Mono- and polynuclear complexes from the reaction of palladium acetate with α-substituted thioethers and thiols

Article abstract of DOI:10.1016/S0022-328X(98)00910-3

Palladium acetate reacts with α-substituted thioethers (RSCH(R′)Z; Z=ester, ketone, sulphone, substituted methyl) and the thiol HSCH₂C(O)Me to give complexes whose composition and nuclearity depend mainly on the electronic properties of the sulphur ligand. If it contains sufficiently acidic hydrogen atoms, the acetato group is partially or totally removed as acetic acid to give complexes of the type [Pd₃(μ-O₂CMe)₃(μ-RSCR′Z) ₃] and [Pd(SCH₂C(O)Me)₂]₆. The stability of the trimers decreases with the steric hindrance of the substituents at the sulphur and at the methine carbon atoms. Stable mixed sphere complexes are obtained also with carboxylato ligands different from acetato as PhCOO^- and MeSCH₂COO^-. When the substituted thioether has poor electronwithdrawing groups, its reaction with palladium acetate affords complexes of the type [Pd(η¹-OAc)₂(RSCH₂Z)₂], in which the sulphur donor atom has simply replaced one oxygen atom of the acetato ligand.

Full text of DOI:10.1016/S0022-328X(98)00910-3

Journal of Organometallic Chemistry 571 (1998) 115–121
Mono- and polynuclear complexes from the reaction of palladium
acetate with h-substituted thioethers and thiols
Marino Basato *, Diego Tommasi, Marco Zecca
Centro di Studio sulla Stabilit a` e Reatti6it a` dei Composti di Coordinazione, CNR, Dipartimento di Chimica Inorganica, Metallorganica e Analitica,
Uni6ersit a` di Pado6a, 6ia Marzolo 1, I-35131 Pado6a, Italy
Received 18 June 1998
Abstract
Palladium acetate reacts with h-substituted thioethers (RSCH(R%)Z; Z=ester, ketone, sulphone, substituted methyl) and the
thiol HSCH C(O)Me to give complexes whose composition and nuclearity depend mainly on the electronic properties of the
2
sulphur ligand. If it contains sufficiently acidic hydrogen atoms, the acetato group is partially or totally removed as acetic acid
to give complexes of the type [Pd (v-O CMe) (v-RSCR%Z) ] and [Pd(SCH C(O)Me) ] . The stability of the trimers decreases with
3
2
3
3
2
2 6
the steric hindrance of the substituents at the sulphur and at the methine carbon atoms. Stable mixed sphere complexes are
−
−
obtained also with carboxylato ligands different from acetato as PhCOO and MeSCH COO . When the substituted thioether
2
1
has poor electronwithdrawing groups, its reaction with palladium acetate affords complexes of the type [Pd(p -OAc) (RSCH Z) ],
2
2
2
in which the sulphur donor atom has simply replaced one oxygen atom of the acetato ligand. © 1998 Elsevier Science S.A. All
rights reserved.
Keywords: Palladium complexes; Sulphur ligand; i-Oxothioethers; Thiolate
1
. Introduction
below, which represents the first example of the coordi-
nation compound of Pd(II) maintaining the trimeric
structure of the starting salt (R=Me; X=C(O)OEt)
Hybrid ligands based on substituted carbonyls are
[3,4] (Scheme 1).
well known; in most cases the additional donor group is
a phosphine, which combines the soft character of its
phosphorus atom with the hard character of the keto
oxygen [1]. Nickel and palladium complexes based on
these O,P ligands are very numerous and some of them
find interesting applications in the activation of carbon
dioxide and as catalysts in the oligomerization of
olefins (SHOP process) [2]. The simple idea at the
beginning of this research was to extend this type of
chemistry to a different donor atom like sulphur and
The formation of [Pd (v-OAc) (v-MeSCHC(O)-
3
3
OEt) ] has several interesting aspects: (i) the sulphur
3
ligand is able to protonate the acetato in the exchange
the first ligand investigated was MeSCH C(O)OEt.
2
Its reaction with palladium acetate in ethanol af-
forded the mixed-sphere palladium complex illustrated
*
Corresponding author. Fax: +39 49 8275223; e-mail:
basato@chim02.unipd.it
Scheme 1.
0022-328X/98/$ - see front matter © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00910-3

116
M. Basato et al. / Journal of Organometallic Chemistry 571 (1998) 115–121
reaction despite its lower acidity (pK ca. 23); (ii) only
and sodium ethoxyde [5]. HSCH C(O)Me was obtained
a
2
half of the acetato groups are substituted; (iii) the
anionic sulphur ligand is coordinated through the car-
bon and sulphur atoms and not as an O,S chelate; (iv)
the carbon and sulphur atoms of the three bridging
ligands have the same configuration and define
R,R,R,R,R,R or S,S,S,S,S,S surfaces.
from NaHS and ClCH C(O)Me in water at 0°C and
stored at a low temperature [6].
