Method
A. To a solution of 0.300 g (0.174 mmol) of [NBu4][(C6F5)2Pt(µ-Cl)-
(µ-dppm)Pt(C6F5)2] in CH2Cl2 (30 mL) was added 0.052 g (0.174 mmol)
of [Ag(OClO3)(SC4H8)], and the mixture was stirred at room temper-
ature for 24 h. The solvent was evaporated to dryness, and the residue
was extracted with diethyl ether. The insoluble AgCl and NBu4ClO4
were filtered off, and after the solution was evaporated to dryness, the
residue was treated with n-hexane, giving complex 7 in 79% yield.
Method B. To a solution of 0.214 g (0.124 mmol) of [NBu4][(C6F5)2-
Pt(µ-Cl)(µ-dppm)Pt(C6F5)2] in CH2Cl2 (30 mL) were added 11.0 µL
(0.124 mmol) of SC4H8 and 0.026 g (0.124 mmol) of AgClO4, and the
mixture was stirred at room temperature for 24 h. The solvent was
evaporated to dryness, and the residue was extracted with diethyl ether.
The insoluble AgCl and NBu4ClO4 were filtered off, and after the
solution was evaporated to dryness, the residue was treated with
n-hexane, giving complex 7 in 74% yield.
Method C. To a solution of 0.250 g (0.158 mmol) of 2 in CH2Cl2
(30 mL) was added 13.9 µL (0.158 mmol) of SC4H8, and the mixture
was stirred at room temperature for 30 min. The insoluble AgCl was
filtered off, the resulting solution was evaporated to dryness, and the
residue was treated with n-hexane, giving complex 7 in 60% yield.
Anal. Found (calcd): C, 41.34 (41.58); H, 1.88 (1.98). IR data
(cm-1) C6F5 X-sensitive7 806(s), 791(s), C6F5 others 1636(m), 1608(m),
1507(m), 1062(vs), 964(vs); dppm 1103(m), 751(m), 733(sh), 691(m),
525(m), 513(m), 484(m), 444(m), 377(m); SC4H8 1201(m), 888(w).
Preparation of Crystals of 7. Suitable crystals for X-ray purposes
were obtained by slow diffusion of n-hexane into a solution of 7 in
CH2Cl2.
of these asymmetric dinuclear platinum complexes to act as
didentate metallo ligands. Such reactions result in the formation
of the corresponding trinuclear Pt2Ag complexes which are more
reactive than the dinuclear platinum starting materials.
Experimental Section
The C, H, and N analyses and conductance measurements were
performed as described elsewhere.3 Infrared spectra (4000-200 cm-1
)
were recorded from Nujol mulls between polyethylene sheets on a
Perkin Elmer 833 or 1710 FTIR spectrophotometer. NMR measure-
ments were done on either a Varian XL200 or a Unity 300 spectrometer.
[NBu4]2[(C6F5)2XPt(µ-dppm)PtX(C6F5)2], [NBu4][(C6F5)2Pt(µ-X)(µ-
dppm)Pt(C6F5)2] (X ) Cl, Br),3 [Ag(OClO3)(PPh3)],5 and [Ag(OClO3)-
(SC4H8)]6 were prepared as described elsewhere. All the reactions
involving silver reagents were carried out under exclusion of light.
Safety Note. Perchlorate salts with organic ligands are potentially
explosive. Only small amounts of material should be prepared, and
these should be handled with great caution.
Syntheses of [(C6F5)2Pt(µ-X)(µ-dppm){Ag(H2O)}Pt(C6F5)2] (X )
Cl (1), Br (2)]. Method A. To a solution of [NBu4][(C6F5)2Pt(µ-X)-
(µ-dppm)Pt(C6F5)2] (X ) Cl, 0.80 g, 0.47 mmol; Br, 0.80 g, 0.45 mmol)
in CH2Cl2 (30 mL) was added an equimolar amount of AgClO4, and
the mixture was stirred at room temperature for 14 h. The solution
was evaporated to dryness, and the residue was extracted with diethyl
ether. The insoluble NBu4ClO4 was filtered off, and after the solution
was evaporated to dryness, the residue was treated with n-hexane,
rendering complexes 1 and 2 (yields: 90 and 71%, respectively).
Method B. To a solution of [NBu4]2[(C6F5)2XPt(µ-dppm)PtX-
(C6F5)2] (X ) Cl, 1.00 g, 0.50 mmol; Br, 0.400 g, 0.192 mmol) in
tetrahydrofuran (30 mL) was added AgClO4 in 1:2 molar ratio, and
the mixture was stirred at room temperature for 45 min. The solvent
was evaporated to dryness, and the residue was extracted with diethyl
ether. The insoluble AgX and NBu4ClO4 were filtered off, and after
the solution was evaporated to dryness, the residue was treated with
n-hexane, rendering complexes 1 and 2 (yields: 72 and 67%,
respectively).
