Platinum(ii) complexes with polydentate N-heterocyclic carbenes: Synthesis, structural characterization and hydrosilylation catalysis

Article abstract of DOI:10.1039/b924587a

The platinum(ii) complexes of multidentate N-heterocyclic carbenes, [Pt(L1)₂Cl](PF₆) (1, L1 = N-methyl-N-(2-pyrimidinyl) imidazolylidene), [Pt(L2)Cl](PF₆) (2, L2 = N-butyl-N-(1,10- phenanthrolin-2-yl)imidazolylidene), [PtL

Full text of DOI:10.1039/b924587a

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Platinum(II) complexes with polydentate N-heterocyclic carbenes: synthesis,
structural characterization and hydrosilylation catalysis†
Chunxin Lu,a Shaojin Gu,a Wanzhi Chen*a and Huayu Qiu*b
Received 23rd November 2009, Accepted 3rd March 2010
First published as an Advance Article on the web 24th March 2010
DOI: 10.1039/b924587a
The platinum(II) complexes of multidentate N-heterocyclic carbenes, [Pt(L1)2Cl](PF6) (1, L1 =
N-methyl-N-(2-pyrimidinyl)imidazolylidene), [Pt(L2)Cl](PF6) (2, L2 = N-butyl-N-
(1,10-phenanthrolin-2-yl)imidazolylidene), [PtL3](PF6)2 (3, L3 = bis(N-picolylimidazolylidenyl)-
methane), [PtL4](PF6)2 (4, L4 = (bis(N-2-pyrimidylimidazolylidenyl)methane) (4) and [Pt(L5)2](PF6)2
[5, L5 = bis(N-pyridylimidazoliumyl)methane] have been synthesized and structurally characterized.
All these complexes exhibit slightly distorted square-planar configuration. These complexes are efficient
catalyst precursors for hydrosilylation of alkynes. Complexes 2 and 4 are much more active than
complexes 1, 3 and 5. In the hydrosilylation of arylacetylenes, relatively long induction periods were
observed for 1, 3 and 5.
they can be easily synthesized from simple platinum(II) and
imidazolium salts by using common bases such as Ag2O or
K2CO3. The platinum complex [PtCl2(bzoxcarb)], which was
Introduction
Hydrosilylation of alkynes is an important reaction for the
preparation of unsaturated organosilicon compounds which are
prepared from 2-benzoxazolyl imidazolium and Pt(cod)Cl2 via
intermediates of silicon materials and versatile building blocks
carbene transfer route, was found to be an active catalyst for
in organic transformations.1 Traditionally, the Speier system
(H2PtCl6/i-PrOH)2 and the Karstedt complex ((Pt2(dvtms)3,
dvtms = divinyltetramethyldisiloxane)3 are most commonly em-
ployed. One of the disadvantages of these catalysts is the ease
of generation of colloidal platinum species, which is responsible
for a number of undesired reactions.4 The side products and the
coloration originated from the colloidal platinum species might
influence their industrial applications. Therefore, many efforts
have been made to improve the stability of platinum catalysts
by using various ligands and the selectivity of hydrosilylation
reaction.5-7 N-Heterocyclic carbenes (NHCs) have become a
very important class of ligands in organometallic chemistry and
catalysis.8 N-Heterocyclic carbenes can form stable M–C bonds
with various transition metals because of their strong s-donating
ability that provides the possibility to develop platinum NHC
complexes as robust hydrosilylation catalysts. Recently, a class of
novel [Pt(dvtms)(NHC)] (dvtms = divinyltetramethyldisiloxane)
complexes have been synthesized by Marko´ et al.9 and have
shown efficiency and good selectivity in the hydrosilylation
of a broad range of alkenes and alkynes. Structurally related
[Pt(alkene)2(NHC)] complexes have been reported by Elsevier
et al. and used as hydrosilylation catalysts.5,6,7,10 Although such
[Pt(alkene)2(NHC)] complexes are air- and moisture-stable, their
preparation requires strict conditions such as air- and moisture-
free atmosphere and a strong base has to be used. Pt(II) complexes
of N-heterocyclic carbenes are better catalyst precursors since
the hydrosilylation of alkenes and alkynes.11 A very recent report
described the synthesis and structural characterization of a few
mono- and biscarbene platinum(II) complexes, which are suitable
catalyst precursors for hydrosilylation of phenylacetylene and
trimethylsilylacetylene.12
We have been interested in the transition-metal chemistry
of pyridine-, pyrazole- and naphthyridine-functionalized NHC
ligands, and the palladium13 and nickel complexes14 containing
such hemilabile ligands showed good catalytic activities for C–
C coupling reactions of various aryl chlorides and bromides.
Here in this paper, we report the synthesis and structural char-
acterization of platinum(II) complexes supported by multidentate
NHC ligands, and their catalytic applications in hydrosilylation of
arylacetylenes.
