Convenient preparation of (η4-alkadiene)dichloroplatinum(II) complexes from [PtCl6]2- anions and their reduction to platinum(0) alkene complexes under phase-transfer catalysis conditions

Article abstract of DOI:10.1016/j.jorganchem.2010.12.043

Convenient one-pot reduction-complexation reactions of hexachloroplatinato(IV) anions to (η⁴-alkadiene) dichloroplatinum(II) complexes (η⁴-alkadiene = COD, DAE, DCPD, NBD) under suitable phase-transfer catalysis conditions are reported. Reduction to zerovalent platinum alkene complexes has been obtained in the presence of an excess of alkene, potassium formate and 18-crown-6 as phase-transfer catalyst (alkene = COD, NB, dba). The crystal and molecular structure of [Pt _1.03(dba)₃]·CH₂Cl₂ has been studied by X-ray diffraction methods: it can be described as a solid solution of Pt(dba)₃ and Pt₂(dba)₃, the mononuclear complex being largely prevailing.

Full text of DOI:10.1016/j.jorganchem.2010.12.043

Journal of Organometallic Chemistry 696 (2011) 1349e1354
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Convenient preparation of (h
4-alkadiene)dichloroplatinum(II) complexes from
[PtCl6]2ꢀ anions and their reduction to platinum(0) alkene complexes under
phase-transfer catalysis conditions
*
Daniela Belli Dell’Amico , Luca Labella, Fabio Marchetti, Simona Samaritani
Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, I-56126 Pisa, Italy
a r t i c l e i n f o
a b s t r a c t
Convenient one-pot reduction-complexation reactions of hexachloroplatinato(IV) anions to (h
4-alka-
Article history:
diene)dichloroplatinum(II) complexes (
h
4-alkadiene ¼ COD, DAE, DCPD, NBD) under suitable phase-
Received 29 October 2010
Received in revised form
17 December 2010
transfer catalysis conditions are reported. Reduction to zerovalent platinum alkene complexes has been
obtained in the presence of an excess of alkene, potassium formate and 18-crown-6 as phase-transfer
catalyst (alkene ¼ COD, NB, dba). The crystal and molecular structure of [Pt1.03(dba)3]$CH2Cl2 has been
studied by X-ray diffraction methods: it can be described as a solid solution of Pt(dba)3 and Pt2(dba)3, the
mononuclear complex being largely prevailing.
Accepted 29 December 2010
Keywords:
Platinum
Olefin complexes
Phase transfer catalysis
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
Interestingly, the reduction of H2PtCl6$xH2O by vinylsiloxane
derivatives in the presence of coordinating alkenes affords plat-
Complexes of platinum(0) find application in the field of
homogeneous catalysis [1]. Among them, the so-called “ligand free”
or “naked” homoleptic alkene complexes are important precursors
to other species of platinum(0), coordinated olefins being easily
replaced by other ligands [1e,f,2]. These complexes are usually
synthesized starting from dichloro-(diene)platinum(II) complexes
inum(0) species [7], but the relatively high temperatures
(50e70 ꢁC) required for this route are inappropriate for the prep-
aration of Pt(alkene)3 complexes with non-functionalized mono-
enes [7c].
As far as platinum(II) precursors are concerned, the preparation
of the widely used dihalo-diene complexes, PtX2(diene) is generally
carried out by reacting tetrachloroplatinate(II) salts with non-
conjugated dienes in a water/acetic acid mixture [8] or in alcohol
[9]. Syntheses starting from H2PtCl6$xH2O or its salts are rather
interesting, as these species are primary products in platinum
chemistry. Diiodo-(diene)platinum(II) complexes have been
synthesized by treating potassium hexachloroplatinate(IV) with KI
in the presence of the suitable diene [10]. The preparation of the
analogous dichloro-derivatives from hexachloroplatinic acid, in
acetic acid solution [11] requires the use of the diene both as
reducing and complexing agent. The outcome of the reaction is
largely dependent on the nature of the diene; when dienes other
than cycloocta-1,5-diene are used, yields are low and the formation
of dark by-products makes the purification step quite long and
tedious [11].
as precursors. The reduction of dichloro-(h
4-1,5-cyclooctadiene)
platinum(II) [PtCl2(COD)] by lithium cyclooctatetraene in the
presence of a strong excess of the alkene (see reaction 1) [2c,g,h,3]
is commonly used.
