Competitive ligation between carbon monoxide and propiononitrile in chloro-complexes of platinum(II)

Article abstract of DOI:10.1016/j.ica.2007.05.019

EtCN partially displaces coordinated carbon monoxide from cis-PtCl₂(CO)₂ giving an equilibrium mixture of the two geometrical isomers of PtCl₂(CO)(NCEt), together with unreacted cis-PtCl₂(CO)₂, as monitored by IR and NMR measurements. The equilibrium has also been studied starting from PtCl₂(NCEt)₂, through displacement of coordinated EtCN by CO. The equilibrium constant of the reaction between PtCl₂(CO)(NCEt) [cis + trans] and CO to produce cis-PtCl₂(CO)₂ (48 ± 6, corresponding to ΔG⁰ = -9.5 ± 0.3 kJ mol^-1) has been measured at 23.4 °C, in the presence of SnCl₂ as catalyst, the uncatalysed reaction being exceedingly slow. With an appropriate control of the CO partial pressure, PtCl₂(CO)(NCEt) was obtained in a nearly quantitative yield either from cis-PtCl₂(CO)₂ + EtCN or from PtCl₂(NCEt)₂ + CO. The molecular and crystal structure of cis-PtCl₂(CO)(NCEt) has been solved by X-ray diffractometry.

Full text of DOI:10.1016/j.ica.2007.05.019

Inorganica Chimica Acta 360 (2007) 3765–3770
www.elsevier.com/locate/ica
Competitive ligation between carbon monoxide and propiononitrile
in chloro-complexes of platinum(II)
*
Daniela Belli Dell’Amico , Fausto Calderazzo, Laura Carbonaro, Luca Labella,
Stefano Libri, Fabio Marchetti
`
Dipartimento di Chimica e Chimica Industriale, Universita di Pisa, Via Risorgimento 35, I-56126 Pisa, Italy
Received 9 March 2007; received in revised form 4 May 2007; accepted 12 May 2007
Available online 23 May 2007
Abstract
EtCN partially displaces coordinated carbon monoxide from cis-PtCl2(CO)2 giving an equilibrium mixture of the two geometrical
isomers of PtCl2(CO)(NCEt), together with unreacted cis-PtCl2(CO)2, as monitored by IR and NMR measurements. The equilibrium
has also been studied starting from PtCl2(NCEt)2, through displacement of coordinated EtCN by CO. The equilibrium constant of
the reaction between PtCl2(CO)(NCEt) [cis + trans] and CO to produce cis-PtCl2(CO)2 (48 6, corresponding to DG0 =
ꢀ9.5 0.3 kJ molꢀ1) has been measured at 23.4 ꢀC, in the presence of SnCl2 as catalyst, the uncatalysed reaction being exceedingly slow.
With an appropriate control of the CO partial pressure, PtCl2(CO)(NCEt) was obtained in a nearly quantitative yield either from cis-
PtCl2(CO)2 + EtCN or from PtCl2(NCEt)2 + CO. The molecular and crystal structure of cis-PtCl2(CO)(NCEt) has been solved by X-ray
diffractometry.
ꢁ 2007 Elsevier B.V. All rights reserved.
Keywords: Nitrile complexes; Carbonyl complexes; Platinum; Equilibrium constant; X-ray crystal structure
1. Introduction
cis-PtCl2(CO)2 and the two geometrical isomers of
PtCl2(CO)(NCEt).
Organic nitriles RCN are frequently used as ligands,
their complexes being convenient precursors to a series of
derivatives, through displacement by other nucleophiles
[1]. How weak the metal–nitrile bond is, compared to other
metal–ligand bonds, however, is a matter to be further
explored, as only a limited number of data is available
[2]. In palladium- and platinum-chemistry, nitrile com-
plexes are known to react with nucleophiles producing
nitrile displacement or attack to the CN moiety [3,4].
Here, we report the substitution of coordinated EtCN
by CO, and viceversa, in chloro-complexes of platinum(II).
We have found that CO reacts with (cis + trans)-
PtCl2(NCEt)2 to give an equilibrium mixture containing
2. Results and discussion
PtCl2(NCEt)2 is easily prepared [5] as the mixture of the
two geometrical isomers (cis/trans molar ratio about 6 at
25 ꢀC) from K2PtCl4 and excess propiononitrile in water.
