Unexpected Reactivity of PdCl2 and PtCl2 Complexes of the Unsaturated Diphosphine o-Me2TTF(PPh2)2 toward Chloride Abstraction with Thallium Triflate

Article abstract of DOI:10.1021/ic035447y

Attempted thallium triflate abstraction of chloride anions from the MCl₂ complexes of the unsaturated chelating diphosphines o-dimethyl-bis(diphenylphosphino)tetrathiafulvalene (P2) (M = Pd, Pt) and cis-1,2-bis(diphenylphosphino)ethylene (dppen) (M = Pd) affords, surprisingly, a Tl(OTf) adduct in the case of (P2)PdCl₂ and (P2)PtCl₂, with no chloride abstraction, and a dicationic bis(palladium) bis(triflate) salt in the case of (cis-dppen)PdCl₂, in which only one Cl anion was removed. The crystal structures of these complexes were determined by X-ray analysis, which established the formulations (P2)MCl₂·Tl(OTf) (M = Pd, Pt) and [(dppen)PdCl]₂(OTf)₂, respectively. These compounds can be seen as possible intermediates in the general chloride abstraction process between (P-P)MCl₂ (M = Pd, Pt) and thallium triflate.

Full text of DOI:10.1021/ic035447y

Inorg. Chem. 2004, 43, 3136−3141
Unexpected Reactivity of PdCl2 and PtCl2 Complexes of the Unsaturated
Diphosphine o-Me2TTF(PPh2)2 toward Chloride Abstraction with Thallium
Triflate
Thomas Devic, Patrick Batail, Marc Fourmigue´, and Narcis Avarvari*
Laboratoire “Chimie Inge´nierie Mole´culaire et Mate´riaux” (CIMMA), UMR 6200
CNRS-UniVersite´ d’Angers, Baˆt. K, UFR Sciences, 2 bd LaVoisier, 49045 Angers, France
Received December 17, 2003
Attempted thallium triflate abstraction of chloride anions from the MCl2 complexes of the unsaturated chelating
diphosphines o-dimethyl-bis(diphenylphosphino)tetrathiafulvalene (P2) (M ) Pd, Pt) and cis-1,2-bis(diphenylphos-
phino)ethylene (dppen) (M ) Pd) affords, surprisingly, a Tl(OTf) adduct in the case of (P2)PdCl2 and (P2)PtCl2,
with no chloride abstraction, and a dicationic bis(palladium) bis(triflate) salt in the case of (cis-dppen)PdCl2, in
which only one Cl anion was removed. The crystal structures of these complexes were determined by X-ray analysis,
which established the formulations (P2)MCl2‚Tl(OTf) (M ) Pd, Pt) and [(dppen)PdCl]2(OTf)2, respectively. These
compounds can be seen as possible intermediates in the general chloride abstraction process between (P−P)MCl2
(M ) Pd, Pt) and thallium triflate.
Introduction
reversibly oxidized to the radical cation species, not only in
the free ligands but also in its metal complexes.8
Numerous palladium or platinum complexes such as
(P-P)M(OTf)2, where OTf is the triflate anion and P-P is
a chelating diphosphine, have been widely used within the
past decade as building blocks for the formation of supramo-
lecular assemblies,1 upon triflate displacement and subse-
quent complexation with bis(pyridines). A variety of chelat-
ing diphosphines were accordingly investigated, with different
bridges such as an alkyl chain, chiral (BINAP,2 DIOP3)
moiety, ferrocenyl group,4 or crown ether.5 In that respect,
redox-active chelating diphosphines such as dimethyl-bis-
(diphenylphosphino)tetrathiafulvalene6 (P2) or tetrakis(di-
phenylphosphino) tetrathiafulvalene7 (P4) are of particular
interest since the TTF redox moiety in P2 or P4 can be
Their coordinating ability has been demonstrated with
various d8 metal cations, as in the mono chelate complex
(P2)NiBr2,6 or in bis chelate complexes such as [(P2)2M]n+
with M ) Rh, n ) 17 or M ) Pd, Pt, n ) 2.9 In both cases,
however, these complexes do not offer any free coordination
site which would allow the formation of extended networks
or supramolecular assemblies upon coordination with various
bis(pyridines). Therefore, the availability of the correspond-
ing (P2)M(OTf)2 triflate complexes, M ) Pd, Pt, could be
a key step for the elaboration of extended networks with
collective electronic properties, upon bis(pyridine) complex-
ation and TTF oxidation. In this paper, we describe first the
synthesis of the redox active square planar complexes (P2)-
MCl2 (M ) Pd, Pt), and subsequently our unexpected results
toward the synthesis of (P-P)M(OTf)2 (M ) Pd, Pt)
complexes, by analogy with that described for (dppp)M-
* Corresponding author. E-mail: narcis.avarvari@univ-angers.fr.
