Synthesis and spectroscopic and spectroelectrochemical characterization of a new family of 44e- tris-phosphido-bridged palladium triangles

Article abstract of DOI:10.1021/ic4009448

Triangular clusters containing a [M₃(μ-PR₂) ₃]⁺ core are very common in platinum chemistry but were virtually unknown for M = Pd. Herein we describe the synthesis and characterization of several palladium derivatives belonging to this class. The trinuclear monohalide clusters {Pd₃}(CO)₂X [{Pd ₃} = Pd₃(μ-PBu^t₂)₃; X = Br, I] were prepared by reacting [ⁿBu₄N]X or KX with the dinuclear complex [Pd(PBu^t₂H)(μ-PBu^t ₂)]₂ and H₂O under an atmosphere of CO. The reaction of {Pd₃}(CO)₂I with CNBu^t leads to the substitution of all the terminal ligands to afford the symmetrical cluster [{Pd₃}(CNBu^t)₃]I. The latter reacts with TlPF₆ (excess) or AgCF₃SO₃ (1:1 ratio) to give anion metathesis, whereas the addition of a second equivalent of Ag⁺ causes cluster oxidation to the thermally stable paramagnetic 43e^- dication [{Pd₃}(CNBu^t)₃]²⁺. The cationic clusters [{Pd₃}(CO)₂(L)]PF₆ (L = NCCH₃, Py or CO) were obtained by reacting {Pd₃}(CO) ₂I with TlPF₆, under nitrogen in acetonitrile or in pyridine or under 1 atm of carbon monoxide in THF. Finally, {Pd ₃}(CO)₂Cl was achieved by the reaction of [{Pd ₃}(CO)₃]PF₆ with [(PPh₃) ₂N]Cl. All clusters have been obtained in good yields and purity and have been characterized by microanalysis and IR and multinuclear NMR spectroscopy. Single crystal X-ray diffraction studies on {Pd ₃}(CO)₂Br and [{Pd₃}(CNBu^t) ₃]CF₃SO₃ are also reported. The cyclovoltammetric profile exhibited by the palladium clusters prepared in this work is characterized by the presence of two monoelectronic oxidation processes whose reversibility and potentials depend on the nature of the ligands. Moreover, the UV-vis and IR spectroelectrochemical analysis of {Pd ₃}(CO)₂I, [{Pd₃}(CO)₃]PF₆ and [{Pd₃}(CNBu^t)₃]PF₆ allowed the spectroscopical characterization of some electrogenerated oxidized species and provided some detail for the redox-coupled reactions of metastable products.

Full text of DOI:10.1021/ic4009448

Article
pubs.acs.org/IC
Synthesis and Spectroscopic and Spectroelectrochemical
−
Characterization of a New Family of 44e Tris-Phosphido-Bridged
Palladium Triangles
Veronica Bonuccelli, Tiziana Funaioli, Piero Leoni,* Fabio Marchetti, and Lorella Marchetti
Dipartimento di Chimica e Chimica Industriale dell’Universita
S Supporting Information
̀
di Pisa, Via Risorgimento 35, I-56126 Pisa, Italy
*
+
ABSTRACT: Triangular clusters containing a [M (μ-PR ) ]
3
2 3
core are very common in platinum chemistry but were virtually
unknown for M = Pd. Herein we describe the synthesis and
characterization of several palladium derivatives belonging to
this class. The trinuclear monohalide clusters {Pd }(CO) X
3
2
t
[
[
{Pd } = Pd (μ-PBu ) ; X = Br, I] were prepared by reacting
Bu N]X or KX with the dinuclear complex [Pd(PBu H)(μ-
PBu )] and H O under an atmosphere of CO. The reaction
of {Pd }(CO) I with CNBu leads to the substitution of all the
3 3 2 3
n
t
4
2
t
2
2
2
t
3
2
terminal ligands to afford the symmetrical cluster [{Pd }-
3
t
(
CNBu ) ]I. The latter reacts with TlPF (excess) or
3
6
AgCF SO (1:1 ratio) to give anion metathesis, whereas the
addition of a second equivalent of Ag causes cluster oxidation
to the thermally stable paramagnetic 43e dication [{Pd }(CNBu ) ] . The cationic clusters [{Pd }(CO) (L)]PF (L =
3
3
+
−
t
2+
3
3
3
2
6
NCCH , Py or CO) were obtained by reacting {Pd }(CO) I with TlPF , under nitrogen in acetonitrile or in pyridine or under 1
3
3
2
6
atm of carbon monoxide in THF. Finally, {Pd }(CO) Cl was achieved by the reaction of [{Pd }(CO) ]PF with [(PPh ) N]Cl.
3
2
3
3
6
3 2
All clusters have been obtained in good yields and purity and have been characterized by microanalysis and IR and multinuclear
t
NMR spectroscopy. Single crystal X-ray diffraction studies on {Pd }(CO) Br and [{Pd }(CNBu ) ]CF SO are also reported.
3
2
3
3
3
3
The cyclovoltammetric profile exhibited by the palladium clusters prepared in this work is characterized by the presence of two
monoelectronic oxidation processes whose reversibility and potentials depend on the nature of the ligands. Moreover, the UV−
t
vis and IR spectroelectrochemical analysis of {Pd }(CO) I, [{Pd }(CO) ]PF and [{Pd }(CNBu ) ]PF allowed the
3
2
3
3
6
3
3
6
spectroscopical characterization of some electrogenerated oxidized species and provided some detail for the redox-coupled
reactions of metastable products.
i
6
1
. INTRODUCTION
PR ) Cl [R = NPr , N(c-Hex) ], and in the primary
2 3 3 2 2
7
1
−4
phosphido derivative, Pd (μ-PHCH Fc) (PPh ) Cl , or con-
3 2 3 3 3 3
Tris-phosphido-bridged clusters of platinum are well-known.
They have a common [Pt (μ-PR ) ] moiety, with a triangular
mixed-valence (Pt3 ) metal core; the structures are completed
by three terminal ligands in the cationic clusters [Pt (μ-
PR ) (L) ] (L = CO, PR , RNC, RCN, C H , or mixtures of
them) or in the neutral derivatives Pt (μ-PR ) (L) X (L = CO,
PR , RNC; X = H, Ar, Cl, Br, I, CCR, SiR ). Many of them
have been prepared in our laboratories, and we have then
shown how they can be employed as precursors of dibridged-
tetrahedral hexanuclear clusters or polycluster structures, in
which two or more cluster units can be inserted into ordered
molecular assemblies by connecting them with strongly bound
alkynyl spacers. In attempting to extend this chemistry to the
analogous palladium derivatives, we found a unique example of
mixed-valence tris-phosphido-bridged triangulo cluster of
−
+
tain bridging phosphinine ligands, as found in the 42e cluster
Pd (μ-PC H -2,4,6-Ph ) (PEt ) . Herein we describe high
yield synthetic procedures for the neutral clusters {Pd }-
(CO) X [{Pd } = Pd (μ-PBu ) ; X = Cl, Br, I] and for
3
2 3
8
4
+
3
5
2
3 3
3 3
3
3
t
+
2 3 3 2 3
2
3
3
3
2
4
[
=
{Pd }(L) L′]X (L = CO, L′ = CO, MeCN, Py, X = PF ; and L
3
2
6
3
2 3
,2
2
t
1
L′ = CNBu , X = I, PF , CF SO ). The new clusters were
6
3
3
3
3
2
characterized by microanalytical and spectroscopical (IR and
1
13
31
H, C, and P NMR) analyses and by cyclovoltammetric and
spectroelectrochemical studies. Single crystal X-ray diffraction
studies on the structures of {Pd }(CO) Br and [{Pd }-
(CNBu ) ]CF SO are also described.
3
4
3
2
3
t
3
3
3
2
. RESULTS AND DISCUSSION
2.1. Syntheses. The neutral monohalide clusters {Pd }-
CO) X [2, X = Br; 3, X = I] were obtained by adding the
t
3
palladium, namely, the chloro derivative Pd (μ-PBu ) (CO) Cl
which, however, was obtained in very low yields (12%) as a
3
2 3
2
(
2
5
byproduct in a reaction conceived for other purposes. Other
less related derivatives reported up to now feature a Pd36+ core,
Received: April 16, 2013
Published: July 24, 2013
as found in the bis(dialkylamino)phosphide derivatives Pd (μ-
3
©
2013 American Chemical Society
8759
dx.doi.org/10.1021/ic4009448 | Inorg. Chem. 2013, 52, 8759−8769

Inorganic Chemistry
Article
corresponding potassium or n-butylammonium halide and a
Scheme 2. Reactions of Cluster 3
molar excess of water to a toluene suspension of the dinuclear
t
t
9
Pd(I) complex [Pd(PBu H)(μ-PBu )] (1). After stirring for
2
2
2
three days at 100 °C under 1 atm of carbon monoxide, the final
3
1
basic mixture was shown by P NMR to contain the free
t
secondary phosphine, PBu H, and 2 or 3 in ca. 3:1 ratio;
2
moreover, the evolution of dihydrogen in the course of the
reaction was verified by GC analysis (see Experimental
Section). We have no clarifying experimental evidence about
the mechanism of these probably complex reactions, although,
t
−
based on the observed formation of PBu H, H , and OH as
2
2
coproducts of the reactions, the precise stoichiometric balance
shown in Scheme 1 can be given. The final products were
Scheme 1. Synthesis of {Pd }(CO) X (X = Br, I)
3
2
atmosphere (unchanged after 6 days in the solid state, τ1/2 ca.