The two isomers are well distinguished by H and 195Pt
1
NMR spectra, see Table 1. They slowly react with CO
(Ptot = PCO + Psolvent = atmospheric pressure) at room
temperature in 1,2-dichloroethane. Eqs. (1) and (2) corre-
spond to the two steps of the process; the former substitu-
tion is completely displaced to the right, while the latter is
an equilibrium. The [PtCl2(CO)2/PtCl2(CO)(NCEt)] molar
ratio at equilibrium, at a fixed temperature and CO pres-
sure, depends on the initial concentration of PtCl2(NCEt)2
(c0), increasing by decreasing c0. Under our conditions, cis-
PtCl2(CO)2 is the predominant product, as inferred by IR
*
Corresponding author. Tel.: +39 0502219206; fax: +39 0502219260.
E-mail address: belli@dcci.unipi.it (D. Belli Dell’Amico).
0020-1693/$ - see front matter ꢁ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.05.019

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D. Belli Dell’Amico et al. / Inorganica Chimica Acta 360 (2007) 3765–3770
Table 1
IR and NMR data of the geometrical isomers of PtCl2L(NCR) (L = RCN, R = Et; L = CO, R = Et, Me)
mCO (cmꢀ1
)
1H NMRd (ppm)e
195Pt NMRa (ppm)f
Ref.
~
Complex
cis-PtCl2(NCEt)2
1.43 (t, JH–H = 7.6 Hz) 2.86 (q); see also Ref. [5]
1.41 (t, JH–H = 7.6 Hz) 2.86 (q); see also Ref. [5]
1.46 (t, JH–H = 7.5 Hz) 2.94 (q, JH–Pt = 11.6 Hz)
1.44 (t, JH–H = 7.6 Hz) 2.84 (q, JH–Pt = 7.6 Hz)
ꢀ2253
ꢀ2342
ꢀ3280
ꢀ3430
this work, see also Ref. [3f]
this work; see also Ref. [3f]
this work
this work
[8]
trans-PtCl2(NCEt)2
cis-PtCl2(CO)(NCEt)
trans-PtCl2(CO)(NCEt)
cis-PtCl2(CO)(NCMe)
trans-PtCl2(CO)(NCMe)
2122a
2137a
2125b (2134)c
2134b (2144)c
[8]
a
In 1,2-dichloroethane.
Nujol mull.
In CHCl3.
In CDCl3.
From TMS.
From H2PtCl6 in D2O.
b
c
d
e
f
and NMR spectra. It is characterized by two IR-active
carbonyl stretching vibrations of nearly equal intensity at
2178 and 2136 cmꢀ1, the latter overlapping with the car-
bonyl absorption due to trans-PtCl2(CO)(NCEt), while
cis-PtCl2(CO)(NCEt) absorbs at 2124 cmꢀ1 (see Table 1)
From the reaction mixture, containing cis- and trans-
PtCl2(CO)(NCEt) and cis-PtCl2(CO)2, the dicarbonyl
product separated out by cooling the solution down to
ꢀ30 ꢀC after addition of heptane and was recovered by fil-
tration (about 38% yield after recrystallization). This
result is consistent with the value of the equilibrium con-
stant of reaction 2 in CDCl3, vide infra, cis-PtCl2(CO)2
being expected to be about 60% of the total platinum.
The filtrate was worked out and the remaining cis-
PtCl2(CO)2 was converted to PtCl2(CO)(NCEt) by evapo-
ration to dryness and by treating the solid residue with an
excess of free nitrile in 1,2-dichloroethane under N2. Addi-
tion of heptane to the concentrated final solution (about
0.7 M in Pt), caused the separation of an orange oil, con-
taining the two geometrical isomers of PtCl2(CO)(NCEt).
At room temperature for about 15 h, the oil produced a
microcrystalline yellow solid constituted essentially by
cis-PtCl2(CO)(NCEt).
In another experiment, see Section 3, a solution of the
two isomers (8 · 10ꢀ2 M) was treated with heptane at room
temperature. Neither precipitation of a solid nor separation
of an oil was observed. On the other hand, from the solu-
tion, cooled at 4 ꢀC, yellow and orange crystals of the two
isomers separated out. The yellow crystals of the cis-isomer
were used for X-ray diffraction studies, vide infra. IR and
NMR data of cis- and trans-PtCl2(CO)(NCEt) are reported
in Table 1.
