New routes to the synthesis of chloro-carbonyls of palladium(II) and platinum(II)

Article abstract of DOI:10.1016/S0022-328X(99)00581-1

[Pt(CO)_x]_n (x～2), the already described species obtained by the reaction of platinum(0) olefin complexes with carbon monoxide, reacts promptly at room temperature with SO₂Cl₂ under CO affording cis-PtCl₂

Full text of DOI:10.1016/S0022-328X(99)00581-1

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 593–594 (2000) 427–430
New routes to the synthesis of chloro-carbonyls of palladium(II)
and platinum(II)
Daniela Belli Dell’Amico *, Luca Labella
Dipartimento di Chimica e Chimica Industriale, Uni6ersita` di Pisa, 6ia Risorgimento, 35, I-56126 Pisa, Italy
Received 28 July 1999; accepted 28 September 1999
Dedicated to Professor Fausto Calderazzo, on the occasion of his 70th anniversary, in recognition of his outstanding contributions to
inorganic and organometallic chemistry.
Abstract
[Pt(CO)x]n (xꢀ2), the already described species obtained by the reaction of platinum(0) olefin complexes with carbon
monoxide, reacts promptly at room temperature with SO2Cl2 under CO affording cis-PtCl2(CO)2. [Pd2(CO)y]n (yꢀ1), obtained
by Pd(dba)2 and CO at room temperature, reacts in the same conditions yielding Pd2Cl4(CO)2. Similarly, although more slowly,
finely divided platinum and palladium, in the form of metal blacks, react with SO2Cl2 and CO at room temperature producing
again cis-PtCl2(CO)2 and Pd2Cl4(CO)2, respectively. In the absence of CO no reaction is observed within 4 weeks. © 2000 Elsevier
Science S.A. All rights reserved.
Keywords: Platinum black; Palladium black; Platinum carbonyl; Palladium carbonyl; Platinum chloride; Palladium chloride
and to a low MꢀCO bond energy in the case of
palladium [6].
1. Introduction
As far as platinum is concerned, the system CO–H2O
as a reductant of chlorocomplexes [PtCl24−, PtCl2(CO)2]
affords species of composition Pt(CO)2 [7]. Although
not sufficiently characterized, they deserve remarkable
interest, in view of the above-mentioned lack of well-
defined platinum binary carbonyls. A recently reported
[8] black material of approximate composition
[Pt(CO)2]n (from now on we will refer to it using this
formula) was obtained by reacting homoleptic olefin
complexes of platinum(0) [9] with CO. Unlike the spe-
cies reported before [7], this compound was found to be
labile and to decompose with irreversible loss of carbon
monoxide at reduced partial pressure of CO and/or at
temperatures higher than about 0°C. Moreover, it was
easily oxidized by iodine under CO atmosphere [8] with
the formation of PtI2(CO)2.
Palladium and platinum as metals are rarely used as
reagents for the synthesis of metal salts or complexes in
mild conditions, although platinum and palladium
blacks [1] are both good examples of readily accessible
finely divided metals. They are both used extensively as
catalysts for many reactions [2]. Therefore, their rela-
tively high (especially for platinum) atomization energy
{DH° (Pt(g))=565.3 kJ mol−1, DH° (Pd(g))=378.2 kJ
mol−1 [3]}, does not prevent their interaction with
several compounds. Some of the catalyzed processes
involve carbon monoxide: focusing on the metal–CO
interaction, it is worth to recall that, despite nickel,
which belongs to the same group, reacts with CO in
mild conditions affording Ni(CO)4 [4], palladium and
platinum tetracarbonyls have not yet been isolated by
any synthetic method, but in matrix conditions [5].
Their assumed low stability has been attributed to a
high metal atomization energy in the case of platinum
These results led us to enlarge our knowledge about
the reactivity of this derivative and to test the chemistry
of palladium in the same field. Moreover, for sake of
comparison, we have also studied the reactivity in
similar conditions of the metal blacks, prepared by the
classical methods [10].
* Corresponding author. Tel.: +39-050-918206; fax: +39-050-
20237.
E-mail address: belli@dcci.unipi.it (D. Belli Dell’Amico)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00581-1

