New studies on the reactivity of allyl difluorophosphate palladium complexes: Synthesis of the first difluorophosphate metallocene derivatives

Article abstract of DOI:10.1016/S0022-328X(98)01074-2

The reaction of [Pd(η³-2Me-C₃H₄)(μ-PO₂F ₂)]₃ 1, previously synthesized by us, with P- or S-donor ligands leads to the new derivatives [Pd(η³-2Me-C₃H₄)(PO₂F ₂)L] (L=PMePh₂; P(OR)₃, R=Me, Et, Ph; SPPh₃) and [Pd(η³-2Me-C₃H₄)L₂]PO ₂F₂ (L=SPPh₃). The neutral and ionic derivatives with L=tetrahydrothiophene, were detected by ¹H-NMR. The fluxional behavior of SPPh₃ complexes has been analyzed and a dissociation of SPPh₃ ligand evidenced. When 1 is made to react with M(η⁵-C₅R₅)₂Cl₂ (M=Ti, R=H, Me; M=Mo, R=H) the new metallocene derivatives M(η⁵-C₅R₅)₂(PO₂F ₂)₂ are obtained. Using M(PPh₃)PF₆ (M=Ag, Cu) the complex [Pd(η³-2Me-C₃H₄)(PPh₃) ₂]PF₆ and M(PO₂F₂)_x (M=Ag, x=1; M=Cu; x=2) are formed. A similar reaction takes place between [Pd(η³-2Me-C₃H₄)(PO₂F ₂)(PPh₃)] and Ag(ClO₄)PPh₃. With AuPPh₃PF₆ and 1 no reaction is observed. The derivatives trans-[PdCl(μ-Cl)(PR₃)]₂ (R=Ph, Cy) and [Pd(η³-2Me-C₃H₄)(PhCN)₂]PO ₂F₂ are formed after the reaction of [Pd(η³-2Me-C₃H₄)(PO₂F ₂)(PR₃)] and PdCl₂(PhCN)₂. 1 or [Pd(η³-2Me-C₃H₄)(PO₂F ₂)(PPh₃)], 2, does not react with weak acids However, HCl gives rise to [Pd(η³-2Me-C₃H₄)Cl(PPh₃)] after the reaction with 2. HBF₄ also reacts with 1 or 2 and by means of ¹⁹F-NMR studies at low temperatures BF₄^- coordination has been observed when a non-coordinating solvent is used.

Full text of DOI:10.1016/S0022-328X(98)01074-2

Journal of Organometallic Chemistry 577 (1999) 271–282
New studies on the reactivity of allyl difluorophosphate palladium
complexes: synthesis of the first difluorophosphate metallocene
derivatives
Rafael Ferna´ndez-Gala´n, Blanca R. Manzano *, Antonio Otero 1
Departamento de Qu´ımica Inorga´nica, Orga´nica y Bioqu´ımica, Facultad de Qu´ımicas Uni6ersidad de Castilla-La Mancha,
A6da Camilo Jose´ Cela, 10. 13071 Ciudad Real, Spain
Received 5 October 1998
Abstract
The reaction of [Pd(h3-2Me-C3H4)(m-PO2F2)]3 1, previously synthesized by us, with P- or S-donor ligands leads to the new
derivatives [Pd(h3-2Me-C3H4)(PO2F2)L] (L=PMePh2; P(OR)3, R=Me, Et, Ph; SPPh3) and [Pd(h3-2Me-C3H4)L2]PO2F2 (L=
1
SPPh3). The neutral and ionic derivatives with L=tetrahydrothiophene, were detected by H-NMR. The fluxional behavior of
SPPh3 complexes has been analyzed and a dissociation of SPPh3 ligand evidenced. When 1 is made to react with M(h5-C5R5)2Cl2
(M=Ti, R=H, Me; M=Mo, R=H) the new metallocene derivatives M(h5-C5R5)2(PO2F2)2 are obtained. Using M(PPh3)PF6
(M=Ag, Cu) the complex [Pd(h3-2Me-C3H4)(PPh3)2]PF6 and M(PO2F2)x (M=Ag, x=1; M=Cu; x=2) are formed. A similar
reaction takes place between [Pd(h3-2Me-C3H4)(PO2F2)(PPh3)] and Ag(ClO4)PPh3. With AuPPh3PF6 and 1 no reaction is
observed. The derivatives trans-[PdCl(m-Cl)(PR3)]2 (R=Ph, Cy) and [Pd(h3-2Me-C3H4)(PhCN)2]PO2F2 are formed after the
reaction of [Pd(h3-2Me-C3H4)(PO2F2)(PR3)] and PdCl2(PhCN)2. 1 or [Pd(h3-2Me-C3H4)(PO2F2)(PPh3)], 2, does not react with
weak acids However, HCl gives rise to [Pd(h3-2Me-C3H4)Cl(PPh3)] after the reaction with 2. HBF4 also reacts with 1 or 2 and
by means of 19F-NMR studies at low temperatures BF4− coordination has been observed when a non-coordinating solvent is used.
© 1999 Elsevier Science S.A. All rights reserved.
Keywords: Pd-, Ti- and Mo-complexes; Difluorophosphate; Fluxional behavior; BF4− coordination
1. Introduction
Our 19F- and 31P-NMR studies of the PF6− hydroly-
sis process in organic solution allowed us to state the
catalytic role of the silver cation and a clear solvent
influence. Also intermediates as POF4− or POF3 were
detected in solution. Interestingly, Cotton et al. [10]
described the structure of a ruthenium complex con-
taining a POF4 ligand, proposed to be formed by
partial hydrolysis of the PF6− ion over the long period
of time required to obtain the crystalline product. We
also described [1] the reaction between [Pd(h3-2Me-
C3H4)Cl]2 and AgPF6 in dichloromethane solution
which led to [Pd(h3-2Me-C3H4)(m-PO2F2)]3, 1, the first
palladium difluorophosphate complex. Some reactivity
of this derivative was initially explored. Its reaction
with PR3 ligands (molar ratio 1:3) allowed the isolation
Recently we described [1] the first study of the hy-
drolysis process of AgPF6 in organic solvents. Before
our work, examples of the partial hydrolysis to PF2O2−
of a PF6− ion acting as a counterion [2–6] or ligand [7]
in several complexes had been described. Also the
presence of AgPO2F2 in old samples had been postu-
lated [8] to account for the formation of PO2F2 com-
plexes. Recently, other cases of PF6− hydrolysis have
been reported [9].
* Corresponding author. Fax: +34-926-295318.
E-mail address: bmanzano@gino-cr.uclm.es (B.R. Manzano)
1 Also corresponding author.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)01074-2

