Bis-phosphine monoxide platinum(II) and palladium(II) cationic complexes as Lewis acid catalysts in Diels-Alder and sulfoxidation reactions

Article abstract of DOI:10.1016/j.jorganchem.2006.05.022

A series of bis-phosphine monoxide (BPMO) palladium(II) and platinum(II) cationic complexes of the type [M(BPMO-κ²-P,O)₂][X]₂ (M = Pd, Pt; BPMO = Ph₂P-(CH₂)_n-P(O)Ph₂ with n = 1 (dppmO), 2 (dppeO), 3 (dpppO); X = BF₄, TfO) were prepared from the corresponding chlorides [MCl₂(BPMO-κ¹-P)₂] upon treatment with 2 equiv. of AgX in wet acetone/CH₂Cl₂ or MeOH solutions. They were characterized by ¹H and ³¹P{¹H} NMR spectroscopies and, in the case of the complex [Pt(dppeO-κ²-P,O)₂][BF₄]₂, also by X-ray crystallography. These complexes were tested as catalysts in some Diels-Alder and oxidation reactions with different substrates. In the latter reaction Pt(II) complexes showed moderate activity, while for the former one, both classes of complexes were active in the C-C coupling, in particular the Pt(II) species showed interesting high endo/exo diasteroselectivity depending on the counteranion.

Full text of DOI:10.1016/j.jorganchem.2006.05.022

Journal of Organometallic Chemistry 691 (2006) 3659–3666
www.elsevier.com/locate/jorganchem
Bis-phosphine monoxide platinum(II) and palladium(II)
cationic complexes as Lewis acid catalysts in Diels–Alder and
sulfoxidation reactions
a
a
b
a
Paolo Sgarbossa , Erika Pizzo , Alessandro Scarso , Silvia Mazzega Sbovata ,
a,
a
b,
c
Rino A. Michelin *, Mirto Mozzon , Giorgio Strukul *, Franco Benetollo
a
`
Dipartimento di Processi Chimici, dell’Ingegneria, Universita di Padova, Via F. Marzolo 9, 35131 Padua, Italy
b
` `
Dipartimento di Chimica, Universita Ca Foscari di Venezia, Dorsoduro 2137, 30123 Venice, Italy
c
ICIS – C.N.R., Corso Stati Uniti 4, 35127 Padua, Italy
Received 21 April 2006; received in revised form 10 May 2006; accepted 11 May 2006
Available online 20 May 2006
Abstract
A series of bis-phosphine monoxide (BPMO) palladium(II) and platinum(II) cationic complexes of the type [M(BPMO-j2-P,O)2][X]2
(M = Pd, Pt; BPMO = Ph2P–(CH2)n–P(O)Ph2 with n = 1 (dppmO), 2 (dppeO), 3 (dpppO); X = BF4, TfO) were prepared from the cor-
responding chlorides [MCl2(BPMO-j1-P)2] upon treatment with 2 equiv. of AgX in wet acetone/CH2Cl2 or MeOH solutions. They were
1
characterized by H and 31P{1H} NMR spectroscopies and, in the case of the complex [Pt(dppeO-j2-P,O)2][BF4]2, also by X-ray crys-
tallography. These complexes were tested as catalysts in some Diels–Alder and oxidation reactions with different substrates. In the latter
reaction Pt(II) complexes showed moderate activity, while for the former one, both classes of complexes were active in the C–C coupling,
in particular the Pt(II) species showed interesting high endo/exo diasteroselectivity depending on the counteranion.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Bis-phosphine monoxides; Platinum; Palladium; Diels–Alder reaction; Sulfoxidation reaction
1. Introduction
neous catalysis. Examples of the latter are, for instance,
the carbonylation of methanol to acetic acid as in the
Monsanto process [2], the carbonylation of esters to car-
boxylic anhydrides [3] and the isomerization of methyl for-
mate to acetic acid [4] using some complexes of rhodium of
the type [(dppeO-j2-P,O)Rh(CO)Cl] (dppeO = Ph2P–
CH2CH2–P(O)Ph2). Complexes Rh–BPMO have been
known for a long time also as catalysts in the hydroformy-
lation of olefins [5] and Gladiali and co-workers have
recently reported the first examples of hydroformylation
of styrene with BINAP(O)–Rh [6] and Pt–Sn [7] catalysts
(BINAP(O) = 2,20-bis(diphenylphosphino)-1,10-binaphthyl
mono-oxide). Systems such as Pd–BPMO are known to
catalyze the hydrocarboxylation of olefins [8]. The com-
plexes Co–BPMO (especially with BPMO = dppmO,
Ph2P–CH2–P(O)Ph2) are instead active in the hydroformy-
lation of epoxides. BPMOs have been successfully used in
Bis-phosphine monoxides (BPMO) of general formula
R1R2P-Y–P(O)R3R4, where Y is a divalent spacer and R
an alkyl/aryl group, constitute an important class of hemil-
abile ligands [1], able to supply easily accessible coordina-
tion sites at the metal center, which for softer metal ions
such as Pd(II) and Pt(II), will likely result from the dissoci-
ation of the M–O bond (Scheme 1).
The availability of a vacant coordination site provides
the system with low activation energy paths to ligand
exchange, oxidative addition, migratory insertion, and
reductive elimination, which are key transformations in
organometallic chemistry and transition metal homoge-
*
Corresponding author. Tel.: +39 049 8275522; fax: +39 049 8275525.
