Construction of an organoruthenium complex (-[biphRuCp]PF6-) within a biphenylene-bridged inorganic-organic hybrid mesoporous material, and its catalytic activity in the selective hydrosilylation of 1-hexyne

Article abstract of DOI:10.1007/s11164-013-1460-1

An organoruthenium complex (-[biphRuCp]PF₆-; biph = -(C ₆H₄)₂-, Cp = C₅H₅), constructed within a biphenylene-bridged inorganic-organic hybrid mesoporous material (HMM-biph) by use of a simple ligand-exchange reaction, has been used as a heterogeneous catalyst. UV-visible and X-ray absorption fine structure (XAFS) studies furnished evidence that the structure of the complex is closely similar to that of [(C₆H₆)RuCp]PF₆, suggesting that the biphenylene moiety within HMM-biph directly coordinates the metal center of the organoruthenium complex. The -[biphRuCp]PF₆- complex constructed within the HMM-biph (HMM-biphRuCp) catalyzes hydrosilylation of 1-hexyne with triethylsilane in a solid-gas heterogeneous system and gives α-vinylsilane as a main product. Moreover, HMM-biphRuCp has higher catalytic activity than the -[phRuCp]PF₆- (ph = -C₆H ₄-) complex constructed within phenylene-bridged HMM (HMM-phRuCp). The high catalytic performance of HMM-biphRuCp can be attributed to the high loading of the HMM-biph with the Ru complex, because of the electron-donating ability of the biphenylene moieties.

Full text of DOI:10.1007/s11164-013-1460-1

Res Chem Intermed
DOI 10.1007/s11164-013-1460-1
Construction of an organoruthenium complex
(–[biphRuCp]PF6–) within a biphenylene-bridged
inorganic–organic hybrid mesoporous material, and its
catalytic activity in the selective hydrosilylation
of 1-hexyne
•
Masakazu Saito Tetsuji Watanabe
•
•
Takashi Kamegawa Yu Horiuchi
Masaya Matsuoka
•
Received: 17 December 2012 / Accepted: 18 February 2013
Ó Springer Science+Business Media Dordrecht 2013
Abstract An organoruthenium complex (–[biphRuCp]PF6–; biph = –(C6H4)2–,
Cp = C5H5), constructed within a biphenylene-bridged inorganic–organic hybrid
mesoporous material (HMM–biph) by use of a simple ligand-exchange reaction, has
been used as a heterogeneous catalyst. UV–visible and X-ray absorption fine
structure (XAFS) studies furnished evidence that the structure of the complex is
closely similar to that of [(C6H6)RuCp]PF6, suggesting that the biphenylene moiety
within HMM–biph directly coordinates the metal center of the organoruthenium
complex. The –[biphRuCp]PF6– complex constructed within the HMM–biph
(HMM–biphRuCp) catalyzes hydrosilylation of 1-hexyne with triethylsilane in a
solid–gas heterogeneous system and gives a-vinylsilane as a main product. More-
over, HMM–biphRuCp has higher catalytic activity than the –[phRuCp]PF6–
(ph = –C6H4–) complex constructed within phenylene-bridged HMM (HMM–
phRuCp). The high catalytic performance of HMM–biphRuCp can be attributed to
the high loading of the HMM–biph with the Ru complex, because of the electron-
donating ability of the biphenylene moieties.
Keywords Inorganic–organic hybrid mesoporous materials ꢀ Periodic
mesoporous organosilicas ꢀ –[biphRuCp]PF6– ꢀ Hydrosilylation ꢀ Biphenylene
moieties
M. Saito ꢀ T. Watanabe ꢀ Y. Horiuchi (&) ꢀ M. Matsuoka (&)
Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University,
1-1, Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan
e-mail: horiuchi@chem.osakafu-u.ac.jp
M. Matsuoka
e-mail: matsumac@chem.osakafu-u.ac.jp
T. Kamegawa
Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka
University, 2-1, Yamada-oka, Suita, Osaka 565-0871, Japan
123