2
2.2.2. MeSCH C(O)OMenthyl(-)
2
This new chiral ester was synthesised by reacting
(
1R,2S,5R)-(-)-menthol with MeSCH C(O)Cl. To a so-
2
It seemed interesting to verify how the nature of the
substituents (both at the sulphur atom and at the
methylene group) and the type of bridging carboxylato
would affect the synthesis and the stability of the
mixed-sphere trinuclear complexes. Therefore, we re-
port here on: (i) the reaction of palladium acetate with
a series of h-substituted thioethers of the type
3
lution of MeSCH C(O)OH (3.50 cm , 4.27 g, 40.2
mmol) in 20 cm of benzene, (COCl) (3.44 cm , 5.00 g,
2
3
3
2
3
9.4 mmol) was added dropwise. The mixture was kept
at reflux for 3 h and treated directly, at 0 °C, with
3
menthol (6.14 g, 39.3 mmol) and pyridine (5 cm , 4.89
g, 61.8 mmol). A white precipitate of pyridinium chlo-
ride was filtered off and the product was obtained as a
pale yellow oil which distillates at 80°C and 0.3 mmHg.
The infrared spectrum is characterised by the strong
t
RSCH(R%)Z (R=Me, Et, Bu; R%=H, Me; Z=
C(O)OMenthyl(-), C(O)Me, S(O) Ph, CH C(O)OMe,
2
2
CH(OMe) ) and with the thiol HSCH C(O)Me; (ii) the
2
2
−
1
absorption at 1710 cm
of the carbonyl stretching.
synthesis of trinuclear mixed-sphere palladium com-
1
(1)
(2)
(3)
H-NMR (in CDCl , menthyl=CH CH [CH -
3
plexes [Pd (v-O CR) (v-MeSCHC(O)OR%) ] (R=Ph,
3
2
3
3
(
4,5)
(6)
2 2 3 2
(7)
(8)
(9)
(10)
(
CH3)2 ]CH CH CH (CH )CH ): l=(predomi-
CH SMe) with bridging carboxylato groups different
2
nant keto form, ca. 85%) 0.73, 0.81, 0.86, 0.94, 1.1-2.0,
from acetato.
2
1
2
.20 (s, 3H, CH S), 3.18 (s, 2H, CH S), 4.70, 4.74 (2t,
3 2
H, (1)); (minor enolic form, ca. 15%) menthyl group+
13
.22 (s, CH S), 3.22 (s, CHS), 5.92 (s, OH). C-NMR
2. Experimental
3
(
in CDCl ): l=(predominant keto form) 16.2 (4 and
3
2.1. Reagents and apparatus
CH S), 20.7 (5), 22.0 (9), 23.3 (6), 26.1 (3), 31.4 (8),
3
3
4.2 (7), 36.0 (CH S), 40.8 (10), 47.0 (2), 75.2 (1), 169.9
2
The reagents (Aldrich-Chemie) were high purity
(C(O)); (minor enolic form) menthyl group+35.5
(CHS), 75.7, 77.1 and 78.6 (1), 174.2 (COH).
products and generally used as received. Solvents were
dried before use and the reaction apparatus carefully
deoxygenated. Reactions were performed under argon
at room temperature and all operations were carried
2.3. Synthesis of the complexes
1
out under an inert atmosphere. The solution H- and
2
.3.1. Synthesis of the mixed sphere acetato complexes
1
3
1
C{ H}-NMR spectra were recorded on a Jeol FX90Q
or on a Bruker AM 250 spectrometer using te-
[
Pd (v-O CMe) (v-MeSCHZ) ] 1–6
3
2
3
3
Complexes 1–6 were obtained by reaction of palla-
13
tramethylsilane as an internal standard. C CP/MAS
dium acetate (typically 1 mmol) with the appropriate
measurements were performed on the Bruker instru-
3
thioether in a 1/1 molar ratio, in ethanol (20 cm ).
13
ment (operating at 62.89 MHz for C), according to
the procedure described previously [4]. Crystalline
polyethylene was used as an external reference and the
chemical shifts were determined with reference to te-
tramethylsilane, assuming the methylene carbon atoms
of polyethylene to resonate at 33.6 ppm. The FT-IR
spectra were recorded on a Biorad FT S7 PC spec-
2
.3.1.1. [Pd (v-O CMe) (v-MeSCHC(O)OMenthyl) ] 1.