E-mail address: rino.michelin@unipd.it (R.A. Michelin).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.05.022

3660
P. Sgarbossa et al. / Journal of Organometallic Chemistry 691 (2006) 3659–3666
(dpppO); X = BF4, TfO) as catalysts in some Diels–Alder
and oxidation reactions with different substrates.
2. Results and discussion
2.1. Synthesis and characterization of the complexes
Scheme 1.
The complexes [M(BPMO-j2-P,O)2][X]2 (X = BF4,
TfO) were prepared according to a general method
reported in the literature [18a,18b], which is illustrated in
Scheme 2.
The procedure involves chloride abstraction from
[MCl2(BPMO-j1-P)2] by treatment with 2 equiv. of AgX
salts in wet acetone/CH2Cl2 or MeOH solutions; after fil-
tration of AgCl, the BPMO complexes were isolated in
high yield (>84%) upon addition of diethyl ether. The plat-
inum compounds are white solids, while those of palladium
are pale yellow.
the Ni and Pd-catalyzed oligomerization of ethylene [9] and
alternating copolymerization [9] and co-oligomerization of
ethylene and CO with Pd [9,10] and Rh [11] catalysts.
Finally, over the past six years, Faller and co-workers have
published a series of papers [12] describing the synthesis of
chiral BPMO–Ru and Os complexes and their use as Lewis
acid catalysts in asymmetric Diels–Alder reactions of cyclo-
pentadiene with substituted acroleins.
Our interest in developing homogeneous catalysts con-
taining transition metals behaving as Lewis acids with free
or easily accessible coordination sites at the metal center
led us to report a number of catalytic processes such as
the epoxidation of olefins with diluted H2O2 [13], the Bae-
yer–Villiger oxidation of ketones to give lactones [14], the
cyclopropanation of olefins [15,16b], the coupling of carb-
enes to give olefins [16] and the insertion of carbenes into
the O–H bond of alcohols to afford esters [16b]. Recently,
some of us have investigated the activity of chiral and achi-
ral complexes of the type [(P–P)M(solv)2][X]2, [(P–P)M(g2-
X)][X], and [(P–P)M(l-Cl)]2[X]2 (where P–P = various
diphosphines, including chiral diphosphines; M = Pd, Pt;
X = TfO, ClO4, BF4) in the Diels–Alder coupling of cyclo-
pentadiene and cyclohexadiene with unsaturated aldehydes
[17]. These catalysts have promoted good conversions in
relatively short times under mild conditions.
The platinum complexes 1a, 1b, 2a, 2b and 3a have been
characterized by multinuclear NMR and elemental analysis
(see Section 4). It should be noted that only 3a is a new
compound while 1a, 1b, 2a and 2b are only formally since
they differ from those previously reported for the counter-
anions employed. Furthermore, it is worthwhile mention-
ing that complex 3a is apparently stable in solution, while
the corresponding Pd complex was isolated as a polymeric
2þ
material of the type f½ðdpppOÞ2Pdꢀ ðBFꢁ4 Þ2gn [18b].
The 31P{1H} NMR data indicate that, upon chelation of
the BMPO ligand, the chemical shift of the oxidized phos-
phorus is shifted downfield by ca. 35–40 ppm compared to
the unbound species. The cis-structure of the cationic com-
plexes shown in Scheme 2 is supported by X-ray structural
determinations carried out for 2a and 3a (see below) and
1
also in the 31P{1H} NMR by the JPt–P values. The latter,
are large for all the platinum complexes reported in this
work and range between 3834 and 3953 Hz, as expected
for P trans to a hard donor such as the oxygen atom [19].
At room temperature no coupling was observed between
195Pt and 31P@O for the complexes [Pt(dppmO-j2-
P,O)2][OTf]2 (1b) and [Pt(dpppO-j2-P,O)2][BF4]2 (3a),
Within the research area described above, we decided to
explore a series of bis-phosphine monoxide palladium(II)
and platinum(II) cationic complexes of the type
[M(BPMO-j2-P,O)2][X]2 (M = Pd, Pt; BPMO = Ph2P–
(CH2)n–P(O)Ph2 with n = 1 (dppmO), 2 (dppeO), 3
Scheme 2.

P. Sgarbossa et al. / Journal of Organometallic Chemistry 691 (2006) 3659–3666
3661
Table 1
although this interaction was detected for the other Pt-
˚
Selected bond distances (A) and angles (ꢁ) in the crystal structure of
[(dppeO-j2-P,O)2Pt][BF4]2 (2a)
complexes (see Section 4). However, upon raising the tem-
2
perature to 320 K, the JPt–P(@O) coupling constant for 1b
Pt–O(1)
Pt–P(3)
2.043(6)
2.226(2)
1.517(7)
1.803(9)
1.803(9)
1.788(9)
1.800(9)
1.843(9)
1.810(9)
1.53(1)
Pt–O(2)
Pt–P(4)
2.096(6)
2.221(2)
1.512(7)
1.784(9)
1.788(9)
1.803(9)
1.812(9)
1.807(9)
1.851(9)
1.53(1)
was shown to be 73.2 Hz, while that of 3a could not be
detected even at the higher temperature. This finding is
P(1)–O(1)
P(1)–C(1)
P(1)–C(13)
P(2)–C(27)
P(3)–C(15)
P(3)–C(14)
P(4)–C(41)
C(13)–C(14)
P(2)–O(2)
P(1)–C(7)
P(2)–C(27)
P(2)–C(33)
P(3)–C(21)
P(4)–C(47)
P(4)–C(40)
C(39)–C(40)
2
not surprising since the values of JPt–P(@O) decrease rap-
idly on going from 1a (74.2 Hz) to 2a (23.6 Hz) and this
behaviour appears to be related to the chain length of the
BMPO ligand. Finally, only for dppeO-j2-P,O chelates
3
2a, 2b, 5a and 5b, the JP–P(@O) of ca. 5–8 Hz could be
detected.