M. Saito et al.
Introduction
Inorganic–organic hybrid mesoporous materials (HMMs), also known as periodic
mesoporous organosilicas, have attracted attention as adsorbents, sensors, and light-
harvesting or emitting optical devices [1–13]. A variety of organic moieties (–C2H4–,
–C6H4–, –(C6H4)2–, etc.) covalently embedded within HMM structures are readily
available for post-synthetic introduction of unique functional sites [11–19]. For example,
Inagaki and coworkers [16–19] developed solid acid and base catalysts by introduction of
sulfuric acid and amino groups, respectively, into the organic moieties of HMMs. Moreover,
the organic moieties, particularly phenylene moieties, of HMMs can be used as ‘‘framework
ligands’’ that directly coordinate the metal centers of organometallic complexes [20, 21].
In our previous work, an organoruthenium complex (–[phRuCp]PF6–; ph = –C6H4–,
Cp = cyclopentadienyl) was successfully constructed within phenylene-bridged HMM
(HMM–ph) by use of a simple ligand-exchange reaction between [(CH3CN)3RuCp]PF6
and the phenylene moiety of HMM–ph [22]. In this complex, the metal center directly
coordinated a phenylene moiety of HMM–ph that behaved as a ‘‘framework ligand’’,
enabling high dispersion of the complex on the HMM–ph [18, 19]. As a consequence, the
constructed organoruthenium complex had excellent catalytic activity in the selective
hydrosilylation of 1-hexyne. Because the chemical properties of organic moieties within
HMMs that can behave as framework ligands are expected to affect the catalytic
performance of the constructed organometallic complexes, there is much interest in the
effect of the type of framework ligand on the catalytic performance of such
organoruthenium complexes.
In the work discussed in this paper we focused on biphenylene-bridged HMM (HMM–
biph; biph = –(C6H4)2–) and attempted to construct an organoruthenium complex
(–[biphRuCp]PF6–) on the biphenylene moiety by means of a simple ligand-exchange
reaction (Scheme 1). The thus-synthesized HMM–biphRuCp was characterized in detail
by X-ray diffraction (XRD), UV–visible, and X-ray absorption fine structure (XAFS)
spectroscopy. To investigate the effect of the type of framework ligand on catalytic
performance, HMM–biphRuCp and HMM–phRuCp were used as catalysts for selective
hydrosilylation of 1-hexyne with triethylsilane in a solid–gas heterogeneous system.
Experimental
Synthesis of HMM–biphRuCp
HMM–biph was prepared by the procedure reported by Inagaki et al. [9, 11, 23].
4,40-bis(triethoxysilyl)biphenyl ((C2H5O)3Si–(C6H4)2–Si(OC2H5)3) (2.5 mmol) was
O
PF6–
Ru+
O
PF6–
Ru+
CHCl3, Reflux
–3 CH3CN
O
Si
Si
+
O
Si
Si
CH3CN
CH3CN
NCCH3
O
O
Scheme 1 Ligand-exchange reaction for construction of –[biphRuCp]PF6– complex within HMM-biph
123

Construction of organoruthenium complexes
added into a mixture of octadecyltrimethylammonium chloride (C18TMACl)
surfactant, 30.4 mmol 6 M sodium hydroxide, and 3.3 mmol distilled water, with
vigorous stirring, at ambient temperature. The suspension was stirred for another
20 h and then heated at ca. 368 K for 22 h under static conditions. The resulting
precipitate was recovered by filtration and washed with deionized water. Finally, the
surfactant was removed from the powder by extraction with a mixture of 150 mL
ethanol and 3.1 g 2 M aqueous HCl solution at ambient temperature for 8 h.
Subsequently, the –[biphRuCp]PF6– complex was constructed within the HMM–
biph by means of a ligand-exchange reaction, using [(CH3CN)3RuCp]PF6 in CHCl3.
Typically, 58 mg [(CH3CN)3RuCp]PF6, which was synthesized in two steps from
readily available bis-benzeneruthenium(II) chloride [24, 25], was dissolved in
20 mL dry-CHCl3. HMM–biph (400 mg) pretreated at 473 K for 2 h under vacuum
was then added to this solution. After heating under reflux for 24 h under an Ar
atmosphere, a white powder was recovered by filtration, repeatedly washed with
CHCl3, and then dried under vacuum, yielding HMM–biphRuCp. For comparison
purposes, HMM–phRuCp was also prepared by the same method except for using
1,4-bis(triethoxysilyl)benzene ((C2H5O)3Si–C6H4–Si(OC2H5)3).
Characterization of HMM–biphRuCp
X-ray diffraction (XRD) patterns were collected by means of a Shimadzu XRD-
˚
6100 using Cu Ka radiation (k = 1.5406 A). Diffuse reflectance UV–visible spectra
were obtained by use of a Shimadzu UV-2200A spectrophotometer. Ru K-edge
X-ray absorption fine structure (XAFS) spectra were also recorded, at the BL-01B1
facility of SPring-8 at the Japan Synchrotron Radiation Research Institute (JASRI).
All spectra were recorded in fluorescence mode with an Si(111) two-crystal
monochromator at 298 K. The extended X-ray absorption fine structure (EXAFS)
data were examined by use of Rigaku REX2000 software. To obtain the radial
structure function, Fourier transformations of k3-weighted EXAFS oscillations in
-1
˚
the range of 3–12 A were performed.
Selective hydrosilylation of 1-hexyne with triethylsilane
Selective hydrosilylation of 1-hexyne with triethylsilane was performed in a closed
solid–gas heterogeneous system at 523 K for 15 h (cell volume 80 mL). Typically,
30 mg catalyst was placed in the reaction cell and pre-treated at 473 K for 3 h in
vacuo. 1-Hexyne and triethylsilane (527 lmol of each) were then added to the
reaction cell by use of a vacuum line. Reactions were conducted at 523 K for 15 h.
The resulting substances were collected by condensation in liquid N2, diluted with
2.0 mL CHCl3, then analyzed by gas chromatography with a Shimadzu GC-14B
equipped with a flame ionization detector and an InertCap 1 capillary column. The
turnover number (TON) was defined as follows:
TON ¼ ½moles of reaction productsꢁ=½mole of Ru in the catalystꢁ:
123

