Syntheses, structures, and immobilization of ruthenium(II) complexes with alkoxysilane groups functionalized N,N′-diamine and phosphine ligands

Article abstract of DOI:10.1080/00958972.2020.1763969

Treatment of [RuCl₂(PPh₃)₃] with N-(β-aminoethyl)-γ-aminopropylmethylbimethoxysilane (L1) in tetrahydrofuran at room temperature gave a mononuclear ruthenium(II) complex [Ru(PPh₃)₂Cl₂ (κ²-N,N-L1)] (1). Condensation of γ-aminopropyltriethoxysilane and potassium diphenylphosphine in the molar ratio of 1:1 in tetrahydrofuran afforded phosphine (PPh₂)(CH₂)₃Si(OEt)₃ (L2) with ethoxysilane groups. Reaction of [Ru(η⁶-p-cymene)Cl₂]₂ with L2 in refluxing tetrahydrofuran afforded a ruthenium(II) phosphine complex [Ru(η⁶-p-cymene)Cl₂(κ-P-L2)] (2). Complexes 1 and 2 were systematically characterized by microanalyses, FT-IR, and NMR spectroscopies. Their structures have been unambiguously established by single-crystal X-ray diffraction. Immobilization of 1 and 2 on SBA-15 and characterization of these hybrid heterogeneous catalysts were studied by transmission electron microscopy (TEM), FT-IR, and low-pressure N₂ adsorption/desorption measurements. Transfer hydrogenation of acetophenone was also briefly investigated with the heterogeneous catalysts.

Full text of DOI:10.1080/00958972.2020.1763969

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
Syntheses, structures, and immobilization of
ruthenium(II) complexes with alkoxysilane groups
functionalized N,N′-diamine and phosphine ligands
Jiao Ji, Li-Miao Shi, Fule Wu, Zhi-Feng Xin, Ai-Quan Jia & Qian-Feng Zhang
To cite this article: Jiao Ji, Li-Miao Shi, Fule Wu, Zhi-Feng Xin, Ai-Quan Jia & Qian-Feng Zhang
(2020): Syntheses, structures, and immobilization of ruthenium(II) complexes with alkoxysilane
groups functionalized N,N′-diamine and phosphine ligands, Journal of Coordination Chemistry, DOI:
10.1080/00958972.2020.1763969
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JOURNAL OF COORDINATION CHEMISTRY
https://doi.org/10.1080/00958972.2020.1763969
Syntheses, structures, and immobilization of ruthenium(II)
complexes with alkoxysilane groups functionalized N,N0-
diamine and phosphine ligands
Jiao Ji, Li-Miao Shi, Fule Wu, Zhi-Feng Xin, Ai-Quan Jia and Qian-Feng Zhang
Institute of Molecular Engineering and Applied Chemistry, Anhui University of Technology, Anhui,
P. R. China
ABSTRACT
ARTICLE HISTORY
Received 28 February 2020
Accepted 23 April 2020
Treatment of [RuCl2(PPh3)3] with N-(b-aminoethyl)-c-aminopropyl-
methylbimethoxysilane (L1) in tetrahydrofuran at room tempera-
ture gave a mononuclear ruthenium(II) complex [Ru(PPh3)2Cl2
(j2-N,N-L1)] (1). Condensation of c-aminopropyltriethoxysilane
and potassium diphenylphosphine in the molar ratio of 1:1 in
tetrahydrofuran afforded phosphine (PPh2)(CH2)3Si(OEt)3 (L2) with
ethoxysilane groups. Reaction of [Ru(g6-p-cymene)Cl2]2 with L2 in
refluxing tetrahydrofuran afforded a ruthenium(II) phosphine com-
plex [Ru(g6-p-cymene)Cl2(j-P-L2)] (2). Complexes 1 and 2 were
systematically characterized by microanalyses, FT-IR, and NMR
spectroscopies. Their structures have been unambiguously estab-
lished by single-crystal X-ray diffraction. Immobilization of 1 and
2 on SBA-15 and characterization of these hybrid heterogeneous
catalysts were studied by transmission electron microscopy (TEM),
FT-IR, and low-pressure N2 adsorption/desorption measurements.
Transfer hydrogenation of acetophenone was also briefly investi-
gated with the heterogeneous catalysts.
KEYWORDS
Ruthenium(II) complex;
N,N0-diamine ligand;
phosphine ligand;
immobilization; heteroge-
neous catalysis;
molecular structure
CONTACT Qian-Feng Zhang
zhangqf@ahut.edu.cn
Institute of Molecular Engineering and Applied Chemistry,
Anhui University of Technology, Ma’anshan, Anhui 243002, P. R. China
Supplemental data for this article is available online at https://doi.org/10.1080/00958972.2020.1763969.
ß 2020 Informa UK Limited, trading as Taylor & Francis Group