O(1)–Pt–P(3)
O(1)–Pt–O(2)
O(1)–Pt–P(4)
O(1)–P(1)–C(13)
C(14)–C(13)–P(1)
C(40)–C(39)–P(2)
P(1)–O(1)–Pt
88.9(2)
80.0(3)
O(2)–Pt–P(4)
P(3)–Pt–P(4)
O(2)–Pt–P(3)
O(2)–P(2)–C(39)
C(13)–C(14)–P(3)
C(39)–C(40)–P(4)
P(2)–O(2)–Pt
90.8(2)
100.2(9)
168.9(2)
109.1(4)
115.2(7)
115.1(7)
126.5(4)
111.1(3)
2.2. Single crystal X-ray diffraction study of [Pt(dppeO-j2-
P,O)2][BF4]2 (2a)
170.8(2)
110.4(4)
113.7(7)
111.6(7)
145.4(4)
108.4(3)
The solid-state structure of the cationic bis-chelate part
of 2a has been determined by a single-crystal X-ray diffrac-
tion study (Fig. 1) and matches closely that of the previ-
ously reported palladium derivative [(dppeO)2Pd]2+ [18b]
and also that of the Pt cation [(dppmO)2Pt]2+ [18c]. Crystal
data together with experimental and structure refinement
details are summarized in Section 4. Relevant bond dis-
tances and angles are reported in Table 1. The Pt atom
and the four atoms constituting the first coordination
sphere (P(3), P(4), O(1) and O(2)) are coplanar within
C(14)–P(3)–Pt
C(40)–P(4)–Pt
lengths in various Pd(II) and Pt(II) hydroxo and alkoxo
complexes which fall in the range 1.99–2.228 A. This sug-
gests that the Pt–O coordination bonds are of considerable
strength despite the fact that they are trans to P ligands
whose trans influence is normally significant. Furthermore,
˚
˚
˚
also the Pt–P distances (2.226(2) and 2.221(2) A) are com-
0.0162(4) A. However, a distortion from the ideal square-
parable with those of the above-mentioned Pd (2.240(4)
planar configuration is observed in the crystal structure,
the bond angles O(1)–Pt–O(2) and P(3)–Pt–P(4) being
80.0(3)ꢁ and 100.2(9)ꢁ, respectively.
˚
˚
and 2.247(5) A) and Pt (2.215(2) and 2.220(2) A) complexes
and also similar to those found for the corresponding
dichloro Pd(II) species [(dppeO)2PdCl2] [18b]. The
observed Pt–P and Pt–O bond lengths indicate that the
bis-chelate dication [(dppeO)2Pt]2+ is remarkably stable
and this structural evidence is of some relevance in explain-
ing the chemical behaviour of these complexes (see below).
It is worthwhile noting that the Pt–O bond distances
˚
(2.043(6) and 2.096(6) A) are both comparable with those
found for the corresponding Pd (2.088(12) and
˚
˚
2.119(10) A) and Pt (2.089(2) and 2.094(2) A) complexes
and also with the M–O (M = Pd [19a], Pt [19b]) bond
Fig. 1. Molecular structure of the bis-chelate dication [Pt(dppeO-j2-P,O)2]2+ (2a) with the atom-labeling scheme. Hydrogen atoms are omitted for clarity.

3662
P. Sgarbossa et al. / Journal of Organometallic Chemistry 691 (2006) 3659–3666
2.3. Catalytic studies
peroxide, as a 31P{1H} analysis of the final reaction mix-
ture clearly indicated the presence of either dppeO2 or
dppmO2 at 36.2 and 38.2 ppm, respectively.
These complexes should conceivably be good Lewis acid
catalysts because of (i) the 2+ charge and (ii) the ease with
which the labile O donor is expectedly displaced by sub-
strates to be transformed. We initially tested the Pt(II)
and Pd(II) complexes as catalysts in two oxidation reac-
tions where the Lewis acidity of the complex catalyst is
known to be important in promoting the transformation,
i.e. the Baeyer–Villiger oxidation of 2-methylcyclohexa-
none [13f–i] and the sulfoxidation of thioanisole [20]
(Scheme 3), but the results were rather disappointing
(Table 2).
Tests were subsequently carried out to check the reactiv-
ity of these complexes in the Diels–Alder (DA) and hetero
Diels–Alder (HDA) reactions (Scheme 4) to compare the
activity observed with that of recently reported Pd(II)
and Pt(II) complexes [17,21]. DA reaction led to the forma-
tion of two different stereoisomers (exo and endo) and, in
the HDA, also to the formation of the so-called ene prod-
uct was observed. Table 3 collects the results obtained with
the different complexes and the various combinations of
dienes and dienophiles.
