Halo-carbonyl complexes of platinum(II) and palladium(II)

Article abstract of DOI:10.1016/S0022-328X(00)00947-5

The mononuclear and binuclear square-planar complexes of palladium(II) and platinum(II) cis-PtCl₂(CO)₂ (1), trans- Pt₂Cl₄(CO)₂ (2), cis-PtBr₂(CO)₂ (3), and cis-Pd₂Cl

Full text of DOI:10.1016/S0022-328X(00)00947-5

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Journal of Organometallic Chemistry 622 (2001) 180–189
Halo-carbonyl complexes of platinum(II) and palladium(II)
Franco Bagnoli a, Daniela Belli Dell’Amico a,*, Fausto Calderazzo a, Ulli Englert b,
Fabio Marchetti c, Alessandra Merigo a,1, Stefano Ramello a,2
a Dipartimento di Chimica e Chimica Industriale, Uni6ersita` di Pisa, 6ia Risorgimento 35, I-56126 Pisa, Italy
b Institut fu¨r Anorganische Chemie der RWTH, Professor-Pirlet-Strasse 1, D-52074 Aachen, Germany
c Dipartimento di Ingegneria Chimica, dei Materiali, delle Materie Prime e Metallurgia, Uni6ersita` degli Studi ‘La Sapienza’,
6ia del Castro Laurenziano 7, I-00161 Rome, Italy
Received 31 October 2000; accepted 12 November 2000
Abstract
The mononuclear and binuclear square-planar complexes of palladium(II) and platinum(II) cis-PtCl2(CO)2 (1), trans-
Pt2Cl4(CO)2 (2), cis-PtBr2(CO)2 (3), and cis-Pd2Cl4(CO)2 (4), have been prepared by new synthetic procedures and some of them
(2, 3, and 4) structurally characterised by X-ray diffraction methods. In the mononuclear platinum derivatives, cis-PtX2(CO)2,
,
,
X=Cl, Br, the molecules are arranged in columns, the Pt···Pt separation being 3.378 A (X=Cl) or 3.65 A (av., X=Br). The
chloride-bridged dinuclear chloro-carbonyl complexes M2Cl4(CO)2, M=Pd, Pt, contain terminal chloride and carbonyl groups,
trans for the platinum derivative 2, but, unexpectedly, cis for the corresponding palladium compound 4. Packing is based on
intermolecular C···X or Pt···Pt interactions, as a function of the nature of the halide. The carbonylation at atmospheric pressure
and room temperature of the tetrahalo complexes of platinum(II) in the presence of AlX3 as halide scavenger leads to
[PtX3(CO)]− or PtX2(CO)2, depending on the Pt/AlX3 molar ratio. The crystal and molecular structural data of
[NBu4][PtBr3(CO)] (5), show the anion to have substantially identical Pt–Br bond distances, the CO ligand performing no trans
influence. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Palladium; Platinum; Carbonyls; Structures
Cl, Br, I) [1a,g,2] and Pd2X4(CO)2 (X=Cl, Br) [1d,e,h]
are known and the reactions between the metal halides
1. Introduction
and carbon monoxide to give the corresponding car-
Halo-carbonyl complexes of palladium(II) and plat-
bonyl derivatives have been studied. Interestingly, the
inum(II) have been studied extensively [1], for their
mononuclear carbonyl derivatives of platinum(II) are
unusual properties [2], for their importance in catalysis
thermodynamically stable at room temperature, see
[3] and, last but not least, for historical reasons, cis-
PtCl2(CO)2 being the first metal carbonyl derivative
ever reported in the literature [4]. On the other hand,
several spectroscopic and structural features are still
unexplored, mainly because of the experimental
difficulties connected with the isolation and handling of
these compounds. The neutral complexes cis-PtX2(CO)2
[1a,c,j] and trans-PtX2(CO)2 [1f, 2], Pt2X4(CO)2 (X=
Eqs. (1a) and (1b), with respect to the corresponding
anhydrous metal halides and CO, as previously re-
ported for PtCl2 [1j] and PtI2 [1g] and observed in the
course of this work for PtBr2. The direct carbonylation
of the three halides is therefore a viable process at room
temperature. On the other hand, the mononuclear halo-
carbonyl derivatives of palladium(II) are unknown and
the dinuclear ones (X=Cl, Br) are in equilibrium with
CO and PdX2 [1e,g,5], see Eq. (2); in the case of X=Cl,
the hexanuclear b-PdCl2 [5] was established to be the
crystalline phase involved in the equilibrium.
In spite of the considerable interest for palladium(II)
and platinum(II) carbonyl derivatives in several fields,
the preparative procedures to these compounds still
* Corresponding author. Fax: +39-50-20237.
E-mail address: belli@dcci.unipi.it (D. Belli Dell’Amico).
1 Present address: Lucchini C.R.S., viale della Resistenza 2, I-57025
Piombino, Livorno, Italy.
2 Present address: Enichem-IGD, Via G. Fauser 4, I-28100 Novara,
Italy.
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00947-5

F. Bagnoli et al. / Journal of Organometallic Chemistry 622 (2001) 180–189
181
required further improvement and, moreover, structural
information about unsubstituted halo-carbonyl deriva-
tives of palladium and platinum is limited. As a matter
of fact, the crystal and molecular structures of
Pt2I4(CO)2 [1g] and cis-PtCl2(CO)2 [1j] only have been
published.
This paper reports new facile preparative methods to
cis-PtX2(CO)2 (X=Cl, Br) and to M2Cl4(CO)2 (M=
Pd, Pt) by operating at atmospheric pressure of carbon
monoxide and describes the crystal and molecular
structures of cis-PtBr2(CO)2, trans-Pt2Cl4(CO)2 and cis-
Pd2Cl4(CO)2.
Chatt [7] reports DG°= −0.7 kcal mol−1 for reaction
(4) in aqueous solution. Thus,
[PtCl3(C2H4)]− +Br− ?[PtCl2Br(C2H4)]− +Cl−
(4)
the hydration free energy [8,9] of Cl− (−74.8 kcal
mol−1) with respect to that of Br− (−67.9 kcal
mol−1
exchange.