ðcis- þ trans-ÞPtCl2ðNCEtÞ2 þ CO
! ðcis- þ trans-ÞPtCl2ðCOÞðNCEtÞ þ EtCN
ðcis- þ trans-ÞPtCl2ðCOÞðNCEtÞ þ CO
ð1Þ
ð2Þ
K
ꢀ cis-PtCl2ðCOÞ2 þ EtCN
The mixture of the two geometrical isomers of
PtCl2(NCEt)2 reacts with CO at room temperature afford-
ing PtCl2(CO)(NCEt) in a trans/cis molar ratio of about
10, see Eq. (1). Since normally the primary substitution
products in square-planar complexes maintain the geome-
try of the parent compounds [6], subsequent isomerization
to the equilibrium composition has evidently occurred.
About the subsequent carbonylation it is interesting to note
that, in spite of the fact that trans-PtCl2(CO)(NCEt) is the
predominant isomer in solution and that coordinated CO
has a higher trans-effect than Clꢀ, no trans-PtCl2(CO)2
was detected. This is contrary to what verified earlier for
the reaction between Pt2Cl4(CO)2 and CO [7], where
trans-PtCl2(CO)2 , the kinetic product, was detected by
IR spectroscopy, the isomerization proceeding at a moder-
ate rate [7]. A reasonable hypothesis about our present
findings is that equilibrium 3 is strongly displaced to the
left and that only reaction 4 is responsible for the forma-
tion of dichlorodicarbonylplatinum(II)
The isomerization of the cis isomer in CDCl3 or 1,2-
dichloroethane was monitored by IR and NMR spectra,
the equilibrium being reached, at room temperature, in
about 20 h {[PtCl2(CO)(NCEt)] about 5 · 10ꢀ2 M}.
The crystal and molecular structure of cis-PtCl2(CO)
(NCEt) is shown in Fig. 1.
The complex, whose geometrical parameters are listed in
Table 2, shows the expected square-planar coordination
around platinum.
trans-PtCl2ðCOÞðNCEtÞ þ CO ꢀtrans-PtCl2ðCOÞ2 þ EtCN
ð3Þ
cis-PtCl2ðCOÞðNCEtÞ þ CO ꢀcis-PtCl2ðCOÞ2 þ EtCN
ð4Þ
The Pt–C distance is significantly shorter than the Pt–N
distance. A search in the Cambridge Crystallographic
Database [9] has shown the presence of well refined struc-
tures of substances containing Pt(II)–CO (35 determina-
tions) or Pt(II)–NC (33 determinations) bonds. The
The use of reactions 1 and 2 for the synthesis of cis-
PtCl2(CO)2 and/or PtCl2(CO)(NCEt) deserves some com-
ments. In the reaction between PtCl2(NCEt)2 (0.11 M; in
1,2-C2H4Cl2) and CO described in Section 3 and carried
out at 50 ꢀC, the CO uptake is complete in a few hours.

D. Belli Dell’Amico et al. / Inorganica Chimica Acta 360 (2007) 3765–3770
3767
Fig. 1. View of the molecular structure of cis-PtCl2(CO)(NCEt).
Ellipsoids are at 30% probability.
0
Fig. 2. The molecular stacking of cis-PtCl2(CO)(NCEt). = x, 1/2 ꢀ y,
00
Table 2
ꢀ1/2 + z; = x, 1/2 ꢀ y, 1/2 + z.
˚
Bond lengths (A) and angles (ꢀ) in cis-PtCl2(CO)(NCEt)
Bond lengths
Pt–C(1)
Pt–N
Pt–Cl(1)
Pt–Cl(2)
C(1)–O
cules to minimize the steric hindrance between the ligated
1.875(14)
1.990(11)
2.276(4)
2.291(3)
1.124(15)
1.113(17)
nitrile groups. The Pt0ꢁ ꢁ ꢁPt and Ptꢁ ꢁ ꢁPt00 distances are
0
00
˚
3.372 A and the Pt ꢁ ꢁ ꢁPtꢁ ꢁ ꢁPt angle is 172.4ꢀ, the platinum
atoms in the column forming a slight zig-zag disposition.
The shortest intermolecular distances are between the plat-
inum atoms and are similar to those found in cis-
N–C(2)
Bond angles
C(1)–Pt–Cl(1)
C(1)–Pt–N
C(1)–Pt–Cl(2)
N–Pt–Cl(1)
N–Pt–Cl(2)
Cl(1)–Pt–Cl(2)
C(2)–N–Pt
˚
PtCl2(CO)2 (3.378 A). In the dicarbonyl compound, the
89.3(4)
92.1(5)
179.5(5)
178.4(3)
88.0(3)
shortest contacts involve the carbon and chlorine atoms
of adjacent molecules in the columns the Clꢁ ꢁ ꢁC interaction
providing the major contribution to the intermolecular
cohesive forces, followed by the Pt–Pt interaction. In cis-
PtCl2(CO)(NCEt), the metalꢁ ꢁ ꢁmetal interaction appears
to predominate.
