Reactivity of the palladium dimer [Pd2(μ-SO2)(μ-dba)(PBz3)2]. Syntheses and structural characterisation of [Pd3(μ-SO2)3(PBz3)3], [Pd2(μ-SO2)(μ-dppm)(PBz3)2], [Pd(SO2)(PBz3)2]

Article abstract of DOI:10.1039/a906444c

The reaction between [Pd₂(dba)₃]·solvent (dba = dibenzylideneacetone, solvent = CHCl₃ or C₆H₆) and PBz₃ (Bz = benzyl) in the presence of SO₂ led to either [Pd₂(μ-SO₂)(μ-dba)(PBz₃)₂] 1 or [Pd₃(μ-SO₂)₃(PBz₃)₃] 2 depending on the absence or presence of an excess of SO₂ in solution or in the recrystallisation. The crystal structure of 2 shows it to be a regular triangulo-cluster with Pd-Pd bond distances 2.7225(9) A. Complex 1 reacted with dppm with displacement of dba to give [Pd₂(μ-SO₂)(μ-dppm)(PBz₃)₂] 3. The crystal structure of 3 shows it to have a much shorter Pd-Pd bond length than 1 [2.670(2) Afor 3 cf. 2.885(2) A for 1], which can be rationalised on the basis of the palladium atoms having been formally oxidised to Pd^I and the SO₂ reduced to SO₂^2-. Complex 1 reacted with PBz₃ to give two mononuclear complexes, the previously characterised [Pd(dba)(PBz₃)₂] and the new complex [Pd(SO₂)(PBz₃)₂] 4 which was characterised by a single crystal X-ray analysis. Complex 4 forms a distorted T-shaped structure with the P-Pd-P angle 163.67(14)°. It contains a η¹-pyramidal SO₂ ligand, and is the first mononuclear palladium SO₂ complex to be crystallographically characterised. Complex 1 reacts with CO to give a mixture of the triangulo-clusters [Pd₃(μ-CO)₂(μ-SO₂)(PBz₃) ₃] 5 and [Pd₃(μ-CO)(μ-SO₂)₂(PBz₃) ₃] 6. Reaction with an excess of CO converted 6 into 5, and the crystal structure of 5 reveals relatively short Pd-Pd bond lengths consistent with a 42-electron cluster. Complex 1 reacted with CNBu^t to give [Pd₃(μ-SO₂)₂(CNBu^t) ₂(PBz₃)₃] which has also been crystallographically characterised. The Royal Society of Chemistry 1999.

Full text of DOI:10.1039/a906444c

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Reactivity of the palladium dimer [Pd2(ꢀ-SO2)(ꢀ-dba)(PBz3)2].
Syntheses and structural characterisation of [Pd3(ꢀ-SO2)3(PBz3)3],
[Pd2(ꢀ-SO2)(ꢀ-dppm)(PBz3)2], [Pd(SO2)(PBz3)2], [Pd3(ꢀ-CO)2-
(ꢀ-SO2)(PBz3)3] and [Pd3(ꢀ-SO2)2(CNBut)2(PBz3)3] (Bz ؍ benzyl)†
Sanja Arifhodzic-Radojevic,c Andrew D. Burrows,b Nick Choi,c Mary McPartlin,c
D. Michael P. Mingos,*a Stephen V. Tarltona and Ramón Vilara
a Department of Chemistry, Imperial College of Science, Technology and Medicine,
South Kensington, London, UK SW7 2AY
b Department of Chemistry, University of Bath, Claverton Down, Bath, UK BA2 7AY
c School of Applied Chemistry, University of North London, London, UK N7 8DB
Received 9th August 1999, Accepted 17th September 1999
The reaction between [Pd2(dba)3]ؒsolvent (dba = dibenzylideneacetone, solvent = CHCl3 or C6H6) and PBz3
(Bz = benzyl) in the presence of SO2 led to either [Pd2(µ-SO2)(µ-dba)(PBz3)2] 1 or [Pd3(µ-SO2)3(PBz3)3] 2 depending
on the absence or presence of an excess of SO2 in solution or in the recrystallisation. The crystal structure of 2
shows it to be a regular triangulo-cluster with Pd–Pd bond distances 2.7225(9) Å. Complex 1 reacted with dppm
with displacement of dba to give [Pd2(µ-SO2)(µ-dppm)(PBz3)2] 3. The crystal structure of 3 shows it to have a
much shorter Pd–Pd bond length than 1 [2.670(2) Å for 3 cf. 2.885(2) Å for 1], which can be rationalised on the
basis of the palladium atoms having been formally oxidised to PdI and the SO2 reduced to SO22Ϫ. Complex 1 reacted
with PBz3 to give two mononuclear complexes, the previously characterised [Pd(dba)(PBz3)2] and the new complex
[Pd(SO2)(PBz3)2] 4 which was characterised by a single crystal X-ray analysis. Complex 4 forms a distorted T-shaped
structure with the P–Pd–P angle 163.67(14)Њ. It contains a η1-pyramidal SO2 ligand, and is the first mononuclear
palladium SO2 complex to be crystallographically characterised. Complex 1 reacts with CO to give a mixture of the
triangulo-clusters [Pd3(µ-CO)2(µ-SO2)(PBz3)3] 5 and [Pd3(µ-CO)(µ-SO2)2(PBz3)3] 6. Reaction with an excess of CO
converted 6 into 5, and the crystal structure of 5 reveals relatively short Pd–Pd bond lengths consistent with a
42-electron cluster. Complex 1 reacted with CNBut to give [Pd3(µ-SO2)2(CNBut)2(PBz3)3] which has also been
crystallographically characterised.
The reactions between zero oxidation state palladium com-
plexes and small molecules such as CO, H2, CNR and SO2
have been implicated in a number of catalytic processes.1 One
of the most versatile palladium(0) sources is the dimer
[Pd2(dba)3]ؒsolvent (dba = dibenzylideneacetone, solvent =
CHCl3 or C6H6).2 When this complex is treated with strongly
co-ordinating ligands such as phosphines the dba molecules are
usually displaced and the in situ formation of palladium(0)
phosphine complexes is observed. Initially, it was assumed that
dba was an “innocent” ligand which would easily be substituted
and not be involved in further reactions. However, during the
last few years there has been an increasing amount of structural
and kinetic evidence which shows that dba is much more
involved in the reaction mechanisms than was originally
thought. It has been demonstrated that it is not uncommon to
keep dba in the co-ordination sphere and not only have com-
pounds such as [Pd(dba)L2] (L = PBz3 or PPh2(C10H7); L2 =
dppe; Bz = CH2Ph) been characterised structurally, but in some
cases addition of an excess of phosphine is unable to displace
dba from the palladium co-ordination sphere.2b,3,4 In addition,
Amatore and co-workers5 have shown that the presence of dba
has a strong influence on the kinetics of substitution and
oxidative-addition reactions of palladium complexes.
vent is treated with two molar equivalents of PBz3 under
an SO2 atmosphere. Complex 1 has a unique bridging dba
molecule which remains labile to substitution reactions, thus
allowing 1 to act as a potential convenient source of “[Pd2-
(µ-SO2)(PBz3)2]” fragments for cluster aggregation reactions.
This has been shown by the reaction between 1 and COS which
gives the tetrametallic cluster [Pd4(µ3-S)(µ-SO2)(CO)(PBz3)4].6b
In this paper the reactions between 1 and carbon monoxide,
tert-butyl isocyanide, bis(diphenylphosphino)methane (dppm)
and tribenzylphosphine are discussed. We also report the
isolation of a triangulo-palladium compound which seems to be
an intermediate in the reaction between [Pd2(dba)3], PBz3 and
SO2 to give the isolated dimer 1.