)
is mainly responsible for the observed
As far as point (b) is concerned, when the prepara-
tion of [NBu4]2[PtBr4] was carried out by treating
t
[NBu4]2[PtCl4] with BuBr in CDCl3, see Eq. (5), a
mixture of the chloride and bromide derivatives was
PtX2+2CO“PtX2(CO)2 (X=Cl, Br)
CO
2PtI2+2CO“Pt2I4(CO)2 ?2PtI2(CO)2
(1a)
(1b)
(2)
t
also obtained. By 195Pt-NMR and using a BuBr/Pt
molar ratio of 5.5 it was established that at room
temperature in
7 days the platinum complexes
2PdX2+2CO?Pd2X4(CO)2 (X=Cl, Br)
[PtBr3Cl]2− (l −2270 ppm), [Pt2Br6]2− (l −2318
ppm) and [PtBr4]2− (l −2559 ppm) are present in
equilibrium with relative intensities 1:3:4. Using a large
2. Results and discussion
t
excess of BuBr it was possible to convert this mixture
to [Pt2Br6]−2− and [PtBr4]2−
.
2.1. Halide substitutions on platinum precursors
[NBu4]2[PtCl4]+4tBuBr“[NBu4]2[PtBr4]+4tBuCl
(5)
The starting materials to bromocarbonyl platinum
complexes were obtained by chloride/bromide substitu-
tion. For instance, the preparation of [NBu4]2[PtBr4]
was accomplished by two alternative methods: (a) from
aqueous K2PtCl4 by halide substitution with KBr, see
Eq. (3), and extracting the resulting [Pt2Br6]2− into
CH2Cl2 using [NBu4]Br as a phase-transfer agent; (b) in
chlorinated solvents from [NBu4]2[PtCl4] by reaction
If [NBu4]2[PtCl4] was treated with the stoichiometric
amount of anhydrous HBr in CH2Cl2 a fast reaction
was observed leading to [NBu4]2[Pt2Br6] exclusively, see
Eq. (6).
2[NBu4]2[PtCl4]+8HBr
“[NBu4]2[PtBr6]+8HCl+2[NBu4]Br
(6)
t
with RBr (R=H, Bu).
t
t
Method (a) requires an excess of KBr. As a matter of
The DG° of BuCl, BuBr, HCl, HBr are –16.0, –7.9,
f
fact, using a Br−/Pt molar ratio of 4.5 at room temper-
−22.8 and –12.8 kcal mol−1, respectively [10]. The
contributions to DG° due to the bromide exchange are
2−
ature, a mixture of the species [PtClnBr4−n
]
(n=0–
−6.9, −8.1 and −10.0 kcal mol−1 for Br(−aq.), BuBr
t
3) resulting from partial substitution was obtained, see
Equilibria (3a)–(3d). The different complex anions can
be detected by 195Pt-NMR [6] as follows: [PtCl3Br]2−, l
−1846 ppm; [PtCl2Br2]2−, two resonances at l −2087
and −2098 ppm, due to the trans- and cis-isomer,
and HBr, respectively, thus justifying the observed ex-
change increasing in the sequence Br−(aq.)BtBuBrB
HBr.
respectively; [PtClBr3]2−, l −2366 ppm and [PtBr4]2−
,
2.2. Syntheses of platinum and palladium halocarbonyls
l −2662 ppm. On the basis of the relative peak
intensities the prevailing species is [PtClBr3]2−. For
complete substitution, a saturated solution of KBr was
used, corresponding to a nominal Br−/Pt molar ratio
]20.
Relevant to the thermodynamics of these systems is
the early preparation [4] of cis-PtCl2(CO)2: Schu¨tzen-
berger first converted [4b] a platinum sponge into a
platinum chloride with chlorine at 250°C, further reac-
tion at lower temperature with CO giving the colourless
cis-PtCl2(CO)2 and Pt2Cl4(CO)2.
We had shown earlier that the dinuclear Pt2Cl4(CO)2
undergoes carbonylation to cis-PtCl2(CO)2 through the
intermediacy of trans-PtCl2(CO)2 [1f]. We have now
established that PtCl2 suspended in CH2Cl2 or SOCl2
reacts at moderate rate with CO at room temperature
and atmospheric pressure producing cis-PtCl2(CO)2 (1),
1 mmol of platinum chloride being converted com-
pletely in about 3 days.
[PtCl4]2− +4Br− ?[PtBr4]2− +4Cl−
[PtCl4]2− +Br− ?[PtBrCl3]2− +Cl−
[PtBrCl3]2− +Br− ?[PtBr2Cl2]2− +Cl−
[PtBr2Cl2]2− +Br− ?[PtBr3Cl]2− +Cl−
[PtBr3Cl]2− +Br− ?[PtBr4]2− +Cl−
(3)
(3a)
(3b)
(3c)
(3d)
Thermodynamic data about substitution reactions of
this type are not numerous: a paper by Leden and

182
F. Bagnoli et al. / Journal of Organometallic Chemistry 622 (2001) 180–189
Compound 1 can be readily prepared also by car-
When the treatment with AlCl3 of the intermediate
[PtCl3(CO)]− was carried out under dinitrogen rather
than under carbon monoxide, the dinuclear complex
trans-Pt2Cl4(CO)2 (2) was obtained exclusively, see Eq.
(11). This methodology can therefore be directed to-
wards the formation of the mononuclear- or the dinu-
clear compound simply by a change of the operating
procedure in the final step.
The preparation of cis-PtBr2(CO)2 (3) was performed
from [NBu4]2[PtBr4] and CO by using AlBr3 as bromide
scavenger. The reaction, monitored by gasvolumetry
and IR spectroscopy, shows similar features to the
corresponding chloride system.
bonylation of [PtCl4]2− in the presence of AlCl3 as
halide scavenger in chlorinated solvents, the tetra-
chloroplatinate(II) anion, as the tetrabutylammonium
derivative, being obtained by solvent-extraction from
aqueous solution, see Eq. (7).
[PtCl ]2−
“[NBu4]2[PtCl4](CH Cl )+2Cl(−aq.)
4 (aq.)+2NBu4Cl(CH Cl )
2
2
(7)
2
2
[NBu4]2[PtCl4]+AlCl3+CO
“[NBu4][PtCl3(CO)]+[NBu4][AlCl4]
[PtCl4]2− +CO?[PtCl3(CO)− +Cl−
[NBu4][PtCl3(CO)]− +AlCl3+CO
“[NBu4][AlCl4]+trans-PtCl2(CO)2
trans-PtCl2(CO)2“cis-PtCl2(CO)2
[NBu4][PtCl3(CO)]+AlCl3
(8)
(9)
[NBu4]2[PtBr4]+CO+AlBr3
“[NBu4][PtBr3(CO)]+[NBu4][AlBr4]
[NBu4][PtBr3(CO)]+CO+AlBr3
“trans-PtBr2(CO)2+[NBu4][AlBr4]
trans-PtBr2(CO)2“cis-PtBr2(CO)2
(12)
(10a)
(10b)
(13)
(14)
“[NBu4][AlCl4]+1/2trans-Pt2Cl4(CO)2
(11)
Compound 3 has been prepared alternatively by react-
s
ing 1 with RBr (R=tBu, Bu), see Eq. (15).
