Second-generation electron-poor platinum(II) complexes as efficient epoxidation catalysts for terminal alkenes with hydrogen peroxide

Article abstract of DOI:10.1021/om060194c

The preparation and characterization of second-generation electron-poor Pt(II) complexes of general formula [(P-P)Pt(C₆F₅)(H ₂O)][X], 1a-h (P-P = diphosphine, X = BF₄, OTf), bearing a pentafluorophenyl ligand is

Full text of DOI:10.1021/om060194c

3056
Organometallics 2006, 25, 3056-3062
Second-Generation Electron-Poor Platinum(II) Complexes as
Efficient Epoxidation Catalysts for Terminal Alkenes with Hydrogen
Peroxide
Erika Pizzo,† Paolo Sgarbossa,† Alessandro Scarso,‡ Rino A. Michelin,*,† and
Giorgio Strukul*,‡
Dipartimento di Processi Chimici dell’Ingegneria, UniVersita` di PadoVa, Via F. Marzolo 9,
35131 PadoVa, Italy, and Dipartimento di Chimica, UniVersita` Ca` Foscari di Venezia, Dorsoduro 2137,
Venice, Italy
ReceiVed February 28, 2006
The preparation and characterization of second-generation electron-poor Pt(II) complexes of general
formula [(P-P)Pt(C6F5)(H2O)][X], 1a-h (P-P ) diphosphine, X ) BF4, OTf), bearing a pentafluo-
rophenyl ligand is reported. The complexes are investigated as catalysts in the epoxidation of alkenes
with hydrogen peroxide in a chlorinated solvent/H2O two-phase system. The effects of the P-P ligands
and of the Lewis acidity of the metal species are discussed with respect to the catalytic activity in the
epoxidation reaction.
Focusing on homogeneous systems employing “green” ter-
minal oxidants such as hydrogen peroxide for alkene epoxida-
tion, examples of organocatalysis10 can be found, but they
require relatively high catalyst loading, while for metal-catalyzed
epoxidation noteworthy examples are based on W(VI),11-14 Mn-
(II),15 Re(V),16 Fe(III),17,18 and V(III). Very recently, bis-(µ-
hydroxo)-bridged di-vanadium species implemented in a per-
oxotungstate framework showed high selective and efficient
H2O2 epoxidation of alkenes, in particular toward terminal
alkenes.19
Several years ago we described the synthesis of electron-
poor Pt(II) diphosphine complexes, characterized by the pres-
ence of an electron-withdrawing trifluoromethyl ligand, and
found that these complexes were very efficient in the activation
of aqueous hydrogen peroxide toward the selective epoxidation
of terminal alkenes under mild catalytic condition.20 Kinetic
studies indicated that this unusual reactivity was due to the
ability of Pt(II) to increase the nucleophilicity of the olefin by
Introduction
Epoxides represent important commodities and, at the same
time, pivotal building blocks for organic synthesis, from both
the industrial and academic points of view.1 In recent years,
their extensive use has prompted the development of a plethora
of efficient and selective methods for the epoxidation of alkenes
under heterogeneous2 and homogeneous3 conditions, the latter
being generally characterized by better selectivities.
Among the many terminal oxidants available for this oxida-
tion reaction, hydrogen peroxide has attracted the attention of
many research groups due to its many advantages, such as low
cost, environmentally friendly character,4 being a waste-avoiding
oxidant,5 and high atom efficiency,6 which are all fundamental
features for practical applications.7
It is noteworthy that most of the known catalytic homoge-
neous systems making use of “green” oxidants such as hydrogen
peroxide are usually applied toward electron-rich olefins such
as di- and trisubstituted CdC or di- and trisubstituted electron-
poor alkenes.3 On the contrary, simple terminal monosubstituted
alkenes, which are much less reactive but more interesting for
industry, have been far less successfully investigated and still
rely on a few efficient catalysts, the most notable one being
TS1.8 Styrene derivatives and allylic alcohols are not included
in this category of substrates, the former because of their
particular reactivity imparted by the aromatic ring, and the latter
for the presence of the hydroxyl group, which allows easy
coordination to the active site.9
(9) Adam, W.; Wirth, T. Acc. Chem. Res. 1999, 32, 703.
(10) Shu, L.; Shi, Y. J. Org. Chem. 2000, 65, 8807.
(11) (a) Noyori, R.; Aoki, M.; Sato, K. Chem. Commun. 2003, 1977.
(b) Sato, K.; Aoki, M.; Ogawa, M.; Hashimoto, T.; Noyori, R. J. Org. Chem.
1996, 61, 8310.
(12) (a) Venturello, C.; Alneri, E.; Ricci, M. J. Org. Chem. 1983, 48,
3831. (b) Venturello, C.; D’Aloisio, R. J. Org. Chem. 1988, 53, 1553.
(13) (a) Murphy, A.; Pace, A.; Stack, T. D. P. Org. Lett. 2004, 6, 3119.
(b) Murphy, A.; Dubois, G.; Stack, T. D. P. J. Am. Chem. Soc. 2003, 125,
5250. (c) Banfi, S.; Montanari, F.; Quici, S.; Barkanova, S. V.; Lakiya, O.
L.; Kopranenkov, V. N.; Luk’yanets, E. A. Tetrahedron Lett. 1995, 36,
2317.
* To whom correspondence should be addressed. E-mail: strukul@unive.it.
† Dipartimento di Processi Chimici dell’Ingegneria, Universita` di Padova.
‡ Dipartimento di Chimica, Universita` Ca` Foscari di Venezia.
(1) van Leeuwen, P. W. N. M. Homogeneous Catalysis; Kluwer
Academic Publishers: Dordrecht, 2004.
(14) Mizuno, N.; Yamaguchi, K.; Kamata, K. Coord. Chem. ReV. 2005,
249, 1944.
(15) De Vos, D. E.; Sels, B. F.; Reynaers, M.; Subba Rao, Y. V.; Jacobs,
P. A. Tetrahedron Lett. 1998, 39, 3221.
(16) (a) Rudolph, J.; Reddy, K. L.; Chiang, J. P.; Sharpless, K. B. J.
Am. Chem. Soc. 1997, 119, 6189. (b) Cope´ret, C.; Adolfsson, H.; Sharpless,
K. B. Chem. Commun. 1997, 1565.
(17) Dubois, G.; Murphy, A.; Stack, T. D. Org. Lett. 2003, 5, 2469.
(18) White, M. C.; Doyle, A. G.; Jacobsen, E. N. J. Am. Chem. Soc.
2001, 123, 7194.
(19) Nakagawa, Y.; Kamata, K.; Kotani, M.; Yamaguchi, K.; Mizuno,
N. Angew. Chem., Int. Ed. 2005, 44, 5136.
(20) (a) Baccin, C.; Gusso, A.; Pinna, F.; Strukul, G. Organometallics
1995, 14, 1161. (b) Strukul, G.; Michelin, R. A. J. Am. Chem. Soc. 1985,
107, 7563. (c) Zanardo, A.; Michelin, R. A.; Pinna, F.; Strukul, G. Inorg.
