Stable Platinum(0) Catalysts for Catalytic Hydrosilylation of Styrene and Synthesis of [Pt(Ar-bian)(η2-alkene)] Complexes

Article abstract of DOI:10.1002/ejic.200300088

The use of alkenes and bidentate N-ligands in the platinum(0)-catalyzed hydrosilylation of styrene with triethylsilane has been evaluated. A number of bidentate N-ligands, phen, bpy, dafo, and phenyl-bian, were tested at various reaction temperatures using in situ formed catalysts with [Pt(nbe)₃] as a precursor. The main conclusions are: (i) ligands, such as phen, which form stable platinum(0) complexes, give lower catalytic activities compared to the ligands which form less stable complexes; (ii) a small ligand effect is observed with dafo and phenyl-bian compared to [Pt(nbe)₃], the precursor complex, displaying the lability of these ligands. The complex [Pt(nbe)₃], that only has labile alkene ligands, is an active catalyst at low temperatures. At higher temperatures, the catalyst is no longer stable and a decrease in yield is observed. Several novel complexes have been synthesized: [Pt(m,m-(CF₃)₂-C₆H ₃-bian)(tcne)], [Pt(m,m-(CF₃)₂-C6H3-bian)(ma)], [Pt(p-MeO-C₆H₄-bian)(ma)], [Pt(p-MeO-C₆H ₄-bian)(dmfu)] and [Pt(phenyl-bian)(dmfu)]. Whereas the two [Pt(Ar-bian)(ma)] complexes are intrinsically more active than the two [Pt(Ar-bian)(dmfu)] complexes, the latter are much more stable, i.e. the nature of the alkene in these complexes is an important factor in determining their catalytic behavior. Compared to [Pt(Me-nq)(nbe)₂], the two [Pt(Ar-bian)(dmfu)] complexes are much more stable resulting in significantly higher overall yields. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejic.200300088

FULL PAPER
Stable Platinum(0) Catalysts for Catalytic Hydrosilylation of Styrene and
Synthesis of [Pt(Ar-bian)(η2-alkene)] Complexes
Jeroen W. Sprengers,[a] Michiel de Greef,[a] Marcel A. Duin,[a] and Cornelis J. Elsevier*[a]
Keywords: Platinum / Hydrosilylations / N ligands / Homogeneous catalysis / Alkene ligands
The use of alkenes and bidentate N-ligands in the plat-
inum(0)-catalyzed hydrosilylation of styrene with triethylsil-
in yield is observed. Several novel complexes have been syn-
thesized: [Pt(m,m-(CF3)2-C6H3-bian)(tcne)], [Pt(m,m-(CF3)2-
ane has been evaluated. A number of bidentate N-ligands, C6H3-bian)(ma)], [Pt(p-MeO-C6H4-bian)(ma)], [Pt(p-MeO-
phen, bpy, dafo, and phenyl-bian, were tested at various re- C6H4-bian)(dmfu)] and [Pt(phenyl-bian)(dmfu)]. Whereas the
action temperatures using in situ formed catalysts with
[Pt(nbe)3] as a precursor. The main conclusions are: (i) li-
two [Pt(Ar-bian)(ma)] complexes are intrinsically more active
than the two [Pt(Ar-bian)(dmfu)] complexes, the latter are
gands, such as phen, which form stable platinum(0) com- much more stable, i.e. the nature of the alkene in these com-
plexes, give lower catalytic activities compared to the ligands
which form less stable complexes; (ii) a small ligand effect is
observed with dafo and phenyl-bian compared to [Pt(nbe)3],
the precursor complex, displaying the lability of these li-
gands. The complex [Pt(nbe)3], that only has labile alkene
ligands, is an active catalyst at low temperatures. At higher
temperatures, the catalyst is no longer stable and a decrease
plexes is an important factor in determining their catalytic
behavior. Compared to [Pt(Me-nq)(nbe)2], the two [Pt(Ar-bi-
an)(dmfu)] complexes are much more stable resulting in sig-
nificantly higher overall yields.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
1. Introduction
ation, including metals of groups 8, 9, and 10. Platinum
catalysts, especially, are very active in the hydrosilylation of
unsaturated carbonϪcarbon bonds. The Speier catalyst,[3]
H2PtCl6 dissolved in 2-propanol, and the Karstedt cata-
lyst,[4] H2PtCl6 dissolved in tetramethyldivinyldisiloxane
[(CH2ϭCHSiMe2)2O], are frequently used.
The catalytic hydrosilylation of unsaturated compounds,
such as alkenes, alkynes, ketones, and imines, is one of the
most elegant methods for the synthesis of organosilicon
compounds [Equation (1)].[1] The use of organosilicon com-
pounds as reagents and synthons for the construction of
natural products has become a powerful tool in synthesis.
In addition to its use in laboratory syntheses, the hydrosilyl-
ation reaction is used in many ways in the industrial manu-
facture of silicon polymers, for example for the curing and
modification of polyorganosiloxanes and the modification
of unsaturated polymers.
However, a problem associated with these platinum cata-
lysts is their very limited stability when exposed to hydrosi-
lylation conditions; rapid formation of platinum colloids,
that are catalytically not active, takes place. The preparative
scope of Speier’s catalyst is further restricted by its long and
variable induction period. The nature of the catalytically
active species, homogeneous vs. heterogeneous, has been
questioned in the literature for a long time.[5] Recently, it
has become clear that the type of platinum compound that
would generate the highest activity is one in which forma-
tion of a single platinum(0) atom and concomitant loss of
ligands is facile.[5] It has been observed that the Karstedt
catalyst contains preponderantly [Pt2(CH2ϭCHSiMe2)2O]3,
a platinum(0) complex containing one bridging tetramethyl-
divinyldisiloxane ligand.[6] A widely accepted mechanism
for hydrosilylation of alkenes is the ChalkϪHarrod mecha-
nism which consists of oxidative addition of a hydrosilane,
insertion of an alkene into the metalϪhydride bond, and
reductive coupling of the alkyl and silyl fragments.[7]
(1)
Since the first report on catalyzed hydrosilylation in 1947
by Sommer et al.,[2] many efforts have been made to develop
optimized catalytic systems. By now, numerous transition
metal based catalysts have been reported for hydrosilyl-
[a]
Institute of Molecular Chemistry, Coordination and
Organometallic Chemistry, Universiteit van Amsterdam,
Nieuwe Achtergracht 166, 1018 WV Amsterdam, The
Netherlands
Osborn et al.[8] published a series of platinum(0) com-
plexes with the general formula [Pt(η2-alkene)(η4-CH2ϭ
CHSiMe2)2O]. When naphthoquinones were used as the co-
Fax: (internat.) ϩ 31-20/5256456
E-mail: elsevier@science.uva.nl
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DOI: 10.1002/ejic.200300088
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J. W. Sprengers, M. de Greef, M. A. Duin, C. J. Elsevier
FULL PAPER
ordinating alkene, highly active catalysts were obtained.