The reaction sequence was followed spectroscopically
by IR and NMR, and by gas-volumetric measurements
of the CO uptake. In order to avoid the intermediate
precipitation of PtCl2, which subsequently would react
slowly with CO to yield 1, the carbonylation is best
carried out by adding the first equivalent of AlCl3, and
allowing the system to form the monocarbonylated
product of Eq. (8). It is interesting to note that
[NBu4]2[PtCl4] itself (i.e. even in the absence of AlCl3)
reacts with CO producing the [PtCl3(CO)]− anion: in
about 40 h at 21°C, a 1.3×10−2 M solution of
[NBu4]2[PtCl4] in sym-C2H4Cl2 absorbed CO up to a
CO/Pt molar ratio of 0.65, as for Equilibrium 9.
Only after the addition of one equivalent of AlCl3,
the equilibrium was displaced to the right upon sub-
traction of Cl− and further carbon monoxide was
rapidly absorbed up to a CO/Pt molar ratio of 1. Under
these conditions, the IR spectrum is characterized by a
band at 2098 cm−1, due to [PtCl3(CO)]−. The addition
of a second equivalent of AlCl3 was followed by the
rapid uptake of further CO forming trans- and then
cis-PtCl2(CO)2, see reactions (10a) and (10b), as evi-
denced by the band at 2098 cm−1 being replaced by
bands at 2150 cm−1 (trans-isomer) and 2138, 2178
cm−1 (cis-isomer). These experiments show that the
trans-isomer is the primary product of the reaction, in
agreement with the strong trans effect of ligated CO,
followed by isomerization to 1. trans-PtCl2(CO)2 was
also found to be the primary product of the carbonyla-
tion of the dinuclear trans-Pt2Cl4(CO)2 [1f]: if the trans
geometry of the dimer (as effectively found in the solid
state, vide infra) is assumed, the strong trans effect of
coordinated CO can be again considered to be responsi-
ble for this observation.
cis-PtCl2(CO)2+2RBr“cis-PtBr2(CO)2+2RCl
(15)
t
By using a slight excess of BuBr in CH2Cl2 as solvent,
the high-yielding reaction is over in a few minutes.
When the reaction was carried out in CCl4, the conver-
1
sion, monitored by H-NMR, was about 75% after 30
s
min. With BuBr the reaction proceeded more slowly, a
conversion of about 33% being observed in 48 h. These
data suggest that the cleavage of the Br–C bond is
probably the rate-determining step.
Another method of preparation of cis-PtBr2(CO)2
consists of treating a suspension of PtBr2 in a chlori-
nated hydrocarbon with CO at room temperature and
atmospheric pressure (under these conditions the reac-
tion is very slow), or under a moderate CO pressure
(about 6 atm).
Dehalogenation of [Pd2Cl6]2− as the tetrabutylam-
monium derivative with AlCl3 in the presence of CO led
to the dinuclear cis-Pd2Cl4(CO)2 (4), see Eq. (16).
[NBu4]2[Pd2Cl6]+2AlCl3+2CO
“Pd2Cl4(CO)2+2NBu4[AlCl4]
(16)
The IR data of the neutral platinum(II) and palladiu-
m(II) carbonyl derivatives are reported in Table 1,
which can be used, with some precaution, for structural
information. Although some of these compounds have
been known for many years, structural information in
the solid state is still rather limited. We therefore
decided to carry out an extended study of their solid-
state structures. As we shall see later, the IR spectra,
suggesting a similar molecular arrangement for the
dinuclear chloro-carbonyl derivatives of platinum(II)

F. Bagnoli et al. / Journal of Organometallic Chemistry 622 (2001) 180–189
183
Table 3
and palladium(II), were misleading as these compounds
,
Main bond lengths (A) and angles (°) of cis-PtBr2(CO)2 (3)
were found to have different solid-state molecular
structures.
Pt(1)–C(1)
Pt(1)–C(2)
Pt(1)–Br(1)
Pt(1)–Br(2)
C(1)–O(1)
C(2)–O(2)
1.86(4)
1.96(6)
2.411(4)
2.417(4)
1.12(4)
1.06(5)
Pt(2)–C(4)
Pt(2)–C(3)
Pt(2)–Br(3)
Pt(2)–Br(4)
C(3)–O(3)
C(4)–O(4)
1.88(3)
1.89(5)
2.416(4)
2.417(4)
1.17(5)
1.12(4)
2.3. Crystal structure determinations
The molecular structure of 2, trans-Pt2Cl4(CO)2, is
shown in Fig. 1. Bond distances and angles are listed in
Table 2.
C(1)–Pt(1)–C(2)
93.8(17)
C(1)–Pt(1)–Br(1) 178.3(12)
C(4)–Pt(2)–C(3)
95.0(14)
C(4)–Pt(2)–Br(4) 176.0(9)
Table 1
C(2)–Pt(1)–Br(1)
C(1)–Pt(1)–Br(2)
87.7(12)
87.1(12)
C(3)–Pt(2)–Br(4)
C(4)–Pt(2)–Br(3)
89.0(10)
85.0(9)
IR spectra (wCO, cm−1) of some carbonyl derivatives of platinum(II)
and palladium(II)
C(2)–Pt(1)–Br(2) 179.0(12)
Br(1)–Pt(1)–Br(2) 91.35(17)
C(3)–Pt(2)–Br(3) 178.8(9)
Br(3)–Pt(2)–Br(4) 91.08(14)
Nujol
sym-C2H2Cl4
Heptane
O(1)–C(1)–Pt(1)
O(2)–C(2)–Pt(1)
177(4)
178(4)
O(3)–C(3)–Pt(2)
O(4)–C(4)–Pt(2)
176(3)
179(3)
cis-PtCl2(CO)2 (1) 2187, 2152 a 2179, 2136 [1c] 2167, 2120 [1g]
a,c
trans-Pt2Cl4(CO)2 2146 [1d]
(2)
2138
2130 [1g]
Compound 2 is constituted by two {PtCl3(CO)}
squares joined by two bridging chlorides. The squares
deviate somewhat from coplanarity, the point symme-
try of the molecule being C2, rather than C2h. For each
{PtCl3(CO)} system, the Pt, Cl(1), Cl(1%), C and O
atoms are coplanar within 0.029 A, while the Cl(2)
atom is 0.228 A out of this plane. Moreover, the
dihedral angle at the bridging chlorides Pt–
a,b
2146
cis-PtBr2(CO)2 (3) 2167, 2122 a 2170, 2130 [1g] 2156, 2115 [1g]
a,b
Pt2Br4(CO)2
2129
2127 [1g]
2122 [1g]
c
d
cis-Pd2Cl4(CO)2 (4) 2167 [1d]
2166 [1h]
2159 [1d]
a This work.