(1) (a) Stang, P. J.; Cao, D. H. J. Am. Chem. Soc. 1994, 116, 4981-
4982. (b) Stang, P. J.; Cao, D. H.; Saito, S.; Arif, A. M. J. Am. Chem.
Soc. 1995, 117, 6273-6283.
(2) Olenyuk, B.; Whiteford, J. A.; Stang, P. J. J. Am. Chem. Soc. 1996,
118, 8221-8230.
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2002, 21, 685-693.
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Smith, R. D. J. Am. Chem. Soc. 1997, 119, 5163-5168.
(6) Fourmigue´, M.; Batail, P. Bull. Soc. Chim. Fr. 1992, 129, 29-36.
(7) Fourmigue´, M.; Uzelmeier, C. E.; Boubekeur, K.; Bartley, S. L.;
Dunbar, K. R. J. Organomet. Chem. 1997, 529, 343-350.
(8) Avarvari, N.; Martin, D.; Fourmigue´, M. J. Organomet. Chem. 2002,
643-644, 292-300.
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1309-1315.
3136 Inorganic Chemistry, Vol. 43, No. 10, 2004
10.1021/ic035447y CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/15/2004

ReactiWity of PdCl2 and PtCl2 Complexes
(OTf)2,1,10 (dppp ) 1,3-bis(diphenylphosphino)propane; M
) Pd, Pt). Chloride abstraction from the corresponding (P2)-
PdCl2 and (P2)PtCl2 complexes with thallium triflate proved
to be difficult, and unprecedented tetrametallic Tl(OTf)
adducts of (P2)MCl2 (M ) Pd, Pt) were obtained instead,
whose structure can be deduced from that of Tl2(PdCl4).
Similar difficulties were encountered with another conjugated
diphosphine such as dppen (dppen ) cis-1,2-bis(diphe-
nylphosphino)ethylene) since Cl abstraction from (dppen)-
PdCl2 led to the substitution of only one Cl atom, as
described hereafter.
Dichloro{dimethylbis(diphenylphosphino)tetrathiafulvalene}-
palladium(II) Thallium(I) Triflate Adduct, (P2)PdCl2,Tl(OTf).
(P2)PdCl2 (120 mg, 1.54 × 10-4 mol) and Tl(OTf) (170 mg, 4.8
× 10-4 mol) were suspended in CH2Cl2 (25 mL) and stirred for 18
h. The suspension was filtered and the red solution concentrated
to 15 mL, and slow Et2O diffusion afforded (P2)PdCl2,Tl(OTf) as
red needles (80 mg, 46%).
31P NMR (δ, CDCl3): 48.0 (b). Anal. Calcd for C37H36Cl2F3O4P2-
PdS5Tl: C, 36.86; H, 3.01. Found: C, 36.32; H, 2.90. Anal. (SEM)
Calcd (normalized weight %): Cl, 11.7; P, 10.3; Pd, 17.6; S, 26.5;
Tl, 33.8. Found: Cl, 17.8; P, 9.1; Pd, 17.0; S, 26.5; Tl, 29.6 (no
standard was available for this element).
Dichloro{dimethylbis(diphenylphosphino)tetrathiafulvalene}-
platinum(II) Thallium(I) Triflate Adduct, (P2)PtCl2,Tl(OTf).
(P2)PtCl2 (133 mg, 1.54 × 10-4 mol) and Tl(OTf) (170 mg, 4.8 ×
10-4 mol) were suspended in CH2Cl2 (25 mL) and stirred for 18 h.
The suspension was filtered, and the red solution concentrated to
15 mL, and slow Et2O diffusion afforded (P2)PtCl2,Tl(OTf) as red
needles (90 mg, 49%).
Experimental Section
Synthesis. The reactions were carried out under an N2 inert
atmosphere by using standard Schlenk techniques. Elemental
analyses were performed at the Service de Microanalyse, Institut
de Chimie des Substances Naturelles, CNRS, Gif/Yvette (France),
while SEM (scanning electron microscopy) analyses were per-
formed on a JEOL JSM-5800 LV microscope operating at 15 kV
and equipped with an energy dispersion spectrometer PGT IMIX-
1
31P NMR (δ, CDCl3): 27.5 (b, JP-Pt ) 3640 Hz). Anal. Calcd
for C37H36Cl2F3O4P2PtS5Tl: C, 34.33; H, 2.80. Found: C, 33.90;
H, 2.71.
