Routes to unique palladium A-frame complexes with a bridging fluoro-ligand

Article abstract of DOI:10.1039/b509032f

Treatment of a toluene solution of [PdMe₂(Cy₂PCH ₂PCy₂)] (1) with pentafluoropyridine in the presence of traces of water affords the generation of the A-frame complexes [(PdMe) ₂{μ-κ²(P,P)Cy₂PCH₂PCy ₂}₂(μ-F)][SiMeF₄] (2a) and [(PdMe) ₂{μ-κ²(P,P)Cy₂PCH₂PCy ₂}₂(μ-F)][OC₅NF₄] (2b). If the reaction is performed in an NMR tube equipped with a PFA inliner, complex 2b is produced, only. Treatment of 1 with pentafluoropyridine in the presence of an excess water yields the pyridyloxy complex [PdMe(OC₅NF ₄)(Cy₂PCH₂PCy₂)] (3). Compound [(PdMe)₂{μ-κ²(P,P)Cy₂PCH ₂PCy₂}₂(μ-F)][FHF] (2c) bearing a bifluoride anion instead of SiMeF₄^- or OC₅NF ₄^- can be generated by reaction of 1 with substoichiometric amounts of Et₃N·3HF. The analogous complex [(PdMe)₂{μ-κ²(P,P)Ph₂PCH ₂PPh₂}₂(μ-F)][FHF] (5c) has been synthesized by addition of Ph₂PCH₂PPh₂ to a solution of [PdMe₂(Me₂NCH₂CH₂NMe₂)] (4) in THF and subsequent treatment of the reaction mixture with Et ₃N·3HF. The structure of the A-frame complex 5c has been determined by X-ray crystallography. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b509032f

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F U L L P A P E R
Routes to unique palladium A-frame complexes with a bridging
fluoro-ligand
Thomas Braun,* Andreas Steffen, Verena Schorlemer, Beate Neumann and
Hans-Georg Stammler
Fakulta¨t fu¨r Chemie, Universita¨t Bielefeld, Postfach 100131, 33501, Bielefeld, Germany.
E-mail: thomas.braun@uni-bielefeld.de
Received 24th June 2005, Accepted 27th July 2005
First published as an Advance Article on the web 25th August 2005
Treatment of a toluene solution of [PdMe2(Cy2PCH2PCy2)] (1) with pentafluoropyridine in the presence of
traces of water affords the generation of the A-frame complexes [(PdMe)2{l-j2(P,P)Cy2PCH2PCy2}2(l-F)][SiMeF4]
(2a) and [(PdMe)2{l-j2(P,P)Cy2PCH2PCy2}2(l-F)][OC5NF4] (2b). If the reaction is performed in an NMR tube
equipped with a PFA inliner, complex 2b is produced, only. Treatment of 1 with pentafluoropyridine in the
presence of an excess water yields the pyridyloxy complex [PdMe(OC5NF4)(Cy2PCH2PCy2)] (3). Compound
[(PdMe)2{l-j2(P,P)Cy2PCH2PCy2}2(l-F)][FHF] (2c) bearing a bifluoride anion instead of SiMeF4 or OC5NF4
−
−
can be generated by reaction of 1 with substoichiometric amounts of Et3N·3HF. The analogous complex
[(PdMe)2{l-j2(P,P)Ph2PCH2PPh2}2(l-F)][FHF] (5c) has been synthesized by addition of Ph2PCH2PPh2 to a
solution of [PdMe2(Me2NCH2CH2NMe2)] (4) in THF and subsequent treatment of the reaction mixture with
Et3N·3HF. The structure of the A-frame complex 5c has been determined by X-ray crystallography.