Results and discussion
Synthesis of [Pd2(ꢀ-SO2)(ꢀ-dba)(PBz3)2] 1 and [Pd3(ꢀ-SO2)3-
(PBz3)3] 2
We have recently reported that the reaction between [Pd2-
(dba)3]ؒsolvent, 2 PBz3 and SO2 gives the orange-yellow dimer
[Pd2(µ-SO2)(µ-dba)(PBz3)2] 1.6a This compound has been struc-
turally and spectroscopically characterised, and its 31P-{1H}
NMR spectrum shows a singlet at δ 2.8. When monitoring this
reaction as a function of time via 31P-{1H} NMR spectroscopy
we found evidence that prior to the formation of dimer 1 a
different species was present in solution. The spectrum of the
initial red solution under an SO2 atmosphere showed only a
single sharp peak at δ 19.3. After removing the solvent under
reduced pressure followed by redissolving the residues under an
We have recently reported the synthesis and structural char-
acterisation of the dimer [Pd2(µ-SO2)(µ-dba)(PBz3)2] 1.6a This
dimer is readily obtained in high yields when [Pd2(dba)3]ؒsol-
† Supplementary data available: rotatable 3-D crystal structure diagram
in CHIME format. See http://www.rsc.org/suppdata/dt/1999/3981/
J. Chem. Soc., Dalton Trans., 1999, 3981–3988
This journal is © The Royal Society of Chemistry 1999
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Table 1 Selected bond lengths (Å) and angles (Њ) for compound 2
Pd(1)–S(1)
Pd(1)–P(1)
Pd(1)–Pd(1B)
S(1)–O(2)
2.2641(19) Pd(1)–S(1A)
2.3367(18) Pd(1)–Pd(1A)
2.2841(18)
2.7225(9)
1.438(6)
2.7225(9)
1.440(6)
S(1)–O(1)
S(1)–Pd(1B)
2.2841(18)
S(1)–Pd(1)–S(1A)
S(1A)–Pd(1)–P(1)
S(1A)–Pd(1)–Pd(1A) 52.90(5)
166.01(6)
99.02(7)
S(1)–Pd(1)–P(1)
S(1)–Pd(1)–Pd(1A)
P(1)–Pd(1)–Pd(1A)
94.70(7)
113.54(5)
151.68(6)
S(1)–Pd(1)–Pd(1B)
P(1)–Pd(1)–Pd(1B)
Pd(1)–S(1)–Pd(1B)
53.57(5)
148.06(6)
73.53(6)
S(1A)–Pd(1)–Pd(1B) 112.87(5)
Pd(1A)–Pd(1)–Pd(1B) 60.0
O(1)–S(1)–O(2)
116.2(4)
Fig. 1 Molecular structure of [Pd3(µ-SO2)3(PBz3)3].
atmosphere of N2 the peak at δ 2.8, corresponding to 1, was
observed in the 31P-{1H} NMR spectrum. This suggested that
the compound with the resonance at δ 19.3 readily decomposes
in the absence of an SO2 atmosphere to yield 1. In order to
isolate this new compound a layer of SO2-saturated ethanol was
added directly to the reaction mixture under an atmosphere of
SO2. Upon slow diffusion of the ethanol layer into the toluene
solution at Ϫ25 ЊC red crystals were formed. IR spectroscopy
of these crystals showed no peaks arising from the carbonyl
group in the dba ligand and confirmed the presence of the SO2
ligand with two intense peaks at 1244 and 1067 cmϪ1. There
were peaks in the FAB-MS with high m/z, indicating the pos-
sible presence of a cluster compound. The C and H elemental
analyses suggested that the formulation of the new compound
should be [Pdx(SO2)x(PBz3)x].
As these results were not conclusive a single crystal X-ray
crystallographic analysis was completed, and this confirmed the
compound to be the trimeric species [Pd3(µ-SO2)3(PBz3)3] 2 (see
Fig. 1). 42-Electron triangulo-clusters of formula [Pt3(µ-SO2)3-
(PR3)3] are well known and have been crystallographically
characterised for PR3 = PPh3 or PCy3. However, the structure
of 2 represents the first example of an analogous palladium
triangle with the general formula [Pd3(µ-SO2)3(PR3)3].
Fig. 2 Schematic representation of a metal triangle formed by three
T-shaped ML3 fragments.
(PCy3)3] and [Pt3(µ-SO2)3L3], can be viewed in terms of three
T-shaped ML3 fragments sharing common bridging groups
(ignoring the bridged metal–metal bonds), Fig. 2.
Consistent with this description the unique S–Pd–S bond
angle in compound 2 is 166.01(6)Њ which is comparable to those
observed in [Pt3(µ-SO2)3(PR3)3] (mean S–Pt–S 167.4Њ). These
values are typical of T-shaped molecules and may be compared
with the P–M–P angle of 159.3Њ reported11 for the d8 complex
[Rh(PPh3)3]ϩ and that of 163(1)Њ observed in the present study
for [Pd(SO2)(PBz3)2] 4 (see below).
The reaction between [Pd2(dba)3]ؒsolvent and PBz3 under an
atmosphere of SO2 is summarised in Scheme 1. An equilibrium
is established between [Pd3(µ-SO2)3(PBz3)3] 2 and [Pd2(µ-SO2)-
(µ-dba)(PBz3)2] 1 with the concentration of SO2 in solution
determining the relative amount of the two complexes.
Removal of the solvent (and hence any excess of SO2) results in
the equilibrium shifting to the right hand side, favouring com-
plex 1. Under an SO2 atmosphere the equilibrium is shifted to
the left hand side, favouring 2.
The compound [Pd3(µ-SO2)3(PBz3)3] crystallises in the high
¯
symmetry space group R3; selected bond lengths and angles are
given in Table 1. The molecular structure of 2 consists of three
palladium atoms arranged in an equilateral triangle with a crys-
tallographically imposed threefold axis and with Pd–Pd equal
to 2.7225(9) Å. These distances are slightly longer than the
range 2.576(1)–2.719(6) Å previously reported for 42 electron
triangulo-palladium clusters.7 The range of Pt–Pt bond lengths
previously reported for the analogous [Pt3(µ-SO2)3(PR3)3]8,9 tri-
angles are 2.813(1)–2.815(1) (R = Cy) and 2.695(1)–2.712(1) Å
(R = Ph).