1
PTS at the Institut Jean Rouxel, CNRS, Nantes (France). H and
31P NMR spectra were taken on a Bruker Avance DRX 500
spectrometer operating at 500.04 MHz for 1H and 202.39 MHz for
31P. Chemical shifts are expressed in parts per million (ppm)
downfield from external TMS (1H) and H3PO4 (31P). The following
abbreviations are used: m, multiplet; b, broad. Mass spectra
(electrospray) were obtained from a JEOL JMS 700 B/ES spec-
trometer. Thallium triflate is known for its toxicity and should be
handled with due precautions. o-Me2TTF(PPh2)2 (P2) was prepared
according to the published procedure.6
Di-µ-chloro-bis{1,2-bis(diphenylphosphino)ethylene}dipal-
ladium(II)bis(triflate), [(dppen)PdCl(OTf)]2. A suspension of
(dppen)PdCl2 (107 mg, 1.87 × 10-4 mol) and thallium triflate (198
mg, 5.61 × 10-4 mol) was stirred in CH2Cl2 (20 mL) for 3 days.
After filtration and concentration to 5 mL, the solution was layered
with Et2O to afford pale yellow crystals of [(dppen)PdCl(OTf)]2
(100 mg, 78%).
31P NMR (δ, CH2Cl2): 80.6 (b), 75.7 (b). Anal. Calcd for C54H44-
Cl2F6O6P4Pd2S2: C, 47.18; H, 3.23. Found: C, 46.90; H, 3.13.
X-ray Crystallography. Details about data collection and
solution refinement are given in Table 1. Data were collected on a
Stoe imaging plate system for the structures (P2)PdCl2‚(CHCl3)2,
(P2)PdCl2‚Tl(OTf)‚(OEt2), and [(dppen)PdCl(OTf)]2 and on a
Bruker-CCD system for the structure (P2)PtCl2‚Tl(OTf)‚(OEt2),
both operating with a Mo KR X-ray tube with a graphite
monochromator. The structures were solved (SHELXS-97) by direct
methods and refined (SHELXL-97) by full-matrix least-squares
procedures on F2.11 Hydrogen atoms were introduced at calculated
positions (riding model), and included in structure factor calcula-
tions, but not refined. The solvent (Et2O) atoms in the structure
(P2)PdCl2‚Tl(OTf)‚(OEt2) and the C37 carbon atom of Et2O in the
structure (P2)PtCl2‚Tl(OTf)‚(OEt2) have been refined isotropically.
All the other heavy atoms have been refined anisotropically. The
moderate R(Fo) value for the structure of (P2)PdCl2 is very likely
due to a partial loss of solvent molecules during the X-ray
diffraction analysis, since the data collection has been performed
at room temperature.
Dichloro{dimethylbis(diphenylphosphino)tetrathiafulvalene}-
palladium (II), (P2)PdCl2. PdCl2 (176 mg, 9.9 × 10-4 mol) and
P2 (300 mg, 5 × 10-4 mol) were suspended in CHCl3 (25 mL),
and the mixture was warmed to reflux overnight. The cooled red
suspension was filtered and the solution concentrated to 10 mL.
Et2O was added to precipitate a red solid, which was washed with
Et2O and dried under vacuum to afford (P2)PdCl2 (353 mg, 91%).
Crystals of good quality for X-ray diffraction were obtained by
slow diffusion of EtOH into a CHCl3 solution of (P2)PdCl2.
1H NMR (δ, CDCl3): 7.88 (m, 8H, Ph), 7.59 (m, 4H, Ph), 7.52
(m, 8H, Ph), 1.90 (s, 6H, Me). 31P NMR (δ, CDCl3): 47.5. MS
(electrospray) m/z (ion, rel intensity): 776 (M+, 100). Anal. Calcd
for C32H26Cl2P2PdS4: C, 49.40; H, 3.37. Found: C, 49.09; H, 3.36.
Anal. (SEM) Calcd (normalized weight %): Cl, 19.3; P, 16.9; Pd,
29.0; S, 34.9. Found: Cl, 19.4; P, 15.3; Pd, 30.2; S, 35.1.
Dichloro{dimethylbis(diphenylphosphino)tetrathiafulvalene}-
platinum (II), (P2)PtCl2. PtCl2 (176 mg, 6.6 × 10-4 mol) and P2
(200 mg, 3.3 × 10-4 mol) were suspended in CHCl3 (25 mL), and
the mixture was warmed to reflux overnight. The cooled red
suspension was filtered and the solution concentrated to 10 mL.