Results and discussion
Reaction of N-methyl-N-pyrimidinylimidazolium with an excess
of Ag2O in acetonitrile yielded a silver imidazolylidene complex,
which was not isolated. Further treatment of the resulting
solution of the silver complex with an equivalent of Pt(cod)Cl2
gave [Pt(N-methyl-N-pyrimidinylimidazolylidene)2Cl](PF6) (1) as
a pale yellow solid. With this procedure we did not obtain the
expected [Pt(N-methyl-N-pyrimidinylimidazolylidene)Cl2]. When
a half equivalent of Pt(cod)Cl2 was employed, the yield could
be improved (Scheme 1). The compound gave analytical data
consistent with the calculated C, H and N percentages. However,
the 1H and 13C NMR spectra of 1 is complicated although
we repeatedly measured spectra in different deuterated solvents
including acetonitrile and dimethyl sulfoxide even using the single-
crystal sample. This phenomenon might result from the fast
dissociation–association process of two pyrimidine groups via
distorted square-pyramid or trigonal-bipyramid intermediates.
aDepartment of Chemistry, Zhejiang University, Xixi Campus, Hangzhou,
310028, People’s Republic of China. E-mail: chenwzz@zju.edu.cn;
Fax: (+)86-571-88273314; Tel: (+)86-571-88273314
bCollege of Material, Chemistry and Chemical Engineering, Hangzhou
Normal University, Hangzhou, 310012, P. R. China
† CCDC reference numbers 755668–755672. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b924587a
4198 | Dalton Trans., 2010, 39, 4198–4204
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Scheme 2 Synthesis of [Pt(L2)Cl](PF6) (2).
Scheme 1 Synthesis of [Pt(L1)2Cl](PF6) (1).
atom, which is consistent with the reported values in the range of
132.5–198.2 ppm for Pt-NHC complexes.17
Such intermediates have been known for nickel(II) complexes with
similar imidazolylidene ligands.14e
X-Ray crystallographic analysis showed that complex 2 has
a square-planar geometry with platinum center surrounded
by the pincer NNC ligand, N-butyl-N-(1,10-phenanthrolin-2-
yl)imidazolylidene, and a chloride ion. The crystal structure
contains two independent molecules per asymmetric unit which
are basically the same, thus only one molecule is shown in
Fig. 2. The compound is isostructural with its palladium and
nickel analogues which have been previously reported by us.16
All the atoms, excluding the butyl group are nearly perfectly
Crystals of 1 suitable for X-ray crystallography were ob-
tained by slow diffusion of diethyl ether into its acetonitrile
solution. The molecular structure of 1 is depicted in Fig. 1.
The central platinum ion is coordinated by two N-methyl-N-(2-
pyrimidinyl)imidazolylidene ligands one of which is bonded in a
monodentate fashion. The two heterocyclic rings of the chelating
ligand are almost perfectly coplanar with the coordination plane.
The imidazole and pyrimidine ring of the mono-coordinated
ligand bisect each other with a dihedral angle of 23.08◦, whereas
the dihedral angle between the coordination plane and imida-
zolylidene is 77.92◦. The two imidazoylidenes are cis-positioned
˚
coplanar. The Pt–C (1.942(8) A) is quite normal as compared
to those of many known platinum–NHC complexes.15,17 The Pt–
˚
˚
N(4) distance (2.089(6) A) is much longer than that of Pt–N(3)
with Pt–C bond distances being 1.96 A. The Pt–C and Pt–Cl bond
distances are within the expected range of platinum complexes
containing NHC ligands.15
˚
(1.950(5) A) due to steric requirement and large trans effect of
imidazolylidene. Weak intermolecular Pt ◊ ◊ ◊ Pt interaction is often
observed for square-planar platinum(II) complexes.18 The shortest
˚
Pt ◊ ◊ ◊ Pt distance for 2 is 7.712 A illustrating no intermolecular
Pt ◊ ◊ ◊ Pt interaction.
Fig. 1 Structural view of 1 showing 30% thermal ellipsoids. All H
-
˚
atoms and PF6 are omitted for clarity. Selected bond lengths (A) and
angles (◦): Pt(1)–C(9) 1.96(2), Pt(1)–C(1) 1.97(2), Pt(1)–N(3) 2.06(2),
Pt(1)–Cl(1) 2.333(5); C(9)–Pt(1)–C(1) 96.7(9), C(9)–Pt(1)–N(3) 174.0(8),
C(1)–Pt(1)–N(3) 79.6(9), C(9)–Pt(1)–Cl(1) 88.9(6), C(1)–Pt(1)–Cl(1)
173.8(6), N(3)–Pt(1)–Cl (1) 94.6(7).
Fig. 2 Structural view of 2 showing 30% thermal ellipsoids. All H
atoms and PF6 are omitted for clarity. Selected bond lengths (A) and
-
˚
angles (◦): Pt(1)–C(3) 1.942(8), Pt(1)–N(3) 1.950(5), Pt(1)–N(4) 2.089(6),
Pt(1)–Cl(1) 2.296(2); C(3)–Pt(1)–N(3) 78.9(3), C(3)–Pt(1)–N(4) 159.0(3),
N(3)–Pt(1)–N(4) 80.1(2), C(3)–Pt(1)–Cl(1) 104.6(2), N(3)–Pt(1)–Cl(1)
176.52(18), N(4)–Pt(1)–Cl(1) 96.38(17).
