Reactivity of phosphido-bridged diplatinum complexes towards electrophiles: Synthesis of new hydrides and related Pt2Cu and Pt2Ag clusters

Article abstract of DOI:10.1039/b206347f

The doubly-bridged, dinuclear complex [Pt₂(μ-PPh₂)(μ-o-C₆H₄PPh ₂)(PPh₃)₂] (1) reacts with electrophiles such as H¹ or [M(PPh₃)]¹ (M = Cu, Ag, Au) first at the metal-metal bond. This is supported by an X-ray diffraction study of [Pt₂{μ-Cu(PPh₃)}(μ-PPh₂)(μ-o-C ₆H₄PPh₂)(PPh₃)₂]PF ₆ (2) which reveals a Pt₂Cu triangular metal core and, unexpectedly, a bonding interaction between the Cu atom and the C_ipso of the orthometalated phenyl. This confers a tetrahedral-like geometry to the Cu atom. In the neutral complex [Pt₂{μ-AgOC(O)CF₃}(μ-PPh₂)(μ-o-C ₆H₄PPh₂)-(PPh₃)₂] (3), the silver atom is coordinated by the terminally bound trifluorocarboxylate anion. Reactions of 1 in a polar solvent with 2 equiv. of acid HA, where A is a weakly nucleophilic anion, afforded the dicationic solvento adducts [Pt₂(μ-H)(μ-PPh₂)(Solv)(PPh₃) ₃]A₂ (5a, Solv = THF, A = PF₆; 5b, Solv = CH₂Cl₂, A = BF₄; 5c, Solv = acetone, A = BF₄) which result from rupture of the Pt-C σ bond and transformation of the cyclometalated bridging ligand into PPh₃. The coordinated solvent molecule is readily displaced by nucleophiles such as PO₂F₂, CF₃SO₃, Cl or Br, thus forming monocationic complexes, 6-9, respectively. An X-ray diffraction study on [Pt₂(μ-H)(μ-PPh₂)(OPOF₂)-(PPh ₃)₃](PF₆)·0.5CH₂Cl ₂ (6·0.5CH₂Cl₂) establishes that the OPOF₂ group is linked by one O atom to platinum, to our knowledge an unprecedented feature.

Full text of DOI:10.1039/b206347f

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Reactivity of phosphido-bridged diplatinum complexes towards
electrophiles: synthesis of new hydrides and related Pt2Cu and
Pt2Ag clusters†
Christine Archambault,a Robert Bender,*a Pierre Braunstein*a and Yves Dusausoyb
a Laboratoire de Chimie de Coordination (UMR 7513 CNRS), Institut Le Bel,
Université Louis Pasteur, 4 rue Blaise Pascal, F-67070 Strasbourg-Cédex, France.
E-mail: braunst@chimie.u-strasbg.fr; Fax: ϩ 33 390 241 322
b Laboratoire de Cristallographie et Modélisation des Matériaux Minéraux et Biologiques,
UPRESA 7036, Université Henri Poincaré, Nancy I, Faculté des Sciences, Boîte postale 239,
F-54206 Vandoeuvre-les-Nancy, France
Received 1st July 2002, Accepted 19th September 2002
First published as an Advance Article on the web 22nd October 2002
The doubly-bridged, dinuclear complex [Pt2(µ-PPh2)(µ-o-C6H4PPh2)(PPh3)2] (1) reacts with electrophiles such as
Hϩ or [M(PPh3)]ϩ (M = Cu, Ag, Au) first at the metal–metal bond. This is supported by an X-ray diffraction study
of [Pt2{µ-Cu(PPh3)}(µ-PPh2)(µ-o-C6H4PPh2)(PPh3)2]PF6 (2) which reveals a Pt2Cu triangular metal core and,
unexpectedly, a bonding interaction between the Cu atom and the Cipso of the orthometalated phenyl. This confers a
tetrahedral-like geometry to the Cu atom. In the neutral complex [Pt2{µ-AgOC(O)CF3}(µ-PPh2)(µ-o-C6H4PPh2)-
(PPh3)2] (3), the silver atom is coordinated by the terminally bound trifluorocarboxylate anion. Reactions of 1 in a
polar solvent with 2 equiv. of acid HA, where A is a weakly nucleophilic anion, afforded the dicationic solvento
adducts [Pt2(µ-H)(µ-PPh2)(Solv)(PPh3)3]A2 (5a, Solv = THF, A = PF6; 5b, Solv = CH2Cl2, A = BF4; 5c, Solv = acetone,
A = BF4) which result from rupture of the Pt–C σ bond and transformation of the cyclometalated bridging ligand
into PPh3. The coordinated solvent molecule is readily displaced by nucleophiles such as PO2F2Ϫ, CF3SO3Ϫ, ClϪ or
BrϪ, thus forming monocationic complexes, 6–9, respectively. An X-ray diffraction study on [Pt2(µ-H)(µ-PPh2)(OPOF2)-
(PPh3)3](PF6)ؒ0.5CH2Cl2 (6ؒ0.5CH2Cl2) establishes that the OPOF2 group is linked by one O atom to platinum, to our
knowledge an unprecedented feature.
Introduction
Diplatinum complexes have been known for several decades
and owing to their regularly growing number, they now form
a very rich class of compounds with interesting chemistry.1
Amongst them, the hydrido complexes constitute a large family,
with diversified structural and spectroscopic features.2–4 The Pt
atoms are often linked through metal–metal bonding and/or
hydrido bridges. A bridging hydride may also be associated with
another, chemically different bridging unit. Although phos-
phido bridges have often been used to ensure the cohesion
of the metallic framework, diplatinum complexes combining
phosphido and hydrido bridges are still rather rare,3–10 and their
synthesis often relies on serendipity.7,8 In addition to their own
fundamental interest owing to diverse structural and spectro-
scopic features, platinum complexes are also known for their
catalytic properties (e.g. in hydrogenation, hydroformylation
and hydrosilylation), but only few such studies have been
reported with diplatinum complexes.11,12 Our interest for the
reactivity of diplatinum complexes such as [Pt2(µ-PPh2)(µ-o-
C6H4PPh2)(PPh3)2] (1), which contains two different, three
electron donor bridging groups, a diphenylphosphido ligand
and an orthometalated triphenylphosphine, originates from
the question of their potential chemoselective reactivity since
various sites are available to electrophiles in such molecules.13
Whereas [Pt2(µ-o-C6H4PPh2)2(PPh3)2] reacts with electrophiles
at the metal–metal bond,14,15 [Pt2(µ-PPh2)2(PPh3)2] adds two
equivalents of [Au(PPh3)]ϩ to give a Pt2Au2 cluster resulting
Scheme 1 Addition products of electrophilic reagents Eϩ and Au-
(PPh3)ϩ to dinuclear Pt()–Pt() complexes, as a function of the bridging
ligands.
from formal addition of the electrophile to the Pt–(µ-P) bond
(Scheme 1)16 and its dipalladium analogue was shown later to
add a proton to a Pd–(µ-P) bond.17,18 It therefore appeared par-
ticularly interesting to investigate and compare the reactivity
of the “mixed-bridged” complex 1 towards electrophilic metal
reagents with that of these dinuclear complexes [Pt2(µ-PPh2)2-
(PPh3)2] and [Pt2(µ-o-C6H4PPh2)2(PPh3)2] (Scheme 1).