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J. JI ET AL.
1. Introduction
The organometallic ruthenium(II) complexes have a wide range of applications in
homogeneous catalysis, in which ligands coordinated to a ruthenium metal center
play an important role, exhibiting significant impact on catalyst efficiency, stability,
and activity [1–3]. It is well known that phosphine ligands have a variety of structures
due to their spatial configuration and electronic properties (strong r-donors, as well
as good p-acceptors). The typical structures of phosphine ligands are PR3 (R ¼ alkyl,
aryl, alkoxyl), which are extensively employed in the synthesis of transition metal com-
plexes [4]. Compared with phosphine ligands, nitrogen-containing ligands have better
stability for the change of the central metal atom and the strength of the coordination
bonds. Moreover, the catalytic activity of the nitrogen-containing transition metal com-
plexes in catalytic reactions could be changed by the steric effects [5–7]. To date,
some transition metal complexes with phosphine and N,N0-diamine ligands have been
prepared and tested in different catalytic reactions, such as silylation of arylalkynes,
nitrile hydration, transfer hydrogenation of ketones, and Suzuki and Heck cross-cou-
pling reactions [7–11]. For example, Carniato reported a hetero-bimetallic carbonyl
cluster stabilized by Ph2PCH2CH2Si(OEt)3 [12]. It was rather unusual, because normally
compounds incorporating the –Si(OEt)3 or –Si(OMe)3 group are oily or waxy materials,
which generally refuse to crystallize [13]. Moreover, the Si(OR)3 groups have the ability
to condense with surface OH groups of inorganic supports and form the immobilizing
sol–gel materials [14].
Immobilization of ruthenium complexes on solid supports emerged as a highly
effective improvement to enhance their potential as catalysts in chemical reactions
[15]. These solid-supported catalysts have the advantages of separating from the prod-
uct readily, removing from the reaction mixture by filtration easily, and reusing in sub-
sequent reactions [16, 17]. Furthermore, they exhibit higher catalytic activity under the
same reaction conditions [18]. However, solid-supported ruthenium catalysts were seldom
employed in the past to carry out hydrogenation reactions and the hydrogenation of ace-
tophenone to achieve high selectivity to 1-phenylethanol, the desired product, is a chal-
lenging issue, which attract our interests [19]. Previously, we reported the synthesis and
immobilization of arene–ruthenium complexes bearing aminophosphine and bisphosphi-
noamine ligands functionalized with methoxysilyl groups [4]. Herein, we report synthesis
and structure of ruthenium(II) complexes bearing N,N0-diamine and phosphine ligands
functionalized with alkoxysilane groups along with immobilization of them on SBA-15,
and the catalytic activity of the heterogeneous catalysts for transferring hydrogenation of
acetophenone are also investigated in this article.
2. Experimental
2.1. General considerations
All manipulations were carried out under nitrogen by standard Schlenk techniques.
Solvents were purified, distilled, and degassed prior to use. [RuCl2(PPh3)3] [20] and
[Ru(g6-p-cymene)Cl2]2 [21] were prepared according to the literature methods.
c-Aminopropyltriethoxysilane, potassium diphenylphosphine, and N-(b-aminoethyl)-