We have been interested in the use of bidentate N-ligands,
[9]
´
Marko et al. used platinum(0) catalysts with N-hetero- especially bidentate N-ligands, for several catalytic and stoi-
cyclic carbenes as ligands. These catalysts were less active chiometric transition metal mediated carbonϪelement
than the Karstedt catalyst, but side-reactions, such as iso- coupling reactions and for the stereoselective cis-hydrogen-
merization and dehydrogenative silylation, were signifi- ation of alkynes.[17Ϫ22] These ligands are known to stabilize
cantly suppressed. Also our group used some N-hetero- platinum(0) compounds when coordinated in a bidentate
cyclic carbene ligands which yielded outstanding cata- manner,[23Ϫ24] yet readily give rise to free coordination sites
lysts.[10]
Hydrosilylation of alkenes is often accompanied by side-
due to their hemilability.[25Ϫ26]
An effective catalyst for hydrogenation or hydrosilylation
reactions such as isomerization and dehydrogenative silyl- requires a low coordination number and valence. Hence,
ation. The latter can be of interest, because it produces vi- hydrosilylation should proceed effectively for those late
nylsilanes, which are very useful synthetic reagents in syn- transition metal compounds that can readily vacate two or
thesis [Equation (2)].
more coordination sites, in order to accommodate sub-
strates, yet is able to stabilize the complex in its resting state
by re-coordination of the hemilabile donor atom. In this
respect, platinum based precatalysts combining a labile al-
kene with a hemilabile, bidentate N-ligand, specifically
1,10-phenanthroline (1) (phen), 2,2Ј-bipyridyl (2) (bpy), 4,5-
diazafluoren-9-one (3) (dafo), and bis(arylimino)acenapht-
ene (4) (Ar-bian), seem to be very promising indeed for
platinum(0)-catalyzed hydrosilylation.
(2)
Of course, it would be desirable to have catalysts that
are selective either to hydrosilylation or to dehydrogenative
silylation. For instance, the catalysts [Ru3(CO)12][11] and
[Fe3(CO)12][12] are known to be very selective towards dehy-
drogenative silylation of several alkenes, which is also true
for rhodium()[13] and palladium() catalysts[14] when em-
ploying an excess of styrene relative to the hydrosilane or a
more steric hydrosilane. Also platinum(0) catalysts can give
rise to a certain extent of dehydrogenative silylation,[15,16]
for which the ChalkϪHarrod mechanism does not account.
Therefore, other mechanisms have been proposed to explain
this reaction. Characteristically, these mechanisms feature
the formation of an olefin-hydride complex, arising from β-
hydride elimination of a β-silylalkyl intermediate [Equa-
tion (3)]. Dissociation of the trans-vinylsilane yields a metal
hydride complex, which is responsible for the hydrogenated
product. This dissociation of the vinylsilane is favored by a
high styrene concentration and by using more steric hydro-
silanes.
As mentioned before, many of the known platinum(0)
catalysts suffer from deactivation. For instance, Steffanut et
al.[8] observed decomposition of [Pt(η2-2-methylnaphtho-
quinone)(η4-CH2ϭCHSiMe2)2O] at temperatures higher
than 20 °C. Moreover, alkene/hydrosilane ratios of two were
used in their experiments, which contributes to a signifi-
cantly higher catalyst stability. It would be desirable to use
an alkene/hydrosilane ratio of one, but then more stable
catalysts are definitely required. Thus, further manipulation
of the coordination sphere of the metal center will be indis-
pensable in order to obtain an active catalyst that is stable
under the reaction conditions.
In this paper, the use of bidentate N-ligands, as ligands
for Pt-catalyzed hydrosilylation of styrene with triethylsil-
ane, is reported. The performance and stability of several in
situ prepared systems, obtained from [Pt(2-norbornene)3],
[Pt(nbe)3], with appropriate bidentate N-ligands, has been
evaluated and compared with several novel [Pt(Ar-bian)(η2-
alkene)] complexes.
2. Results and Discussion
Bidentate N-Ligands as Ligands in the Hydrosilylation of
Styrene by Triethylsilane
First, the platinum(0) complex [Pt(nbe)3][27] was used as
a precursor for the hydrosilylation of styrene with triethylsi-
lane yielding products I and II (Scheme 1). The hydrosilyl-
ation of styrene is always accompanied by dehydrogenative
silylation, yielding products III and IV. Throughout, ethyl-
benzene (IV) was always formed in the same amount as the
unsaturated silyl product (III) by subsequent hydrogenation
of styrene. Since the nbe ligands readily dissociate from
platinum, active, coordinately unsaturated platinum(0) spec-
ies are readily obtained.
(3)
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Platinum(0) Catalysts for Catalytic Hydrosilylation of Styrene
FULL PAPER
Scheme 1. Hydrosilylation and dehydrogenative silylation of styrene with triethylsilane
The bidentate N-ligands are expected to coordinate to the same trend in deactivation at higher temperatures is ob-
platinum immediately upon their addition, prior to the start served and only a small increase in the yield of product I
of catalysis. Thus influencing the activity and stability of relative to the other products was observed. So, Me-nq is
the hydrosilylation reaction. Liedtke et al.[28] also used not able to act as a stabilizing ligand at higher tempera-
[Pt(nbe)3] as a precursor in their hydrosilylation reactions tures.[8] Furthermore, the use of Me-nq does not lead to a
with certain phosphiranes as ligands. These experiments higher yield at 30 °C compared to [Pt(nbe)3] itself, which
were performed at different temperatures and at a styrene/ generates highly active platinum species. This observation is
hydrosilane ratio of 2.8. For comparison, 2-methylnaphtho- in agreement with the common view that single unsaturated
quinone (Me-nq), Osborn’s ligand,[8] and bis(diphenylphos- platinum(0) atoms are highly active hydrosilylation cata-
phanyl)ethane (dppe), a strongly coordinating ligand, which lysts.[5,8]
results in a platinum complex with low activity,[29] were also
A completely different catalytic behavior is observed
tested in this catalytic system. The results of these catalytic
hydrosilylations have been collected in Table 1.
when 1,10-phenanthroline (phen) is used as the ligand (En-
try 3). In this case, hydrosilylation only takes place at a very
slow rate at 100 °C. Apparently, phen forms a very stable
platinum(0) complex. This idea is supported by the fact that
no significant catalyst deactivation was observed, even
when running this reaction at 100 °C for 24 h, which re-
sulted in a total yield (I ϩ II ϩ III) of 81%. The relative
amount of dehydrogenative silylation has increased using
phen, which can be explained by invoking the strong biden-
tate coordination of phen to the Pt center, favoring the dis-
sociation of the trans-vinylsilane.