PtCl2(COD) þ Li2(C8H8) þ x alkene / Pt(alkene)x þ 2LiCl
þ C8H8 þ COD
(1)
This route affords satisfactory results both for platinum deriva-
tives {for instance tris(bicyclo[2.2.1]heptene)platinum(0), [Pt(NB)3],
and bis(cycloocta-1,5-diene)platinum(0), [Pt(COD)2], can be ob-
tained in 40e74% yields [2f,3]} and for the usually unstable palla-
dium compounds [2h,4]. Alternatively, dicyclopentadienylcobalt(II)
[5] and samarium(II) iodide [6] have been reported as reducing
agents for platinum(II) complexes.
Although many procedures have been reported [12] describing
the use of PT catalysts for the preparation of organic compounds,
only few examples are known where PT catalysis conditions are
applied to the preparation of organometallic derivatives [13]. Under
these conditions it is usually possible to maintain the concentration
of the reagents in the organic phase low enough to be tolerated by
* Corresponding author. Tel.: þ39 050 2219210; fax: þ39 050 2219246.
E-mail address: belli@dcci.unipi.it (D.B. Dell’Amico).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.12.043

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D.B. Dell’Amico et al. / Journal of Organometallic Chemistry 696 (2011) 1349e1354
Table 1
Preparations of [PtCl2(diene)] according to Scheme 1.a
List of the acronyms
Entry
Diene
COD
COD
NBD
DCPD
DAE
[Diene/Pt] molar ratio
7/1
2/1
2/1
2/1
2/1
%Yield
COD
DAE
dba
1,5-Cyclooctadiene
1
75
78
78
61
75
2
3
4
5
4-Oxahepta-1,6-diene (diallylether)
E,E-1,5-diphenyl-3-oxopenta-1,4-diene
(dibenzylidenacetone)
DCPD
NB
NBD
TBA
DCE
Dicyclopentadiene
a
Reducing agent H2NꢀNH2$2HCl; [Pt/(H2NꢀNH2$2HCl)] molar ratio ¼ 2.
Bicyclo[2.2.1]heptene (norbornene)
Bicyclo[2.2.1]hepta-2,5-diene (norbornadiene)
Tetrabutylammonium
It has to be pointed out that no formation of platinum metal was
1,2-Dichloroethane
observed, although the standard potential for the reduction of
[PtCl4]2ꢀ to Pt(0) in water is only slightly higher than the corre-
sponding standard potential [15] for the reduction of [PtCl6]2ꢀ to
[PtCl4]2ꢀ (0.755 and 0.680 V, respectively). This outcome is
reasonable due to the presence of the complexing diene in the
organic phase: as soon as tetrachloroplatinate(II) ion is produced in
water, it is extracted as [TBA]2[PtCl4] into the chlorinated solvent
and converted to the slightly soluble diene complex with release of
the TBACl catalyst (Scheme 1). Thus, the concentration of tetra-
chloroplatinate(II) ions in the aqueous phase is never high enough
for their reduction to become competitive.1
Similar experimental conditions (Table 1, entry 2) successfully
afforded platinum(II) complexes of norbornadiene 2, dicyclopenta-
diene 3, and diallylether 4, (Table 1, entries 3e5 respectively). All
products were sparingly soluble in 1,2-dichloroethane and could be
easily isolated as chemically pure crystalline solids in good yields.
DMSO Dimethylsulfoxide
PT Phase transfer
sensitive substrates. We thus thought that this approach could be
useful for the preparation of both platinum(II) and platinum(0)
species.
The reasons discussed above prompted us to search, under PT
catalysis conditions, for: (a) a new and more direct route to convert
hexachloroplatinate(IV) salts into dichloro-(diene)platinum(II)
complexes and (b) a simple and economic way to obtain platinum
(0) complexes with the composition Pt(alkene)n. The results we
have obtained are here presented and discussed.
2. Results and discussion
2.2. Preparation of (alkene)platinum(0) derivatives from dichloro-
(diene)platinum(II) complexes
2.1. Preparation of dichloro-(diene)platinum(II) complexes from
[PtCl6]2ꢀ
Previous outcome in the preparation of platinum(II) dichloro
diene complexes prompted us to investigate if PT conditions could
be also suitable to synthesize platinum(0) complexes. Experiments
were carried out using potassium formate as reducing agent.
Although alkali metal formates are used for the reduction of plat-
inum salts to platinum-black [16], at the best of our knowledge
their use is not reported for the synthesis of platinum(0)
complexes. A suspension of [PtCl2(COD)] in 1,2-dichloroethane was
treated, in the presence of COD and 18-crown-6 as PT catalyst, with
an aqueous solution containing a threefold excess of potassium
formate. Under these experimental conditions the platinum(II)
precursor was reduced but no complexation occurred: 1H- and
195Pt-NMR spectra of the organic phase showed the absence of
signals attributable to platinum(0) complexes. Platinum metal was
recovered, together with some brown by-products, possibly due to
base-promoted isomerisation/oligomerisation of the 1,5-diene [17].