We have already reported the synthesis and characterization
of [M(N-butyl-N-(1,10-phenanthrolin-2-yl)imidazolylidene)Cl]
(PF6) (M = Ni, Pd).16 Similar reaction of N-butyl-N-(1,10-
phenanthrolin-2-yl)imidazolium with Ag2O and subsequently
Pt(cod)Cl2
afforded
[Pt(N-butyl-N-(1,10-phenanthrolin-2-
Through carbene transfer reactions we were able to ob-
tain [Pt(bis(N-picolylimidazolylidenyl)methane)](PF6)2 (3) and
[Pt(bis(N-pyrimidylimidazolylidenyl)methane)](PF6)2 (4) from
bis(N-picolylimidazoliumyl)methane and bis(N-pyrimidylimida-
zoliumyl)methane in moderate yields as shown in Scheme 3.
Reaction of the in situ formed trisilver carbene complex, [Ag3(bis-
(N-pyridylimidazoliumyl)methane)2(CH3CN)2](PF6)3,14a with one
yl)imidazolylidene)Cl](PF6) (2) as a yellow compound (Scheme 2).
1
The H NMR spectrum of 2 in DMSO-d6 shows characteristic
resonance signals due to phenanthroline and imidazoylidene
moieties with a splitting pattern similar to its nickel and palladium
analogues. The 13C NMR spectrum of 2 in DMSO-d6 exhibits a
resonance signal at 150.6 ppm ascribed to the carbenic carbon
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Scheme 3 Synthesis of [Pt(L3)](PF6)2 (3) and [Pt(L4)](PF6)2 (4).
equivalent of [Pt(cod)Cl2] yielded [Pt(bis(N-pyridylimida-
zoliumyl)methane]](PF6)2 (5) as a white solid (Scheme 4). The
1H NMR spectrum of 3 showed four set of peaks at 8.53 (d), 7.81
(t), 7.37 (t) and 7.23 (d) ppm assignable to the pyridine group.
Two doublets appeared at 7.73 and 7.41 ppm with small coupling
constants (J = 2 Hz) which can be ascribed to imidazolylidene
backbone protons. The methylene linking the two imidazolylidene
Fig. 3 Structural view of 3 showing 30% thermal ellipsoids. All H
atoms and PF6 are omitted for clarity. Selected bond lengths (A) and
-
˚
angles (◦): Pt(1)–C(11) 1.932(7), Pt(1)–C(2) 1.952(8), Pt(1)–N(3) 2.101(6),
Pt(1)–N(6) 2.101(6); C(11)–Pt(1)–C(2) 89.3(3), C(11)–Pt(1)–N(3) 165.3(3),
C(2)–Pt(1)–N(3) 90.7(3), C(11)–Pt(1)–N(6) 88.5(3), C(2)–Pt(1)–N(6)
169.5(2), N(3)–Pt(1)–N(6) 94.1(2).
2
groups was found at 6.40 and 6.36 ppm as doublets with J =
13.6 Hz, whereas the methylenes linking imidazolylidene and
pyridine also showed their peaks as two doublets at 5.08 and
2
4.65 ppm with J = 14.4 Hz, illustrating that the two protons
attached to each methylene are magnetically inequivalent. In the
1H NMR spectrum of 4, the methylene group only shows a
singlet at 7.26 ppm. Complex 5 shows two doublets at 6.64 and
6.48 ppm due to CH2 groups. These platinum bis(carbene) and
tetrakis(carbene) complexes gave a carbenic carbon resonance at
around 162 ppm without significance difference.
Scheme 4 Synthesis of [Pt(L5)2](PF6)2 (5).
Fig. 4 Structural view of 4 showing 30% thermal ellipsoids. All H
atoms and PF6 are omitted for clarity. Selected bond lengths (A) and
Crystals of 3 were obtained by slow diffusion of diethyl ether
into an acetonitrile solution of 3. The molecular structure of
3 is shown in Fig. 3. The coordination geometry is distorted
square planar with platinum coordinated to two carbenes and
two pyridine groups. The two cis-arranged imidazolylidene rings
are approximately parallel to the coordination plane with small
dihedral angles of 10.07 and 15.31◦. The two pyridine groups
extend out of the coordination plane. The Pt–C bond distances
are typical for platinum–NHC complexes. The Pt–N distances are
slightly longer than those of platinum(II) complexes containing
-
˚
angles (◦): Pt(1)–C(9) 1.881(9), Pt(1)–C(2) 1.898(10), Pt(1)–N(3) 2.129(8),
Pt(1)–N(7) 2.148(7); C(9)–Pt(1)–C(2) 86.5(4), C(9)–Pt(1)–N(3) 165.3(4),
C(2)–Pt(1)–N(3) 79.2(4), C(9)–Pt(1)–N(7) 78.0(4), C(2)–Pt(1)–N(7)
164.5(4), N(3)–Pt(1)–N(7) 116.1(3).