,
b PCTFE (polychlorotrifluoroethylene).
c CH2Cl2.
,
d Cyclohexane.
Cl(1)···Cl(1%)–Pt% is 171.8° and the Pt–Cl(1) and Pt–
,
Cl(1%) distances differ by 0.11 A. The Pt–Clt
(Clt=terminal chloride) and Pt–CO distances are simi-
lar to those observed in cis-PtCl2(CO)2, whereas the
Pt–Clb (Clb=bridging chloride) distances are, as ex-
,
pected, longer by 0.16 and 0.27 A, respectively. The
molecules are stacked on each other, with completely
Fig. 1. The molecular structure of trans-Pt2Cl4(CO)2 (2). The apex in
the labels have the same meaning as in Table 2. Thermal ellipsoids
are at 30% probability.
,
eclipsed atoms, the separation being 3.525 A (c transla-
tion). Different from 3 (vide infra) and cis-PtCl2(CO)2
[1j], where the shortest contacts are between the halide
and the carbonyl carbon, the shortest contact is be-
tween the platinum atoms.
The molecular structure of cis-PtBr2(CO)2, 3, is
shown in Fig. 2. Bond distances and angles are listed in
Table 3.
The molecular structure consists of a square-planar
disposition of two bromines and two carbonyl groups
around platinum.
Table 2
Bond lengths (A) and angles (°) for trans-Pt2 Cl4(CO)2 (2) a
,
Pt–C
Pt–Cl(2)
Pt–Cl(1)
1.86(5)
2.127(8)
2.287(13)
Pt–Cl(1%)
C–O
2.396(12)
1.08(5)
C–Pt–Cl(2)
C–Pt–Cl(1)
Cl(2)–Pt–Cl(1)
C–Pt–Cl(1%)
89.4(17)
176.6(18)
93.8(4)
Cl(2)–Pt–Cl(1%)
Cl(1)–Pt–Cl(1%)
Pt–Cl(1)–Pt%
O–C–Pt
173.7(7)
85.2(2)
94.5(2)
176(4)
91.5(18)
The geometry is similar to that of cis-PtCl2(CO)2 [1j].
However, two independent molecules of cis-PtBr2(CO)2
are present in the asymmetric unit. As in the crystal of
cis-PtCl2(CO)2, the molecules are stacked with the bro-
mide facing the carbonyl carbon of the nearest
molecules, the C···Br distances being: C(1)···Br(1),
a Symmetry transformations used to generate equivalent atoms:
%=−x+2, −y+1, z.
3.599;
C(2)···Br(2),
3.581;
C(3)···Br(3),
3.603;
,
C(4)···Br(4), 3.665 A. The two independent molecules
form stacks along the a and b directions, respectively.
The Pt···Pt distances within the stacks are 3.615 and
,
,
3.656 A and 3.640 and 3.702 A, respectively, whereas
the Pt···Pt···Pt angles are 157 and 170°, respectively.
The wider stacking of the bromide derivative with
Fig. 2. The molecular structure of the two independent molecules in
the crystal of cis-PtBr2(CO)2 (3). Thermal ellipsoids are at 30%
probability.

184
F. Bagnoli et al. / Journal of Organometallic Chemistry 622 (2001) 180–189
these three cases. Moreover, the C(1)–Pd distance is
respect to cis-PtCl2(CO)2 is due to the larger size of the
bromide.
The molecular structure of 4, cis-Pd2Cl4(CO)2, is
shown in Fig. 3 and Table 4 lists the bond distances
and angles.
,
1.87(1) A, i.e. practically the same as the C–Pt distance
of the corresponding platinum complex, in agreement
with the substantially identical ionic radii of platinu-
,
,
m(II) (0.60 A) and palladium(II) (0.64 A) [12].
In 4 the CO groups are in cis positions. The two {Pd
Cl3(CO)} squares are almost exactly planar (maximum
3. Conclusions
,
deviation, 0.019 A) and share the Cl(2)···Cl(3) edge at a
dihedral angle of 174.9°. The inversion centres present
in the crystal structure produce pairs of molecules,
This paper, which is believed to be relevant for
people interested in carbonyl derivatives of platinum(II)
and palladium(II), has produced some new observa-
tions.
,
whose centroids are 3.75 A apart, with the carbonyl
groups of the two molecules within each pair pointing
out in opposite directions. The Pd···Pd non-bonding
1. The dinuclear platinum(II) and palladium(II)
chloro-carbonyl complexes M2Cl4(CO)2 are not
isostructural and have a different arrangement of
the ligands. In fact, while the platinum(II) derivative
2 has the trans structure, the palladium(II) com-
pound 4 has been shown to prefer a cis arrangement
of the ligands in the solid state. This was unexpected
in view of the similarity of the IR spectra, see Table
1, in Nujol as medium or in solution (sym-C2H2Cl4
or heptane), once the shift of the CO stretching
vibrations towards high wavenumbers for palladiu-
m(II), vide infra, is taken into consideration. It is
interesting to note that the cis structure 4 was
considered as a possibility for the uncharged chloro-
carbonyl of palladium(II) [13], although a less likely
one on the basis of the ‘une6en distribution of elec-
tron density in the molecule and une6en strengths of
bonds linking similar atoms’. The presence of only
one wCO for the palladium(II) derivative was taken
initially as evidence [1d,h] for a trans arrangement.
This structural assignment must now be revised.
Assuming that the cis structure persists in solution
too, the IR observation is to be attributed to the
fact that the two fragments of the molecule are not
vibrationally coupled.
,
contact within each pair is 3.624 A. The shortest non-
bonding contacts are, however, between atoms belong-
,
ing to molecules of different pairs, namely 3.388 A for
,
,
Cl(4)···Pd(2%), 3.262 A for Cl(1)···O(1¦) and 3.358 A for
Cl(1)···C(1§) (%= −1/2−x, −1/2+y, 1/2−z; ¦=x,
−1+y, z; §=1/2−x, −1/2+y, 1/2−z).