M. Saito et al.
Results and discussion
Figure 1 shows XRD patterns of the synthesized HMM–ph and HMM–biph. In both
˚
XRD patterns, a sharp diffraction peak was observed at 2h = 2.0° (d = 44 A),
corresponding to the (100) reflection of the hexagonal structure of mesopores [9,
23]. The pattern of HMM–ph also contained three other peaks in the range
˚
2h = 10–40° (d = 7.6, 3.8, and 2.5 A) derived from the periodicity of the
phenylene and silica layers (i.e., O1.5–Si–C6H4–Si–O1.5 units) with a spacing of
˚
7.6 A in the pore wall [11]. The pattern of HMM–biph, on the other hand, contained
˚
five peaks in the range 2h = 6–40° (d = 11.6, 5.9, 3.9, 2.9, and 2.4 A) derived from
the periodicity of biphenylene and silica layers (i.e., O1.5–Si–C6H4–C6H4–Si–O1.5
˚
units) with a spacing of 11.6 A in the pore wall [9, 23]. This different periodicity is
because of the different lengths of the organic moieties, that is, longer biphenylene
moieties than phenylene moieties lead to the increase in the interval of the
periodicity. These results reveal that phenylene or biphenylene units were
successfully embedded in the periodic mesoporous structures. Moreover, the
diffraction patterns of both HMMs were almost maintained even after ligand-
exchange reactions. In addition, the BET surface area of HMM–biphRuCp
(878 m2 g-1) was larger than that of HMM–phRuCp (789 m2 g-1).
Subsequently, UV–visible measurements were performed to verify the construc-
tion of the –[biphRuCp]PF6– complex within the HMM–biph framework [22].
Figure 2 shows diffuse reflectance UV–visible spectra of HMM–biph before and
after the ligand-exchange reaction. The UV–visible absorption spectra of
[(C6H6)RuCp]PF6 and [(CH3CN)3RuCp]PF6 complexes dissolved in CH3CN, as
reference compounds, are also shown in the inset of Fig. 2. The spectrum of
[(CH3CN)3RuCp]PF6 in CH3CN contained an absorption band at 370 nm with a tail
extending into the visible region, whereas that of [(C6H6)RuCp]PF6 in CH3CN
contained an absorption band assigned to a d–d transition in the UV-wavelength
region only. It was found that the synthesized HMM–biph furnished no absorption
bands above 330 nm, although a new absorption band was observed in the range
300–400 nm after the ligand-exchange reaction. The position of the new band was
identical with that of d–d transition band of the [(C6H6)RuCp]PF6 complex
(k = *325 nm), indicating that a similar complex to [(C6H6)RuCp]PF6 was
Fig. 1 XRD patterns of
a HMM–ph, b HMM–phRuCp,
c HMM–biph, and d HMM–
biphRuCp
123