Anal. Found (calcd) for [(C6F5)2Pt(µ-Cl)(µ-dppm){Ag(H2O)}Pt-
(C6F5)2] (1): C, 36.98 (36.69); H, 1.93 (1.51). IR data (cm-1): C6F5
X-sensitive7 808(s), 790(s). C6F5 others 1638(m), 1611(m), 1506(vs),
1060(vs), 959(vs); dppm 1100(m), 768(m), 740(m), 690(m), 623(w),
572(m), 482(m); ν(Pt-Cl) 315(d); H2O ν(O-H) 3676(m), 3610(m).
Anal. Found (calcd) for [(C6F5)2Pt(µ-Br)(µ-dppm){Ag(H2O)}Pt-
(C6F5)2] (2) C, 36.08 (35.70); H, 1.26 (1.47). IR data (cm-1): C6F5
X-sensitive7 807(s), 786(s), C6F5 others 1636(m), 1609(m), 1507(m),
1061(vs), 958(m); dppm: 1101(m), 769(sh), 691(m), 525(m), 487(m);
H2O 3605(m, br).
Syntheses of [(C6F5)2Pt(µ-X)(µ-dppm){Ag(PPh3)}Pt(C6F5)2], (X
) Cl (3), Br (4), OH (5)]. To a solution of [NBu4][(C6F5)2Pt(µ-X)-
(µ-dppm)Pt(C6F5)2] (X ) Cl, 0.216 g, 0.126 mmol; Br, 0.100 g, 0.057
mmol; OH (see below), 0.150 g, 0.088 mmol) in CH2Cl2 (30 mL) was
added an equimolar amount of [Ag(OClO3)(PPh3)], and the mixture
was stirred at room temperature for 5 min. The solution was evaporated
to dryness, and the residue was extracted with diethyl ether. The
insoluble NBu4ClO4 was filtered off, and after the solution was
evaporated to dryness, the residue was treated with n-hexane, rendering
complexes 3-5 (yields: 75, 70, and 65% respectively).
Complex 3 was also prepared as follows: To a solution of 0.200 g
(0.126 mmol) of 2 in CH2Cl2 (30 mL) was added 0.033 g (0.126 mmol)
of PPh3, and the mixture was stirred at room temperature for 5 min.
The solution was evaporated to dryness, and the residue was treated
with n-hexane, rendering complex 3 in 73% yield.
Complex 5 can also be prepared as follows: To a solution of 3 in
30 mL of CH2Cl2 is added 1 mL of water. The mixture is stirred for
48 h, and then the CH2Cl2 is removed by evaporation. The remaining
solid is filtered off and identified as 5 (80% yield).
Crystal Structure Determination of Compound 5‚C7H8. Relevant
crystal information is listed in Table 1. A crystal of 5‚C7H8 was
mounted at the end of a glass fiber and held in place with epoxy glue.
Crystallographic data were collected on an Enraf-Nonius CAD4
diffractometer. Cell constants were refined from 2θ values of 25
reflections (24.1 < 2θ < 31.9°). An absorption correction based on
540 Ψ scans was applied; transmission coefficients were in the range
0.815-0.668. Three standard reflections were measured every 160 min,
and they showed no decay. The structure was solved by Patterson
methods and refined against F2 using the program SHELXL-93.8 All
non-hydrogen atoms, except for the disordered carbon atoms, were
(5) Cotton, F. A.; Falvello, L. R.; Uso´n, R.; Fornie´s, J.; Toma´s, M.; Casas,
J. M.; Ara, I. Inorg. Chem. 1987, 26, 1366.
(6) Uso´n, R.; Fornie´s, J.; Toma´s, M.; Ara, I.; Casas, J. M.; Mart´ın, A. J.
Chem. Soc., Dalton Trans. 1991, 2253.
(7) Maslowski, E., Jr. Vibrational Spectra of Organometallic Compounds;
Wiley, New York, 1977; p 437.