† Dedicated to Prof. D. Fenske on the occasion of his 60th birthday,
with our most sincere congratulations and best wishes.
4084
J. Chem. Soc., Dalton Trans., 2002, 4084–4090
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b206347f

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Table 1 Selected bond distances (Å) and angles (Њ) for [Pt2{µ-Cu-
(PPh3)}(µ-PPh2)(µ-o-C6H4PPh2)(PPh3)2]PF6 (2)a
Previous studies on phosphido-bridged Pt–W complexes
have indicated that electrophiles react at the metal–metal
bond.19,20 We have already evidenced the electron-rich character
of the dinuclear complex 1 which contains 16e metal centres
and good electron donor ligands.13 In this paper, we report
the synthesis of a novel, neutral Pt2Ag complex obtained by
reaction of 1 with [AgOC(O)CF3], the crystal structure of
[Pt2{µ-Cu(PPh3)}(µ-o-C6H4PPh2)(µ-PPh2)(PPh3)2]PF6 (2) which
displays an unusual 3c–2e Pt–C–Cu system, and the reactivity
of complex 1 with acids having a poorly coordinating con-
jugated base, which afforded new cationic hydrido complexes.
Pt(1)–Pt(2)
Pt(1)–Cu
Pt(2)–Cu
Pt(1)–P(3)
Pt(1)–P(4)
Pt(1)–C(73)
2.657(1)
2.536(3)
2.595(3)
2.278(6)
2.248(5)
2.11(2)
Pt(2)–P(1)
Pt(2)–P(2)
Pt(2)–P(4)
Cu–P(5)
Cu–C(73)
Cu–C(78)
C(73)–C(78)
2.302(5)
2.283(5)
2.292(5)
2.180(6)
2.52(1)
2.87(1)
1.39(1)
Cu–Pt(1)–P(4)
96.2(1)
55.0(1)
162.8(1)
59.9(1)
102.0(3)
64.9(3)
95.2(3)
62.4(1)
151.5(2)
139.0(1)
120.9(7)
P(2)–C(78)–C(73)
Pt(1)–Pt(2)–Cu
Pt(1)–Pt(2)–P(4)
Cu–Pt(2)–P(4)
Pt(1)–Pt(2)–P(2)
Cu–Pt(2)–P(2)
Pt(1)–Pt(2)–P(1)
Cu–Pt(2)–P(1)
P(1)–Pt(2)–P(2)
Pt(2)–P(4)–Pt(1)
Pt(2)–P(2)–C(78)
118.4(7)
57.7(1)
53.4(1)
93.5(2)
85.3(1)
76.5(2)
160.9(1)
125.8(1)
113.8(2)
71.6(2)
113.8(4)
Pt(2)–Pt(1)–P(4)
Pt(2)–Pt(1)–P(3)
Pt(2)–Pt(1)–Cu
P(3)–Pt(1)–C(73)
Cu–Pt(1)–C(73)
C(73)–Pt(1)–Pt(2)
Pt(1)–Cu–Pt(2)
P(5)–Cu–Pt(1)
Results
Reactions of [Pt2(ꢀ-PPh2)(ꢀ-o-C6H4PPh2)(PPh3)2] (1) with
electrophilic metal reagents and X-ray structure of [Pt2{ꢀ-Cu-
(PPh3)}(ꢀ-PPh2)(ꢀ-o-C6H4PPh2)(PPh3)2]PF6 (2)
P(5)–Cu–Pt(2)
Pt(1)–C(73)–C(78)
We have previously shown that complex 1 reacts with the electro-
philes [M(PPh3)]ϩ (M = Cu, Ag, Au) to afford cationic clusters
of general formula [Pt2{µ-M(PPh3)}(µ-PPh2)(µ-o-C6H4PPh2)-
(PPh3)2]ϩ.13 On the basis of their spectroscopic properties, we
concluded that the M(PPh3) fragment bridges the Pt–Pt bond,
thus indicating that the basicity of the metal–metal bond in 1
is sufficient to lead to thermodynamically stable addition
products. Crystals of 2 suitable for X-ray diffraction could now
be obtained, which revealed interesting features (Scheme 2,
Fig. 1 and Table 1).
a For the numbering of the atoms, see Fig. 1. The P(1) and P(3) labels
are interchanged in the NMR section.
Fig. 1 View of the crystal structure of [Pt2{µ-Cu(PPh3)}(µ-PPh2)(µ-o-
C6H4PPh2) (PPh3)2]PF6 (2) with the atom numbering scheme. Note that
the numbering of P(1) and P(3) is interchanged with respect to the
labels used for the NMR study of the other compounds and for the
structure of 6ؒ0.5CH2Cl2 (Fig. 3).