JOURNAL OF COORDINATION CHEMISTRY
3
c-aminopropylmethylbimethoxysilane (L1) were purchased from Alfa Aesar Ltd. and
used as received. NMR spectra were recorded on a Bruker ALX400 spectrometer oper-
ating at 400 and 162 MHz for 1H and 31P, respectively. Chemical shifts (d, in ppm)
were reported with reference to SiMe4 (1H) and 85% H3PO4 (31P). Infrared spectra were
recorded on a Perkin-Elmer 16 PC FT-IR spectrophotometer. Elemental analyses were
carried out using a Perkin-Elmer 2400 CHN analyzer. N2 adsorption/desorption isotherms
were obtained at 77 K with a Micromeritics ASAP 2020M þ C system after the samples
were first degassed at 393 K for 6 h. TEM images were collected on a JEM-2100 electron
microscope at 200 kV. Gas chromatography analyses were performed with an FID detector
on a Shimadzu GC-2010 Plus spectrometer using the RTX-5 column.
2.2. Synthesis of (PPh2)(CH2)3Si(OEt)3 (L2)
Potassium diphenylphosphine (1.12 g, 5 mmol) was dissolved in tetrahydrofuran
(15 mL) and cooled to ꢀ78 ꢁC. c-Aminopropyltriethoxysilane (1.11 g, 5 mmol) was
added dropwise while stirring vigorously. After continuous stirring for 2 h at room
temperature, there was a color change from red to colorless. Then, the mixture was fil-
trated, the solvent was removed by vacuum, and the residue was washed with diethyl
ether to give L2 as a clear, viscous liquid (1.77 g, 91%). IR (KBr disk, cmꢀ1): ꢀ(P–C)
1445 (m), ꢀ(Si–C) 1241 (m), ꢀ(Si–O) 1084 (s). 1H NMR (400 MHz, CDCl3), d (ppm):
7.71–7.31 (m, 10H, C6H5), 3.86 (m, 6H, OCH2), 1.45–1.40 (m, 4H, PCH2CH2), 1.21 (t, 9H,
OCH2CH3), 0.48 (s, 2H, CH2Si); 31P NMR (162 MHz, CDCl3), d (ppm): ꢀ17.43.
2.3. Syntheses of [Ru(PPh3)2Cl2(j2-N,N-L1)] (1)
[RuCl2(PPh3)3] (48.2 mg, 0.05 mmol) and L1 (11.3 mg, 0.05 mmol) were dissolved in
tetrahydrofuran (15 mL), and the mixture was stirred at room temperature for 4 h, dur-
ing which the color changed from red brown to dark red. The solvent was removed
by vacuum, and the residue was washed with diethyl ether (5 mL
ꢂ
3).
Recrystallization from CH2Cl2/n-hexane (1:3) gave red crystals of [Ru(PPh3)2Cl2(j2-N,N-
L1)] (1). Yield: 29.3 mg, 58% (based on ruthenium). IR (KBr disk, cmꢀ1): ꢀ(N–C) 1473
1
(m), ꢀ(Si–C) 1260 (m), ꢀ(Si–O) 1093 (s). H NMR (400 MHz, CDCl3), d (ppm): 7.89–7.43
(m, 30H, C6H5), 3.35 (s, 6H, OCH3), 2.81–2.51 (m, 6H, NCH2), 2.23–1.85 (m, 3H, NH2 and
NH), 1.58 (m, 2H, CH2), 0.58 (m, 2H, SiCH2), 0.15 (m, 3H, SiCH3); 31P NMR (162 MHz,
CDCl3), d (ppm): 28.1, 29.2. Anal. Calcd for C48H62N2O4SiP2Cl2Ru: C, 58.06%; H, 6.29%;
N, 2.82%. Found: C, 58.09%; H, 6.27%; N, 2.83%.
2.4. Syntheses of [Ru(g6-p-cymene)Cl2(j-P-L2)] (2)
[Ru(g6-p-cymene)Cl2]2 (30.6 mg, 0.05 mmol) and L2 (78.1 mg, 0.10 mmol) were dissolved
in tetrahydrofuran (15 mL), and the mixture was refluxed for 4 h, during which the
color changed from orange to dark red. The solvent was removed by vacuum, and the
residue was washed with diethyl ether (5 mL ꢂ 3). Recrystallization from dichlorome-
thane/diethyl ether (1:4) afforded red block crystals of [Ru(g6-p-cymene)Cl2(j-P-L2)] (2)
suitable for X-ray diffraction in five days. Yield: 114.5 mg, 82% (based on ruthenium).