treatment with Et3N·3HF, depending on the stoichiometry.19,24
Note that at rhodium hydroxides or methoxides can be used in
a comparable fashion to prepare rhodium fluorides.28 We found
that treatment of the hydrido compound [HRh(PEt3)3] with
Et3N·3HF yields the fluoro complex [RhF(PEt3)3].18,26 Perutz
and co-workers used ruthenium hydride precursors, some of
which give by reaction with Et3N·3HF the fluoride-bridged
ruthenium complexes [Ru2(l-F)3(PR3)6][F(HF)n] (R = Et, Pr,
Bu; n ≈ 3).15,16
Introduction
The combination of soft metals and hard ligands is known to
lead often to complexes with unique properties and therefore
an interesting synthetic chemistry.1 In particular, transition-
metal fluoro complexes reveal intriguing features, because the
characteristics of fluorine impart an unusual reactivity to the
metal–fluorine bond which can be exploited in preparative
organometallic chemistry or in catalysis.2–8 The nature of the
metal–fluorine bond has been discussed controversely.2,4,5,7–13
Thus, it has been reasoned that fluorine is a better p-donor than
iodine or other halogen ligands.4,10 At square-planar transition
d8 metal complexes this can lead to a destabilisation, because
of a M–F dp–pp filled/filled interaction. This model has been
questioned by several research groups, who suggest that fluorine
is a very poor p-donor, but the properties of the transition-metal
fluorine bond can be explained by its ionic component.4,11,13 At
square-planar d8 complexes electrostatic interactions lead to a
raise in energy of the metal based orbitals.13 In either case a
stabilisation can be achieved by a push/pull interaction induced
by a p-acceptor ligand in the trans-position to the fluoride.4,10,13
An alternative way to stabilise a late transition-metal fluoro
moiety is to alleviate electron density from the fluorine. This can
be achieved by a bridging mode of the fluoro ligand between
two metal atoms or by a hydrogen bond, for example from the
metal-bound fluorine to H2O, to a CH unit, or to HF like in
platinum-metal bifluoride complexes.5,14–21
There are a number of methods of introduction of fluo-
rine at late transition-metal centres,14–30 some of which have
been surveyed in several reviews.5,22 We found that palladium
fluorides are accessible by oxidative addition of fluorinated
aromatics.21–23 As an alternative palladium iodides can be treated
with AgF.8,19,24,25 It has been shown by Grushin and Marshall that
the latter method also led to the binuclear complexes [PdPh-
(l-F)(PR3)]2 (R = Cy, iPr) bearing a bridging fluoride.17 XeF2
has been employed by Vigalok and co-workers to prepare
palladium fluoro complexes by treatment of Pd(II) dimethyl
phosphine compounds.25
In this paper we describe the generation of cationic palladium
complexes, which exhibit an A-frame structure and a bridging
fluoro ligand. The compounds can be synthesised via two
routes: (i) by treatment of a palladium(II) dimethyl complex
with pentafluoropyridine in the presence of small amounts of
water; or (ii) by reactions of palladium(II) dimethyl precursors
with Et3N·3HF.
Results
Pentafluoropyridine as fluoride source
Treatment of a toluene solution of [PdMe2(Cy2PCH2PCy2)]
(1) with pentafluoropyridine at room temperature in a glass
NMR tube affords after 7 d the generation of the binu-
clear palladium complex [(PdMe)2{l-j2(P,P)Cy2PCH2PCy2}2-
(l-F)][SiMeF4] (2a) as a low-soluble white powder (Scheme 1).
An NMR investigation of the reaction solution reveals the pres-
ence of small amounts of [(PdMe)2{l-j2(P,P)Cy2PCH2PCy2}2-
(l-F)][OC5NF4] (2b). The addition of Et3N as a base has no
influence on the product distribution. A reaction of 1 with 2,4,6-
trifluoropyrimidine also yields 2a, but a variety of additional
organic products could not be further identified.