1
0 days in solution).
The stepwise substitution of the terminal ligands of cluster 3,
t
t
obtained analytically pure in satisfactory to good yields (2, 63%;
, 85%) as dark red microcrystalline solids soluble in polar and
yielding [Pd (μ-PBu ) (CO) (CNBu )]I or Pd (μ-
PBu ) (CNBu ) I, was attempted by reacting the cluster with
2 3 2
an equimolar amount or a 2-fold excess of CNBu , but in all
cases we isolated only mixtures of the starting material 3 and of
the persubstituted cluster (6)I. Conversely, the iodo ligand may
be cleanly and quantitatively removed by reacting cluster 3 with
an excess of TlPF6 in acetonitrile or in pyridine. These
3 2 3 2 3
t
t
3
t
nonpolar organic solvents. In contrast, the synthesis of the
chloro derivative {Pd }(CO) Cl (4), attempted by reacting 1
3
2
n
4
and [Bu N]Cl under analogous conditions, was unsuccessful
and gave only complex mixtures of unidentified products. This
failure must be assigned to the instability of an intermediate,
since 4 was successfully prepared in high yield by an alternative
route (vide infra).
t
reactions afford [Pd (μ-PBu ) (CO) (NCCH )]PF , (7)PF
(86%), or [Pd (μ-PBu ) (CO) (Py)]PF , (8)PF (74%),
3
2 3
2
3
6
6
t
3
2
3
2
6
6
Cluster 3 is air stable both in the solid state and in solution,
whereas 2 is air stable only in the solid state and decomposes in
solution after a few days, giving a mixture of unidentified
compounds; both compounds are stable under nitrogen. As
confirmed by a crystallographic study (see below), the clusters
contain six bulky tert-butyl substituents which hinder and
stabilize the central Pd P core, leaving only three reactive
respectively, as dark red solids.
Moreover, by treating a dry THF solution of 3 with TlPF6,
under 1 atm of carbon monoxide, the symmetrical cationic
t
cluster [Pd (μ-PBu ) (CO) ]PF , (5)PF (77%), was obtained
3
2 3
3
6
6
as a red solid. The latter was employed as the precursor of the
previously mentioned cluster 4, which was obtained by adding
an equimolar amount of [(PPh ) N]Cl to a solution of (5)PF
6
3
3
3 2
positions available for the functionalization of the cluster, i.e.,
those occupied by the terminal ligands, which are localized on
the Pd P plane and mutually directed at 120°. Analogous
in dry acetone.
+
Significant IR and NMR parameters for clusters 2−8 are
shown in Table 1. The IR ν absorptions of the neutral
3
3
CO
−1
features were observed in the parent platinum derivatives Pt (μ-
monohalides 2−4 were found at ca. 2030−2040 cm , which, in
3
t
+
PBu ) (CO) X, and make them suitable synthons for the
comparison to the corresponding bands of cation 5 (ν
=
CO
2
3
2
4a,b
−1
synthesis of large molecular frameworks.
2094, 2053 cm ), are shifted as expected for the substitution of
Compound 3 proved to be an excellent precursor for other
trinuclear palladium clusters. The reaction of 3 with the
isocyanide donor CNBu (Scheme 2) leads to the substitution
a π-acceptor carbonyl with a σ-donor halide ligand and for the
resulting charge reduction. Cations 7 and 8 , containing a σ-
+
+
t
donor nitrogen ligand, show ν absorptions at intermediate+
CO
−1
of all the terminal ligands and affords the symmetrical cationic
frequencies (2044−2066 cm ). The isocyanide derivative 6
t
t
−1
cluster [Pd (μ-PBu ) (CNBu ) ]I, (6)I, which was isolated as
shows the ν absorption at 2156 cm , higher than in free
3
2 3
3
CN
t
−1
an orange solid in good yield (87%, Scheme 2). The iodide
anion, which complicates the cyclovoltammetric profile of the
cation (vide infra), was exchanged by treating (6)I with an
excess of TlPF or with a stoichiometric amount of AgCF SO .
CNBu (2136 cm ); similar frequencies were found in other
trinuclear palladium clusters with terminal isocyanide ligands
−
1
( ν C N
=
2 1 7 5 a n d 2 1 4 8 c m
i n [ P d ( μ -
3
t
10
−1
SO ) (CNBu ) (PBz ) ]
and 2138 cm
in [Pd (μ-
3
6
3
3
2
2
2
3
3
t
11
The metathesis reactions afford in quantitative yields (6)PF or
PBu ) (CN-C H -p-Me) ](CF SO ) ]).
6
2 2 6 4 5 3 3 2
(
6
6)CF SO , respectively. The paramagnetic dicationic product
The IR spectra of 6(PF ) show the expected shift of the ν
6 2 CN
absorption (2193 cm , solid state) compared to the
3
3
−
1
(PF ) was isolated in nearly quantitative yield as a dark pink
6
2
solid after addition of a 2-fold excess of AgPF to a dry CH Cl
monocationic 6(I). Identical data were found for the dication
6
2
2
2+
solution of 6(I). Under ambient atmosphere, 6(PF6)2
decomposes in few hours both in the solid state and in
CH Cl solution, whereas it is relatively stable under inert
6
obtained after electrolysis during the IR spectroelec-
trochemical experiments (see below). Due to the para-
31
1
magnetism of 6(PF ) , its P{ H} NMR spectrum does not
2
2
6 2
8
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Inorganic Chemistry
Table 1. Significant IR ν [cm , Solid State (CH Cl Solution)] and NMR δ [ppm] Parameters for Clusters 2−(8)PF
Article
−1
2
2
6
a
ν(CO) in 2−4, (5)PF , (7)PF , and (8)PF ; ν(CN) in (6)I and (6)PF .
6
6
6
6
Table 2. Selected Bond Distances (Å) and Angles (deg) in the Structures of Clusters 2 and (6)CF SO
3
3
a
2
: Pnma
4: Pnma
(6)CF SO : P2 /n
3 3 1
Pd(1)−Pd(1)′
Pd(1)−Pd(2)
P(1)−Pd(1)
P(2)−Pd(1)
P(2)−Pd(2)
Pd(1)−C
C−O
Pd(2)−X
Pd(1)−Pd(2)−Pd(1)′
Pd(2)−Pd(1)−Pd(1)′
Pd(1)−P(1)−Pd(1)′
Pd(1)−P(2)−Pd(2)
P(2)−Pd(2)−X
P(2)−Pd(2)−Pd(1)
Pd(1)−C−O
2.9960(13)
2.9474(10)
2.314(2)
3.000(5)
2.949(6)
2.315(2)
2.305(2)
2.273(10)
1.888(10)
1.109(10)
2.343(10)
61.15(4)
59.43(4)
80.78(6)
80.20(7)
99.1(3)
Pd(1)−Pd(2)
Pd(1)−Pd(3)
Pd(2)−Pd(3)
Pd(1)−P(1)
Pd(1)−P(3)
Pd(1)−C(1)
Pd(2)−C(6)
Pd(3)−C(11)
Pd(2)−Pd(1)−Pd(3)
P(1)−Pd(2)−Pd(1)
Pd(1)−P(1)−Pd(2)
N(3)−C(11)−Pd(3)
C(6)−Pd(2)−P(1)
C(6)−N(2)−C(7)
2.9526(6)
3.0056(6)
2.9683(6)
2.2941(16)
2.2950(16)
1.947(7)
2.298(2)
2.273(2)
1.874(10)
1.124(11)
2.4601(16)
61.10(3)
1.933(6)
1.950(7)
59.752(15)
49.93(4)
59.452(15)
80.69(10)
80.30(7)
80.01(5)
177.5(6)
99.24(6)
100.35(18)
176.1(8)
50.22(6)
50.38(7)
178.4(9)
177.5(9)
a
Data for the structure of 4 are taken from ref 5.