Et2O was added to precipitate a red solid, which was washed with
Et2O and dried under vacuum to afford (P2)PtCl2 (203 mg, 70%).
1H NMR (δ, CDCl3): 7.86 (m, 8H, Ph), 7.59 (m, 4H, Ph), 7.51
(m, 8H, Ph), 1.90 (s, 6H, Me). 31P NMR (δ, CDCl3): 27.5 (1JP-Pt
) 3640 Hz). MS (electrospray) m/z (ion, rel intensity): 866 (M+,
100). Anal. Calcd for C32H26Cl2P2PtS4: C, 44.34; H, 3.02. Found:
C, 44.10; H, 3.14. Anal. (SEM) Calcd (normalized weight %): Cl,
15.5; P, 13.6; Pt, 42.8; S, 28.1. Found: Cl, 16.9; P, 12.9; Pt, 39.3;
S, 30.9.
Results and Discussion
PdCl2 and PtCl2 complexes of the chelating, redox active
o-MeTTF(PPh2)2 (P2) diphosphine were obtained directly
from P2 and the metal chloride in refluxing chloroform, as
already described for (P2)NiCl2 or (P2)NiBr2.6 Chemical
shifts in 31P NMR spectra (see Experimental Section) are in
the expected range for both complexes, downfield shifts
being observed when compared to the free P2 (δ ) -18
ppm). Interestingly, the 1JP-Pt coupling constant for the (P2)-
(10) Appleton, T. G.; Bennett, M. A.; Tomkins, I. B. J. Chem. Soc., Dalton
Trans. 1976, 439-446.
(11) Sheldrick, G. M. Programs for the Refinement of Crystal Structures;
University of Go¨ttingen: Go¨ttingen, Germany, 1996.
Inorganic Chemistry, Vol. 43, No. 10, 2004 3137

Devic et al.
Table 1. Crystallographic Data
(P2)PdCl2‚(CHCl3)2
(P2)PdCl2‚Tl(OTf)‚(OEt2)
(P2)PtCl2‚Tl(OTf)‚(OEt2)
[(dppen)PdCl(OTf)]2
formula
mw
cryst syst
space group
a (Å)
C34H28Cl8P2PdS4
1016.74
monoclinic
P21/n
17.0352(13)
15.7744(11)
17.8266(14)
C37H36Cl2F3O4P2PdS5Tl
1205.57
monoclinic
P21/n
9.9545(5)
18.5549(13)
23.9138(13)
C37H36Cl2F3O4P2PtS5Tl
1294.26
monoclinic
P21/n
10.0411(4)
18.958(2)
23.730(4)
C54H44Cl2F6O6P4Pd2S2
1374.59
triclinic
P1h
9.1915(9)
13.5486(15)
23.500(3)
97.939(13)
99.110(13)
95.102(13)
2843.5(5)
2
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
118.152(8)
96.044(6)
97.363(5)
4223.7(5)
4
1.599
4392.4(4)
4
1.823
4479.9(9)
4
1.919
d
calcd, g cm-3
1.605
0.98
293(2)
0.71073
0.0439
µ (mm-1
T (K)
)
1.244
4.556
7.185
293(2)
0.71073
0.0892
0.2806
293(2)
0.71073
0.0394
0.0945
293(2)
0.71073
0.0493
0.1156
λ (Å)
R(Fo)a
2
Rw(Fo )a
0.0840
a R(Fo) ) ∑||Fo| - |Fc||/∑|Fo|; Rw(Fo ) ) [∑[w(Fo - Fc )2]/∑[w(Fo )2]]1/2
.
2
2
2
2
Figure 1. ORTEP view of (P2)PdCl2‚(CHCl3)2.
PtCl2 complex is 3640 Hz (vide infra). Slow diffusion of
Et2O into CHCl3 solutions led to crystallization of (P2)PdCl2
and (P2)PtCl2. Both complexes are isostructural with (P2)-
NiBr2‚(CHCl3)2 and crystallize in the monoclinic system,
space group P21/n, with two CHCl3 molecules included. Only
the structure of (P2)PdCl2 has been solved completely and
is reported here. The Pd atom adopts a square-planar
configuration (Figure 1) while the two Cl atoms are engaged
in a C-H‚‚‚Cl hydrogen bond interaction with the chloro-
form molecules. Such hydrogen bonds with the activated CH
moiety of chloroform are now well established,12 and their
geometrical characteristics (d(C‚‚‚Cl) ) 3.51(1), 3.59(1) Å,
d(H‚‚‚Cl) ) 2.60, 2.74 Å, and (C-H‚‚‚Cl) ) 154.0,
146.4°) are in the expected range.