Chem. 1989, 28, 1648.
(2) For review articles: (a) De Vos, D. E.; Sels, B. F.; Jacobs, P. A.
AdV. Synth. Catal. 2003, 345, 457. (b) Lambert, R. M.; Williams, F. J.;
Cropley, R. L.; Palermo, A. J. Mol. Catal. A 2005, 228, 27.
(3) Lane, B. S.; Burgess, K. Chem. ReV. 2003, 103, 2457.
(4) Strukul, G., Ed. Catalytic Oxidations with Hydrogen Peroxide as
Oxidant; Kluwer Academic: Dordrecht, The Netherlands, 1992.
(5) Grigoropoulou, G.; Clark, J. H.; Elings, J. A. Green Chem. 2003, 5,
1-7.
(6) Trost, B. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 259-281.
(7) Noyori, R.; Aoki, M.; Sato K. Chem. Commun. 2003, 1977-1986.
(8) Notari, B. Catal. Today 1993, 18, 63, and references therein.
10.1021/om060194c CCC: $33.50 © 2006 American Chemical Society
Publication on Web 05/03/2006

Electron-Poor Pt(II) Complexes as Catalysts
Organometallics, Vol. 25, No. 12, 2006 3057
applies to both epoxidation20 and Baeyer-Villiger oxidation of
ketones.22,23 Spurred by this general observation we decided to
prepare a homologous series of Pt(II) complexes 1a-h (Scheme
1), bearing a pentafluorophenyl group and different diphosphine
ligands 2a-h, aiming at elucidating the effect of both the
activity and selectivity toward alkene epoxidation. Recently,
similar complexes bearing alkyl diphosphines were reported in
the literature,24 and now we have extended the procedure to a
wide range of diphosphine ligands, following and, in some cases,
adapting and improving the previously published procedure
(Scheme 2). The latter is a very flexible synthetic pathway that
allows the preparation of homologous complexes with a wide
variety of diphosphine ligands, at variance with the old
complexes, where the introduction of the -CF3 ligand was quite
elaborate, hampering the desired synthetic flexibility.20 The
diphosphine ligands employed are commercially available except
for 2g, which was prepared following a procedure reported in
the literature.25 The synthesis started with the preparation of
the dimeric species [Pt(µ-Cl)(C6F5)(tht)]2 (tht ) tetrahy-
drothiophene) by means of lithium aryl reaction on [PtCl2-
(tht)2].26 Treatment of the binuclear complex in dichloromethane
with 2 equiv of the corresponding diaryl diphosphine 2a-h led
in all cases to the formation of the neutral complexes [(P-P)-
Pt(C6F5)Cl] 3a-h in good to high yields (70-99%). In the
reaction with ligand 2a we observed the formation of a
byproduct, whose 31P{1H} NMR (CD2Cl2) spectrum showed a
singlet at 10.53 ppm flanked by 195Pt satellites (1JP-Pt ) 2594
Hz). This impurity can be readily removed by treating the
mixture with chloroform, followed by filtration of the solution
containing the pure product.
Scheme 1. New, Second-Generation Monocationic Pt(II)
Complexes 1a-h
coordination, thereby changing the traditional electrophile/
nucleophile roles in the system.20d
In this work we present the synthesis of second-generation
Pt(II) complexes with general structure [(P-P)Pt(C6F5)(H2O)]-
[X], 1a-h (P-P ) diphosphine, X ) BF4, OTf), bearing the
more bulky electron-withdrawing perfluorophenyl ligand (Scheme
1), and the employment of these new complexes as catalysts in
the epoxidation of alkenes with hydrogen peroxide. This choice
allows a more straightforward and versatile preparation method
with respect to the old complexes and the possibility to evaluate
the influence on the reactivity of a bulky ligand in close
proximity of the vacant coordination site.
Subsequent abstraction of the halide ligand from 3a-h in
dichloromethane using a wet acetone solution of AgX (X )
BF4 or OTf) produced the corresponding aquo complexes of
general formula [(P-P)Pt(C6F5)(H2O)][X], 1a-h, in good to
high yields (70-98%). After filtration of AgCl, they were
isolated as white solids upon addition of n-pentane. It is worth
noting that we did not observe any disproportionation reaction
to form the diaryl complex [(P-P)Pt(C6F5)2], as reported in the
case of [(dmpe)Pt(C6F5)Cl] (dmpe ) 1,2-bis(dimethylphosphi-
no)ethane) upon treatment with AgOTf.24 31P{1H} NMR data
support the chelate structure of the monomeric complex 1a due
to the observation of only one set of signals, in contrast with
previous findings related to the analogous reaction involving
the CF3 complex [(dppm)Pt(CF3)(OH)](OTf), where, along with
the monomeric species, two more dinuclear species were present
Results and Discussion
Synthesis of Complexes. The Lewis acid character of metal
complexes is a key issue in the activation of oxidants for
catalytic oxygen transfer reactions,21 and in our studies we
observed several times that in oxidation processes high activity
correlates well with high Lewis acidity of metal catalysts. This
Scheme 2. Synthesis of the Pt(II) Monocationic Catalysts 1a-h Bearing a Perfluorophenyl Residue

3058 Organometallics, Vol. 25, No. 12, 2006
Pizzo et al.
Table 1. Catalytic Epoxidation of Different Categories of
Alkenes with Hydrogen Peroxide Mediated by 1ba
differing in the relative orientation of trifluoro methyl and
hydroxy residues in the dimer.20c
The complexes [(P-P)Pt(C6F5)Cl] (3a-h) and [(P-P)Pt-
(C6F5)(H2O)][X] (X ) BF4, OTf) (1a-h) with P-P ) dppm
(2a), dppe (2b), diphoe (2c), dppp (2d), dppb (2e), dfppe (2f),
dippe (2g), and (2S),(3S)-chiraphos (2h) are all new compounds
and were characterized by elemental analysis and multinuclear
1H, 31P{1H}, and 19F{1H} NMR spectroscopy, as reported in
the Experimental Section.
31P{1H} NMR spectra of chloride complexes 3a-h show,
as expected, two different P resonances. The P atom trans to
chlorine appears as a singlet or a doublet (due to P-P coupling)
depending on the type of the diphosphine, with 1JP-Pt values in
the range 3300-3800 Hz. In the case of the P atom trans to
the pentafluorophenyl group the corresponding resonances
showed more complex multiplicity due to coupling with the
fluorine atoms of the C6F5 ligand. The observed P-Pt coupling
constants are found in the range 1800-2200 Hz (significantly
lower than those trans to chlorine), owing to the higher trans
influence of the aryl ligand.27
a Experimental conditions: [substrate]0 ) 0.83 mmol, [H2O2]0 ) 0.83
mmol, [1b]0 ) 0.0166 mmol (2%), solvent 1 mL of DCE at RT.