Single crystals of 5 suitable for X-ray diffraction analy-
sis were obtained by slow diffusion of diethyl ether into its
acetonitrile solution. The structure of complex 5 is depicted in
Fig. 5. The structure consists of a platinum(II) complex in a
square-planar coordination geometry with two coordinated bis(N-
pyridylimidazolylidenyl)methane ligands. The pyridine groups
are not coordinated. The Pt–C bond distances of 2.036(5) and
˚
pyridine ligands, which are normally in the range of 2.0–2.1 A,
because of large trans effect of NHC ligands.19
The structure of 4 as determined by X-ray diffraction analysis is
shown in Fig. 4. The platinum center has slightly distorted square-
planar conformation with the imidazolylidene and pyrimidine
rings lying in the coordination plane. The co-planarity can be
illustrated by the small dihedral angles ranging from 2.65 to 6.78◦
between the four heteroaryl rings and the coordination plane. The
planar structure resembles those of other metal (M = Fe, Co, Ni)
complexes containing bis(N-pyrimidylimidazolylidenyl)methane
and bis(N-pyridylimidazolylidenyl)methane ligands.14a,20 The Pt–
C bonds are shorter compared to those of complexes 1–3.
˚
2.041(5) A are relatively longer than those of complexes 1–4 due
to large trans effect of the NHC ligand and the steric repulsion. The
two trans-positioned imidazolylidene rings are basically coplanar,
and the cis-arranged imidazolylidene rings show a dihedral angle
of 55.01◦. The imidazolylidene rings are all bisected with the
coordination plane defined by C(10)C(2)C(10A)C(2A) (symmetry
code: A -x, -y, -z + 2) with dihedral angles of 39.46 and 41.20◦. So
far, N-heterocyclic platinum(II) tetra(carbene) complexes are rare.
The first platinum complex containing a multidentate tetracarbene
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Fig. 6 Conversion vs. reaction time of hydrosilylation of phenylacetylene
in toluene. Reaction conditions: triethylsilane/alkyne = 1.2, T = 100 ◦C.
Fig. 5 Structural view of 5 showing 30% thermal ellipsoids. All H
-
˚
atoms and PF6 are omitted for clarity. Selected bond lengths (A) and
angles (◦): Pt(1)–C(10) 2.036(5), Pt(1)–C(2) 2.041(5); C(10)–Pt(1)–C(10A)
180.0, C(10)–Pt(1)–C(2) 95.71(19), C(10)–Pt(1)–C(2A) 84.29(19),
C(2)–Pt(1)–C(2A) 180.0. Symmetry code: A -x, -y, -z + 2.
of complexes 1–5 with different hydrosilanes. Further work is
needed to clarify the mechanism.
In the hydrosilylation of phenylacetylene with triethylsilane
catalyzed by 1–4, (E)-triethyl(styryl)silane was found to be the
major product with A/B ratios of 1.1–4.5. However, when 5
was employed, triethyl(1-phenylvinyl)silane (B) became the major
product with A/B ratio of 0.6.
Complexes 2 and 4 are superior to complexes 1, 3 and 5 in
terms of rate of the hydrosilylation of phenylacetylene, and thus
the reaction can be performed at quite low catalyst loading with
satisfactory conversions. They were thus selected for further stud-
ies of other silanes and alkynes. At a catalyst loading of 0.1 mol%,
the hydrosilylation of phenylacetylene and p-tolylacetylene with
different hydrosilanes were studied, and the results are summarized
in Table 1. Both phenylacetylene and p-tolylacetylene could be
converted to unsaturated silanes in nearly quantitative yields. We
found that the activities of the catalysts decreased slightly when
the more hindered silane was employed; the reaction time was
longer but the selectivity did not change. When phenylacetylene
ligand with crown ether topology was reported by Hahn et al. in
2005 via a smart template-controlled reaction.21a Very recently,
a few homoleptic tetra(carbene) complexes were prepared from
bis(imidazolium) salts and PtCl2 or Pt(acac)2 in the presence of
NaOAc at elevated temperature.21b,c
Catalytic hydrosilylation of acetylenes
Initially, we screened the catalytic activities of complexes 1–5 in
a model reaction involving the hydrosilylation of phenylacetylene
with triethylsilane at a catalyst loading of 1 mol% at 100 ◦C.
The hydrosilylation of phenylacetylene with 1.2 equiv. of Et3SiH
gave full conversion within 24 h, generally yielding a mixture of
(E)-triethyl(styryl)silane (A), triethyl(1-phenylvinyl)silane (B) and
(Z)-triethyl(styryl)silane (C). Similar to other platinum catalysts,
the reaction afforded cis addition products A and B as the major
products, and trace amounts of trans-addition product C were
also detected in less than 1% yield. The hydrogenated product,
styrene was not observed by gas chromatography. The reaction
profiles of phenylacetylene hydrosilylation catalyzed by 1–5 are
shown in Fig. 6. Obviously, complexes 2 and 4 show much higher
catalytic activities than 1, 3 and 5. The hydrosilylation could
be completed within 1–2 h in the cases of 2 and 4, whereas the
reactions took 10–20 h under the same conditions when 1, 3 and
5 were employed. For catalysts 2 and 4, after an induction period
of ca. 10 min, the catalytic transformation of alkyne to vinylsilane
commenced giving full conversion within 1 h. The hydrosilylation
with complexes 1, 3 and 5 occurred with relatively long induction
periods of 2–8 h followed by a rapid increase in catalytic activities.