+
Figure 1. ORTEP views of the molecular structure of cluster 2 (left) and of cation 6 (right). Thermal ellipsoids are at 20% probability.
1
show signals, whereas the H NMR spectrum contains only a
very broad signal, due to the tert-butyl protons, at ca. 16 ppm.
The 31P{ H} NMR spectra of the neutral complexes 2−4
and of the cationic derivatives (7)PF and (8)PF contain low-
2.2. Crystal and Molecular Structures. Single crystals of
2 suitable for crystallographic studies were obtained by slow
evaporation from hexane solutions. Single crystals of (6)-
CF SO were obtained by layering n-hexane on a CH Cl
2
1
6
6
3
3
2
field signals assigned to the equivalent nuclei P and to P . The
solution of the cluster.
2
1
symmetrical cationic clusters (5)PF and (6)X [X = I, PF ,
Selected bond distances and angles are reported in Table 2,
and ORTEP projections of the molecular structures are shown
in Figure 1. Cluster 2 belongs to the Pnma space group, and its
6
6
CF SO ] show only a singlet due to the three equivalent P
3
3
−
nuclei. Ionic compounds containing the PF6 anion show also
1
12,13
5
the expected heptet at ca. −140 ppm ( J = ca. 700 Hz).
structure is similar to the one reported for the isotypic chloro
PF
1
13
1
The H NMR and C{ H} NMR spectra show signals with the
expected frequencies and intensities (see the Experimental
Section for more details).
derivative 4. The coordination neighborhood of the palladium
centers is planar, the maximum deviation [P(1)] being 0.19 Å.
The asymmetric unit contains half a molecule with a mirror
8
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Inorganic Chemistry
Article
Table 3. Formal Electrode Potentials (V vs SCE) and Peak-to-Peak Separations (mV) for the Redox Processes Exhibited in
CH Cl Solution by [{Pd }L Xn](
1−n)+
and, for Comparison (in Parentheses), by the Corresponding Platinum Clusters
2
2
3
3−n
{Pt }L Xn](
1−n)+
[
3 3−n
oxidation processes
reduction processes
a
a
complex
E°1
ΔEp
E°2
ΔEp
E°3
b
d
d
d
d
d
d
e
d
d
d
d
e
a
,
c
c,d
4
2
3
0.83 (0.91)
90 (70)
0.41 (0.31)
0.41 (0.29)
0.38 (0.28)
1.14 (1.13)
0.35 (0.26)
0.79
76 (60)
80 (60)
70 (70)
64 (90)
65 (65)
70
−1.84 , (−1.91)
c,d
a
,
c
d
d
0.90 (0.88)
(70)
(−1.91)
a,c
d
d
c,d
0.85 (0.86)
74 (70)
−1.73 (−1.91)
c,d
a
,
c
c d
ac
(
(
(
(
5)PF6
6)PF6
7)PF6
8)PF6
1.75 (1.56 )
−1.27 (−1.29)
e
e
1.14 (0.82)
65 (65)
a
,
c
a
,
,
c
c
1.50
1.54
−1.35
−1.36
a
,
c
a
0.80
80
a
−1
b
c
d
e
Measured at 0.1 V s . Coupled to relatively fast chemical reactions. Peak potential value for irreversible processes. Reference 2b. Unpublished
t
t
results for [Pt (μ-PBu ) (CNBu ) ]PF .
3
2
3
3
6
2
b
plane passing through Br, Pd(2), P(1) and the two carbon
clusters, were observed also in the cyclic voltammograms of
the palladium clusters described here. The former is reversible
in the CV time scale, while the second oxidation is reversible
atoms connected to P(1). The Pd triangle is isosceles with two
3
Pd(1)−Pd(2) distances [2.9474(10) Å] slightly shorter than
the one opposing the bromide ligand [Pd(1)−Pd(1′)
+
only for clusters 3 and 6 and complicated by a subsequent
2
.9960(13) Å]. The P(1) atom, bridging the longer Pd−Pd
chemical reaction for all the others. In the cathodic region, one
irreversible reduction is observed for several compounds. The
formal electrode potentials for the observed electron transfers
are summarized in Table 3, and the CV profiles of 3, 5 , and 6
are shown in Figure 2.
bond, shows Pd−P distances [Pd(1)−P(1) = 2.314(2) Å]
slightly longer than the other ones [Pd(1)−P(2) = 2.298(2) Å
and Pd(2)−P(2) = 2.273(2) Å]. The Pd(2)−Br distance
+
+
[
[
2.4601(16) Å] is almost coincident with the average calculated
2.456 Å] for ca. 180 known terminal bromides of palladium.
14
+
Cation 6 belongs entirely to the asymmetric unit and does
not show any rigorously valid symmetry operation. However, it
locally approaches the 3m symmetry, C3v in the Schonflies
̈
notation, which is not completely satisfied due to slight
rotations of the tert-butyl groups of the isocyanide ligands. The
molecule exhibits a scalene Pd triangular core with two shorter
3
and slightly different Pd(1)−Pd(2) and Pd(2)−Pd(3) bonds
[
2.9525(6) and 2.9686(6) Å, respectively] and one slightly
longer Pd(1)−Pd(3) distance [3.0055(6) Å]. The Pd−P
distances, between 2.293 and 2.299 Å, are similar to those
found in 2. The three isocyanide ligands are coordinated in an
approximately linear fashion (Pd−C−N angles ca. 177°, C−N−
C angles ca. 176°).
The Pd−C(isocyanide) distances [Pd(1)−C(1) = 1.947(6)
Å, Pd(2)−C(6) = 1.936(6) Å, and Pd(3)−C(11) = 1.948(7)
Å] are longer than the Pd−CO ones found in 2 [1.874(10) Å]
but are similar to the corresponding distances in other
trinuclear palladium clusters with terminal isocyanide ligands
t
10
(
i.e., Pd−C ca. 2.0 Å in [Pd (μ-SO ) (CNBu ) (PBz ) ] and
3
2 2
2
3 3
t
Pd−C 1.94−2.06 Å in [Pd (μ-PBu ) (CN−C H -p-Me) ]-
CF SO ) ). As compared to the known structures of cluster
3
2 2
6
4
5
1
1
5
(
3 3 2
4
and of the numerous parent platinum derivatives [Pt (μ-
Figure 2. Cyclic voltammograms recorded at a platinum electrode in
3
+
+
n
t
(1−n)+
1−4
CH Cl solutions of (a) 3, (b) 6 , and (c) 5 . [ Bu N]PF (0.2 mol
PBu ) L Xn]
(n = 0, 1),
the main features of the
2
2
4
6
2
3 3−n
−3
−1
t
dm ) as supporting electrolyte. Scan rates: 0.2 V s .
Pd (μ-PBu ) core remain roughly unchanged, with the Pd, P,
CN (in cation 6 ) virtually on the same plane (maximum
deviation 0.19 Å in 6 [P(2)]). The central Pd triangle is
nearly equilateral with quite long Pd−Pd distances (ca. 3 Å)
well-matched with the M−M bond order (0.66) expected for
mixed valence derivatives of this type. Pd−P, Pd−C, and Pd−
halogen bond distances fall in the range observed for the
corresponding moieties in the literature.
3
2 3
+
+
3
The neutral monohalide clusters 2−4 are oxidized in two
steps at ca. 0.40 and 0.85 V, the first oxidation being fully
15
−1
reversible on the CV time scale (i /i = 1 at 0.2 V s ); the
c
a
second one is reversible for 3 while, for 2 and 4, it is
complicated by a subsequent chemical reaction.
As expected for the presence of the positive charge and for
the substitution of a σ-donor halide with a π-acid carbonyl
ligand, the two oxidations occur at higher potentials (+1.14 and
2.3. Electrochemistry. The electrochemical properties of
the clusters were studied by cyclic voltammetry in CH Cl
solutions containing [ Bu N]PF (0.2 mol dm ) as the
supporting electrolyte.
Two sequential monoelectronic oxidations, typifying the
redox fingerprint of the analogous 44e [{Pt }L3−nXn]
2
2
n
−3
+1.75 V) for the cationic tricarbonyl derivative (5)PF . The
4
6
6
+
substitution of one of the carbonyl ligands in 5 with a good σ-
donor as an acetonitrile or a pyridine molecule facilitates the
−
(1−n)+
+
+
removal of both the first (0.79 for 7 and 0.80 V for 8 ) and the
3
8
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Figure 3. IR spectral changes recorded in an OTTLE cell (a) during and (b) immediately and (c) 30 min after the progressive one electron
n
−3
oxidation of 3 in CH Cl with [ Bu N]PF (0.2 mol dm ) as the supporting electrolyte. A reference spectrum, collected before the application of an
2
2
4
6
oxidation potential, is used to calculate the differential absorbance spectra (a). The final spectrum, giving the differential spectrum represented by the
black line in panel a, is used to calculate the differential absorbance spectra (b and c).