The oxidation of 2-methylcyclohexanone was practically
negligible, even when increasing either the amount of cata-
lyst or the reaction temperature up to 70 ꢁC, while the sul-
foxidation of thioanisole gave poor yields. In the latter case
the selectivity to sulfoxide was >99%, only traces of sulfone
being observed. The reasons for this modest reactivity are
probably due to the catalyst not withstanding hydrogen
The reaction between cyclohexadiene and acrolein
(entries 1–9) was always rather productive, albeit much
less than in the presence of the closely related [(diphos-
phine)M(solv)2]2+ complexes (M = Pd, Pt; solvent =
MeCN, THF) [17] where similar reactivities could be
observed at 0 ꢁC, indicating that the P@O ligand is prob-
ably more strongly bound than MeCN or THF. However,
they showed some interesting endo/exo selectivities partic-
ularly when BFꢁ4 is the counteranion. The less sterically
demanding endo product was generally favoured in these
reactions and, expectedly, the presence of bulky ligands
around the Lewis acidic transition metal (Fig. 1) increased
the endo/exo ratio in catalyzed reactions. This is not so
with TfOꢁ as the counteranion (Table 3, entries 5, 6, 9):
this observation may suggest that triflate is probably able
to displace one of the oxygen donors in complexes
thereby leading to a less sterically demanding catalytic
species.
O
O
cat.
O
+ H2O
+ H2O2(aq)
DCE
O
O O
S
S
S
cat.
+ H2O2(aq)
+
- H2O, DCE
Scheme 3.
The use of methacrolein as the dienophile (Table 3,
entries 10–18) resulted in lower conversions with the
endo/exo ratio being practically the same for all catalysts.
On the other hand, and despite the lower temperature
(25 ꢁC), changing the diene to the highly reactive cyclo-
pentadiene (Table 3, entries 19–24) resulted in an appre-
ciable catalytic effect only in the case of methacrolein as
the dienophile, as can be seen by a comparison with the
control experiments carried out in the absence of
catalyst.
Table 2
Oxidation of 2-methylcyclohexanone and thioanisole with hydrogen
peroxide catalyzed by [Pt(BPMO-j2-P,O)2][X]2 derivatives
Catalyst
Substrate
Conversion (%)
1a
2a
2-Methyl-cyclohexanone
0.8
0.7
1aa
2aa
Thioanisole
19
16
Reaction conditions: catalyst 0.0083 mmol, substrate 0.83 mmol, H2O2
0.91 mmol, DCE 3 ml, T = 25 ꢁC, N2 1 atm.
As to the hetero Diels–Alder reaction, only the cycload-
dition of ethyl glyoxylate to 2,3-dimethylbutadiene was
a
Catalyst 0.0166 mmol.
O
O
R
H
R
DA
+
+
H
R
O
H
endo
R = H, Me
exo
dienophile
diene
O
O
O
O
O
+
H
+
O
O
OH
O
C-ene
HDA
Scheme 4.

P. Sgarbossa et al. / Journal of Organometallic Chemistry 691 (2006) 3659–3666
3663
Table 3
Diels–Alder (DA) and hetero Diels–Alder (HDA) reactions catalyzed by (BPMO-j2-P,O)Pd(II) and -Pt(II) complexes shown in Scheme 1
Entry
Diene
Dienophile
Temperature (ꢁC)
Catalyst
Conversion (%)
endo/exo
O
1
2
3
4
5
6
7
8
9
65
–
4.7
98
88
76
78
100
89
81
14
37
33
14
8
3.7
41
30
10
1a
2a
3a
1ba
2b
4a
5a
5b
H
96
10
11
12
13
14
15
16
17
18
65
–
0
16
8
4
9
22
5
4
O
H
1a
2a
3a
1ba
2b
4a
5a
5b
2.8
2.8
2.7
2.8
2.8
2.9
2.8
2.9
10
b
19
20
21
25
25
65
–
58
54
57
3.6
4.1
4.1
O
H
2ab
5ab
22
23
24
–
2a
5a
55
81
72
4.6
4.5
4.4
O
H
O
25
26
27
28
29
30
–
0
26
23
18
17
20
HDA/ene
1
1.1
1
1.2
1.3
H
O
1a
2a
3a
4a
5a
O
Reaction conditions: catalyst 0.0106 mmol, diene 0.53 mmol, dienophile 0.53 mmol, solvent 1 ml dichloroethane (DCE), reaction time 24 h.
a
Not soluble.
Reaction time 2.5 h.
b
found to yield moderate amounts of products but with
quite a poor HDA/C-ene selectivity in keeping with the lit-
erature [22] (Table 3, entries 25–30). No reaction was
observed with a common bidentate dienophile as in the
case of e.g. 1,3-cyclohexadiene with phenylacryloyl-N-
oxazolidinone.
4. Experimental
4.1. General procedures and materials
All work was carried out with the exclusion of atmo-
spheric oxygen under a dinitrogen atmosphere using stan-
dard Schlenck techniques. Solvents were dried and purified
according to standard methods. Substrates were purified
by passing through neutral alumina and stored in the dark
at low temperature. Hydrogen peroxide (35% Fluka) was a
commercial product and used without purification. All
dienes, dienophiles and substrates for oxidation reactions
employed were purchased from Aldrich and used without
any further purification. cis-[MCl2(BPMO-j1-P)2] com-
plexes (M = Pt, BPMO = dppmO, dppeO, dpppO; M =
Pd, BPMO = dppeO) were synthesized by treatment of
[PtCl2(COD)] and [PdCl2(CH3CN)2] with 2 equiv. of BPMO
in dichloromethane at room temperature, similarly to proce-
dures reported in the literature [18a,18b]. Complexes 4a and
5a were prepared as reported in the literature [18b]. 1H NMR
3. Conclusions
A range of bis-cationic Pt(II) and Pd(II) monomeric
complexes bearing two molecules of bis-phosphine monox-
ide ligands and different counteranions have been prepared.
The cis coordination of the ligand was confirmed by X-ray
diffraction study. Such complexes were investigated as
Lewis acids in catalytic oxidation with modest results, as
well as in the DA and HDA reactions with interesting
results in terms of activity and more markedly of diaste-
roselectivity. The catalytic results here reported indicate
that the new complexes synthesized are indeed Lewis acids
containing hemilabile ligands.