Construction of organoruthenium complexes
Fig. 2 Diffuse reflectance UV–visible spectra of HMM–biph (dotted line) and HMM–biphRuCp (solid
line). Inset shows UV–visible absorption spectra of a [(C6H6)RuCp]PF6 and b [(CH3CN)3RuCp]PF6 in
CH3CN
formed by the ligand-exchange reaction between [(CH3CN)3RuCp]PF6 and the
biphenylene moiety of HMM–biph [26, 27]. Similarly, the spectrum of HMM–
phRuCp contained an absorption band at approximately 325 nm, indicative of
construction of the –[phRuCp]PF6– complex within HMM–ph [22]. These findings
revealed that this ligand-exchange reaction is an effective method for construction
of –[biphRuCp]PF6– and –[phRuCp]PF6– complexes within HMMs containing
arene moieties.
To gain insight into the local structures of the –[phRuCp]PF6– and
–[biphRuCp]PF6– complexes constructed within HMM–phRuCp and HMM–
biphRuCp, respectively, Ru K-edge XAFS measurements were performed. Figure 3
shows the X-ray absorption near-edge structure (XANES) and Fourier transform of
EXAFS (FT-EXAFS) spectra of HMM–phRuCp and HMM–biphRuCp, with those
of [(C6H6)RuCp]PF6 and [(CH3CN)3RuCp]PF6. The edge positions and spectral
shapes, particularly in the region of the white line, in the XANES spectra of HMM–
phRuCp and HMM–biphRuCp corresponded well to those in the [(C6H6)RuCp]PF6
spectrum. This result strongly suggests that –[phRuCp]PF6– and –[biphRuCp]PF6–
complexes were constructed within the respective frameworks of HMM–ph and
HMM–biph by direct coordination of ruthenium centers with the phenylene
moieties in their frameworks.
˚
All the the FT-EXAFS spectra contained an intense, sharp peak at ca. 1.7 A (without
phase-shift correction) assigned to Ru–C or Ru–N bonds; curve-fitting analysis of
EXAFS spectra revealed the different coordination environments, however (Table 1).
For HMM–phRuCp and HMM–biphRuCp this peak could be assigned to bonds
between the ruthenium atom and the neighboring carbon atoms of the phenylene (Cph)
and cyclopentadienyl (CCp) ligands. The bond lengths were determined to be
123

M. Saito et al.
A
B
(a)
(b)
(c)
(d)
(a)
(b)
(c)
(d)
22100
22200
22300
0
1
2
3
4
5
6
Energy / eV
Distance /
Fig. 3 Ru K-edge a XANES and b Fourier transform of EXAFS spectra of a HMM–phRuCp, b HMM–
biphRuCp, c [(C6H6)RuCp]PF6, and d [(CH3CN)3RuCp]PF6
Table 1 Results from curve-
fitting analysis of the EXAFS
spectra of the different catalysts
a
R (A)
˚
Catalyst
Shell
CNb
HMM–phRuCp
Ru–Cph
Ru–CCp
Ru–Cph
Ru–CCp
Ru–Cph
Ru–CCp
Ru–N
2.23
2.17
2.23
2.18
2.24
2.18
2.10
2.16
6.2
5.2
6.1
5.1
6.0
5.1
3.4
5.5
HMM–biphRuCp
[(C6H6)RuCp]PF6
[(CH3CN)3RuCp]PF6
a
Bond distance
Ru–CCp
b
Coordination number
˚
Ru–Cph = 2.23 A (coordination number (CN) = 6.2) and Ru–CCp = 2.17 A
˚
˚
(CN = 5.2) for HMM–phRuCp, and Ru–CCp = 2.23 A (CN = 6.1) and Ru–
˚
CCp = 2.18 A (CN = 5.1)for HMM–biphRuCp. Thesevalues wereingoodagreement
˚
with the bond lengths of [(C6H6)RuCp]PF6 (Ru–Cph = 2.24 A (CN = 6.0), Ru–
˚
CCp = 2.18 A (CN = 5.1)). The curve-fitting analysis for [(CH3CN)3RuCp]PF6
˚
revealed the existence of Ru–N bonding (2.1 A, CN = 3.4) and Ru–CCp bonding
˚
(2.16 A, CN = 5.5), which was different from that in HMM–phRuCp and HMM–
biphRuCp. These results provide evidence that –[phRuCp]PF6– and –[biphRuCp]PF6–
complexes are constructed withinthe respectiveHMM–phand HMM–biphframeworks
by the ligand-exchange reactions with [(CH3CN)3RuCp]PF6. Furthermore, no other
˚
peaks were observed in the ranges of 2.0–3.0 A, assigned to Ru–Ru bond, indicating
that aggregated species and dimeric ruthenium complexes were not present in HMM–
phRuCp and HMM–biphRuCp [28, 29].
123