+
+
17,18
second electron (1.50 for 7 and 1.54 V for 8 ). Again, for
complexes has been observed previously
and has been
+
+
+
17a
either 5 , 7 , or 8 , the first oxidation is reversible on the CV
time scale (i /i = 1 at 0.2 V s ) and the second oxidation is
followed by a fast chemical reaction. Moreover, cations 7 and
slowly decompose in CH Cl solution, and, on standing,
redox processes attributable to decomposition products
become evident in the CV profile. Finally the cationic cluster
6)PF , with three good σ-donor and relatively poor π-acid
assigned to the higher softness of platinum. In some cases a
broad agreement has been found between the experimental
peak potential differences and variations of the calculated
energies of the HOMO and LUMO orbitals, both of which
−1
c
a
+
+
8
2 2
17b
were found to increase when exchanging Pd with Pt.
Contrary to our clusters, and despite the lower average Pd
oxidation state (Pd32+ instead of Pd3 ), the tris-dppm bridged
4+
(
6
2+
alkyl-isocyanide ligands, and its oxidation products distinguish
themselves for their remarkable stability.
trinuclear dication [Pd (μ -dppm) (CO)] (dppm = bis-
3 2 3
(diphenylphosphino)methane) gives stable species upon
reduction and decomposes upon oxidation. In fact, its CV
profile exhibits monoelectronic reduction processes at −0.21,
−0.47, and −2.35 V (reversible) and at −2.69 V (irreversible)
in THF and two irreversible 2-electron oxidations at +0.95
and +1.15 V in CH CN. The instability of the oxidized
In spite of the positive charge and compared to all the
clusters analyzed in this study, the removal of the first electron
occurs at the lowest potential (+0.35 V). The potential of the
second oxidation (+1.14 V) is lower than those of the other
cations but is higher in comparison to those of the neutral
derivatives 2−4. Both oxidation processes possess features of
chemical reversibility in the CV time scale. (6)I behaves as
19
19
3
species in these cases is reasonably due to an unbearable
concentration of positive charge.
(
6)PF , showing two reversible oxidations in the CV time scale,
although the first process is superimposed to the oxidation of
6
2.4. Spectroelectrochemistry. 2.4.1. Cluster 3. Even
though the first monoelectronic oxidation of 3 is reversible in+
the CV time scale, the lability of the electrogenerated species 3
becomes evident in the longer times of the macroelectrolysis
experiments (Ew = +0.5 V). In fact, during the exhaustive
electrolysis, the CV of the solution shows that the accumulation
−
I .
+
It is worth noting that only for cluster 3 and cation 6 both
oxidation processes are reversible in the CV time scale and,
+
furthermore, 6 exhibits the largest ΔE° gap (E° − E° = 0.79
1
2
V). This value points to a large thermodynamic stability for the
+
of the oxidized species 3 is accompanied by a decrease of the
2
+
mono-oxidized species 6 , as indicated by the large
total concentration of the 3/3+ couple, while new peaks
1
3
16
comproportionation constant K (ca. 10 , eqs 1, 2) and
experimentally confirmed by the above-mentioned isolation of
the thermally stable 43e species (6)(PF ) .
c
become evident: a reversible oxidation at 1.14 V, two reversible
reductions at −0.27 and −0.52 V, and three irreversible
reductions at −0.87, −1.16, and −1.27 V. The UV−vis and IR
spectroelectrochemical changes following the oxidation of 3 in
correspondence of the first oxidation process show the
presence of well-defined isosbestic points for the time required
for the quasi-complete oxidation of 3, suggesting the initial
−
6
2
−
−
+
e
+e
63+
2+
+
Xoooooooooo oo Y 6 XooooooooooooY 6
−
−
−
e
−e
E° ′=0.35 V
E° ′=1.14 V
(1)
(2)
1
2
2
+ 2
+
formation of a metastable cation 3 that is then consumed by a
[
6 ]
= eFΔE°/RT = 2.26 × 1013
Kc =
3+
+
subsequent reaction. As illustrated in Figure 3a, the CO
stretching absorption exhibited by 3 at 2049 cm− vanishes
rapidly upon oxidation while a new absorption, assigned to the
[
6 ][6 ]
1
Most of the half-wave potentials shown in Table 3 are shifted
anodically in comparison with the corresponding potentials of
their platinum analogues; thus the latter are easier to oxidize
−
+
−1
43e species 3 , grows at 2089 cm .
This band is then slowly replaced (Figure 3b) by a new
absorption at 2079 cm , that can be unambiguously assigned
to the 44 e tricarbonyl cation 5 (by comparison of its IR, UV,
and P NMR signals with those of an authentic sample and by
the above-mentioned CV peaks at +1.14 and −1.27 V observed
after electrolysis), and by a transient absorption at 2097 cm
(Figure 3b,c), that we tentatively assign to the 42e cluster
−1
and harder to reduce. The shift is generally significant (E° (Pd)
n
−
+
−
E° (Pt) = 70−190 mV) and in one case quite large (320 mV
n
+
31
for E° of cation 6 ), although, occasionally, also very small
1
(
10−20 mV) or even reversed shifts (−10 and −80 mV for E°1
−1
of clusters 3 and 4, respectively) were observed. A similar trend
−
in the redox potentials of homologous series of Pt and Pd
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t
+
+
+
[
Pd (μ-PBu ) (CO)I ] , 9 . As highlighted in Scheme 3, 2
643 nm, assigned to 3 , keep growing. Their intensity increases
until cluster 3 has nearly disappeared at the end of the current
flow in the cell. The absorbance changes observed after this
3
2 3
2
+
equiv of the metastable oxidized species 3 could produce a 1:1
Scheme 3. Possible Pathway to the Mixture of Cations 5+
+
step confirm the decay of 3 : the three absorptions at 555, 592,
+
and 9
and 643 nm are replaced by two bands at 441 and 635 nm, the+
former of which is consistent with the formation of cluster 5
while the second may be assigned to unidentified decom-
position compounds. The pathway outlined in Scheme 3 is also
suggested by some analogies and differences that have been
found in the behavior of complex 3 and of its platinum
t
20
analogue, Pt (μ-PBu ) (CO) I, 10, which may be reversibly
3
2 3
2
oxidized (chemically or electrochemically) to its corresponding
−
+
4
3e monocation 10 .
Although, contrary to 3 , this species is thermally stable, in
+
−
−
the presence of an excess of I it undergoes CO/I scrambling
and electron transfer to afford, initially, a 1:1 mixture of [Pt (μ-
3
t
+
−
+
PBu ) (CO) ] , the Pt equivalent of the 44e derivative 5 ,
2
3
3
and of the first tris-phosphido-bridged triangular cluster of
−
platinum stable with 42 instead of 44e , namely, Pt (μ-
3
t
PBu ) I , which has been isolated as a stable crystalline solid
2
3 3
−
and fully characterized. In the presence of I , which reacts with
t
+
[
Pt (μ-PBu ) (CO) ] to regenerate cluster 10, and of the
3 2 3 3
oxidant, the reaction continues until complete conversion of
t
t
20
+
+
Pt (μ-PBu ) (CO) I into Pt (μ-PBu ) I .
The results described here suggest that any 42e Pd species,
mixture of 5 and 9 , but the latter does not accumulate due to
3 2 3 2 3 2 3 3
−
its rapid decomposition. According to this picture, the small
upfield shift of 8−10 cm per removed electron, observed for
the value of ν in the series 5 (44e ) → 3 (43 e ) → 9 (42
3
t
−1
including the hypothetical cluster Pd (μ-PBu ) I which could
3
2 3 3
+
−
+
−
+
−
+
simply be formed by the reaction of 9 with I , would not be
easily isolable.