In compound 2 each metal atom is bound to two bridging
sulfur dioxide ligands and one tribenzylphosphine group. There
is a small but significant difference between the distances from
each palladium atom to the two sulfur atoms bonded to it
[Pd(1)–S(1) 2.264(2) and Pd(1)–S(1A) 2.284(2) Å]. This differ-
ence is also reflected in the two S–Pd–Pd angles of each SO2-
bridged edge [S(1A)–Pd(1)–Pd(1A) 52.90(5)Њ and S(1)–Pd(1)–
Pd(1B) 53.57(5)Њ]. The palladium, phosphorus and sulfur atoms
are situated in approximately planar arrangements, the three
sulfur atoms lying –0.674 Å below the Pd3 plane and the phos-
phorus atoms 0.1196 Å above it. Mingos and co-workers10 have
suggested that this virtually planar geometry, which is observed
in 42 electron triangulo-platinum clusters such as [Pt3(µ-CO)3-
Scheme 1
Synthesis of [Pd2(ꢀ-SO2)(ꢀ-dppm)(PBz3)2] 3
The possibility of replacing the dba ligand from compound 1
by another bridging ligand was explored by treating 1 with
dppm (Ph2PCH2PPh2). Although dppm can chelate to a single
metal atom the bite angle associated with dppm is also
appropriate for it to form bridged binuclear complexes in which
the two metal centres are held together and may form a metal–
3982
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Table 2 Selected bond lengths (Å) and angles (Њ) for [Pd2(µ-SO2)(µ-dba)(PBz3)2] 1 and [Pd2(µ-SO2)(µ-dppm)(PBz3)2] 3
1
3
1
3
Pd(1)–Pd(2)
Pd(1)–P(1)
Pd(1)–P(3)
Pd(2)–P(2)
Pd(2)–P(4)
Pd(1)–S(1)
Pd(2)–S(1)
S(1)–O(1)
S(1)–O(2)
2.885(2)
2.325(4)
—
2.335(4)
—
2.246(4)
2.252(4)
1.473(10)
1.458(11)
2.6703(14)
2.326(2)
2.322(2)
2.326(2)
2.324(2)
2.239(2)
2.241(3)
1.496(8)
1.498(8)
S(1)–Pd(1)–P(1)
S(1)–Pd(2)–P(2)
S(1)–Pd(2)–Pd(1)
S(1)–Pd(1)–Pd(2)
O(1)–S(1)–O(2)
P(1)–Pd(1)–Pd(2)
P(2)–Pd(2)–Pd(1)
93.64(14)
91.21(14)
50.01(9)
50.19(10)
113.9(6)
139.10(11)
140.25(11)
104.30(12)
104.76(12)
53.09(9)
53.75(8)
109.8(5)
154.59(8)
157.45(8)
Fig. 3 Molecular structure of [Pd2(µ-SO2)(µ-dppm)(PBz3)2].
Scheme 2
metal bond. The addition of a benzene solution containing one
molar equivalent of dppm to a benzene solution of 1 immedi-
ately gave rise to a change from orange-yellow to yellow. The
solid, which was obtained by the removal of the solvent under
reduced pressure, followed by washing with methanol, analysed
correctly for [Pd2(SO2)(dppm)(PBz3)2]ؒ2MeOH. The isolated
product gave rise to two peaks in the 31P-{1H} NMR at δ 22.2
and 7.7 (C6D6) which are observed as triplets with a small coup-
ling constant of 10 Hz. These suggest the presence of an
AAЈXXЈ system of phosphorus nuclei and are consistent with
the replacement of dba by a bridging dppm ligand and the
retention of the PBz3 ligands. The SO2 stretching vibrations in
the IR spectrum at 1025 and 1147 cmϪ1 are lower than those
found in [Pd2(µ-SO2)(µ-dba)(PBz3)2], indicating stronger Pd–
SO2 back donation interactions. This could be a consequence of
stronger electron donation from the phosphine to the metal. No
peaks corresponding to the carbonyl stretching vibration were
observed in the IR spectrum, indicating that the dba ligand
had been displaced in the reaction. The FAB mass spectrum
contains the parent molecular ion, [Pd2(SO2)(Ph2PCH2PPh2)-
(PBz3)2]ϩ, with m/z 1272. The formulation of the compound 3
as [Pd2(µ-SO2)(µ-dppm)(PBz3)2] was confirmed by a single
crystal X-ray crystal diffraction study (see Fig. 3).
sidered to be neutral, the dimer formally contains palladium(0)
centres but the metal–metal distance is in fact more character-
istic of the Pd–Pd bond lengths observed in palladium()
dimers.12 For example similar Pd–Pd bond lengths have been
observed for palladium() dimers containing dppm and dpmMe
(dpmMe = 1,1-bis(diphenylphosphino)ethane) {e.g. 2.699(5) Å
in [Pd2(µ-dppm)2Br2]13a and 2.6639(7) in [Pd2(µ-dpmMe)2-
Cl2]13b}. It is not the small bite angle of the dppm ligand that
is responsible for the short Pd–Pd distance in 3 because in
the palladium(0) dimer [Pd2(µ-dppm)3] the Pd–Pd bond length
is 2.959(2) Å.14
The mean Pd–S distance in complex 3 of 2.240(3) Å is not
significantly shorter than that of 2.249(4) Å in 1, but the mean
S–O distance of 1.496(8) Å in 3 is longer than that of 1.466(10)
Å in 1, and correspondingly 3 has the lower ν(SO2) stretching
vibrations in the IR spectrum. This indicates that the SO2 lig-
and in 3 is more strongly electron-accepting and could account
for the fact that Pd–Pd distance indicates a formal palladium
oxidation state of ϩ1 and hence a Pd–Pd bond order of 1, if the
SO2 ligand is formally considered as an (SO2)2Ϫ species.
The other major difference between complexes 1 and 3 is the
larger angles in 3, for example S(1)–Pd(1)–P(1) and S(1)–Pd(2)–
P(2) have a mean value of 104.55(9)Њ in 3 compared to
92.43(14)Њ in 1. This can be attributed to the greater flexibility
of the dppm ligand compared to the dba ligand which leads to
less steric crowding. The phenyl rings of dppm are more able to
orientate themselves into the most sterically favourable position
whereas the dba ligand is more rigid due to the conjugation
between the unsaturated groups across the ligand. The tribenz-
ylphosphine ligands are of approximately equal distance from
the palladium atoms in both dimers.
This dimer crystallises with four molecules of methanol and
half a molecule of benzene per molecule. Some of the struc-
tural features of 3 are compared with equivalent data for the
starting material [Pd2(µ-SO2)(µ-dba)(PBz3)2] in Table 2. One of
the most notable features of complex 3 is the relatively short
distance between the two palladium atoms [2.6703(14) Å]. This
distance is significantly shorter than in complex 1 and also
shorter than has been previously observed in SO2-containing
palladium(0) cluster compounds.7 If the SO2 ligand is con-
The compound [Pd2(µ-SO2)(µ-dppm)(PBz3)2] is very stable
J. Chem. Soc., Dalton Trans., 1999, 3981–3988
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Table 3 Selected bond lengths (Å) and angles (Њ) for [M(SO2)L2]
and can be kept in air for many months. This is probably due to
the sulfur atom being co-ordinatively saturated since it is utilis-
ing both the HOMO and LUMO in its bonding to the two
metal atoms. Similar complexes of palladium() dimers, [(Ph3P)-
Pd(µ-SC6F5)(µ-dppm)Pd(SC6F5)]ؒ1.4CH2Cl2 and [(Ph3P)Pd-
(µ-SC6F5)(µ-dppm)Pd(PPh3)][SO3CF3]ؒ2CH2Cl2, have recently
been synthesized.15 These complexes also have bicyclic
structures formed through the simultaneous bridging of the
palladium() centres by a dppm and a sulfur ligand.