The expected square-planar coordination around
platinum(II) was found for the ionic compound 5
[NBu4][PtBr3(CO)]. The structural parameters [C(1)–Pt,
1.85(2), Br(1)–Pt, 2.427(2); Br(2)–Pt, 2.423(2); Br(3)–
,
Pt, 2.428 A; C(1)–Pt–Br(2) 177.4°] correspond to prac-
tically identical Pt–Br distances, in agreement with the
earlier findings for the corresponding chloride deriva-
tive [NBu4][PtCl3(CO)] [11],which has a Pt–Cl distance
trans to the CO ligand of 2.289(3) A. In other words, as
noted earlier also for [NBu4][PdX3(CO)] [1h], X=Cl,
Br, the CO ligand has no appreciable trans influence in
,
Fig. 3. The molecular structure of cis-Pd2Cl4(CO)2 (4). Thermal
2. The IR data of Table 1 confirm the earlier notion
[1d,h] that palladium(II) carbonyl derivatives have
wCOs higher than those of the corresponding platinu-
m(II) derivatives. This has been attributed [2] to the
presumably negligible p–back bond component
within the Pd–CO bond. Other interpretations of
the experimental observations concerning the high
wCOs for carbonyl derivatives of late transition
metals [Pd(II), Pt(II), Ag(I), Au(I)] in their usual
oxidation states, both neutral and cationic, have
been proposed [14a,b]. However, we still prefer to
maintain the earlier suggestion [2], corroborated by
further experimental data by Strauss and coworkers
[15a,b] and by Aubke and coworkers [15c–e] that
p–backbonding should not be heavily involved in a
satisfactory description of these metal complexes.
3. In the [MX3(CO)]− anions of platinum(II) and pal-
ladium(II), for which three structural determina-
ellipsoids are at 30% probability.
Table 4
,
Bond lengths (A) and angles (°) of cis-Pd2Cl4(CO)2 (4)
Pd(1)–C(1)
Pd(1)–Cl(1)
Pd(1)–Cl(3)
Pd(1)–Cl(2)
C(1)–O(1)
1.891(13)
2.260(3)
2.327(3)
2.331(3)
1.105(13)
Pd(2)–C(2)
Pd(2)–Cl(4)
Pd(2)–Cl(3)
Pd(2)–Cl(2)
C(2)–O(2)
1.879(15)
2.260(3)
2.328(3)
2.336(3)
1.112(14)
C(1)–Pd(1)–Cl(1)
86.1(3)
C(2)–Pd(2)–Cl(4)
C(2)–Pd(2)–Cl(3) 178.5(4)
Cl(4)–Pd(2)–Cl(3) 91.62(12)
87.0(4)
C(1)–Pd(1)–Cl(3) 177.6(3)
Cl(1)–Pd(1)–Cl(3) 91.55(12)
C(1)–Pd(1)–Cl(2)
95.5(3)
C(2)–Pd(2)–Cl(2)
94.7(4)
Cl(1)–Pd(1)–Cl(2) 177.93(11)
Cl(3)–Pd(1)–Cl(2) 86.84(11)
Pd(1)–Cl(2)–Pd(2) 92.91(11)
O(1)–C(1)–Pd(1) 177.4(11)
Cl(4)–Pd(2)–Cl(2) 178.18(13)
Cl(3)–Pd(2)–Cl(2) 86.70(11)
Pd(1)–Cl(3)–Pd(2) 93.23(11)
O(2)–C(2)–Pd(2) 178.4(11)

F. Bagnoli et al. / Journal of Organometallic Chemistry 622 (2001) 180–189
185
tions are now available [1h,11] with the same coun-
tercation, no elongation of the halide ligand trans to
the carbonyl group has been observed.
over P4O10 in vacuo for 3 h (9.35 g, 81.8% yield). Anal.
Calc for C32H72Cl4N2Pt: Cl, 17.2; Pt, 23.7. Found: Cl,
16.9; Pt, 23.1%. H-NMR (CDCl3, 298 K): l 3.65 (2 H,
1
4. In conjunction with the structural data reported
earlier for trans-Pt2I4(CO)2 [1g] this paper shows
that within the dinuclear units, the non-bonding
t, NCH2); 1.78 (2 H, m, NCH2CH2); 1.56 (2 H,
sext,CH2CH3); 0.99 (3 H, t, CH3) ppm. 195Pt-NMR
(CDCl3, 298 K): l −1574 ppm.
,
Pt···Pt distance increases from 3.441 A in trans-
,
Pt2Cl4(CO)2 (2), to 3.846 A in trans-Pt2I4(CO)2. It is
4.3. Halide exchange
interesting to note that the intramolecular Pd···Pd
distance in the dinuclear cis-Pd2Cl4(CO)2 (4) is 3.383
4.3.1. From aqueous K2[PtCl4]
,
A, i.e. similar to the corresponding contact in the
platinum(II) complex, in agreement again with the
similar ionic radii, as noted above. The intramolecu-
An aqueous solution of K2PtCl4 (0.154 M, 17 ml,
2.62 mmol) was saturated with KBr. The orange solu-
tion became red-brown and was shaken with a solution
of NBu4Br (1.71 g, 5.30 mmol) in CH2Cl2 (40 ml) in a
separatory funnel. The organic layer immediately be-
came red-brown, and the aqueous phase discoloured.
The CH2Cl2 solution was separated and evaporated to
dryness under reduced pressure. The oily residue was
treated in vacuo at 50°C for 2 h. The product thus
obtained was dried over P4O10 for 3 h in vacuo (2.11 g,
80.6% yield). Anal. Calc for [NBu4]2[PtBr4],
C32H72Br4N2Pt: Br, 32.0; Pt, 19.5. Found: Br, 32.5; Pt,
18.9%. 1H-NMR (CDCl3, 298 K): l 3.63 (2 H, t,
NCH2); 1.75 (2 H, m, NCH2CH2); 1.54 (2 H,
sext,CH2CH3); 0.98 (3 H, t, CH3) ppm. 195Pt-NMR
(CDCl3, 298 K): l −2560 ppm. After 15 d at room
temperature (r.t.) a new resonance of low intensity at l
−2318 ppm was detected due to [Pt2Br6]2− (vide infra).
In an experiment, KBr (49.5 mg, 0.416 mmol) and
1.1 ml of water were added to 0.720 g of an aqueous
solution of K2PtCl4 (2.47% platinum; 1.78×10−2 g of
Pt; 9.11×10−2 mol). The resulting solution was trans-
ferred into a NMR tube containing 0.3 ml of D2O for
195Pt-NMR monitoring. After 18 h the spectrum
showed resonances at −1846 {[PtBrCl3]2−}, −2087
and −2098 {trans- and cis-[PtBr2Cl2]2−}, −2366
{[PtBr3Cl]2−} and −2662 ppm {[PtBr4]2−}, the most
intense peak being that at −2366 ppm. Spectra
recorded after several days showed no change.