CO
−
e ), may be assigned to the substitution of a π-acceptor
As expected, by performing the IR spectroelectrochemical
carbonyl with a σ-donor iodide in each step (which,
furthermore, leaves unchanged the total charge in spite of the
oxidation). This process nearly counterbalances the reduction
of π-basicity of the metal centers caused by the removal of
electrons. Unfortunately, the full characterization of 9 was
prevented by its fast decomposition (Figure 3c), which
proceeds by forming, among other products, a further amount
of 5 . The latter is the only carbonyl species that was detected
in solution after exhaustive electrolysis, when the IR spectrum
shows a unique carbonyl absorption at 2079 cm . The P{ H}
NMR spectrum of this solution contains an intense singlet at
n
analysis of 3 in the presence of an excess of [ Bu N]I, which
4
converts back rapidly 5+ into cluster 3, we observed the
appearance of only the transient absorption assigned to cation
+
+
9
and, eventually, complete decomposition to a complex
mixture of noncarbonyl derivatives. Moreover, after an
exhaustive electrolysis, the CV of the solution shows two
weak waves for reversible reductions in the cathodic region
+
21
(−0.27 and −0.88 V), that we may tentatively assign to the
−1
31
1
+
unstable cation 9 . We recall that the redox potentials for the
t
+
+
related reductions of [Pt
(μ-PBu ) (CO)I ] , 11 , the elusive
3 2 3 2
+
+
2
95.6 ppm, due to 5 (Table 1), together with several weak
platinum analogue of cation 9 , were estimated to be +0.06
+/0
0/−1
20
singlets for unidentified noncarbonyl derivatives in the region
between 0 and 200 ppm. The UV−vis spectroelectrochemistry
Figure 4) agrees with this picture: the broad absorption at 464
(11 ) and −0.47 (11 ) V.
+
2.4.2. Cation 5 . IR and UV−vis in situ spectroelectrochem-
ical experiments on CH Cl solutions of 5+ allowed the
(
2
2
nm observed in the original sample of 3 decreases during
electrolysis at+0.5 V, while three new bands at 555, 592, and
characterization of the product of its monoelectronic oxidation
2+
+
−1
5 . Upon oxidation, the ν absorption of 5 at 2079 cm is
CO
n
−3
Figure 4. UV−vis spectra of 3 in CH Cl solution containing [ Bu N]PF (0.2 mol dm ) as the supporting electrolyte recorded in an OTTLE cell
2
2
4
6
(
a) during and (b) after one electron oxidation.
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gradually replaced by a new band at 2115 cm−1 (Figure 5). On
the time scale of the IR experiment, however, the oxidation is
421 nm band due to 6 is accompanied by the growth of an
+
absorption at 524 nm together with a weak band at 690 nm.
3
. CONCLUSIONS
After this work a new class of palladium triangular clusters with
three bridging phosphides, that was practically unknown before,
becomes available to the inorganic chemistry community.
Although, as expected, these clusters are somewhat less stable
than their well-known platinum analogues, they can be
prepared in high yield and purity and can be stored for further
studies. The presence of easily displaceable terminal ligands as
acetonitrile, pyridine, or even the halides, is expected to allow
many different types of functionalization of the relatively stable
+
{
Pd } core. Moreover, cationic [{Pd }(L) ] systems have
3
3
3
three identical ligands lying at 120° on the molecular plane, and
in neutral {Pd }(L) X derivatives the reactivity of the L and X
3
2
ligands is substantially different. All these features make these
systems well-suited to be employed as branching points or as
end-caps in polycluster macromolecular structures in which the
cluster-to-cluster connection can be effected, for example, with
Figure 5. IR spectral changes recorded in an OTTLE cell during the
+
progressive one electron oxidation of 5 in CH Cl2 solution;
2
n
−3
[
Bu N]PF (0.2 mol dm ) as the supporting electrolyte. A reference
4 6
spectrum, collected before the application of an oxidation potential, is
used to calculate the differential absorbance spectra.
4
,4′-dipyridyl or bis-isocyanide ligands. The reversibility of the
first monoelectronic oxidation process and the remarkable
stability of the resulting paramagnetic 43e species, particularly
−
followed by a partial decomposition that did not allow the
complete recovery of the starting compound in the backward
high in the isocyanide clusters, may allow the construction of
ordered and stable polyradical frameworks, in which the spin−
spin intercluster interactions may be triggered by modifying the
nature of the spacer.
2+
+
reduction of 5 . The removal of one electron from 5 produces
a markedly different pattern of the absorption bands in the
visible region of the electronic spectrum (Figure 6). The 441
nm band of the starting cluster is substituted, during the course
of the spectroelectrochemical oxidation, by three new
absorptions at 521, 555, and 710 nm.
4
. EXPERIMENTAL SECTION
4.1. General Data. The reactions were carried out under a
nitrogen atmosphere, using standard Schlenk techniques. [Pd-
t
t
9
22
(
PBu H)(μ-PBu )] (1) and decamethylferrocene were prepared
2 2 2
n
n
according to the literature. [ Bu N]Br, [ Bu N]I, AgBF , Ag[CF SO ],
4
4
4
3
3
t
[
(PPh ) N]Cl, CNBu , purchased from Sigma Aldrich, and TlPF ,
3
2
6
purchased from Apollo Scientific, were used as received. Solvents were
dried by refluxing over the appropriate drying agent [sodium/
benzophenone (toluene, thf, Et O, n-pentane, n-hexane); CaH
2
2
(
CH CN, pyridine); K CO (acetone)] and distilled under nitrogen
3 2 3
prior to use. Deuterated solvents were purchased from Cambridge
Isotope Laboratories and were used without further purification but
were deoxygenated by freeze−pump−thaw cycles and stored over 4 Å
molecular sieves under an inert atmosphere. IR spectra were recorded
on a Perkin-Elmer FT-IR 1725X or a Spectrum 100 FT-IT
spectrophotometer. NMR spectra were recorded on a Varian Gemini
2
00 BB instrument; frequencies are referenced to the residual
1
13
resonances of the deuterated solvent ( H, C) or 85% H PO
+
3
4
Figure 6. UV−vis spectra of 5 in CH Cl2 solution containing
31
2
(
P). UV−vis spectra were recorded on a Perkin-Elmer Lambda
n
−3
[
Bu N]PF (0.2 mol dm ) as the supporting electrolyte recorded in
4 6
EZ201 spectrophotometer. Molecular hydrogen evolved during the
reactions was detected by gas chromatographic analysis performed
with a DANI 3200 instrument equipped with a D-SM 5A column.
an OTTLE cell during one electron oxidation.
4
.2. Electrochemistry and Spectroelectrochemistry. Electro-
+
2
.4.3. Cation 6 . The IR spectroelectrochemical changes
chemical measurements were recorded on a Princeton Applied
Research (PAR) 273A potentiostat/galvanostat and were performed
in dichloromethane solutions containing [ Bu N]PF (0.2 mol dm )
as the supporting electrolyte. HPLC grade dichloromethane (Sigma-
Aldrich) was stored under argon over 3 Å molecular sieves.
following the stepwise two-electron oxidation of cation (6)PF6
Figure 7) show the appearance of well-defined and with-
standing isosbestic points and confirm a remarkable stability of
the oxidized clusters 6 and 6 . The ν absorptions exhibit a
(
n
−3
4
6
2
+
3+
CN
−
1
n
linear upfield shift of 24 cm per removed electron: the
Electrochemical grade [ Bu
4
N]PF
6
was purchased from Fluka and
−1
+
used without further purification. Cyclic voltammetry was performed
in a three-electrode cell, having a platinum reference electrode, a
platinum-spiral counter electrode, and a platinum-disk working
electrode, and containing a 5 × 10 M analyte solution. After a
sufficient number of voltammograms were recorded, a small amount of
decamethylferrocene was added to the solution and a further
voltammogram was recorded. Potential values were determined by
placing the redox couple decamethylferrocenium/decamethylferrocene
original absorption found at 2164 cm in 6 moves to 2188
cm upon one electron oxidation, and to 2212 cm−1 after
−1
removal of the second electron.
Quantitative restoration of the IR band of the starting 6 was
observed in the backward reduction step. The stepwise
oxidation of 6 in a UV−vis spectroelectrochemical experiment
is shown in Figure 8. Only the removal of the first electron
−4
+
+
gives rise to evident spectral changes: the disappearance of the
[Eredox calculated as (Epc + E )/2] at −0.16 V vs SCE. Controlled
pa
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+
Figure 7. IR spectral changes recorded in an OTTLE cell during the first (a) and the second (b) monoelectronic oxidation of 6 in CH Cl solution,
2
2
n
−3
with [ Bu N]PF (0.2 mol dm ) as the supporting electrolyte. A reference spectrum, collected before the application of an oxidation potential, was
4
6
used to calculate the differential absorbance spectra (a). The final spectrum, giving the differential spectrum represented by the black line in panel a,
is used to calculate the differential absorbance spectra (b).
+
n
−3
Figure 8. UV−vis spectra of 6 in CH Cl solution containing [ Bu N]PF (0.2 mol dm ) as the supporting electrolyte recorded in an OTTLE cell
2
2
4
6
during one electron oxidation.
−
1
potential coulometry was performed in an H-shaped cell with anodic
and cathodic compartments separated by a sintered-glass disk. The
working macroelectrode was a platinum gauze; a platinum-spiral was
used as the counter electrode.
P). IR (solid state): 2040 (ν
) cm . Elemental analysis calcd (%)
CO
for C H O P Pd Br: C 35.1, H 6.11. Found: C 34.9, H 6.13.