This crystal structure confirms that the Cu atom is linked to
both Pt atoms, in a slightly asymmetric fashion [Cu–Pt(1) =
2.536(3) Å and Cu–Pt(2) = 2.595(3) Å)] but also reveals an
additional, weak interaction between the Cu atom and the pz
orbital of the metalated sp2 carbon C(73) [Cu–C(73) = 2.52(1)
Å]. The longer Cu–C(78) distance of 2.87(1) Å is not consistent
with a description of this interaction as involving the C(73)–
C(78) double bond. The Pt2Cu plane makes a dihedral angle of
64.0(1)Њ with the mean plane of the core atoms Pt(1), P(4),
Pt(2), P(2), C(78) and C(73). The coordination of the Cu(PPh3)
fragment to 1 does not significantly affect the geometry and
bonding parameters of the latter moiety; in particular the Pt–Pt
distances in complexes 1 and 2 are similar.13 The largest vari-
ations observed on going from 1 to 2 are in the P(2)–C(78)–
C(73) orthometalated bridge, with a slight closing of the C(73)–
C(78)–P(2) angle from 124(2) to 118.4(7)Њ, and an opening of
Scheme 2
J. Chem. Soc., Dalton Trans., 2002, 4084–4090
4085

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Table 2 Selected 1H and 31P{1H} NMR data for complexes 1 and 3–9 (δ in ppm and J in Hz)
1
3
4
5a
5b
Ϫ5.44
418, 489
75, 67,
14, 14
14.7
9.0
23.1
113.8
3899
2450
4380
1878
3207
249
66
5c
6
7
8
9
δ(1H)
—
—
—
—
—
—
Ϫ5.10
383, 521
80, 68,
14.5,14.5
23.3
28.4
30.4
—
—
—
—
—
—
Ϫ5.08
385, 517
80, 70,
15
15.6
11.3
—
—
—
Ϫ4.68
367, 524
81,70,
15.5,13.5
14.6
10.5
21.5
Ϫ4.58
372, 519
80,70,
15, 13
14.3
10.8
20.7
139.6
3893
2407
4306
1902
2904
211
1J(H–Pt)
2J(H–P)
δ(P1)
28.4
9.1
31.3
29.1
16.0
31.0
14.8
10.3
22.7
15.3
9.0
23.4
14.9
11.5
23.3
δ(P2)
δ(P3)
23.3
112.5
δ(P4)
164.6
3607
182.2
3799
2809
3575
2078
2435
214
167.8
112.1
3902
114.3
3935
2472
4375
1885
3192
—
—
221
—
114
132.2
1J(P1–Pt1)
1J(P2–Pt2)
1J(P3–Pt2)
1J(P4–Pt1)
1J(P4–Pt2)
2J(P1–Pt2)
2J( P2–Pt1)
2J(P3–Pt1)
3J(P1–P2)
3J(P1–P3)
2J(P1–P4)
2J(P2–P3)
2J(P2–P4)
2J(P3–P4)
3770
3046
4575
3505
4778
40
3890
2417
4388
1847
3315
223
73
3887
2453
4385
1859
3388
—
3895
2392
4340
1872
2942
213
64
3210
3343
2116
2645
215
73
2422
4384
1855
3336
249
36
55.5
322
98
94
63
255
19
63
298
20
526
6
266
20
238
20
255
21
300
20
—
—
151
30
9
213
< 5
140
17
—
220
—
109
60
—
279
58
50
8
49
45
—
—
—
277
—
47
57
10
58
8
—
—
—
—
—
—
—
—
—
277
—
282
—
283
—
279
—
264
—
264
—
the P(3)–Pt(1)–C(73) angle from 98.5(5) to 102.0(3)Њ and of
the Pt(1)–C(73)–C(78) angle from 114(1) to 120.9(7)Њ. These
deformations are probably induced by the 2e–3c Pt–C(73)–Cu
interaction. Crystal structures of complexes containing a
Pt–Cu bond are rather rare,21a and only three of them contain a
Pt–Cu–phosphine sequence.22–24 The Pt–Cu distances in 2 are
close to those observed in [CuPt3(µ-CO)3(PPh3)5]BF4, where the
Cu(PPh3) group caps a triangle of Pt atoms.22 The Cu–P dis-
tance in 2 is shorter than those observed in other complexes
containing the Cu–PPh3 moiety.22,23,25
simulations afforded chemical shifts and coupling constants
very similar to the experimental values and they confirmed the
analysis of the spectrum. Therefore, the experimental values
for 3 may be used with confidence for the description of this
spectrum. For consistency, only the experimental values of the
other compounds are reported (Table 2).
The most deshielded 31P{1H} NMR resonance (δ 182.2 ppm)
is attributed to the bridging P(4) atom, its chemical shift
indicating the presence of a Pt–Pt bond.26 The other three
signals belong to the terminal and orthometalated phosphines.
The large value of the P–P coupling constants correspond to
Complex 1 reacted with 1 equiv. [AgOC(O)CF3] in toluene at
room temperature to afford the neutral, heterotrinuclear cluster
[Pt2{µ-AgOC(O)CF3}(µ-PPh2)(µ-o-C6H4PPh2)(PPh3)2] (3). This
compound is soluble in THF, CH2Cl2 or in toluene where it
slowly decomposes at room temperature with formation of
metallic silver, in the daylight or in the dark. The IR spectrum
of 3 showed intense absorption bands at 1667, 1200 and 1135
cmϪ1 due to the trifluoroacetato ligand and a medium band at
724 cmϪ1 characteristic of the orthometalation.13 The mass
spectrum of 3 did not contain the peak corresponding to Mϩ at
m/z = 1576.9, but peaks at 1469.1 and 1361.2 due to the frag-
ments [M–CF3CO2]ϩ and [M–AgOC(O)CF3]ϩ (1ϩ), respectively.
The 31P{1H} NMR spectrum of 3 resembles that of 1 with
resonances for four chemically and magnetically different
2
nuclei in mutual trans positions: P(2) and P(4) with J[P(2)–
3
P(4)] = 220 Hz and P(1) and P(3) with J[P(1)–P(3)] = 140 Hz.
The small values of the other P–P couplings or their absence are
2
due to the relative cis positions of P(1) and P(4) with J[P(1)–
P(4)] = 17 Hz and of P(3) and P(2) and P(4), respectively. No
2J(Ag–P) coupling constant could be observed in the spectrum,
in contrast to the case of the complex cation [Pt2{µ-Ag-
(PPh3)}(µ-PPh2)(µ-o-C6H4PPh2)(PPh3)2]ϩ.13 Nevertheless, on
the basis of the spectroscopic data available, we assign to cluster
3 a structure comparable to that of 2, i.e. with a planar Pt2P4
core, as in 1, and the AgOC(O)CF3 group bridging the Pt–Pt
bond. This group has previously been found to coordinate to
the triplatinum core of [Pt3(µ-PPh2)3Ph(PPh3)3] to form a tetra-
hedral Pt3Ag cluster in which the CF3CO2 ligand is coordinated
to Ag by only one oxygen atom.27 Since the trifluoroacetate
ligand leads in the IR spectrum to the same three absorptions in
both clusters, we propose a similar coordination mode for this
ligand on the Ag atom in 3.
1
or
31P nuclei, flanked by satellites due to
2J(P–Pt) couplings
(Table 2). The chemical shifts and coupling constants 2 or 3J(P–
1
or
P) and
2J(P–Pt) are comparable to those for the Pt2P4 core
of the related cationic cluster [Pt2{µ-Ag(PPh3)}(µ-PPh2)(µ-o-
C6H4PPh2)(PPh3)2]ϩ.13 The P(2) and P(4) nuclei of 3 are only
slightly deshielded when compared with those in complex 1.