,
lar nonbonding distance (3.525 A) is comparable to
the interlayer Pt···Pt distance of trans-Pt2Cl4(CO)2.
5. In view of the high reactivity of these systems of
platinum(II) and palladium(II) towards nucleophilic
reagents, some of the compounds reported in this
paper have been [16] and will be further used for the
chemical deposition under mild conditions of the
corresponding metals on metal oxide surfaces.
4. Experimental
4.1. General
All manipulations were performed under an atmo-
sphere of prepurified dry dinitrogen or carbon monox-
ide. Solvents were carefully dried by conventional
methods prior to use. IR spectra were recorded with
Perkin–Elmer spectrophotometers (mod. 283 B or
1725X FT-IR) in solution or as Nujol or polychloro-
trifluoroethylene (PCTFE) mulls prepared under rigor-
ous exclusion of moisture. 1H-, 13C-, 31P- and
195Pt-NMR spectra were recorded with a Varian Gem-
ini 200 BB spectrometer, chemical shifts being reported
in ppm versus SiMe4 for 1H and 13C, versus 85% H3PO4
and H2PtCl6 in D2O for 31P and 195Pt, respectively.
Commercial aqueous solutions of K2PtCl4 (Chimet
S.p.A., Badia al Pino, Arezzo, Italy) were used. The
halides AlCl3 and AlBr3 (Aldrich) were sublimed in
vacuo and stored under N2, while cis-Pd2Cl4(CO)2 was
prepared according to the literature [1d,e] or from
[NBu4]2[Pd2Cl6], as described below.
In another experiment, K2PtCl4 (9.20×10−2 mol)
was treated with KBr (77.5 mg, 0.651 mmol) in H2O+
D2O (0.6 ml+0.3 ml). After 90 min, a 195Pt-NMR
spectrum showed resonances at −1625 {[PtCl4]2−},
−1846 {[PtBrCl3]2−}, −2087 {trans-[PtBr2Cl2]2−},
−2366 {[PtBr3Cl]2−} and −2662 ppm {[PtBr4]2−},
the most intense being the first one. After 24 h, the last
two resonances only were observed. After addition of
more KBr (138 mg, 1.16 mmol), a spectrum recorded
18 h later showed the resonances due to [PtBr3Cl]2−
and [PtBr4]2−, the latter being predominant.
4.2. [NBu4]2[PtCl4] by sol6ent extraction
An aqueous solution of K2PtCl4 (0.154 M, 90 ml,
13.9 mmol) was shaken in a separatory funnel with a
solution of NBu4Cl (7.72 g, 27.8 mmol) in CH2Cl2 (130
ml). The organic layer immediately became red, while
the aqueous solution discoloured. The CH2Cl2 layer
was separated, concentrated to a small volume by gen-
tle warming at atmospheric pressure and then evapo-
rated to dryness in vacuo. The red product was dried
4.3.2. From [NBu4]2[PtCl4] in CDCl3
t
4.3.2.1. With BuBr. A solution in CDCl3 (1 ml) of
tBuBr (0.1 ml, d=1.189 g ml−1, 0.868 mmol) and
[NBu4]2[PtCl4] (129 mg, 0.157 mmol) was prepared in a

186
F. Bagnoli et al. / Journal of Organometallic Chemistry 622 (2001) 180–189
NMR tube. After 20 h a 195Pt-NMR spectrum of the
solution showed three peaks at −2004 {[PtBr2Cl2]2−},
−2270 {[PtBr3Cl]2−}, and −2560 ppm {[PtBr4]2−}.
After 48 h the spectrum showed a new peak of low
intensity at −2318 ppm {[Pt2Br6]2−}. After 72 h the
intensities of the peaks at −2004 and −2270 ppm
decreased, while increased the peak at −2318 ppm.
After 6 days at r.t. and three days at 40°C, the intensity
of the peaks at −2318 and −2560 ppm increased.
stirred under CO for 6 h at atmospheric pressure at r.t.
[carbonyl bands at 2178 and 2138 cm−1 due to cis-
PtCl2(CO)2]. The suspension was filtered and the filtrate
was evaporated to dryness. The colourless residue was
extracted with CCl4 (100 ml) in a Soxhlet for 5 h. The
analytically and spectroscopically pure product was
recovered by filtration of the extract and dried in vacuo
(1.28 g, 60.6% yield).
In a gas-volumetric experiment carried out in 1,2-
dichloroethane (20 ml) at 21.4°C, 213 mg (0.259 mmol)
of [NBu4]2[PtCl4] absorbed CO up to a CO/Pt molar
ratio of 0.65 in 40 h. By addition of AlCl3 (37.5 mg,
0.281 mmol) further CO was absorbed in 2 h (final
CO/Pt molar ratio of 0.97). Additional AlCl3 (44.8 mg,
0.336 mmol) gave new CO uptake (1.5 h) corresponding
to a total CO/Pt molar ratio of 1.90. The IR spectrum
of the solution showed bands at 2178 and 2138 cm−1
[cis-PtCl2(CO)2] and at 2150 cm−1 [trans-PtCl2(CO)2].
After 15 h under CO, only the bands due to the
cis-isomer were observed.
t
Addition of an excess of BuBr (1.00 ml, 8.68 mmol)
caused the disappearance of the lower field resonances,
and the peaks at −2318 and −2560 ppm had an
intensity ratio of 1.25.
4.3.2.2. With HBr. In a 100 ml flask, equipped with a
silicone-rubber stopper, CH2Cl2 (20 ml) and
[NBu4]2[PtCl4] (0.420 g, 0.511 mmol) were introduced
under N2. After evacuation, gaseous HBr (50 ml, about
2 mmol) was added through the plug by syringe. A
195Pt-NMR spectrum recorded after 15 h showed the
peak at −2297 ppm due to [Pt2Br6]2− only. The
assignment was confirmed in the following manner. To
a suspension of PtBr2 (0.240 g, 0.676 mmol) in CH2Cl2
(20 ml) NBu4Br (0.230 g, 0.713 mmol) was added, giving
a red–brown solution. The solid residue obtained by
evaporating the solvent under reduced pressure was
collected (0.37 g, 77% yield). Anal. Calc. for
[NBu4]2[Pt2Br6], C32H72Br6N2Pt2: Br, 35.4; Pt, 28.8.
Found: Br, 34.6; Pt, 27.9%. 195Pt-NMR (CH2Cl2), l
−2297 ppm.