When bpy is used in the hydrosilylation (Entry 4), the
yield obtained increases when going from 30 to 50 °C due
to the increased lability of bpy with temperature. The low
yield observed at 100 °C is caused by the deactivation of
the catalyst at this temperature. The selectivity (I/II/III) ob-
tained with this ligand changes significantly with tempera-
ture and differs from the selectivity obtained in Entries 1
and 3. Furthermore, bpy shows an increased amount of de-
hydrogenative silylation compared to [Pt(nbe)3], but not to
the same degree as phen. This can be understood from dif-
ferences in the fluxional behavior of phen and bpy: by its
rigidity, phen forms complexes more readily than bpy, but
bpy is more flexible and can easily adapt to the η1-coordi-
nate structure.
Table 1. Hydrosilylation of styrene with triethylsilane
Entry Ligand[a]
Temp. [°C] Yield [%][b] Selectivity [%][c]
I/II/III
1
2
3
4
5
6
7
Ϫ
30
50
100
30
50
100
30
50
100
30
50
91.9
60.4
19.7
92.5
62.3
20.7
Ϫ
2.0:67.0:31.0
2.5:68.0:29.5
2.7:67.6:29.7
2.0:66.9:31.1
2.7:68.5:28.8
3.0:66.0:31.0
Ϫ
Me-nq
phen
bpy
Ϫ
Ϫ
16.7
31.7
81.7
19.1
88.1
69.6
14.6
86.0
66.0
26.9
Ϫ
4.4:54.3:41.3
2.0:72.6:25.4
2.6:63.9:33.5
3.8:60.0:36.2
2.0:66.8:31.2
2.6:65.2:32.2
3.1:65.4:31.4
2.0:67.5:30.5
2.6:67.8:29.6
3.4:67.4:29.2
Ϫ
100
30
50
dafo
100
phenyl-bian 30
50
100
30
50
dppe
Ϫ
Ϫ
100
5.1
3.5:67.2:29.3
[a]
[b]
0.36 mol % of catalyst, styrene/triethylsilane ratio 2.8, toluene.
The ligand dafo (Entry 5) shows a behavior completely
different from phen and bpy. Only a very small decrease
in yield and the same selectivity compared to [Pt(nbe)3] is
observed. These results indicate that dafo coordinates rela-
tively weakly, in a bidentate fashion, to the platinum(0)
Combined GC yield, after 2 h, of products I, II, and III using
[c]
n-decane as the internal standard.
served in the same amount as product III, therefore the amount of
IV has been omitted.
Product IV was always ob-
It is clear that the precursor complex [Pt(nbe)3] is an ac- atom, which is most likely due to the larger bite angle of
tive catalyst at 30 °C, but that it progressively loses its ac- this ligand (about 82°) compared to phen and bpy (about
tivity at higher temperatures due to deactivation of the cata- 77°). Indeed, Klein et al.[26] have previously observed an
lyst (Entry 1). Addition of 1 equiv. of Me-nq to [Pt(nbe)3] enhanced aptitude for dissociation of one of the donor
(Entry 2) gives results that are similar to those of [Pt(nbe)3]: atoms of dafo in platinum(0) and palladium(0) complexes,
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FULL PAPER
due to the reduced overlap between relevant metal and li- using a styrene/triethylsilane ratio of 2.8 (Table 1, Entry 1).
gand orbitals caused by the larger bite angle. Also dimeric However, when the reaction using a styrene/triethylsilane
palladium() complexes have already been synthesized with ratio of 1.0 was repeated, but now without 20 mL of toluene
dafo as a bridging ligand.[30]
as the solvent, an increase in yield was also observed: from
Although phenyl-bian (Entry 6) possesses a bite angle 32 to 88%. Caseri and Pregosin[16] reported that [Pt(styr-
similar to phen and bpy (about 77°), the catalytic results ene)3] was more active than trans-[PtCl2(PhCHϭCH2)2]
obtained with this ligand differ completely from that of and that this complex did not show an induction period.
phen and bpy. In fact, almost the same yield and selectivity From our results, we can say that [Pt(nbe)3] also generates
were obtained as observed for dafo. Similarly to dafo, phe- highly active platinum(0) species, probably similar to
nyl-bian displays a significant lability. Although plati- [Pt(styrene)3][16] although we did not check if this complex
num(0) or palladium(0) complexes in which the Ar-bian li- is formed during catalysis.
gands act as monodentate ligands are not known, several
The lability of the phenyl-bian ligand was studied in
palladium() complexes containing monodentate Ar-bian more detail by substituting the aryl groups of this ligand.
ligands are known.[25,31] These studies have shown that rigid Thus, ligands 4Ϫ9 were synthesized and tested in the cata-
bidentate N-ligands are more prone to hemilabile behavior lytic hydrosilylation of styrene with triethylsilane at 30 °C.
than the more flexible ones. Assuming partial dissociation The results are collected in Table 2.
of Ar-bian in such cases may explain the observed selec-
Table 2. Hydrosilylation of styrene with triethylsilane using Ar-
bian ligands
tivity for phenyl-bian.
Results obtained for dppe (Entry 7) again demonstrate
that this bidentate phosphane ligand forms a stable chelate
with platinum(0), resulting in zero activity at 30 and 50 °C
and only a very low activity at 100 °C. Triphenylphosphane
was also tested once in the hydrosilylation at 30 °C. After
2 h, a total yield of only 8.5% was obtained with a selec-
tivity of 3.0:73.0:24.0 (I/II/III).