1
The aquo complexes 1a-h showed clearly, in the H NMR
spectra, the presence of bound water that fall in the range 2.7-
2.8 ppm. In the 31P NMR spectra we observed similar multiplic-
ity of the P resonances compared to the previously described
chloride derivatives 3a-h, but significant changes of the 1JP-Pt
values for the P atom trans to H2O were observed, which now
fall in the range 3800-4700 Hz, the lowest value belonging to
complex 1a, while the highest to 1f. The observed increase in
the coupling constants can be explained with the lower trans
influence of the aquo ligand compared to chloride. Again
1
different JP-Pt values were observed for the various diphos-
phines, reflecting a different electron-withdrawing character of
the ligands.28
Figure 1. Epoxidation of 1-octene with 35% hydrogen peroxide
mediated by 1b: 1-octene (2), 1,2-epoxyoctane (b), heptanal (0).
Experimental conditions: [1-octene]0 ) 0.83 mmol, [H2O2]0 ) 0.83
mmol, [1b]0 ) 0.0166 mmol (2%), solvent 1 mL of DCE at RT.
Catalytic Epoxidation. The scope of the reaction with respect
to substrate properties was briefly investigated with triflate
catalyst 1b, exploring its reactivity toward different CdC double
bonds.
As can be seen from Table 1, only the terminal alkene
1-hexene is a suitable substrate (89% epoxide yield), while with
styrene the reaction is sluggish, and even at higher temperature
low conversion is observed. Disubstituted alkenes such as
cyclohexene or methylenecyclohexane, being more electron-
rich substrates, are both not oxidized. This substrate specificity
is in agreement with what was observed with first-generation
Pt(II) epoxidation complexes bearing a -CF3 residue instead
of -C6F5.29 In our previous paper using -CF3 derivatives30 we
suggested olefin coordination as the key feature toward oxida-
tion. Given the electronic analogies with the present catalysts,
we tend to assume that, in the present case, the reaction occurs
with similar features. However, these results may also suggest
the existence of a strong steric effect in this kind of oxidation
reaction, conceivably due to the narrow space available between
the aryl groups of the diphosphine ligand and the perfluoro
aromatic ligand to activate the substrate by displacement of the
water molecule. As a consequence, only terminal alkenes are
able to easily sneak in and reach the Pt(II) active species.
Further investigations were carried out on 1-octene comparing
the activity of all the aquo complexes (1a-h) prepared. A
typical reaction profile is shown in Figure 1, while a summary
of the catalytic properties of the different complexes is collected
in Table 2.
(21) (a) Corma, A.; Garcia, H. Chem. ReV. 2003, 103, 4307-4366. (b)
Corma, A.; Garcia, H. Chem. ReV. 2002, 102, 3837-3892. (c) Strukul, G.
Top. Catal. 2002, 19, 33.
(22) Michelin, R. A.; Pizzo, E.; Scarso, A.; Sgarbossa, P.; Strukul, G.;
Tassan, A. Organometallics 2005, 24, 1012-1017.
(23) Brunetta, A.; Strukul, G. Eur. J. Inorg. Chem. 2004, 5, 1030-1038.
(24) Hughes, R. P.; Ward, A. J.; Golen, J. A.; Incarvito, C. D.; Rheingold,
A. L.; Zakharov, L. N. J. Chem. Soc., Dalton Trans. 2004, 2720.
(25) Fryzuk, M. D.; Jones, T.; Einstein, F. W. B. Organometallics 1984,
3, 185.
(26) (a) Uson, R.; Fornies, J.; Espinet, P.; Alfranca, G. Synth. React.
Inorg. Met.-Org. Chem. 1980, 10, 597. (b) Uson, R.; Fornies, J.; Martinez,
F.; Tomas, M. J. Chem. Soc., Dalton Trans. 1980, 888.
(27) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. ReV.
1973, 10, 335.
(28) Appleton, T. G.; Bennett, M. A. Inorg. Chem. 1978, 17, 738.
(29) Strukul, G.; Michelin, R. A. J. Chem. Soc., Chem. Commun. 1984,
1538.
Weakly coordinating counteranions do not influence the cata-
lytic activity (entries 2, 3), while only hydrogen peroxide emerg-
es as the best oxidant (entries 3, 5, 6). The diphosphine ligand
plays a major role, with the best results observed with 1b, while
the more electron-deficient ligand 2f as well as the sterically
crowded ligand 2g suppress the activity (1f and 1g are both
sparingly soluble in 1,2-dichloroethane; therefore addition of
4% methanol for complete solubilization was required). Indeed,
the presence of methanol might alter the catalytic properties of
the complexes. For this reason we also carried out a test with
1b as catalyst using the same 4% methanol in dichoroethane
reaction medium. The results (entry 4 in Table 2) clearly indicate
that such a change in the solvent polarity does not significantly
alter either the activity or the productivity of the catalyst,
(30) Zanardo, A.; Pinna, F.; Michelin, R. A.; Strukul, G. Inorg. Chem.
1988, 27, 1966-1973.

Electron-Poor Pt(II) Complexes as Catalysts
Organometallics, Vol. 25, No. 12, 2006 3059
1
Table 2. Catalytic Epoxidation of 1-Octene with Hydrogen
Table 3. JP-Pt Coupling Constants for Complexes
[(P-P)Pt(C6F5)(H2O)](OTf), ∆νj (cm-1) of 2,6-Dimethyl
Phenylisocyanide Derivatives Prepared in Situ by Water
Exchange, and ∆δ (ppm) for Ligands 2a-h
Peroxide Mediated by Pt(II) Complexes 1a-ha
time yield
initial rate
entry
catalyst
oxidant
(h)
(%)
TON × 106 (M‚s-1
)
1JP-Pt (trans to
H2O) (Hz)
1
2
3
4
5
6
7
8
9
1a‚CF3SO3
1b‚BF4
H2O2
H2O2
H2O2
H2O2
UHPb
t-BuOOH
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
6
4
4
39
81
80
74
2
20
40
40
37
1
0
35
3
7
0.5
1
36
25
280
315
305
ligand
∆νj (cm-1
)
∆δ (ppm)
1b‚CF3SO3
1b‚CF3SO3
1b‚CF3SO3
1b‚CF3SO3
1c‚CF3SO3
1d‚CF3SO3
2a
2b
2c
2d
2e
2f
3821
4353
4440
4148
4530
4712
4284
4272
82.72
78.91
80.95
78.20
77.10
93.22
71.68
78.67
-26.02
45.47
55.74
6.61
32.16
33.29
49.12
40.18
d
6
24
24
5
24
3
24
24
4
0
70
6
191
22
61
14c
1
c
1e‚CF3SO3
2g
2h
d
10
11
12
1f‚CF3SO3
1g‚CF3SO3
d
e
2
73
1h‚CF3SO3
180
dimethyl phenylisocyanide provides valuable information about
the electrophilicity of the isocyanide carbon atom, which is
known to correlate well to the Lewis acidity of the metal com-
plex.32 This approach was recently employed successfully on
other Pt(II) complexes bearing partially fluorinated aryl diphos-
phine used as catalysts in the Baeyer-Villiger oxidation of
cyclic ketones to the corresponding lactones with hydrogen
peroxide.22
On this basis, we prepared in situ a homologous series of
isocyanide complexes of general formula [Pt(C6F5)(CN-2,6-
(CH3)2C6H3)(P-P)](OTf) (P-P ) 2a-h) by simple addition
of a stoichiometric amount of 2,6-dimethyl phenylisocyanide
to a solution of the aquo complexes 1a-h.