3664
P. Sgarbossa et al. / Journal of Organometallic Chemistry 691 (2006) 3659–3666
spectra were run either on a Bruker AC300 spectrometer
operating at 300.13 or on a Bruker AC200 spectrometer
operating at 200.13 MHz at 298 K. 31P{1H} NMR spectra
were run at 298 K, unless otherwise stated, on a Bruker
AC200 spectrometer operating at 81.015 MHz; d values
in ppm are relative to SiMe4, 85% H3PO4. GLC measure-
ment were taken on a Hewlett–Packard 5890A gas chro-
matograph equipped with a FID detector (gas carrier He).
Identification of products was made with GLC by compari-
son with authentic samples. Elemental analyses were per-
formed by the Department of Analytical, Inorganic and
Organometallic Chemistry of the University of Padua.
4.2.4. Synthesis of [Pt(dppmO-j2-P,O)2](OTf)2 (1b)
To a suspension of cis-[PtCl2(dppmO-j1-P)2] (0.30 g,
0.28 mmol) in dichloromethane (20 ml) room temperature
was added 1.46 ml (0.58 mmol) of a 0.40 M acetone solution
of AgOTf. The reaction mixture was stirred under nitrogen
for 3 h and then the solid AgCl formed was filtered off. After
concentration, the solution was treated with n-pentane to
give a white solid, which was filtered off. The solid was
recrystallized from methanol/Et2O and dried under vac-
uum. Yield: 0.32 g, 87%. Anal. Calc. for C52H44F6O8P4PtS2:
C, 48.27; H, 3.43; S, 4.96. Found: C, 48.32; H, 3.13; S,
4.79%. 1H NMR (CD3)2SO: d 7.2–8.0 (m, Ar), 4.9 (m,
PCH2P). 31P{1H} NMR (CD3)2SO, 320 K: d 3.6 (P, s,
1JPt–P = 3878 Hz), 66.5 (P@O, s, 2JPt–P = 73.2 Hz).
4.2. Synthesis of the [M(BPMO-j2-P,O)2][X]2 complexes
4.2.1. [Pt(dppmO-j2-P,O)2][BF4]2 (1a)
4.2.5. Synthesis of [Pt(dppeO-j2-P,O)2](OTf)2 (2b)
To a solution of cis-[PtCl2(dppeO-j1-P)2] (0.34 g,
0.31 mmol) in dichloromethane (20 ml) at room tempera-
ture was added 1.59 ml (0.64 mmol) of a 0.40 M acetone
solution of AgOTf. The reaction mixture was stirred under
nitrogen for 3 h and then the solid AgCl formed was fil-
tered off. After concentration, the solution was treated with
Et2O to give a white solid, which was filtered off and dried
under vacuum. Yield: 0.34 g, 84%. Anal. Calc. for
C54H48F6O8P4PtS2: C, 49.06; H, 3.66; S, 4.85. Found: C,
49.47; H, 3.16; S, 4.84%. 1H NMR (CDCl3): d 7.2–8.0
(m, Ar), 3.0 (m, PCH2). 31P{1H} NMR (CDCl3): d 1.6
To a solution of cis-[PtCl2(dppmO-j1-P)2] (0.40 g,
0.38 mmol) in dichloromethane (20 ml) and acetone
(20 ml) at room temperature was added 0.16 g (0.82 mmol)
of AgBF4. The reaction mixture was stirred under nitrogen
for 3 h and then the solid AgCl formed was filtered off.
After concentration, the solution was treated with Et2O
to give a white solid, which was filtered off and dried under
vacuum. Yield: 0.42 g, 97%. Anal. Calc. for C50H44B2-
F8O2P4Pt: C, 51.35; H, 3.79. Found: C, 51.32; H, 3.63%.
1H NMR (d (CD3)2CO): 7.2–8.0 (m, Ar), 4.7 (m, PCH2P).
1
31P{1H} NMR (CD2Cl2): d 2.8 (P, s, JPt–P = 3834 Hz),
2
1
3
66.7 (P@O, s, JPt–P(O) = 74.2 Hz).
(P, d, JPt–P = 3917 Hz, JP–PO = 5.5 Hz), 52.2 (P@O, d,
3
2JPt–P = 99.5 Hz, JP–PO = 5.5 Hz).
4.2.2. [Pt(dppeO-j2-P,O)2][BF4]2 (2a)
To a suspension of cis-[PtCl2(dppeO-j1-P)2] (0.35 g,
0.32 mmol) in methanol (20 ml) and acetone (20 ml) at
room temperature was added 0.66 ml (0.66 mmol) of
1.0 M acetone solution of AgBF4. The reaction mixture
was stirred under nitrogen for 3 h and then the solid AgCl
formed was filtered off. After concentration, the solution
was treated with Et2O to give a white solid, which was fil-
tered off and dried under vacuum. Yield: 0.34 g, 89%. Anal.