Taking into account that crown ethers are very good PT catalysts in
As mentioned in Section 1, the conversion of hexachloroplatinic
acid into dichloro-(diene) platinum(II) complexes was claimed to
occur in good yields in acetic acid solution [11]; in our hands, when
dienes other than cycloocta-1,5-diene were used, low yields were
always obtained. Since the metal precursor and the complexing
agent have different solubility properties, it seemed interesting to
investigate PT catalysis conditions in biphasic water/organic
solvent systems. Tetraalkylammonium halides are often useful as
liquideliquid phase transfer catalysts, thanks to their good solu-
bility in water as well as in many common organic solvents.
Moreover, it is known that PtCl2nꢀ (n ¼ 4, 6) can be extracted from
aqueous solutions of H2PtCln into chlorinated solvents in the
presence of suitable alkylammonium salts [14]. In a preliminary
experiment H2PtCl6$nH2O was dissolved in water and treated with
a 1,2-dichloroethane solution containing an excess of cycloocta-1,5-
diene (COD, Pt/COD molar ratio ¼ 1/7) and a catalytic amount (7%
mol) of tetrabutylammonium chloride. After prolonged reflux
(80 ꢁC) of the mixture platinum(II) complexes were not obtained.
Since the excess diene did not afford any reduction product, in
a following experiment (Table 1, entry 1) hydrazine dihydro-
chloride was added as reducing agent in stoichiometric amount.
The resulting biphasic mixture was refluxed, till the aqueous phase
completely discoloured with formation of a colourless crystalline
heterogeneous solid-liquid systems [18],
a
suspension of
[PtCl2(COD)] in 1,2-dichloroethane was treated at room tempera-
ture with a threefold excess of potassium formate in the presence of
a strong excess of COD and a catalytic amount of 18-crown-6, while
no water was deliberately added (Table 2, entry 1). Long reaction
times (12e24 h) were necessary for a complete conversion of the
substrate into the expected bis(cycloocta-1,5-diene)platinum(0),
solid, identified as the expected dichloro-(h
4-1,5-cyclooctadiene)
platinum(II) ([PtCl2(COD)] 1) by 1H- and 195Pt NMR analysis. The
complex was easily obtained (75% yield), even when the COD/Pt
molar ratio was lowered from 7 to 2 (Table 1, entry 2). The overall
reduction/complexation process under PT conditions can be sum-
marised as in Eq. (2).
1
This hypothesis was indirectly confirmed by the following experiment:
a sample of [TBA]2[PtCl6] was dissolved in 1,2-dichloroethane and treated with an
aqueous solution containing a stoichiometric amount of hydrazine dihydrochloride
([Pt/H2NeNH2$2HCl] molar ratio ¼ 2) under the conditions used to prepare the
diene complexes of platinum(II), in the absence of the complexing agent. In this
case some platinum metal formed at the interface of the biphasic system and the
organic phase contained [TBA]2[PtCl4] and unreacted [TBA]2[PtCl6] in about 80/20
molar ratio (195Pt NMR).
2[PtCl6]2ꢀ þ H2N ꢀ NH2 þ 2diene / 2[PtCl2(diene)] þ 4Clꢀ
þ 4HCl þ N2
(2)

D.B. Dell’Amico et al. / Journal of Organometallic Chemistry 696 (2011) 1349e1354
1351
Scheme 2.
contains only [Pt(dba)3] with about 3% of upside down molecules to
give an end-for-end disorder. Due to the small fraction of mis-
aligned molecules our X-ray experiment does not allow to exclude
this possibility. We prefer however the first hypothesis by consid-
ering the results reported for the already described [Pt1.44(dba)3]$
CH2Cl2 [20], whose geometrical features are similar to the ones of
our derivative (see Table 3).
Pt1 and the three C]C groups around it are nearly coplanar,
while the C]C axes around Pt2 are approximately perpendicular to
the metal coordination plane.
Scheme 1.
[Pt(COD)2] 5, (1H- and 195Pt-NMR). The yield could be increased
from 25% to 40% (Table 2, entry 2) by using Et2O instead of 1,2-
dichloroethane as solvent. As a matter of fact, oxidative addition of
the chlorinated solvents to platinum(0) derivatives may occur to
some extent over long reaction times. The experimental procedure
was successfully applied in good yields also to the preparation of
tris(bicyclo[2.2.1]heptene)platinum(0), [Pt(NB)3] 6, (Table 2, entry
3). Furthermore, when [PtCl2(NBD)] was reacted with dibenzyli-
denacetone (dba), the reaction afforded the yellow-brown product
of analytical composition [Pt(dba)2]n 7, (89% yield, Table 2, entry 4),
scarcely soluble in diethyl ether. Platinum(0) complexes with dba
as ligand are well known and the compositions [Pt(dba)2], [Pt
(dba)3] and [Pt2(dba)3] have been reported [19]. Structural data are
available [20] only for a species with dba/Pt molar ratio of about 2,
[Pt1.44(dba)3$CH2Cl2], corresponding to a mixture of the dinuclear
[Pt2(dba)3] and the mononuclear [Pt(dba)3] species. For sake of
comparison, in the course of this work we have prepared [Pt(dba)3]
8, according to the experimental procedure described by Moseley
and Maitlis [19b]: yellow crystals of this product were obtained and
the crystal and molecular structure of this substance was estab-
lished, as discussed in Section 2.3 of this paper.