[Pd(SO2)-
(PBz3)2] 4
[Ni(SO2)-
(PCy3)2]19
[Pt(SO2)-
(PCy3)2]16
M–S
2.282(4)
2.312(3)
2.328(3)
1.428(13)
1.467(13)
2.150a
2.211
2.299(1)
2.304(1)
2.309(1)
1.465(3)
1.461(3)
M–P(1)
M–P(2)
S–O(1)
S–O(2)
2.211
1.540a
1.560a
P(1)–M–P(2)
S–M–P(1)
S–M–P(2)
M–S–O(1)
M–S–O(2)
O(1)–S–O(2)
163.67(14)
96.52(14)
97.27(14)
104.8(5)
106.8(5)
112.4(9)
118.5
165.72(4)
95.03(4)
97.39(4)
104.8(1)
104.1(1)
113.1(2)
114.3a
127.0a
116.0a
103.0a
130.0a
Reaction of [Pd2(ꢀ-SO2)(ꢀ-dba)(PBz3)2] with PBz3
Since the addition of dppm to [Pd2(µ-SO2)(µ-dba)(PBz3)2]
resulted in the simple substitution of the dba ligand, the reac-
tion of the dimer with tribenzylphosphine was also studied.
The addition of two molar equivalents of tribenzylphosphine
to a benzene solution containing complex 1 gave rise to a ruby-
red solution within a few seconds. The 31P-{1H} NMR spec-
trum of this solution contained two signals of equal intensity,
one at δ 20.5 and the other at δ 7.8. The signal at δ 7.8 consists
of one sharp intense peak surrounded by two small and broad
peaks at δ 9.2 and 6.4. This signal has been previously assigned
to the presence of [Pd(dba)(PBz3)2] in solution.6a Half of the
dimer, therefore, is converted into this complex and the other
half into a new product 4 which appears as a singlet at δ 20.5
in the 31P-{1H} NMR spectrum. In order to convert all of the
reaction mixture into the new product 4, sulfur dioxide gas was
bubbled through the solution for 5 min. The 31P-{1H} NMR
spectrum of the resultant solution consisted of just one single
sharp peak at δ 20.5. The solvent was removed under reduced
pressure and the residual solids were washed with several por-
tions of methanol to remove the excess of dba; orange crystals
of 4 were grown by redissolving the product in dichloro-
methane and adding a methanol layer above the solution. The
IR spectrum of the crystals obtained confirmed that there was
no dba in compound 4 and sharp bands for SO2 vibrations
were observed at 1033 and 1182 cmϪ1. Crystals of 4 analysed
correctly for [Pd(SO2)(PBz3)2]ؒCH2Cl2 and this formulation
was corroborated by a single crystal X-ray crystallographic
determination.
The X-ray crystal analysis shows that complex 4 is a three-co-
ordinate palladium complex with two PBz3 ligands and an η1-
SO2 molecule as illustrated in Fig. 4. The Pd, S, and the two
P atoms are approximately coplanar, the palladium atom
being 0.157 Å out of the plane of the three donor atoms. The
co-ordination of the palladium atom may be described as
T-shaped with a P(1)–Pd–P(2) angle of 163.67(14)Њ consider-
ably greater than that of 107.2(3)Њ in the related three-co-
ordinate [Pd(dba)(PBz3)2], a difference that may be attributed to
the greater bulk of the dba ligand compared to SO2. The SO2
ligand is co-ordinated in a pyramidal mode (mean Pd–S–O
105.8(5)Њ), with the two oxygen atoms lying on opposite sides of
the mean co-ordination plane (deviations O(1) Ϫ1.365 and O(2)
0.956 Å).
a Denotes averaged atomic positions.
Fig. 4 Molecular structure of [Pd(SO2)(PBz3)2].
fact that whereas the palladium and platinum complexes have
definite T-shaped co-ordination geometry at the metal centre
[P–Pd–P 163.6(1) and P–Pt–P 165.72(4)Њ], the nickel compound
is more appropriately described as trigonal planar (P–Ni–P
118.5, mean S–Ni–P 120.9Њ). Similarly the palladium and plat-
inum compounds both exhibit pyramidal M–SO2 co-ordination
with approximately tetrahedral angles at S (mean S–M–P
96.9(1) and 96.18(4)Њ, O–S–O 113.2(8) and 113.1Њ respectively),
whereas the nickel complex has a virtually planar Ni–SO2
arrangement (mean S–Ni–O 109.5Њ and O–S–O 130.0Њ). The η1-
pyramidal co-ordination of SO2 in the palladium and platinum
compounds means that the ML2 (M = Pd or Pt) fragment makes
use of its σ-donating ability to co-ordinate to SO2.18 In the
nickel complexes the SO2 is co-ordinated in a η1-planar mode
consistent with the lower basicity of the first row transition
metal.
The reactions of the dimer [Pd2(µ-SO2)(µ-dba)(PBz3)2] with
other phosphines were also studied. However, these investi-
gations proved to be inconclusive since mixtures of products
were obtained, and further work is required to separate the
range of products formed.
For platinum the first structurally characterised three co-
ordinate bis(phosphine) sulfur dioxide complex, [Pt(SO2)-
(PCy3)2], was reported in 198316 but to our knowledge 4 is the
first example of a mononuclear three-co-ordinate palladium
phosphine SO2 complex that has been crystallographically
characterised, though complexes of the general formulae
[Pd(SO2)(PR3)2] and [Pd(SO2)(PR3)3] have been reported
and characterised by IR spectroscopy.17 Three-co-ordinate
nickel(0)–sulfur dioxide complexes of similar formulation have
also been reported with the bulky organophosphines PCy3,
PCy2Ph and PBz2Ph. Crystal structure studies of the nickel(0)
complex [Ni(SO2)(PCy3)2] shows large differences in the three-
co-ordinate structure from those of the related palladium and
platinum complexes, 4 and [Pt(SO2)(PCy3)2]. Selected bond
lengths and angles for these three compounds are listed in
Table 3 for ease of comparison. The main difference lies in the
Reaction of [Pd2(ꢀ-SO2)(ꢀ-dba)(PBz3)2] with CO
In order to study the possible aggregation of compound 1 into
higher nuclearity clusters its reactions with CO and CNBut
were studied. On bubbling CO gas through a THF solution of 1
a rapid change to dark red occurred. The 31P-{1H} NMR spec-
trum of this solution showed the presence of two products,
both characterised as unsymmetrical triangulo-clusters by the
presence of a doublet and triplet in 2:1 intensity ratio. The
major compound (5) showed a triplet at δ 15.5 and a doublet at
δ 9.6, with a coupling constant of 41 Hz. The minor compound
(6) gave a doublet at δ 16.5 and a triplet at δ 8.8, with a coupling
constant of 52 Hz. Further bubbling of CO gas through the
solution led to the disappearance of the peaks associated with
6, demonstrating that 6 can be converted into 5 by addition of
3984
J. Chem. Soc., Dalton Trans., 1999, 3981–3988

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Table 4 Selected bond lengths (Å) and angles (Њ) for compound 5
Pd(1)–Pd(2)
Pd(1)–Pd(3)
Pd(1)–P(1)
Pd(1)–C(1)
Pd(1)–C(2)
Pd(2)–Pd(3)
Pd(2)–P(2)
Pd(2)–S(1)
2.6850(6)
2.6942(6)
2.332(1)
2.068(6)
2.048(6)
2.7192(6)
2.312(1)
2.270(1)
Pd(2)–C(1)
Pd(3)–P(3)
Pd(3)–S(1)
Pd(3)–C(2)
S(1)–O(1)
S(1)–O(2)
C(1)–O(3)
C(2)–O(4)
2.086(6)
2.322(1)
2.264(1)
2.068(6)
1.446(4)
1.453(4)
1.138(7)
1.139(7)
Pd(3)–Pd(1)–Pd(2)
C(1)–Pd(1)–C(2)
Pd(1)–Pd(2)–Pd(3)
C(1)–Pd(2)–S(1)
Pd(1)–Pd(3)–Pd(2)
S(1)–Pd(3)–C(2)
Pd(2)–C(1)–Pd(1)
60.73(1)
147.9(2)
59.80(1)
159.9(2)
59.47(1)
159.9(2)
80.5(2)
O(3)–C(1)–Pd(1)
O(3)–C(1)–Pd(2)
Pd(1)–C(2)–Pd(3)
O(4)–C(2)–Pd(1)
O(4)–C(2)–Pd(3)
Pd(2)–S(1)–Pd(3)
O(1)–S(1)–O(2)
137.7(5)
140.1(5)
81.8(2)
137.8(5)
140.2(5)
73.70(4)
113.1(2)
Although compound 6 was not isolated, it is reasonable to
assign its identity to the other mixed CO/SO2 triangulo-cluster,
[Pd3(µ-CO)(µ-SO2)2(PBz3)3].