a Experimental conditions: [1-octene]0 ) 0.83 mmol, [oxidant]0 ) 0.83
b
mmol [cat]0 ) 0.0166 mmol (2%), solvent 1 mL of DCE at RT. Urea
hydrogen peroxide adduct; c 24% of alkene isomerization to cis- and trans-
2-octene; d DCE/MeOH, 96:4. e ee 64% determined by 1H NMR integration
in the presence of the chiral shift reagent europium tris[3-(heptafluoropro-
pylhydroxymethylene)-(+)-camphorate] at RT.
suggesting that the low conversions observed for 1f and 1g are
due to their intrinsic electronic and/or steric properties.
The spacer between the P atoms in the diphosphines influ-
ences the catalytic activity (Table 2) with a marked decrease in
conversion both with the small diphosphine 2a and with large
diphosphines 2d and 2e. Surprisingly in the latter case, a
concurrent isomerization to internal cis- and trans-2-octene takes
place. The latter products are not reactive under the experimental
conditions used, being disubstituted alkenes (Table 1). The para-
sitic alkene isomerization reaction is activated by the catalysts
(no reaction occurs in their absence under the same conditions);
in particular with complex 1e this side reaction reaches 24% of
1-octene conversion, while with the other complexes it never
exceeds 1-3%. Increasing the rigidity of the catalyst from 1b
to 1c decreases the catalytic activity, at variance with what was
observed in the past with similar catalysts, where diphoe 2c
ensured the highest activity and productivity.20c With the most
active complexes 1b a byproduct due to overoxidation of the
oxirane ring starts being observed only at high epoxide con-
centrations. At the end of the reaction 3% heptanal (confirmed
by NMR and GC-MS analysis) was observed. It is worth noting
that with ligand 2h a chiral complex 1h is obtained, only slightly
lower in activity and productivity compared to 1b. This chiral
complex affords 1-octene epoxide with 64% ee at RT. This value
is particularly interesting in view of the few enantioselective
epoxidation catalysts known for terminal alkenes.31
With ligands 2b, 2d, and 2e the activity for first- and second-
generation complexes parallels well,20c with a similar decrease
in activity, even though the former complexes bearing -CF3
residues are intrinsically more reactive probably because of a
lower steric hindrance with respect to the -C6F5 counterparts.
Determination of the Lewis Acidity of 1a-h and Cor-
relation with Their Catalytic Activity. The electron-withdraw-
ing ability of the pentafluorophenyl ligand and the concomitant
effect of the diphosphine ligands should influence the Lewis
acidity of complexes 1a-h. To assess whether there is a quali-
tative correlation between the catalytic activity and their Lewis
acid character, 2,6-dimethyl phenylisocyanide was used as a
molecular probe. In fact, the value of the wavenumber shift (∆νj
) νj(CtN)coord - νj(CtN)free) for the CtN stretching of 2,6-
In Table 3 the ∆νj for the different complexes are reported,
from which, at first sight, it is evident that the fluorinated
complex 1f is characterized by the highest Lewis acidity, while
1g is the least acidic because of the presence of more electron-
donating alkyl residues on the P atoms. All the other complexes
fall in a narrow ∆νj range, suggesting similar Lewis acidity.
However, some moderate differences are present, presumably
due to the bite angle and steric properties of the different ligands.
More in detail, upon increasing the size of the metal-
diphosphine ring, ∆νj moderately decreases, suggesting a
decrease in the Lewis acidic character of the metal center. Chiral
ligand 2h produces effects similar to those of 2b, while the
presence of a double bond as in 2c slightly increases the Lewis
acidity of the complex.
In an attempt to compare the catalytic activity (initial rate of
epoxidation) with the Lewis acidity determined as above, the
lack of direct correlation is quite evident (Figure 2). Unreactive
complexes such as 1g and 1f are respectively the least and the
most acidic of the series. It must be remembered that, because
of solubility problems, the conditions in which these complexes
were tested cannot directly compare to the other ones. However,
we have also demonstrated that the different solvent should not
significantly change their catalytic properties. Complex 1b,
which is the most active and productive, is characterized by an
intermediate ∆νj value. Even though 1b shows similar Lewis
acidity compared to many other complexes, the reactivity of
the latter is very different and probably dependent on the
different ring size, bite angle, and substituents of the complexes
under investigation. Moreover, 1d and 1h, which are very similar
in acidity with respect to 1b, are much less active. On this basis,
the Lewis acidic character gives only very rough indications
and does not appear to be a sufficient parameter to rationalize
the reactivity within this class of complexes. Other properties,
in particular steric requirements, may have a strong influence.
Clearly, simple Lewis acidity determination by means of 2,6-
dimethyl phenylisocyanide cannot take them into account.
(31) (a) Sinigalia, R.; Michelin, R. A.; Pinna, F.; Strukul, G. Organo-
metallics 1987, 6, 728. (b) Collman, J. P.; Wang, Z.; Straumanis, A.;
Quelquejeu, M. J. Am. Chem. Soc. 1999, 121, 460. (c) Matsumoto, K.;
Sawada, Y.; Saito, B.; Sakai, K.; Katsuki, T. Angew. Chem., Int. Ed. 2005,
44, 4935. (d) Valodkar, V. B.; Tembe, G. L.; Ram, R. N.; Rama, H. S.
Catal. Lett. 2003, 90, 91.
(32) (a) Michelin, R. A.; da Silva, M. F. C. G.; Pombeiro, A. J. L. Coord.
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Crociani, B. J. Organomet. Chem. 1983, 250, 565.

3060 Organometallics, Vol. 25, No. 12, 2006
Pizzo et al.
Figure 4. Plot of the initial rates of epoxidation of 1-octene
catalyzed by complexes 1a-h vs the ∆δ values for free and
coordinated ligands 2a-h. Experimental conditions as in Table 2.
Figure 2. Plot of the initial rates of epoxidation of 1-octene
catalyzed by complexes 1a-h vs the ∆νj values (cm-1) of 2,6-
dimethyl phenylisocyanide coordinated to the complexes 1a-h.