3
2
3
3
After 5 h, traces of palladium metal were filtered off,
the solution was reduced to a small volume and treated
with hexane+ether. The solid was recovered upon
filtration and washed with hexane (0.15 g, yield 30%).
Elemental analysis, Calc. for C H O PdS (F =
−
1
15 25
4
w
trophotometer at 2 cm
resolution in KBr disks.
4
6
08.85): C, 44.18; H, 6.18; S, 7.86; found: C, 44.56; H,
Molecular weight measurements were carried out with a
Knauer Vapour Pressure Osmometer and XPS analyses
with a Perkin Elmer F 5600ci instrument.
.36; S, 8.74. The sample always contains small
1
amounts of free ester. H-NMR (in CDCl ): l=0.70–
3
1
3
4
1
.03 (protons of the menthyl group), 1.91 and 2.02 (s,
H, CH C(O)O), 2.39 and 2.45 (s, 3H, CH S), 3.97 and
2.2. Synthesis of the ligands
3
3
13
.01 (s, 1H, CH). C-NMR (in CDCl ): l=15.8 and
6.6 (4), 20.9 and 21.1 (5), 22.7 (9), 23.5, 23.7, 23.9 and
3
2
.2.1. MeSCH C(O)Me, EtSCH C(O)Me,
2
2
(
Me) CSCH C(O)Me
24.1 (CH C(O)O and CH S), 24.8 and 25.2 (CH), 25.7
3 3
3
2
They were prepared by reaction in ethanol of
and 26.4 (3), 31.4 (8), 34.0 (7), 41.1 and 41.3 (10), 47.4
and 48.1 (2), 74.2 and 74.6 (1), 170.6 and 171.0
(C(O)OMenthyl), 182.7 and 183.0 (MeC(O)O). FT-IR:
ClCH C(O)Me with the sodium salt RSNa, either com-
2
mercially available or prepared in situ from the thiol

M. Basato et al. / Journal of Organometallic Chemistry 571 (1998) 115–121
117
−
1
1
cm
701 cm
(CꢀO stretching, ester), 1551 and 1418
pound is rather unstable and prolonged reaction times
afforded solids containing remarkable amounts of ni-
trogen. One sample had: C, 22.93; H, 2.19; N, 1.49; S,
13.72 and molar ratios, determined by XPS: Pd(II) 1;
−
1
(acetate).
2
2
.3.1.2. [Pd (v-O CMe) (v-MeSCHC(O)Me) ] 2. After
4 h, traces of palladium metal were filtered off, the
3
2
3
3
13
Pd(0) 0.28; S, 1.48; N, 0.28. C-NMR (solid state):
solution was reduced to a small volume and treated
with ether. The yellow solid was recovered upon filtra-
tion and dried under vacuum (0.20 g, yield 68%).
Elemental analysis, Calc. for C H O Pd S (M =
l=25.0 (CH S, CH C(O)O, CH), 130.1 (Ph), 184.0
3
3
−
1
(MeC(O)O). FT-IR: 1552 and 1401 cm
(acetate),
−
1
1298 and 1151 cm
(OꢀSꢀO).
1
8
30
9
3
3
w
805.81, determined in DCE at 50°C=787): C, 26.83; H,
2.3.1.6. [Pd (v-O CMe) (v-MeSC(Me)C(O)Me) ] 6. Af-
3
2
3
3
3
.75; S, 11.94; found: C, 26.21; H, 3.74; S, 11.59.
ter 30 min palladium metal was filtered off, the solution
was reduced to a small volume and treated with ether.
The brown solid was filtered and washed with ether
(0.33 g, yield 90%). Elemental analysis, Calc. for
C H O PdS (F =272.89): C, 29.74; H, 4.28; S, 11.34;
1
H-NMR (in CDCl ): l=2.03 and 2.18 (2s, 3H+3H,
CH S and CH C(O)O), 2.31 (s, 3H, CH C(O)), 4.00 (s,
1
3
3
3
3
1
3
H, CH). C-NMR (in CDCl ): l=23.4 and 24.1
3
(
CH C(O)O and CH S), 30.2 (CH C(O)), 36.7 (CH),
3
3
3
7
12
3
w
−
−
1
1
1
81.6 (MeC(O)O), 200.6 (MeC(O)). FT-IR: 1665 cm
found: C, 30.32; H, 4.33; S, 13.18. Also in this case
samples were often contaminated by the presence of
(
(
CꢀO stretching, carbonyl), 1557 and 1414 cm
acetate).