Reaction of [Pd2(ꢀ-SO2)(ꢀ-dba)(PBz3)2] with CNBut
Fig. 5 Molecular structure of [Pd3(µ-CO)2(µ-SO2)(PBz3)3]. The benzyl
groups have been omitted for clarity.
On adding two molar equivalents of tert-butyl isocyanide to a
toluene solution of [Pd2(µ-SO2)(µ-dba)(PBz3)2] the solution
changed to light yellow. After removing the solvent under
reduced pressure and washing with methanol to remove the dba
the 31P-{1H} NMR spectrum (C6D6) contained a doublet at
δ 11.7 and a triplet at δ 2.3 in a ratio of 2:1 with a coupling
3
constant JP, P = 34 Hz. This spectrum suggested that
a
triangulo-palladium cluster compound with two phosphorus
environments in a 2:1 ratio had been formed. Together with the
other spectroscopic data this enabled us to formulate it as
[Pd3(µ-SO2)2(CNBut)2(PBz3)3] 7. For a balanced equation, (1),
Ϫ3dba
3[Pd2(SO2)(dba)(PBz3)2] ϩ SO2 ϩ 4ButNC
2[Pd3(SO2)2(CNBut)2(PBz3)3] (1)
between 1 and 7, additional sulfur dioxide needs to be present.
In accordance with this equation, when the synthesis of 7 was
carried out under an atmosphere of SO2 the yield was greatly
improved and the product more readily isolated.
The isocyanide ligands of this product showed ν(CN) bands
at 2175 and 2148 cmϪ1 which are higher than that of free tert-
butyl isocyanide which appears at 2136 cmϪ1. The analogous
tert-butyl isocyanide triangulo-palladium cluster [Pd3(µ-
SO2)2(CNBut)5] also shows an increase in ν(CN) from free
CNBut with peaks observed in the IR spectrum at 2170 and
Scheme 3
CO (Scheme 3). The IR spectrum of 5 confirmed the presence
of both CO and SO2 with ν(CO) at 1911 and 1857 cmϪ1, and
ν(SO2) at 1056 and 1187 cmϪ1 respectively. Crystals of this
product were grown from a THF–hexane mixture and, upon
X-ray analysis, were found to be a palladium cluster of formula
[Pd3(µ-CO)2(µ-SO2)(PBz3)3] 5 which is consistent with the
31P-{1H} NMR and IR data.
Compound 5 is a 42-electron triangulo-cluster complex with
Pd–Pd bond distances of 2.6850(6), 2.6942(6) and 2.7192(6) Å,
the longest bond length being that bridged by SO2 (see Fig. 5).
These distances are all shorter than the Pd–Pd bond lengths
previously reported for other Pd–SO2 triangles which cover a
range from 2.7225(9) (complex 2) to 2.994(1) Å.7 Two of the
Pd–Pd edges in 5 are bridged by carbon monoxide ligands and
the third edge is bridged by a sulfur dioxide ligand, creating a
pseudo-C2v symmetry axis along the vector which runs through
the unique palladium atom (bonded to both CO ligands) and
bisects the SO2-bridged Pd–Pd edge. The palladium triangle,
carbon monoxide ligands, phosphorus and sulfur atoms all lie
in approximately the same plane. This geometry is typical of 42-
electron triangulo-cluster compounds of platinum and pal-
ladium. Selected bond lengths and angles for 5 are given in
Table 4.
2155 cmϪ1 20 A decrease in ν(CN) from that of free CNBut
.
might have been expected as isocyanides, like carbon monoxide,
are π-acceptor ligands. An increase in ν(CN) indicates that
little, if any, electron density is being donated from the metal
centre into the π* antibonding orbital of the isocyanide ligand.
Complex 7 also shows an intense and sharp SO2 peak at
1012 cmϪ1 and no peaks due to dba could be identified. The
FAB-MS showed the expected fragmentation pattern for a
compound of formula [Pd3(SO2)2(CNBut)2(PBz3)3]. The peak
with the highest m/z was observed at 1527 and assigned as [M]ϩ.
The assignments of the fragments are shown in Table 5.
Crystals suitable for a single crystal structural analysis were
obtained from a benzene–methanol solution (see Fig. 6). This
analysis confirmed that 7 is the triangulo-cluster compound
[Pd3(µ-SO2)2(CNBut)2(PBz3)3] which contains two edge-
bridging SO2 ligands and two terminal isocyanide ligands. The
compound crystallises with half a molecule of H2O which
presumably was incorporated from the atmosphere during the
process of recrystallisation. The calculated elemental analyses
based on this formulation were more consistent with the
J. Chem. Soc., Dalton Trans., 1999, 3981–3988
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Table 5 Details for the positive ion FAB mass spectrum of com-
pound 7
Table 6 Selected bond lengths (Å) and angles (Њ) for complex 7
Pd(1)–Pd(3)
Pd(2)–Pd(3)
Pd(1)–S(1)
Pd(2)–C(2)
Pd(2)–P(2)
Pd(3)–S(2)
2.722(2)
2.801(2)
2.272(4)
2.006(14)
2.309(4)
2.240(4)
Pd(1)–Pd(2)
Pd(1)–S(2)
Pd(1)–P(1)
Pd(2)–S(1)
Pd(3)–C(4)
Pd(3)–P(3)
2.764(2)
2.272(4)
2.296(5)
2.240(4)
2.005(14)
2.309(4)
m/z
Intensity (%)
Fragment
1527
1223
1140
1050
1002
919
836
821
745
729
18
24
50
10
14
52
22
58
12
54
[M]ϩ
[M Ϫ PBz3]ϩ
[M Ϫ ButNC Ϫ PBz3]ϩ
[M Ϫ ButNC Ϫ PBz3 Ϫ Bz]ϩ
[M Ϫ 2PBz3]ϩ
S(1)–Pd(1)–S(2)
S(2)–Pd(1)–P(1)
S(2)–Pd(1)–Pd(3)
S(1)–Pd(1)–Pd(2)
P(1)–Pd(1)–Pd(2)
C(2)–Pd(2)–S(1)
S(1)–Pd(2)–Pd(1)
C(2)–Pd(2)–Pd(3)
P(2)–Pd(2)–Pd(3)
C(4)–Pd(3)–Pd(1)
S(2)–Pd(3)–Pd(2)
149.00(19)
109.24(18)
52.36(9)
51.69(10)
146.89(15)
160.5(6)
52.76(9)
69.5(5)
163.02(13)
100.4(6)
97.57(13)
S(1)–Pd(1)–P(1)
S(1)–Pd(1)–Pd(3)
P(1)–Pd(1)–Pd(3)
S(2)–Pd(1)–Pd(2)
Pd(3)–Pd(1)–Pd(2)
C(2)–Pd(2)–P(2)
P(2)–Pd(2)–Pd(1)
S(1)–Pd(2)–Pd(3)
Pd(1)–Pd(2)–Pd(3)
C(4)–Pd(3)–Pd(2)
Pd(1)–Pd(3)–Pd(2)
101.36(18)
100.81(13)
151.57(15)
97.84(13)
61.39(5)
[M Ϫ ButNC Ϫ 2PBz3]ϩ
[M Ϫ 2ButNC Ϫ 2PBz3]ϩ
[M Ϫ Pd Ϫ 2ButNC Ϫ 2SO2 Ϫ PBz3]ϩ
[M Ϫ 2ButNC Ϫ 2PBz3 Ϫ Bz]ϩ
[M Ϫ Pd Ϫ 2ButNC Ϫ 2SO2 Ϫ PBz3 Ϫ Bz]ϩ
102.5(5)
137.88(14)
99.33(13)
58.57(5)
71.7(5)
60.04(5)
for [Pd3(µ-SO2)2(CNXyl)2(PPh3)3] (Xyl = xylyl, 2,6-dimethyl-
phenyl).22
It is interesting that the compounds [Pd3(µ-SO2)2(CNXyl)2-
(PCy3)3] and [Pd3(µ-SO2)2(CNXyl)2(PPh3)3] were prepared from
the reaction of higher nuclearity clusters with 2,6-dimethyl-
phenyl isocyanide. The other known compound of this type,
[Pd3(µ-SO2)2(CNBut)5], does not contain any phosphine ligands
and was prepared from [Pd3(µ-CNBut)3(CNBut)3] and an excess
of SO2. The synthetic route to complex 7 is therefore unusual
for this type of trinuclear cluster compound.