Figure 2. The tetrametallic motif associating two (P2)PdCl2 and two Tl+
cations in (P2)PdCl2‚Tl(OTf)‚Et2O.
Scheme 1
ment in general position in the unit cell, associated two by
two through inversion center (Figure 2). Each Tl cation is
coordinated by four Cl atoms, with Tl‚‚‚Cl distances of
3.157(2), 3.195(2), 3.207(2), and 3.356(2) Å. Further coor-
dination involves two oxygen atoms of the triflate anion
(Tl‚‚‚O distances at 2.916(8) and 3.37(1) Å) and the oxygen
atom of the diethyl ether molecule at a Tl‚‚‚O distance of
3.84(1) Å.
A similar reactivity was observed for the platinum complex
(P2)PtCl2 upon reaction with Tl(OTf). The red crystalline
needles of the adduct (P2)PtCl2‚Tl(OTf), recovered by
layering Et2O onto a CH2Cl2 solution of the complex, proved
to be isostructural with the palladium counterpart. The Pt-
(II) center lies, as expected, in a square planar environment
formed by the two chlorine atoms (Pt-Cl(1) 2.368(2) Å and
Pt-Cl(2) 2.3671(18) Å) and the two phosphorus atoms (Pt-
P(1) 2.2236(17) Å and Pt-P(2) 2.225(2) Å). The P(1)-Pt-
Chloride abstraction of (P2)PdCl2 to form (P2)Pd(OTf)2
was not attempted with silver triflate, because of the
oxidation sensitive nature of the TTF core, but rather with
thallium triflate. The latter is also known to react more
rapidly as checked on (dppp)PdCl2 by 31P NMR. Even with
prolonged heating in refluxing CH2Cl2, the reaction of (P2)-
PdCl2 with Tl(OTf) (Scheme 1) did not afford the expected
triflate salt. The red crystals recovered from the CH2Cl2
solution upon slow diffusion of Et2O proved to be, somewhat
surprisingly, a thallium triflate adduct of the starting material,
i.e., (P2)PdCl2‚Tl(OTf), crystallizing as Et2O solvate.
This complex adduct crystallizes in the monoclinic system,
space group P21/n, with one (P2)PdCl2‚Tl(OTf)‚Et2O frag-
(12) Desiraju, G. R.; Steiner, T. The Weak Hydrogen Bond; Oxford
University Press: Oxford, 1999.
3138 Inorganic Chemistry, Vol. 43, No. 10, 2004

ReactiWity of PdCl2 and PtCl2 Complexes
Scheme 2
surprising, when considering the proved efficiency of the
thallium triflate for this purpose. Indeed, in the case of
saturated links between the phosphino groups, i.e., dppe (1,2-
bis(diphenylphosphino)ethane) or dppp, the corresponding
adducts cannot be isolated, but one obtains directly the triflate
salts. However, the formation of a Tl(OTf) adduct with a
halogenated transition metal complex was also observed
recently in the case of a iodinated Ni3 cluster.19 Indeed, in
this case, instead of the expected iodide abstraction, an
insertion of the Tl+ ion into the Ni-I bonds occurred.
In order to evaluate whether the reluctance of (P2)MCl2
(M ) Pd, Pt) to undergo chloride abstraction was due to
some specificity of the P2 ligand, we investigated this
reaction in the case of palladium with another chelating
diphosphine such as dppen20,21 with a similar double bond
between the two diphenylphosphino groups. Reaction of
(dppen)PdCl2, prepared according to the published proce-
dure,20,21 with an excess of thallium triflate in CH2Cl2
(Scheme 2) afforded a complex salt, formulated as [(dppen)-
PdCl]2(OTf)2, i.e., indicating a partial dechlorination, despite
prolonged treatment with an excess of thallium triflate.
Figure 3. Comparison of the Tl+ environment in (P2)PdCl2‚Tl(OTf)‚Et2O
(a), Tl2PdCl4 (b), and TlCl (c).
P(2) bite angle within the metallacycle amounts to 88.49(7)°.