4
J. JI ET AL.
Table 1. Crystallographic data and experimental details for [Ru(PPh3)2Cl2(j2-N,N-L1)]ꢃ(C2H5)2O
(1ꢃ(C2H5)2O) and [Ru(g6-p-cymene)Cl2(j-P-L2)] (2).
Complex
1ꢃ(C2H5)2O
2
Empirical formula
Formula weight
Crystal system
a (Å)
C48H62N2O4SiP2 Cl2Ru
977.00
C31H45O3SiPCl2Ru
696.70
Monoclinic
19.536(6)
10.997(3)
22.782(7)
92.402(5)
4890(3)
P21/c
Monoclinic
13.989(12)
14.458(12)
17.231(14)
100.737(13)
3424(5)
P21/c
b (Å)
c (Å)
b (ꢁ)
V (Å3)
Space group
Z
4
4
Dcalc (g cmꢀ3
)
1.327
1.352
Temperature (K)
F(0 0 0)
296(2)
2040
0.561
29,782
296(2)
1448
0.724
21,018
l(Mo Ka) (mmꢀ1
Total refln.
)
Independent refln.
Parameters
11,163
549
7903
358
Rint
0.0992
0.0402
R1a, wR2b (I > 2r(I))
R1, wR2 (all data)
GoFc
0.0649, 0.1304
0.1510, 0.1679
0.973
0.0527, 0.1324
0.0978, 0.1583
1.020
aR1 ¼ jjFoj ꢀ jFcjj/jFoj.
bwR2 ¼ [w(jFo j ꢀ jFc j)2/wjFo j ]
.
2
2
2 2 1/2
cGoF ¼ [w(jFoj ꢀ jFcj)2/(Nobs ꢀ Nparam)]1/2
.
IR (KBr disk, cmꢀ1): ꢀ(P–C) 1469 (m), ꢀ(Si–C) 1258 (m), ꢀ(Si–O) 1078 (s). 1H NMR
(400 MHz, CDCl3), d (ppm): 7.89–7.44 (m, 14H, Ar), 3.74 (m, 6H, OCH2), 2.87–2.34 (m,
4H, PhCH and PhCH3), 1.43–1.38 (m, 4H, PCH2CH2), 1.25–1.20 (m, 15H, CH(CH3)2 and
OCH2CH3), 0.78 (m, 2H, SiCH2); 31P NMR (162 MHz, CDCl3), d (ppm): 23.3 (s). Anal. Calcd
for C31H45O3SiPCl2Ru: C, 53.44%; H, 6.51%. Found: C, 53.45%; H, 6.49%.
2.5. X-ray crystallography
Crystallographic data and experimental details for ruthenium(II) complexes
[Ru(PPh3)2Cl2(j2-N,N-L1)]ꢃ(C2H5)2O (1ꢃ(C2H5)2O) and [Ru(g6-p-cymene)Cl2(j-P-L2)] (2) are
summarized in Table 1. Intensity data were collected on a Bruker SMART APEX 1000 CCD
diffractometer using graphite-monochromated Mo K radiation (k ¼ 0.71073 Å) at 296(2) K.
The collected frames were processed with the software SAINT [22]. The data were cor-
rected for absorption using the program SADABS [23]. Structures were solved by Direct
Methods and refined by full-matrix least-squares on F2 using the SHELXTL software pack-
age [24, 25]. All non-hydrogen atoms were refined anisotropically. The positions of all
hydrogens were generated geometrically (Csp3–H¼ 0.96 Å,
C
sp2–H¼ 0.93 Å, and
N–H¼ 0.86 Å), assigned isotropic thermal parameters, and allowed to ride on their respect-
ive parent carbon atoms before the final cycle of least-squares refinement.
2.6. Immobilization of ruthenium(II) complexes 1 and 2 anchored onto SBA-15
SBA-15 (100 mg) was introduced into a three-necked flask connected to a vacuum
pump and heated at 473 K for 4 h in order to remove the water and air adsorbed on