4.5.2. From PtCl2
A suspension of PtCl2 (280 mg, 1.05 mmol) in CH2Cl2
(30 ml) was stirred under CO at r.t. for 3 days. The
resulting colourless solution, which showed the IR
bands of cis-PtCl2(CO)2, was added of heptane (100 ml)
and stored at −30°C for 3 days. The product was
collected by filtration and dried in vacuo (284 mg, 84%
yield). Analogous results were obtained by operating in
SOCl2. In a gas-volumetric experiment carried out in
sym-C2H2Cl4 (25 ml) 215 mg (0.81 mmol) of PtCl2
absorbed CO at 18.6°C up to a CO/Pt molar ratio of
1.92 in 3 days.
4.4. [NBu4]2[Pd2Cl6]
An aqueous acidic (for hydrochloric acid) solution
(33 ml) of PdCl2 (4.70 mmol) was treated in a separatory
funnel with a solution of NBu4Cl (1.303 g, 4.69 mmol)
in sym-C2H2Cl4 (50 ml). The aqueous layer immediately
discoloured and the organic layer became red–orange:
the latter one was transferred to a flask and evaporated
to dryness under reduced pressure. The red residue was
treated with heptane (30 ml). The suspension was
filtered and the solid dried in vacuo (90% yield). Anal.
Calc. for [NBu4]2[Pd2Cl6], C32H72Cl6N2Pd2: C, 42.2; H,
8.0; N, 3.1. Found: C, 42.0; H, 7.9; N, 2.6%.
4.6. trans-Pt2Cl4(CO)2 (2)
By operating under CO, solid [NBu4]2PtCl4 obtained
from an aqueous solution of K2PtCl4 (6.60 mmol) was
dissolved in 1,2-C2H4Cl2 (50 ml), and the resulting
solution was added of 0.890 g (6.67 mmol) of AlCl3.
After 18 h stirring, an IR spectrum showed the band at
2098 cm−1 due to [NBu4][PtCl3(CO)]. The solution was
degassed and saturated with N2. A second equivalent of
AlCl3 (0.88 g, 6.60 mmol) was added and the solution
turned orange. After 1 h, an IR spectrum showed the
band at 2138 cm−1 due to trans-Pt2Cl4(CO)2. After
filtration, the solution was stored at 0°C for 2 days.
Orange crystals, suitable for an X-ray diffraction study,
separated out, which were filtered and dried in vacuo
(0.69 g, 35.6% yield).
4.5. cis-PtCl2(CO)2 (1)
4.5.1. From [NBu4]2PtCl4
Solid [NBu4]2PtCl4, obtained from an aqueous solu-
tion of K2PtCl4 (6.70 mmol) as for the above descrip-
tion, was dissolved in CH2Cl2 (50 ml). The solution was
saturated with CO and 0.850 g (6.37 mmol) of AlCl3
were added. After stirring for 20 h, an IR spectrum
showed an intense band at 2098 cm−1 due to
[NBu4][PtCl3(CO)]. A second equivalent of AlCl3 (0.900
g, 6.75 mmol) was introduced and the mixture was
4.7. cis-PtBr2(CO)2 (3)
4.7.1. From [NBu4]2[PtBr4]
Compound 3 was obtained from [NBu4]2[PtBr4] and
CO, using AlBr3 as halide scavenger in two separate

F. Bagnoli et al. / Journal of Organometallic Chemistry 622 (2001) 180–189
187
steps (22.5% yield after extraction with CCl4). In a
gas-volumetric experiment, the CO uptake by
[NBu4]2[PtBr4] in dichloroethane at 16.6°C was mea-
sured, corresponding to a CO/Pt molar ratio of 0.99 (in
2 h) and 1.9 (in 0.5 h, after addition of the second
equivalent of AlBr3). The IR spectrum of the solution
showed a band at 2142 cm−1 due to trans-PtBr2(CO)2.
After 24 h under CO, this band had disappeared, being
substituted by bands at 2170 and 2130 cm−1 of the
cis-isomer.
compound was filtered and dried for a short time under
a CO flux (76% yield). The product had correct elemen-
tal analysis (Cl, Pd) and IR [1d].
4.9. Crystal structure determinations
Due to the extreme sensitivity to moisture of the
compounds, single crystals were selected under a pro-
tecting atmosphere of an accurately dried gas. The
X-ray diffraction measurements were carried out by
means of an ENRAF-Nonius-CAD4 diffractometer
equipped with a graphite-monochromated Ag–Ka radi-
4.7.2. From cis-PtCl2(CO)2
,
To a suspension of cis-PtCl2(CO)2 (0.580 g, 1.80
ation (u=0.56087 A) for compound 2 at 203 K and
with a Siemens P4 diffractometer equipped with a
t
mmol) in CCl4 (10 ml), BuBr (0.50 ml, 4.34 mmol) was
1
added. After 30 min a H-NMR spectrum showed the
graphite-monochromated Mo–Ka radiation (u=
0.71073 A) for compounds 3, 4, and 5 at r.t. (T=293
peaks at 1.62 ppm (tBuBr) and at 1.45 ppm (tBuCl) in
the 1:2.6 ratio. After 24 h stirring the suspension was
filtered and the solid was dried in vacuo (0.46 g, 62%
yield). Found: Br, 38.6; Pt, 46.6. C2Br2O2Pt requires:
,
K). The samples were sealed in glass capillaries under
an inert atmosphere. The ꢀ/2q scan mode was used for
intensity data collection, a redundant set of data allow-
ing diffraction symmetry and reliability of the absorp-
tion correction procedure to be checked. Three
standard reflections were measured every 97 measure-
ments to check sample decay. The intensities were
corrected for Lorentz and polarisation effects and for
absorption by means of a „-scan method [17]. The
intensities of compound 3 were also corrected for decay
[18]. The structure solutions were obtained by means of
the Patterson method and the refinements, based on
full-matrix least-squares on F2, were done by means of
the SHELX-97 programme [19].
Br, 38.9; Pt, 47.5%. IR (Nujol): 2167 and 2122 cm−1
.
195Pt-NMR (CH2Cl2): l −4243 ppm. In another exper-
t
iment carried out in CH2Cl2 and using a BuBr/Pt
molar ratio of 2.7 at r.t., a 0.13 M solution of cis-
PtCl2(CO)2 was rapidly (about 10 min) converted into
the corresponding bromide, the latter being recovered
by precipitation with heptane (75.5% yield).
4.7.3. From PtBr2
A suspension of PtBr2 (0.81 g, 2.28 mmol) in sym-
C2H4Cl2 (75 ml) was pressurized in a glass autoclave
with CO (6 atm). After 1 h stirring at r.t. the solid had
disappeared. The mixture was heated at 60°C for 3 h
and a yellow solution was obtained which was siphoned
into a flask under N2 and concentrated under reduced
pressure. An IR spectrum of the solution showed the
bands at 2170 and 2130 cm−1 due to cis-PtBr2(CO)2.