2
or
1 or
Their
3J(P–P) values are almost identical and the
2J(P–
Reactions of [Pt2(ꢀ-PPh2)(ꢀ-o-C6H4PPh2)(PPh3)2] (1) with acids
Pt) vary only slightly, remaining in the usual range.7,8 The
31P{1H} NMR spectrum of 3 has been satisfactory simulated
using the gNMR software for three of the four isotopomers,
those with the spin systems ABEM (M = µ-P, abundance
43.82%, no 195Pt), ABEMX (X = 195Pt(1), 22.38%) and ABEMY
(Y = 195Pt(2), 22.38%). The spectrum of the isotopomer with
the spin system ABEMXY (X, Y = 195Pt, 11.42%) has not been
simulated because the corresponding signals were too weak to
be clearly identified in the experimental spectrum. The spectral
The reaction of a THF solution of the diplatinum complex 1
with 1 equiv. HPF6 diluted in H2O afforded complex 4 whereas
reaction of 1 in a polar solvent with 2 equiv. of acid HA, where
A is a weakly nucleophilic conjugated base, afforded the di-
cationic solvento adducts [Pt2(µ-H)(µ-PPh2)(Solv)(PPh3)3]A2
(5a, Solv = THF, A = PF6; 5b, Solv = CH2Cl2, A = BF4; 5c, Solv
= acetone, A = BF4) (Scheme 2). Complex 5a is insoluble in
THF and upon dissolution in CH2Cl2, its coordinated THF
4086
J. Chem. Soc., Dalton Trans., 2002, 4084–4090

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2
molecule probably exchanges with CH2Cl2, as indicated by the
similarity of its 31P NMR spectrum with that of 5b. The slight
differences observed may be due to incomplete displacement of
THF, which is a better donor ligand than CH2Cl2,28a although
in our case the latter is present in considerable excess. Further-
more, 5a is difficult to dry and the remaining water resulted in
rapid hydrolysis, in CH2Cl2 solution, of one of the PF6 anions,
affording compound 6, which contains a PO2F2 anion as ligand
in place of the solvent molecule. A related complex, [Pt2(µ-H)-
(µ-PPh2)(OSO2CF3)(PPh3)3] (SO3CF3) (7), was obtained by
reaction of 1 with 2 equiv. of CF3SO3H. The 31P NMR spectra
of 6 and 7 are very similar (Table 2). Dichoromethane solutions
of 5b contained small quantities of the BF4 salt of the mono-
cationic chloro complex present in 8, as seen by 31P{1H} NMR
(Scheme 2). The same cation was formed quantitatively by
reaction of 1 with a mixture of 1 equiv. HCl and 1 equiv. HPF6
or CF3SO3H. Its bromo analogue 9 was obtained by reaction of
1 with a mixture of 1 equiv. HBr and 1 equiv. HPF6 (Scheme 2).
Unexpectedly, crystals of 8c were obtained upon crystallisation
from CH2Cl2/Et2O of the BF4 analogue of 4. Although the
poor quality of the crystals prevented complete structural reso-
lution, both the core structure of the dinuclear cation contained
in 8 and the presence of the chloro ligand, which must originate
from the solvent (or from HCl contamination), have been con-
firmed by a preliminary X-ray diffraction study.29
plicity of this signal arises from four J(P–H) coupling con-
stants, two of them of ca. 14 Hz for two 31P nuclei in cis
position with respect to the proton and the other two of ca. 70
and 80 Hz due to two 31P nuclei in trans positions. These data
are indicative of the bridging position of the proton on the
Pt–Pt bond, as found for the isolobal [Cu(PPh3)]ϩ group in
cluster 2.
Molecular structure of [Pt2(ꢀ-H)(ꢀ-PPh2)(OPOF2)(PPh3)3]-
(PF6)ؒ0.5CH2Cl2 (6ؒ0.5CH2Cl2)
The molecular structure of 6ؒ0.5CH2Cl2 has been determined
by X-ray diffraction on crystals obtained from a mixture
CH2Cl2/diethyl ether. A view of the structure is shown in Fig. 3
and selected bond distances and angles are reported in Table 3.
This structure is based on two Pt atoms linked by a metal–metal
bond [Pt(1)–Pt(2) = 2.8711(4) Å] and an asymmetric PPh2
bridge [Pt(1)–P(4) = 2.206(2) Å, Pt(2)–P(4) = 2.296(2) Å]. These
values are in the range found in structurally related molecules.7,8
The new complexes 4–9 present in their IR spectra absorp-
tion bands characteristic of their anions: ν(PF6) = 836–839 cmϪ1
,
ν(BF4) = 1055 cmϪ1, ν(CF3SO3) = 1260 and 1125 (SO3) and 1220
Ϫ
and 1140 cmϪ1 (CF3).28b In addition, PF6 shows the usual
septet in the 31P{1H} NMR spectrum at δ Ϫ143, with 1J(P–F) =
711 Hz.30 Only 4 shows the characteristic orthometalation
absorption at 724 cm ,
Ϫ1 13 thus indicating that after protonation
of 1, the orthometalation P–C bond was retained in 4, but
cleaved in 5–9. The free coordination site thus liberated was
occupied by a molecule of solvent, THF, CH2Cl2 or acetone or
by the anions OPOF2, OSO2CF3, Cl or Br. The presence of
THF was evidenced by 1H NMR spectroscopy of a solution of
5a in CH2Cl2, with two triplets of equal intensity at δ 1.85 and
3.75, respectively, due to the THF liberated upon dissolution.
The acetone ligand of 5c accounts for an IR ν(C=O) absorption
band at 1642 cmϪ1. The PO2F2 ligand in 6 leads in the IR spec-
trum to ν(PO) and ν(PF) bands at 1312 (vs) and 838 (vs) cmϪ1
,
respectively,30–32 and in the 31P{1H} NMR spectrum to a broad
triplet at δ Ϫ16.7 (1J(PF) = 967 Hz),33 which suggests small,
unresolved coupling constants with Pt and other P nuclei.
The similarity of the 31P{1H} NMR spectra of 1 with those
of complexes 4–9 suggests analogous molecular structures for
these complexes. These spectra, as well as the 1H NMR spectra,
could be analyzed using the first order approximation since
spectral simulations using gNMR gave very similar values to
the experimental ones, for complex 4, as well as for 3. Therefore
only the absolute values of the coupling constants are reported
in Table 2. Like 1, the new complexes display 31P{1H} NMR
spectral patterns corresponding to four chemically and mag-
netically different 31P nuclei, all of them being flanked by
Fig. 2 (a) 1H and (b) 31P{1H} NMR spectra of [Pt2(µ-H)(µ-PPh2)-
Br(PPh3)3](PF6) (9) in CD2Cl2.