Experimental conditions as in Table 2.
This difference can be ascribed basically to the shielding effect
on P due to the metal and the C6F5 ligand upon coordination,
significantly reflecting both conformational changes and steric
interactions. Ligand 2a upon complexation experiences an
unexpected increase in shielding, probably due to the formation
of the strained four-membered ring with the metal center. All
other complexes are characterized by a deshielding at P (positive
∆δ); in particular ∆δ increases strongly in 1b and 1c, which
form five-membered rings with Pt,34 it increases only slightly
in the six-membered ring complex 1d, and it increases further
with the seven-membered ring complex 1e. This clearly indicates
that the size of the formed ring, the bite angle, and other
conformational and steric features have an effect on the 31P
chemical shift of the ligand. Figure 4 shows the correlation
between the initial rates of epoxidation of 1-octene with the
∆δ values for the investigated complexes. Starting from complex
1a, which is a weak Lewis acid, there is a clear increase in
activity on going from 1d to 1h to 1b. On the contrary, 1c,
which is characterized by the highest ∆δ, is less active than 1b
probably because of the increased rigidity imparted by the alkene
spacer between the P atoms, but, over long reaction times, it
showed a productivity similar to 1b. This results again in a plot
with a maximum for 1b (Figure 4).
Figure 3. Plot of the initial rates of epoxidation of 1-octene
catalyzed by complexes 1a-h vs the 1JP-Pt (Hz) trans to the water
ligand of the complexes. Experimental conditions as in Table 2.
We searched for another qualitative correlation between
activity and spectroscopic properties of the complexes. Analysis
of 1JP-Pt coupling constants for the P atom trans to the solvent
molecule (Table 3) provides an indication of the lability of the
latter and can be assumed as an indication of the availability of
the metal for binding the reaction substrates.27 Complex 1a
The general picture that arises from these considerations
clearly speaks for an epoxidation reaction catalyzed by Pt(II)
complexes where both the steric hindrance of the ligand as well
as the ability to exchange water play a key role, with five-
membered ring complexes as the most active catalysts. Among
others, complex 1b emerges as the most active one and the chiral
version 1h only slightly less productive.
1
shows the smallest JP-Pt, indicative of strong binding of the
water molecule, which results in a sluggish epoxidation reaction.
1
Considering complexes with increasing values of JP-Pt (de-
creasing water binding affinity), a gradual increase of reactivity
up to complex 1b is observed, followed by a decrease, giving
a plot (Figure 3) with a maximum centered on 1b. This behavior
reflects the fact that if the complex coordinates the water
molecule too strongly (small 1JP-Pt), the latter is hardly available
for exchange with the substrate, and analogously if the water
molecule binds too weakly (large 1JP-Pt), it is conceivable that
also the substrate will bind weakly. An intermediate value of
1JP-Pt is the optimum, as observed by the profile reported in
Figure 3. This plot strongly resembles the volcano curves
relating chemisorption to catalytic activity in heterogeneous-
catalysis.33 Of course, 1JP-Pt values refer to water coordination
and not alkene, which is much more sterically demanding.
31P NMR investigation of ∆δ (δcoord - δfree) for the P atom
trans to water in 1a-h compared to P resonances of the free
2a-h ligands provided more arguments to address the problem.
No clear parallel is observed with the results reported in the
past with the first-generation electron-poor Pt(II) complexes
bearing the -CF3 ligand of general formula [(P-P)Pt(CF3)(CH2-
Cl2)]ClO4.20c In the latter complexes the order of activity
observed as function of the ligand was 2c > 2h > 2b > 2a >
2d > 2e, while for -C6F5 complexes it is 2b > 2c ≈ 2h > 2e
> 2a > 2d. In both cases, the most reactive complexes are those
characterized by five-membered rings, while the ring size effect
is not similar. This is not surprising because of the observed
steric influence on reactivity. Clearly, the -CF3 ligand is much
less sterically demanding than -C6F5. Nevertheless, rates of
epoxidation are similar between the two classes, while the
overall turnover numbers are slightly better for the new class
of complexes.20c
(33) See for example: Bond, G. C. Heterogeneous Catalysis: Principles
and Applications, 2nd ed.; Clarendon Press: Oxford, 1987.
(34) Garrou, P. E. Chem. ReV. 1981, 81, 229.

Electron-Poor Pt(II) Complexes as Catalysts
Organometallics, Vol. 25, No. 12, 2006 3061
58.9 Hz). 19F{1H} NMR (δ, CDCl3): -120.19 (t, o-F,3JPt-F ) 275
Hz, 3JF-F ) 40.7 Hz), -162.60 (t, p-F, 3JF-F ) 39.5 Hz), -165.11
(m, m-F).
Conclusion
Herein we reported the synthesis and characterization of
second-generation Pt(II) complexes 1a-h containing a perflu-
orinated aryl ligand that proved to be highly active epoxidation
catalysts with hydrogen peroxide as terminal oxidant. Remark-
able features of the present catalytic system are the complete
selectivity toward terminal alkenes and the high activity with
low catalyst loading (2% mol) under very mild conditions, which
allows reaction times of a few hours with no need of over-
stoichiometric amounts of oxidant. The preliminary results
obtained are highly encouraging and stimulate a more extensive
investigation of the regio- and diasteroselectivity of the epoxi-
dation process, as well as the need to get insight into the
mechanistic aspects of catalysis. This new set of catalysts are
characterized by a more straightforward preparation procedure
compared to the first generation,20 and this feature allows the
extension of the system to the investigation of the chiral complex
1h and similar congeners in the asymmetric epoxidation of
terminal alkenes. These issues are currently under investigation.
[PtCl(C6F5)(dppe)] (3b). This compound was prepared using a
procedure similar to that described above for complex 3a starting
from [Pt(µ-Cl)(C6F5)(tht)]2 (0.30 g, 0.31 mmol) in chloroform (30
mL) and 0.26 g (0.65 mmol) of dppe. Yield: 0.492 g, 100%. Anal.
Calc for C32H24ClF5P2Pt: C, 48.28; H, 3.04. Found: C, 47.97; H,
1
2.91. H NMR (δ, CDCl3): 7.33-8.00 (m, Ar), 2.10-2.55 (m,
PCH2). 31P{1H} NMR (δ, CDCl3): 39.55 (d, PCl-trans, 1JPt-P ) 3722
Hz, 2JP-P ) 6.2 Hz); 40.70 (d, PC-trans, 1JPt-P ) 2256 Hz, 2JP-P
)
6.2 Hz). 19F{1H} NMR (δ, CDCl3): -120.27 (t, o-F,3JPt-F ) 268
Hz, 3JF-F ) 19.0 Hz), -163.29 (t, p-F, 3JF-F ) 20.7 Hz), -165.16
(m, m-F).