90.56(13)
176.3(11)
Equilibrium 2 was quantitatively monitored by 1H
NMR experiments which have been carried out in CDCl3
by reacting PtCl2(NCEt)2 (4.4 · 10ꢀ2 M) with CO
(T = 23.4 ꢀC, PCO ꢂ 1 atm), in the presence of a catalytic
amount of SnCl2 (Sn/Pt molar ratio 1.3 · 10ꢀ2). In the
absence of the catalyst, and under similar conditions of
˚
˚
corresponding mean values of 1.887 A and 1.999 A, respec-
tively, almost coincide with the distances found in our com-
˚
pound. The Pt–Cl bond (2.291 A) trans to CO is
significantly longer than that trans to EtCN. A similar dif-
ference between the two non-equivalent Pt–Cl distances, on
the other hand, has been observed also in cis-PtCl2(CO)2
[10], where both Cl ligands are trans to CO. The angles
around platinum are very close to 90ꢀ. A useful comparison
can be made between the metrical data of cis-PtCl2(NCEt)2
[3e,3f] and cis-PtCl2(CO)2 [10]: in cis-PtCl2(CO)2 the Pt–Cl,
Pt–C and C–O bond distances are (average) 2.291, 1.897
and 1.115 A, respectively, to be compared with 2.291,
1.88 and 1.12 A in cis-PtCl2(CO)(NCEt). In cis-
PtCl2(NCEt)2 [3f] the Pt–N and C–N bond distances are
1.98 and 1.12 A, respectively, to be compared with the
pressure and temperature,
a
0.12 M solution of
[PtCl2(NCEt)2] did not reach equilibrium after 15 d. The
composition of the equilibrium mixture was monitored
through the NMR peaks of the CH2 groups, the methylene
signal of the uncomplexed nitrile (2.4 ppm) being well sep-
arated from those of the two geometrical isomers of
PtCl2(CO)(NCEt), see Table 1. The equilibrium constant
was thus evaluated to be 48 6, corresponding to
DG0 = ꢀ9.5 0.3 kJ molꢀ1. Therefore, carbon monoxide
is preferred to EtCN by the [PtCl2(CO)] fragment. Also,
CO is preferred to EtCN by the fragment [PtCl2(NCEt)],
whereby reaction 1 is completely displaced to the right
and PtCl2(CO)(NCEt) does not undergo CO displacement
by EtCN by decreasing the CO partial pressure or even in
the presence of a strong excess of the nitrile. A similar
behavior has been observed in the cis-PtCl2(CO)2/cis-
PtCl2(CO)(alkene) (alkene = cyclohexene, 1-octene) sys-
tems [11], where carbon monoxide is preferred to the
alkene, the dicarbonyl complex being obtained according
˚
˚
˚
˚
Pt–N and C–N bond distances of 1.990 and 1.113 A,
respectively, in our product.
The molecules are stacked in the c-direction following
the operation of a glide, spanned by c/2, see Fig. 2. The
contiguous molecules in the stacks are rotated around the
stacking axis by about 45ꢀ and lay in planes forming a
small angle, alternatively, of 3.6ꢀ and ꢀ3.6ꢀ. Thus, the
Pt0 and Pt00 coordination planes are parallel and nearly
eclipsed. This arrangement allows the contiguous mole-

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D. Belli Dell’Amico et al. / Inorganica Chimica Acta 360 (2007) 3765–3770
to equilibrium 5, the equilibrium constant at 21 ꢀC corre-
sponding to (4.1 0.5) · 102 and to 36 5 for cyclohexene
and 1-octene, respectively. Furthermore, cis-PtCl2(CO)-
(alkene) does not undergo CO displacement even at low
CO partial pressure and in the presence of a strong excess
of the alkene
about 1 atm. After 10 h the solution was cooled down to
room temperature. An IR spectrum in the 2200–
2000 cmꢀ1 region showed the presence of cis-PtCl2(CO)2
and of the two geometric isomers of PtCl2(CO)(NCEt).