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R. Ferna´ndez-Gala´n et al. / Journal of Organometallic Chemistry 577 (1999) 271–282
Table 1
1H-NMR data for 5–15 and 19a
Complex h3-2-Methylallyl group
P- or S-donor ligand
–CH3
H1
H2
H1
H2
syn
anti
anti
syn
5
2.02 (s)
2.00 (s)
2.08 (s)
2.04 (s)
1.4 (s)
3.76 (d),
HP=9.3
3.73 (d),
HP=13.9
3.87 (d),
HP=14.0
3.74 (d),
HP=14.0
3.71 (d),
HP=13.9
2.51 (s)
2.11 (s)
2.17 (s)
2.17 (s)
1.84 (s)
3.27 (pst),
4.74 (d),
HP=6.3
4.69 (d),
HP=9.8
4.74 (d),
HP=9.8
4.72 (d),
HP=9.8
4.75 (d),
HP=10.5
2.91 (s)
1.99 (d, Me), JHP=9.3, 7.4–7.5 (m, Ph)
3.66 (d, Me), JHP=12.4
J
J
6
2.64 (s)
J
J
6b
7
2.68 (s)
3.75 (d, Me), JHP=12.5
J
J
2.71 (s)
1.31 (t, CH3), JHH=7.1, 4.08 (m, CH2),
JHP=9.1, 7.1–7.6 (m, Ph)
J
J
8
2.93 (s)
J
J
9
1.82 (s)
1.85 (s)
1.84 (s)
3.27 (pst),
4.51 (pst, br),
4.51 (pst, br),
3.67 (pst, br, Me)
J* =9.3
J* =9.3
J* =4.5
J* =4.5
HP
HP
HP
HP
10
11
3.38 (pst),
3.38 (pst),
4.44 (pst, br)
4.44 (pst, br)
1.33 (t, CH3), JHH=7.1, 4.06 (m, CH2)
7.1–7.6 (m, Ph)
J* =9.3
J* =9.3
HP
HP
3.34 (pst),
3.34 (pst),
4.02 (pst, br)
4.02 (pst, br)
J* =9.0
HP
J* =9.0
HP
12
13
1.96 (s)
1.98 (s)
1.86 (s)
1.85 (s)
1.63 (s)
1.63 (s)
2.14 (s)
2.30 (bs)
3.17 (bs)
2.60 (bs)
2.62 (bs)
2.41 (bs)
2.62 (bs)
2.89 (s)
2.30 (bs)
3.17 (bs)
2.60 (bs)
2.62 (bs)
2.41 (bs)
2.62 (bs)
2.89 (s)
3.79 (s)
3.84 (s)
3.72 (s)
3.64 (s)
3.45 (s)
3.51 (s)
3.93 (s)
3.79 (s)
3.84 (s)
3.72 (s)
3.64 (s)
3.45 (s)
3.51 (s)
3.93 (s)
1.92 (bs, CH2), 2.98 (bs, CH2–S)
1.93 (bs, CH2), 2.98 (bs, CH2–S)
7.5–7.8 (m, Ph)
7.6–7.9 (m, Ph)
7.5–7.8 (m, Ph)
14
14b
15
15b
19
7.6–7.9 (m, Ph)
7.5–7.9 (m, Ph)
a When two different ligands are present the subscript 1 refers to the allylic protons cis to the PO2F2− group. In CDCl3 unless specified. Coupling
constants in Hz. J*, apparent coupling constant; pst, pseudotriplet; bs, broad singlet.
b (CD3)2CO.
of the complexes [Pd(h3-2Me-C3H4)(PO2F2)(PR3)]
(R=Ph, 2; Cy, 3; p-tolyl, 4) while it did not react with
CH3CN. However, the complex [Pd(h3-2Me-
C3H4)(CH3CN)2]PF6 was obtained from the trimer spe-
cies 1 and [Cu(CH3CN)4]PF6 with the concomitant
formation of CuPO2F2.
We report here on the results of the reactivity studies
we have pursued with 1 and its PR3 derivatives, 2 and
3, which include reactions with (i) other ligands, (ii)
early and late transition metal complexes and (iii) acids.
The aim of the work was to explore the behavior of
complexes containing this unusual anion in a broad
range of processes.
[Pd(h3-C4H7)(m-PO2F2)]3+3L
“3[Pd(h3-C4H7)(PO2F2)L]
L=PMePh2, 5; P(OMe)3, 6; P(OEt)3, 7; P(OPh)3, 8
(1)
When phosphites were used as ligands the ionic deriva-
tives [Pd(h3-C4H7)L2]PO2F2, (L=(P(OMe)3), 9;
(P(OEt)3), 10; (P(OPh)3), 11), were also formed as
minor components in a mixture with the neutral deriva-
tives. It was not possible, even after several crystalliza-
tion attempts, to separate the two complexes from the
oily mixture (see Section 4) and they were identified by
1
the H- and 13C{1H}-NMR signals in solution.
1
The H- and 13C{1H}-NMR data for the new com-
plexes are collected in Tables 1 and 2, respectively. In
the H-NMR spectra of all the neutral complexes (5–8)
2. Results and discussion
1
2.1. Reactions with ligands
an asymmetric allyl group is seen with two Hsyn and
two Hanti signals. The protons situated trans to phos-
phorus appear at higher chemical shift and exhibit the
corresponding coupling constant (higher for the Hanti
than for the Hsyn). The signals of the phosphine or
phosphite groups are also observed. For the determina-
tion of the corresponding coupling constants INDOR
and heteronuclear decoupling experiments were made.
The 13C{1H}-NMR data confirmed the asymmetric na-
ture of the allyl groups showing two different signals
We carried out the reaction between the trimer com-
plex 1 and other ligands as PMePh2, phosphites,
(P(OR)3, R=methyl, ethyl, phenyl) and also the S-
donor
ligands
tetrahydrothiophene
(tht)
or
triphenylphosphine sulfide.
The P-donor ligands reacted with 1 in a ratio Pd:L=
1 and the complexes[Pd(h3-2Me-C3H4)(PO2F2)L], were
obtained (Eq. (1)).