Ag-Pt2 Interactions in Pentafluorophenyl Complexes
Inorganic Chemistry, Vol. 35, No. 26, 1996 7869
Table 1. Crystallographic Dataa for [(C6F5)2Pt(µ-OH)(µ-dppm){Ag(PPh3)}Pt(C6F5)2]‚C7H8 (5‚C7H8) and
[(C6F5)2Pt(µ-SC4H8)(µ-dppm)Pt(C6F5)2]‚1/2C6H14 (7‚1/2C6H14)
compd
5‚C7H8
7‚1/2C6H14
empirical formula
formula wt
temp (K)
space group
unit cell dimens a (Å)
b (Å)
C74H46AgF20OP3Pt2
C56H37F20P2Pt2S
1922.07
150(1)
P21/n
14.360(1)
1574.04
200(1)
P21/n
22.258(6)
21.590(1)
11.351(3)
c (Å)
21.585(2)
90.85(1)
6691.3(8)
22.268(5)
106.21(3)
5402.6(16)
â (deg)
V (Å3)
Z
F
4
4
calc (Mg/m3)
1.908
4.635
1.935
5.379
abs coeff (mm-1
)
final R indices [I > 2σ(I)]b
R indices (all data)
R1 ) 0.0546, wR2 ) 0.0846
R1 ) 0.1190, wR2 ) 0.1032
R1 ) 0.0444, wR2 ) 0.1030
R1 ) 0.0761, wR2 ) 0.1174
2
2
a Wavelength for both compounds: 0.710 73 Å. b R1 ) Σ||Fo| - |Fc|| /Σ|Fo|; wR2 ) [Σ[w(Fo - Fc2)2/Σ[w(Fo )2]1/2
.
Scheme 1a
assigned anisotropic displacement parameters and refined without
positional constraints. All hydrogen atoms, except the hydroxy
hydrogen atom, were constrained to idealized geometries and assigned
a common refined isotropic displacement parameter. Two phenyl rings
of the triphenylphosphine ligand were disordered over two sets of
positions and were refined with partial occupancy of 0.5/0.5 [C(50)]
and 0.7/0.3 [C(62)]; and their geometry was constrained to regular
hexagons. Full-matrix least-squares refinement of this model converged
to final residual indices listed in Table 1. Final difference electron
density maps showed no features above 1 e/Å3, with the largest peaks
lying closer than 1.1 Å to the platinum atoms.
Crystal Structure Determination of Compound 7‚C6H14. Rel-
evant crystal information is listed in Table 1. A crystal of 7‚C6H14
was mounted at the end of a glass fiber and held in place with epoxy
glue. Crystallographic data were collected on a four-circle Siemens
STOE/AED2 diffractometer. Cell constants were refined from 2θ
values of 48 reflections, including Friedel pairs (21.4° < 2θ < 33.4°).
An absorption correction based on 504 Ψ scans was applied, transmis-
sion coefficients were in the range 0.678-0.432. Three standard
reflections were measured every 120 min, and they showed no decay.
The structure was solved by Patterson methods and refined against F2
using the program SHELXL-93.8 All non-hydrogen atoms, except for
the solvent atoms, were assigned anisotropic displacement parameters
and refined without positional constraints. All hydrogen atoms were
constrained to idealized geometries and assigned isotropic displacement
parameters equal to 1.2 times (1.5 for the methyl hydrogen atoms) the
Ueq of their parent carbon atoms. The solvent atoms lie near an
inversion center and were refined with a 0.5 occupancy, a common
thermal parameter for all the carbon atoms and restrained geometry.
Full-matrix least-squares refinement of this model converged to final
residual indices listed in Table 1. Final difference electron density
maps showed seven features above 1 e/Å3 (max/min 1.89/-2.60 e/Å3),
with the largest peaks lying closer than 1.16 Å to the platinum atoms.
a (a) +AgClO4, -NBu4ClO4, CH2Cl2 wet; (b) +2AgClO4, -AgCl,
-2NBu4ClO4; (c) +[Ag(OClO3)(PPh3)], -NBu4ClO4; (d) +PPh3; (e)
+H2O, -HX; (f) +[Ag(OClO3)(PPh3)], -NBu4ClO4; (g) +KOH,
reflux, -KX; (h) +[Ag(OClO3)(SC4H8)], -AgX, -NBu4ClO4; (i)
+SC4H8, -AgX; (j) SC4H8.
white residue with diethyl ether allows the separation of NBu4-
ClO4 as a white solid (identified by IR). The remaining solution,
after evaporation of the solvent, renders the complexes [(C6F5)2-
Pt(µ-X)(µ-dppm){Ag(H2O)}Pt(C6F5)2] [X ) Cl (1), Br (2)] as
white solids (Scheme 1a). The presence of Ag+ in these
materials is confirmed by dissolving small amounts of them in
acetone and adding some drops of a methanol solution of HCl.
The immediate precipitation of AgCl is observed in both cases.