In olefin complexes of zerovalent platinum of the type Pt(alkene)3
the three coordinated C]C groups, in the absence of geometrical
constraints, are disposed on the coordination plane. Such a geometry
can be observed, for instance, in tris(bicyclo(2.2.1)heptene) platinum
(0) [2g] or in (
[1e].
h h
2-maleic anhydride)-bis( 2-norbornene)-platinum(0)
To discuss the geometrical features of our complex we have to
consider that three conformers are possible for dba, as outlined in
The synthetic procedure used to prepare Pt(0) complexes is
summarized in Scheme 2: the reductionecomplexation process is
accompanied by the formation of CO2 and HCl, a threefold excess of
potassium formate preventing HCl addition to the complexing
alkene [21]. Moreover, a strong excess of alkene (alkene/Pt molar
ratioes in the 7e10 range) is necessary in order to replace the diene
completely and to obtain a pure product.
2.3. Crystal and molecular structure of [Pt(dba)3], 8
Yellow single crystals of product 8 were studied by X-ray
diffraction methods. In the metal complex (see Fig. 1) two positions
are potentially present, both suitable to insert a platinum atom at
the right distance from three C]C double bonds. One of these
positions is fully occupied while in the other only a weak electron
density is measured, corresponding to a calculated degree of
occupancy of 0.03. According to these data, we have considered the
species as a solid solution of [Pt(dba)3] and [Pt2(dba)3], of average
composition [Pt1.03(dba)3]. The formation of a solid solution is
compatible with the expected close geometric resemblance of the
two molecules. An alternative explanation could be that the sample
Table 2
Synthesis of platinum(0) complexes, Pt(alkene)n, according to Scheme 2.a
Entry
Precursor
Alkene
Solvent
n
Yield %
Product
1
2
3
4
[PtCl2(COD)]
[PtCl2(COD)]
[PtCl2(COD)]
[PtCl2(NBD)]
CODb
CODb
NBb
1,2-DCE
Et2O
Et2O
2
2
3
2
25
40
62
89
5
5
6
7
dbac
Et2O
a
HCOOK/Pt molar ratio ¼ 3.
Alkene/Pt molar ratio ¼ 10.
dba/Pt molar ratio ¼ 7.
b
c
Fig. 1. Different views of the molecular model of 0.97 Ptdba3$0.03Pt2dba3. Thermal
ellipsoids are at 30% probability.

1352
D.B. Dell’Amico et al. / Journal of Organometallic Chemistry 696 (2011) 1349e1354
ꢀ
ꢀ
Table 3
distance of 2.204 A. This value is comparable with the 2.183 A
Bond distances (Å) and angles (ꢁ) around Pt in the crystal structure of 8,
0.97Ptdba3$0.03Pt2dba3$CH2Cl2.
distance observed in tris(bicyclo(2.2.1)heptene) platinum(0) [2h].
On the other hand, the three cis p-systems appear to form a weaker
ꢀ
Pt1ꢀC10A
2.181(7)
2.217(8)
2.190(7)
2.225(8)
2.201(8)
2.209(8)
3.158(10)
118.1(3)
120.3(3)
119.8(3)
85.5(3)
Pt2ꢀC7A
Pt2ꢀC8A
Pt2ꢀC7B
Pt2ꢀC8B
Pt2ꢀC7C
Pt2ꢀC8C
2.514(13)
2.292(13)
2.488(14)
2.273(14)
2.441(14)
2.343(14)
bond to the metal, although the mean Pt2eC distance of 2.392 A
cannot be directly compared being an average value derived from
bonded and non-bonded olefin groups. In the species described by
Lewis et al. [20] the Pt2(dba)3/Pt(dba)3 molar ratio is 0.44, to be
compared with the value of 0.03 in our derivative. The two phases
are probably miscible in a large range of composition.