R. Ferna´ndez-Gala´n et al. / Journal of Organometallic Chemistry 577 (1999) 271–282
273
Table 2
13C{1H}-NMR in CDCl3 data for 6–11 and 14, 15a
Complex h3-2- Methylallyl group
P- or S-donor ligand
CH3
C1
C2
C3
6
23.1 (s)
23.9 (s)
21.9 (s)
23.9 (s)
83.2 (d,
52.2 (s)
51.0 (s)
50.2 (s)
71.6 (pst,
125.9 (s)
136.1 (s)
49.6 (s, CH3)
J
CP=43.8)
83.2 (d,
CP=43.9)
84.1 (d,
CP=44.1)
7
16.7 (s, CH3). 62.1 (bs, CH2)
J
8
126.6 (s)
120.1 (d, JCP=5.6, Cortho), 125.7 (s, Cpara), 130.0 (s, Cmeta), 150.2
(d, JCP=4.6, Cipso)
52.0 (pst, Me)
J
b
9
71.6 (pst,
J* =23.0)
CP
J* =23.0)
CP
10
11
14
15
24.2 (s)
71.7 (pst,
71.7 (pst,
135.9 (s)
16.9 (s, CH3). 62.6 (bs, CH2)
J* =24.0)
J* =24.0)
CP
CP
b
b
73.2 (pst, br)
73.2 (pst, br)
136.3 (d, JCP=8.6, Cortho), 120.3 (s, Cpara), 130.6 (s, Cmeta), 149.7
(s, Cipso
)
22.3 (s)
22.2 (s)
62.8 (bs)
62.8 (bs)
127.9 (s)
128.4 (s)
129.0 (d, JCP=17.5, Cortho), 133.0 (d, JCP=4.5, Cpara), 132.7 (d,
b
JCP=14.7, Cmeta), Cipso
66.1 (bs)
66.1 (bs)
136.3 (d, JCP=13.0, Cortho), 133.1 (bs, Cpara), 132.1 (d, JCP=11.0,
b
Cmeta), Cipso
a C1 and C2 refers to the carbons cis or trans to the PO2F2− group, respectively. C3, central carbon; J*, pseudocoupling constant; pst,
pseudotriplet; bs, broad singlet.
b Not observed.
A different behavior was observed when 1 was made
to react with other S-donor ligand as SPPh3. In this
case, and using a ratio L:Pd=1 or 2, the new com-
plexes [Pd(h3-C4H7)(PO2F2)(SPPh3)], 14, and [Pd(h3-
C4H7)(SPPh3)2]PO2F2, 15, respectively, were easily
obtained.
for the terminal carbons with a chemical shift at lower
field for those situated trans to phosphorus. This result
is in accordance with the higher trans influence of the
phosphine or phosphite ligands [11] as compared to the
PO2F2− group.
In the 31P-NMR spectra a singlet is observed for the
neutral ligands while the difluorophosphate gives rise to
a triplet (JPF=953–963 Hz). The corresponding dou-
blet is observed in the 19F-NMR spectra for this group.
When the reaction of 1 with three equivalents of tht
(tht=tetrahydrothiophene) was monitored in a NMR
tube (CDCl3 solution) the formation of a new complex
12, as well as the complete disappearance of 1, was
observed. Apparently the allyl group is symmetric al-
though the broad appearance of the Hanti and Hsyn
signals might be indicative of a fluxional process. The
addition of another equivalent of tht per palladium
center gave rise to a different derivative, 13, with
unique and narrow signals for the Hanti and Hsyn shifted
to lower field with respect to 12. In both cases, the
corresponding signals of the tht group were observed.
The sequence of reactions reflected in ref. Eq. (2) could
account the NMR data.
When the reaction was made in a Schlenk to isolate
the corresponding complexes, only the derivative 1 is
obtained. Probably when vacuum is applied to the
solid, the tht group that must be slightly bonded, is
replaced by the PO2F2− group. This can be easily
understood if we consider the numerous examples of
late transition metal complexes where this ligand is
easily replaced by other groups [12].
1/3[Pd(h3-C4H7)(m-PO2F2)]3+L
“[Pd(h3-C4H7)(PO2F2)L] (12, 14)
“[Pd(h3-C4H7)L2](PO2F2) (13, 15)
(2)
L=tht (12, 13); SPPh3 (14, 15)
1
The H-NMR spectrum of 14, besides the signals of the
phenyl and methyl groups, show only two resonances,
one for each type of allylic proton (Hsyn and Hanti). This
is not in accordance with the expected asymmetric
environment of the allyl group in this complex. A
similar observation has been made for the correspond-
ing tht complex and it contrasts with the four signals
obtained for the syn and anti protons in case of phos-
phine or phosphite complexes of similar stoichiometry
(for complex 3 an increase in the temperature up to
55°C, does not affect the chemical shift of these four
signals). In the 13C{1H}-NMR spectrum of 14 also a
unique, although broad, signal is obtained for the ter-
minal allylic carbons. All these data indicate that a
fluxional process that interconverts both ends of the
allylic group (syn–syn, anti–anti interconversion) is
1
taking place (see below for discussion). The H- and
13C{1H}-NMR spectra of 15 exhibit the expected reso-
nances considering the symmetry of the allyl group.
However, the signals corresponding to the Hanti, Hsyn