1
or
satellites due to
2J(P–Pt) couplings. In all these complexes,
P(4) resonates at low field, indicating a phosphido group
bridging a metal–metal bond, while the other resonances are
in the usual range for terminal phosphines. The large value of
ca. 270 Hz for 2J[P(2)–P(4)] in complexes 4–9 indicates the
mutual trans position of these nuclei.
On going from 1 to 4, the values of 1J[Pt(2)–P(3)] and of both
1J[Pt–P(4)] couplings increase significantly, with the latter being
among the largest values found for 1J(Pt–P) couplings involving
a µ-PPh2 group. In contrast, a comparison of 4 with 5–9 shows
1
1
1
a decrease of J[Pt–P(2)] and J[Pt–P(4)], while J[Pt–P(1 or 3)
Fig. 3 View of the crystal structure of [Pt2(µ-H)(µ-PPh2)(OPOF2)-
(PPh3)3](PF6) in 6ؒ0.5CH2Cl2 with the atom numbering scheme. For
clarity, only the ipso phenyl carbons are represented and the hydride
ligand bridging the Pt(1)–Pt(2) bond is not shown. The projection view
is not in the plane Pt(1)–Pt(2)–P(4).
1
remain comparable. The H NMR spectra of the new com-
plexes 4–9 contain a dddd pattern around Ϫ5 ppm, with two
sets of satellites due to two different 1J(H–Pt) couplings, in the
range 367–418 and 489–524 Hz, respectively (Fig. 2). The multi-
J. Chem. Soc., Dalton Trans., 2002, 4084–4090
4087

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Table 3 Selected bond distances (Å) and angles (Њ) for [Pt2(µ-H)-
(µ-PPh2)(OPOF2)(PPh3)3](PF6)ؒ0.5CH2Cl2 (6ؒ0.5CH2Cl2)
When an acid with a weakly coordinating conjugated base
was reacted with 1, the proton goes to a bridging position on
the Pt–Pt bond of 1, without rupture of the orthometalated Pt–
C bond. Only a second proton induces the breaking of this
bond, with formation of a terminal triphenylphosphine ligand
and liberation of a vacant coordination site on platinum, which
is then occupied by a solvent molecule. The resulting complexes
5 are thus dicationic. When a more nucleophilic reagent XϪ
is present in solution (X = PO2F2, CF3SO3, Cl, Br), it occupies
this vacant site to form a new monocationic complex, 6–9,
respectively. Although monocationic diplatinum hydrides
have long been known,3a and can adopt various geometries,2
examples containing an additional phosphido bridge are
rarer,3,5–9 and, to our knowledge, no such dicationic species has
been previously observed.
The orthometalated Pt–C bond is no longer present in com-
plexes 5–9 and these complexes present a similar set of NMR
data, suggesting that their geometry and the localization of the
bridging proton are similar, probably in the Pt2P4 plane of the
cation. A similar disposition is found in [Pt2Ph(µ-H)(µ-PPh2)-
(PPh3)3]ϩ.7,8 Complex 4 shows a set of 31P NMR resonances of
which some are very different from those of 1 or 5–9. This could
be the consequence of a different geometry for 4, and particu-
larly a non-planarity of the Pt2P4 core. Indeed, the persistence
of the orthometalated cycle in 4 certainly hinders the localiza-
tion of the proton in this plane and as a consequence, P(1) and
P(3), which lie in transoid positions with respect to the proton
and whose 2J(P–Pt) are much lower compared to the other
complexes, should be located out of the molecular plane, on
the opposite side to the proton (A-frame type structure). The
opening of the Pt–C bond in complexes 5–9 allows a re-
arrangement of the geometry of 4 into a planar one, with the
bridging proton located now between the former ortho-
metalated phosphine P(2) and the new incoming ligand (solvent
or ligand X).
Pt(1)–Pt(2)
Pt(1)–P(1)
Pt(1)–O(1)
Pt(1)–P(4)
Pt(2)–P(2)
Pt(2)–P(3)
2.8711(4)
2.282(2)
2.156(4)
2.206(2)
2.355(2)
2.291(2)
Pt(2)–P(4)
P(5)–O(1)
P(5)–O(2)
P(5)–F(1)
P(5)–F(2)
2.296(2)
1.494(5)
1.432(6)
1.546(5)
1.547(6)
P(1)–Pt(1)–Pt(2)
P(1)–Pt(1)–P(4)
P(1)–Pt(1)–O(1)
O(1)–Pt(1)–Pt(2)
O(1)–Pt(1)–P(4)
Pt(2)–Pt(1)–P(4)
P(2)–Pt(2)–Pt(1)
P(2)–Pt(2)–P(4)
P(2)–Pt(2)–P(3)
Pt(1)–Pt(2)–P(3)
153.13(5)
102.42(6)
87.2(1)
119.2(1)
169.7(1)
51.76(4)
108.46(4)
152.41(6)
99.42(6)
150.47(4)
P(3)–Pt(2)–P(4)
Pt(1)–Pt(2)–P(4)
Pt(1)–P(4)–Pt(2)
O(1)–P(5)–O(2)
O(1)–P(5)–F(1)
O(1)–P(5)–F(2)
F(1)–P(5)–O(2)
F(2)–P(5)–O(2)
F(1)–P(5)–F(2)
P(5)–O(1)–Pt(1)
101.39(6)
49.00(4)
79.24(5)
121.3(3)
109.0(3)
106.9(3)
110.5(3)
108.2(4)
98.6(4)
130.3(3)
Two terminal phosphines P(1) and P(3) lie respectively in
trans position to the Pt–Pt bond, and the coordination spheres
of the metal atoms are completed by an OPOF2 ligand for
Pt(1) and a third phosphine P(2) for Pt(2). The latter ligands
are both in transoid position with respect to the µ-PPh2 group.