Heptane was added (200 mL) and the mixture was cooled
down to ꢀ30 ꢀC. After 12 h, the suspension was filtered
and the colourless cis-PtCl2(CO)2 was recovered and
recrystallized from 1,2-dichloroethane/heptane (2.01 g,
37.7% yield).
cis-PtCl2ðCOÞðalkeneÞ þ CO ꢀ cis-PtCl2ðCOÞ2 þ alkene
ð5Þ
The filtrate was concentrated to dryness. By operating
under N2, the yellow solid residue was dissolved in 1,2-
dichloroethane and EtCN was added (3.0 mL). The
solution was heated to 50 ꢀC and vacuum/N2 cycles were
periodically performed to remove the carbon monoxide
produced by the reverse of reaction 4. After 6 h, an IR
These results suggest that the coordination ability of the al-
kyl nitrile towards the [PtCl2(CO)] fragment, is similar to
that of terminal olefins.
3. Experimental
spectrum of the solution showed the band at 2178 cmꢀ1
,
3.1. General procedures and instruments
typical of cis-PtCl2(CO)2, to be no longer present. The
solution was concentrated to 15 mL and heptane was
added (150 mL). The orange-yellow oil which separated
out converted to the microcrystalline yellow cis-PtCl2-
(CO)(NCEt) over about 15 h. The solid was recovered by
filtration and dried in vacuo (2.06 g; 35.7% yield). Anal.
Calc. for C4H5Cl2NOPt: C, 13.8; H, 1.4; N, 4.0. Found:
C, 13.2; H, 1.4; N, 4.0%. IR in 1,2-dichloroethane: mCO
The tetrachloroplatinate(II) K2[PtCl4] was purchased
(Aldrich) or obtained by reduction of K2PtCl6 (Chimet
S.p.A., I-52041 Badia al Pino, Arezzo). Research grade
CO was purchased by Rivoira and purified by bubbling
through concentrated H2SO4 and an aqueous solution of
KOH. 1,2-Dichloroethane was freshly distilled from
P4O10 under a dinitrogen atmosphere. Toluene and hep-
tane were distilled from sodium. EtCN was refluxed over
CaH2 and distilled before use. CDCl3 (99.9%, Aldrich)
was treated with P4O10 and distilled before use.
1
2122 cmꢀ1; for the H and 195Pt NMR data, see Table 1.
3.3. Reaction of cis-Pt(CO)2Cl2 with EtCN
1H and 195Pt NMR spectra were recorded with a Varian
Gemini 200BB spectrometer. Chemical shifts were mea-
sured in ppm (d) and referenced to external TMS via resid-
ual solvent peaks (1H) and to aqueous (D2O)
hexachloroplatinic acid (195Pt). IR spectra were obtained
using a Perkin–Elmer spectrophotometer FTIR1725X
equipped with an IR Data Manager software. Elemental
analyses (C, H, and N) were performed by Laboratorio di
Microanalisi, Dipartimento di Scienze Farmaceutiche, Uni-
By operating under dinitrogen, 4.94 mL of a 0.337 M
solution of EtCN (1.66 mmol) in 1,2-dichloroethane were
added to a solution of cis-PtCl2(CO)2 (268 mg, 0.832
mmol) in the same solvent (100 mL) under dinitrogen.
The solution was stirred at room temperature and the
evolved CO was periodically removed under reduced pres-
sure. The reaction was monitored by IR spectra, cis-
PtCl2(CO)2 being characterized by the absorptions at
2136 and 2178 cmꢀ1, whereas PtCl2(CO)(NCEt) shows a
band at 2137 cmꢀ1 due to the trans-isomer, the predomi-
nant one in solution, accompanied by a shoulder at
2122 cmꢀ1 due to the cis-isomer. When the band at
2178 cmꢀ1 had disappeared (10 d), heptane (100 mL) was
added and the mixture was cooled down to 4 ꢀC. After
about 12 h orange and yellow crystals were formed, corre-
sponding to the two isomers of PtCl2(CO)(NCEt), as con-
firmed by IR and NMR spectra in solution, see Table 1. A
crystal of the cis-isomer was selected for the X-ray struc-
tural study, vide infra.
`
versita di Pisa, with a C. Erba mod. 1106 elemental analyzer.
All reactions and manipulations were carried out under
a controlled (dinitrogen, or carbon monoxide, as specified)
atmosphere. The compounds cis-Pt(CO)2Cl2 [10] and
PtCl2(NCEt)2 [5] were prepared according to the literature.
By operating under dinitrogen, anhydrous SnCl2 was
obtained by reacting SnCl4 with Sn in dimethoxyethane.