The NMR data of 2a suggest the existence of a binuclear
cation with A-frame configuration and the phosphines and one
fluoro ligand in bridging positions.31 The bridging fluoro ligand
in 2a appears in the 19F NMR spectrum as a broad signal at
high field at d −387.15,17 The resonance resolves to a quintet
(JPF = 14.7 Hz) in the proton decoupled spectrum. The 31P NMR
spectrum reveals only one signal at d 19.7 with a characteristic
doublet splitting (JPF = 16.2 Hz) for the equivalent phosphorus
nuclei. The protons at the CH2 groups in the phosphines are
Late transition-metal fluorides have also been synthesised by
treatment of suitable precursors with Et3N·3HF, which is a mild
source of HF.15,16,18,19,26,28 However, this route often leads to the
formation of bifluorides. Thus, palladium hydroxo complexes
can be converted into palladium fluorides or bifluorides on
1
prochiral, which results in a signal at d 3.68 in the H NMR
spectrum. A COSY NMR spectrum confirms that the second
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
D a l t o n T r a n s . , 2 0 0 5 , 3 3 3 1 – 3 3 3 6
3 3 3 1
©

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Scheme 1 Reactivity of 1 towards pentafluoropyridinepyridine and water.
resonance at d 1.9 is covered by the signals of the cyclohexyl
group. A quartet (JFH = 5 Hz) with 29Si satellites (JSiF = 216 Hz)
at d −111 ppm in the 19F NMR spectrum and a quintet at d
Treatment of 1 with pentafluoropyridine in the pres-
ence of an excess water yields the pyridyloxy com-
plex [PdMe(OC5NF4)(Cy2PCH2PCy2)] (3) (Scheme 1). Al-
1
0.01 ppm (JHF = 5.0 Hz) in the H NMR spectrum can be
ternatively 3 can also be synthesised from 1 and 4-
assigned to the SiMeF4 anion.32 The NMR data of 2b suggest
hydroxytetrafluoropyridine. The 1H NMR spectrum of 3 reveals,
apart for the signals of the metal bound phosphine ligand, a reso-
nance at d 0.26 for the methyl ligand at palladium. The 19F NMR
spectrum displays two multiplets at d −97.9 and −167.2 for the
tetrafluoropyridyloxy group. These chemical shifts are compara-
ble to these found for [PdMe(OC5NF4)(Me2NCH2CH2NMe2)],
but distinctively different from the values obtained for a
tetrafluoropyridyl ligand, which is directly connected to a metal
centre at the 4-position.21,35,38
−
a similar cationic A-frame structure as it has been found for 2a.
Two signals in the 19F NMR spectrum at d −101.7 and d −171.1
reveal the presence of a tetrafluoropyridyloxy anion, which has
been identified by comparison of its 19F NMR data with these
of its sodium salt.33
The presence of SiMeF4− evidently arises from HF or fluoride
attack at the glass tubes.20,29,34 Sources of the fluoride anions can
be fluoro complexes such as [Pd(F)(Me)(Cy2PCH2PCy2)] (I),
[{(Pd(F)(Me)}2{l-j2(P,P)Cy2PCH2PCy2}2] (II) or [(PdMe)2-
{l-j2(P,P)Cy2PCH2PCy2}2(l-F)]F (III). Especially an interme-
diate such as III, which exhibits an outer-sphere anion as a
source for a “naked fluoride” seems to be precedented for
Synthesis of palladium A-frame complexes with Et3N·3HF as
fluorinating agent
the formation of an SiMeF4 anion.34 Compounds I–III are
−
In an alternative procedure to the C–F activation re-
actions described above, compound [(PdMe)2{l-j2(P,P)-
Cy2PCH2PCy2}2(l-F)][FHF] (2c) bearing a bifluoride anion
presumably intermediates for the formation of 2a and are
produced by reaction of 1 with HF. HF itself could be generated
in a palladium-mediated process from pentafluoropyridine in
presence of adventitious water, as it has been shown before.35
Note, that for the synthesis of 1 water has been used in the
work-up process.36 Therefore, we performed the reactions in an
NMR tube equippedwithaPFAinliner usingbatches of 1, which
had been recrystallised several times. After treatment of 1 with
pentafluoropyridine only tiny amounts of 2b were formed and no
2a was generated. Deliberate addition of small amounts of water
to the reaction mixture gave immediately 2b, confirming the
assumption that a reaction of pentafluoropyridine with water is
the source of the pyrdyloxy anion. Note that neither 1 reacts with
water without the presence of the pentafluoropyridine, nor does
the heterocycle react with water at room temperature without
the presence of 1.