Conclusion
The dimer [Pd2(µ-dba)(µ-SO2)(PBz3)2] has proved to be a good
starting material for the formation of novel dimeric and
triangulo-palladium compounds. The formation of [Pd(SO2)-
(PBz3)2] when treating 1 with PBz3 and of [Pd2(µ-SO2)(µ-dppm)-
(PBz3)2] when using dppm, together with the evidence of differ-
ent reactions between 1 and a range of phosphines, suggest that
this is a fruitful area for the synthesis of novel Pd/SO2/PR3
complexes. During the synthesis of 1 the novel triangulo-cluster
[Pd3(µ-SO2)3(PBz3)3] 2 has been isolated and crystallographi-
cally characterised. The selective formation of 1 or 2 strongly
depends on the concentration of SO2.
Fig. 6 Molecular structure of [Pd3(µ-SO2)2(CNBut)2(PBz3)3].
observed elemental analyses than the unhydrated complex, but
are still not completely satisfactory.
Complex 7 consists of a palladium triangle with two Pd–Pd
edges bridged by a sulfur dioxide ligand. The two palladium
atoms of the unbridged edge are each terminally bonded to an
isocyanide ligand. Each palladium atom is also terminally
bonded to a phosphine ligand in the plane of the palladium
triangle {maximum deviations from [Pd(1), Pd(2), Pd(3), P(1),
P(2), P(3)] mean plane: Pd(1) 0.0325, Pd(2) 0.0519, Pd(3)
Ϫ0.0587, P(1) Ϫ0.0167, P(2) Ϫ0.0260, P(3) 0.0169 Å}. The C2
rotational symmetry axis observed in [Pd3(µ-CO)2(µ-SO2)-
(PBz3)3] is also present, with this axis bisecting the Pd(2)–Pd(3)
bond and passing through Pd(1). However the vertical plane
of symmetry observed in [Pd3(µ-CO)2(µ-SO2)(PBz3)3] is not
present due to the isocyanide and sulfur dioxide ligands being
greatly displaced from the plane of the palladium triangle.
Selected bond lengths and angles for 7 are given in Table 6.
Unlike [Pd3(µ-CO)2(µ-SO2)(PBz3)3], which has a cluster
valence electron count of 42, [Pd3(µ-SO2)2(CNBut)2(PBz3)3] is a
44-electron complex with Pd–Pd bond lengths between 2.722(2)
and 2.801(2) Å. The Pd–Pd bond lengths in other crystallo-
graphically characterised 44-electron complexes range between
2.734(4) and 3.000(5) Å.21 The Pd(1)–Pd(3) distance in complex
7 is therefore the shortest observed Pd–Pd bond length in all of
these complexes. The longest Pd–Pd bond in complex 7 is the
non-bridged bond [Pd(2)–Pd(3)] but this is longer than Pd(1)–
Pd(2) by the same amount that Pd(1)–Pd(2) is to Pd(1)–Pd(3).
In other words, although the Pd(2)–Pd(3) distance is the longest
bond, the palladium triangle does not exhibit a regular isosceles
geometry. A similar geometry has been noted previously
Experimental
General
All the reactions were routinely carried out using standard
Schlenk-line techniques under an atmosphere of pure nitrogen.
The solvents were used dry and free of oxygen. Infrared spectra
were recorded on a Perkin-Elmer 1720 Fourier-transform spec-
trometer between 4000 and 250 cmϪ1 as KBr pellets, 31P-{1H}
NMR spectra on a JEOL JNM-EX270 Fourier-transform spec-
trometer operating at a frequency of 109.4 MHz with chemical
shifts reported relative to H3PO4 and mass spectra by Mr J.
Barton at Imperial College on a VG AutoApec-Q as FAB using
3-nitrobenzyl alcohol as matrix. The compound [Pd2(dba)3]ؒ
solvent was prepared according to literature procedures.23
Other reagents were used as obtained from commercial sources.
Syntheses
[Pd2(ꢀ-SO2)(ꢀ-dba)(PBz3)2] 1. The compound PBz3 (184 mg,
0.60 mmol) was dissolved in 15 cm3 toluene and SO2 gas was
bubbled through for 1 min. This solution was then added to a
solution of [Pd2(dba)3]ؒC6H6 (300 mg, 0.30 mmol) in 25 cm3
toluene, followed by the further addition of SO2 gas (ca. 10
min) whereupon the solution changed from deep purple to red.
The mixture was stirred under an atmosphere of SO2 for 30 min
to ensure completion of the reaction. The solvent was removed
3986
J. Chem. Soc., Dalton Trans., 1999, 3981–3988

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Table 7 Crystallographic details for complexes 2, 3, 4, 5 and 7
2
3
4
5
7
Chemical formula
Formula weight
C63H63O6P3Pd3S3
1424.42
C74H83O6P4Pd2S
1437.1
C43H44Cl2O2P2PdS
864.08
C65H63O4P3Pd3S
1352.4
C73H82N2O4.5P3Pd3S2
1535.34
T/K
223(2)
Trigonal, R3
24.985(2)
24.985(2)
16.219(3)
173(2)
Monoclinic, P21/c
22.498(7)
14.064(3)
23.376(13)
293(2)
Triclinic, P1
293(2)
Trigonal, R3
44.09(4)
44.09(4)
16.22(1)
299(2)
Orthorhombic, Pbca
22.985(9)
24.213(10)
26.93(2)
¯
¯
¯
System, space group
a/Å
b/Å
c/Å
α/Њ
β/Њ
9.931(3)
11.331(2)
19.275(4)
84.427(12)
87.31(2)
64.216(14)
1943.9(8)
2
112.47(3)
γ/Њ
U/Å3
8768.0(19)
6
1.154
4121
6835(4)
4
0.70
27306(2)
18
1.02
12417
14985(13)
8
0.878
10814
Z
µ(Mo-Kα)/mmϪ1
Reflections collected
Independent
reflections
Final R1, wR2
[I > 2σ(I)]
0.788
5108
11348
3354 [R(int) = 0.0471] 9505 [R(int) = 0.1248]
4178 [R(int) = 0.0314]
6500 [R(int) = 0.017]
9186 [R(int) = 0.0959]
0.0491, 0.1105 0.0738, 0.1637
0.0870, 0.2234
0.027, 0.035
0.0750, 0.1715
under reduced pressure and the yellow-red residue washed with
two successive 30 cm3 portions of ethanol to remove the free
dba. The remaining yellow powder was recrystallised from a
toluene–diethyl ether mixture at 4 ЊC. Yield 302 mg (89%).