IR spectra of complexes 1 and 2 confirm the presence of the
expected ligands and show some broad signals in the 3600 cm-1
region, indicating the presence of water, possibly coordinated
to the silver center (Scheme 1a). The presence of water can be
Results and Discussion
All the reactions presented in this paper are summarized in
Scheme 1. Complexes [NBu4][(C6F5)2Pt(µ-X)(µ-dppm)Pt-
(C6F5)2] [X ) Cl (A), Br (B)] contain one halogen atom acting
as a bridge between the two platinum centers.3 Thus, two
possible pathways for their reactivity toward silver(I) compounds
could be expected: (i) elimination of the halogen atoms as the
corresponding silver halide or (ii) coordination of the silver atom
to the platinum center forming PtfAg donor-acceptor bonds.
When AgClO4 is added to a CH2Cl2 solution of [NBu4][(C6F5)2-
Pt(µ-X)(µ-dppm)Pt(C6F5)2] (1:1 molar ratio), no precipitation
of the corresponding AgX is observed. After several hours of
stirring in the dark, the silver perchlorate dissolves completely
and the solution is evaporated to dryness. The treatment of the
1
explained by the use of solvents not perfectly dried. The H
NMR spectra of complexes 1 and 2 show signals due to the
hydrogen atoms of water, besides those corresponding to the
dppm ligand. The 19F and 31P NMR spectra are consistent with
the expected geometry; the values for the chemical displace-
ments and coupling constants with 195Pt (when present) are listed
in Table 2.
As expected, complexes 1 and 2 can also be prepared by
reacting the precursors of A and B, [NBu4]2[(C6F5)2XPt(µ-
dppm)PtX(C6F5)2] [X ) Cl (D), Br (E)]3 with AgClO4 in
(8) Sheldrick, G. M. SHELXL-93, a program for crystal structure
refinement; University of Go¨ttingen: Germany, 1993.

7870 Inorganic Chemistry, Vol. 35, No. 26, 1996
Table 2. 19F and 31P NMR Data for Complexes 1-7
Casas et al.
19F NMR a
31P NMR a
1JPt-P (Hz)
2147
complex
δ(Fo)
δ(Fm)
δ(Fp)
3JPt-Fo (Hz)
δ(dppm)
9.72
[(C6F5)2Pt(µ-Cl)(µ-dppm){Ag(H2O)}Pt(C6F5)2] (1)
-117.35
-119.31
-116.76
c
-163.56
b
-161.00
-161.41
-160.14
-162.18
-157.47
-159.78
513.9
391.4
538.8
c
339.0
511.2
330.7
479.5
451.9
e
501.2
351.3
281.2
338.7
[(C6F5)2Pt(µ-Br)(µ-dppm){Ag(H2O)}Pt(C6F5)2] (2)
[(C6F5)2Pt(µ-Cl)(µ-dppm){Ag(PPh3)}Pt(C6F5)2] (3)
[(C6F5)2Pt(µ-Br)(µ-dppm){Ag(PPh3)}Pt(C6F5)2] (4)
[(C6F5)2Pt(µ-OH)(µ-dppm){Ag(PPh3)}Pt(C6F5)2] (5)
[NBu4][(C6F5)2Pt(µ-OH)(µ-dppm)Pt(C6F5)2] (6)
[(C6F5)2Pt(µ-SC4H8)(µ-dppm)Pt(C6F5)2] (7)
8.81
2169
-116.89
-118.18
-116.18
-118.31
-118.34
-119.56
-118.30
-119.44
-117.88
-118.33
f
13.22
2460
PPh3 ) 13.15
1JAg-P ) 693, 800
2447
-165.05
-160.24
13.00
-163.33
PPh3 ) 13.40
9.38
PPh3 ) ca. 9
1JAg-P ) 670, 774
2420
d
e
1JAg-P
2691
-165.32
-163.64
-167.47
-158.36
-162.10
8.68
-167.65
-161.75
-163.99
a In CDCl3 solution. b Both signals appear overlapped. c Broad signal at -117.9 ppm with poor resolution. d Several signals at ca. -164 ppm.
e Due to the poor resolution of the signal it is not possible to measure the value of the coupling constant. f Two broad signals at -163.6 and -165.6
ppm with poor resolution.
tetrahydrofuran in a 1:2 molar ratio (Scheme 1b). In this case
we can observe the formation of the silver halide AgX as well.
When the complex [Ag(OClO3)(PPh3)] is added to a solution
of A or B in CH2Cl2 in a 1:1 molar ratio, no change in the
color of the solution is observed. After 5 min of stirring, the
solvent is eliminated and the residue is treated with diethyl ether.