13
nitrogen and of palladium(0). C-NMR (solid state):
l=13.3 and 16.0 (C(CH )), 25.8 (CH S, CH C(O)O),
3
3
3
2
2
.3.1.3. [Pd (v-O CMe) (v-EtSCHC(O)Me) ] 3. After
4 h, traces of palladium metal were filtered off, the
37.5 (CH C(O)), 42.3 and 48.7 (CMe), 181.8
3
2
3
3
3
−
1
(MeC(O)O), 205.6 (MeC(O)). FT-IR: 1688 cm
(CꢀO
−
1
solution was reduced to a small volume and treated
with ether. The yellow–brown solid was recovered
upon filtration and washed with ether (0.36 g, yield
8
2
4
stretching, carbonyl), 1559 and 1428 cm
(acetate).
2.3.2. Synthesis of the carboxylato complexes
[Pd (v-O CR) (v-MeSCHC(O)OR%) ]
7%). Elemental analysis, Calc. for C H O PdS (F =
7 12 3 w
3
2
3
3
80.89): C, 29.75; H, 4.30; S, 11.34; found: C, 29.15; H,
1
.21; S, 11.34. H-NMR (in CDCl ): l=1.23 (t, 3H,
2.3.2.1. [Pd (v-O CPh) (v-MeSCHC(O)OEt) ] 7. To a
3
3
2
3
3
CH CH ), 2.17 (s, 3H, CH C(O)O), 2.31 (s, 3H,
suspension of palladium benzoate [7] (0.23 g, 0.66
3
2
3
13
3
CH C(O)), 2.33 (q, 2H, CH ), 4.04 (s, 1H, CH). C-
mmol) in 15 cm of ethanol, MeSCH C(O)OEt (0.11
3
2
2
3
NMR (in CDCl3): l=13.3 (CH CH ), 24.1
cm , 0.11 g, 0.80 mmol) was added. After 2 h the yellow
3
2
(
1
CH C(O)O), 29.9 (CH C(O)), 33.3 (CH ), 34.3 (CH),
81.3 (MeC(O)O), 200.8 (MeC(O)). FT-IR: 1671 cm
complex was filtered and dried under vacuum (0.18 g,
3
3
2
−
−
1
1
yield
76%).
Elemental
analysis,
Calc.
for
(
(
CꢀO stretching, carbonyl), 1554 and 1414 cm
acetate).
C H O Pd S (M =1082.16, determined in DCE at
36
42 12
3
3
w
50°C=1040): C, 39.42; H, 3.90; S, 8.90; found: C,
1
4
0.31; H, 3.88; S, 9.18. H-NMR (in CDCl ): l=1.26
3
2
.3.1.4. [Pd (v-O CMe) (v-(Me) CSCHC(O)Me) ] 4.
(t, 3H, CH CH ), 2.23 (s, 3H, CH S), 3.87 (s, 1H, CH),
4.1 (cm, 2H, CH CH ), 7.2–8.1 (Ph). C-NMR (in
3 2
3
2
3
3
3
3 2 3
13
After 6 h, traces of palladium metal were filtered off,
the solution was reduced to a small volume, treated
with ether and cooled in an ice bath. The orange solid
was filtered rapidly and washed with cold ether (0.20 g,
yield 58%). Elemental analysis, Calc. for C H O PdS
CDCl ): l=14.4 (CH CH ), 24.6 (CH S), 25.8 (CH),
3
3
2
3
61.4 (CH CH ), 127.6–134.2 (Ph), 172.3 (C(O)OEt)
3
2
−
1
and 180.9 (PhC(O)O). FT-IR: 1707 cm
stretching, ester), 1543 and 1397 cm
(CꢀO
−
1
(benzoate).
9
16
3
(
3
F =311.06): C, 34.79; H, 5.19; S, 10.32; found: C,
w
1
5.79; H, 5.37; S, 10.93. H-NMR (in CDCl ): l (most
2.3.2.2. [Pd (v-O CCH SMe) (v-MeSCHC(O)OMe) ]
3 2 2 3 3
3
significant peaks)=1.57 (s, CH C), 2.01 and ca. 2.2 (2s,
8. [Pd (v-O CMe) (v-MeSCHC(O)OMe) ] (0.25 g, 0.29
mmol) [8] was suspended in 15 cm of ethanol and
3
3
2
3
3
13
3
CH C(O) and CH C(O)O), ca. 4.5 (s, CH). C-NMR
3
3
(
3
5
in CDCl ): l=23.3, 23.8, 23.9 (CH C(O)O), 29.1,
treated with MeSCH COOH (80 ml, 0.92 mmol). After
3
3
2
0.0, 30.8, 31.5 (CH C and CH C(O)), ca. 35 (CH),
1 h the yellow–greenish precipitate was filtered and
recrystallised from dichloromethane+ether (0.23 g,
yield 80%). Elemental analysis, Calc. for C H O PdS
3
3
1.7 (Me C), 180.4 (MeC(O)O), 199.1, 202.9, 205.6
3
−
1
(
MeC(O)). FT-IR: 1681 cm
(C=O stretching, car-
(acetate).