In a separate experiment, a solution of KBr (18 mg; 0.151 mmol) in
H O (1 mL) was added to a suspension of complex 1 (124 mg, 0.156
26
54
2
3
3
2
UV−vis and infrared (IR) spectroelectrochemical measurements
were carried out using an optically transparent thin-layer electro-
chemical (OTTLE) cell equipped with CaF2 windows, platinum
minigrid working and auxiliary electrodes, and silver wire pseudor-
mmol) in toluene (10 mL) under 1 atm of CO. After stirring for 3
days at 100 °C the color of the solution turned red, while H was
2
evolved (GC). At the end of the reaction the aqueous phase turned
basic and the 31P{ H} NMR spectrum of the toluene solution showed
1
23
eference electrode. Controlled-potential electrolyses were carried out
with a BAS CV-27 electrochemical analyzer. Argon-saturated CH Cl
the presence of free PBu H and 2 in ca. 3:1 ratio as the predominant
2
products. After workup according to the precedent procedure, 2 was
2
2
−3
−2
solutions (10 M or 10 M for UV−vis or IR analysis, respectively)
of the compound under study, containing [ Bu N]PF 0.2 M as the
isolated as a red solid (56 mg; 0.063 mmol, 60% yield).
n
t
n
4.4. Synthesis of Pd (μ-PBu ) (CO) I (3). [ Bu N]I (51 mg,
4
6
3 2 3 2 4
supporting electrolyte, were used. The in situ spectroelectrochemical
experiments have been performed by collecting spectra of the
compound under investigation during the stepwise oxidation obtained
by increasing the initial working potential by ΔE steps of 25 mV (Δt =
0.139 mmol) and H O (0.5 mL) were added to a suspension of
2
complex 1 (166 mg, 0.208 mmol) in toluene (15 mL); the flask was
filled with CO (1 atm), and the reaction mixture was stirred for 3 days
at 100 °C. The solid residue was filtered off, and the remaining red
solution was evaporated. The residue was purified by column
chromatography on neutral alumina (hexane−acetone 20:1). Yield:
1
or 2 min for IR or UV−vis analysis, respectively).
t
n
4
.3. Synthesis of Pd (μ-PBu ) (CO) Br (2). [ Bu N]Br (39 mg,
3 2 3 2 4
1
0
.12 mmol) and H O (0.5 mL) were added to a suspension of
85% (110 mg, 0.12 mmol) of red solid. H NMR (200 MHz, C D ,
2
6
6
3
5
complex 1 (145 mg, 0.18 mmol) in toluene (10 mL). The flask was
then filled with CO (1 atm), and the reaction mixture was stirred for 3
days at 100 °C. The solid residue was filtered off, and the remaining
red solution was evaporated. The residue was purified by column
293 K): δ = 1.50 (vt, J(H,P) + J(H,P) = 7.0 Hz, CCH , 36 H), 1.13
ppm (d, J(H,P) = 14.5 Hz, CCH , 18 H). C{ H} NMR (50.3 MHz,
3
3
13
1
3
C D , 293 K): δ = 188.4 (s, CO), 41.1, 39.1 (s, PC−CH ), 34.2, 33.3
6
6
3
31
1
ppm (s, PC−CH ). P{ H} NMR (81.0 MHz, C D , 293 K): δ =
292.5 (d, J(P,P) = 116 Hz, 2 P), 213.4 ppm (t, J(P,P) = 116 Hz, 1
P). IR (CH Cl ): 2049 (ν
cm . Elemental analysis calcd (%) for C H O P Pd I: C 33.3, H
3
6
6
2
2
chromatography on neutral alumina (hexane−acetone 20:1) yielding
1
−1
6
7 mg (0.076 mmol, 63% yield) of 2 as red solid. H NMR (200 MHz,
) cm . IR (solid state): 2034 (ν
)
2
2
CO
CO
3
5
−1
C D , 293 K): δ (ppm) = 1.47 (vt, J(H,P) + J(H,P) = 7.1 Hz, CCH ,
6
6
3
26 54 2 3 3
3
13
1
3
6 H), 1.13 (d, J(H,P) = 14.6 Hz, CCH , 18 H). C{ H} NMR (50.3
5.80. Found: C 33.1, H 5.85.
3
MHz, C D , 293 K): δ = 188.6 (s, CO); 40.8, 38.9 (s, PC−CH ), 33.3,
In a separate experiment, a solution of KI (18 mg; 0.151 mmol) in
6
6
3
31
1
2
2
9.9 ppm (s, PC−CH ). P{ H} NMR (81.0 MHz, C D , 293 K): δ =
H O (1 mL) was added to a suspension of complex 1 (156 mg, 0.196
3
6
6
2
2
2
82.7 (d, J(P,P) = 116 Hz, 2 P), 206.4 ppm (t, J(P,P) = 116 Hz, 1
mmol) in toluene (10 mL) under 1 atm of CO. After stirring for 3
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1
days at 100 °C the color of the solution turned red, while H was
CCH , 18 H). 13C{ H} NMR (50.3 MHz, acetone-d , 293 K): δ =
2
3
6
evolved (GC). At the end of the reaction the aqueous phase turned
185.2 (s, CO), 124.3 (s, NCCH ), 41.7, 40.6 (s, PC−CH ), 32.8, 32.3
31 1
3
3
basic and the 31P{ H} NMR spectrum of the toluene solution showed
1
(s, PC−CH ), 2.6 ppm (s, NCCH ). P{ H} NMR (81.0 MHz,
3
3
t
2
the presence of free PBu H and 3 in ca. 3:1 ratio as the predominant
acetone-d , 293 K): δ = 275.8 (d, J(P,P) = 128 Hz, 2 P), 245.4 (t,
2
6
2
1
products. After workup according to the precedent procedure, 3 was
J(P,P) = 128 Hz, 1 P), −137.1 ppm (hept, J(P,F) = 697 Hz, PF , 1
P). IR (solid state): 2058, 2044 (ν
6
−1
isolated as a red solid (102 mg, 0.109 mmol, 83% yield).
) cm . Elemental analysis calcd
CO
t
4
.5. Synthesis of [Pd (μ-PBu ) (CO) ]PF , (5)PF . TlPF (67
(%) for C H NF O P Pd : C 33.7, N 1.41, H 5.76. Found: C 33.9, N
3
2 3
3
6
6
6
28 57 6 2 4 3
mg, 0.19 mmol) was added to a solution of 3 (90 mg, 0.096 mmol) in
5 mL of dry THF. The red solution was stirred overnight under 1
1.39, H 5.78.
4.11. Preparation of [Pd (μ-PBu ) (CO) (NC H )]PF , (8)PF .
An excess of TlPF (32 mg, 0.094 mmol) was added to a red solution
of 3 (44 mg, 0.047 mmol) in pyridine (3 mL) and the mixture was
stirred for 3 days at room temperature. After this period the solvent
was evaporated. The crude residue was washed with hexane and
t
2
3
2 3
2
5
5
6
6
atm of carbon monoxide. TlI was filtered off, and the solvent was
6
evaporated. The crude residue was washed with hexane and vacuum-
dried. 73 mg of (5)PF (0.074 mmol) was obtained as a reddish solid,
6
1
yield 77%. H NMR (200 MHz, acetone-d , 293 K): δ = 1.42 ppm (vt,
J(H,P) + J(H,P) = 7.5 Hz, CCH , 54 H). C{ H} NMR (50.3 MHz,
6
3
5
13
1
3
dissolved in acetone, and TlI was filtered off. Complex (8)PF was
6
acetone-d , 293 K): δ = 185.8 (s, CO), 42.4 (s, PC−CH ), 33.5 ppm
obtained as a dark red solid (36 mg, 0.035 mmol, yield 74%) after
evaporation of the solvent under vacuum. 1H NMR (200 MHz,
acetone-d , 293 K): δ = 8.21 (m, NC H , 2 H), 7.87 (m, NC H , 1 H),
6
3
31
1
(
s, PC−CH ). P{ H} NMR (81.0 MHz, acetone-d , 293 K): δ =
3
6
1
2
95.6 (s, 3 P), −142.2 ppm (hept, J(P,F) = 708 Hz, PF , 1 P). IR
CH Cl ): 2079 (ν
6
6
5
5
5
5
−1
3
(
) cm . IR (solid state): 2094, 2053 (ν
)
7.63 (m, NC H , 2 H), 1.41 (d, J(H,P) = 15.0 Hz, CCH , 18 H), 1.29
2
2
CO
CO
5
5
3
−
1
3
5
13
1
cm . Elemental analysis calcd (%) for C H F O P Pd : C 33.0, H
ppm (vt, J(H,P) + J(H,P) = 7.4 Hz, CCH , 36 H). C{ H} NMR
27
54
6
3
4
3
3
5
.53. Found: C 32.2, H 5.49.