[PtCl(C6F5)(diphoe)] (3c). This compound was prepared using
a procedure similar to that described above for complex 3a starting
from [Pt(µ-Cl)(C6F5)(tht)]2 (0.15 g, 0.16 mmol), dissolved in acetone
(20 mL), and diphoe (0.13 g, 0.32 mmol). Yield: 0.154 g, 59%.
Anal. Calc for C32H22ClF5P2Pt: C, 48.41; H, 2.79. Found: C, 47.98;
H, 2.89. 1H NMR (δ, CDCl3): 7.37-7.87 (m, Ar), 5.30 (m, PCH).
31P{1H} NMR (δ, CDCl3): 55.42 (m, PC-trans, 1JPt-P ) 2289 Hz);
1
46.49 (s, PCl-trans, JPt-P ) 3778 Hz). 19F{1H} NMR (δ, CDCl3):
Experimental Section
-120.30 (m, o-F), -162.51 (m, p-F), -165.18 (m, m-F).
General Procedures and Materials. All synthetic steps were
carried out under a dinitrogen atmosphere using standard 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. The diphosphines
1,2-bis(dichlorophosphino)ethane, 1,1′-bis(diphenylphosphino)-
methane (2a; dppm), 1,2-bis(diphenylphosphino)ethane (2b; dppe),
1,2-bis(diphenylphosphino)ethylene (2c; diphoe), 1,3-bis(diphe-
nylphosphino)propane (2d; dppp), 1,4-bis(diphenylphosphino)-
butane (2e; dppb), and 1,2-bis(dipentafluorophenylphosphino)ethane
(2f; dfppe) were commercially available and were used as pur-
chased. The diphosphine 1,2-bis(di-isopropylphosphino)ethane35
(2g; dippe) and [Pt(C6F5)(µ-Cl)(tht)]225 were synthesized following
procedures reported in the literature. Hydrogen peroxide (35%
Fluka), MgCl-iPr, AgBF4, and AgOTf were commercial products
and used without purification.
IR spectra were taken in CH2Cl2 solution using CaF2 windows
using a FT-IR AVATAR 320 spectrophotometer from Nicolet
Instrument Corporation; wavenumbers are given in cm-1. Measure-
ments were carried out in dichloromethane solutions of the aquo
complexes treated with an excess of 2,6-dimethyl phenylisocyanide.
1H NMR, 31P{1H} NMR, and 19F NMR spectra were run on a
Bruker AC200 spectrometer operating at 200.13, 81.015, and 188.25
MHz, respectively, at 298 K, unless otherwise stated; δ values in
ppm are relative to Si(CH3)4, 85% H3PO4, and CFCl3. GLC
measurements were taken on a Hewlett-Packard 5890A gas
chromatograph equipped with a FID detector (carrier gas He).
Quenching of reaction samples was performed by addition of
triphenyl phosphine. Identification of products was made with GLC
and NMR by comparison with authentic samples. Elemental
analyses were performed by the Department of Analytical, Inorganic
and Organometallic Chemistry of Universita` di Padova.
[PtCl(C6F5)(dppp)] (3d). This compound was prepared using a
procedure similar to that described above for complex 3a starting
from [Pt(µ-Cl)(C6F5)(tht)]2 (0.201 g, 0.21 mmol), dissolved in
acetone (20 mL), and dppp (0.174 g, 0.42 mmol). Anal. Calc for
C33H26ClF5P2Pt: C, 48.93; H, 3.24. Found: C, 48.81; H, 3.36. 1H
NMR (δ, CDCl3): 7.13-7.80 (Ar); 2.02-2.89 (CH2). 31P NMR
(δ, CDCl3): -4.33 (Ptrans-Cl, JPt-P ) 3605 Hz, JP-P ) 27 Hz); -4.39
(Ptrans-C, JPt-P ) 2081 Hz). 19F NMR (δ, CDCl3): -120.29 (o-F),
-164.10 (p-F), -165.34 (m-F).
[PtCl(C6F5)(dppb)] (3e). This compound was prepared using a
procedure similar to that described above for complex 3a starting
from [Pt(µ-Cl)(C6F5)(tht)]2 (0.15 g, 0.15 mmol) and dppb (0.14 g,
0.32 mmol). Yield: 0.24 g, 93.5%. Anal. Calc for C34H28ClF5P2-
1
Pt: C, 49.56; H, 3.42. Found: C, 49.87; H, 3.24. H NMR (δ,
(CD3)2SO): 7.24-7.74 (m, Ar), 1.37-2.99 (m, CH2). 31P{1H}
NMR (δ, (CD3)2SO): 20.14 (d, PCl-trans, 1JPt-P ) 3776 Hz,2JP-P
)
1
21.9 Hz); 1.18 (m, PC-trans, JPt-P )2149 Hz). 19F{1H} NMR (δ,
3
(CD3)2SO): -118.71 (t, o-F,3JPt-F ) 297 Hz, JF-F ) 19.6 Hz),
3
-164.42 (t, p-F, JF-F ) 19.3 Hz), -164.98 (m, m-F).
[PtCl(C6F5)(dfppe)] (3f). This compound was prepared using a
procedure similar to that described above for complex 3a starting
from [Pt(µ-Cl)(C6F5)(tht)]2 (0.20 g, 0.21 mmol) and dfppe (0.33 g,
0.43 mmol). Yield: 0.41 g, 86.3%. Anal. Calc for C32H4ClF25P2-
1
Pt: C, 33.25; H, 0.35. Found: C, 33.45; H, 0.54. H NMR (δ,
(CD3)2CO): 3.36-3.60 (m, PCH2). 31P{1H} NMR (δ, (CD3)2CO):
1
1
3.78 (s, PCl-trans, JPt-P ) 3799 Hz); 23.29 (s, PC-trans, JPt-P
)