−
−
instead of SiMeF4 or OC5NF4 can be generated by reaction
of 1 with substoichiometric amounts of Et3N·3HF (Scheme 2).
The NMR data for the cation in 2c are the same as these
for 2a or 2b. However, instead of the signals for the silicate
anion or pyridyloxy anion a new resonance at d −155 ppm
appears in the 19F NMR spectrum. This observation and a
1
broad signal in the H NMR spectrum at d 16.2 suggest the
presence of bifluoride anion.16,39 Low-temperature NMR data
of 2c at 193 K indeed reveal the expected triplet (JHF = 123 Hz)
1
in the H NMR spectrum and the corresponding doublet in
the 19F NMR spectrum. The broadness of the signals at room
temperature can be attributed to a dynamic behaviour involving
the bifluoride anion. The exact nature of the fluoxionality is not
clear, but variable-temperature NMR experiments reveal neither
Scheme 2 Formation of cationic complexes with A-frame structure.
D a l t o n T r a n s . , 2 0 0 5 , 3 3 3 1 – 3 3 3 6
3 3 3 2

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a broadening of the signals for the methyl or methylene group
in the H NMR spectrum nor a shift of the resonance for the
other through the bridging fluoride. The Pd–F–Pd angle at
the fluoro ligand of 87.92(5)◦ is smaller than the comparable
angle in [PdPh(l-F)(PiPr3)]2 of 101.26◦, possibly because of the
1
bridging fluoride in the 19F NMR spectrum. This suggests that
the A-frame geometry stays intact and indicates that a process
in which a face-to-face dimer is formed is not involved.15–17,40 We
speculate that HF exchange between FHF− and small amounts
of polyfluoride anions [F(HF)x]− might be the reason for the
broadening.15
phosphine brace in 5c.17 The Pd–Pd separation is 2.9956(2) A.
˚
Complex 5c has C2 symmetry. The eight-membered Pd2P4C2
ring adopts a twisted boat conformation, such that the CH2
groups are oriented towards the bridging fluorine (Fig. 2). Along
the Pd–Pd vector the cation exhibits a chiral axis defined by a
torsion angle P–Pd–Pd–P of 19.1◦. Similar distorted A-frame
boat conformations with the halogen atom and the CH2 groups
on the same face of the Pd2P4 plane have been determined for
other palladium complexes with a bridging chloride, iodide or
bromide.31,42 Only in one case a boat conformation with the
CH2 groups and the bridging halogen lying on opposite faces
of the Pd2P4 plane has been observed.43 The palladium fluoride
Because a complex analogous to the starting compound
1 bearing Ph2PCH2PPh2 instead of Cy2PCH2PCy2 can not
be prepared,37 complex [(PdMe)2{l-j2(P,P)Ph2PCH2PPh2}2-
(l-F)][FHF] (5c) has been synthesised by addition of
Ph2PCH2PPh2 to a solution of [PdMe2(Me2NCH2CH2NMe2)]
(4) in THF and subsequent treatment of the reaction mix-
1
ture with Et3N·3HF (Scheme 2). The H NMR spectroscopic
˚
data of the reaction solution reveal that the conversion is
accompanied by the formation of methane and [(Pd3(l-j2(P,P)-
Ph2PCH2PPh2)3].37 However, 5c can be isolated in a yield of
16%, because of its low solubility in THF. The 19F and 31P NMR
spectroscopic data 5c resemble the data found for 2c.