Found: C, 63.0; H, 5.3. C59H56O3P2Pd2S requires C, 63.2; H,
mixture was stirred under an atmosphere of SO2 for 30 min.
After reducing the volume of THF to approximately 5 cm3,
diethyl ether was added to precipitate the orange solid, followed
by filtration. Orange crystals of [Pd(SO2)(PBz3)2]ؒCH2Cl2 were
obtained by redissolving the compound in CH2Cl2 followed by
the addition of a methanol layer and cooling to Ϫ25 ЊC. Yield
119 mg (77%). Found: C, 61.6; H, 5.0. C43H44Cl2O2P2PdS
requires C, 59.8; H, 5.1%). νmax(SO2)/cmϪ1 1182 and 1033.
δP (C6D6) 20.5 (s). FAB-MSϩ: m/z 1240, 881, 811, 713 {[Pd-
(PBz3)2]ϩ}, 501, 409 {[Pd(PBz3)]ϩ} and 321.
5.0%. νmax/cmϪ1 1606 (C᎐O), 1195 (SO ) and 1054 (SO ).
᎐
2
2
δP [(CD3)2CO] 2.8 (s). FAB-MSϩ: m/z 1120 {[M]ϩ}, 822
{[Pd2(PBz3)2]ϩ} and 731 {[Pd2(PBz3)(PBz2)]ϩ}.
[Pd3(ꢀ-SO2)3(PBz3)3] 2. A mixture of [Pd2(dba)3]ؒC6H6 (300
mg, 0.30 mmol) and PBz3 (184 mg, 0.60 mmol) in 20 cm3 tolu-
ene was stirred for 30 min followed by the addition of SO2 gas
(ca. 10 min) whereupon the solution changed from deep purple
to red. The mixture was stirred under an atmosphere of SO2 for
30 min to ensure completion of the reaction, then was filtered
under an atmosphere of SO2 and an SO2-degassed ethanol
(30 cm3) layer was added. The mixture was kept under SO2 and
cooled slowly to –25 ЊC, whereupon dark red-purple crystals of
[Pd3(µ-SO2)3(PBz3)3] separated. Yield 240 mg (84%). Crystals
suitable for a single crystal X-ray analysis were grown from a
toluene–ethanol mixture under an atmosphere of SO2. Found:
[Pd3(ꢀ-CO)2(ꢀ-SO2)(PBz3)3] 5. Carbon monoxide was
bubbled through a solution of [Pd2(µ-SO2)(µ-dba)(PBz3)2] (150
mg, 0.13 mmol) in THF (20 cm3) with stirring, and an immedi-
ate change to red was observed. After 5 min the solvent was
removed under reduced pressure and the 31P-{1H} NMR spec-
trum recorded, showing a mixture of compounds 5 and 6. The
crude solid was dissolved in toluene and CO passed through
the solution at 50 ЊC for 30 min. The solvent was removed
under reduced pressure and the crude solid recrystallised from
THF–hexane. Yield 93 mg (77%). Found: C, 58.4; H, 4.88.
C65H63O4P3Pd3SؒC4H8O requires C, 58.2; H, 5.02%. νmax/cmϪ1
1911s (CO), 1857vs (CO), 1187s (SO2) and 1056vs (SO2).
δP (C6D6) 15.5 (t, 1P, 3JPP = 41) and 9.6 (d, 2P, 3JPP = 41 Hz). For
6: δP (C6D6) 16.5 (d, 2P, 3JPP = 52) and 8.8 (t, 1P, 3JPP = 52 Hz).
C, 52.6; H, 4.3. C21H21O2PPdS requires C, 53.1; H, 4.5%). νmax
/
cmϪ1 1244 (SO2) and 1067 (SO2). δP (C6D6) 19.3 (s).
[Pd2(ꢀ-SO2)(ꢀ-Ph2PCH2PPh2)(PBz3)2] 3. To a benzene (20
cm3) solution of [Pd2(µ-SO2)(µ-dba)(PBz3)2] (100 mg, 0.09
mmol) a benzene solution (20 cm3) containing bis(diphenyl-
phosphino)methane (34 mg, 0.09 mmol) was added. The
orange–yellow solution immediately changed to a brighter yel-
low. After 1 h the solvent was removed under reduced pressure
and the residue washed with five 20 cm3 portions of methanol
to remove the dba. Yellow crystals suitable for a single-crystal
X-ray analysis were obtained on recrystallisation from a
benzene–methanol mixture and cooling slowly to 4 ЊC. Yield
103 mg (86%). Found: C, 61.5; H, 5.0 for the solid obtained
before recrystallisation. C67H64O2P4Pd2Sؒ2MeOH requires C,
62.1; H, 5.4%. νmax(SO2)/cmϪ1 1147 and 1025. δP (C6D6) 22.2
(t, J = 10, 2P) and 7.7 (t, J = 10 Hz, 2P). FAB-MSϩ: m/z 1272
{[Pd2(SO2)(Ph2PCH2PPh2)(PBz3)2]ϩ}, 1207 {[Pd2(Ph2PCH2-
PPh2)(PBz3)2]ϩ}, 1113 {[Pd2(Ph2PCH2PPh2)(PBz3)(PBz2)]ϩ}
and 902 {[Pd2(Ph2PCH2PPh2)(PBz3)]ϩ}.
[Pd3(ꢀ-SO2)2(CNBut)2(PBz3)3] 7. tert-Butyl isocyanide (30
mg, 0.36 mmol) in toluene (15 cm3) was added to a SO2
saturated solution of [Pd2(µ-SO2)(µ-dba)(PBz3)2] (200 mg, 0.18
mmol) in toluene (40 cm3). An instant change to yellow was
observed. After stirring the mixture for 30 min under an atmos-
phere of SO2, all of the solvent was removed under reduced
pressure and diethyl ether added to the remaining oil to obtain
a solid. The diethyl ether was removed by filtration and several
washings with cold methanol portions were needed to remove
the free dba. Crystals of [Pd3(µ-SO2)2(CNBut)2(PBz3)3]ؒ0.5H2O
were obtained by dissolving the complex in benzene and adding
an equal quantity of methanol, followed by slow evaporation of
benzene under an air atmosphere at room temperature. Yield
149 mg (79%). Found: C, 55.7; H, 4.7. C73H81N2O4P3Pd3S2ؒ
2H2O requires C, 56.1; H, 5.5%). νmax/cmϪ1 2175 (NC), 2148
3
(NC), 1160 (SO2) and 1012 (SO2). δP (C6D6) 11.7 (d, 2P, JPP
=
34) and 2.3 (t, 1P, 3JPP = 34 Hz).