428
D. Belli Dell’Amico, L. Labella / Journal of Organometallic Chemistry 593–594 (2000) 427–430
2. Results and discussion
The use of sulphuryl chloride as an oxidant for
platinum metals has been reported [15b]. Palladium
black is converted to b-PdCl2 in 3 days at 400°C and
platinum to b-PtCl2 in 7 days at 450–500°C or to PtCl4
in 7 days at 350°C. From a thermodynamic point of
view, the formation of MCl2 (M=Pd, Pt) from M and
SO2Cl2 (see Eqs. (1) and (2)) appears to be feasible at
room temperature in both cases.
Among the homoleptic palladium olefin complexes
[11], the well characterized derivatives Pd2(dba)3
(dba=dibenzylideneacetone) and Pd3(tbaa)3 (tbaa=
tribenzylideneacetylacetone) are reported to react with
CO with decomposition to palladium metal and free
olefin [11d, e]. In our hands, Pd(dba)2 prepared accord-
ing to the literature [11f], reacted rapidly with CO
(P=1 atm.) at room temperature in toluene or cyclo-
hexane with uptake of carbon monoxide, corresponding
to a molar ratio CO/Pd=0.5, and formation of a black
powder. This material, [Pd2(CO)y]n (yꢀ1; we will refer
to it with the formula [Pd2(CO)]n), whose nature we are
currently exploring, decomposes easily with loss of CO.
IR spectra of the product do not show any bands in the
carbonyl stretching region: it is likely that decomposi-
tion occurs during the sample work up.
As part of an ongoing research program in the field
of noble metal halo-carbonyl complexes, the derivatives
[Pt(CO)2]n [8] and [Pd2(CO)]n have been used as
reagents for the syntheses of chloro-carbonyls.
[Pt(CO)2]n, by reaction with SO2Cl2 at room tempera-
ture under CO atmosphere, afforded rapidly cis-
PtCl2(CO)2 in good yield. The complete disappearance
of the black reagent and the formation of a pale yellow
solution are clear evidences of the completeness of the
reaction. The product, recovered in high yield (92%),
was characterized by IR spectroscopy (w˜CO at 2168 and
2127 cm−1 [12]).
Pt(s)+SO2Cl2(l)“PtCl2(s)+SO2(g)
Pd(s)+SO2Cl2(l)“PdCl2(s)+SO2(g)
(1)
(2)
DH° values of −13 and −70 kJ mol−1 are obtained
for platinum and palladium, respectively, by the stan-
dard enthalpy formation of SO2Cl2 (−394.1 kJ mol−1
[3]), SO2 (−296.8 kJ mol−1 [3]), PtCl2 (−110.5 kJ
mol−1 [16]) and PdCl2 (−166.8 kJ mol−1 [16]). More-
over, these exoergonic reactions are entropically
favored.
Nevertheless, our attempts to obtain MCl2 from the
metal blacks and SO2Cl2 in the absence of CO at room
temperature met with failure. It is possible that insolu-
ble metal chlorides initially formed on the surface pro-
tect the metals from further attack. This hypothesis
does not contrast with our analytical data (at the end of
the treatment only traces of chlorine were found in the
black solids, once washed and dried) because the for-
mation of metal chlorides on the particle surface (esti-
mated medium diameter 50 nm [1b]) would require a
negligible percentage of chlorine in the material.
As a matter of fact, the addition of CO modifies the
chemical systems (see Eqs. (3) and (4)), and, in view of
the well established stability of the chloro-carbonyl
derivatives of platinum (see Eq. (5)) [17] and palladium
(see Eq. (6), DH°= −57 kJ mol−1; DS°= −129 J
Similarly, [Pd2(CO)]n instantaneously reacted at room
temperature with SO2Cl2 under CO in SOCl2 as solvent,
giving an orange solution of Pd2Cl4(CO)2. The IR
spectrum showed a band at 2163 cm−1 [13] due to the
CO stretching in the complex, whose absorbance corre-
sponded to a yield of 94%.
mol−1
K
−1) [13], Eqs. (3) and (4) can be considered, at
room temperature, more favored than Eqs. (1) and (2),
respectively.
The high reactivity of these materials is presumably
related to their probable cluster-like structure and to
their higher fragmentation in comparison with the bulk
metal. On this basis, we considered it interesting to test
the reactivity, if any, of the finely divided metals in
analogous conditions and palladium and platinum
blacks appeared to be suitable candidates to carry out
these experiments. Although they are widely used in
catalysis, there are not many studies on their morphol-
ogy and structure [14]. They have been used as reagents
in the synthesis of metal salts or complexes only with
strong oxidants often at high temperature, an example
being the preparations of the metal chlorides [15].
The metal blacks treated with SO2Cl2 yielded, in the
presence of CO (P=1 atm.), the above mentioned
chloro-carbonyl products. Approximately 1 mmol of
palladium was converted to Pd2Cl4(CO)2 in 2 h at
about 25°C operating in a solution of SO2Cl2 in SOCl2
1:1 in volume. Platinum reacted in the same conditions
about 100 times more slowly.
Pt(s)+SO2Cl2(l)+2CO(g)“cis-PtCl2(CO)2(solv)+SO2(g)
(3)
2Pd(s)+2SO2Cl2(l)+2CO(g)
“Pd2Cl4(CO)2(solv)+2SO2(g)
(4)
(5)
(6)
PtCl2(s)+2CO(g)“cis-PtCl2(CO)2(solv)
2PdCl2(s)+2CO(g) X Pd2Cl4(CO)2(solv)
The first step of the process could be the formation
of a surface metal chloride, followed by CO uptake to
produce the metal chloro-carbonyls, as recently pro-
posed [18] in the study of the reaction of a platinum
film with a mixture of CO and Cl2. Nevertheless, we
cannot exclude that the reactions proceed by formation
of surface metal carbonyls and subsequent chlorination.
The rapid formation of the chloro-carbonyl complexes
from [Pt(CO)2]n or [Pd2(CO)]n and SO2Cl2 supports the
latter hypothesis, although does not exclude the former.