As mentioned before, the selectivities of platinum cata-
lysts depend strongly on the styrene/triethylsilane ratio. For
example, applying a styrene/triethylsilane ratio of 0.5 using
[Pt(nbe)3] as the catalyst yielded a selectivity (I/II/III) of
2.0:90.0:8.0. However, when a styrene/triethylsilane ratio of
Entry
Ligand[a]
Yield [%][b]
Selectivity [%][c]
I/II/III
1
2
3
4
5
6
4
5
6
7
8
9
86.0
84.7
87.0
91.0
90.1
90.0
2.0:67.5:30.5
2.0:67.5:30.5
2.0:67.0:31.0
2.0:67.5:30.5
2.0:66.5:31.5
2.0:67.5:30.5
[a]
0.36 mol % of catalyst, styrene/triethylsilane ratio 2.8, toluene,
[b]
30 °C. Combined GC yield, after 2 h, of products I, II, and III
using n-decane as the internal standard. Product IV was always
[c]
6.4 was used, an enormous increase in dehydrogenative si- observed in the same amount as product III, therefore the amount
lylation was observed: 37% of product III was obtained.
of IV has been omitted.
This observation supports the idea[13,14] that the dis-
sociation of the vinylsilane is favored by a higher styrene
concentration [Equation (3)]. Comparing our selectivities
obtained with already reported catalysts is not straightfor-
ward since the conditions applied can have a significant in-
fluence. For example, Skoda-Földes et al.[29] obtained 12.3%
of III with PtCl2 as a catalyst and using a styrene/triethylsil-
ane ratio of 1.0 in the hydrosilylation of styrene with trie-
It is immediately evident from Table 2 that substitution
thylsilane. Employing 2.8 equiv. of styrene, we obtained
of the Ar-bian ligands has no significant influence on the
31.0% of product III using [Pt(nbe)3] as the catalyst. How-
selectivity of the hydrosilylation. There seems to be a re-
ever, when using a styrene/triethylsilane ratio of 1.0 with
lation between the yield and the inductive effect of the para
this catalyst, product III was observed in only 11.0%, which
substituents on the aryl groups of the Ar-bian ligand, as
is almost similar to the result obtained by Skoda-Földes et
al. with PtCl2. Also, Dötz et al.[15] and Caseri and Prego-
sin[16] obtained considerable amounts of product III in this
reaction, using [Pt(η2-2-methylnaphthoquinone)(η4-CH2ϭ
CHSiMe2)2O] and trans-[PtCl2(PhCHϭCH2)2] as the cata-
lyst, respectively.
The activities of our catalysts are influenced by several
reaction conditions; temperature was already discussed, but
the styrene concentration also influences the reaction signif-
icantly. In general, a higher styrene concentration contrib-
increasing yields are observed with decreasing electron-do-
nating ability. This can be explained by the fact that elec-
tron-donating substituents increase the basicity of the Ar-
bian ligand, resulting in more stable platinum(0) complexes.
As a consequence, the lowest yield is obtained for p-MeO-
C6H4-bian (Entry 2), but the differences are small.
Synthesis of [Pt(Ar-bian)(η2-alkene)] Complexes
When obtaining the catalysts in situ, there may be com-
utes to a higher stability of the catalyst. Consequently, when petition for the substrate, due to the relatively large amount
[Pt(nbe)3] was used as a catalyst using a styrene/triethylsil- (2Ϫ3 equiv.) of alkene liberated upon reaction of [Pt(nbe)3]
ane ratio of 1.0, a yield of only 32% was obtained after 2 with the bidentate N-ligand (Scheme 2). On the other hand,
h, which is rather low when compared to the 91.9% yield the Ar-bian ligands are also labile. Therefore, we were inter-
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Platinum(0) Catalysts for Catalytic Hydrosilylation of Styrene
FULL PAPER
Scheme 2. Synthesis of [Pt(Ar-bian)(η2-alkene)] complexes
ested in comparing our hitherto obtained results with suggested incomplete ligand substitution. Better results
experiments employing predefined [Pt(Ar-bian)(η2-alkene)] were obtained, when m,m-(CF3)2-C6H3-bian was added to
complexes as catalyst precursors in the hydrosilylation of an ice cold concentrated solution of ma and [Pt(nbe)3].
styrene with triethylsilane. The stability of these complexes After washing the crude reaction product with pentane,
will depend on the nature of the Ar-bian ligand as well as of [Pt{m,m-(CF3)2-C6H3-bian}(ma)] readily precipitated from
the alkene. Electron-donating substituents on the Ar-bian the combined organic extract and was obtained as a pure
ligand, concomitant with the use of electron-poor alkenes compound.
is expected to increase the stability of complexes of this
Similarly, the synthesis of [Pt{m,m-(CF3)2-C6H3-
type. Van Asselt et al.[24] already synthesized several [Pt(Ar- bian}(tcne)] was straightforward and proceeded as ex-
bian)(η2-alkene)] complexes. By employing p-Me-C6H4- pected. In order to probe the influence of electronic effects
bian and o,oЈ-iPr2-bian with fumaronitrile (fn), maleic an- on the synthesis of platinum(0) complexes of type [Pt{m,m-
hydride (ma), and tetracyanoethylene (tcne) as coordinating (CF3)2-C6H3-bian}(η2-alkene)], it was attempted to use
alkenes, stable complexes were obtained starting from electron-rich instead of electron-deficient alkenes. Thus,
[Pt(dba)2]. However, complexes with the less electron-poor synthesis of [Pt{m,m-(CF3)2-C6H3-bian}(trimethylvinyl-
dimethyl fumarate (dmfu) could not be obtained by using silane)] was attempted by stirring equimolar amounts of
this method, which includes heating in THF at 45 °C for [Pt(nbe)3], m,m-(CF3)2-C6H3-bian, and trimethylvinylsilane
16 h. Since our aim was the synthesis of several new com- in tetrahydrofuran. Although nearly all of the starting ma-
plexes with alkenes like dmfu, which at the same time have terials had reacted after 4 h of stirring at room temperature,
Ar-bian ligands containing electron-withdrawing substitu- at least six different reaction products were formed as was
ents, such as m,m-(CF3)2-C6H3-bian, we selected [Pt(nbe)3] evident from TLC and no efforts were made to further pu-
instead of [Pt(dba)2] as the precursor, allowing milder reac- rify the crude reaction product.