(50.3 MHz, acetone-d , 293 K): δ = 186.2 (s, CO), 156.0 (s, NC H , 2
6
5
5
t
4
.6. Synthesis of Pd (μ-PBu ) (CO) Cl (4). [(PPh ) N]Cl (40
C), 140.2 (s, NC H , 1 C), 127.6 (s, NC H , 2 C), 41.5, 41.3 (s, PC−
3
2 3
2
3
2
5
5
5
5
31 1
mg, 0.070 mmol) was added to a red solution of (5)PF (69 mg, 0.070
CH ), 33.8, 33.4 ppm (s, PC−CH ). P{ H} NMR (81.0 MHz,
acetone-d , 293 K): δ = 258.9 (d, J(P,P) = 121 Hz, 2 P), 250.8 (t,
J(P,P) = 121 Hz, 1 P), −137.1 ppm (hept, J(P,F) = 702 Hz, PF , 1
P). IR (solid state): 2066 (ν
6
3
3
2
mmol) in 5 mL of dry acetone, and the mixture was stirred for 1 h at
room temperature. After this period, the solvent was evaporated and
the residue was dissolved in 5 mL of n-pentane. A colorless solid was
6
2
1
6
−
1
) cm . Elemental analysis calcd (%)
CO
filtered off, and 4 was collected as a red solid after solvent evaporation
for C H NF O P Pd : C 36.0, N 1.35, H 5.75. Found: C 35.7, N
31 59 6 2 4 3
1
(
46 mg, 0.054 mmol, yield 77%). H NMR (200 MHz, C D , 293 K):
1.36, H 5.73.
4.12. Synthesis of [Pd (μ-PBu ) (CNBu ) ](PF ) , 6(PF ) .
6
6
3
5
t
t
δ = 1.46 (vt, J(H,P) + J(H,P) = 7.1 Hz, CCH , 36 H), 1.12 ppm (d,
3
3
2 3
3
6 2
6 2
3
13
1
J(H,P) = 14.6 Hz, CCH , 18 H). C{ H} NMR (50.3 MHz, C D ,
AgPF (13.4 mg, 0.053 mmol) was added to a solution of 6(I) (30
3
6
6
6
2
93 K): δ = 188.4 (s, CO), 40.6, 38.9 (s, PC−CH ), 33.3, 32.9 ppm (s,
mg, 0.026 mmol) in 3 mL of CH Cl . The orange solution turned
3
2
2
31
1
0
PC−CH ). P{ H} NMR (81.0 MHz, C D , 293 K): δ = 277.4 (d,
immediately to dark pink, and a dark solid (Ag and AgI) precipitated
out. The precipitate was filtered off, and the solvent was evaporated
under vacuum. The crude residue was then washed with diethyl ether
3
6
6
2
2
J(P,P) = 115 Hz, 2 P), 204.8 ppm (t, J(P,P) = 115 Hz, 1 P). IR
−1
(
solid state): 2038 (ν
) cm . Elemental analysis calcd (%) for
CO
C H O P Pd Cl: C 36.9, H 6.43. Found: C 37.2, H 6.39.
(3 × 2 mL). 6(PF
mmol, yield 92%) after solvent evaporation. H NMR (200 MHz,
acetone-d , 293 K): δ = 16.00 ppm (bs, PCCH , 54 H). IR (CH Cl ):
6 2
) was obtained as a dark pink solid (31 mg, 0.024
2
6
4
54
2
3
3
t
t
t
1
.7. Synthesis of [Pd (μ-PBu ) (CNBu ) ]I, (6)I. CNBu (32 μL,
3 2 3 3
0
1
.288 mmol) and complex 3 (90 mg, 0.096 mmol) were dissolved in
0 mL of toluene. Immediately an orange solid precipitated out. The
6
3
2
2
−
1
−1
2188 (νCN) cm . IR (solid state): 2193 (νCN) cm .
mixture was stirred for a further 1 h, and the orange solid was filtered,
4.13. X-ray Diffraction Studies. The X-ray diffraction experi-
ments were carried out at room temperature (T = 293 K) by means of
a Bruker P4 diffractometer for 2 and a Bruker Smart Breeze CCD
diffractometer for 6(CF SO ). Both instruments operate with
washed with toluene (3 × 5 mL), and vacuum-dried (94 mg, 0.083
1
mmol, yield 87%). H NMR (200 MHz, acetone-d , 293 K): δ = 1.32
6
(
vt, 3J(H,P) + 5J(H,P) = 7.0 Hz, PCCH , 54 H), 1.72 ppm (s,
3
3
3
13
1
CNCCH , 27 H). C{ H} NMR (50.3 MHz, acetone-d , 293 K): δ =
graphite-monochromated Mo Kα radiation. The samples were glued
at the end of glass capillaries, and the intensity data collections were
carried out until 2θ maximum of about 53°. The intensities were
corrected for Lorentz and polarization effects and for absorption by
3
6
1
37.4 (s, CN), 59.9 (s, NC−CH ), 40.0 (s, PC−CH ), 34.0 (s, PC−
3
3
31 1
CH ), 30.5 ppm (s, NC−CH ). P{ H} NMR (81.0 MHz, acetone-
3
3
−
1
d , 293 K): δ = 257.2 (s, 3 P). IR (CH Cl ): 2164 (ν
) cm . IR
6
2
2
CN
−1
24
(
solid state): 2156 (ν
) cm . Elemental analysis calcd (%) for
means of semiempirical ψ-scan method for the first sample and
CN
2
5
C H N P Pd I: C 41.4, N 3,71, H 7.22. Found: C 41.2, N 3.69, H
multiscan method for the second.
The unit cell parameters and diffraction symmetry suggested that
39
81
3
3
3
7
.25.
t
t
t
5
4
.8. Synthesis of [Pd (μ-PBu ) (CNBu ) ]PF , (6)PF . TlPF (31
the crystal structures of 2 and the one of Pd (μ-PBu ) (CO) Cl were
3
2 3
3
6
6
6
3 2 3 2
mg, 0.088 mmol) was added to a solution of (6)I (50 mg, 0.044
isotypic. Thus the refinement was started from the coordinates of the
heavy atoms found in the latter. The hydrogen atoms were placed in
calculated positions and were left to “ride” on the connected carbon
atoms. The more relevant reliability factors obtained at the end of the
refinement are listed in Table 4. The structure solution of 6(CF SO )
was obtained by the direct methods contained in SHELXS97. The
slightly inconsistent geometry and the abnormal thermal parameters
denounced the presence of a significant disorder in the anionic portion
of the structure. The anion was refined as a rigid group placed in two
partially superimposed limit positions, with the total occupancy fixed
to 1.0. The excessive elongation of thermal ellipsoids of some carbon
atoms of the tert-butyl groups of the cation suggested that they also
were disordered. The two tert-butyl groups with the more anisotropic
thermal ellipsoids in the final stages of the refinement were then
introduced in the model, split in two limit positions. Some soft
restraints had to be introduced in the refinement in order to limit the
anisotropy of displacement parameters.
mmol) in CH Cl /THF 1:1 (3 mL), and the reaction mixture was
2
2
stirred for 24 h at 40 °C. After this period, the solvent was evaporated
under vacuum. The crude residue was then dissolved in CH Cl , and
2
2
TlI was filtered off. (6)PF was obtained as an orange solid (48 mg,
6
3
3
2
6
0
.042 mmol, yield 95%) after solvent evaporation.
t
t
4
.9. Synthesis of [Pd (μ-PBu ) (CNBu ) ]CF SO , (6)CF SO . A
3 2 3 3 3 3 3 3
stoichiometric amount of AgCF SO (14 mg, 0.053 mmol) was added
3
3
to a CH Cl2 (3 mL) solution of (6)I (60 mg, 0.053 mmol).
2
Immediately AgI precipitated out. (6)CF SO was obtained as orange
3
3
solid (57 mg, 0.049 mmol, 92% yield), after removal of the salt by
filtration and solvent evaporation.
t
4
.10. Synthesis of [Pd (μ-PBu ) (CO) (NCCH )]PF , (7)PF .