The OPOF2 group is linked by one O atom to Pt(1), to our
knowledge an unprecedented feature, although the distances
and angles within this ligand are in good agreement with the
rare examples found in the literature for a monocoordinated
difluorophosphate on other metals.30,33–36 The core atoms of 6,
Pt(1), Pt(2), P(1), P(3), P(4) and O(1) are almost coplanar;
the P(2) atom lies at 1.017 Å from their mean plane. This
confirms the results of the 31P{1H} NMR study. A PF6 anion
Ϫ
and half a molecule of CH2Cl2 of crystallisation are associated
with each dinuclear cation. The bridging proton evidenced
1
by H NMR spectroscopy could not be located in the X-ray
study, but the long Pt(1)–Pt(2) distance is indicative of such a
All complexes 1 and 4–9 possess 30 electrons and display a
metal–metal bond, which leads to a 16e environment for each
Pt atom. In 1, both Pt atoms should be formally considered as
Pt(), whereas in complexes 4–9, they are better considered as
Pt() centres, as in [Pt2Ph(µ-H)(µ-PPh2)(PPh3)3]ϩ. With this
formalism, the incoming proton has been formally reduced into
a hydride and both Pt atoms have been oxidized from Pt() to
Pt(). The second proton, upon breaking the metal–carbon
σ bond of the orthometalated phenyl group, does not change
the oxidation state of the Pt atoms in complexes 5–9.
bridge.7,8
Discussion
The Pt–Pt bond of complex 1 is sufficiently electron-rich to
coordinate a proton or the isolobal electrophilic groups
[M(PPh3)]ϩ (M = Cu, Ag, Au). This indicates for 1 a reactivity
towards electrophiles closer to that of [Pt2(µ-o-C6H4PPh2)2-
(PPh3)2]14,15 than of [Pt2(µ-PPh2)2(PPh3)2].16 The molecular
structure of the Pt2Cu cluster 2 shows that the core structure of
its precursor 1 is not significantly altered and the Pt–Pt bond
distance is similar in both complexes, suggesting that the inter-
action of the [Cu(PPh3)]ϩ group with 1 is weak. The relatively
short Cu–C(73) distance indicates a bonding interaction of the
Cu atom with this Cipso of the orthometalated phenyl, which
confers a tetrahedral-like geometry to the Cu atom, prefered
here over the trigonal one.23 Although related bonding situ-
ations have been observed in homonuclear Pt3 complexes,37
such situations are relatively rare with copper38,39 and 2 appears
to be the first example of a 2e–3c bond involving a Pt–C–
Cu(PPh3) moiety. In the Pt2Ag cluster 3, the neutral fragment
AgOC(O)CF3 also occupies a bridging position on the Pt–Pt
bond of 1. It is often more difficult or even impossible to obtain
stable complexes with group 11 metals other than gold, which is
related to the increased lability of the related copper and silver
complexes.21 Thus for example, the diplatinum complex [Pt2(µ-
PPh2)2(PPh3)2] formed a stable compound with two Au(PPh3)ϩ
fragments (Scheme 1),16 while neither [Cu(PPh3)]ϩ, [Ag(PPh3)]ϩ
nor [AgOC(O)CF3] gave stable, isolable compounds. Cluster 3
is not as stable as the related cationic cluster [Pt2{µ-Ag-
(PPh3)}(µ-PPh2)(µ-o-C6H4PPh2)(PPh3)2]ϩ, but the stabilisation
of Ag() by the O atom of CF3CO2 permits its isolation and
seems to slow down the redox process that leads to the form-
ation of metallic silver.
Experimental
All experiments were performed under an inert atmosphere of
deoxygenated and dried nitrogen with the use of the Schlenk
techniques. The complexes [Pt2(µ-o-C6H4PPh2)(µ-PPh2) (PPh3)2]
and
[Pt2{µ-Cu(PPh3)}(µ-PPh2)(µ-o-C6H4PPh2)(PPh3)2](PF6)
were prepared as described in the literature.13 Solvents were
dried and distilled under nitrogen prior to use. Infrared spectra
were measured in KBr pellets on a Nicolet 205 FT-IR spec-
trometer and NMR spectra on Bruker AM 400 (31P at 161.977
MHz) and on a FT-Bruker WP 200 SY instrument (31P at
81.02 MHz and 1H at 200.13 MHz). Phosphorus chemical shifts
were externally referenced to 85% H3PO4 in H2O, with down-
field chemical shifts reported as positive. Proton chemical shifts
were positive downfield relative to external SiMe4. FAB mass
spectra were measured using a VG ZAB-HF mass spectrometer,
in a NBA matrix.
Preparations
[Pt2{ꢀ-AgOC(O)CF3}(ꢀ-o-C6H4PPh2)(ꢀ-PPh2)(PPh3)2] (3).
Toluene (3 mL) was added to a mixture of solid [Pt2(µ-PPh2)(µ-
o-C6H4PPh2)(PPh3)2] 1 (170 mg, 0.125 mmol) and [AgOC(O)-
CF3] (29 mg, 0.131mmol, 5% excess). The mixture was stirred at
4088
J. Chem. Soc., Dalton Trans., 2002, 4084–4090

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Table 4 Crystallographic details for [Pt2Cu{µ-o-C6H4PPh2}(µ-PPh2)-
(PPh3)3][PF6] and [Pt2(µ-H)(µ-PPh2)(OPOF2)(PPh3)3][PF6]ؒ
0.5CH2Cl2 (6ؒ0.5CH2Cl2)
room temperature for 5 min and its colour quickly turned
brown. Addition of hexane (ca. 5 mL) yielded a beige powder
of 3 (154 mg, 78%). Anal. calc. for C68H54AgF3O2P4Pt2 (Mr =
1582.09): C, 51.62; H, 3.44. Found: C, 52.77; H, 3.75. IR (KBr):
1667(s), 1200(s), 1135(s) cmϪ1 (CF3CO2), 724(m) cmϪ1 (ν
orthometalation). FABMS (p-O2NC6H4CH2OH, NBA matrix):
m/z = 1469.1 (M Ϫ CF3CO2)ϩ, 1361.2 (M Ϫ CF3CO2Ag)ϩ.
Details of the 31P{1H} and 1H NMR studies are summarized in
Table 2.
(2)
2
6ؒ0.5CH2Cl2
C66.5H57ClF8O2P6Pt
1651.57
Formula
M
C84H69CuF6P6Pt2
1832.04
T /K
Crystal system
Space group
293
173
triclinic
triclinic
¯
¯
P1
P1
a/Å
b/Å
c/Å
α/Њ
13.319(2)
17.472(2)
18.380(3)
84.59(1)
80.87(1)
86.56(1)
4199
12.847(1)
13.511(1)
19.107(1)
84.58(1)
86.19(1)
86.95(1)
3290.9
[Pt2(ꢀ-H)(ꢀ-PPh2)(ꢀ-o-C6H4PPh2)(PPh3)2]PF6 (4). HPF6
(10.5 µL, 75% in H2O, 0.1 mmol) was added to a solution of
[Pt2(µ-PPh2)(µ-o-C6H4PPh2)(PPh3)2] (136.8 mg, 0.1 mmol) in
THF (15 mL). The colour of the solution rapidly changed from
orange to red and then to pale orange. The mixture was stirred
for 5 h at room temperature and the solvent was evaporated to
dryness under reduced pressure. The 31P{1H} NMR spectrum
of the solid residue dissolved in CH2Cl2/C6D6 showed only one
product formed in quantitative yield. Anal. calc. for C66H55F6-
P5Pt2 (Mr = 1507.182): C, 52.60; H, 3.68. Found: C 51.21; H,
4.05. IR (KBr): 836(s) (PF6) cmϪ1. FABMS (p-O2NC6H4CH2-
OH) (NBA) matrix: m/z = 1361.0 (M)ϩ, 1283.9 (M Ϫ Ph)ϩ,
1098.9 (M Ϫ PPh3)ϩ, 1021.8 (M Ϫ PPh3 Ϫ Ph)ϩ. See NMR
details in Table 2.