2192 Hz). 19F{1H} NMR (δ, (CD3)2CO): -121.11 (t, Pt-C6F5,
o-F,3JPt-F ) 130 Hz), -127.34, -129.38 (m, P-C6F5, o-F),
3
-127.31 (m, P-C6F5, p-F), -164.42 (t, Pt-C6F5, p-F, JF-F
19.3 Hz), -161.31 (m, P-C6F5, m-F) -164.98 (m, Pt-C6F5, m-F).
)
[PtCl(C6F5)(dippe)] (3g). This compound was prepared using
a procedure similar to that described above for complex 3a starting
from [Pt(µ-Cl)(C6F5)(tht)]2 (0.35 g, 0.36 mmol) and dippe (0.20 g,
0.75 mmol). Yield: 0.30 g, 63.2%. Anal. Calc for C20H32ClF5P2-
Synthesis. [PtCl(C6F5)(dppm)] (3a). To a solution of [Pt(µ-
Cl)(C6F5)(tht)]2 (0.11 g, 0.12 mmol) in acetone (20 mL) at room
temperature was added 0.09 g (0.24 mmol) of dppm. The solution
was stirred for 2 h, then was concentrated and treated with
n-pentane, giving a white solid, which was filtered off and dried
under vacuum. Yield: 0.132 g, 69%. Anal. Calc for C31H22ClF5P2-
1
Pt: C, 36.40; H, 4.89. Found: C, 36.23; H, 4.78. H NMR (δ,
CDCl3): 2.20-2.72 (m, CH), 1.61-1.96 (m, PCH2), 0.98-1.48 (m,
CH3). 31P{1H} NMR (δ, CDCl3): 66.94 (s, PCl-trans, 1JPt-P ) 3708
Hz); 72.22 (m, PC-trans,
1JPt-P ) 2292 Hz). 19F{1H} NMR (δ,
1
Pt: C, 47.61; H, 2.84. Found: C, 47.87; H, 3.02. H NMR (δ,
CDCl3): 7.26-7.80 (m, Ar), 4.43 (t, PCH2, 2JP-H ) 8.5 Hz). 31P-
CDCl3): -119.01 (m, o-F), -162.92 (m, p-F), -164.69 (m, m-F).
1
{1H} NMR (δ, CDCl3): -51.07 (d, PCl-trans, JPt-P ) 3330 Hz,
[PtCl(C6F5)((2S),(3S)-Chiraphos)] (3h). This compound was
prepared using a procedure similar to that described above for
complex 3a starting from [Pt(µ-Cl)(C6F5)(tht)]2 (0.204 g, 0.21
mmol) and (2S),(3S)-chiraphos (0.182 g, 0.43 mmol). Yield: 0.243
1
2
2JP-P ) 58.9 Hz); -51.48 (d, PC-trans, JPt-P ) 1865 Hz, JP-P
)
(35) Fryzuk, M. D.; Jones, T.; Einstein, F. W. B. Organometallics 1984,
3, 185.
1
g, 70%. H NMR (δ, CDCl3): 7.08-7.98 (m, Ar), 2.01-2.58 (m,

3062 Organometallics, Vol. 25, No. 12, 2006
Pizzo et al.
PCH), 1.06-1.15 (m, CH3). 31P{1H} NMR (δ, CDCl3): 39.45 (d,
PC-trans, 1JPt-P ) 2136 Hz). 19F{1H} NMR (δ, CDCl3): -79.53 (s,
1
2
3
3
P
Cl-trans, JPt-P ) 3654 Hz, JP-P ) 16.1 Hz); 39.54 (m, PC-trans,
OTf), -120.80 (t, o-F, JPt-F ) 267.1 Hz, JF-F ) 18.4 Hz),
1JPt-P ) 2194 Hz). 19F{1H} NMR (δ, CDCl3): -120.62, -121.39
3
-161.52 (t, p-F, JF-F ) 19.1 Hz), -164.89 (m, m-F).
3
(m, o-F), -163.77 (t, p-F, JF-F ) 19.9 Hz), -164.91, -165.54
[Pt(C6F5)(H2O)(dfppe)][OTf] (1f). This compound was prepared
using a procedure similar to that described above for complex 1a
starting from [PtCl(C6F5)(dfppe)] (0.31 g, 0.27 mmol) in acetone
(20 mL) and dichloromethane (20 mL). Yield: 0.344 g, 94%. Anal.
Calc for C33H6F28O4P2PtS: C, 30.79; H, 0.47. Found: C, 30.45;
H, 0.56. 1H NMR (δ, CDCl3): 3.26-3.72 (m, PCH2), 2.72 (s, OH2).
31P{1H} NMR (δ, CDCl3): -9.20 (m, PO-trans, 1JPt-P ) 4712 Hz);
(m, m-F).
[Pt(C6F5)(H2O)(dppm)][OTf] (1a). To a solution of [PtCl(C6F5)-
(dppm)] (0.13 g, 0.16 mmol) in wet dichloromethane (20 mL) was
added 0.50 mL of an acetone solution of AgOTf (0.17 mmol). The
suspension was stirred for 3 h, then the solid AgCl was filtered off
and the solution was concentrated. Upon treatment with n-pentane,
a white solid was obtained, filtered off, and dried under vacuum.
Yield: 0.15 g, 98.1%. Anal. Calc for C32H24F8O4P2PtS: C, 42.07;
1
21.24 (m, PC-trans, JPt-P ) 2176 Hz). 19F{1H} NMR (δ, CDCl3):
-121.49 (m, Pt-C6F5, o-F), -128.50, -128.91 (m, P-C6F5, o-F),
-145.53, -146.37 (m, P-C6F5, p-F), -159.42 (m, Pt-C6F5, p-F),
-161.45 (m, P-C6F5, m-F) -164.01 (m, Pt-C6F5, m-F).
1
H, 2.65. Found: C, 41.89; H, 2.89. H NMR (δ, CDCl3): 7.40-
7.82 (m, Ar), 5.35 (m, PCH2), 2.75 (s, OH2). 31P{1H} NMR (δ,
1
2
CDCl3): -49.73 (d, PO-trans, JPt-P ) 3821 Hz, JP-P ) 59.4 Hz);
-37.80 (m, PC-trans, 1JPt-P ) 1872 Hz). 19F{1H} NMR (δ, CDCl3):
-79.3 (s, OTf), -121.49 (t, o-F, 3JPt-F ) 268 Hz), -160.18 (t,
p-F), -164.29 (m, m-F).
[Pt(C6F5)(H2O)(dippe)][OTf] (1g). This compound was pre-
pared using a procedure similar to that described above for complex
1a starting from [PtCl(C6F5)(dippe)] (0.25 g, 0.38 mmol). Yield:
0.243 g, 77%. Anal. Calc for C21H34F8O4P2PtS: C, 31.86; H, 4.33.
[Pt(C6F5)(H2O)(dppe)][BF4] (1b‚BF4). To a solution of [PtCl-
(C6F5)(dppe)] (0.30 g, 0.38 mmol) in wet dichloromethane (20 mL)
was added 0.94 mL of an acetone solution of AgBF4 (0.40 mmol).
The suspension was stirred for an hour, then the solid AgCl was
filtered off and the solution was concentrated. Upon treatment with
n-pentane, a pale yellow solid was obtained, filtered off, and dried
under vacuum. Yield: 0.263 g, 76%. Anal. Calc for C32H26BF9-
OP2Pt: C, 44.41; H, 3.03. Found: C, 44.65; H, 2.75. 1H NMR (δ,
CDCl3): 7.26-7.80 (m, Ar), 2.81 (s, OH2), 2.13-2.62 (m, PCH2).
1
Found: C, 31.45; H, 4.54. H NMR (δ, CDCl3): 2.11-2.59 (m,
CH), 2.72 (s, OH2), 1.65-2.05 (m, PCH2), 1.00-1.45 (m, CH3).