Tin granules (13.07 g, 110 mmol) were stirred with SnCl4
(ꢂ10 mL, ꢂ85 mmol) in dimethoxyethane (300 mL) at
room temperature for 2 d. Unreacted tin was filtered off
and the filtrate was evaporated to dryness. The solid resi-
due was added of heptane and the resulting suspension
was filtered. The colourless solid was dried in vacuo (91%
yield). Anal. Calc. for SnCl2: Cl, 37.4. Found: Cl, 38.0%.
3.4. cis ! trans isomerization of PtCl2(CO)(NCEt)
cis-PtCl2(CO)(NCEt) (64.5 mg, 0.185 mmol) was dis-
solved in CDCl3 (3.5 mL) under N2. 1H NMR spectra were
recorded after 3 min, 1 h and 24 h (T = 25 ꢀC). The inten-
sity of the peaks due to the trans isomer, hardly visible in
the first spectrum, progressively increased. In 24 h the equi-
librium, corresponding to an approximate trans/cis molar
ratio of 10, was reached. In another experiment cis-
3.2. Reaction of PtCl2(NCEt)2 with CO
A solution of PtCl2(NCEt)2 (6.22 g, 16.54 mmol) in 1,2-
dichloroethane (150 mL) was saturated with CO and
heated at 50 ꢀC, the total pressure being maintained at

D. Belli Dell’Amico et al. / Inorganica Chimica Acta 360 (2007) 3765–3770
3769
PtCl2(CO)(NCEt) (12.1 mg, 0.035 mmol) was dissolved in
1,2-dichloroethane (1.5 mL) under N2. The IR spectra of
the solution were recorded after 3 min, and after 24 h at
25 ꢀC: initially, only the band at 2122 cmꢀ1 was observed,
while after 24 h the strong band at 2137 cmꢀ1 of the
3.6. The equilibrium PtCl2(CO)(NCEt) + CO ꢀ cis-PtCl2-
(CO)2 + NCEt
By operating under dinitrogen, PtCl2(NCEt)2 (49.7 mg,
0.132 mmol) was added of 30 lL of a solution containing
1.7 · 10ꢀ6 mol of tin. After evaporation to dryness in
vacuo, CDCl3 (4.526 g) was added under CO and the yel-
low solution thus obtained became colorless after some
hours.
trans-isomer was accompanied by a shoulder at 2122 cmꢀ1
.
3.5. X-ray crystal structure determination
A tabular crystal of cis-PtCl2(CO)(NCEt) of dimensions
0.48 · 0.28 · 0.06 mm, cut from a larger laminar crystal,
was sealed in a Lindemann capillary and used for the dif-
fractometric experiment. The measurements were carried
out by using a Bruker AXS P4 diffractometer equipped
with graphite-monochromated Mo Ka radiation (k =
0.71073 A). The unit cell parameters listed in Table 3
were calculated from the setting angles of 37 strong
reflections.
After 24 h stirring at 23.4 ꢀC, an aliquot of the solution
was transferred under CO into an NMR tube. The longi-
tudinal relaxation times of the free and coordinated nitrile
protons were determined by the ‘‘Inversion Recovery
Technique’’. They correspond to 9.74(4) and 8.7(1) s for
the CH3 and the CH2 protons, respectively, of the free
ligand, and to 3.82(9) and 2.02(8)s for the CH3 and the
CH2 protons, respectively, of the coordinated ligand.
˚
1
The H NMR spectra were recorded every day for 7 days,
All data were collected in the x/2h scan mode, and
three standard reflections were monitored every 97
measurements for checking crystal decay and equipment
stability. Data reduction was by the XSCANS program
[12]. A set of 2144 intensity data (2.22ꢀ 6 h 6 25.49ꢀ)
were corrected for Lorentz polarization and absorption
effects by an integration method based on the crystal
shape [13]. After merging the equivalent reflections
ðRint ¼ ½R j F 2o ꢀ F o2ðmeanÞ j =RðF 2oÞꢃ ¼ 0:0449Þ, 1556 inde-
pendent reflections were obtained. The structure solution
was by standard direct methods in the P21/c space group,
univocally suggested by the systematic absences. The
hydrogen atoms were placed in calculated positions and
in the refinement were let to ‘ride’ on the connected car-
bon atoms. The final reliability factors (anisotropic
thermal parameters for all heavy atoms) are listed in
Table 3. The calculations were done by using the SHELXTL
program [13] and some routines contained in the WINGX
suite [14].
using a delay time of 35 s (T = 23.4 ꢀC), in order to avoid
systematic errors due to saturation problems. After the
first day, no significant differences were noted. The quan-
titative determination of the species at equilibrium was
based on the areas of the quartets of the free and coordi-
nated nitriles.