As in the case of the palladium adduct, the thallium center
is coordinated by four Cl atoms, with Tl‚‚‚Cl distances of
3.192(2), 3.241(2), 3.253(2), and 3.411(2) Å, two oxygen
atoms of the triflate anion (Tl‚‚‚O distances at 2.847(10) and
3.291(12) Å), and the oxygen atom of the Et2O molecule at
a Tl‚‚‚O distance of 3.717(7) Å. Full details about structural
parameters are given in the Supporting Information.
The coordination chemistry of the Tl+ cation has been the
subject of recent investigations,13,14 mainly concerned with
the exceedingly low coordination numbers in geometries
which leave a large part of the coordination sphere seemingly
unoccupied, a phenomenon tentatively ascribed to the
stereochemically active 6s2 lone pair. Besides, the recurrent
observation of Tl-Tl contacts (up to 4 Å) in such complexes
has been tentatively described as a “thallophilic” interaction,15
by analogy with well-established aurophilic bonding between
Au+ complexes.16 In the complexes described here, the
coordination sphere appears largely covered despite the steric
hindrance of the phenyl groups while the Tl-Tl distance
amounts to 4.0130(8) Å in the case of the palladium adduct,
at the limit value where “thallophilic” contacts could be
invoked. Note also that the coordination sphere of Tl+ within
the (P2)PdCl2‚Tl(OTf) adduct (Figure 3a), or the platinum
one, is reminiscent of that observed for example in Tl2PdCl4
(Figure 3b) where each Tl+ cation is surrounded by eight Cl
atoms,17 at Tl-Cl distances [3.324(1) Å] close to those
observed in (P2)PdCl2‚Tl(OTf). Remarkably, the same
environment is even found in the TlCl structure (Figure 3c)
with an interionic distance of 3.32 Å.18
Clearly, these tetrametallic complexes which we crystal-
lized can be seen as intermediate adducts between the starting
(P2)MCl2 and the targeted (P2)M(OTf)2 (M ) Pd, Pt). Very
likely, the M-Cl‚‚‚Tl interaction occurs also in solution and
not only in the solid state, since a significant broadening of
the peaks at δ ) 48 ppm (Pd adduct) and δ ) 27.5 ppm (Pt
adduct) in the 31P NMR spectra of the reaction mixtures or
of the redissolved (P2)MCl2‚Tl(OTf) crystals is observed.
At a first glance, this lack of reactivity toward the chloride
abstraction from the starting complex appears to be somewhat
2+
Dicationic complexes of [(P-P)M(µ-Cl)]2 type (M )
Pd, Pt), although not synthesized via the procedure described
herein, are well-known in the literature.22 For example, the
dppe based complex, formulated as [(dppe)Pd(µ-Cl)]2[BF4]2,
was crystallized upon evaporation of a CDCl3 solution of
[(dppe)Pd(MeCN)2][BF4]2.22a A very similar complex, for-
mulated as [(dppe)Pd(µ-Cl)]2[ClO4]2, was synthesized by
reacting (dppe)PdCl2 with silver perchlorate.22g
[(dppen)PdCl]2(OTf)2 crystallizes in the triclinic system,
space group P1h, with a dimeric entity in general position in
the unit cell (Figure 4).
Each Pd cation adopts a square-planar coordination, with
two chloride anions in µ2 position. The triflate anions act as
hydrogen bond acceptors in weak C-H‚‚‚O hydrogen bonds
involving the H atoms of the ethylene bridge. While the dppe
or dppp PdCl2 complexes are known to afford the triflate
salts upon treatment with Ag(OTf)1 or Tl(OTf), it therefore
(19) Johnson, M. J. A.; Gantzel, P. K.; Kubiak, C. P. Organometallics 2002,
21, 3831-3832.
(20) Oberhauser, W.; Bachman, C.; Bru¨ggeller, P. Inorg. Chim. Acta. 1995,
238, 35-43.
(21) Chow, K. K.; Levason, W.; MacAuliffe, C. A. Inorg. Chim. Acta 1974,
15, 79-83.
(22) (a) Abu-Surrah, A. S.; Klinga, M.; Repo, T.; Leskela, M.; Debaerde-
maeker, T.; Rieger, B. Acta Crystallogr., Sect. C: Cryst. Struct.
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Goddard, R. Russ. Chem. Bull. 1998, 47, 904-913. (c) Bravo, J.;
Cativiela, C.; Chaves, J. E.; Navarro, R.; Urriolabeitia, E. P. Inorg.
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A. D.; Spencer, J. L. Acta Crystallogr., Sect. C: Cryst. Struct.