The reactions with 2 and 4 as catalysts conducted under the same
conditions occurred without any kinetically significant induction
period. These long induction periods suggest that the kinetic
behavior should be related with propensity of the reduction of
Pt(II) to Pt(0) species. It has been recognized that Pt(0) is the real
catalytically active species in hydrosilylation.1,5–7 Hydrosilane can
act as a reducing agent. We have not been able to isolate and
identify Pt(0) species or platinum–silyl species from the reactions
Table 1 Hydrosilylation of alkynes with different silanes in toluene
catalyzed by 2 and 4a
Entry Alkyne
Silane
Cat. t/h Conv. (%)
A
B
1
2
3
4
5
6
7
8
9
Phenylacetylene Ph2MeSiH
Phenylacetylene Ph3SiH
Phenylacetylene Ph2MeSiH
Phenylacetylene Ph3SiH
p-Tolylacetylene Et3SiH
p-Tolylacetylene Ph2MeSiH
p-Tolylacetylene Ph3SiH
p-Tolylacetylene Et3SiH
p-Tolylacetylene Ph2MeSiH
p-Tolylacetylene Ph3SiH
2
2
4
4
2
2
2
4
4
4
1
8
2
98
95
95
85
82 18
87 13
80 20
85 15
85 15
88 12
79 21
64 36
76 24
90 10
24
0.5 98
0.4 99
6
1
1
99
98
95
90
10
24
a Reaction conditions: silane/alkyne ratio = 1.2, T = 100 ◦C; yield and
selectivity of products were measured by 1H NMR and GC-MS.
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was replaced with p-tolylacetylene to test the activity of the
catalysts 2 and 4, we found that p-tolylacetylene was hydrosilylated
more quickly. In the cases of Et3SiH and Ph2MeSiH, over 95%
conversions to silylated products were obtained after 1 h. When
alkynes are hydrosilylated in the presence of either 2 or 4, only
a- and b-(E) regioisomers are produced with the latter being
predominant.
In summary, we have successfully synthesized several plat-
inum(II) complexes supported by multidentate N-heterocyclic
carbenes via simple carbene transfer reaction between in situ
formed silver carbene complexes and Pt(cod)Cl2. These square-
planar complexes have been crystallographically characterized.
The platinum(II) complexes are air- and moisture-stable, and they
are efficient catalyst precursors for hydrosilylation of alkynes at
low catalyst loading and mild conditions. The catalyst activity
varies depending upon the ancillary ligands and thus one can
further improve the catalytic efficiency by tuning N-heterocyclic
carbenes.
Synthesis of [Pt(L3)](PF6)2 (3)
The compound was obtained as a yellow solid using the same
procedure as for 1 by using H2L3(PF6)2 (186.6 mg, 0.30 mmol),
Ag2O (69.6 mg, 0.30 mmol) and Pt(cod)Cl2 (112.2 mg, 0.30 mmol).
Yield: 91 mg, 38%. Anal. Calc. for C21H25F12N7OP2Pt (3·CH3CN):
C, 28.78; H, 2.87; N, 11.19. Found: C, 28.78; H, 2.87; N, 10.89%.
1H NMR (400 MHz, DMSO-d6): d 8.53 (d, J = 4.4 Hz, C5H4N,
2H), 7.82 (t, J = 7.6 Hz, C5H4N, 2H), 7.73, 7.41 (both d, J =
1.2 Hz, C3H2N2, 2H), 7.37 (t, J = 5.2 Hz, C5H4N, 2H), 7.23 (d,
J = 7.2 Hz, 2H), 6.40, 6.36 (both d, J = 13.6 Hz, CH2, each
1H), 5.08, 4.65 (both d, J = 14.4 Hz, CH2, each 2H). 13C NMR
(100 MHz, DMSO-d6): d 161.8 (Pt–C), 154.5, 150.9, 138.6, 124.2,
123.9, 123.8, 123.2, 63.5 (CH2), 55.1 (CH2).
Synthesis of [Pt(L4)](PF6)2 (4)
The compound was obtained as a pale yellow solid using the same
procedure as for 1 by using H2L4(PF6)2 (23.3 mg, 0.05 mmol),
Ag2O (11.6 mg, 0.05 mmol) and Pt(cod)Cl2 (18.7 mg, 0.05 mmol).
Yield: 26.4 mg, 68%. Anal. Calc. for C15H14F12N8OP2Pt 4: C, 22.32;
H, 1.75; N, 13.88. Found: C, 22.73; H, 1.63; N, 13.57%. 1H NMR
(400 MHz, DMSO-d6): d 9.54 (d, J = 5.2 Hz, 4- and 6-C4H3N2,
4H), 8.54 (d, J = 2.0 Hz, C3H2N2, 2H), 8.26 (d, J = 2.0 Hz,
C3H2N2, 2H), 8.08 (t, J = 4.8 Hz, 5-C4H3N2, 2H), 7.26 (s, CH2,
2H). 13C NMR (100 MHz, DMSO-d6): d 162.8 (Pt–C), 157.2,
144.7, 124.5, 121.3, 119.2, 66.6 (CH2).
Experimental
All the chemicals were obtained from commercial suppliers and
used without further purification. The imidazolium salts13d,14e,16
and Pt(cod)Cl222 were prepared according to the known procedure.