Calc. for C52H48B2F8O2P4Pt: C, 52.15; H, 4.04. Found: C,
4.2.6. Synthesis of [Pd(dppeO-j2-P,O)2][OTf]2 (5b)
To a orange-yellow solution of cis-[PdCl2(dppeO-j1-P)2]
(0.33 g, 0.33 mmol) in dichloromethane (20 ml) at room
temperature was added 1.67 ml (0.67 mmol) of a 0.40 M
acetone solution of AgOTf. The reaction mixture was stir-
red under nitrogen for 2 h and then the solid AgCl formed
was filtered off. After concentration, the solution was trea-
ted with Et2O to give a pale yellow solid, which was filtered
off and dried under vacuum. Yield: 0.37 g, 92%. Anal. Calc.
for C54H48F6O8P4PdS2: C, 52.59; H, 3.92; S, 5.20. Found:
1
51.51; H, 4.07%. H NMR (d (CD3)2CO): 7.2–8.2 (m, Ar),
3.2 (m, PCH2). 31P{1H} NMR (CD2Cl2): d 3.2 (P, dd,
C, 52.64; H, 3.54; S, 5.11%. H NMR (CDCl3): d 7.2–7.9
1
3
1JPt–P = 3953 Hz, JP–PO = 6.2 Hz), 52.9 (P@O, dd,
(m, Ar), 2.9 (m, PCH2). 31P{1H} NMR (CDCl3): d 36.5
3
3
3
2JPt–P = 23.6 Hz, JP–PO = 6.2 Hz).
(P, d, JP–PO = 7.3 Hz, PPd), 48.5 (P@O, d, JP–PO =
7.3 Hz).
4.2.3. [Pt(dpppO-j2-P,O)2][BF4]2 (3a)
To a solution of cis-[PtCl2(dpppO-j1-P)2] (0.37 g,
0.33 mmol) in dichloromethane (15 ml) at room temperature
was added 0.60 ml (0.66 mmol) of a 1.1 M acetone solution
of AgBF4. The reaction mixture was stirred under nitrogen
for 2 h and then the solid AgCl formed was filtered off. After
concentration, the solution was treated with Et2O to give a
white solid, which was filtered off and dried under vacuum.
Yield: 0.36 g, 89%. Anal. Calc. for C54H52B2F8O2P4Pt: C,
52.92; H, 4.28. Found: C, 52.51; H, 4.26%. 1H NMR
(CDCl3): d 7.2–7.6 (m, 40H, Ar), 1.9 (m, 4H, C(CH2)C),
2.7 (m, 4H, CH2PPt), 3.2 (m, 4H, CH2PO). 31P{1H} NMR
(CDCl3): d ꢁ1.6 (P, s, 1JPt–P = 3949 Hz), 61.4 (P@O, s).
4.3. X-ray diffraction studies
Crystal data for cis-[Pt(dppeO-j2-P,O)2][BF4]2 Æ CH2Cl2;
C53H50O2P4B2F8Cl2Pt, Mr = 1282.47, monoclinic, space
˚
˚
group P21/a, with a = 20.478(3) A, b = 25.009(3) A,
3
˚
˚
c = 10.405(2) A, b = 90.10(3)ꢁ, V = 5329(1) A , Z = 4,
3
˚
q
calc = 1.599 Mg/m , F(000) = 2552, k = 0.71073 A, l (Mo
Ka) = 2.922 mmꢁ1
, crystal size 0.320 · 0.34 · .026 mm.
A prismatic colorless crystal was centered on a four-circle
Philips PW1100 (Febo System) diffractometer operating in
h/2h scan mode with graphite-monochromated Mo Ka
˚
radiation (k = 0.71073 A), following standard procedures

P. Sgarbossa et al. / Journal of Organometallic Chemistry 691 (2006) 3659–3666
3665
at room temperature. There were no significant fluctuations
of intensities other than those expected from Poisson statis-
tics. The intensity data were corrected for Lorentz-Polariza-
tion effects and for absorption, as described by North et al.
[23]. The structure was solved by direct methods SIR-97 [24].
Refinement was carried out by full-matrix least-squares
procedures using anisotropic temperature factors for all
non-hydrogen atoms. The H-atoms were placed in calcu-
lated positions with fixed, isotropic thermal parameters
(1.2U equiv. of the parent carbon atom). For a total of
650 parameters and for 8104 reflections having (I P 2r(I)),
with a microsyringe after quenching with triphenyl phos-
phine; n-decane was used as internal standard. Separation
of the products was performed on a Hewlett–Packard
5890A gas chromatograph equipped with a FID detector
(carrier gas He) and a 25 m HP-5 capillary. Identification
of products was made with GLC and 1H NMR by compar-
ison with authentic samples.
5. Supplementary data
P
P
Crystallographic data for the structures here reported
have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publications No. CCDC
602962. Copies of the available material can be obtained,
free of charge from CCDC,12 Unino Road, Cambridge
CH2 1EZ, UK (fax: +44 1223 336 033 or e-mail: depos-
it@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
2
2 1=2
wR2 ¼ ½ wðF 2o ꢁ F 2cÞ = wðF 2oÞ ꢀ ¼ 0:138, S = 1.344,
and conventional R = 0.058; minimum/maximum residual
electron density ꢁ0.964/0.674 e Aꢁ3. Structure refinement
˚
and final geometrical calculations were carried out with
SHELXL-97 [25] program, implemented in the WinGX pack-
age [26], drawings were produced using ORTEP3 [27].
4.4. Catalytic studies
Acknowledgements
4.4.1. Diels–Alder reactions
`
R.A.M. and G.S. thank MIUR, Universita di Padova
These were carried out in a 3 ml round bottomed flask
fitted with a screw-capped silicone septum to allow sam-
pling. Stirring was performed by a Teflon-coated bar driven
externally by a magnetic stirrer. Constant temperature (20
or 65 ꢁC) was maintained by water circulation through an
external jacket connected with a thermostat. The required
amount of catalyst (2% mol, 9.4 mM) was placed in solid
form in the reactor, followed by 1 ml of 1,2-dichloroethane.