7
12
4
2
−
1
bonyl), 1552 and 1401 cm
(F =330.69): C, 25.42; H, 3.66; S, 19.39; found: C,
w
1
2
5.09; H, 3.58; S, 19.04. H-NMR (in CDCl ): l=2.31
3
2
.3.1.5. [Pd (v-O CMe) (v-MeSCHS(O) Ph) ] 5. After
and 2.45 (s, ca. 3H, CH SCH ), 2.66 (s, 3H, CH S),
3
2
3
2
3
3 2 3
3
5 min, the red solid was filtered and washed with
3.44 and ca. 3.60 (s, ca. 2H, CH SCH ), 3.75 (s, 4H,
3 2
13
ethanol (0.40 g, yield 91%). Elemental analysis, Calc.
CH O and CH). C-NMR (in CDCl ): l=21.1, 22.4,
3
3
for C H O PdS (F =367.76): C, 32.75; H, 3.29; S,
24.5, 26.4 and 26.7 (CH SCH , CH and CH S), 41.2,
3 2 3
1
0
12
4
2
w
17.48; found: C, 32.15; H, 3.10; S, 19.70. The com-
42.2, 42.9 (CH SCH ), 52.4 (CH O), 171.9, 172.9, 173.2
3 2 3

118
M. Basato et al. / Journal of Organometallic Chemistry 571 (1998) 115–121
(
C(O)OMe) and 175.7, 176.1, 176.6 (CH C(O)O). FT-
3. Results and discussion
2
−
1
IR: 1697 cm
cm
(CꢀO stretching, ester), 1614 and 1429
−
1
(carboxylate).
The type of palladium complexes resulting from the
reaction of palladium acetate with h-substituted
2.3.3. Synthesis of the complexes
thioethers RSCH Z mainly depends on the presence of
2
[
Pd(O CMe) (MeSCH Z) ]
acidic sites, on their relative strength and on the elec-
tronwithdrawing properties of Z.
2
2
2
2
2
.3.3.1. [Pd(O CMe) (MeSCH CH C(O)OMe) ] 9. To a
The reaction with thioethers having in h one ester,
ketonic or sulphonyl substituent proceeds with ex-
change of half of the acetate ligands, according to Eq.
(1).
2
2
2
2
2
suspension of palladium acetate (0.31 g, 1.4 mmol) in
2
0
3
3
0 cm of ethanol, MeSCH CH C(O)OMe (0.35 cm ,
2 2
.38 g, 2.8 mmol) was added slowly. After 24 h traces
of palladium were filtered off, the solution reduced of
volume and treated with ether. The resulting light
brown solid was filtered and washed with ether (0.56 g,
yield 82%). Elemental analysis, Calc. for C H O PdS
[
Pd (v-OAc) ]+3RSCH Z
3 6 2
“[Pd (v-OAc) (v-RSCHZ) ] (1–5)+3HOAc
(1)
3
3
3
1
4
26
8
2
1
: R=Me, Z=C(O)OMenthyl(-); 2: R=Me, Z=
(
3
M =491.25): C, 34.11; H, 5.31; S, 13.01; found: C,
w
1
C(O)Me; 3: R=Et, Z=C(O)Me; 4: R=Me C, Z=
C(O)Me; 5: R=Me, Z=S(O) Ph.
3
4.08; H, 5.32; S, 13.42. H-NMR (in CDCl ): l=1.87
3
2
(
4
s, 3H, CH C(O)O), 2.20 (s, 3H, CH S), 2.85 (s broad,
3
3
1
3
The same type of complex is obtained when a
H, CH CH ), 3.66 (s, 3H, CH O). C-NMR (in
2 2 3
methylene hydrogen is substituted by a methyl group
(
CDCl ): l=18.7 (CH C(O)O), 22.5 (CH S), 31.9
3
3
3
[Pd (v-O CMe) (v-MeSCMeC(O)Me) ] (6)).
3
2
3
3
(
CH CH ), 51.6 (CH O), 170.9 (C(O)OMe) and 177.3
2 2 3
−
1
In all cases the FT-IR spectroscopic data indicate
(
MeC(O)O). FT-IR: 1736 cm (CꢀO stretching, ester),
−
1
that the carbonyl or sulphonyl group is not directly
bonded to the metal atom (the stretching bands of such
groups present only slight shifts in wavenumbers with
respect to the free ligands, if any) and disclose the
presence of the acetato ligands (asymmetric and sym-
1
574 and 1408 cm
(acetate).