Elemental analyses were performed on a Flash EA1112 instru-
ment. 1H and 13C NMR spectra were recorded on Bruker Avance-
400 (400 MHz) spectrometer. Chemical shifts (d) are expressed in
ppm downfield to TMS at d = 0 ppm and coupling constants (J)
are expressed in Hz.
Synthesis of [Pt(L5)2](PF6)2 (5)
The compound was obtained as a colorless solid using the same
procedure as for 1 by using H2L5(PF6)2 (118.8 mg, 0.2 mmol),
Ag2O (46.4 mg, 0.2 mmol) and Pt(cod)Cl2 (37.4 mg, 0.1 mmol).
Yield: 18.4 mg, 23.0%. Anal. Calc. for C34H34F12N12O3P2Pt
(5·CH3CN): C, 35.70; H, 3.00; N, 14.70. Found: C, 35.55; H, 2.64;
N, 14.36%. 1H NMR (400 MHz, DMSO-d6): d 8.56 (d, J = 3.6 Hz,
C5H4N, 4H), 8.03 (t, J = 7.2 Hz, C5H4N, 4H), 7.85 (d, J = 8.0 Hz,
C5H4N, 4H), 7.69, 7.60 (both s, C3H2N2, each 4H), 7.45 (t, J =
Synthesis of [Pt(L1)2Cl](PF6) (1)
A solution of HL1(PF6) (61.2 mg, 0.20 mmol) in 5 mL of
acetonitrile was treated with Ag2O (23.2 mg, 0.10 mmol) at 50 ◦C.
After 10 h, Ag2O completely disappeared and Pt(cod)Cl2 (74.8 mg,
0.20 mmol) was added to the filtrate. After it was stirred for 12 h at
room temperature, the solution was filtered. The filtrate was then
concentrated to ca. 2 mL. Addition of Et2O (20 mL) to the filtrate
afforded a yellow precipitate. The precipitate was collected and
washed with Et2O to obtain the pale yellow solid. Yield: 25 mg,
17%. Anal. Calc. for C16H18ClF6N8OPPt 1: C, 26.92; H, 2.54; N,
15.70. Found: C, 26.98; H, 2.52; N, 15.36%.
6.0 Hz, 4H), 6.64, 6.48 (both d, J = 13.6 Hz, CH2, each 2H). 13
C
NMR (100 MHz, DMSO-d6): d 161.4 (Pt–C), 149.0, 148.9, 138.7,
124.6, 122.8, 121.4, 63.3 (CH2).
General procedure for the hydrosilylation of terminal alkynes
In a Schlenk tube a solution of 1 (0.01 mmol) in toluene (2.0 mL)
was prepared under N2 atmosphere. Alkyne (1.0 mmol) together
with silane (1.2 mmol) was added in quick succession via a
syringe. The yellow solution was stirred at 100 ◦C. Samples were
taken periodically in intervals for GC analysis. After the reaction
was completed, the reaction was stopped and the solvent was
removed under vacuum. The obtained residue was purified by
flash chromatography to give the desired product and the ratio of
products was determined by 1H NMR spectroscopy.
Synthesis of [Pt(L2)Cl](PF6) (2)
The compound was obtained as a yellow solid using the same
procedure as for 1 by using HL2(PF6) (44.2 mg, 0.1 mmol), Ag2O
(11.6 mg, 0.05 mmol) and Pt(cod)Cl2 (37.4 mg, 0.10 mmol). Yield:
60 mg, 75%. Anal. Calc. for C19H18ClF6N4PPt 2: C, 33.66; H, 2.68;
N, 8.27. Found: C, 33.72; H, 2.65; N, 7.84%. 1H NMR (400 MHz,
DMSO-d6): d 8.99 (d, J = 8.8 Hz, 1H), 8.90 (d, J = 8.4 Hz,
1H), 8.62 (d, J = 4.4 Hz, 1H), 8.46, 7.85 (both d, J = 2.0 Hz,
C3H2N2, each 1H), 8.31 (d, J = 9.2 Hz, 1H), 8.10 (m, 1H), 4.27 (t,
J = 6.8 Hz, –CH2CH2CH2CH3, 2H), 1.77 (m, –CH2CH2CH2CH3,
2H), 1.32 (m, –CH2CH2CH2CH3, 2H), 0.91 (t, J = 7.2 Hz, –
CH2CH2CH2CH3, 3H). 13C NMR (100 MHz, DMSO-d6): d 150.6
(Pt–C), 149.2, 147.9, 144.1, 142.8, 142.7, 140.8, 131.8, 127.9, 127.8,
127.5, 126.9, 124.1, 120.0, 112.9, 49.8, 32.5, 19.6, 13.8.