bond of 2.1578(10) A is longer than the Pd–F separation in
mononuclear palladium fluoro complexes, and also longer than
the comparable distances found in [PdPh(l-F)(PiPr3)]2 [2.098(1),
2.118(1) A].12,17,21,24,25 The F–F distance in the bifluoride anion of
˚
41
˚
2.29 A is comparable to those found in other bifluoride salts.
The IR spectra of 2c and 5c exhibit a broad absorption band
between 1600 and 1800 cm−1, which is compatible with a free
bifluoride anion.16,41 Conductivity measurements of solutions in
CH2Cl2 are also in accordance with the presence of an ionic
compound.39,40 A reaction of 5c with Me3SiCl affords Me3SiF
and the binuclear palladium complex [(PdClMe)2{l-j2(P,P)-
Ph2PCH2PPh2}2] (6), which has been described before.31
Structure of 5c in the solid state
The colourless complex 5c was crystallized at 20 C from a
◦
solution in THF. The crystal structure was determined by X-
ray diffraction at 100 K. The structure of the cation [(PdMe)2-
{l-j2(P,P)Ph2PCH2PPh2}2(l-F)]+ is depicted in Fig. 1. Selected
bond lengths and angles are summarised in Table 1. The cation
exhibits an approximately square-planar geometry about each
palladium atom, with the two planes inclined towards each
Fig. 2 Structure of the cation in 5c; The phenyl groups are omitted for
clarity.
Discussion
The syntheses of the A-frame complexes 2a–2c and 5c using
pentafluoropyridine–water or Et3N·3HF as sources of HF are
shown in the Schemes 1 and 2. Mechanistically either an initial
protonation at the metal—followed by reductive elimination
of methane—or a protonation of the methyl ligand yielding
methane and [Pd(F)(Me)(Cy2PCH2PCy2] (I) are conceivable.18
In the presence of Et3N·3HF two molecules of I rearrange to
give the binuclear A-frame structures 2c or 5c and the bifluoride
anion (Scheme 2).
Concerning the reaction pathway for the formation of 2a
and 2b, there is some evidence that HF and 4-hydroxytetra-
fluoropyridine can be produced as intermediates from pentaflu-
oropyridine and water in the presence of 1. Note that it has been
suggested before that [PdMe2(Me2NCH2CH2NMe2)] (4) can
induce a substitution of fluorine by a hydroxy group in pentaflu-
oropyridine to give HF and 4-hydroxytetrafluoropyridine from
water.35 We speculate about a similar transformation. Both
compounds HF and intermediate 4-hydroxytetrafluoropyridine
could react with 1 to afford [Pd(F)(Me)(Cy2PCH2PCy2)]
(I) and [PdMe(OC5NF4)(Cy2PCH2PCy2)] (3), respectively
(Scheme 3). In particular, the latter conversion might ben-
efit from the fact that 4-hydroxytetrafluoropyridine, is al-
ready present in the coordination sphere of 1. It also has
been confirmed by an independent experiment that treat-
ment of 1 with 4-hydroxytetrafluoropyridine yields complex
3. From a mixture of I and 3 the A-frame complex 2b
can be furnished. Alternatively, binuclear complexes such as
[{(Pd(F)(Me)}2{l-j2(P,P)Cy2PCH2PCy2}2] (II) or [(PdMe)2-
{l-j2(P,P)Cy2PCH2PCy2}2(l-F)]F (III) might react with in-
termediate 4-hydroxytetrafluoropyridine to yield 2b and HF
(Scheme 3). However, although 1 does not react with water
Fig. 1 Structure of the cation in 5c.
◦
˚
Table 1 Selected bond lengths (A) and angles ( ) of [(PdMe)2-
{l-j2(P,P)Ph2PCH2PPh2}2(l-F)][FHF] (5c) with the estimated stan-
dard deviations in parentheses
Pd(1)–F(1)
Pd(1)–P(1)
Pd(1)–P(2)
Pd(1)–C(26)
2.1578(10)
2.3066(4)
2.3025(4)
2.0407(16)
Pd(1)–Pd(1)
P(1)–C(25)
P(2a)–C(25)
F(2)–C(H2a)
2.9956(2)
1.8387(15)
1.8405(16)
1.452(10)
C(26)–Pd(1)–F(1)
P(2)–Pd(1)–P(1)
C(26)–Pd(1)–P(1)
C(26)–Pd(1)–P(2)
174.11(5)
171.997(15) F(1)–Pd(1)–P(1)
92.80(5)
92.66(5)
F(1)–Pd(1)–P(2)
92.038(11)
82.906(12)
87.92(5)
Pd(1)–F(1)–Pd(1a)
P(1)–C(25)–P(2a)
116.32(8)
D a l t o n T r a n s . , 2 0 0 5 , 3 3 3 1 – 3 3 3 6
3 3 3 3

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Scheme 3 Possible reaction pathways for the formation of 2a and 2b.