After thermostating at the required temperature for a few
minutes, the proper amount of dienophile (0.53 mmol)
was added, followed by the appropriate amount of diene
(0.53 mmol) and time was started. All reactions were mon-
`
`
and Universita Ca Foscari di Venezia for financial support
(PRIN 2003). R.A.M. thanks CIRCC (Consorzio Interuni-
versitario Reattivita Chimica e Catalisi) for a fellowship to
E.P. G.S. wishes to thank Johnson-Matthey for the loan of
platinum.
`
References
[1] (a) V.V. Grushin, Chem. Rev. 104 (2004) 1629, and references
therein;
(b) N.D. Jones, B.R. James, Can. J. Chem./Rev. Can. Chim. 83
(2005) 546;
(c) M.P. Felicissimo, A.A. Batista, A.G. Ferreira, J. Ellena, E.E.
Castellano, Polyhedron 24 (2005) 1063;
(d) N. Oberbeckmann-Winter, X. Morise, P. Braunstein, R. Welter,
Inorg. Chem. 44 (2005) 1391.
1
itored with H NMR by periodic direct sampling of 20 lL
of solution from the reaction mixtures with a microsyringe.
Quenching of reaction samples was performed by dilution
up to 200 times with deuterated solvent and spectra were
immediately acquired. Identification of products was made
with NMR by comparison with authentic samples. Prod-
ucts yield and diasteromeric distribution were determined
[2] R.W. Wegman, A.G. Abatjoglou, A.M. Harrison, J. Chem. Soc.,
Chem. Commun. (1987) 1891;
R.W. Wegman, D. Schrek, J. Eur. Pat. Appl. EP 173170, 1986;
R.W. Wegman, A.G. Abatjoglou, PCT Int. Appl. 8600888, 1986; US
Patent 4670570, 1987.
1
by integration of the H NMR spectra.
[3] R.W. Wegman, US Patent 4563309, 1986.
[4] R.W. Wegman, PCT Int. Appl. 8600889, 1986.
[5] K. Weissermel, H.-J. Arpe, Industrial Organic Chemistry, third ed.,
Wiley–VCH, Weinheim, 1997;
4.4.2. Oxidation reactions
These were carried out in a 3 ml round bottomed flask
fitted with a screw-capped silicone septum to allow sam-
pling. Stirring was performed by a Teflon-coated bar dri-
A.G. Abatjoglou, E. Billing, Eur. Pat. Appl. EP 73961, 1983; US
Patent 4400548, 1983; US Patent 4522933, 1985;
A.G. Abatjoglou, D.R. Bryant, Eur. Pat. Appl. EP 73398, 1983; US
Patent 4491675, 1985; US Patent 4593011, 1986;
J.N. Argyropoulos, D.R. Bryant, D.L. Morrison, K.E. Stockman,
A.G. Abatjoglou, US Patent 5932772, 1999;
C. Abu-Gnim, I. Amer, J. Organomet. Chem. 516 (1996) 235;
Y. Liu, D.-H. He, C.-B. Li, T.-E. Wang, J.-Y. Liu, Q.-M. Zhu, Fenzi
Cuihua 14 (2000) 337;
ven externally by
a
magnetic stirrer. Constant
temperature (20 or 65 ꢁC) was maintained by water circula-
tion through an external jacket connected with a thermo-
stat. The required amount of catalyst (2% mol, 2 mM)
was placed in solid form in the reactor. To this, 3 ml of
1,2-dichloroethane were added. After thermostating at
the required temperature for a few minutes, the proper
amount of substrate (0.83 mmol) was added, followed by
1.1 equiv. of 35% hydrogen peroxide and time was started.
All reactions were monitored with GLC by direct injection
of samples taken periodically from the reaction mixtures
M.I. Terekhova, T.E. Kron, Yu.G. Noskov, E.S. Petrov, Zh. Obshch.
Khim. 64 (1994) 1966.
[6] S. Gladiali, S. Medici, T. Ke’gl, L. Kolla‘r, Monatsh. Chem. 131
(2000) 1351.
[7] S. Gladiali, E. Alberico, S. Pulacchini, L. Kolla‘r, J. Mol. Catal. A
143 (1999) 155.

3666
P. Sgarbossa et al. / Journal of Organometallic Chemistry 691 (2006) 3659–3666
[8] M.I. Terekhova, T.E. Kron, N.A. Bondarenko, E.S. Petrov, E.N.
Tsvetkov, Izv. Akad. Nauk SSSR, Ser. Khim. (1992) 2003;
T.-C. Wu, US Patent 5482596, 1996; US Patent 5902898, 1999.
[9] I. Brassat, W. Keim, S. Killat, M. Mothrath, P. Mastrorilli, C.F.
Nobile, G.P. Suranna, J. Mol. Catal. A 157 (2000) 41.
[10] W. Kaim, H. Maas, S.Z. Mecking, Z. Naturforsch. B 50 (1995) 430.
[11] R.A.M. Robertson, A.D. Poole, M.J. Payne, D.J. Cole-Hamilton,
Chem. Commun. (2001) 47.
[16] (a) R.A. Michelin, R. Bertani, M. Mozzon, A. Sassi, M. Basato, A.
Biffis, M. Zecca, Inorg. Chem. Commun. 4 (2001) 281;
(b) R. Bertani, M. Biasiolo, K. Darini, R.A. Michelin, M. Mozzon,
F. Visentin, L. Zanotto, J. Organomet. Chem. 642 (2002) 32.
[17] K. Pignat, J. Vallotto, F. Pinna, G. Strukul, Organometallics 19
(2000) 5160.