tion conditions.[23,32,33] First, the synthesis of various plati-
Next, in order to study the influence of electronic effects
num(0) complexes of type [Pt(m,m-(CF3)2-C6H3-bian)(η2- on the synthesis of platinum(0) complexes of type [Pt(Ar-
alkene)] was addressed by treating [Pt(nbe)3] with stoichio- bian)(η2-alkene)] and also on their catalytic hydrosilylation
metric amounts of the ligands. Attempts to prepare behavior, the synthesis of various platinum(0) complexes of
[Pt(m,m-(CF3)2-C6H3-bian)(dmfu)] were not successful. Al- type [Pt(p-MeO-C6H4-bian)(η2-alkene)] was addressed. As
lowing equimolar amounts of [Pt(nbe)3], m,m-(CF3)2-C6H3- opposed to the synthesis of [Pt{m,m-(CF3)2-C6H3-
bian, and dmfu to react in tetrahydrofuran at room tem- bian}(dmfu)], the synthesis of [Pt(p-MeO-C6H4-bi-
perature led to the formation of mixtures of starting materi- an)(dmfu)] was successful and yielded the desired reaction
als and reaction products. Similar results were obtained product in excellent yield. Likewise, the synthesis of [Pt(p-
when diethyl ether instead of tetrahydrofuran was used as MeO-C6H4-bian)(ma)] was straightforward, but the syn-
a solvent. In both cases, purification of the reaction product thesis of [Pt(p-MeO-C6H4-bian)(acrylonitrile)] was more
was troublesome due to its complete solubility in most com- troublesome. Although TLC revealed that all of the starting
1
mon organic solvents. H NMR spectroscopy of the crude materials had reacted after 2 h of stirring at room tempera-
reaction product suggested that ligand substitution had not ture, it was not possible to unambiguously characterize the
been complete: large amounts of uncomplexed m,m-(CF3)2- residue obtained after washing the crude reaction mixture
C6H3-bian were present. Using [Pt(cod)2] as starting mate- with diethyl ether/pentane. Finally, the complex [Pt(phenyl-
rial, [Pt{m,m-(CF3)2-C6H3-bian}(dmfu)] could not be ob- bian)(dmfu)] was also synthesized in good yield using the
tained either.
same procedure.
Initial attempts to prepare [Pt{m,m-(CF3)2-C6H3-
Synthesis of [Pt(dafo)(dmfu)], [Pt(dafo)(ma)], and
bian}(ma)] by adding [Pt(nbe)3] to a dilute solution of equi- [Pt(dafo)(tcne)] was also addressed, but these attempts were
molar amounts of m,m-(CF3)2-C6H3-bian and maleic anhy- not successful. Adding dafo to a concentrated solution of
dride in tetrahydrofuran were in vain. Similar to the case [Pt(nbe)3] and 1.20 equiv. of dmfu in tetrahydrofuran did
of [Pt{m,m-(CF3)2-C6H3-bian}(dmfu)], purification of the not result in the formation of [Pt(dafo)(dmfu)] after over-
1
reaction product was tedious and H NMR spectroscopy night stirring at reflux. None of the starting dafo had re-
Eur. J. Inorg. Chem. 2003, 3811Ϫ3819
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3815

J. W. Sprengers, M. de Greef, M. A. Duin, C. J. Elsevier
FULL PAPER
1
acted, as was evident from H NMR spectroscopy. Like- 32.5% was obtained with [Pt(Me-nq)(nbe)2], which is al-
wise, the synthesis of [Pt(dafo)(ma)] and [Pt(dafo)(tcne)] did most similar to [Pt{m,m-(CF3)2-C6H3-bian}(ma)] (27.1%)
not succeed. In the latter cases a slight amount of com- and [Pt(p-MeO-C6H4-bian)(ma)] (31.1%). Although [Pt(p-
1
plexed dafo was observed by H NMR spectroscopy, but MeO-C6H4-bian)(dmfu)] and [Pt(C6H5-bian)(dmfu)] are
the yields remained very low, in keeping with the weak ligat- less active catalysts, there stability resulted in higher overall
ing properties of dafo.
yields of 41.1% and 44.9%, respectively, after 6 h with the
catalysts still being active after this time. After 24 h, a yield
of 65% was obtained for [Pt(p-MeO-C6H4-bian)(dmfu)].
For all complexes, compound II was observed as the
major product (85Ϫ87%) along with a minor amount of
compound I (about 2%). The dehydrogenative silylation
product III was observed in about 11Ϫ13% yield. The selec-
tivities obtained with these catalysts were constant in time.
The decreased amount of dehydrogenative silylation, com-
pared to the reactions with in situ prepared catalysts, is
caused by the lower styrene concentration compared to the
other experiments, since a styrene/triethylsilane ratio of 1.0
instead of 2.8 was employed. As discussed before, the selec-
tivities obtained are quite similar to those obtained using
PtCl2 as the catalyst.[29] PtCl2, in fact every platinum() or
platinum() catalyst, is deemed to be reduced to a plati-
num(0) species. The reduction process, often of variable
duration, causes the frequently observed induction periods
for these catalysts.[3a] For example, using [PtCl2(PhCHϭ
CH2)2] as a catalyst, Caseri and Pregosin showed that the
hydrosilylation of styrene proceeded by reduction of the PtII
complex to [Pt(styrene)3] with concomitant formation of 2
equiv. of R3SiCl and 1 equiv. of ethylbenzene.[37] From Fig-
ure 1 it becomes quite obvious that our [Pt(Ar-bian)(η2-al-
kene)] complexes do not suffer from an induction period;
the hydrosilylation reactions start immediately after ad-
dition of the substrates. This behavior is in agreement with
that observed for other platinum(0) catalysts.[8Ϫ10,16]
Hydrosilylation of Styrene by Triethylsilane Catalyzed by
[Pt(Ar-bian)(η2-alkene)] Complexes
In order to study the catalytic behavior of platinum(0)
complexes of type [Pt(Ar-bian)(η2-alkene)], [Pt{m,m-
(CF3)2-C6H3-bian}(ma)],
[Pt(p-MeO-C6H4-bian)(ma)],
[Pt(p-MeO-C6H4-bian)(dmfu)], and [Pt(C6H5-bian)(dmfu)]
were tested as catalysts in the hydrosilylation of styrene by
triethylsilane, applying a styrene/triethylsilane ratio of only
1.0. The complex [Pt(Me-nq)(nbe)2], an active hydrosilyl-
ation catalyst,[8] was also tested. The yields of the combined
silyl products against time are shown in Figure 1.