274
R. Ferna´ndez-Gala´n et al. / Journal of Organometallic Chemistry 577 (1999) 271–282
cesses are observed in complexes with S-donor ligands,
we decided to explore the possibility of the dissociation
of the SPPh3 group as the origin of the observed
behavior of 14 and 15.
and terminal allylic carbons are broad which also point
to a possible dynamic behavior.
Several mechanisms have been proposed to account
for the syn–syn, anti–anti interconversion. Although
the simple rotation of the allyl ligand is a mechanism
often proposed to explain some isomerizations in com-
plexes of metals as Mo, W and Fe [13], it is not widely
accepted for square-planar palladium complexes and
orbital considerations suggest a high activation barrier
in square-planar geometries [14]. This rotation is appar-
ently a more facile process via a possible pentacoordi-
nate intermediate [14]. Dissociative pathways, via
tricoordinate palladium intermediates, with monoden-
tate ligands such as CO [15], SnCl3 [16], amines [17],
macrocycles [18], polyenes [19], and also N-donor
chelate ligands [20] have been proposed to explain the
dynamic behavior in asymmetric allyl palladium com-
plexes. A h3-h1-h3 mechanism is not considered in our
case because it would lead to a different interchange
(syn–anti ). Besides, when the temperature is increased,
a change in the Hsyn, Hanti chemical shifts is not
observed.
A
31P-NMR variable temperature study of a mixture
of 15 and free SPPh3 in acetone-d6 was undertaken. At
room temperature (r.t.) only one signal was seen (be-
sides the triplet of the PO2F2− group) while at low
temperature two clearly separated peaks, corresponding
to 15 and free SPPh3, were observed. The coalescence
temperature was −34°C and the calculated free energy
of activation 43.0 kJ mol−1. Consequently, for complex
15 an interchange between free and coordinated SPPh3
is taking place. From this experiment it is not possible
to conclude if the interchange occurs via a previous
coordination of the free ligand and formation of a
pentacoordinate intermediate (path a, Scheme 1) or via
a spontaneous dissociation of SPPh3 (path b, Scheme 1)
and the participation of 14 as a possible intermediate.
In order to test the possible spontaneous dissociation
of SPPh3 in 15 in the absence of free ligand, we have
made to react 15 with 1 in a NMR tube (CDCl3). A
31P-NMR made instantaneously shows that 14 is the
only palladium complex present (Eq. (3)).
We carried out several experiments in order to study
1
the possible fluxional behavior of 14 and 15. An H-
NMR variable temperature study of 14 in CD2Cl2 was
carried out with the aim of splitting the Hanti and Hsyn
resonances and observe the corresponding coalescences.
Lowering the temperature these signals are broadened
and split in a very complex way without being possible
to measure any clear coalescence temperature. Also the
methyl resonance is split and at least three different
methyl groups are observed. Obviously, this implies
that different allylic groups coexist in solution at low
temperature.
[Pd(h3-C4H7)(SPPh3)2]PO2F2 (15)
+1/3[Pd(h3-C4H7)(m-PO2F2)]3 (1)
“2[Pd(h3-C4H7)(PO2F2)(SPPh3)] (14)
(3)
Consequently, complex 15 is capable of dissociating
SPPh3 in the absence of free ligand. The PO2F2− group
may enter the coordination sphere of the palladium
center to occupy the position of an SPPh3 ligand that is
lost and the equilibrium, probably shifted to the left,
reflected in Scheme 2 may be established. The existence
of this equilibrium might explain the broad appearance
Considering that the PO2F2− group is also present in
the phosphine or phosphite complexes which do not
exhibit fluxional behavior and that the dynamic pro-
1
of the H- and 13C-NMR resonances.
Scheme 1.

R. Ferna´ndez-Gala´n et al. / Journal of Organometallic Chemistry 577 (1999) 271–282
275
Scheme 2.
Supposing that, like 15, 14 may also dissociate SPPh3,
the intermediate thus formed could be stabilized by a
chelate coordination of the PO2F2− group or via the
formation of oligomeric species with the PO2F2− ligands
acting as bridges between two metal centers (see Scheme
3). The opening of a Pd–O bond and recoordination of
the SPPh3 ligand in a different position complete the
process that makes equivalent the two halves of the
allylic group. The existence of different species acting as
intermediates may explain the complexity of the spec-
trum of 14 at low temperature.
pure products were obtained which allowed their com-
plete characterization (an alumina chromatographic
column made to separate 16 and [Pd(h3-C4H7)Cl]2 led to
decomposition of the titanium complex).
Only one resonance is seen in the 1H-NMR spectra of
16–18 showing the equivalence of the two cyclopentadi-
enyl groups. According with that, complexes 16 and 18
give rise to a unique signal in the corresponding
13C{1H}–NMR spectra while 17 exhibits the two signals
of the methyl and cyclopentadienyl carbons. In the 31P-
and 19F-NMR spectra, the resonances corresponding to
the PO2F2− groups are observed.
The possibility of formation of a pentacoordinate
intermediate without dissociation of a SPPh3 group and
via coordination of an oxygen atom of another molecule
can not be fully excluded. In this intermediate the
rotation of the allyl group should be more facile and this
would account for the r.t. 1H- and 13C{1H}-NMR
spectra. However, this mechanism is less appropriate to
The similar reaction of 1 with ZrCpR2 Cl2 {CpR=C5H5
([22]a), C5H4(SiMe3), C5H3(SiMe3)2 ([22]b)} also led to
the formation of [Pd(h3-C4H7)Cl]2 which is indicative of
a PO2F2− transfer process. However, the expected zirco-
nium complex ZrCp2R(PO2F2)2 can not be isolated and a
very insoluble white solid was obtained which was not
fully characterized.
1
explain the low temperature H-NMR spectrum.
To our knowledge complexes 16–18 are the first
described metallocene derivatives containing the difl-
uorophosphate group. Although some difluorophos-
phate titanium derivatives as TiCl2(PO2F2)2 have been
described [23], 16 and 17 are the first organometallic
complexes of titanium containing this group. As far as
we know, difluorophosphate molybdenum derivatives
have not been previously reported.
The reaction of 1 with [MPPh3]PF6 (M=Cu, Ag),
freshly prepared in THF solution from AgClPPh3 [24]
or [CuClPPh3]4 [25] and TlPF6, did not give the expected
heteronuclear PO2F2− bridged complexes but the known
derivative [Pd(h3-C4H7)(PPh3)2]PF6. When M=Ag+,
AgPO2F2 was also obtained and for M=Cu the species
CuPO2F2 that could be initially formed must dispropor-
tionate and Cu(0) and Cu(PO2F2)2 were obtained. Ac-
cording with the stoichiometry the solvato complex
[Pd(h3-C4H7)(S)2]PF6 could remain in solution but it
decomposes when the solution is evaporated to dryness
(see Eq. (4)).
2.2. Reactions with early and late transition metal
complexes
Some reactions of 1 or its phosphine derivatives 2 and
3 with early and late transition metal complexes were
explored. The high oxophilicity of the first type of
metals would probably lead to a transfer of the PO2F2−
group and, consequently, to the generation of new
complexes. The second type of metals having a not very
different oxophilicity from palladium could give rise to
new derivatives with a bridging PO2F2− group. The
ability of this ligand to act as a bridge not only in
homonuclear but also in heteronuclear complexes is well
established [21].
Derivatives of the type MCpR2 Cl2 where chosen to
react with 1 for two reasons: (i) the high stability of the
‘MCpR2 ’ fragment and (ii) the presence of the chloride
groups that could favor the transfer process by the
formation of the highly stable palladium dimer [Pd(h3-
C4H7)Cl]2. According to our proposal, the reaction of
M(h5-C5R5)2Cl2 (M=Ti, R=H, Me; Mo, R=H) with
1 leads to the formation of the new derivatives 16–18,
as is shown in Scheme 4.
Complexes 16–18 exhibit solubility properties very
similar to those of [Pd(h3-C4H7)Cl]2. Consequently, it
was not possible to achieve proper separation of the two
products that are obtained in the corresponding reac-
tion. After careful crystallization small amounts of the
(4)