The solution was treated with heptane (100 ml) and the
pale yellow product precipitated out. The suspension
was stored at −30°C for 2 days and then filtered. The
solid was dried in vacuo (0.70 g, 74.7% yield). The
filtrate was evaporated to dryness and the residue, after
addition of heptane (5 ml), was recovered by filtration
and dried in vacuo (0.16 g, 91.7% total yield). The
product had correct elemental analysis (Br, Pt) and IR.
The same reaction carried out in CH2Cl2 at r.t. and
pCOꢀ0.5 atm proceeded very slowly.
4.9.1. Crystal structure of 2
Orange needle-like single crystals were obtained by
cooling (0°C) a solution of 2 in dichloroethane. Several
crystals were tested, the best results being obtained with
a sample of dimensions 0.52×0.04×0.04 mm. The cell
parameters were calculated from the setting angles of
25 reflections having 6.0°BqB10.0°. They are listed,
together with some other structural parameters in Table
5. A total of 811 independent reflections were measured
(1.4°BqB21.0°). The structure solution was obtained
in the space group P42, see Table 5.
4.9.2. Crystal structure of 3
Colourless prismatic crystals of 3, obtained by subli-
mation under reduced pressure (about 10−2 mmHg) in
a sealed ampoule in the temperature gradient 100–
30°C, were mounted in glass capillaries under an argon
atmosphere. The crystal used for structure solution had
dimensions 0.23×0.18×0.06 mm. The cell parameters,
calculated from the setting angles of 25 reflections
having 5.0°BqB12.0°, are listed in Table 5, together
with some other structural details. A total of 2292
independent reflections were measured between 2.9°B
qB25.0°. During data collection, a 15% decay of the
standard reflections was observed, while the crystal
4.8. cis-Pd2Cl4(CO)2 (4)
A solution of [NBu4]2[Pd2Cl6] (752 mg, 0.83 mmol) in
30 ml of CH2Cl2, prepared as described above, was
treated under CO with AlCl3 (219 mg, 1.64 mmol).
After 2 days stirring at r.t. the IR spectrum of the
solution showed an intense band at 2166 cm−1 due to
cis-Pd2Cl4(CO)2. The solution was treated with heptane
(120 ml) and cooled down to −30°C. The orange

188
F. Bagnoli et al. / Journal of Organometallic Chemistry 622 (2001) 180–189
Table 5
Crystal data and structure refinementa
Compound
2
3
4
5
Empirical formula
Formula weight
Temperature (K)
C2Cl4O2Pt2
588.01
203(2)
C2Br2O2Pt
410.93
293(2)
C2Cl4O2Pd2
410.67
293(2)
C17H36Br3NOPt
705.29
293(2)
,
Wavelength (A)
Crystal system, space group Tetragonal, P42 (no.
0.56087
0.71073
Triclinic, P1 (no. 2)
0.71073
Monoclinic, P21/n (no. 14)
0.71073
Monoclinic, P21/n (no. 14)
(
77)
Unit cell dimensions
,
a (A)
11.183(3)
11.183(3)
3.525(2)
–
–
–
7.126(1)
7.315(1)
13.525(3)
75.31(1)
78.12(1)
75.04(1)
651.4(2)
4
4.190
33.706
2292/0/128
0.0738
0.1611
10.451(1)
6.649(1)
13.032(1)
–
97.83(1)
–
897.1(2)
4
3.040
14.992(2)
9.158(1)
18.642(2)
–
106.93(1)
–
2448.6(5)
4
1.913
10.630
4267/0/209
0.0529
0.1078
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
Volume (A )
Z
440.8(3)
2
zcalc (Mg m−3
)
4.430
17.864
811/33/47
0.0368
0.0462
v (mm−1
)
4.532
Data/restraints/parameters
1908/0/91
0.0468
0.0850
R(Fo) a [I\2|(I)]
Rw(F2o) a [I\2|(I)]
a R(Fo)=ꢀ ꢁꢁ Foꢁ−ꢁFc ꢁꢁ /S ꢁ Fo ꢁ ; Rw(F2o)=[ꢀ[w(Fo2−Fc2)2]/ꢀ[w(Fo2)2]]1/2; w=1/[|2(F2o)+(AQ)2+BQ] where Q=[max(Fo2, 0)+2F2c]/3.
5. Supplementary material
became yellow–orange. Three collections on three dif-
ferent specimens gave the same results. The structure
Crystallographic data for the structures reported in
this paper have been deposited with the Cambridge
Crystallographic Data Centre, CCDC no. 151361 for
compound 2, CCDC no. 151362 for compound 3,
CCDC no. 151363 for compound 4 and CCDC no.
151364 for compound 5. Copies of this information
may be obtained free of charge from the Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(fax: +44-1223-336033; e-mail: deposit@ccdc.cam.
ac.uk or http://www.ccdc.cam.ac.uk).
(
solution was obtained in the space group P1. The final
refinement cycles gave the reliability factors listed in
Table 5.
4.9.3. Crystal structure of 4
Red–orange needle-like single crystals were obtained
by cooling (−40°C) a solution of 4 in thionyl chloride/
heptane (1:3). One of them, of dimensions 0.51×
0.10×0.05 mm was mounted on the diffractometer and
the cell parameters were calculated from the setting
angles of 23 reflections having 5.3°BqB12.5°. Other
structural details are in Table 5. The intensities of 1908
independent reflections with 2.35°BqB30.0° were col-
lected. The structure solution was obtained in the space
group P21. The final refinement cycles gave the reliabil-
ity factors listed in Table 5.
Acknowledgements
The authors wish to thank the Consiglio Nazionale
delle Ricerche (C.N.R., Rome), Progetto Finalizzato
Materiali Speciali per Tecnologie Avanzate II, and e
della Ricerca Scientifica e Tecnologica (MURST), Pro-
getti di Rilevante Interesse Nazionale 1998–9, for
financial support and Chimet S.p.A., I-52041 Badia al
Pino, Arezzo, Italy, for a loan of palladium and
platinum.
4.9.4. Crystal structure of 5
A fragment of a yellow needle-like crystal of 5 of
dimensions 0.88×0.18×0.08 mm was mounted on the
diffractometer and the cell parameters were calculated
from the setting angles of 27 reflections having 5.4°B
qB12.45°. The lattice parameters, together with some
other structural details, are listed in Table 5. The
intensities of 4267 independent reflections with 2.07°B
qB25.01° were collected. The structure solution was
obtained in the space group P21/n. The final refinement
cycles gave the reliability factors listed in Table 5.
References
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