Commun. 1992, C48, 913-915. (e) Evans, D. R.; Huang, M.; Fettinger,
J. C.; Williams, T. L. Inorg. Chem. 2002, 41, 5986-6000. (f) Longato,
B.; Pilloni, G.; Valle, G.; Corain, B. Inorg. Chem. 1988, 27, 956-
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(13) Janiak, C. Coord. Chem. ReV. 1997, 163, 107-216.
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(18) (a) Wells, A. F. In Structural Inorganic Chemistry, 5th ed.; Oxford
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Inorganic Chemistry, Vol. 43, No. 10, 2004 3139

Devic et al.
ligand, in the spirit of Dewar-Chatt-Duncanson model,25,26
or as analyzed by Frenking through the CDA (charge
decomposition analysis) model, to a more covalent character
of the C2P2Pd metallacycle,27 keeping in mind that within
this class of complexes the M-P bonding is very likely
dominated by the σ-interactions rather than by the π-bonding
(vide supra). A more reliable experimental tool allowing us
to compare the strengths of Pt-P bonds in a series of (P-
P)PtCl2 complexes, having the same metallacycle ring size,
1
consists of the analysis of the JP-Pt coupling constants as
measured by 31P NMR. Thus, for the complex (P2)PtCl2, a
value of 3640 Hz for the JP-Pt coupling constant has been
2+
1
Figure 4. ORTEP view of the bimetallic motif [(dppen)PdCl]2 in
[(dppen)PdCl]2(OTf)2.
measured (see Experimental Section), which is larger than
those described in the literature for the corresponding
Table 2. Pd-P and Pd-Cl Bond Distances in (P-P)PdCl2 Complexes
(dppen)PtCl2 (1JP-Pt ) 3623 Hz) and (dppe)PtCl2 (1JP-Pt
)
Pd-P (Å)
Pd-Cl (Å)
ref
3600 Hz).28 The variation of these coupling constants,
although the range is very small, tends to confirm that the
strength of the Pt-P bonds increases in the series (dppe)-
PtCl2, (dppen)PtCl2, and (P2)PtCl2, as a consequence of a
stronger σ-bonding effect. Consequently, the strengths of the
Pt-Cl bonds within this series should follow the same trend.
Very likely, this is also the case within the palladium
corresponding series, since we have shown that (P2)PdCl2
and (P2)PtCl2 have the same reactivity toward Tl(OTf).
The three examples shown here might resemble the
intermediates or the transition states in the general process
of (P-P)MCl2 (M ) Pd, Pt) chloride abstraction with Tl-
(OTf): (i) coordination of Tl+ of the chloride atoms in (P-
P)MCl2 complex as shown in the (P2)MCl2‚[Tl(OTf)] adduct
as first step, (ii) in the case of palladium, removal of one
Cl- anion to afford for example the lacunary [(dppen)-
PdCl0]+ which here dimerizes into [(dppen)PdCl]22+, (iii)
further coordination and chloride abstraction to give the
dechlorinated (dppp)M(OTf)2.1
(dppm)PdCl2
(dppe)PdCl2
(dppe)PdCl2‚(CH2Cl2)
(dppp)PdCl2
2.234(1), 2.250(1) 2.362(1), 2.352(1) 29
2.284(3), 2.264(3) 2.415(3), 2.394(3) 30
2.226(2), 2.233(2) 2.361(2), 2.357(2) 29
2.244(1), 2.249(2) 2.351(1), 2.358(1) 29
(dppen)PdCl2‚(CHCl3)2 2.229(1)
2.367(1)
31
(P2)PdCl2‚(CHCl3)2
2.217(3), 2.220(3) 2.341(3), 2.349(3) this work
2.227(2), 2.228(2) 2.353(2), 2.360(2) this work
[(P2)PdCl2]‚[Tl(OTf)]
appears that the tetrathiafulvalenyl P2 or the dppen unsatur-
ated diphosphines are strongly reluctant to undergo such
anion exchange under the experimental conditions we
employed in the present study, indicating a possibly stronger
Pd-Cl bond than in (dppe)PdCl2 or (dppp)PdCl2. The
structural and reactivity differences between (dppen)MCl2
and (dppe)MCl2 (M ) Pd, Pt) complexes have been widely
addressed throughout a series of recent papers.20,23 The
authors assigned the special properties of the cis-dppen ligand
when compared with the saturated dppe counterpart to an
enhancement of the M-to-P π bonding interaction, due to
the unsaturated nature of the aliphatic backbone in dppen.