276
R. Ferna´ndez-Gala´n et al. / Journal of Organometallic Chemistry 577 (1999) 271–282
Scheme 3.
In order to prevent the formation of the solvato deriva-
tive, the complex [Pd(h3-C3H7)(PO2F2)(PPh3)] was used
as starting product. The silver derivative utilized was
Ag(ClO4)PPh3 [24b]. The reaction led clearly to the
formation of [Pd(h3-C4H7)(PPh3)2]PF6 and AgPO2F2
(Eq. (5)).
2.3. Reaction with acids
In the process of formation of 1 that implies the
hydrolysis of the PF6− anion, HF is simultaneously
formed [1]. Under the reaction conditions, 1 does not
react with this acid. However, we decided to find out if
changes in the strength of the acid or in the coordinat-
ing ability of the anion could lead to the protonation of
the difluorophosphate group in 1 or in its derivative 3
that contains a monodentate PO2F2− group.
[Pd(h3-C4H7)(PO2F2)(PPh3)]+Ag(ClO4)PPh3
“[Pd(h3-C4H7)(PPh3)2]ClO4+AgPO2F2
(5)
When 1 is made to react, in a 1:3 molar ratio, with
acetylacetone or CF3COOH, both with conjugated
bases anions of good coordinating ability, no reaction
was observed after 6 h in CDCl3 at r.t. However, when
the reaction of 1 with HBF4 · Et2O, (1:3 ratio), a
stronger acid but with a weak coordinating anion, was
The behavior of against THF solution of
1
a
[AuPPh3]PF6 [26] was different. The transfer of PPh3
and PO2F2− did not take place and 1 was recovered
unaltered even after long reaction times.
Complexes 2 and 3 reacted instantaneously with
PdCl2(PhCN)2 [27], a bright red color appearing in the
solution. After appropriate work up, two products were
separated from the reaction mixture: trans-[PdCl(m-
1
monitored by H-NMR (acetone-d6) an instantaneous
reaction was detected. A product with a symmetric allyl
group, different to 1, was observed. A broad signal at
11.72 ppm was also seen. The complex [Pd(h3-
C4H7){(CD3)2CO}2]BF4, already described with non
deuterated acetone [31], is probably formed as it is
reflected in Eq. (6).
Cl)(PR3)]2
[28],
R=Ph,
Cy
and
[Pd(h3-
C4H7)(PhCN)2]PO2F2 (19) (see Scheme 5)
Consequently, a mutual transfer of PR3 and PhCN
ligands between the ‘PdCl2’ and ‘Pd(h3-C4H7)’ frag-
ments takes place. The previously described dimer com-
plexes [29] exhibit in the stretching M–Cl region of the
corresponding IR spectra, the expected three normal
vibration modes characteristic of C2h square-planar
complexes of the type trans-MX4L2 [30]. A single reso-
nance is observed in their 31P-NMR spectra.
[Pd(h3-C4H7)(m-PO2F2)]3+3HBF4
“3[Pd(h3-C4H7){(CD3)2CO}2]BF4+3HPO2F2
(6)
Considering these results, and looking for a coordina-
tion of the tetrafluoroborate anion, the same reaction
was performed in a non coordinating solvent as CDCl3.
Signals corresponding to a symmetric allyl group, dif-
ferent to 1, and a broad singlet at 8.43 ppm, were
observed. The triplet and the quartet of the Et2O
molecule appeared at 3.8 and 1.4 ppm, shifted to lower
field with respect to the expected signals of free Et2O in
this solvent, pointing out to a coordination of the
molecule to the palladium center. In the 19F-NMR a
complex signal was observed in the BF4− region at r.t.
and, consequently, a variable temperature NMR study
was undertaken. In Fig. 1 the appearance of the region
In the mass spectrum of trans-[PdCl2(PCy3)]2 peaks
are observed at m/z 915 [M+], 881 [M−Cl]+, 527
[M−3Cl−PCy3]+and 421 [PdCl(PCy3)]+.
Although the cation of complex 19 has already been
described [31], the complex with the difluorophosphate
anion has not been previously reported. The existence
of a symmetric allyl group is deduced from the 1H-
NMR spectrum (one type of Hanti and Hsyn) where the
corresponding resonances of the PhCN group are also
observed. In the 31P- and 19F-NMR spectra the ex-
pected signals for the PO2F2− are seen.