By approximating activities to concentrations, the fol-
lowing equation was obtained for the equilibrium constant
of reaction 2
½PtCl2ðCOÞ2ꢃ ꢁ ½NCCH2CH3ꢃ
½COꢃ ꢁ ½PtCl2ðCOÞðNCEtÞꢃ
1
Car ꢁ Nit
K ¼
¼
ꢁ
V ꢁ ½COꢃ
Mix
ð6Þ
where V is the solvent volume/L; Car is the PtCl2(CO)2/
mol; Nit is the free nitrile/mol; Mix is the (cis- + trans-)-
PtCl2(CO)(NCEt)/mol; [CO] = 6.1 · 10ꢀ3/mol Lꢀ1
.
The CO concentration in the saturated solution has been
calculated by using the Ostwald coefficient for the gas sol-
ubility in CHCl3 [15]. Correction for the vapour pressure of
the solvent was applied [16].
By taking into consideration that the precursor
PtCl2(NCEt)2 is not present at equilibrium, the following
equations can be written
Table 3
Crystal data and structure refinement of cis-PtCl2(CO)(NCEt)
8
Empirical formula
Formula weight
Crystal system
Space group
C4H5Cl2NOPt
349.08
Car þ Mix ¼ n
>
0
<
monoclinic
P21/c (no. 14)
9.251(2)
13.556(2)
6.729(1)
97.70(3)
836.3(3)
4
2.773
17.343
2144
1556 [0.0449]
83
Mix þ Nit ¼ 2n0
ð7Þ
>
:
Mix
Nit
A
B
¼
˚
a (A)
˚
b (A)
where n0 = initial PtCl2(NCEt)2/mol.
˚
c (A)
A and B correspond to the integrals of the CH2 reso-
b (ꢀ)
3
˚
U (A )
nance of the coordinated and free nitrile, respectively
Z
8
2n0A
Dcalc (g cmꢀ3
)
Mix ¼
Nit ¼
>
AþB
<
l (mmꢀ1
)
2n0B
ð8Þ
AþB
Number measured
Number unique [Rint
Number parameters
R1, wR2 [I > 2r(I)]
R1, wR2 (all data)
>
:
BꢀA
AþB
]
Car ¼ n0
0.0384, 0.0737
0.0695, 0.0901
1.062
By substituting in (6), expression (9) was obtained,
through which the equilibrium constant (48 6) was
determined
Goodness-of-fit on F2

3770
D. Belli Dell’Amico et al. / Inorganica Chimica Acta 360 (2007) 3765–3770
(c) D. Fraccarollo, R. Bertani, M. Mozzon, U. Belluco, R.A.
n0
B2 ꢀ AB
A2 þ AB
K ¼
ꢁ
ð9Þ
Michelin, Inorg. Chim. Acta 201 (1992) 15;
(d) V.Yu. Kukushkin, V.M. Tkachuk, Z. Anorg. Allg. Chem. 613
(1992) 123;
V ꢁ ½COꢃ
˚
(e) P. Svensson, K. Lo¨vqvist, V.Yu. Kukushkin, A. Oskarsson, Acta
4. Supplementary material
Chem. Scand. 49 (1995) 72;
(f) F.D. Rochon, R. Melanson, E. Thouin, A.L. Beauchamp, C.
Bensimon, Can. J. Chem. 74 (1996) 144;
(g) V.Yu. Kukushkin, Russ. J. Coord. Chem. 24 (1998) 173.
[4] (a) R.A. Michelin, M. Mozzon, R. Bertani, Coord. Chem. Rev. 147
(1996) 299;
CCDC 628698 contains the supplementary crystallo-
graphic data for cis-PtCl2(CO)(NCEt). These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@
ccdc.cam.ac.uk.
(b) V.Yu. Kukushkin, Platinum Metals Rev. 42 (1998) 106;
(c) G. Natile, M. Coluccia, Coord. Chem. Rev. 216–217 (2001)
383;
(d) U. Belluco, F. Benetollo, R. Bertani, G. Bombieri, R.A.
Michelin, M. Mozzon, O. Tonon, A.J.L. Pombeiro, F.C. Guedes
da Silva, Inorg. Chim. Acta 334 (2002) 437;
(e) V.Yu. Kukushkin, A.J.L. Pombeiro, Chem. Rev. 102 (2002)
1771;
Acknowledgements
(f) A.J.L. Pombeiro, V.Yu. Kukushkin, in: J.A. McCleverty, T.J.