2
.3.3.2. [Pd(O CMe) (MeSCH CH(OMe) ) ] 10. To a
2
2
2
2 2
suspension of palladium acetate (0.40 g, 1.8 mmol) in
3
3
2
0 cm of ethanol, MeSCH CH(OMe) (0.48 cm , 0.49
2 2
−
1
metric stretching at 1551–1559 and 1412–1428 cm
respectively).
,
g, 3.6 mmol) was added slowly. After 4 h traces of
palladium were filtered off, the solution was reduced to
a small volume and treated with ether+hexane. The
resulting brown solid was filtered and dried under
vacuum (0.63 g, yield 70%). Elemental analysis, Calc.
for C H O PdS (M =496.85): C, 33.84; H, 6.09; S,
The trimeric nature of complexes 1–6 is suggested by
the close analogy of their physico-chemical properties
with those of [Pd (v-O CMe) (v-MeSCHC(O)OEt) ],
3
2
3
3
whose structure was determined by X-ray analysis, and
for 2 also by osmometric measurement of the molecular
weight [3].
The yield and stability of the isolated complexes
markedly depend on the nature of the ligand and
generally increase in the order h-sulphonylthioether
1
4
30
8
2
w
1
1
2.90; found: C, 31.53; H, 5.52; S, 12.21. H-NMR (in
CDCl ): l=1.79 (s, 3H, CH C(O)O), 2.16 (s, 3H,
3
3
CH S), 2.75 (d, 2H, CH ), 3.28 (s, 6H, CH O), 4.67 (t,
3
2
3
1
3
1
H, CH).
C-NMR (in CDCl3):
l
=19.8
(
CH C(O)O), 22.8 (CH S), 39.0 (CH ), 54.1 (CH O),
3 3 2 3
(
Z=S(O) Ph)Bi-ketothioether
(Z=C(O)Me)Bh-
1
1
02.6 (CH) and 177.7 (MeC(O)O). FT-IR: 1568 and
2
−
1
alkylcarboxythioether (Z=C(O)OEt). In the i-ketoth-
ioether complexes, both the carbon (34.3–36.7 ppm)
and proton (4.00–4.50 ppm) resonances of the coordi-
nated methine moiety are observed downfield with re-
spect to the more stable products (24.8–25.2 ( C) and
3.62–4.01 ( H) ppm). This is probably due to a lower p
408 cm
(acetate).
2
.3.4. Synthesis of [Pd(v-SCH C(O)Me) ] 11
2
2 6
To a suspension of palladium acetate (0.29 g, 1.3
3
13
mmol) in 20 cm of ethanol, thermostatted at 0°C,
1
HSCH C(O)Me (0.30 g, 2.6 mmol) was added slowly.
2
After 1 h the yellow precipitate was filtered, washed
with ethanol and dried under vacuum (0.34 g, yield
character of the carbon orbitals employed in the Pd–C
bond which consequently results to be weaker. Also,
increasing bulkiness of the sulphur ligand decreases the
stability of the complex. Thus, complexes 1 (Z=
9
2%). Elemental analysis, Calc. for C H O Pd S
36 60 12 6 12
(
M =1707.96, determined in DCE at 50°C=1553): C,
w
2
2
5.32; H, 3.54; S, 22.52; found: C, 25.18; H, 3.33; S,
C(O)OMenthyl(-)), 4 (R=Me C) and 6 do not seem
3
1
2.66. H-NMR (in CDCl ): l=2.12, 2.16, 2.18, 2.52
particularly stable and tend to evolve in solution.
The menthyl substituent is a very hindering lipophilic
group which makes the complex [Pd (v-O CMe) (v-
3
(
4s, 3H, CH ), 3.24, 3.28, 3.40, 3.48 (4s, 2H, CH ).
3
2
1
3
C-NMR (in CDCl ): l=29.0, 29.1, 29.6 (CH ), 39.6,
3
3
3
2
3
4
0.1, 44.3 (CH ), 202.7, 203.0, 203.4, 203.8 (C(O)Me).
MeSCHC(O)OMenthyl) ] very difficult to purify, be-
cause of its extremely high solubility and of some
2
3
1
3
C-NMR (solid state): l=30.4 (CH ), 44.6 (CH ),
3
2
−
1
205.0 (C(O)Me). FTIR: 1712 cm
(CꢀO stretching).
tendency to release MeSCH C(O)OMenthyl(-). As a
2

M. Basato et al. / Journal of Organometallic Chemistry 571 (1998) 115–121
119
matter of fact, the solution NMR spectra of 1 always
indicates the presence of free sulphur ligand. The struc-
ture of the complex is, however, well supported by the
presence of two distinct sets of H and C signals. In
particular, the methyl and methine proton nuclei res-
ply replaces one bite of the bridging acetato, which
becomes coordinated p to the palladium (Eq. (2)).