[Pd(SO2)(PBz3)2] 4. The compound PBz3 (54 mg, 0.18 mmol)
was added directly to a solution of 100 mg (0.09 mmol) [Pd2(µ-
SO2)(µ-dba)(PBz3)2] in 20 cm3 THF with stirring. The phos-
phine dissolved and reacted in a few seconds to give a ruby-red
solution. Sulfur dioxide gas was then bubbled through the
solution for 10 min upon which it changed to orange and the
Crystallography
X-Ray data were collected on a Siemens P4 four-circle diffract-
ometer for compounds 2, 3, 4 and 7 and on an Enraf-Nonius
J. Chem. Soc., Dalton Trans., 1999, 3981–3988
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380; (c) C. Amatore, A. Jutand, F. Khalil, M. A. M’Barki and
CAD4 diffractometer for 5. Details of data collection, refine-
ment and crystal data are listed in Table 7. Lorentz-polarisation
and absorption corrections were applied to the data of all
compounds.
L. Mottier, Organometallics, 1993, 12, 3168 and refs. therein.
3 W. A. Herrmann, W. R. Thiel, C. Broßmer, K. Öfele, T. Priermeier
and W. Scherer, J. Organomet. Chem., 1993, 461, 51.
4 J. Fawcett, R. D. W. Kemmitt, D. R. Russell and O. Serindag,
J. Organomet. Chem., 1995, 486, 171.
Structure solution and refinement. For all compounds the
positions of the metals and most of the non-hydrogen atoms
were located using direct methods. The remaining non-
hydrogen atoms, in all cases, were revealed from subsequent
Fourier-difference syntheses. Refinement was based on F 2.23
The carbon atom on one methanol solvate in 3 was disordered
and resolved into two components of 0.75:0.25 site occupancy.
Chemically equivalent bonds within the ligands in compounds
2, 3, 4 and 7 were constrained to be equal within e.s.d.s of
0.01–0.05 in the refinement. The phenyl rings in 7 were refined
as rigid hexagons and for, all compounds, hydrogen atoms
(except those on the methanol oxygen atom in 3) were placed
in calculated positions with displacement parameters equal
to 1.2Ueq and 1.5Ueq of the parent carbon atoms for phenyl and
methyl hydrogen atoms respectively. Semi-empirical absorption
correction using ψ scans were applied to the data of 3 and,
after initial refinement with isotropic displacement parameters,
empirical absorption corrections24 were applied to the data of
2, 4 and 7. All non-hydrogen atoms were assigned anisotropic
displacement parameters in the final cycles of full-matrix least-
squares refinement.
5 C. Amatore and A. Jutand, Coord. Chem. Rev., 1998, 178–180, 511;
C. Amatore, G. Broeker, A. Jutand and F. Khalil, J. Am. Chem.
Soc., 1997, 119, 5176.
6 (a) A. D. Burrows, N. Choi, M. McPartlin, D. M. P. Mingos,
S. V. Tarlton and R. Vilar, J. Organomet. Chem., 1999, 573, 313;
(b) S. V. Tarlton, N. Choi, M. McPartlin, D. M. P. Mingos and
R. Vilar, J. Chem. Soc., Dalton Trans., 1999, 653.
7 A. D. Burrows and D. M. P. Mingos, Transition Met. Chem., 1993,
18, 129.
8 S. G. Bott, M. F. Hallam, O. J. Ezomo, D. M. P. Mingos and
I. D. Williams, J. Chem. Soc., Dalton Trans., 1988, 1461.
9 O. Heyke, C. Maichle, R. Hübener and I.-P. Lorenz, Z. Anorg. Allg.
Chem., 1993, 619, 1793; D. C. Moody and R. R. Ryan, Inorg. Chem.,
1977, 16, 1052.
10 M. F. Hallan, N. D. Howells, D. M. P. Mingos and R. W. N. Wardle,
J. Chem. Soc., Dalton Trans., 1985, 845.
11 Y. W. Yared, S. L. Miles, R. Bau and C. A. Reed, J. Am. Chem. Soc.,
1977, 99, 7076.
12 W. Lin, S. R. Wilson and G. S. Girolami, Inorg. Chem., 1994, 33,
2265; R. Vilar, D. M. P. Mingos and C. J. Cardin, J. Chem. Soc.,
Dalton Trans., 1996, 4313.
13 (a) R. G. Holloway, B. R. Penfold, R. Colton and M. J. McCormick,
J. Chem. Soc., Chem. Commun., 1976, 485; (b) C.-L. Lee, Y.-P. Yong,
S. J. Rettig, B. R. James, D. A. Nelson and M. A. Lilga, Organo-
metallics, 1986, 5, 2220.
14 R. U. Kirss and R. Eisenberg, Inorg. Chem., 1989, 28, 3372.
15 R. Usón, J. Forniés, J. F. Sanz, M. A. Usón, I. Usón and S. Herrero,
Inorg. Chem., 1997, 36, 1912.
For crystal 4 relatively high anisotropy in the displacement
parameters indicates some rotation disorder of the phenyl rings
but it was not possible to resolve this; the crystal diffracted
relatively poorly at high angle and data in the limited θ range
1.06 to 21Њ were used in the refinement.
CCDC reference number 186/1655.
See http://www.rsc.org/suppdata/dt/1999/3981/ for crystallo-
graphic files in .cif format.
16 J. M. Ritchey, D. C. Moody and R. R. Ryan, Inorg. Chem., 1983, 22,
2276.
17 J. J. Levison and S. D. Robinson, Chem. Commun., 1967, 198;
J. Chem. Soc., Chem. Commun., 1972, 2013; P. Zdunneck, A.
Häusler and E. Wenschuh, Z. Chem., 1986, 26, 302.
18 G. J. Kubas, Acc. Chem. Res., 1994, 27, 183.
19 T. Hoffmann, B. Ziemer, C. Mügge, U. Bertholdt, E. Wenschuh and
P. Leibnitz, Z. Anorg. Allg. Chem., 1991, 600, 55.
20 S. Otsuka, Y. Tatsuno, M. Miki, T. Aoki, M. Matsumoto, H.
Yoshioka and K. Nakatsu, J. Chem. Soc., Chem. Commun., 1973,
445.
Acknowledgements
We thank EPSRC for financial support, BP plc for endowing
D. M. P. M.’s chair and Dr Chris Hill for the crystal structure
of compound 5.
21 A. D. Burrows and D. M. P. Mingos, Coord. Chem. Rev., 1996, 154,
19.
22 A. D. Burrows, J. C. Machell, D. M. P. Mingos and H. R. Powell,
J. Chem. Soc., Dalton Trans., 1992, 1521.
23 T. Ukai, H. Kawazura, Y. Ishii, J. J. Bonnet and J. A. Ibers,
J. Organomet. Chem., 1974, 65, 253.
24 SHELTXL (PC version 5.03), Siemens Analytical Instruments Inc.,
Madison, WI, 1994.
References
1 R. F. Heck, Palladium Reagents in Organic Synthesis, Academic
Press, London, 1985; J. Tsuji, Palladium Reagents and Catalysts:
Innovation in Organic Synthesis, Wiley, Chichester, 1995.
2 Some examples are: (a) Y. Inoue, T. Hibi, M. Satake and H.
Hashimoto, J. Chem. Soc., Chem. Commun., 1979, 982; (b) J.
Andrieu, P. Braunstein and A. D. Burrows, J. Chem. Res. (S), 1993,
Paper 9/06444C
3988
J. Chem. Soc., Dalton Trans., 1999, 3981–3988