44
without the presence of the heterocycle, we can not entirely
exclude that under the reaction conditions an intermediate
hydroxo complex is generated (e.g. from a palladium fluoride),
which could react with pentafluoropyridine to give HF and
[PdMe(OC5NF4)(Cy2PCH2PCy2)] (3). We were not able to
identify any hydroxo complex or other intermediate by low-
temperature NMR experiments.
(4)36 and Ph2PCH2PPh2 were prepared according to the
literature.
The NMR spectra were recorded on a Bruker DRX 500 (1H,
31P{ H} and 19F NMR spectra) or a Bruker Avance 600 (19F{ H}
NMR spectra) spectrometer. The 1H NMR chemical shifts were
referenced to residual CHDCl2 at d 5.3 or C6H5D at d 7.15. The
1
1
31P{ H} NMR spectra are reported downfield of an external
1
It has been indicated in the introduction, that a strong p-
acceptor ligand trans to the fluoride can stabilise a metal–
fluorine interaction by diminishing the dp–pp filled/filled repul-
sion or the ionic character of the metal–fluorine bond. The insta-
bility of an intermediate such as [Pd(F)(Me)(Cy2PCH2PCy2)] (I)
could therefore be attributed to a less favourable trans-position
of the fluoride and the phosphine, which leads to the lability of
the fluoro ligand (Scheme 3). On the other hand, Vigalok and
co-workers described recently the square-planar palladium flu-
oro complexes [PdF2(L2)] (L2 = diisopropylphosphinopropane,
dicyclohexylphosphinopropane) with a phosphine unit in the
trans-position to the fluoride.25 The existence of square-planar
trisphosphine rhodium fluoro complexes also indicates that a
phosphine ligand in the trans position to the fluoride might be
sufficient.18,26,28 Therefore, the formation of an A-frame structure
might rather be attributed to the small bite angle of R2PCH2PR2
(R = Cy, Ph) at palladium and the tendency of R2PCH2PR2 to
adopt a bridging coordination mode initially resulting in the
binuclear complex [{(Pd(F)(Me)}2{l-j2(P,P)Cy2PCH2PCy2}2]
(II).31,40 The trans arrangement of fluoride and the methyl
ligand in a complex such as II would be strongly disfavoured
resulting in the A-frame geometry, in which a bridging mode of
the fluoro ligand stabilises the transition-metal fluoro moiety.15
Note that the molecular structure of the chloro compound
[(PdClMe)2{l-j2(P,P)Ph2PCH2PPh2}2] has been reported. In
this case, the complex exhibits a binuclear face-to-face geometry
with bridging phosphines.31
solution of H3PO4 (85%). The 19F NMR spectra were referenced
to external C6F6 at d −162.9. The infrared spectra were recorded
on a Bruker IFS-66 spectrometer.