D. Belli Dell’Amico, L. Labella / Journal of Organometallic Chemistry 593–594 (2000) 427–430
429
3. Experimental
3.3. Reaction of [Pd2(CO)]n with SO2Cl2
All preparations were carried out using standard
Schlenk techniques. All organic solvents were freshly
distilled over conventional drying agents under dinitro-
gen and all reactions were carried out under an atmo-
sphere of dinitrogen, or carbon monoxide, as stated.
SO2Cl2 (Aldrich) and SOCl2 (C. Erba) were used as
received. Platinum and palladium blacks [10],
[Pt(CO)2]n [8] and Pd(dba)2 [11f] were prepared accord-
ing to the literature. IR spectra were recorded on a
FT-IR Perkin–Elmer mod. 1725X spectrophotometer.
The molar extinction coefficients of the CO stretching
vibration of cis-PtCl2(CO)2 in toluene (2168 cm−1),
m=1200 mol−1 l cm−1 [12] and of Pd2Cl4(CO)2 in
SOCl2 (2163 cm−1), m=1415 mol−1 l cm−1 [13] were
used for yield determinations. The thickness of the cell
(1.1×10−2 cm) was determined by the interference
method. Elemental analyses (C, H) were performed in
the Laboratorio di Microanali, Facolta` di Farmacia,
Universita` di Pisa, with a C. Erba mod. 1106 elemental
analyzer. Chlorine analyses were performed according
to Volhard method after attack of the samples with
an excess of boiling aqueous solution of sodium formi-
ate.
A solution of SO2Cl2 (12.5 cm3) in SOCl2 (12.5 cm3)
was saturated with CO and [Pd2(CO)]n (0.026 g, 0.22
mmol of Pd) was added. A yellow solution was immedi-
ately obtained. An IR spectrum showed the band due
to Pd2Cl4(CO)2 at 2163 cm−1 with an absorbance
A=0.064, corresponding to a 94% yield.
3.4. Reaction of platinum black with CO and SO2Cl2
Platinum black (0.231 g, 1.18 mmol) was added to a
solution of SO2Cl2 (20 cm3) in SOCl2 (20 cm3) under
CO atmosphere. After about 150 h, a pale yellow
solution was obtained. The solution was evaporated to
dryness and the residue was dissolved in toluene (51
cm3). An IR spectrum of the solution showed the bands
due to cis-PtCl2(CO)2 at 2168 and 2127 cm−1, the
former with absorbance A=0.28, corresponding to a
92% yield.
In another experiment platinum black (0.061 g, 0.31
mmol), SO2Cl2 (10 cm3) and SOCl2 (10 cm3) were
introduced in a tube (500 cm3 volume) under CO (P=1
atm.) The tube was flame-sealed and the suspension
was stirred at 60°C. After 30 h, a pale yellow solution
was obtained. The IR spectrum showed the band at
2168 cm−1 due to cis-PtCl2(CO)2 with an absorbance
corresponding to a nearly quantitative yield.
3.1. Reaction of Pd(dba)2 with CO
A suspension of Pd(dba)2 (0.476 g, 0.83 mmol) in
toluene (50 cm3) was saturated with CO (P=1 atm.) at
room temperature. A rapid absorption of CO was
observed. The black suspension was decanted, the solid
was washed three times with cyclohexane and dried
under carbon monoxide (0.083 g, 83% yield as
[Pd2(CO)]n). Anal. Calc. for CPd2O: C, 5.0%. Found:
C, 4.1%. IR spectra registered on Nujol-mulls did not
show any bands in the CO stretching region. The free
ligand was recovered unchanged (IR comparison) from