Figure 1. Hydrosilylation of styrene by triethylsilane catalyzed by
[Pt(m,m-(CF3)2-C6H3-bian)(ma)] (open triangles), [Pt(p-MeO-
C6H4-bian)(ma)] (filled triangles), [Pt(p-MeO-C6H4-bian)(dmfu)]
(open circles), [Pt(C6H5-bian)(dmfu)] (filled circles), and [Pt(Me-
nq)(nbe)2] (filled squares); conditions: 0.36 mol % of catalyst, styr-
ene/triethylsilane ratio 1.0, toluene, 30 °C; yield is the combined
GC yield after 2 h of products I, II, and III using n-decane as the
internal standard
Since the palladium complexes [Pd(Ar-bian)(η2-alkene)]
are versatile catalysts for the selective hydrogenation of
alkynes to (Z)-alkenes,[21] we also tested [Pd(p-MeO-C6H4-
bian)(dmfu)] as a hydrosilylation catalyst and compared its
catalytic behavior with its platinum analogue. However, it
appears that this compound does not catalyze the hydrosi-
lylation reaction at all: the complex immediately decom-
From these results, it is obvious that the nature of the posed under hydrosilylation conditions in both THF and
coordinated alkene determines the catalytic behavior of the toluene at 30 °C.
complexes. [Pt(p-MeO-C6H4-bian)(dmfu)] and [Pt(C6H5-bi-
an)(dmfu)] show an almost completely identical catalytic
activity and stability. The complexes [Pt{m,m-(CF3)2-C6H3-
bian}(ma)] and [Pt(p-MeO-C6H4-bian)(ma)] give different
results compared to the two dmfu complexes: they show a
Conclusion
higher initial activity, but decompose faster, resulting in a
In conclusion, several bidentate N-ligands have been
lower overall yield. From the synthetic experiments (see evaluated in the hydrosilylation of styrene with triethylsil-
above), it is known that electron-donating substituents on ane at different temperatures, using in situ formed catalysts
the Ar-bian ligand increase the stability of the complex. with [Pt(nbe)3] as a precursor. In general, the ligands which
However, for the two maleic anhydride complexes only a form more stable platinum(0) complexes result in a lower
small difference in catalytic behavior is observed. In the be- catalytic activity and somewhat more dehydrogenative silyl-
ginning of the reaction, [Pt(p-MeO-C6H4-bian)(ma)] is ation compared to the ligands which form less stable com-
slightly less active than [Pt{m,m-(CF3)2-C6H3-bian}(ma)], plexes. Consequently, the precursor complex, [Pt(nbe)3] it-
but is slightly more stable. [Pt(Me-nq)(nbe)2] is a very active self, which has only labile alkene ligands, is an active cata-
catalyst, but decomposition of the catalyst starts immedi- lyst at 30 °C and at a styrene to triethylsilane ratio of 2.8.
ately after addition of triethylsilane. After 6 h, a yield of At higher temperatures, the catalyst is no longer stable and
3816
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2003, 3811Ϫ3819

Platinum(0) Catalysts for Catalytic Hydrosilylation of Styrene
FULL PAPER
a decrease in yield is observed when the temperature is in-
creased. The complex [Pt(Me-nq)(nbe)2], does not give sig-
nificantly higher yields. Common bidentate ligands such as
phen and dppe form stable complexes, resulting in no or
very low hydrosilylation activity. However, for the ligands
dafo and phenyl-bian, a small ligand effect is observed.
Substituting the aryl groups of phenyl-bian ligand does not
influence the catalysis significantly. By studying the be-
havior of various [Pt(Ar-bian)(alkene)] complexes, it has be-
come clear that the nature of the alkene ligand in these
complexes determines its catalytic behavior; the [Pt(Ar-bi-
an)(ma)] complexes are intrinsically slightly more active
than the two [Pt(Ar-bian)(dmfu)] complexes, however, the
[Pt(Ar-bian)(dmfu)] complexes result in much more stable
catalysts. The fact that the different Ar-bian ligands do not
have a major influence on the catalytic behavior of the com-
plexes demonstrates the lability of these bidentate ligands
compared to several alkenes. Importantly, compared to
[Pt(Me-nq)(nbe)2], the two [Pt(Ar-bian)(dmfu)] complexes
show an intrinsically lower activity, but are at the same time
much more stable, resulting in significantly higher overall
yields under similar conditions. We are at present investiga-
ting the use of alkenes as ligands in the platinum(0)-cata-
lyzed hydrosilylation in more detail.
Bis(4-fluorophenylimino)acenaphthene (p-F-C6H4-bian, 7): The li-
gand was prepared analogous to the method described in the litera-
ture[36] for that of acenaphthenequinone and 4-fluoroaniline and
was obtained as an orange solid. Yield: 1.81 g, 75%. 1H NMR
3
(300.1 MHz, CDCl3): δ ϭ 6.94 (d, J ϭ 7.14 Hz, 2 H, 3-H), 7.10
3
(m, 4 H, 9-H), 7.18 (m, 4 H, 10-H), 7.42 (pst, J ϭ 7.42 Hz, 2 H,
4-H), 7.93 (d, 3J ϭ 7.14 Hz, 2 H, 5-H) ppm. 13C NMR (75.5 MHz,
CDCl3): δ ϭ 116.52 (d, 2JF,C ϭ 22.57 Hz, C-10), 119.95 (d, 3JF,C ϭ
8.06 Hz, C-9), 124.10 (C-3), 127.91 (C-4), 128.48 (C-2), 129.46 (C-
1
5), 131.47 (C-6), 142.03 (C-7), 147.71 (C-8), 160.28 (d, JF,C
ϭ
243.46 Hz, C-11), 162.00 (C-1) ppm. 19F NMR (282.4 MHz,
CDCl3): δ ϭ Ϫ119.31 ppm.