R. Ferna´ndez-Gala´n et al. / Journal of Organometallic Chemistry 577 (1999) 271–282
277
Scheme 4.
reached at 20°C. At 60°C a unique thin doublet is
observed. The corresponding triplets are observed in
the 31P-NMR spectra. The coupling constants are
higher than those observed for complexes with the
difluorophosphate group and similar to that described
for the difluorophosphoric acid, 974 Hz [39] (other
authors have reported a JPF of 992 Hz for this acid
[40]). As a consequence two types of HPO2F2 must be
present in solution.
Considering all these data, we propose the existence
of an equilibrium between species A, B and C as shown
in Scheme 6. The formation of a hydrogen bond with
the BF4− group might favor the coordination of the
acid in A. This group will be in equilibrium with free
acid HPO2F2.
at selected temperatures is collected. The four signals
(two thin and two slightly broad) seen at −75°C were
transformed into two thin singlets at −60°C. When the
temperature was increased, two effects were observed:
(i) a coalescence of the two signals at ca. 40°C and (ii)
the appearance of a third singlet whose intensity in-
creased with temperature.
Although the BF4− anion is considered to be of very
weak coordinating ability (see [32] for a comparative
study of different anions), several examples of BF4−
coordination have been described. The coordination
has been proposed from IR spectra [33] or unam-
bigously seen by X-ray diffraction studies [34]. 19F-
NMR [35] has also been used to find some of the
M–FBF3 interactions. With metals such as Mo, W [36],
or Fe [37] two signals at very different chemical shifts
(usually a quartet and doublet) have been found for the
two types of fluorine atoms, but in other cases a singlet,
as a consequence of fluorine interchange, has been
observed for a coordinated BF4− [35,38]. Also equilibria
between free and coordinated groups have been de-
scribed [33a] with the amount of the former usually
increasing with temperature [35]. Considering these
ideas we propose that in our case at −75°C the less
intense signals that appear at −147.9 and −148.2
ppm correspond to two types of fluorine atoms (three
for the broad signal) of a coordinated BF4− group. The
same must apply for the two intense signals that appear
at −151.0 and −151.2 ppm for another type of BF4−,
also coordinated. An increase in temperature leads to a
rapid interchange of the two types of fluorine atoms of
each group. Further increasing of temperature finally
leads to interchange between these two groups. The
new central signal may be due to free BF4− whose ratio
reasonably increases with temperature. The possible
coalescence between the 19F-NMR signals of free and
coordinated groups can not be seen perhaps due to the
limit of the solvent boiling point.
At low temperature only one type of allyl is seen in
1
the H-NMR spectrum. Perhaps the chemical shift dif-
ferences between the different signals are not big
enough to give rise to separate signals at low
temperature.
We have also explored the reactivity of complex 2
with acids. No reaction was observed with CF3COOH.
When 2 was made to react with a HCl solution in Et2O,
a complex is obtained whose analytical and spectro-
scopic data correspond with the known complex
[Pd(h3-C4H7)Cl(PPh3)] [41] (see Eq. (7)). A broad sin-
glet in the 1H-NMR spectrum may correspond to
HPO2F2.
[Pd(h3-C4H7)(PO2F2)(PPh3)] (2)+HCl · Et2O
“[Pd(h3-C4H7)Cl(PPh3)]+HPO2F2
(7)
The reaction of 2 with HBF4 · Et2O in (CD3)2CO in an
1
NMR tube was analyzed by H-, 19F- and 31P-NMR.
After 10 min three types of allyl groups, two symmetric
1
and one asymmetric, were seen in the H-NMR. One
product was unambiguously identified as [Pd(h3-
C4H7)(PPh3)2]BF4 [31]. Two doublets were seen in the
difluorophosphate region of the 19F-NMR (JPF=973.6
and 964.4 Hz) that may correspond to the acid and the
anion. In the BF4− region three singlets (one minor) are
observed. In the 31P-NMR spectrum, besides the two
expected triplets, two singlets corresponding to two
different PPh3 groups were seen. Considering all this
data, we cannot propose specific formulations for the
Before proposing the possible species that could co-
exist in solution the PO2F2− region of the 19F-NMR
spectra must be considered (see Fig. 2). At low temper-
ature two doublets with a similar JPF of 973–976 Hz
and 7:3 ratio are observed. After increasing the temper-
ature both are broadened until the coalescence is

278
R. Ferna´ndez-Gala´n et al. / Journal of Organometallic Chemistry 577 (1999) 271–282
Scheme 5.
unknown complexes. They must be adducts where coor-
dination of PPh3, (CD3)2CO, PO2F2− (or the acid) and
BF4− to the allyl fragment is possible. We have also
recorded the corresponding spectra after 3 h of reaction.
The most remarkable fact is the appearance of three
doublets (JPF=927.8, 967.4 and 961.4 Hz) in the difl-
uorophosphate region of the 19F-NMR spectrum. The
same coupling constant are found in three doublets of
the corresponding 31P-NMR spectrum. Consequently an
evolution of HPO2F2 (or PO2F2−) towards species con-
taining a single fluorine atom bonded to phosphorus,
has taken place.
nitrogen. Solvents were distilled from appropriate dry-
ing agents and degassed before use. Elemental analyses
were performed with a Perkin-Elmer 2400 microanaly-
ser. IR spectra were recorded as KBr pellets or Nujol
mulls with a Perkin-Elmer PE 883 IR spectrometer.
NMR spectra were recorded on a Varian Unity 300
MHz and a Gemini 200 MHz. Chemical shifts (ppm) are
relative to SiMe4 (1H- and 13C-NMR),CClF3 (19F-
NMR) and 85% H3PO4 (31P-NMR). Coupling constants
(J) are in Hertz. Mass spectra were performed with a
VG Autospec instrument using the FAB technique and
nitrobenzyl alcohol as matrix. [Pd(h3-C4H7)(m-PO2F2)]3
(1) and [Pd(h3-C4H7)(PO2F2)(PR3)] (R=Ph, 2; Cy, 3;
p-tolyl, 4) [1], [Ti(h5-C5H5)2Cl2] [42], [Ti(h5-C5Me5)2Cl2]
[43], [Mo(h5-C5H5)2Cl2] [44] and PdCl2(PhCN)2 [27]
were prepared according to the published methods. Free
energies of activation were calculated from the coales-
cence temperature (Tc), and the frequency difference
3. Conclusions
The results reported above indicate that in palladium
complexes the difluorophosphate group is easily re-
placed by P-donor ligands. In case of S-donor ligands,
a competition between the two groups is observed and
a dissociation of SPPh3 evidenced. The difluorophos-
phate anion is easily transferred to early metals and this
process has allowed the synthesis of the first metal-
locene–PO2F2 complexes. The formation of the highly
insoluble salts AgPO2F2 or Cu(PO2F2)2 seems to prevent
the formation of heteronuclear Pd–Ag or Pd–Cu com-
plexes. The formation of the stable dimers trans-[Pd(m-
Cl)Cl(PR3)]2, R=Ph, Cy leads to the mutual transfer of
PR3 and PhCN ligands between the ‘PdCl2’ and ‘Pd(h3-
C4H7)’ fragments while the difluorophosphate group
remains uncoordinated. It is possible to remove the
PO2F2 fragment by protonation only with strong acids.
When the process is carried out with HBF4 in a non
coordinating solvent, it is possible to see at low temper-
ature species with the BF4− anion coordinated.
between the coalescing signals with the formula DG"
=
aTc(10.319+log Tc/k); k values were calculated accord-
ing to the Shanan-Atidi and Bar-Eli method [45].
4.2. Synthesis of [Pd(p3-C4H7)(PO2F2)(PMePh2)] (5)
To a solution of 1 (0.200 g, 0.254 mmol) in 20 ml of
CH2Cl2, PMePh2 (143.39 ml, 0.762 mmol) was added.
The reaction mixture was allowed to stir at r.t. and after
1 h the solvent was removed in vacuo and an oil was
isolated. 19F-NMR (CDCl3): −81.5 (d, JFP=962.9
Hz). 31P{1H}-NMR (CDCl3): −11.2 (t, PO2F2); 13.4 (s,
PMePh2).
4.3. Reaction of 1 with the phosphites P(OMe)3,
P(OEt)3 and P(OPh)3
The procedure is identical to that described for the
isolation of complex 5. Amounts used are as follows:
1 (0.150 g, 0.190 mmol) in 20 ml of CH2Cl2 and
P(OMe)3 (69.31 ml, 0.570 mmol). An oil is obtained
corresponding to a mixture of complex 6 with minor
amounts of complex 9. 6: 19F-NMR ((CD3)2CO): −
82.3 (d, JFP=953.1 Hz). 31P{1H}-NMR ((CD3)2CO):
−9.5 (t, PO2F2); 134.7 (s, P(OMe)3). 9: 19F-NMR
((CD3)2CO): −82.3 (d, JFP=953.1 Hz). 31P{1H}-NMR
((CD3)2CO): −9.5 (t, PO2F2); 136.7 (s, P(OMe)3).
1 (0.150 g, 0.190 mmol) in 20 ml of CH2Cl2 and
P(OEt)3 (99.43 ml, 0.570 mmol). An oil is obtained
corresponding to a mixture of complex 7 with minor
In summary, the results presented in this paper give
an illustration of the potential of the difluorophosphate
complexes, being that a group easily seen in 19F- and
31P-NMR that may constitute an alternative to other
more common anions.
4. Experimental details
4.1. General
All reactions were performed using standard Schlenk
techniques under an atmosphere of dry, oxygen-free,