the filtrate in a 83% yield.
In a gasvolumetric experiment, Pd(dba)2 (0.511
g, 0.89 mmol) in toluene (25 cm3) reacted with CO
(P=760 torr) for about 3 min at T=23°C with a
CO uptake corresponding to CO/Pd molar ratio
0.53.
3.5. Reaction of palladium black with CO and SO2Cl2
Palladium black (0.045 g, 0.42 mmol) was added
under CO to a solution of SO2Cl2 (10 cm3) in SOCl2 (10
cm3). The suspension was stirred at room temperature.
After 1 h, an orange solution was obtained. The IR
spectrum showed the band at 2163 cm−1 due to
Pd2Cl4(CO)2 with A=0.16 corresponding to a nearly
quantitative yield.
3.6. Treatment of platinum black with SO2Cl2
Platinum black (0.300 g, 1.54 mmol) was added
under N2 to a solution of SO2Cl2 (10 cm3) in SOCl2 (10
cm3). The suspension was stirred at room temperature
for 30 days, and filtered. The black solid, washed
several times with heptane and dried in vacuo, con-
tained only traces of chlorine.
3.2. Reaction of [Pt(CO)2]n with SO2Cl2
A solution of SO2Cl2 (0.20 cm3; 2.48 mmol) in
toluene (20 cm3) was saturated with CO at room tem-
perature and [Pt(CO)2]n (0.172 g, 0.69 mmol) was
added. After a few minutes, a yellow solution was
obtained. An IR spectrum showed the bands of
PtCl2(CO)2 at 2168 and 2127 cm−1. The absorbance of
the former band was A=0.42, corresponding to a 92%
yield.
3.7. Treatment of palladium black with SO2Cl2
Palladium black (0.088 g, 0.83 mmol) was added
under N2 to a solution of SO2Cl2 (10 cm3) in SOCl2 (10
cm3). The suspension was stirred at room temperature
for 30 days, and filtered. The black solid, washed
several times with heptane and dried in vacuo, con-
tained only traces of chlorine.

430
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[Pt(CO)2]n [8] and [Pd2(CO)]n, obtained by treating
Pd(dba)2 with CO, afforded smoothly cis-PtCl2(CO)2
and Pd2Cl4(CO)2, respectively, by reacting with SO2Cl2.
Additionally, we have found that, although palla-
dium and especially platinum are oxidized with
difficulty in mild conditions, the metal blacks react at
room temperature with SO2Cl2 in the presence of CO
producing the chloro-carbonyl complexes. No metal
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These reactions constitute new routes to the synthe-
ses of chloro-carbonyls of palladium and platinum.
Furthermore, the study of the reactivity of [Pt(CO)2]n
and [Pd2(CO)]n can be useful to better understand the
nature of these two elusive derivatives, which are inter-
esting either as members of the binary metal carbonyl
family, or as examples of transient species in processes
going from molecular towards bulk metal materials [8].
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Acknowledgements
The authors are grateful to the Ministero dell’Uni-
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versita`
e della Ricerca Scientifica e Tecnologica
(MURST) for financial support and to Chimet SpA,
Badia al Pino, Arezzo, Italy, for a loan of platinum and
palladium.
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