31P{1H} NMR (δ, CD2Cl2): 61.39 (s, PO-trans, 1JPt-P ) 3930 Hz);
78.65 (m, PC-trans, 1JPt-P ) 2456 Hz). 19F{1H} NMR (δ, CD2Cl2):
-79.31 (s, OTf), -119.57 (m, o-F), -160.68 (m, p-F), -164.57
(m, m-F).
[Pt(C6F5)(H2O)((2S),(3S)-Chiraphos)][OTf] (1h). This com-
pound was prepared using a procedure similar to that described
above for complex 1a starting from [PtCl(C6F5)((2S),(3S)-chira-
1
31P{1H} NMR (δ, CDCl3): 32.07 (d, PO-trans, JPt-P ) 4189 Hz,
1
2JP-P ) 6.3 Hz); 46.38 (m, PC-trans, JPt-P ) 2312 Hz). 19F{1H}
1
phos)] (0.152 g, 0.18 mmol). Yield: 0.142 g, 74%. H NMR (δ,
NMR (δ, CDCl3): -120.52 (m, o-F), -153.21 (s, BF4), -159.44
(s, p-F), -163.46 (s, m-F).
CDCl3): 7.15-8.03 (m, Ar), 2.79 (s, OH2), 2.02-2.64 (m, PCH),
1.02-1.13 (m, CH3). 31P{1H} NMR (δ, CDCl3): 32.60 (d, PO-trans
,
[Pt(C6F5)(H2O)(dppe)][OTf] (1b‚OTf). This compound was
prepared using a procedure similar to that described above for
complex 1a starting from [PtCl(C6F5)(dppe)] (0.30 g, 0.38 mmol).
Yield: 0.313 g, 83.1%. Anal. Calc for C33H26F8O4P2PtS: C, 42.73;
1
1JPt-P ) 4272 Hz,2JP-P ) 16.8 Hz); 45.51 (m, PC-trans, JPt-P
)
2222 Hz). 19F{1H} NMR (δ, CDCl3): -79.34 (s, OTf), -120.91,
-121.77 (m, o-F), -161.30 (m, p-F), -164.41, -165.02 (m, m-F).
1
H, 2.83. Found: C, 42.97; H, 2.59. H NMR (δ, CDCl3): 7.36-
Catalytic Studies. These were carried out in a 2 mL vial fitted
with a screw-capped silicone septum to allow sampling. Stirring
was performed by a Teflon-coated bar driven externally by a
magnetic stirrer. Constant temperature (20 °C) was maintained by
water circulation through an external jacket connected with a
thermostat. The concentration of the commercial 35% H2O2 solution
was checked iodometrically prior to use.
7.52 (m, Ar), 2.78 (s, OH2), 2.05-2.66 (m, PCH2). 31P{1H} NMR
(δ, CDCl3): 31.63 (d, PO-trans, 1JPt-P ) 4353 Hz, 2JP-P ) 6.6 Hz);
1
46.33 (m, PC-trans, JPt-P ) 2309 Hz). 19F{1H} NMR (δ, CDCl3):
-79.27 (s, OTf), -120.73 (m, o-F), -160.86 (m, p-F), -164.68
(m, m-F).
[Pt(C6F5)(H2O)(diphoe)][OTf] (1c). This compound was pre-
pared using a procedure similar to that described above for complex
1a starting from [PtCl(C6F5)(diphoe)] (0.13 g, 0.16 mmol) in
dichloromethane (20 mL). Yield: 0.143 g, 95%. Anal. Calc for
C33H24F8O4P2PtS: C, 42.82; H, 2.61. Found: C, 42.44; H, 2.86.
The required amount of catalyst (0.0166 mmol, 2% with respect
to substrate and oxidant) was placed in solid form in the reactor.
To this was added 1 mL of 1,2-dichloroethane, followed by the
proper amount of substrate (0.83 mmol). After thermostating at the
required temperature for a few minutes, a 35% H2O2 solution in
the appropriate amount (0.83 mmol) was injected through the
septum and time was started.
1H NMR (δ, (CDCl3): 7.33-7.85 (m, Ar), 3.47 (m, PCH), 2.75
1
(s, OH2); 31P{1H} NMR (δ, (CDCl3): 59.03 (m, PC-trans, JPt-P
)
2318 Hz); 33.19 (s, PO-trans, 1JPt-P ) 4441 Hz). 19F{1H} NMR (δ,
(CDCl3): -79.25 (s, OTf), -119.57 (m, o-F), -160.68 (m, p-F),
-164.57 (m, m-F).
All reactions were monitored with GLC by direct injection of
samples taken periodically from the reaction mixtures with a
microsyringe; n-decane was used as internal standard. Initial rate
data were determined from conversion versus time plots. Separation
of the products was performed on a 25 m HP-5 capillary column
using a flame ionization detector.
[Pt(C6F5)(H2O)(dppp)][OTf] (1d). This compound was prepared
using a procedure similar to that described above for complex 1a
starting from [PtCl(C6F5)(dppp)] (0.211 g, 0.26 mmol). Yield: 0.223
g, 91%. Anal. Calc for C34H28F8O4P2PtS: C, 43.37; H, 3.00.
1
Found: C, 43.27; H, 3.12. H NMR (δ, CDCl3): 7.18-7.75 (m,
Ar), 2.73 (s, OH2), 2.08-2.87 (m, CH2). 31P{1H} NMR (δ, CDCl3):
1
-9.36 (d, PO-trans, JPt-P ) 4148 Hz,2JP-P ) 26.9 Hz); 0.91 (m,
1
P
C-trans, JPt-P ) 2128 Hz). 19F NMR (δ, CDCl3): -79.76 (OTf),
Acknowledgment. R.A.M. and G.S. thank MIUR, Universita`
di Padova, and Universita` Ca` Foscari di Venezia for financial
support (PRIN 2003). R.A.M. thanks CIRCC (Consorzio
Interuniversitario Reattivita` Chimica e Catalisi) for a fellowship
to E.P. G.S. wishes to thank Johnson-Matthey for the loan of
platinum. L. Sperni is gratefully acknowledged for GC-MS
analysis.
-120.75 (o-F), -161.38 (p-F), -164.79 (m-F).
[Pt(C6F5)(H2O)(dppb)][OTf] (1e). This compound was prepared
using a procedure similar to that described above for complex 1a
starting from [PtCl(C6F5)(dppb)] (0.15 g, 0.18 mmol). Yield: 0.147
g, 79%. Anal. Calc for C35H30F8O4P2PtS: C, 43.99; H, 3.16.
1
Found: C, 43.87; H, 2.88. H NMR (δ, CDCl3): 7.18-7.61 (m,
Ar), 1.58-2.87 (m, CH2 and s, OH2). 31P{1H} NMR (δ, CDCl3):
1
14.76 (d, PO-trans, JPt-P ) 4530 Hz,2JP-P ) 21.6 Hz); 7.34 (m,
OM060194C