Construction of organoruthenium complexes
The XANES data also provide information about the loading of the Ru
complexes. On the basis of the peak intensity of the white line, the amounts of the
–[phRuCp]PF6– and –[biphRuCp]PF6– complexes loaded were determined to be 1.1
and 1.7 % (w/w) Ru metal, respectively. Furthermore, from calculation based on
these values, conversion of the organic moieties within the frameworks to the
corresponding complexes was estimated to be 5.3 % for HMM–phRuCp and 9.5 %
for HMM–biphRuCp. This difference is because the electron-donating ability of
biphenylene moieties is greater than that of phenylene moieties, because arene
ligands bearing electron-donating substituents can stabilize CpRu complexes [30].
Following successful formation of –[phRuCp]PF6– and –[biphRuCp]PF6– com-
plexes within the HMMs, selective hydrosilylation of 1-hexyne with triethylsilane
was performed in a solid–gas heterogeneous system at 523 K (Scheme 2). It is
apparent from Fig. 4 that [(C6H6)RuCp]PF6, HMM–phRuCp, and HMM–biphRuCp
had catalytic activity in this hydrosilylation reaction, and gave a-vinylsilane with
high selectivity. In contrast, HMM–ph and HMM–biph had almost no catalytic
activity under the same reaction conditions. These results clearly indicate that
–[phRuCp]PF6– and –[biphRuCp]PF6– complexes act as catalysts for the selective
hydrosilylation reaction. Considering that [(C6H6)RuCp]PF6 has no catalytic
activity in the hydrosilylation reaction in a solid–liquid heterogeneous system at
298 K (data not shown), coordinatively unsaturated sites on the Ru(II) center could
be formed by thermal activation of –[phRuCp]PF6– and –[biphRuCp]PF6–
complexes at 523 K. It was also found that [(C6H6)RuCp]PF6 had less catalytic
activity than HMM–phRuCp and HMM–biphRuCp, possibly because of aggrega-
tion of complexes, that is, the ligand-exchange reaction enabled immobilization of
–[phRuCp]PF6– and –[biphRuCp]PF6– complexes on the HMMs in a highly
dispersed state, resulting in improvement of the catalytic activity. Although the
TON of HMM–biphRuCp (36.9) was lower than that of HMM–phRuCp (45.7), it
was found that HMM–biphRuCp had greater catalytic activity than HMM–phRuCp
180
α-vinylsilane
150
120
90
60
30
0
β-vinylsilanes
(a)
(b)
(c)
(d)
(e)
Fig. 4 Yields of products from selective hydrosilylation of 1-hexyne with triethylsilane on a HMM–ph,
b HMM–biph, c [(C6H6)RuCp]PF6, d HMM–phRuCp, and e HMM–biphRuCp. Reaction conditions:
1-hexyne and triethylsilane (527 lmol), catalyst (30 mg), 15 h, 523 K
123

M. Saito et al.
Scheme 2 Hydrosilylation of 1-hexyne with triethylsilane
on the basis of the weight of catalyst used for the reaction. This could be because of
the greater loading of the Ru complex, derived from the electron-donating ability of
biphenylene moieties. This shows that organic moieties within HMMs that behave
as framework ligands affect the chemical properties, herein stability, of the
complexes constructed on them, resulting in a change in their catalytic activity.
Conclusion
Construction of the –[biphRuCp]PF6– complex within HMM–biph was achieved by
ligand-exchange reaction between [(CH3CN)3RuCp]PF6 and the biphenylene
moiety of HMM–biph. UV–visible and XAFS studies revealed that the
–[biphRuCp]PF6– complex was present in a highly dispersed state within the
HMM–biph framework, and that aggregated and dimeric ruthenium species were
not formed. HMM–biphRuCp catalyzed selective hydrosilylation of 1-hexyne in a
solid–gas heterogeneous system and gave a-vinylsilane as the main product. It was
also found that HMM–biphRuCp had greater catalytic activity than HMM–phRuCp.
This high catalytic activity of HMM–biphRuCp was because of the greater loading
of the Ru complex in HMM–biph, because of the high electron-donating ability of
biphenylene moieties.
Acknowledgments This work was financially supported by a Grant-in-Aid for Scientific Research
(KAKENHI) from Ministry of Education, Culture, Sports, Science and Technology of Japan (no.
21550192). The X-ray absorption measurements were performed at the BL-01B1 facility of SPring-8 at
the Japan Synchrotron Radiation Research Institute (JASRI) (nos 2012A1310, 2010B1530, 2007A1669).
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