X-Ray diffraction analysis
Single-crystal X-ray diffraction data were collected at 298(2) K on
a Siemens Smart-CCD area-detector diffractometer with a Mo-
˚
Ka radiation (l = 0.71073 A) by using aw–2q scanmode. Unit-cell
dimensions were obtained with least-squares refinement. The data
were corrected for Lorentz and polarization effects with SMART
4202 | Dalton Trans., 2010, 39, 4198–4204
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Table 2 Crystallographic data for complexes 1–5
1
2
3
4
5
Formula
Mr
C36H39Cl2F12N18P2Pt2
C19H18ClF6N4PPt
677.88
Triclinic
¯
P1
C19H18F12N6P2Pt
815.42
Triclinic
¯
P1
C15H12F12N8P2Pt
789.36
Triclinic
¯
P1
C38H34F12N14P2Pt
1171.82
Triclinic
¯
P1
1474.87
Orthorhombic
P212121
6.9251(8)
21.38(2)
33.695(3)
90
90
90
4988(5)
4
1.964
Crystal system
Space group
˚
a/A
13.274(1)
13.558(1)
14.973(1)
114.853(2)
105.017(1)
103.731(1)
2169.5(4)
4
2.075
11278
7517
0.0294
10.543(1)
10.909(1)
12.935(2)
82.480(2)
72.266(1)
64.247(1)
1276.3(2)
2
2.122
6662
4427
0.0238
8.566(1)
9.606(1)
14.532(2)
78.945(1)
81.359(2)
74.986(1)
1127.1(2)
2
2.326
5859
3915
0.0437
8.436(1)
11.517(1)
12. 600(1)
107.890(2)
102.804(1)
100.030(1)
1096.5(2)
1
1.775
5772
3814
0.0274
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
Dc/Mg m-3
Reflections collected
Reflections independent
Rint
26228
8807
0.0689
1.109
0.0731, 0.1625
Goodness-of-fit on F2
R (I > 2sI)
1.012
0.0354, 0.0871
1.021
0.0374, 0.0940
1.019
0.0474, 0.1128
1.048
0.0353, 0.0901
suite programs23 and for absorption effects with SADABS.24 The
structures were solved by direct methods, and the non-hydrogen
atoms were subjected to anisotropic refinement by full-matrix least
squares on F2 using the SHELXTXL package.25 Hydrogen atom
positions for all of the structures were calculated and allowed to
9 (a) I. E. Marko´, S. Ste´rin, O. Buisine, G. Mignani, P. Branlard, B. Tinant
and J.-P. Declercq, Science, 2002, 298, 204; (b) G. Berthon-Gelloz, J.-M.
Schumers, G. De Bo and I. E. Marko´, J. Org. Chem., 2008, 73, 4190;
(c) O. Buisine, G. Berthon-Gelloz, J.-F. Brie`re, S. Ste´rin, G. Mignani, P.
Branlard, B. Tinant, J.-P. Declercq and I. E. Marko´, Chem. Commun.,
2005, 3856; (d) G. De Bo, G. Berthon-Gelloz, B. Tinant and I. E.
Marko´, Organometallics, 2006, 25, 1881; (e) I. E. Marko´, S. Ste´rin, O.
Buisine, G. Berthon, G. Michaud, B. Tinant and J. P. Declercq, Adv.
Synth. Catal., 2004, 346, 1429; (f) G. Berthon-Gelloz, O. Busine, J. F.
Brie`re, S. Ste´rin, G. Mignani, P. Branlard, B. Tinant, J. P. Declerq, D.
Chapon and I. E. Marko´, J. Organomet. Chem., 2005, 690, 6156.
10 (a) M. A. Duin, N. D. Clement, K. J. Cavell and C. J. Elsevier, Chem.
Commun., 2003, 400; (b) M. A. Duin, M. Lutz, A. L. Spek and C. J.
Elsevier, J. Organomet. Chem., 2005, 690, 5804.
˚
ride on their respective C atoms with C–H distances of 0.93–0.97 A
and Uiso(H) = 1.2 or 1.5 ¥ Ueq(C). Further details of the structural
analyses are summarized in Table 2.
Acknowledgements
11 M. Poyatos, A. Maisse-Franois, S. Bellemin-Laponnaz and L. H. Gade,
Organometallics, 2006, 25, 2634.
We are grateful to the NSF of China (20872129 and J0830413),
the PhD Programs Foundation of Ministry of Education of China
(200803350011) and the Chinese Universities Scientific Fund
(2009QNA3004) for financial support.
12 J. Hu, F. Li and T. S. A. Hor, Organometallics, 2009, 28, 1212.
13 (a) X. Zhang, Z. Xi, A. Liu and W. Chen, Organometallics, 2008, 27,
4401; (b) X. Zhang, A. Liu and W. Chen, Org. Lett., 2008, 10, 3849;
(c) J. Ye, X. Zhang, W. Chen and S. Shimada, Organometallics, 2008,
27, 4166; (d) J. Ye, W. Chen and D. Wang, Dalton Trans., 2008, 4015.
14 (a) Z. Xi, X. Zhang, W. Chen, S. Fu and D. Wang, Organometallics,
2007, 26, 6636; (b) Z. Xi, B. Liu and W. Chen, J. Org. Chem., 2008, 73,
3954; (c) Z. Xi, Y. Zhou and W. Chen, J. Org. Chem., 2008, 73, 8497;
(d) Y. Zhou, Z. Xi and W. Chen, Organometallics, 2008, 27, 5911; (e) X.
Zhang, B. Liu, A. Liu, W. Xie and W. Chen, Organometallics, 2009, 28,
1336.
Notes and references
1 (a) M. Blug, X.-F. Le Goff, N. Me´zailles and P. Le Floch,
Organometallics, 2009, 28, 2360; (b) B. M. Trost and Z. T. Ball, J. Am.