(σ-N,σ-NЈ-Bis{3,5-bis(trifluoromethyl)phenylimino}acenaphthene)-
(η2maleic anhydride)platinum(0) (10a): THF (2.5 mL) was added to
maleic anhydride (127.0 mg, 275 µmol). The colorless solution was
cooled to 0 °C, after which [Pt(nbe)3] (119.5 mg, 250 µmol) was
added. The solution was stirred at 0 °C for 15 min, after which
m,m-(CF3)2-C6H3-bian (164.9 mg, 273 µmol) was added. Stirring
was continued at 0 °C for 45 min, followed by the heating of the
reaction mixture to room temperature. The orange solution was
concentrated to dryness and the residue dissolved in 2 mL of di-
chloromethane. Pentane (20 mL) was added to the solution, after
which a dark precipitate formed. The solvent was removed via a
syringe and the solid was washed with pentane (4 ϫ 20 mL) and
dried in vacuo. The isolated dark purple powder was analyzed by
NMR spectroscopy and appeared to be a mixture of reaction prod-
ucts. However, upon standing, a dark solid had precipitated from
the combined organic extract. The precipitate was washed with
pentane (8 ϫ 10 mL) and dried in vacuo, after which 10a was ob-
Experimental Section
General Remarks: All experiments were carried out by using stand-
ard Schlenk techniques under dry nitrogen. The solvents were dried
according to standard procedures and distilled before use. Quanti-
tative gas liquid chromatography (GLC) analyses were carried out
with a Varian 3300 apparatus equipped with a semicapillary col-
umn (J&W, DB 5, 30 m ϫ 1 µm) with n-decane as internal stand-
ard. Elemental analyses were carried out by Kolbe, Mikroanaly-
tisches Laboratorium, Mülheim a. d. Ruhr, Germany. 1H, 13C, and
19F NMR spectra were recorded at 300.1, 75.5, and 282.4 MHz,
respectively, with a Varian Mercury 300 and with a Varian Inova
500 spectrometer at 499.8 and 125.7 MHz, respectively. Chemical
1
tained as a dark purple powder. Yield: 96.5 mg, 43.0%. H NMR
(499.8 MHz, CD2Cl2): δ ϭ 3.76 (s, JPt-H ϭ 89.84 Hz, 2 H, ma),
3
3
7.49 (d, J ϭ 7.32 Hz, 2 H, 3-H), 7.63 (pst, J ϭ 7.70 Hz, 2 H, 4-
3
H), 8.10 (s, 2 H, 11-H), 8.21 (s, 4 H, 9-H), 8.38 (d, J ϭ 8.24 Hz,
2 H, 5-H) ppm. No 13C NMR spectrum was recorded due to the
low solubility and stability of the complex. 19F NMR (282.4 MHz,
CD2Cl2): δ ϭ Ϫ63.35 ppm. C32H14F12N2O3Pt (897.52): calcd. C
42.82, H 1.57, N 3.12; found C 42.67, H 1.63, N 3.04.
shift values are in ppm relative to external TMS or Cl3CF with (σ-N,σ-NЈ-Bis{3,5-bis(trifluoromethyl)phenylimino}acenaph-
high frequency shifts signed as positive. Abbreviations used are s ϭ
singlet, d ϭ doublet, pst ϭ peudotriplet, m ϭ multiplet; multi-
thene)(η2-tetracyanoethene)platinum(0) (10b): THF (20 mL) was ad-
ded to m,m-(CF3)2-C6H3-bian (121 mg, 200 µmol), and tetracyano-
plicity, number of protons and coupling constants (Hz) in parenth- ethene (26.3 mg, 205 µmol). [Pt(nbe)3] (92.1 mg, 193 µmol) was ad-
eses. Triethylsilane (Acros), n-decane (Acros), dimethyl fumarate ded to this mixture, and the solution changed color from bright
(Merck), tetracyanoethylene (Fluka), 1,10-phenanthroline (Ald-
orange to deep red. The mixture was stirred for 4 h at room tem-
rich), 2,2Ј-dipyridyl (Aldrich), triphenylphosphane (Aldrich), perature, after which the reaction was complete as was evident from
bis(diphenylphosphanyl)ethane (Strem), 2-methyl-2,4-naphthoqui- TLC. The solvent was removed in vacuo and the residue washed
none (Aldrich), acenaphthenequinone (Aldrich), and 4-fluoroani-
line (Janssen Chimica) were used as received. Styrene (Acros) was
purified by flash chromatography on alumina immediately prior to 7.80 (d, J ϭ 7.33 Hz, 2 H, 3-H), 7.85 (pst, J ϭ 7.81 Hz, 2 H, 4-
with diethyl ether (3 ϫ 2 mL) to afford 10b as an orange solid.
Yield: 151 mg, 81.6%. 1H NMR (499.8 MHz, [D6]acetone): δ ϭ
3
3
3
use. Maleic anhydride (EGA) was recrystallized from dichloro-
H), 8.38 (s, 2 H, 11-H), 8.52 (s, 4 H, 9-H), 8.58 (d, J ϭ 8.06 Hz,
methane. [Pt(nbe)3],[27] [Pd(p-MeO-C6H4-bian)(DMFU)],[24] phe- 2 H, 5-H) ppm. 13C NMR (125.7 MHz, [D6]acetone): δ ϭ 115.07
nyl-bian,[34] p-MeO-C6H4-bian,[34] p-Br-C6H4-bian,[34] p-NO2- (CN), 123.92 (q, JF,C ϭ 272.68 Hz, CF3), 124.08 (C-9), 124.35
1
C6H4-bian,[35] and m,m-(CF3)2-C6H3-bian[35] were synthesized ac- (C3), 125.84 (C-2), 126.78 (C-4), 130.77 (C-5), 133.18 (C-6), 134.44
cording to published procedures. 4.5-Diazafluoren-9-one[36] was
synthesized according to the literature, but was additionally puri-
fied using column chromatography [silica, MeOH/dichlorometh-
ane (5:95)].
(q, 2JF,C ϭ 33.94 Hz, C-10), 134.45 (C-11), 149.69 (C-8), 150.07 (C-
7), 176.67 (C-1) ppm. 19F NMR (282.4 MHz, [D6]acetone): δ ϭ
Ϫ63.57 ppm. C34H12F12N6Pt (927.56): calcd. C 44.03, H 1.30, N
9.06; found C 44.11, H 1.36, N 9.13.