Pt1ꢀC11A
Pt1ꢀC10B
Pt1ꢀC11B
Pt1ꢀC10C
Pt1ꢀC11C
Pt1/Pt2
C10AꢀPt1ꢀC10B
C10AꢀPt1ꢀC10C
C10BꢀPt1ꢀC10C
C10AꢀPt1ꢀC11C
C10BꢀPt1ꢀC11C
C10CꢀPt1ꢀC11C
C10AꢀPt1ꢀC11A
C10BꢀPt1ꢀC11A
C10CꢀPt1ꢀC11A
C11CꢀPt1ꢀC11A
C10AꢀPt1ꢀC11B
C10BꢀPt1ꢀC11B
C10CꢀPt1ꢀC11B
C11CꢀPt1ꢀC11B
C11AꢀPt1ꢀC11B
C8BꢀPt2ꢀC8A
C8BꢀPt2ꢀC8C
C8AꢀPt2ꢀC8C
C8BꢀPt2ꢀC7C
C8AꢀPt2ꢀC7C
C8CꢀPt2ꢀC7C
C8BꢀPt2ꢀC7B
C8AꢀPt2ꢀC7B
C8CꢀPt2ꢀC7B
C7CꢀPt2ꢀC7B
C8BꢀPt2ꢀC7A
C8AꢀPt2ꢀC7A
C8CꢀPt2ꢀC7A
C7CꢀPt2ꢀC7A
C7BꢀPt2ꢀC7A
117.5(5)
115.8(5)
112.6(5)
115.7(5)
126.3(6)
31.7(3)
3. Conclusions
156.4(3)
37.5(3)
We have described a convenient two-step process for the
synthesis of platinum(0) alkene complexes under PT catalysis
conditions. This method affords products in moderate to good
yields (30e70%) starting from commercial hexachloroplatinic acid
and with the use of easy to handle reducing agents. Furthermore,
the reduction is selective so that platinum-black has never been
observed and tedious purification procedures can be avoided.
Among the platinum(0) complexes, we have obtained crystals of
[Pt1.03(dba)3]$CH2Cl2, which can be considered as a solid solution of
Pt(dba)3 and Pt2(dba)3, with the mononuclear complex being
largely prevailing. In view of their similar geometrical features, it is
reasonable to conclude that the two complexes are in equilibrium
in solution, Eq. (3), solid solution of various composition precipi-
tating out depending on the dba concentration.
36.5(3)
31.4(3)
84.4(3)
116.6(5)
130.4(6)
112.1(5)
130.9(5)
31.5(3)
155.8(3)
118.5(3)
153.8(3)
37.0(3)
85.8(3)
119.7(3)
117.5(3)
112.9(5)
108.7(5)
111.9(5)
Fig. 2. They differ in stability because of their different H/H non-
bonding interactions. Due to the presence of the terminal phenyl
residues, the dba groups, independent of their conformation, have
an elongated shape in a direction perpendicular to the C]O bond.
Solid dba adopts the s-cis,cis conformation [22], where the H/H
repulsions appear to be substantially absent. In this conformation
the molecules are not planar, their two halves being twisted by
52.5ꢁ.
2 Pt(dba)3 # Pt2(dba)3 þ 3dba
(3)
4. Experimental
In Mx(dba)3 complexes, the coordination to the metal imposes to
three dba ligands to approach each other so that the twisted shapes
will be disfavored. In fact the three dba ligands in Ptx(dba)3 or
Pdx(dba)3 (x ¼ 1e2) are flat. In all these coordination compounds
the ligands approach each other in a trigonal prism disposition,
similar to the structure of our compound.
In coordinated dba the s-trans conformations appear to be more
stable. In Pd(dba)3 [23] all the ligands show the s-cis,trans confor-
mation, with the palladium coordinated to the trans-conformed
olefins with formation of a planar Pd(C]C)3 moiety. The same dba
conformation is the most frequently found in Pd2(dba)3 [24] and
Pt1.44(dba)3 [20]. Nevertheless, in the dinuclear species the two
coordination sites furnished by the tern of ligands cannot offer the
possibility of two planar M(C]C)3 moieties because of the skeletal
requirements of dba, independent of its conformation. For instance
in Pd2(dba)3$CH2Cl2 [24] a s-trans,trans conformer is also found and
the two Pd centres in the molecule have, at least, one C]C bond
lying in its coordination plane.