Chem. Soc., 2005, 127, 17644; (c) V. S. Sridevi, W. Y. Fan and W. K.
Leong, Organometallics, 2007, 26, 1157; (d) S. V. Maifeld, M. N. Tran
and D. Lee, Tetrahedron Lett., 2005, 46, 105; (e) Li. Yong, K. Kirleis
and H. Butenscho¨n, Adv. Synth. Catal., 2006, 348, 833.
2 J. L. Speier, Adv. Organomet. Chem., 1979, 17, 407.
3 (a) B. D. Karstedt, (General Electric), US Pat., 3715334, 1973; (b) P. B.
Hitchcock, M. F. Lappert and N. J. W. Warhurst, Angew. Chem., Int.
Ed. Engl., 1991, 30, 438.
4 J. Stein, L. N. Lewis, Y. Gao and R. A. Scott, J. Am. Chem. Soc., 1999,
121, 3693.
5 J. W. Sprengers, M. J. Agerbeek and C. J. Elsevier, Organometallics,
2004, 23, 3117.
15 (a) D. Brissy, M. Skander, P. Retailleau, G. Frison and A. Marinetti,
Organometallics, 2009, 28, 140; (b) C. P. Newman, R. J. Deeth, G. J.
Clarkson and J. P. Rourke, Organometallics, 2007, 26, 6225; (c) S.
Fantasia, J. L. Petersen, H. Jacobsen, L. Cavallo and S. P. Nolan,
Organometallics, 2007, 26, 5880; (d) Y. Han, H. V. Huynh and G. K.
Tan, Organometallics, 2007, 26, 4612; (e) S. Fantasia, H. Jacobsen, L.
Cavallo and S. P. Nolan, Organometallics, 2007, 26, 3286.
16 S. Gu and W. Chen, Organometallics, 2009, 28, 909.
17 (a) S. Ahrens, E. Herdtweck, S. Goutal and T. Strassner, Eur. J. Inorg.
Chem., 2006, 1268; (b) Q. Liu, F. Xu, Q. Li, H. Song and Z. Zhang,
Organometallics, 2004, 23, 610.
6 J. W. Sprengers, M. J. Mars, M. A. Duin, K. J. Cavell and C. J. Elsevier,
J. Organomet. Chem., 2003, 679, 149.
7 J. W. Sprengers, M. D. Greef, M. A. Duin and C. J. Elsevier, Eur. J. Inorg.
Chem., 2003, 3811.
8 (a) W. A. Herrmann, Angew. Chem., Int. Ed., 2002, 41, 1290; (b) F. E.
Hahn and M. C. Jahnke, Angew. Chem., Int. Ed., 2008, 47, 3122; (c) S.
D´ıez-Gonza´lez, N. Marion and S. P. Nolan, Chem. Rev., 2009, 109,
3612; (d) M. Poyatos, J. A. Mata and E. Peris, Chem. Rev., 2009, 109,
3677.
18 (a) B. Ma, J. Li, P. I. Djurovich, M. Yousufuddin, R. Bau and M. E.
Thompson, J. Am. Chem. Soc., 2005, 127, 28; (b) W. B. Connick, R. E.
Marsh, W. P. Schaefer and H. B. Gray, Inorg. Chem., 1997, 36, 913;
(c) F. Liu, W. Chen and D. Wang, Dalton Trans., 2006, 3445.
19 (a) A. Yoneda, G. R. Newkome, Y. Morimoto, S. Ohfuchi and N.
Yasuoka, Anal. Sci., 1997, 13, 877; (b) J. Breu, K.-J. Range, A. von
Zelewsky and H. Yersin, Acta Crystallogr., Sect. C: Cryst. Struct.
Commun., 1997, 53, 562; (c) S. Develay, O. Blackburn, A. L. Thompson
and J. A. G. Williams, Inorg. Chem., 2008, 47, 11129.
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 4198–4204 | 4203
©

View Article Online
20 B. Liu, Q. Xia and W. Chen, Angew. Chem., Int. Ed., 2009, 48, 5513.
21 (a) F. E. Hahn, V. Langenhahn, T. Lu¨gger, T. Pape and D. L. Van,
Angew. Chem., Int. Ed., 2005, 44, 3759; (b) Y. Unger, A. Zeller, M. A.
Taige and T. Strassner, Dalton Trans., 2009, 4786; (c) Y. Unger, A.
Zeller, S. Ahrensy and T. Strassner, Chem. Commun., 2008, 3263.
22 J. X. McDermott, J. F. White and J. M. Whitesides, J. Am. Chem. Soc.,
1976, 98, 6521.
23 SMART-CCD Software, version 4.05; Siemens Analytical X-ray In-
struments, Madison, WI, 1996.
24 G. M. Sheldrick, SADABS, Software for Empirical Absorption Cor-
rection, 1996.
25 G. M. Sheldrick, SHELXS-97 and SHELXL-97, Program for X-ray
Crystal Structure Refinement; University of Go¨ttingen, Go¨ttingen,
Germany, 1997.
4204 | Dalton Trans., 2010, 39, 4198–4204
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The Royal Society of Chemistry 2010
©