β/Њ
γ/Њ
V/Å3
Z
2
2
ρcalc/g cmϪ1
1.436
3.893
16179
9089 [I > 3σ(I)]
0.0506
1.667
4.498
15019
11092 [I > 2σ(I)]
0.0414
µ(Mo–Kα)/mmϪ1
Reflections collected
Independent reflections
Final R1
Rw
0.0485
0.1156
[Pt2Cl(ꢀ-H)(ꢀ-PPh2)(PPh3)3]PF6 (8a). Complex 4 in a CH2-
Cl2 solution transformed into 8a in 1 day at room temperature,
the HCl originating from the solvent. Evaporation of the
solvent to dryness afforded 8a quantitatively. Its purity was
monitored by 31P{1H} NMR in CH2Cl2/C6D6. See NMR details
in Table 2.
[Pt2(ꢀ-H)(ꢀ-PPh2)(PPh3)3(THF)](PF6)2 (5a). HPF6 (13 µL,
75% in H2O, 0.124 mmol) was added to a solution of 1
(84.5 mg, 0.062 mmol) in THF (15 mL). The colour of the
solution rapidly changed from orange to yellow. After stirring
at room temperature for 1 h, a white precipitate was formed,
filtered, washed with cold THF and dried under reduced
pressure. Complex 5a was isolated in 71% yield. Anal. calc. for
C70H64OF12P6Pt2 (Mr = 1725.26): C, 48.73; H, 3.74. Found:
[Pt2Cl(ꢀ-H)(ꢀ-PPh2)(PPh3)3]SO3CF3 (8b). Pure CF3SO3H
(4.4 µL, 0.05 mmol), then HCl (4.2 µL, 37% in H2O, 0.05 mmol)
were added to a solution of 1 (68.0 mg, 0.05 mmol) in THF
(10 mL). The colour of the solution rapidly changed from
orange to red, and then to yellow. After the solution was stirred
for 5 h at room temperature, the solvent was removed under
reduced pressure and the product dried in vacuo. The spectro-
scopic yield (31P{1H} NMR) was quantitative and the purity
of 8b was monitored by 31P{1H} NMR in a mixture of CH2Cl2
and C6D6. Details of the 1H and 31P{1H} NMR data are
summarized in Table 2. FABMS (p-O2NC6H4CH2OH) (NBA
matrix): m/z 1397.8 (Mϩ), 1134.8 (M Ϫ PPh3)ϩ.
C, 48.60; H, 3.58. IR (nujol): 838 (s) (PF6) cmϪ1
.
[Pt2(ꢀ-H)(ꢀ-PPh2)(PPh3)3(CH2Cl2)](BF4)2 (5b). HBF4 (42 µL,
34% in H2O, 0.20 mmol) was added to a solution of [Pt2(µ-
PPh2)(µ-o-C6H4PPh2)(PPh3)2] 1 (136 mg, 0.10 mmol) in CH2Cl2
(50 mL). The colour of the solution rapidly changed from
orange to pale yellow. After stirring at room temperature for 4
h, evaporation of the solvent under reduced pressure overnight
afforded a yellow precipitate. See NMR details in Table 2.
[Pt2Br(ꢀ-H)(ꢀ-PPh2)(PPh3)3]PF6 (9). HPF6 (10.5 µL, 75% in
H2O, 0.1 mmol), then HBr (114 µL, 48% in H2O diluted 10
times, 0.1 mmol) were added to a solution of 1 (136.0 mg,
0.1 mmol) in THF (30 mL). The colour of the solution rapidly
changed from orange to colourless. After the solution was
stirred for 3 h at room temperature, the solvent was removed
under reduced pressure and the purity of the solid was moni-
tored by 31P{1H} NMR in CD2Cl2. Details of the 1H and
31P{1H} NMR data are summarized in Table 2.
[Pt2(ꢀ-H)(ꢀ-PPh2)(PPh3)3{(CH3)2CO}](BF4)2 (5c). The pro-
cedure was similar to that for 5b, except that the reaction was
carried out in acetone (50 mL). Recrystallisation from a
mixture of acetone and diethyl ether gave colourless 5c as
shown by 31P{1H} NMR. IR (KBr): 1644 (m) (ν(C᎐O) of
᎐
coordinated acetone), 1054(s) (ν(BF4)) cmϪ1. See NMR details
in Table 2.
Crystallographic studies
[Pt2(ꢀ-H)(ꢀ-PPh2)(OPOF2)(PPh3)3](PF6)ؒ0.5CH2Cl2
(6ؒ0.5CH2Cl2). When 5a was not carefully dried and contained
residual water, it transformed in CH2Cl2 into [Pt2(µ-H)(µ-
PPh2)(OPOF2)(PPh3)3]PF6 6 in less than 2 h, as seen by 1H and
31P{1H} NMR (see details in Table 2). Traces of 8a are also
present. X-ray quality crystals of 6ؒ0.5CH2Cl2 were obtained by
addition of diethyl ether to this solution and crystallisation at
Experimental details are given in Table 4. Unit cell parameters
for 2 were determined from 25 reflections having 2Њ < 2θ < 15Њ.
The data were corrected for Lorentz and polarization
effects and an empirical absorption correction was applied
(DIFABS).40 Data reduction was made by SDP package with
decay correction.41 The position of the copper and platinum
atoms was deduced from the Patterson map and subsequent
room temperature. IR (KBr): 1312 (ν(PO)), 837 (ν(PF6)) cmϪ1
.