4.1. General procedures
All manipulations were performed under a dinitrogen atmo-
sphere. Hexachloroplatinic acid (aqueous solution, Chimet S.p.A.,
I-52041 Badia al Pino, Arezzo), bicyclo[2.2.1]hepta-2,5-diene (NBD,
Aldrich), dicyclopentadiene (DCPD, Aldrich), 4-oxahepta-1,6-diene
(DAE, Aldrich), [2.2.1]bicycloheptene (NB, Aldrich), tetrabuty-
lammonium chloride ([TBA]Cl, Fluka) were commercial products
used without further purification.1,5-cyclooctadiene (COD, Aldrich)
was distilled before use. (E,E)-1,5-Diphenyl-3-oxopenta-1,4-diene
(dba) was prepared according to literature.[25] 1,2-Dichloroethane
(DCE) was distilled from P4O10. Diethyl ether was distilled from
LiAlH4. CD2Cl2 (99.5%, Aldrich) was treated with P4O10 and distilled
before use. C6D6 (99.6%, Aldrich) was deoxygenated before use.
Potassium formate (Aldrich) and 18-crown-6 were dried in vacuo
before use.
1H-, 13C- and 195Pt-NMR spectra were recorded with a Varian
Gemini 200BB spectrometer. Chemical shifts were measured in ppm
The s-cis,trans conformation of the three ligands with all the
(d
) from TMS by residual solvent peaks for 1H and13C and from
C10]C11 trans
p systems on the same side is particularly favour-
aqueous (D2O) hexachloroplatinic acid for 195Pt. A sealed capillary
containing C6D6 was introduced in the NMR tube to lock the spec-
trometer to the deuterium signal when non-deuterated solvents
were used. Elemental analyses (C, H) were performed by Laboratorio
di Microanalisi, Dipartimento di Scienze Farmaceutiche, Università
di Pisa, with a C. Erba mod. 1106 elemental analyser.
able for Pt1, which can efficiently bond to them at a mean Pt1eC
Ph
Ph
H
Ph
H
H
H
H
H
H
O
H
H
O
O
4.2. Synthesis of dichloro(diene)platinum(II) complexes
H
H
H
A 250 ml round bottomed flask equipped with a magnetic stirrer
was charged with 5.0 ml of aqueous H2PtCl6 (7.7 mmol Pt), 30 ml of
1,2-dichloroethane, 30 ml of H2O, 150 mg of tetrabutylammonium
chloride (0.54 mmol) and 15.4 mmol of the diene (diene/[Pt] molar
ratio ¼ 2). A solution of 1.0 M NaOH was added in portions until the
Ph
Ph
Ph
s-cis,cis
s-cis,trans
s-trans,trans
Fig. 2. The three conformers of dba.

D.B. Dell’Amico et al. / Journal of Organometallic Chemistry 696 (2011) 1349e1354
1353
final pH of the aqueous layer turned basic. A solution of 398 mg
(3.8 mmol) of hydrazine dihydrochloride in 10 ml of H2O was added
under stirring at room temperature (25 ꢁC). The colour of the
aqueous layer turned from orange to red in a few minutes; when
gas evolution ceased, the biphasic mixture was refluxed until the
aqueous layer was colourless (6 h). After discarding the aqueous
layer, the product was washed with portions of heptane (2 ꢂ10 ml)
and dried in vacuum. The recovered complexes are reported below.
Elimination of solvents in vacuo from the combined pale yellow
filtrates afforded 469 mg (62% yield) of pale grey tris(bicyclo[2.2.1]
heptene)platinum(0). Anal. Calcd. for C21H30Pt: C, 52.8; H, 6.3.
Found: C, 52.5; H, 6.6%. 1H-NMR (C6D6, ppm): 3.25 (s, 6 H,
2JHꢀPt ¼ 63 Hz); 2.84 (m, 12 H); 1.60 (m, 12 H); 1.29 (m, 12 H); 0.25
(m, 6 H); 0.22 (m, 6 H).
4.3.3. Bis[(E,E)-1,5-diphenyl-3-oxopenta-1,4-diene]platinum(0) [Pt
(dba)2] 7
Dichloro-(h
4-1,5-cyclooctadiene)platinum(II), [PtCl2(COD)] 1:
(78% yield). Anal. Calcd. for C8H12Cl2Pt: C, 25.7; H, 3.2. Found: C,
25.5; H, 2.9%. IR (cmꢀ1): 3008, 2962, 1475, 1450, 1424, 1339, 1179,
1008, 910, 871, 831, 780, 694. NMR (ppm): 1H: 5.63 (m, 4H,
2JHePt ¼ 68 Hz); 2.73 (m, 4H); 2.28 (m, 4H); 195Pt: ꢀ3337.
A 100 ml Schlenk tube equipped with a magnetic stirrer was
charged with 380 mg of finely divided [PtCl2(NBD)] (1.06 mmol),
1.640 g of (E,E)-1,5-diphenyl-3-oxopenta-1,4-diene (dba, 7.0 mmol),
14 mg of 18-crown-6 (0.05 mmol) and 30 ml of dry diethyl ether.