R. Ferna´ndez-Gala´n et al. / Journal of Organometallic Chemistry 577 (1999) 271–282
279
Fig. 1. Selected spectra from the variable-temperature 19F-NMR study for the reaction between complex 1 and HBF4 · Et2O (CDCl3) in the BF4−
region.
amounts of complex 10. 7: 19F-NMR (CDCl3): −82.4
(d, JFP=963.2 Hz). 31P{1H}-NMR (CDCl3): −9.2 (t,
PO2F2); 130.2 (s, P(OEt)3). 10: 19F-NMR (CDCl3):
−82.4 (d, JFP=963.2 Hz). 31P{1H}-NMR (CDCl3):
−9.2 (t, PO2F2); 128.0 (s, P(OEt)3).
1 (0.150 g, 0.190 mmol) in 20 ml of CH2Cl2 and
P(OPh)3 (0.150 ml, 0.570 mmol). An oil is obtained
corresponding to a mixture of complex 8 with minor
amounts of complex 11. 8: 19F-NMR (CDCl3): −84.0
(d, JFP=961.0 Hz). 31P{1H}-NMR (CDCl3): −9.1 (t,
PO2F2); 125.5 (s, P(OPh3)). 11: 19F-NMR (CDCl3):
−84.0 (d, JFP=961.0 Hz). 31P{1H}-NMR (CDCl3):
−9.1 (t, PO2F2); 123.3 (s, P(OPh3)).
Several attempts were made to crystallize the oils
obtained in Sections 4.2 and 4.3. The oils were treated
with different solvent mixtures (CH2Cl2/Et2O, CH2Cl2/
pentane, thf/hexane, thf/Et2O) or dried under vacuum
for a long period of time at low temperature. Only in
the case of P(OPh)3 a solid was obtained at low temper-
ature but it became an oil when it was warmed to r.t.
4.4. Spectroscopic characterization of
[Pd(p3-C4H7)(PO2F2)(tht)] (12)
To a yellow solution of 1 (0.030 g, 0.038 mmol) in 5
ml of CDCl3 was added tht (10.15 ml, 0.114 mmol) in a
NMR tube and the solution changed to a pale yellow
color. After 5 min the solution was studied by 1H-
NMR.
4.5. Spectroscopic characterization of
[Pd(p3-C4H7)(tht)2](PO2F2) (13)
Fig. 2. Selected spectra from the variable-temperature 19F-NMR
study for the reaction between complex 1 and HBF4 · Et2O (CDCl3)
in the PO2F2− region.
To a yellow solution of 1 (0.030 g, 0.038 mmol) in 5
ml of CDCl3 in a NMR tube, tht (20.30 ml, 0.228 mmol)