1
1
/3[Pd (v-OAc) ]+2MeSCH Z
3 6 2
1
13
“[Pd(OAc) (MeSCH Z) ] (9, 10)
(2)
2
2
2
onate at 1.91, 2.02 (MeCO ), 2.39, 2.45 (MeS) and 3.97,
2
9
: Z=CH C(O)OMe; 10: Z=CH(OMe)2
In this case, the methylene group is apparently not
2
4.01 (CH) ppm and, in correspondence, three couples
of signals (23.51, 23.69, 23.90, 24.14 and 24.81, 25.25
acid enough to allow the intramolecular proton ex-
1
3
ppm) are observed in the C spectrum. These data
clearly indicate that the use of the optically pure
1
13
change with the adjacent acetato. The H- and C-
NMR spectra of the complexes are simple and coherent
with the proposed nature of the products, as well as
their FT-IR spectra. In particular, the monohapto ac-
etato in complex 9 shows the asymmetric and symmet-
MeSCH C(O)OMenthyl(-) produces two diastereoiso-
2
mers in a 1/1 molar ratio, which differ for the configu-
ration of the six S and C donor atoms (S,S,S,S,S,S or
R,R,R,R,R,R).
Complexes 4–6 are rather unstable and give by-prod-
ucts containing palladium(0) and nitrogen. The pres-
ence of this last element has been verified by both
elemental analysis and XPS spectroscopy. It has been
observed that the nitrogen is positively charged (BE 1s
−
1
ric stretchings at 1574 and 1408 cm
cm , 10) and NMR resonances at 1.87 ppm (CH ),
(1568 and 1408
−
1
3
−
1
8.7 (CH ) and 177.3 ppm (CO ) (1.79, 19.8 and 177.7
3 2
ppm, 10).
Under the same experimental conditions the replace-
ment of an alkylthio by a thiol group in the ligand
favours the exchange of all acetates with formation of
the homoleptic complex 11 (Eq. (3)).
403.8 eV) and is always accompanied by palladium(0)
(
BE 3d5/2 336.0 eV) in an approximate 1/1 ratio. If one
considers that the synthesis and purification of these
products do not involve nitrogen containing chemicals,
it seems possible that these complexes or their evolution
products (palladium colloids?) are able to adsorb and
activate molecular nitrogen from the air, to which they
2[Pd (v-OAc) ]+12HSCH C(O)Me
3
6
2
“
[Pd(SCH C(O)Me) ] (11)+12HOAc
(3)
Its infrared spectrum clearly indicates that the car-
bonyl oxygen is not bonded to the metal centre [w(CO)
2
2 6
are
exposed
during
the
physico-chemical
−
1
characterization.
Reaction of palladium benzoate, instead of acetate,
1712 cm ] and also shows the absence of acetato
ligands. The H-NMR is characterized by the presence
1
with MeSCH C(O)OEt also occurs according to Eq.
of four distinct resonances for the methylene and
methyl protons. The intensities of the signals of the
same set are different and in the case of CH2 two
singlets have an intensity double with respect to the
others. This high number of signals is maintained in the
2
(
1), to give the mixed sphere trimer [Pd (v-O CPh) (v-
3 2 3
MeSCHC(O)OEt) ] (7). The stability and nuclearity of
3
the complex has been checked by molecular weight
determination in 1,2-dichloroethane at 50°C and the
infrared and NMR data are very similar to those of the
acetato analogue. This strongly suggests that the nature
of the bridging carboxylato ligands scarcely affects the
type of coordination of the sulphur ligands (C,S).
The large scope of the employable carboxylato
groups and the good coordinating properties of anionic
h-alkylcarboxythioethers is well illustrated by the reac-
tion of [Pd (v-O CMe) (v-MeSCHC(O)OMe) ] with
13
C solution spectrum, so supporting the polynuclear
molecular structure determined by osmometric mea-
surements. Similar values for the chemical shifts, but
1
3
very large single signals are instead observed in the
C
CP/MAS solid state spectrum: 30.4 (CH ), 44.6 (CH )
3
2
and 205.0 (C(O)Me) ppm. With these data, it seems
reasonable to propose a coordination, in which the
sulphur atom bridges two palladium centres in a cyclic
toroidal structure, as found in other metal thiolato
complexes [9].