[18] (a) S.J. Higgins, R. Taylor, B.L. Shaw, J. Organomet. Chem. 325
(1987) 285;
[12] J.W. Faller, B.P. Patel, M.A. Albrizzio, M. Curtis, Organometallics
18 (1999) 3096;
(b) R.J. Coyle, Yu.L. Slovokhotov, M.Yu. Antipin, V.V. Grushin,
Polyhedron 17 (1998) 3059;
J.W. Faller, B.J. Grimmond, D.G. D’Alliessi, J. Am. Chem. Soc. 123
(2001) 2525;
(c) M.J. Arendse, G.K. Anderson, N.P. Rath, Acta Crystallogr.,
Sect. C 57 (2001) 237.
J.W. Faller, X. Liu, J. Parr, Chirality 12 (2000) 325;
J.W. Faller, J. Parr, Organometallics 19 (2000) 1829;
J.W. Faller, B.J. Grimmond, M. Curtis, Organometallics 19 (2000)
5174;
J.W. Faller, A.R. Lavoie, B.J. Grimmond, Organometallics 21 (2002)
1662;
[19] (a) J.W. Gilje, H.W. Roesky, Chem. Rev. 94 (1994) 895;
(b) H.E. Bryndza, W. Tam, Chem. Rev. 88 (1988) 1163.
[20] (a) A. Corma, H. Garcia, Chem. Rev. 102 (2002) 3837;
(b) A. Corma, H. Garcia, Chem. Rev. 103 (2003) 4307;
(c) K. Kaczorowska, Z. Kolarska, K. Mitka, P. Kowalski, Tetrahe-
dron 61 (2005) 8315.
J.W. Faller, J. Parr, Organometallics 19 (2000) 3556;
J.W. Faller, J. Parr, Organometallics 20 (2001) 697.
[13] (a) G. Strukul, R.A. Michelin, J. Am. Chem. Soc. 107 (1985) 7563;
(b) A. Marsella, S. Agapakis, F. Pinna, G. Strukul, Organometallics
11 (1992) 3578;
[21] (a) A.K. Ghosh, H. Matsuda, Org. Lett. 1 (1999) 2157;
`
(b) N.M. Brunkan, P.S. White, M.R. Gagne, Organometallics 21
(2002) 1565;
(c) A. Cendron, G. Strukul, J. Mol. Catal. A 204–205 (2003)
187;
(c) M. Del Todesco Frisone, F. Pinna, G. Strukul, Organometallics
12 (1993) 148;
(d) C. Baccin, A. Gusso, F. Pinna, G. Strukul, Organometallics 14
(1995) 1161;
(e) G. Strukul, Angew. Chem., Int. Ed. Engl. 37 (1998) 1198;
(f) A. Brunetta, G. Strukul, Eur. J. Inorg. Chem. 5 (2004) 1030;
(g) A. Brunetta, P. Sgarbossa, G. Strukul, Catal. Today 99 (2005)
227;
(h) R.A. Michelin, E. Pizzo, A. Scarso, P. Sgarbossa, G. Strukul,
Organometallics 24 (2005) 1012;
(d) J. Hao, M. Hatano, K. Mikami, Org. Lett. 2 (2000) 4059;
(e) S. Oi, E. Terada, K. Ohuchi, T. Kato, Y. Tachibana, Y. Inoue, J.
Org. Chem. 64 (1999) 8660;
(f) T. Hattori, Y. Suzuki, O. Uesugi, S. Oi, S. Miyana, Chem.
Commun. (2000) 73;
(g) D. Ferraris, B. Young, T. Dudding, T. Lectka, J. Am. Chem. Soc.
120 (1998) 4548;
(h) K. Hori, H. Kodama, T. Ohta, I. Furukawa, J. Org. Chem. 64
(1999) 5017;
(i) A. Furstner, D. Voigtla¨nder, W. Schraber, D. Giebel, M. Reetz,
¨
(i) G. Strukul, Top. Catal. 19 (2002) 33.
Org. Lett. 3 (2001) 417.
[14] (a) A. Gusso, C. Baccin, F. Pinna, G. Strukul, Organometallics 13
(1994) 3442;
[22] See for example: M. Johannsen, K.A. Jørgensen, J. Org. Chem. 60
(1995) 5757.
(b) R. Gavagnin, M. Cataldo, F. Pinna, G. Strukul, Organometallics
17 (1998) 661;
[23] A.T.C. North, D.C. Philips, F.S. Mathews, Acta Crystallogr., Sect. A
24 (1968) 351.
(c) C. Paneghetti, R. Gavagnin, F. Pinna, G. Strukul, Organomet-
allics 18 (1999) 5056.
[15] R. Bertani, R.A. Michelin, M. Mozzon, P. Traldi, R. Seraglia,
M.F.C.G. Silva, A.J.L. Pombeiro, Organometallics 14 (1995)
551;
[24] A. Altomare, M.C. Burla, M. Camalli, G.L. Cascarano, C. Giaco-
vazzo, A. Guagliardi, A.G.G. Moliterni, G. Polidori, R. Spagna SIR-
97, J. Appl. Crystallogr. 32 (1999) 115.
[25] G.M. Sheldrick, SHELXL-97: Program for the Refinement of Crystal
Structures, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[26] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.
[27] ORTEP3 for Windows L.J. Farrugia, J. Appl. Crystallogr. 30 (1997)
565.
R. Bertani, R.A. Michelin, M. Mozzon, P. Traldi, R. Seraglia,
L. Busetto, M.C. Cassani, P. Tagliatesta, G. D’Arcangelo,
Organometallics 16 (1997) 3229.