JOURNAL OF COORDINATION CHEMISTRY
5
Scheme 1. Syntheses of ruthenium(II) complexes 1 and 2.
the surface. Complex 1 or 2 (10 mg) was dissolved in tetrahydrofuran which was
degassed with N2 bubbling for 15 min. The activated SBA-15 was suspended into the
above solution, and the mixture was stirred at room temperature for 6 h. The excess
of tetrahydrofuran was removed using a rotary evaporator, and the resulting yellow
solid was dried at 80 ꢁC overnight. The product was washed with tetrahydrofuran and
diethyl ether until the filtrate became colorless. Finally, the brown solid products (1)/
SBA-15 and (2)/SBA-15 were dried in vacuo for 2 h and stored for further applications.
FT-IR (KBr) for (1)/SBA-15: 3425 [ꢀ(O–H)], 1081 [m(Si–O–Si)] cmꢀ1; for (2)/SBA-15: 3451
[ꢀ(O–H)], 1088 [ꢀ(Si–O–Si)] cmꢀ1
.
2.7. Catalyst testing
In a typical experiment, a testing tube was filled with acetophenone (1 mmol), KOH in
i
iPrOH (0.05 mmol KOH in degassed PrOH (10 mL)), heterogeneous catalyst precursors
(1)/SBA-15 or (2)/SBA-15 (0.01 mmol ruthenium). The resulting suspension was stirred
at 70–80 ꢁC for the appropriate times (0.5, 1, 3, 10, and 20 h). Then, the resulted mix-
ture was filtered, and the filtrate was diluted with acetone and then analyzed immedi-
ately by gas chromatography.
3. Results and discussion
3.1. Synthetic reactions
The methoxy-modified amine N-(b-aminoethyl)-c-aminopropylmethylbimethoxysilane
NH2(CH2)2NH(CH2)3SiCH3(OCH3)2 (L1) is commercially available. Condensation of c-ami-
nopropyltriethoxysilane with potassium diphenylphosphine in tetrahydrofuran afforded
the corresponding ligand (EtO)3Si(CH2)3PPh2 (L2) (Scheme 1). Reaction of ruthenium
starting compound [RuCl2(PPh3)3] and L1 in tetrahydrofuran led to the isolation of a
typical ruthenium(II) complex [Ru(PPh3)2Cl2(j2-N,N-L1)] (1) as red crystals. L1 coordi-
nated to the ruthenium center to replace one PPh3 ligand in the starting five-coordin-
ate compound [RuCl2(PPh3)3], similar to the reported complex [Ru(PPh3)2Cl2(j2-N,N-L)]
(L ¼ N1-(3-(trimethoxysilyl)propyl)-ethane1,2-diamine) [26]. L2 was used to react with
the dimeric choloride-bridged compound [Ru(g6-p-cymene)Cl2]2 to give the according
ruthenium complex bearing ethoxysilyl groups [Ru(g6-p-cymene)Cl2(j-P-L2)] (2) in
good yields. Some other P-bound mononuclear ruthenium complexes have also been

6
J. JI ET AL.
Figure 1. Molecular structure of [Ru(PPh3)2Cl2(j2-N,N-L1)] (1); the diethyl ether molecule is omitted
for clarity. Thermal ellipsoids are drawn at the 35% probability level. Selected bond lengths (Å) and
angles (ꢁ): Ru(1)–N(1) ¼ 2.208(5), Ru(1)–N(2)¼ 2.155(5), Ru(1)–P(1) ¼ 2.316(2), Ru(1)–P(2)¼ 2.326(2),
Ru(1)–Cl(1)¼ 2.421(2), Ru(1)–Cl(2) ¼ 2.413(2), Si(1)–O(2) ¼ 1.409(1), Si(1)–O(1) ¼ 1.592(5), Si(1)–C(41) ¼
1.823(6), Si(1)–C(42) ¼ 1.980(11); Cl(2)–Ru(1)–Cl(1) ¼ 165.94(5), N(2)–Ru(1)–N(1) ¼ 78.6(2).
synthesized according to a Cambridge Crystallographic Data Center (CCDC) searching
map [27–35], such as [RuCp(dppp)](OTs) (dppp ¼ 1,3-bis(diphenylphosphino)pro-
pane) [36].
3.2. Spectroscopic characterization
The Si ꢀ O stretching vibration modes appeared at around 1080 cmꢀ1 in the IR spectra
of 1 and 2, which are comparable to those in other related ruthenium(II) complexes
(1070 cmꢀ1) [29]. The 31P NMR spectrum of 1 display phosphorus resonances at 28.1
and 29.2 ppm, indicating that the two triphenylphosphine ligands are cis to each
other. The 31P NMR spectrum of 2 shows single resonance at 23.3 ppm, which is
assigned to the PPh2 moiety of L2. Moreover, the –NH and –NH2 protons in 1 were
observed at 1.85–2.23 ppm in the 1H NMR spectrum, which are close to those in
related complexes methoxysilyl groups [4]. The highfield chemical shift (ꢄ0.58 ppm) of
–CH2SiCH3(OMe)2 protons in 1 are close to those of –CH2Si(OEt)3 protons in 2.
3.3. X-ray crystal structures of ruthenium complexes 1 and 2
It is noted that complexes bearing the alkoxysilyl groups are normally obtained as oily
or waxy states, which are difficult to crystallize and could not be chromatographed
over silica gel. Relatively, good quality single-crystals of 1ꢃ(C2H5)2O and 2 were
obtained due to many efforts during our experiments. The perspective views of the
molecular structures of 1 and 2 with selected bond lengths and angles are shown in
Figures 1 and 2, respectively. Complex 1ꢃ(C2H5)2O can be formulated as a six-coordin-
ate ruthenium(II) complex, with ruthenium coordinated by two PPh3 groups, two