280
R. Ferna´ndez-Gala´n et al. / Journal of Organometallic Chemistry 577 (1999) 271–282
Scheme 6.
was added. The solution turned pale yellow. After 5
min the solution was studied by H-NMR.
C10H10F4O4P2Ti: C, 31.61; H, 2.65. Found: C, 31.68; H,
2.73%. 19F-NMR (acetone-d6): −85.4 (d, JFP=958.3
Hz, PO2F2). 31P{1H}-NMR (acetone-d6): −16.1 (t,
PO2F2). IR: wassym (PO2) 1311; wsym (PO2) 1149; wsym
(PF2) 834; l(PO2) 550; l(POF) 496 cm−1 and for Cp
1
4.6. Synthesis of [Pd(p3-C4H7)(PO2F2)(SPPh3)] (14)
ligand w(C–C) 1442, l(C–H) 1018 cm−1
.
To a yellow solution of 1 (0.150 g. 0.190 mmol) in 20
ml of CH2Cl2, SPPh3 (0.171 g, 0.570 mmol) was added.
The solution was allowed to stir at r.t. and after 14 h
the solvent was removed in vacuo. Dry hexane was
added to triturate the beige oil. The resulting solid was
isolated by filtration and crystallized from CH2Cl2 lay-
ered with Et2O. Anal. Calc. for C22H22F2O2P2PdS: C,
47.45; H, 3.98. Found: C, 47.21; H, 4.21%. 19F-NMR
(CDCl3): −83.1 (d, JFP=967.4 Hz). 31P{1H}-NMR
(CDCl3): −14.4 (t, PO2F2); 45.7 (s, SPPh3); (free SPPh3
45.2 (s) in CDCl3). IR: wassym (PO2) 1310; wsym (PO2)
1152; wassym (PF2) 849; wsym (PF2) 836; l(PO2) 513;
4.9. Synthesis of [Ti(p5-C5Me5)2(PO2F2)2] (17)
To a yellow solution of 1 (0.150 g, 0.190 mmol) in 20
ml of THF, [Ti(h5-C5Me5)2Cl2] (0.111 g, 0.285 mmol)
was added. The deep brown solution thus formed was
stirred for 16 h. at r.t. and then filtered, and evaporated
under reduced pressure to a small volume. Diethyl ether
was added to the concentrated solution. After standing
for 24 h, a mixture of yellow and brown crystals were
obtained by filtration. The two types of crystals were
manually separated. The resulting brown crystals were
complex 17. Anal. Calc. for C20H30 F4O4P2Ti: C, 46.17;
H, 5.81. Found: C, 46.32; H, 5.75%. IR: wassym (PO2)
1323; wsym (PO2) 1111; wassym (PF2) 851; l(PO2) 537;
l(POF) 485 cm−1 and for Cp ligand, w(C–C) 1490.
l(POF) 497 cm−1
.
4.7. Synthesis of [Pd(p3-C4H7)(SPPh3)2](PO2F2) (15)
To a yellow solution of 1 (0.100 g, 0.127 mmol) in 20
ml of CH2Cl2, SPPh3 (0.229 g, 0.762 mmol) was added.
The pale green solution thus formed was allowed to stir
at r.t. and after 20 h the solvent was removed in vacuo.
Dry hexane was added to triturate the beige oil. The
resulting solid was isolate via filtration and crystallized
from CH2Cl2 layered with Et2O. Anal. Calc. for
C40H37F2O2P3PdS2: C, 47.45; H, 3.98. Found: C, 47.21;
H, 4.21%. 31P{1H}-NMR (acetone-d6): −10.7 (t,
PO2F2, JPF=949.0 Hz); 46.8 (s, SPPh3). IR: wassym
(PO2) 1320; wsym (PO2) 1152; wassym (PF2) 850; wsym (PF2)
4.10. Synthesis of [Mo(p5-C5H5)2(PO2F2)2] (18)
To a yellow solution of 1 (0.144 g, 0.182 mmol) in 20
ml of THF, [Mo(h5-C5H5)2Cl2] (0.814 g, 0.274 mmol)
was added. The green solution was stirred for 15 min at
r.t. and then evaporated under reduced pressure to a
small volume. Hexane was added to the concentrated
solution. A mixture of yellow and green crystals were
obtained by filtration. The two types of crystals were
manually separated. The resulting green crystals were
complex 18. Anal. Calc. for C10H10F4O4P2Mo: C,
28.06; H, 2.35. Found: C, 27.60; H, 2.70%. 19F-NMR
807; l(PO2) 515 cm−1
.
4.8. Synthesis of [Ti(p5-C5H5)2(PO2F2)2] (16)
(acetone-d6): −75.4 (d, PO2F2,
JFP=955.2 Hz).
31P{1H}-NMR (acetone-d6): −5.5 (t, PO2F2). IR: wassym
(PO2) 1311; wsym (PO2) 1109; wassym (PF2) 887; wsym (PF2)
839; l(PO2) 542; l(POF) 496 cm−1 and for Cp ligand
To a yellow solution of 1 (0.150 g, 0.190 mmol) in 20
ml of THF, [Ti(h5-C5H5)2Cl2] (0.071 g, 0.285 mmol)
was added. The orange solution thus formed was
stirred for 15 min and then evaporated under reduced
pressure to a small volume. After that, toluene was
added. After standing for 24 h, a mixture of yellow and
red crystals were obtained by filtration. The two types
of crystals were manually separated. The resulting
red crystals were complex 16. Anal. Calc. for
w(C–C) 1426, l(C–H) 1019 cm−1
.
4.11. Reaction of [Pd(p3-C4H7)(PO2F2)(PPh3)] (2) or
[Pd(p3-C4H7)(PO2F2)(PCy3)] (3) with PdCl2(PhCN)2
To a yellow solution of complex 2 (0.150 g, 0.286
mmol) in 20ml of CH2Cl2, PdCl2(PhCN)2 (0.110 g,

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281
0.286 mmol) was added at r.t. The red solution was
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NMR (CDCl3): 31.32 (s, PPh3).
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C18H17F2N2O2PPd: C, 46.15; H, 3.66. Found: C, 45.83;
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to the isolation of [PdCl(m-Cl)(PCy3)2]2 · 2CH2Cl2 and
[Pd(m3-C4H7)(PhCN)2]PO2F2 (19). Yield of [PdCl(m-
Cl)(PCy3)2]2 · 2CH2Cl2: 0.129 g (77%). 31P{1H}-NMR
(CDCl3): 58.93 (s, PCy3).
4.12. Reaction of [Pd(p3-C4H7)(v-PO2F2)]3 (1) with
HBF4 · Et2O (54% Et2O)
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To a yellow solution of complex 1 (0.030 g, 0.038
mmol) in acetone-d6 (0.75 ml),
a
solution of
HBF4 · Et2O (16.40 ml, 0.114 mmol) was added in a
NMR tube. The NMR spectra were immediately per-
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solvent.
4.13. Reaction of 2 with an Et2O solution of HCl
To a yellow solution of complex 2 (0.100 g, 0.190
mmol) in CH2Cl2 (50 ml), an Et2O solution of HCl 0.26
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from the Direccio´n General de Investigacio´n Cient´ıfica
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The authors would like to thank Dr Mariano Laguna
who recorded the mass spectra.

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