This assignment was based on earlier theoretical calculations
dealing with the π-accepting abilities of phosphines in
transition metal complexes,24 although these studies refer to
zerovalent metal complexes. Indeed, it seems more judicious
to think that the M-P bonding in planar Pd(II) and Pt(II)
complexes is dominated by the σ-bonding. The analysis of
intramolecular bond lengths within (dppe)PdCl2, (dppen)-
PdCl2, and (P2)PdCl2 (Table 2), all of these complexes
including a five-membered ring chelate, shows only a very
modest tendency to exhibit shorter Pd-P and Pd-Cl bonds
with the unsaturated dppen and P2 diphosphines when
compared with dppe, and even with dppm (bis(diphen-
ylphosphino)methane) or dppp. Note also that the Pd-P and
Pd-Cl distances within (dppen)PdCl2‚(CHCl3)2 and (dppe)-
PdCl2‚(CH2Cl2) solvated complexes span the same range of
values. The modest shortening of the Pd-P and Pd-Cl
distances in the series (dppe)PdCl2 (solvent free), (dppen)-
PdCl2, and (P2)PdCl2 can be tentatively attributed to the
π-back retrodonation from the metal to the unsaturated
Conclusions
PdCl2 and PtCl2 complexes of the redox active diphosphine
P2 have been synthesized, and the palladium one has been
structurally characterized. Both complexes have been further
reacted with thallium triflate, and instead of the expected
dicationic bis(triflate) salt, a Tl(OTf) adduct of the starting
complexes was isolated. The single crystal X-ray analyses
proved the tetrametallic “M2Tl2” (M ) Pd, Pt) nature of this
adduct, formulated as [(P2)MCl2‚Tl(OTf)‚Et2O]2, whose
inner [TlCl] motif is that found in the extended solid TlCl.
Another unexpected result was provided by the reaction of
(dppen)PdCl2 with Tl(OTf), which afforded a dicationic
“Pd2” complex, also analyzed by X-ray on single crystals.
Thus, the compounds [(P2)MCl2]‚[Tl(OTf)] (M ) Pd, Pt)
(25) Dewar, M. J. S. Bull. Soc. Chim. Fr. 1951, 18, C71-C79.
(26) Chatt, J.; Duncanson, L. A. J. Chem. Soc. 1953, 2939-2947.
(27) Frenking, G.; Pidun, U. J. Chem. Soc., Dalton Trans. 1997, 1653-
1662.
(23) (a) Oberhauser, W.; Bachmann, C.; Stampfl, T.; Haid, R.; Bru¨ggeller,
P. Polyhedron 1997, 16, 2827-2835. (b) Oberhauser, W.; Bachmann,
C.; Stampfl, T.; Haid, R.; Langes, C.; Rieder, A.; Bru¨ggeller, P. Inorg.
Chim. Acta 1998, 274, 143-154.
(24) (a) Xiao, S.-X.; Trogler, W. C.; Ellis, D. E.; Berkovitch-Yellin, Z. J.
Am. Chem. Soc. 1983, 105, 7033-7037. (b) Marynick, D. S. J. Am.
Chem. Soc. 1984, 106, 4064-4065.
(28) Hope, E. G.; Levason, W.; Powell, N. A. Inorg. Chim. Acta 1986,
115, 187-192.
(29) Steffen, W. L.; Palenik, G. J. Inorg. Chem. 1976, 15, 2432-2439.
(30) Singh, S.; Jha, N. K. Acta Crystallogr. 1995, C51, 593-595.
(31) Juanatey, P.; Suarez, A.; Lopez, M.; Vila, J. M.; Ortigueira, J. M.;
Fernandez, A. Acta Crystallogr., Sect. C: Cryst. Struct. Commun.
1999, 55, IUC9900062.
3140 Inorganic Chemistry, Vol. 43, No. 10, 2004

ReactiWity of PdCl2 and PtCl2 Complexes
and [(dppen)PdCl]2(OTf)2 can be seen as possible intermedi-
ates in the general chloride abstraction process from (P-
P)MCl2 (M ) Pd, Pt) complexes with thallium triflate.
mass spectra measurements. The authors would like to
acknowledge also one of the reviewers of the paper for his
suggestions and comments.
Acknowledgment. Financial support from CNRS (Centre
National de la Recherche Scientifique), the Ministe`re de
l’Education et de la Recherche (grant for T.D.), and
University of Angers is gratefully acknowledged. The authors
thank Dr. D. Rondeau (University of Angers) for electrospray
Supporting Information Available: Crystallographic data for
the four X-ray crystal structures, in CIF format. This material is
available free of charge via the Internet at http://pubs.acs.org.
IC035447Y
Inorganic Chemistry, Vol. 43, No. 10, 2004 3141