JOURNAL OF COORDINATION CHEMISTRY
7
Figure 2. Molecular structure of [Ru(g6-p-cymene)Cl2(j-P-L2)] (2). Thermal ellipsoids are drawn at
the 35% probability level. Selected bond lengths (Å) and angles (ꢁ): Ru(1)–P(1) ¼ 2.346(2),
Ru(1)–Cl(1) ¼ 2.401(2),
Ru(1)–Cl(2) ¼ 2.398(2),
Si(1)–O(1) ¼ 1.631(7),
Si(1)–O(2) ¼ 1.609(7),
Si(1)–O(3)¼ 1.608(5), Si(1)–C(25) ¼ 1.827(6); Cl(2)–Ru(1)–Cl(1) ¼ 88.05(6), P(1)–Ru(1)–Cl(1) ¼ 85.40(4),
P(1)–Ru(1)–Cl(2) ¼ 89.02(6).
chloro ligands, and one L1 ligand in an j2-N,N coordination mode. Complex 2 could
be found that the cymene moiety occupied three coordination sites. The bite angle of
N–Ru–N is 78.6(2)ꢁ in 1, similar to that in the structure-related complex
[Ru(PPh3)2Cl2(j2-N,N-L)] (L ¼ N1-(3-(trimethoxysilyl)propyl)ethane-1,2-diamine, 78.9(2)ꢁ)
[26]. The Ru–N bond lengths of 2.155(5) and 2.208(5) Å in 1 are normal, similar to
those in ruthenium complex [Ru(PPh3)2Cl2(j2-N,N-L)] (L ¼ N1-(3-(trimethoxysilyl)propyl)-
ethane1,2-diamine, 2.149(5) and 2.214(5) Å) [26]. The Ru–Cl bond lengths in 1 and 2
are in the ranges of 2.398(2)–2.421(2) Å, comparable to those in ruthenium complexes
[Ru(g6-C6H6)Cl2(j1-P-L)] (L ¼ (CH3O)3Si(CH2)3NHPPh2, 2.397(1) and 2.413(1) Å) [4]. The
Cl–Ru–Cl bond angle of 165.94(5)ꢁ in 1 is much larger than that in 2 (88.05(6)ꢁ), pos-
sibly due to the existence of the large PPh3 ligand in 1. The Ru–P bond lengths in 1
and 2 are in the range of 2.315(1)–2.346(2) Å, which are similar to those in other
related ruthenium complex [Ru(g6-C6H6)Cl2(j1-P-L)] (L ¼ (CH3O)3Si(CH2)3NHPPh2,
2.327(1) Å) [4]. In 2, the Si–C and average Si–O bond lengths are 1.827(6) and
1.616(5) Å, respectively, similar to those in [RuCl(CO)2(g1-O-L1)(g2-O,N-L1)] (L1 was
given by the treatment of c-aminopropyltriethoxysilane with 4-(diethylamino)salicylal-
dehyde, av. Si–C 1.825(4) Å and av. Si–O 1.599(5) Å) [36].
3.4. Preparation, characterization, and application of SBA-15 supported
ruthenium complexes
Immobilization of ruthenium complexes 1 and 2 functionalized with alkoxysilane
groups on mesoporous SBA-15 by condensation is shown in Scheme 2. The organic
silicon group connected with SBA-15 in the form of –Si–O–Si–, and one of the silicon-
group connected with the organometallic ruthenium complex [37]. The supported
ruthenium(II) complexes were further characterized by methods of FT-IR, TEM, and N2