Synthesis of [(PdMe)2{l-j2(P,P)Cy2PCH2PCy2}2-
(l-F)][SiMeF4] (2a)
Complex [PdMe2(Cy2PCH2PCy2)] (1) (422 mg, 0.77 mmol)
was suspended in toluene (20 mL), and pentafluoropyridine
(100 lL, 0.92 mmol) was added. The yellow reaction mix-
ture was stirred for 7 days at room temperature and the
orange solution was filtered through a cannula. The 19F NMR
spectra confirmed that the filtrate contains small amounts of
[(PdMe)2{l-j2(P,P)Cy2PCH2PCy2}2(l-F)][OC5NF4] (2b). The
remaining solid was washed with toluene (5 mL) and dried
in the vacuum giving a colourless powder. Yield (2a) 114 mg
(34%) (Found: C, 58.48; H, 9.18. C53H101F5P4PdSi requires C,
58.31; H, 9.32%). 1H NMR (500 MHz, CD2Cl2): d 3.68 (m, 2H,
CHAHB), 1.14–2.01 (m, 92 H, Cy, CHAHB), 0.39 (m, d in 1H{ P}
31
NMR, JFH = 1.5 Hz, 6 H, PdCH3), 0.01 (qnt, 3H, JHF = 5.0 Hz,
SiMeF4−). 31P{ H} NMR (202.5 MHz, CD2Cl2): d 19.7 (d, JPF
=
1
16.2 Hz). 19F NMR (470.4 MHz, CD2Cl2): d −111.2 (q with 29Si
satellites, JFH = 5, JSiF = 216 Hz, SiMeF4−), −387 (s, br, qnt
in 19F{ H} NMR, JPF = 14.7 Hz, PdF). NMR spectroscopic
1
data for 2b: d 3.68 (m, 2H, CHAHB), 1.14–2.01 (m, 92 H, Cy,
CHAHB), 0.39 (m, 6 H, PdCH3). 31P{ H} NMR (202.5 MHz,
1
C6D6): d 19.7 (d, JPF = 17.1 Hz). 19F NMR (470.4 MHz, C6D6):
d −101.7 (s, br, 2F, CF), −171.1 (s, br, 2F, CF), −387 (s, br, qnt
Conclusions
in 19F{ H} NMR, JPF = 14.7 Hz, PdF).
1
In conclusion several routes to cationic palladium complexes
with a bridging fluoro ligand have been elaborated. The reac-
tions result in binuclear compounds with a distorted A-frame
structure. So far, only two palladium complexes with a fluorine
ligand in the bridging position have been reported.17 The studies
underline that late transition-metal fluoro complexes can be
stabilised by a bridging coordination mode of the fluoro ligand.15
Synthesis of [PdMe(OC5NF4)(Cy2PCH2PCy2)] (3)
166 mg (0.30 mmol) of 1 were dissolved in 5 ml THF at
−30 ◦C and treated with a solution of 44 mg (0.26 mmol)
4-hydroxytetrafluoropyridine in 5 ml THF. After stirring the
yellow reaction mixture for 2 h at 0 ◦C, the volatiles were removed
in vacuo and the residue was washed twice with 3 mL toluene. A
pale yellow substance remained. Yield 154 mg (85%) (Found: C,
53.70; H, 7.34; N 1.69. C31H49F4NOP2Pd requires C, 53.50; H,
Experimental
The synthetic work was carried out on a Schlenk line or a
nitrogen-filled glove box with oxygen levels below 10 ppm. All
solvents were purified and dried by conventional methods and
distilled under argon before use. Et3N·3HF and pentafluoropy-
ridine were obtained from Aldrich and ABCR, respectively.
[PdMe2(Cy2PCH2PCy2)] (1),37 [PdMe2(Me2NCH2CH2NMe2)]
7.05; N 2.01%). 1H NMR (500 MHz, CD2Cl2): d 2.58 (dd, JPH
=
10.0, JPH = 6.9 Hz, 2H, PCH2), 1.70–2.10 (m, 22 H, Cy), 0.26 (d,
JPH = 8.8 Hz, 3 H, PdCH3). 31P{ H} NMR (202.5 MHz, C6D6):
1
d 14.3 (d, JPP = 59.7 Hz), −21.0 (d, JPP = 59.7 Hz). 19F NMR
(470.4 MHz, C6D6): d −97.9 (s, br, 2F), −167.2 (s, br, 2F).