¯
sets of Fourier and difference Fourier synthesis in the P1 space
[Pt2(ꢀ-H)(ꢀ-PPh2)(PPh3)3(OSO2CF3)](SO3CF3) (7). Pure
CF3SO3H (44 µL, 0.5 mmol) was added to a solution of 1
(136.8 mg, 0.1 mmol) in CH2Cl2 (15 mL). The colour of the
solution rapidly turned from orange to pale yellow. After
stirring for 5 h at room temperature, addition of diethyl ether
afforded colourless crystals (110 mg, yield 72%). The purity of
the solid was checked by 31P{1H} NMR in a CH2Cl2–CD2Cl2
mixture. See NMR details in Table 2.
group revealed the entire structure.42 The fractional coordinates
of all hydrogen atoms were calculated and these atoms were
assigned constant isotropic temperature factors equal those of
Ϫ
the bonded carbon. The PF6 anion has a high thermal agita-
tion with two positions for each fluorine atom, so that the
coordinates of these seven atoms were fixed at the observed
positions in the map. Full least-squares refinement minimizing
the function Σw(|Fo| Ϫ |Fc|)2 converged to the R values given in
J. Chem. Soc., Dalton Trans., 2002, 4084–4090
4089

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12 C. A. Tsipis, J. Organomet. Chem., 1980, 187, 427.
Table 4. Atomic scattering factors and anomalous dispersion
corrections were taken from standard sources.42,43
13 R. Bender, S.-E. Bouaoud, P. Braunstein, Y. Dusausoy, N. Merabet,
J. Raya and D. Rouag, J. Chem. Soc., Dalton Trans., 1999, 735.
14 M. A. Bennett, D. E. Berry, S. K. Bhargava, E. J. Ditzel,
G. B. Robertson and A. C. Willis, J. Chem. Soc., Chem. Commun.,
1987, 1613.
For 6ؒ0.5CH2Cl2, quantitative data were obtained at Ϫ100 ЊC
using a Nonius Kappa CCD diffractometer (see Table 4). The
resulting data-set was transfered to a DEC Alpha workstation,
and for all subsequent calculations the Nonius OpenMoleN
package was used.44 The structure was solved using direct
methods. Absorption corrections are part of the scaling pro-
cedure of data reduction. After refinement of the heavy
atoms, a difference-Fourier map revealed maximas of residual
electronic density close to the positions expected for hydrogen
atoms; they were introduced as fixed contributors in structure
factor calculations by their computed coordinates (C–H = 0.95
Å) and isotropic temperature factors such as B(H) = 1.3 Beqv(C)
Å2 but not refined; the hydride bridging between the Pt atoms
and the CH2Cl2 protons were omitted. Full least-squares
refinements on |F 2|. A final difference map revealed no signifi-
cant maxima. The scattering factor coefficients and anomalous
dispersion coefficients come respectively from ref. 45a and b.
CCDC reference numbers 189281 (2) and 188401 (6ؒ
0.5CH2Cl2).
15 M. A. Bennett, D. E. Berry and K. A. Beveridge, Inorg. Chem., 1990,
29, 4148.
16 R. Bender, P. Braunstein, A. Dedieu and Y. Dusausoy, Angew.
Chem., Int. Ed. Engl., 1989, 28, 923.
17 P. Leoni, M. Pasquali, M. Sommovigo, M. Laschi, P. Zanello,
A. Albinati, F. Lianza, P. S. Pregosin and H. Rüegger, Organo-
metallics, 1993, 12, 1702.
18 P. Leoni, G. Pieri and M. Pasquali, J. Chem. Soc., Dalton Trans.,
1998, 657.
19 T. Blum, P. Braunstein, A. Tiripicchio and M. Tiripicchio-Camellini,
New J. Chem., 1988, 12, 539.
20 T. Blum and P. Braunstein, Organometallics, 1989, 8, 2497.
21 (a) I. D. Salter, in Comprehensive Organometallic Chemistry II,
ed. E. W. Abel, F. G. A. Stone and G. Wilkinson, Pergamon Press,
Oxford, 1995; (b) T. Beringhelli, G. D’Alfonso, M. G. Garavaglia,
M. Panigati, P. Mercandelli and A. Sironi, Organometallics, 2002,
21, 2705 and references cited.
22 P. Braunstein, S. Freyburger and O. Bars, J. Organomet. Chem.,
1988, 352, C29.
23 S. A. Batten, J. C. Jeffery, P. L. Jones, D. F. Mullica, M. D. Rudd,
E. L. Sappenfield, F. G. A. Stone and A. Wolf, Inorg. Chem., 1997,
36, 2570.
See http://www.rsc.org/suppdata/dt/b2/b206347f/ for crystal-
lographic data for 188401 in CIF or other electronic format.
24 T. Tanase, H. Toda and Y. Yamamoto, Inorg. Chem., 1997, 36,
1571.
25 J. C. Dyason, P. C. Healy, M. Engelhardt, C. Pakawatchai,
V. A. Patrick, C. L. Raston and A. H. White, J. Chem. Soc., Dalton
Trans., 1985, 831.
26 P. E. Garrou, Chem. Rev., 1985, 85, 171.
27 C. Archambault, R. Bender, P. Braunstein, A. DeCian and
J. Fischer, Chem. Commun., 1996, 2729.
Acknowledgements
We are grateful to Prof. J. Fischer and Dr. A. DeCian
(Strasbourg) for the X-ray structure determination of 6ؒ
0.5CH2Cl2 and to Prof. R. Welter (Strasbourg) and Ms. F.
Porcher (Nancy) for assistance. We thank the Centre National
de la Recherche Scientifique and the Ministère de la Recherche
for support. This project was also supported by the Fonds
International de Coopération Universitaire – FICU (AUPELF-
UREF, Agence Universitaire de la Francophonie).
28 (a) W. Beck and K. Sünkel, Chem. Rev., 1988, 88, 1405;
(b) G. A. Lawrance, Chem. Rev., 1986, 86, 17.
29 J. Fischer and A. DeCian, personal communication, 2000.
30 H. Bauer, U. Nagel and W. Beck, J. Organomet. Chem., 1985, 290,
219.
31 M. A. Bennett, T. W. Matheson, G. B. Robertson, W. L. Steffen and
T. W. Turney, J. Chem. Soc., Chem. Commun., 1979, 32.
32 K. Sünkel, G. Urban and W. Beck, J. Organomet. Chem., 1985, 290,
231.
33 R. Fernández-Galán, B. R. Manzano, A. Otero, M. Lanfranchi and
M. A. Pellinghelli, Inorg. Chem., 1994, 33, 2309.
34 E. Horn and M. R. Snow, Aust. J. Chem., 1980, 33, 2369.
35 U. Bossek, G. Haselhorst, S. Ross, K. Wieghardt and B. Nuber,
J. Chem. Soc., Dalton Trans., 1994, 2041.
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