The NBu4ClO4, insoluble in this solvent, is filtered off, and from
the solution, complexes [(C6F5)2Pt(µ-X)(µ-dppm){Ag(PPh3)}-
Pt(C6F5)2] [X ) Cl (3), Br (4)] are isolated as white solids
(Scheme 1c). The IR spectra of 3 and 4 show absorptions
assignable to PPh3. 1H, 19F, and 31P NMR spectra of 3 and 4
are in accordance with the proposed geometry; the chemical
shifts of their signals are collected in Table 2.
On the other hand, water coordinated to the silver center in
[(C6F5)2Pt(µ-Cl)(µ-dppm){Ag(H2O)}Pt(C6F5)2] (1) can be dis-
placed by PPh3 without cleavage of the PtfAg bond. When 1
is reacted with an equimolar amount of PPh3 in CH2Cl2, the
complex [(C6F5)2Pt(µ-Cl)(µ-dppm){Ag(PPh3)}Pt(C6F5)2] (3) is
obtained from the solution (Scheme 1d).
When some drops of water are added to a CH2Cl2 solution
of 3 and the mixture is stirred for several days, it is possible to
obtain a material the infrared spectrum of which shows a sharp
absorption at 3609 cm-1, typical for ν(O-H).9 Further inves-
tigation of this solid leads to its identification as [(C6F5)2Pt(µ-
OH)(µ-dppm){Ag(PPh3)}Pt(C6F5)2] (5, Scheme 1e). This is a
noteworthy result, since in our previous work3 we observed that
the halogen bridges in complexes A-C are very inert and do
not react with halides, PPh3, SC4H8, or NCMe. The substitution
of the bridging chloride in 3 under such mild conditions suggests
that the donor-acceptor PtfAg bonds activate this substitution.
The donation of electron density by the platinum atom to silver
causes the withdrawal of metal electron density from the Pt-
Cl bonds, increasing their reactivity. Nevertheless, when the
substitution on 3 is attempted by using NBu4OH, we observe
the immediate precipitation of black Ag2O and the chloride
bridging complex A is recovered from the resulting solution.
As can be seen, the substitution of the bridging Cl can only be
achieved with very weak bases, such as water.
have tried to prepare 6 by using a procedure similar to the one
used for the syntheses of A-C. The first step in the syntheses
of complexes A-C involves the cleavage of the halogen bridges
in the complexes [NBu4]2[Pt2(µ-X)2(C6F5)4] with dppm. In short
reaction times (10 min) the precursors to complexes A-C,
[NBu4]2[(C6F5)2XPt(µ-dppm)PtX(C6F5)2] [X ) Cl (D), Br (E),
I (F)], can be obtained with good yields (ca. 90%), whereas
when longer periods are allowed, a mixture of starting material
and [Pt(C6F5)2(dppm)] is formed. This behavior indicates that
the complexes [NBu4]2[(C6F5)2XPt(µ-dppm)PtX(C6F5)2] are the
kinetic products of the cleavage of the bridges. Nevertheless,
dppm is not able to cleave the OH bridges in complex [NBu4]2-
[Pt2(µ-OH)2(C6F5)4],9 since even with long reaction periods the
unaltered starting material is recovered.
The only way to prepare complex 6 is by substitution of the
bromine ligand in complex B by the OH group. This substitu-
tion does not take place under mild conditions, since the reaction
of B with bases such as NBu4OH or KOH does not progress at
room temperature. It is necessary to reflux a solution of B and
an excess of KOH in a MeOH/H2O mixture for 24 h to obtain
the complex [NBu4][(C6F5)2Pt(µ-OH)(µ-dppm)Pt(C6F5)2] (6)
i
after removal of the MeOH and addition of PrOH, in which
the product is not soluble (Scheme 1g). The yield is 78%. The
severe conditions which are necessary for the substitution of
the bromine ligand in B contrast with the facility of hydrolysis
of 3 brought about by the presence of the silver bonded to the
platinum centers.
The stoichiometry of 6 is confirmed by its elemental (C, H,
1
N) analyses, IR spectrum, and H, 19F, and 31P NMR spectra.
The IR spectrum shows an absorption at 3621 cm-1 assignable
to ν(O-H).9 In the 1H NMR spectrum, the hydroxyl hydrogen
atom appears at 2.15 ppm. The 19F and 31P NMR spectra are
consistent with the expected geometry; the values for the
chemical shifts and coupling constants with 195Pt (when present)
are listed in Table 2.
We have also studied the reaction of [NBu4][(C6F5)2Pt(µ-
Cl)(µ-dppm)Pt(C6F5)2] (A) with [Ag(OClO3)(SC4H8)] in order
to prepare the analogous complex to 3 with the tetrahy-
drothiophene ligand (SC4H8) coordinated to the silver atom.