Meyer, (Eds.), Comprehensive Coordination Chemistry II, vol. 1.
2004, pp. 639;
The authors thank the Ministero dell’Istruzione, dell’
`
Universita e della Ricerca (MIUR), Programmi di Ricerca
(g) V.Yu. Kukushkin, A.J.L. Pombeiro, Inorg. Chim. Acta 358
(2005) 1;
Scientifica di Rilevante Interesse Nazionale, PRIN 2004,
and the Consiglio Nazionale delle Ricerche (C.N.R.), Prog-
etto CNR/MIUR ‘‘Sviluppo di microcelle a combustibile’’,
for financial support.
(h) A.V. Khripun, V.Yu. Kukushkin, S.I. Selivanov, M. Haukka,
J.L. Pombeiro, Inorg. Chem. 45 (2006) 5073.
´
˚
[5] V.Yu. Kukushkin, A. Oskarsson, L.I. Elding, Inorg. Synth. 31 (1998)
280.
[6] M.L. Tobe, Inorganic Reaction Mechanisms, Nelson, London,
1972.
References
`
[7] D. Belli Dell’Amico, F. Calderazzo, C.A. Veracini, N. Zandona,
Inorg. Chem. 23 (1984) 3030.
[1] (a) R.A. Walton, Q. Rev. Chem. Soc. 19 (1965) 126;
(b) B.N. Storhoff, H.C. Lewis, Coord. Chem. Rev. 23 (1977) 1;
(c) J.A. Davies, F.R. Hartley, Chem. Rev. 81 (1981) 79;
(d) H. Endres, in: G. Wilkinson, J.A. McCleverty, R.G. Gillard
(Eds.), Comprehensive Coordination Chemistry 2 (1987) 261.
[2] (a) L.E. Manzer, C.A. Tolman, J. Am. Chem. Soc. 97 (1975) 1955;
(b) H. Kurosawa, T. Majima, N. Asada, J. Am. Chem. Soc. 102
(1980) 6996;
[8] (a) T. Weil, L. Spaulding, M. Orchin, J. Coord. Chem. 1 (1971) 25;
(b) L. Spaulding, B.A. Reinhardt, M. Orchin, Inorg. Chem. 11 (1972)
2092.
[9] F.H. Allen, Acta Crystallogr., Sect. B 58 (2002) 380.
[10] F. Bagnoli, D. Belli Dell’Amico, F. Calderazzo, U. Englert, F.
Marchetti, G.E. Herberich, N. Pasqualetti, S. Ramello, J. Chem. Soc.,
Dalton Trans. (1996) 4317.
[11] D. Belli Dell’Amico, R. Bini, F. Calderazzo, L. Carbonaro, L.
Labella, A. Vitullo, Organometallics 24 (2005) 4427.
[12] XSCANS, X-ray Single Crystal Analysis System, rel. 2.1 Bruker AXS
Inc., Madison, WI, USA, 1994.
(c) S.P. Nolan, R. Lopez de la Vega, C.D. Hoff, Organometallics 5
(1986) 2529;
(d) F.C. Rix, M. Brookhart, P.S. White, J. Am. Chem. Soc. 118
(1996) 4746;
[13] G.M. Sheldrick, SHELXTL-Plus, Rel. 5.03, Bruker AXS Inc., Madison,
WI, USA, 1995.
[14] L.J. Farrugia, J. Appl. Cryst. 32 (1999) 837.
[15] A. Seidell, Solubilities of Inorganic and Organic Compounds, Van
Nostrand Company Inc., New York, 1928.
(e) J. Shearer, H.L. Jackson, D. Schweitzer, D.K. Rittenberg, T.M.
Leavy, W. Kaminsky, R.C. Scarrow, J.A. Kovacs, J. Am. Chem. Soc.
124 (2002) 11417.
[3] (a) T. Uchiyama, Y. Toshiyasu, Y. Nakamura, T. Miwa, S.
Kawaguchi, Bull. Chem. Soc. Jpn. 54 (1981) 181;
(b) F.P. Fanizzi, F.P. Intini, L. Maresca, G. Natile, J. Chem. Soc.,
Dalton Trans. (1990) 199;
[16] D.R. Lide (Ed.), Handbook of Chemistry and Physics, 82nd ed., CRC
Press, Boca Raton, 2001, pp. 6–72.