3 3 3 4
D a l t o n T r a n s . , 2 0 0 5 , 3 3 3 1 – 3 3 3 6

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Synthesis of [(PdMe)2{l-j2(P,P)Cy2PCH2PCy2}2(l-F)][FHF]
References
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A solution of [PdMe2(Cy2PCH2PCy2)] (1) (291 mg, 0.53 mmol)
in toluene (20 mL) was treated with a solution of Et3N·3HF
in THF (180 lL, 0.18 mmol). After 3 h stirring at room
temperature, the yellow suspension was filtered. The colourless
residue was washed twice with toluene (5 mL) and dried
under vacuum. Yield 102 mg (35%) (Found: C, 61.59; H,
9.38. C52H99F3P4Pd requires C, 61.74; H, 9.86%). The NMR
spectroscopic data of the cation are similar to the data obtained
for 2a. Molar conductivity (KM/S cm2 mol−1) = 42. The anion
has been identified by comparison of the NMR and IR data
with these in the literature.16,39,41
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Synthesis of [(PdMe)2{l-j2(P,P)Ph2PCH2PPh2}2(l-F)][FHF]
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(5c)
A solution of [PdMe2(Me2NCH2CH2NMe2)] (4) (273 mg,
1.08 mmol) in THF (7 mL) was treated with Ph2PCH2PPh2
(436 mg, 1.13 mmol). The solution was stirred for 5 min and a
solution of Et3N·3HF in THF (55 lL, 0.54 mmol) was added.
After 2 h stirring at room temperature, the yellow suspension
was filtered. The colourless residue was washed twice with
THF (5 mL) and dried under vacuum. Yield 191 mg (16%)
(Found: C, 64.68; H, 5.23. C52H51F3P4Pd requires C, 64.84;
ˇ
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1
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1
in 31P{ H}, JHH = 13.4 Hz, 2H, CHAHB), 3.36 (m, 2H, d in
1
31P{ H}, JHH = 13.4 Hz, CHAHB), 0.43 (m, 6 H, PdCH3).
1
31P{ H} NMR (202.5 MHz, CD2Cl2): d 13.8 (d, JPF = 15.4 Hz).
19F NMR (470.4 MHz, CD2Cl2): d −377 (m, br, PdF). Molar
conductivity (KM/S cm2 mol−1) = 38. The anion has been
identified by comparison of the NMR and IR data with these in
the literature.16,39,41
Formation of [(PdClMe)2{l-j2(P,P)Ph2PCH2PPh2}2] (6)
A solution of 5c (12 mg, 0.01 mmol) in CD2Cl2 (0.6 mL)
was treated with Me3SiCl (23 lL, 0.12 mmol). The NMR
spectroscopic data reveal the formation of 6.31
Structure determination for complex 5c·2THF
Colourless crystals of 5c·2THF were obtained at 20 ◦C from a
solution in THF. Diffraction data were collected for a fragment
with the dimensions 0.20 × 0.10 × 0.07 mm on a Nonius
KappaCCD diffractometer.
Crystal data. C60H67F3O2P4Pd2, M = 1213.82, monoclinic,
space group C2/c, a = 24.6810(3), b = 9.23800(10), c =
◦
3
˚
˚
25.2280(3) A, b = 108.8150(6) , V = 5444.70(11) A , T = 100(2)
K, Z = 4, l(Mo-Ka) = 0.831 mm−1, 57348 reflections measured,
7922 unique (Rint = 0.042). The structure was solved by direct
methods (SHELXTL PLUS) and refined with the full matrix
least squares methods on F2 (SHELX-97).45 Final R1, wR2 values
on all data: 0.0327, 0.0633. R1, wR2 values for 6861 reflections
with Io > 2r(Io): 0.0259, 0.0607. Hydrogen atoms were placed at
calculated positions and refined using a riding model except for
H(2A), which was refined isotropically. The symmetry generated
atoms are related to those in the asymmetric unit by the −x +
1, y, −z + 1/2 symmetry operation.
CCDC reference number 276221.
See http://dx.doi.org/10.1039/b509032f for crystallographic
data in CIF or other electronic format.
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Sladek, T. Braun, B. Neumann and H.-G. Stammler, J. Chem. Soc.,
Acknowledgements
We would like to acknowledge the Deutsche Forschungsgemein-
schaft (grant BR-2065/1-5) for financial support. We also like to
thank Ms A. Penner and Ms C. Koen for experimental assistance
and are grateful to Professor P. Jutzi for his generous support.
D a l t o n T r a n s . , 2 0 0 5 , 3 3 3 1 – 3 3 3 6
3 3 3 5

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3 3 3 6
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