However, this process does not result in the formation of the
expected trinuclear complex. Thus, when [Ag(OClO3)(SC4H8)]
is added to a solution of A in CH2Cl2 (1:1 molar ratio) and the
resulting solution is stirred at room temperature for 24 h, the
presence of a solid is observed. The removal of the solvent
and the addition of diethyl ether allow the elimination by
filtration of a solid which is identified as a mixture of AgCl
Complex 5 can also be prepared straightforwardly by reacting
[NBu4][(C6F5)2Pt(µ-OH)(µ-dppm)Pt(C6F5)2] (6) with [Ag-
(OClO3)(PPh3)] (1:1 molar ratio) in CH2Cl2 (Scheme 1f).
However, the synthesis of the starting material 6 involves some
peculiarities which are worth commenting on. First of all, we
(9) Lo´pez, G.; Ruiz, J.; Garc´ıa, G.; Vicente, C.; Casabo´, J.; Molins, E.;
Miravitlles, C. Inorg. Chem. 1991, 30, 2605.

Ag-Pt2 Interactions in Pentafluorophenyl Complexes
Inorganic Chemistry, Vol. 35, No. 26, 1996 7871
Table 3. Selected Bond Distances (Å) and Angles (deg) for Complex [(C6F5)2Pt(µ-OH)(µ-dppm){Ag(PPh3)}Pt(C6F5)2]‚C7H8 (5‚C7H8)
Pt(1)-Ag
Pt(1)-O
Pt(1)-P(1)
2.791(1)
2.100(6)
2.302(3)
Pt(2)-Ag
Pt(2)-O
Pt(2)-P(2)
2.832(1)
2.084(7)
2.296(3)
Pt(1)-C(1)
Pt(1)-C(7)
Ag-P(3)
1.992(10)
2.058(11)
2.422(3)
Pt(2)-C(13)
Pt(2)-C(19)
Pt(1)‚‚‚Pt(2)
2.015(12)
2.071(11)
3.479(1)
Ag-Pt(1)-O
85.3(2)
Ag-Pt(2)-O
84.5(2)
O-Pt(1)-C(1)
O-Pt(1)-C(7)
P(1)-Pt(1)-C(1)
P(1)-Pt(1)-C(7)
C(1)-Pt(1)-C(7)
Pt(1)-Ag-P(3)
Pt(1)-Ag-Pt(2)
176.2(4)
O-Pt(2)-C(13)
O-Pt(2)-C(19)
P(2)-Pt(2)-C(13)
P(2)-Pt(2)-C(19)
C(13)-Pt(2)-C(19)
Pt(2)-Ag-P(3)
177.2(4)
88.1(4)
91.6(3)
171.3(3)
91.4(4)
140.5(1)
Ag-Pt(1)-P(1)
Ag-Pt(1)-C(1)
Ag-Pt(1)-C(7)
Pt(1)-O-Pt(2)
Pt(1)-P(1)-C(25)
O-Pt(1)-P(1)
95.2(1)
98.3(3)
90.4(3)
112.5(3)
115.8(3)
88.3(2)
Ag-Pt(2)-P(2)
Ag-Pt(2)-C(13)
Ag-Pt(2)-C(19)
P(1)-C(25)-P(2)
Pt(2)-P(2)-C(25)
O-Pt(2)-P(2)
94.1(1)
98.3(3)
93.6(3)
116.0(6)
117.0(4)
88.5(2)
89.2(3)
92.7(3)
173.7(3)
89.5(4)
143.0(1)
76.4(1)
Table 4. Selected Bond Distances (Å) and Angles (deg) for Complex [(C6F5)2Pt(µ-SC4H8)(µ-dppm)Pt(C6F5)2]‚1/2C6H14 (7‚1/2C6H14)
Pt(1)-S
Pt(1)-P(1)
Pt(1)-C(1)
2.356(2)
2.289(2)
2.030(8)
Pt(2)-O
Pt(2)-P(2)
Pt(2)-C(13)
2.354(2)
2.292(2)
2.008(8)
Pt(1)-C(7)
Ag-P(3)
2.054(9)
2.422(3)
Pt(2)-C(19)
Pt(1)...Pt(2)
2.067(8)
4.150(1)
Pt(1)-S-Pt(2)
Pt(1)-P(1)-C(25)
S-Pt(1)-P(1)
S-Pt(1)-C(1)
123.6(1)
114.8(3)
92.6(1)
P(1)-C(25)-P(2)
Pt(2)-P(2)-C(25)
S-Pt(2)-P(2)
117.7(4)
114.3(3)
91.5(1)
S-Pt(1)-C(7)
91.4(2)
90.4(2)
175.2(2)
85.3(3)
S-Pt(2)-C(19)
93.6(2)
92.0(2)
174.6(2)
83.0(3)
P(1)-Pt(1)-C(1)
P(1)-Pt(1)-C(7)
C(1)-Pt(1)-C(7)
P(2)-Pt(2)-C(13)
P(2)-Pt(2)-C(19)
C(13)-Pt(2)-C(19)
174.8(2)
S-Pt(2)-C(13)
173.8(3)
Figure 1. Drawing of the complex [(C6F5)2Pt(µ-OH)(µ-dppm){Ag-
(PPh3)}Pt(C6F5)2] (5), showing the atom-labeling scheme. Heavy atoms
are represented by their 50% probability ellipsoids. For clarity, only
one set of the disordered atoms is represented.