The suspension was stirred at room temperature and 252 mg of
potassium formate (3.0 mmol) were added. Stirring was continued
at room temperature (25 ꢁC, 20 h) and a yellow-brown solid formed.
The mixture was filtered and the recovered solid was washed with
diethyl ether (10 ml), petroleum ether (10 ml), dried, washed with
water (2 ꢂ 25 ml) and finally dried under vacuum (10ꢀ1 mmHg,
20 h). The yellow-brown [Pt(dba)2] was obtained (0.592 g, 89%
yield). Anal. Calcd. for C34H28O2Pt: C, 61.5; H, 4.2. Found: C, 60.2; H,
4.0%.
Dichloro-(h
4-bicyclo[2.2.1]hepta-2,5-diene)platinum(II), [PtCl2(NBD)]
2: (78% yield). Anal. Calcd. for C7H8Cl2Pt: C, 23.5; H, 2.3. Found: C,
23.6; H, 1.6%. IR (cmꢀ1): 3051,1435, 1388, 1309, 1226, 1180, 980, 848,
1
831, 799, 774. NMR (ppm): H: 5.34 (dd, 4H, J ¼ J0 ¼ 2.5 Hz,
2JHePt ¼ 69 Hz), 4.35 (m, 2H), 1.75 (dd, 2H, J ¼ J0 ¼ 1.5 Hz); 195Pt (d6-
DMSO): ꢀ3113.
Dichloro-(h
4-dicyclopentadiene)platinum(II), [PtCl2(DCPD)] 3:
(61% yield). Anal. Calcd. for C10H12Cl2Pt: C, 30.2; H, 3.0. Found: C,
31.3; H, 3.0%. IR (cmꢀ1): 3038, 3018, 2985, 2884, 1421, 1332, 1297,
1266, 1239, 1182, 993, 960, 918, 860, 811, 804, 724. NMR (ppm): 1H:
6.90 (m,1H, 2JHePt ¼ 80 Hz), 6.51 (m,1H, 2JHePt ¼ 71 Hz), 6.11 (m,1H,
4.3.4. X-ray crystallography
2
2JHePt ¼ 80 Hz), 5.83 (m, 1H, JHePt ¼ 71 Hz), 3.71 (m, 2H), 2.90 (m,
The X-ray diffraction experiment was carried out at room
temperature (T ¼ 293 K) by means of a Bruker P4 four-circle
diffractometer equipped with graphite-monochromated Mo-Ka
radiation. The more relevant crystal parameters are listed in Table 4.
2H), 2.4e1.6 (m, 4H); 13C: 116.1 (1JCePt ¼ 143 Hz), 105.3
(1JCePt ¼ 119 Hz), 100.3 (1JCePt ¼ 142 Hz), 97.4 (1JCePt ¼ 152 Hz); 60.0
(2JCePt ¼ 84 Hz), 56.1, 55.4, 43.6, 43.4, 33.7; 195Pt: ꢀ3236.
Dichloro-(
h
4-[4-oxahepta-1,6-diene])platinum(II), [PtCl2(DAE)] 4:
The intensity data were collected until a maximum 2
the /2 scan mode, collecting a redundant set of data. The inten-
q
of 50ꢁ with
(75% yield). Anal. Calcd. for C6H10Cl2OPt: C, 19.8; H, 2.8. Found: C,
19.5; H, 2.6%. IR (cmꢀ1): 3100, 3087, 3021, 2982, 2905, 2860, 1513,
1455, 1403, 1381, 1301, 1263, 1225, 1126, 1101, 1052, 1018, 979, 939,
876, 778. NMR (ppm): 1H (CD2Cl2): 5.72 (m, 1H); 5.00 (d, 1H,
u q
sities were corrected for Lorentz and polarisation effects and for
absorption by means of an integration method based on the crystal
shape [26]. The structure solution was obtained by means of the
automatic direct methods contained in the SHELXS97 program [27].
The refinement, based on full-matrix least-squares on F2, was done
by means of the SHELXL97 [27] program. Some other utilities
contained in the WINGX suite [28] were also used. The asymmetric
unit contains a dichloromethane molecule and a molecule of the
metal complex formed by three dibenzylideneacetone ligands, each
connected through one of its double bonds to a platinum atom. In
the difference Fourier map a low electron density peak was
observed in the region surrounded by the remaining three double
2
2
J ¼ 8.8 Hz, JHePt ¼ 66 Hz); 4.54 (d, 1H, J ¼ 13.9 Hz, JHePt ¼ 49 Hz);
3.83 (m, 2H); 195Pt (d6-DMSO): ꢀ3444.