3
2
3
3
MeSCH COOH. The exchange reaction involves only
2
the acetato group to give again a mixed-sphere com-
plex, [Pd (v-O CCH SMe) (v-MeSCHC(O)OMe) ] (8).
It may be concluded that the nature of the products
obtained in the reaction of palladium acetate with
substituted thioethers or thiols depends on the proper-
ties of the sulphur ligand employed. If it does not
possess any acidic hydrogen atom, a simple addition
reaction takes place. The affinity of the soft sulphur
atoms towards palladium(II), a soft metal centre, forces
the acetato ligands to change their hapticity for allow-
ing the coordination of two additional ligands.
3
2
13
2
3
3
1
The H- and C-NMR spectra show multiple reso-
nances for some functional groups, thus suggesting a
non symmetric molecular structure. This can arise from
the presence of a S donor atom in the carboxylato
ligand, which can compete with one O atom in coordi-
nation to the palladium centre.
A second type of complexes is obtained from the
reaction of palladium acetate with dimethyl sulphides
bearing poor electron-withdrawing substituents, like
When the thioethers RSCH Z are substituted with
2
1,1-dimethoxy-2-(methylthio)ethane and methyl 3-
electron-withdrawing groups (Z=C(O)R%, C(O)OR%,
(
methylthio)propionate. The sulphur donor atom sim-
S(O) Ph), the sulphur bonded methylene protons are
2

120
M. Basato et al. / Journal of Organometallic Chemistry 571 (1998) 115–121
Scheme 2.
activated. In spite of the relatively low acidity of these
compounds with respect to acetic acid [10], the latter is
displaced and mixed sphere complexes, in which half of
the acetato ligands are replaced by anionic sulphur
ligands, are formed. In this case, precoordination of the
neutral thioether via the sulphur atom and change of
the acetato hapticity are likely to occur. In this way, the
acidic methylene protons are brought close to one
acetato oxygen and this circumstance could lead to an
intermediate (or transition state) in which the proton
transfer from the methylene to the acetato is accompa-
nied by the formation of the Pd–CH bond. In general,
all these mixed sphere complexes exhibit the same
formula and nuclearity.
‘toroidal’ structures containing four, six or eight
‘M(SR) ’ units are already known for the Ni(II) and
2
Pd(II) complexes [9].
This synthetic evidence supports a mechanism, which
implies for all reactions the preliminary coordination of
the neutral ligand via its sulphur atom (Scheme 2).
In the absence of acidic sites a second neutral sulphur
ligand enters the coordination sphere of the palladium
centre (Eq. (2)), otherwise a proton exchange reaction
takes place with the methylene (Eq. (1)) or thiol (Eq.
(3)) groups. Upon coordination, the sulphur and car-
bon donors become stereogenic. The stereochemistry of
the reaction seems governed by the configuration of the
sulphur atom which gets attached first to the trimeric
molecule of [Pd (OAc) ]. In fact, the carbon atom of
Finally, when the thiol is reacted with palladium
3
6
acetate,
the
homoleptic
thiolate
complex
the adjacent methine group assumes the same configu-
ration, as well as the donor atoms of the two further
ligands. The observation that only half of the acetato
group are substituted in Eq. (1) can be explained on the
basis of the X-ray structure of [Pd (v-OAc) (v-
[Pd(SCH C(O)Me) ] is formed. In this case, the acidity
2
2 6
of the HS group and the bridging coordination mode of
the resulting S donor allow the quantitative displace-
−
ment of acetic acid. The stoichiometry of these com-
plexes implies that the thiolate ligands behave as
bridging ligands and that the products are cyclic
oligomers or infinite linear polymers. The former hy-
pothesis is supported by the literature data, in that
3
3
MeSCHC(O)OEt) ]. In fact, the OCO angle and OO
3
distance of the residual acetate are slightly smaller than
in the starting salt [3,11], which would make substitu-
tion by a CS bridge sterically unfavourable.

M. Basato et al. / Journal of Organometallic Chemistry 571 (1998) 115–121
121
The formation of these mixed-sphere palladium
trimers does not depend on the synthetic procedure
employed; in fact, treatment of the neutral complexes
Chimiche Innovative’, CNR, for partial financial sup-
port of this research.
[
PdCl (RSCH C(O)R%) ] with silver acetate gives in
2 2 2
one step [Pd (v-OAc) (v-RSCHC(O)R%) ], without any
References
3
3
3
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complexes [12]. It is remarkable that this monomer–
trimer process is regio- and stereoselective and this
clearly underlines the particular stability of the com-
plexes with this mixed CSOO set of donor atoms. This
is further confirmed by the easy synthesis of analogous
[
[
[
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2
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.