Figure 2. Drawing of the complex [(C6F5)2Pt(µ-SC4H8)(µ-dppm)Pt-
(C6F5)2] (7), showing the atom-labeling scheme. Heavy atoms are
represented by their 50% probability ellipsoids.
SC4H8 to act as a bridging ligand may be responsible for this
differing behavior.
and NBu4ClO4. By evaporation of the OEt2 from the filtrate a
white solid, [(C6F5)2Pt(µ-SC4H8)(µ-dppm)Pt(C6F5)2] (7), is
obtained (Scheme 1h). A similar result is obtained if an
equimolar mixture of AgClO4 and SC4H8 is used instead of the
complex [Ag(OClO3)(SC4H8)]. Furthermore, the reaction of
[(C6F5)2Pt(µ-Cl)(µ-dppm){Ag(H2O)}Pt(C6F5)2] (1) with SC4H8
renders complex 7 as well (Scheme 1i). 1H, 19F, and 31P NMR
spectra for 7 (see Table 2) are in accord with the proposed
structure, which has been established by X-ray diffraction.
Crystal Structures of [(C6F5)2Pt(µ-OH)(µ-dppm){Ag-
(PPh3)}Pt(C6F5)2]‚C7H8 (5‚C7H8) and [(C6F5)2Pt(µ-SC4H8)-
(µ-dppm)Pt(C6F5)2]‚1/2C6H14 (7‚1/2C6H14). We have carried
out single-crystal X-ray diffraction studies on 5 and 7. The
structure of the neutral complex 5 is shown in Figure 1; selected
bond distances and angles are listed in Table 3, and relevant
crystallographic data are compiled in Table 1. The neutral
complex [(C6F5)2Pt(µ-OH)(µ-dppm){Ag(PPh3)}Pt(C6F5)2] can
be regarded as formed by two “Pt(C6F5)2” fragments linked
together by the dppm and hydroxy ligands and by the silver
atom. The environment of each platinum atom is a square
pyramid, and the two pyramids share an edge. Each platinum
atom lies in the center of the base of the pyramid. Bond
distances and angles are equal within experimental error for the
two platinum environments and are in the range usually found
in Pt(II) complexes containing these kinds of ligands.10 The
Ag-Pt-L angles are near 90°, with Ag-Pt-O smaller (ca.
85°), and with larger values (near 100°) for the pentafluorophe-
nyl groups trans to the oxygen atom. The angles between the
perpendicular to the best basal plane for each platinum and the
Pt-Ag line are 7.6(1)° and 7.1(1)°, indicating that each Pt-
Again, the presence of the silver atom bonded to the platinum
centers activates the halogen bridge toward substitution. This
replacement of the Cl atom by the tetrahydrothiophene ligand
can only be achieved with the Pt-Ag compound, while the
addition of SC4H8 to a solution of A does not cause any reaction
after several days of stirring (Scheme 1j).3
The influence of the ligand L bonded to the silver center [Ag-
(OClO3)(SC4H8)] (L ) PPh3, SC4H8; Scheme 1f,g) on the nature
of the final products is also noteworthy, since for L ) PPh3 the
trinuclear system Pt2Ag is formed or maintained, whereas for
L ) SC4H8, precipitation of AgCl and formation of 7 take place
in both cases. Lower steric requirements and the ability of

7872 Inorganic Chemistry, Vol. 35, No. 26, 1996
Casas et al.
that the Ag-P distance found for pentahalophenyl complexes
in which only one Pt-Ag bond is present.10 The environment
of the silver atom is planar and symmetric, since the Pt-Ag-P
angles are very similar (see Table 3). Finally, as has been
observed previously,1,2 the four pentafluorophenyl groups are
oriented in such a way that one of their ortho fluorine atoms
points toward the silver atom. The distances range from
2.754(8) to 2.982(6) Å and might indicate the existence of some
kind of Ag‚‚‚F interaction contributing to the overall stability
of the complex.