3
2 3
2
3
6
6
TlPF (52 mg, 0.149 mmol) was added to a solution of 3 (70 mg,
6
0
.075 mmol) in dry acetonitrile (3 mL); the mixture was stirred
overnight at room temperature. TlI was filtered off, and the solvent
was evaporated. The crude residue was washed with hexane and
diethyl ether and vacuum-dried. Complex (7)PF was obtained as a
Subsequent cycles of refinement were made with anisotropic
thermal parameters for the heavy atoms not involved in the disorder
and led to a nearly equal occupancy of the two limit positions of the
anion. The final reliability factors of the refinement are listed in Table
6
1
dark red solid (64 mg, 0.064 mmol, yield 86%). H NMR (200 MHz,
3
acetone-d , 293 K): δ = 2.90 (s, NCCH , 3 H), 1.40 (vt, J(H,P) +
6
3
5
3
J(H,P) = 7.4 Hz, CCH , 36 H), 1.38 ppm (d, J(H,P) = 15.1 Hz,
3
8
767
dx.doi.org/10.1021/ic4009448 | Inorg. Chem. 2013, 52, 8759−8769

Inorganic Chemistry
Article
Pasquali, M.; Albinati, A. Inorg. Chem. 1996, 35, 6045−6052.
Table 4. Experimental Data for the X-ray Diffraction Studies
t
(
d) Fabrizi de Biani, F.; Manca, G.; Marchetti, L.; Leoni, P.;
of Pd (PBu ) (CO) Br (2) and
3
2 3
2
t
t
Bruzzone, S.; Guidotti, C.; Atrei, A.; Albinati, A.; Rizzato, S. Inorg.
Chem. 2009, 48, 10126−10137.
(3) (a) Fabrizi de Biani, F.; Ienco, A.; Laschi, F.; Leoni, P.; Marchetti,
F.; Marchetti, L.; Mealli, C.; Zanello, P. J. Am. Chem. Soc. 2005, 127,
[
Pd (PBu ) (CNBu ) ](CF SO ), 6(CF SO )
3 2 3 3 3 3 3 3
2
6(CF SO )
3
3
empirical formula
C H BrO P Pd
C H F N O P SPd
40 81 3 3 3 3 3
2
6
52
2
3
3
3
076−3089. (b) Leoni, P.; Marchetti, F.; Marchetti, L.; Pasquali, M.;
Quaglierini, S. Angew. Chem., Int. Ed. 2001, 40, 3617−3618.
4) (a) Albinati, A.; Leoni, P.; Marchetti, L.; Rizzato, S. Angew. Chem.,
formula weight
888.70
1153.25
crystal system
space group
a/Å
orthorhombic
Pnma (No. 62)
18.084(2)
monoclinic
(
P2 /n (No. 14)
1
Int. Ed. 2003, 42, 5990−5993. (b) Leoni, P.; Marchetti, F.; Marchetti,
L.; Pasquali, M. Chem. Commun. 2003, 2372−2373. (c) Albinati, A.;
Balzano, F.; Fabrizi de Biani, F.; Leoni, P.; Manca, G.; Marchetti, L.;
Rizzato, S.; Uccello-Barretta, G.; Zanello, P. Inorg. Chem. 2010, 49,
3714−3720.
9.7168(6)
19.8254(12)
28.9139(17)
92.257(2)
5565.6(6)
4
b/Å
17.808(2)
c/Å
11.8374(14)
β/deg
U/Å3
3812.1(8)
4
(5) Arif, A. M.; Heaton, D. E.; Jones, R. A.; Nunn, C. M. Inorg. Chem.
1987, 26, 4228−4231.
Z
−
3
Dcalc/Mg·m
μ/mm
1.548
1.376
(6) Dyer, P. W.; Fawcett, J.; Hanton, M. J.; Mingos, D. M. P.;
Williamson, A.-M. Dalton Trans. 2004, 2400−2401.
−
1
2.592
1.126
(7) Dell’Anna, M. M.; Mastrorilli, P.; Nobile, C. F.; Calmuschi-Cula,
no. measured
5080
42271
B.; Englert, U.; Peruzzini, M. Dalton Trans. 2008, 6005−6013.
8) Reetz, M. T.; Bohres, E.; Goddard, R.; Holthausen, M. C.; Thiel,
W. Chem.Eur. J. 1999, 5, 2101−2108.
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Organomet. Chem. 1992, 423, 263−270.
10) Arifhodzic-Radojevic, S.; Burrows, A. D.; Choi, N.; McPartlin,
no. unique [Rint]
no. of parameters
R1, wR2 [I > 2σ(I)]
4090 [0.0458]
170
10556 [0.0371]
479
(
a
0.0565, 0.0979
0.1277, 0.1205
0.988
0.0516, 0.1286
0.0788, 0.1465
(
a
R1, wR2 [all data]
goodness of fit on F2
a
1.026
(
a
2
o
2
o
2 2
R(F ) = ∑||F | − |F ||/∑|F |; R (F ) = [∑[w(F − F ) ]/
M.; Mingos, D. M. P.; Tarlton, S. V.; Vilar, R. J. Chem. Soc., Dalton
Trans. 1999, 3981−3988.
o
o
c
o
w
c
2
2
1/2
2
2
o
2
∑
[w(F ) ]]
; w = 1/[σ (F ) + (AQ) + BQ] where Q =
o
2
2
2
2
2
1/2
[
MAX(F ,0) + 2F ]/3; GOF = [∑[w(F − F ) ]/(N − P)]
where N and P are the numbers of observations and parameters,
,
(11) Leoni, P.; Vichi, E.; Lencioni, S.; Pasquali, M.; Chiarentin, E.;
Albinati, A. Organometallics 2000, 19, 3062−3068.
o
c
o
c
respectively.
(12) (a) Bonaccorsi, C.; Fabrizi de Biani, F.; Leoni, P.; Marchetti, F.;
Marchetti, L.; Zanello, P. Chem.Eur. J. 2008, 14, 847−856.
(b) Leoni, P.; Pasquali, M.; Fortunelli, A.; Germano, G.; Albinati, A.
4
. In addition to the aforementioned software, other control
calculations and preparation of publication material were performed
with the programs contained in the suite WINGX.
J. Am. Chem. Soc. 1998, 120, 9564−9573. (c) Leoni, P.; Marchetti, F.;
Pasquali, M.; Marchetti, L.; Albinati, A. Organometallics 2002, 21,
27
2
1
(
176−2182. (d) Leoni, P.; Marchetti, F.; Paoletti, M. Organometallics
997, 16, 2146−2151.
ASSOCIATED CONTENT
Supporting Information
CIF files for compounds 2 and 6(CF SO ). This material is
13) Scott, D.; Pregosin, P. S.; Veiros, L. F.; Calhorda, M. J.
■
*
S
Organometallics 2005, 24, 5710−5717.
(14) (a) The CSD System. The Cambridge Structural Database: A
3
3
quarter of a million crystal structures and rising: Allen, F. H. Acta
Crystallogr. 2002, B58, 380−388. (b) ConQuest: New software for
searching the Cambridge Structural Database and visualizing crystal
structures: Bruno, I. J.; Cole, J. C.; Edgington, P. R.; Kessler, M.;
Macrae, C. F.; McCabe, P.; Pearson, J.; Taylor, R. Acta Crystallogr.
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
E-mail: leoni@dcci.unipi.it.
■
*
2
002, B58, 389−397.
Notes
(15) Mealli, C. J. Am. Chem. Soc. 1985, 107, 2245−2253.
(16) (a) Geiger, W. E.; Barriere, F. Acc. Chem. Res. 2010, 43, 1030−
039. (b) Evans, D. H. Chem. Rev. 2008, 108, 2113−2144.
The authors declare no competing financial interest.
1
(
17) (a) Janzen, D. E.; vanDeerver, D. G.; Mehne, L. F.; da Silva
ACKNOWLEDGMENTS
This work was supported by the Ministero dell’Istruzione,
■
Filho, D. A.; Bredas, J.-L.; Grant, G. J. Dalton Trans. 2008, 1872−1882.
(
b) Dey, S.; Jain, V. K.; Knodler, A.; Klein, A.; Kaim, W.; Zalis, S. Inorg.
̈
Universita
̀
e Ricerca (MIUR), Project PRIN2008 No.
Chem. 2002, 41, 2864−2870. (c) Evrard, D.; Clement, S.; Lucas, D.;
Hanquet, B.; Knorr, M.; Strohmann, C.; Decken, A.; Mugnier, Y.;
Harvey, P. D. Inorg. Chem. 2006, 45, 1305−1315. (d) Roy, S.;
Hartenbach, I.; Sarkar, B. Eur. J. Inorg. Chem. 2009, 2553−2558.
2
008RFEB3X, and by the Fondazione Cassa di Risparmio di
Pisa under the “POLOPTEL” project no. 167/09.
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dx.doi.org/10.1021/ic4009448 | Inorg. Chem. 2013, 52, 8759−8769

Inorganic Chemistry
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dx.doi.org/10.1021/ic4009448 | Inorg. Chem. 2013, 52, 8759−8769