Eur. J. Inorg. Chem. 2003, 3811Ϫ3819
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3817

J. W. Sprengers, M. de Greef, M. A. Duin, C. J. Elsevier
FULL PAPER
(σ-N,σ-NЈ-Bis{4-methoxyphenylimino}acenaphthene)(η2-maleic an-
General Procedure for the Hydrosilylation of Styrene with Triethyl-
hydride)platinum(0) (11a): THF (3.5 mL) was added to p-MeO- silane: A two-necked Schlenk tube equipped with a septum, a reflux
C6H4-bian (107.3 mg, 273 µmol), and maleic anhydride (27.2 mg, condenser and a stirring bar was charged with the appropriate
277 µmol). [Pt(nbe)3] (120 mg, 251 µmol) was added to this solution
after which the solution changed color from deep red to dark green.
platinum complex (0.022 mmol) and, in the case of the in situ pre-
pared catalysts, 1 equiv. of ligand. The Schlenk tube was evacuated
The mixture was stirred at room temperature for 60 min, and the and filled with nitrogen three times. Then toluene (20 mL), styrene
solvent was removed in vacuo. The dark residue was washed with
diethyl ether (3 ϫ 3 mL), dried, dissolved in 5 mL of dichlorometh-
ane, and filtered through Celite Hyflo. Pentane (20 mL) was added
to the filtrate followed by the formation of a dark precipitate. The
solid was washed with pentane (4 ϫ 10 mL) and dried in vacuo,
after which 11a was obtained as a brown red solid. Yield: 98.3 mg,
(6.16 mmol or 17.24 mmol), n-decane (3.08 mmol), and triethylsil-
ane (6.16 mmol) were added, in this order, in quick succession from
syringes through the septum. The reactor was immediately im-
mersed in an oil bath, which was kept at the required reaction tem-
perature. Samples were taken periodically for GC analyses. Prod-
ucts were characterized using NMR spectroscopy and GC-MS.
57.3%. 1H NMR (499.8 MHz, CD2Cl2): δ ϭ 3.55 (s, JPt-H
ϭ
84.46 Hz, 2 H, ma), 3.93 (s, 6 H, MeO), 7.09 (d, 3J ϭ 9.03 Hz, 4
H, 9-H), 7.48 (pst, 3J ϭ 7.81 Hz, 2 H, 4-H), 7.63Ϫ7.71 (m, 6 H, 3-
H and 10-H), 8.17 (d, 3J ϭ 8.06 Hz, 2 H, 5-H) ppm. 13C NMR
(125.7 MHz, CD2Cl2): δ ϭ 25.97 (ma), 55.81 (MeO), 114.45 (C-
10), 123.39 (C-9), 124.97 (C-3), 127.30 (C-2), 128.94 (C-4), 130.41
(C-5), 132.19 (C-6), 141.26 (C-8), 145.50 (C-7), 160.47 (C-11),
168.64 (C-1), 174.51 (ma) ppm. C30H22N2O5Pt (685.58): calcd. C
52.56, H 3.23, N 4.09; found C 52.48, H 3.20, N 3.99.
Acknowledgments
The research has been performed within the National Research
School Combination Catalysis (project number: 2000-14), which is
gratefully acknowledged for financial support. We thank M. W. van
Laren for synthesizing [Pd(p-MeO-C6H4-bian)(dmfu)].
(σ-N,σ-NЈ-Bis{4-methoxyphenylimino}acenaphthene)(η2-dimethyl
fumarate)platinum(0) (11c): THF (20 mL) was added to p-MeO-
C6H4-bian (78 mg, 199 µmol) and dimethyl fumarate (31.0 mg, 215
µmol). The solution changed color from deep red to dark green
upon addition of [Pt(nbe)3] (120 mg, 251 µmol). The mixture was
stirred at room temperature for 90 min, after which the reaction
was complete as was evident from TLC. The solvent was removed
in vacuo and the dark brown residue washed with diethyl ether (2 ϫ
3 mL) and dissolved in 5 mL of dichloromethane. The dark brown
solution was filtered through Celite Hyflo and the filtrate concen-
trated to dryness in vacuo. The desired reaction product 11c was
obtained as a dark brown solid. Yield: 137 mg; 94.0%. 1H NMR
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ϭ
3
91.22 Hz, 2 H, dmfu), 3.98 (s, 6 H, MeO), 7.49 (d, J ϭ 7.42 Hz,
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3
´
´
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2 H, 3-H), 7.63 (pst, J ϭ 7.70 Hz, 2 H, 4-H), 8.10 (s, 2 H, 10-H),
8.21 (s, 4 H, 9-H), 8.14 (d, 3J ϭ 8.24 Hz, 2 H, 5-H) ppm. 13C NMR
(125.7 MHz, CD2Cl2): δ ϭ 27.29 (dmfu), 50.57 (dmfu), 56.17
(MeO), 115.07 (C-10), 123.54 (C-9), 125.72 (C-3), 129.21 (C-2),
130.11 (C-4), 130.71 (C-5), 133.43 (C-6), 134.04 (C-8), 142.62 (C-
7), 160.92 (C-11), 168.93 (C-1), 176.45 (dmfu) ppm. C32H28N2O6Pt
(731.65): calcd. C 52.53, H 3.86, N 3.83; found C 52.34, H 3.76,
N 3.95.
[10]
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[13]
[14]
(σ-N,σ-NЈ-Bis{phenylimino}acenaphthene)(η2-dimethyl fumarate)-
platinum(0) (12c): [Pt(nbe)3] (0.92 g, 1.93 mmol), C6H5-bian (0.70 g,
2.11 mmol) and dimethyl fumarate (0.31 g, 2.15 mmol) were dis-
solved in THF (20 mL). The color of the solution changed to dark
green immediately. The mixture was stirred at room temperature
for 60 min and the solution was filtered through Celite Hyflo. The
filtrate was concentrated to dryness in vacuo and was washed with
a 50-mL pentane/diethyl ether (1:1) mixture and 2 ϫ 50 mL of
pentane. The desired reaction product 12c was obtained as a dark
[15]
[16]
[17]
[18]
[19]
[20]
[21]
1
green solid. Yield: 1.04 g; 80.0%. H NMR (300.1 MHz, CD2Cl2):
δ ϭ 3.33 (s, 6 H, dmfu), 3.71 (s, JPt-H ϭ 93.15 Hz, 2 H, dmfu),
7.46Ϫ7.53 (m, 6 H, 3-H ϩ 4-H ϩ 11-H), 7.60 (m, 8 H, 9-H ϩ 10-
[22]
3
3
H), 8.21 (d, J ϭ 5.50 Hz, 1 H, 5-H), 8.23 (d, J ϭ 5.50 Hz, 1 H,
5-H) ppm. 13C NMR (125.7 MHz, CD2Cl2): δ ϭ 27.93 (dmfu),
50.96 (dmfu), 122.87 (C-9), 123.76 (C-3), 128.30 (C-2), 128.62 (C-
4), 129.87 (C-11), 130.16 (C-10), 130.43 (C-5), 132.7 (C-6), 145.85
(C-7), 149.19 (C-8), 169.65 (C-1), 176.47 (dmfu) ppm.
C30H24N2O4Pt (671.60): calcd. C 53.65, H 3.60, N 4.17; found C
53.88, H 3.74, N 4.08.
[23]
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