The structure of neutral complex 7 is shown in Figure 2;
selected bond distances and angles are listed in Table 4, and
relevant crystallographic data are compiled in Table 1. As can
be seen, the two “Pt(C6F5)2” moieties are bridged by the dppm
ligand and the sulfur atom of the tetrahydrothiophene ligand.
Bond distances involving the platinum atoms are equal within
experimental error in both moieties, and all of them are in the
range usually found for this kind of complex. The metal atoms
lie in the center of square planar environments, the angle
between these being 133.2(1)°, greater than that corresponding
to complex 5 and similar to those previously reported for the
anion of complex C (Figure 3a), [(C6F5)2Pt(µ-I)(µ-dppm)Pt-
(C6F5)2]- [135.1(1)°].3 It is noteworthy that, as in C, the
skeleton of complex 7 is twisted (Figure 3b) and the angle
formed by the Pt-Pt and P-P lines has a value of 41.0(1)°
[40.4(1)° for C]. Nevertheless, for 5 these lines are almost
parallel, the angle being 0.7(1)°, and the six-membered ring
formed by the two Pt atoms, P(1), P(2), O, and C(25) has a
chair conformation (Figure 3c). This “open book” symmetric
disposition for 5 is probably due to the presence of the silver
atom coordinated to the two platinum centers simultaneously.
When this “restraint” is not present, as in 7 or C, the
six-membered ring twists to adopt a more distorted disposition.
The Pt-Pt nonbonding distances are also clearly different for
5 and 7 (and C). The shorter distance is found for 5, 3.479(1)
Å, probably due to the “tweezers” effect of the silver atom,
whereas for 7, the intermetallic distance is 4.150(1) Å [4.446(1)
Å for C]. Nevertheless, the size of the bridging atom between
the platinum centers cannot be rejected as a possible cause of
these variations in the Pt-Pt distances.
Figure 3. View of the cores of the complexes (a) [(C6F5)2Pt(µ-I)(µ-
dppm)Pt(C6F5)2]- (C),3 (b) [(C6F5)2Pt(µ-SC4H8)(µ-dppm)Pt(C6F5)2] (7),
and (c) [(C6F5)2Pt(µ-OH)(µ-dppm){Ag(PPh3)}Pt(C6F5)2] (5).
Conclusions
The dinuclear complexes [NBu4][(C6F5)2Pt(µ-X)(µ-dppm)-
Pt(C6F5)2] (X ) Cl, Br) are able to act as didentate chelating
metallo ligands toward [AgL]+. The formation of the PtfAg
bonds obliges the dinuclear platinum starting material to twist
its two coordination planes to reach the final “open book”
disposition necessary for the formation of the Pt-Ag bonds.
Another important effect introduced by the silver coordination
is an increase in the reactivity of the bridging halide, which is
inert in the dinuclear platinum starting materials.
Ag bond is almost perpendicular to the base of the corresponding
pyramid. The dihedral angle between the two platinum basal
planes is 114.4(2)°. The short Pt-Ag distances, 2.791(1) and
2.832(1) Å, are characteristic of PtfAg bonds which are not
supported by any other ligand covalently bonded to both metal
centers. The lengths of these Pt-Ag bonds lie in the range of
values previously found for other trinuclear complexes in which
the silver atom is bonded simultaneously to two platinum
centers, such as in [NBu4][(µ-Cl)2(C6F5)4Pt2Ag(OEt2)] and
[NBu4][(µ-C6F5)2(C6F5)4Pt2Ag(L)] (L ) OEt2, SC4H8).2 The
coordination sphere of the silver atom is completed by the
triphenylphosphine ligand. The Ag-P(3) distance is 2.422(3)
Å, similar to others found in the literature11 but slightly longer
Acknowledgment. We thank the Comisio´n Interministerial
de Ciencia y Tecnolog´ıa (Spain) for financial support (Projects
PB92-0360 and PB92-0364).
Supporting Information Available: X-ray crystallographic files
in CIF format for compounds 5‚C7H8 and 7‚1/2C6H14 are available on
the Internet only. Access information is given on any current masthead
page.
(10) Uso´n, R.; Fornie´s, J. AdV. Organomet. Chem. 1988, 288, 219 and
references cited therein. Uso´n, R.; Fornie´s, J.; Toma´s, M. J. Orga-
nomet. Chem. 1988, 358, 525 and references cited therein.
(11) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D.
G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1.
IC9605332