4.3. Synthesis of platinum(0) complexes
4.3.1. Bis(cycloocta-1,5-diene)platinum(0) [Pt(COD)2] 5
A 100 ml Schlenk tube equipped with a magnetic stirrer was
charged with 765 mg of finely divided [PtCl2(COD)] (2.04 mmol),
2.20 g of cycloocta-1,5-diene (20.4 mmol), 90 mg of 18-crown-6
(0.35 mmol) and 30 ml of dry diethyl ether. The colourless
suspension was cooled (0 ꢁC) and 580 mg of potassium formate
(6.9 mmol) were added under stirring. The suspension, stirred at
0 ꢁC (4 h) and then at room temperature (25 ꢁC, 20 h), turned dark
brown. Solid components were eliminated by filtration under
dinitrogen and washed with diethyl ether (20 ml) and heptane
(20 ml). The brown solution was concentrated (10 ml) and filtered
on a short package (5 cm) of aluminum oxide. Elimination of
solvents afforded 335.3 mg (40% yield) of bis(cycloocta-1,5-diene)
platinum(0). Anal. Calcd. for C16H24Pt: C, 46.7; H, 5.9. Found: C,
Table 4
Crystal data and structure refinement of 8.
Empirical formula
Formula weight
Crystal system
Space group
a [Å]
C52H44Cl2O3Pt1.03
988.13
triclinic
P1 (no. 2)
12.433(3)
13.212(1)
14.941(2)
114.88(1)
97.34(1)
95.79(1)
2175.4(6)
2
b [Å]
c [Å]
2
46.3; H, 5.8%. 1H-NMR (C6D6, ppm): 4.19 (s, 8 H, JHePt ¼ 56 Hz);
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
2.20 (m, 16 H).
V [Å3]
4.3.2. Tris(bicyclo[2.2.1]heptene)platinum(0), [Pt(NB)3] 6
Z
A 100 ml Schlenk tube equipped with a magnetic stirrer was
charged with 591 mg of finely divided [PtCl2(COD)] (1.58 mmol),
1.509 g of [2.2.1]bicycloheptene (16.1 mmol), 63 mg of 18-crown-6
(0.23 mmol) and 30 ml of dry diethyl ether. The colourless
suspension was cooled (0 ꢁC) and 420 mg of potassium formate
(5.0 mmol) were added under stirring. The suspension, stirred at
0 ꢁC (4 h) and then at room temperature (25 ꢁC, 20 h), turned pale
grey. Solid components were eliminated by filtration under dini-
trogen and washed with diethyl ether (20 ml) and heptane (20 ml).
Dcalc [g cmꢀ3
]
1.509
3.477
m
[mmꢀ1
]
F(000)
988
Collected reflections
Independent reflections
No. of parameters
GOF on F2
8152
7035
455
1.017
R1 (I > 2sI/all data)
wR2 (all data)
0.0470/0.0682
0.1158
1.787/ꢀ1.563
Largest diff. peak/hole [e Åꢀ3
]

1354
D.B. Dell’Amico et al. / Journal of Organometallic Chemistry 696 (2011) 1349e1354
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(1991) 243e252;
bonds, at a distance compatible with the presence of a second
platinum atom. Nevertheless, the height of this peak is only about
4 e A . This feature has been inferred as the result of the presence
ꢀꢀ3
(k) F.G.A. Stone, Inorg. Chim. Acta 50 (1981) 33e42.
in the structure, together with molecules of composition Pt(dba)3,
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solid solution. Both platinum atoms were introduced in the model,
fixing to 1.0 the population parameter of the first one and tenta-
tively adjusting the second in order to obtain about the same
thermal parameters in the refinement. As the adjusted population
parameter for the “lighter” platinum is only about 0.03, this atom
has been refined with isotropic thermal parameters. All the other
non-hydrogen atoms were refined with anisotropic thermal
parameters. Hydrogen atoms were introduced in calculated posi-
tions with isotropic constrained thermal parameters and let to
move following the “riding” convention. Final reliability factors are
listed in Table 4.
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Acknowledgements
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[12] For a recent review see: M. Ikunaka Org. Proc. Res. Dev. 12 (2008) 698e709.
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(b) I.J.B. Lin, H.Y.C. Lai, S.C. Wu, L. Hwan, J. Organomet. Chem. 304 (1986)
C24eC26;
This work was financially supported by Ministero dell’Università
e della Ricerca Universitaria (MIUR), Progetti di Ricerca di Rilevante
Interesse Nazionale (PRIN 2007). We thank Chimet S.p.A., I-52041
Badia al Pino (Arezzo), for a loan of platinum.
(c) J.A.S. Howell, J. Chem. Educ. 74 (1997) 577.
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Appendix A. Supplementary material
CCDC No. 798262 contains crystallographic data for the struc-
tural analysis of compound 8. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
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