8
J. JI ET AL.
Scheme 2. Immobilization of ruthenium(II) complexes 1 and 2 on SBA-15 by condensation.
adsorption/desorption measurements. The bands at about 1085 and 800 cmꢀ1 in the
infrared spectra are typical for parent calcined mesoporous SBA-15 and grafted sam-
ples, which could be attributed to stretching vibrations of the mesoporous framework
(Si–O–Si) [38], as displayed in Figure S1. Additionally, the well supported organic sili-
con ruthenium(II) complexes were also tested by TEM. The supported materials (1)/
SBA-15 and (2)/SBA-15 showed the similar ordered mesoporous structure compared
with SBA-15 (Figure S2). The channel of SBA-15 was clearly visible while the channel
of (1)/SBA-15 and (2)/SBA-15 seemed obviously unclear, which are due to the loading
of 1 and 2 on the pore wall of SBA-15 [39].
The pore structures of SBA-15, (1)/SBA-15, and (2)/SBA-15 were further detected by
low pressure N2 adsorption/desorption measurement at 77 K, as seen in Figure 3. The
characteristic shape of the N2 sorption isotherms (type IV isotherm with an H1 hyster-
esis loop) of (1)/SBA-15 and (2)/SBA-15 did not change. And N2 uptakes and surface
area were obviously decreased, suggesting that part of the original pore structure of
SBA-15 was occupied by the organic silicon ruthenium(II) complexes [40]. As expected,
the pore width distributions of (1)/SBA-15 (5.89 nm) and (2)/SBA-15 (5.82 nm) were
smaller than that of SBA-15 (6.22 nm). Additionally, the BET surface area was decreased

JOURNAL OF COORDINATION CHEMISTRY
9
Figure 3. N2 sorption isotherms of (a) SBA-15, (b) (1)/SBA-15, and (c) (2)/SBA-15.
from 777.80 m2 g–1 (SBA-15) to 513.18 m2 g–1 ((1)/SBA-15) or 466.95 m2 g–1 ((2)/SBA-15).
The above results of N2 adsorption/desorption measurement were caused by the load-
ing of 1 and 2 on the pore of SBA-15, which were in agreement with the results of
the TEM images.
Previously, there are many reports on supported ruthenium for the hydrogenation
of ketones, for example, in the presence of ruthenium catalysts (4 wt% Ru) supported
on gel-type methacrylate–styrene resin (FCN), which performed ca. 80% selectivity of
transferring acetophenone to 1-phenylethanol [41]. It was also reported that immobil-
ization of presynthesized [Ru(acac)2(CH3CN)2] onto amine-modified SiO2 afforded het-
erogeneous catalyst with good reusability for the reduction of carbonyls, in which
various substituted aryl secondary alcohols including heteroaryl alcohols were isolated
in 88–99% yields [42, 43]. Under this guidance, transfer hydrogenation of acetophe-
none with heterogeneous materials (1)/SBA-15 and (2)/SBA-15 was investigated at
70–80 ꢁC. Treatment of acetophenone with (1)/SBA-15 and KOH in isopropanol led to
1-phenylethanol in 70% yield in 10 h, compared with the homogeneous catalytic sys-
tem [Ruf(2-CH2-6-MeC6H3)PPh2g(en)(CO)2]Cl (en ¼ ethylenediamine, yield ꢄ65%) [44].
The yield was not improved after longer reaction time. It was found that the yield of
1-phenylethanol was slightly higher with (2)/SBA-15 as catalyst precursor after 10 h of
reaction (78%). Additionally, the immobilized material (2)/SBA-15 could be recycled for
three cycles for the transfer hydrogenation without an obvious yield decrease though lon-
ger reaction periods were needed for reactions after the second cycle. However, the
reported silica-supported ruthenium catalyst (SiO2)–O–[RuCl2(Si(CH2)3N(CH2PPh2)2)2] with
reuse potential had a yield of 82% for hydrogenation of acetophenone, a little higher
than catalyst (2)/SBA-15, indicating (2)/SBA-15 performed lower catalytic activity [17].
4. Conclusion
Two new ruthenium(II) complexes functionalized with terminal alkoxysilane groups
were synthesized and spectroscopically characterized. Structures of the two
ruthenium(II) complexes were unambiguously established by single-crystal X-ray dif-
fraction. Up to now, few ruthenium(II) complexes bearing alkoxysilyl moieties were
reported, to our best knowledge, possibly due to their oily or waxy states and diffi-
culty in crystallization [45, 46]. Immobilization of the two mononuclear ruthenium(II)
complexes on SBA-15, and characterization of these heterogeneous materials were

10
J. JI ET AL.
studied by IR, TEM, and N2 adsorption/desorption measurements. The grafted materials
were investigated as heterogeneous catalysts for transfer hydrogenation of acetophe-
none and could be recycled several times. Exploration of surface-bound ruthenium
alkoxysilyl species for other organic transformation reactions and photocatalytic prop-
erties is underway in our laboratory.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This project was supported by the Natural Science Foundation of China [21372007].
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