Silylated organometals: A family of recyclable homogeneous catalysts

Article abstract of DOI:10.1039/c4gc01586j

A general strategy has been developed to synthesize a family of silylated organometals (M-PPh₂-T_S and DPEN-Ru-PPh₂-Ts, M = Pd²⁺, Rh⁺, Pt²⁺, Ir⁺, or Ru²⁺, PPh₂-Ts = PPh₂CH₂CH₂Si(OEt)₃), DPEN = (1R,2R)-1,2-diphenylethylenediamine). They can act as homogeneous catalysts with high efficiencies in various organic reactions using THF, CH₂Cl₂ or toluene as the reaction medium. After reaction, they could be thoroughly settled down by adding pentane and then used repeatedly owing to the complete catalyst recovery and good preservation of the catalyst structure. This is particularly important due to the increasing concerns regarding the cost, toxicity and limited availability of these nonrenewable transition metals.

Full text of DOI:10.1039/c4gc01586j

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Silylated organometals: a family of recyclable
homogeneous catalysts†
Cite this: DOI: 10.1039/c4gc01586j
Jian-Lin Huang,a Jun-Zhong Wang,a He-Xing Li,*b Haibing Guo*c and
George A. O’Dohertyd
A general strategy has been developed to synthesize a family of silylated organometals (M-PPh2-TS and
DPEN-Ru-PPh2-Ts, M = Pd2+, Rh+, Pt2+, Ir+, or Ru2+, PPh2-Ts = PPh2CH2CH2Si(OEt)3), DPEN = (1R,2R)-
1,2-diphenylethylenediamine). They can act as homogeneous catalysts with high efficiencies in various
organic reactions using THF, CH2Cl2 or toluene as the reaction medium. After reaction, they could be
thoroughly settled down by adding pentane and then used repeatedly owing to the complete catalyst
recovery and good preservation of the catalyst structure. This is particularly important due to the increas-
ing concerns regarding the cost, toxicity and limited availability of these nonrenewable transition metals.
Received 15th August 2014,
Accepted 14th November 2014
DOI: 10.1039/c4gc01586j
www.rsc.org/greenchem
Green chemistry requires chemical reactions to be conducted redox-,8 photo-9 and phase-switchable10 technologies.
with low cost, clean reactants, products and processes, recycl- However, their discovery and design are quite rare, which
able and environmentally friendly catalysts, and high activity greatly limits the number of catalysts and their practical appli-
and selectivity (i.e., economic reactions). Homogeneous cations. Obviously, a universal method for preparing recyclable
organometal catalysts have been widely used in organic syn- homogeneous catalysts is strongly desired.
thesis and have enjoyed great success as a result of their high
Herein, we reported a general way to synthesize a family of
activity, selectivity and stereoselectivity.1 However, they are silylated organometals using in situ coordinating metallic ions
difficult to be recycled and reused, leading to enhanced costs with the PPh2-ligand in PPh2CH2CH2Si(OEt)3, denoted as
and even environmental pollution from heavy metallic ions.2 M-PPh2-Ts, where M refers to Pd2+, Rh+, Pt2+, Ir+, or Ru2+,
Immobilized homogeneous catalysts on solid supports are while PPh2-Ts corresponds to PPh2CH2CH2Si(OEt)3. They
easily recycled and reused, but they usually display remarkably behaved as homogeneous catalysts with high activities and
decreased catalytic efficiencies due to the enhanced diffusion selectivities in various organic reactions using common sol-
limit, reduced dispersion degree and unmatchable chemical vents including THF, CH2Cl2 or toluene as the reaction media.
microenvironment of the active sites.3 There is always a dream After reaction, they could be completely precipitated by adding
of designing recyclable homogeneous catalysts combining the pentane and then used repeatedly without a significant decrease
merits of both homogeneous and heterogeneous catalysts. in the catalytic efficiencies. Moreover, we could further syn-
Such catalysts could be used homogeneously during reactions thesize the chiral catalyst DPEN-Ru-PPh2-Ts by further coordi-
and then easily recycled after reactions for subsequent reuse. nating Ru-PPh2-Ts with DPEN-ligand, where DPEN refers to
To date, only a few recyclable homogeneous catalysts have (1R,2R)-1,2-diphenylethylenediamine. DPEN-Ru-PPh2-Ts could
been reported, which can be settled down and recycled by act as a homogeneous chiral catalyst in CH2Cl2-medium organic
interphase,4 clathrate-enabled,5 ionic-6 and fluorous-tagged,7 reactions with high efficiencies and ee values. After each round
of reactions, it could also be totally recovered by adding pentane
and then used repeatedly many times. Obviously, these homo-
geneous silylated catalysts combine the advantages of both the
typical homogeneous and heterogeneous catalysts.
A general approach to prepare silylated organometals
(M-PPh2-Ts and DPEN-Ru-PPh2-Ts) is illustrated in Scheme 1
aKey Laboratory of Carbon Materials, Institute of Coal Chemistry, Chinese Academy
of Sciences, Taiyuan 030001, P. R. China. E-mail: jlhuang@sxicc.ac.cn
bThe Chinese Education Ministry Key Lab of Resource Chemistry, Shanghai
University of Electric Power, Shanghai 200090, P. R. China.
E-mail: Hexing-Li@shnu.eud.cn
cThe College of Nuclear Technology, Chemistry and Biology, Hubei University of
Science and Technology, Xianning, Hubei 437100, P. R. China.
E-mail: haibingguojj@yahoo.com
dDepartment of Chemistry and Chemical Biology, Northeastern University, Boston,
Massachusetts 02115, United States. E-mail: G.O'Doherty@neu.edu
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
c4gc01586j
(see ESI† for experimental details). It is noteworthy that when
the resulting complex was treated with pentane, it was precipi-
tated out and a pure product was obtained after washing with
pentane without using chromatography. This implies that the
silylated complex can indeed be easily purified and potentially
recycled. To determine the catalyst compositions, the metal
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DPEN-Ru-PPh2-Ts displayed three signals at around 20, 35,
and 47 ppm, corresponding to three kinds of P-Ru coordi-
nation models.15 Meanwhile, according to the FTIR spectra
(Fig. S2†), all the M-PPh2-Ts samples displayed absorbance
bands at around 695, 2897, 2973, 1439, and 1083 cm−1 due to
the asymmetric and symmetric stretching vibrations of C–H,
P–CH2, Si–O bonds, and the -H out-of-plane deformation of
the monosubstituted benzene ring.16 The DPEN-Ru-PPh2-Ts
exhibited a new absorption band at 1641 cm−1 owing to the
N–H stretching vibration.17 Furthermore, the TG curves
(Fig. S3†) revealed a total weight loss of around 60.2% at
around 250 °C for all the M-PPh2-Ts samples, which could be
attributed to the subsequent combustion of the PPh2-CH2-
CH2- and the C2H5-groups, in good accordance with theoretical
values. The DPEN-Ru-PPh2-Ts showed 10% more weight loss
resulting from the removal of the additional DPEN ligand. In
addition, the XPS spectra (Fig. S4†) revealed that all the Pd
and Ru species were present in the +2 oxidation state while the
Rh species were present in the +1 oxidation state, corres-
ponding to binding energies (BE) of 338.0, 280.6 and 307.7 eV
in the Pd3d5/2, Ru3d5/2 and Rh3d5/2 levels, respectively.18 One
could see that the metallic ions in either M-PPh2-Ts or M
(PPh3)xCly (M = Pd2+ and Rh+) displayed slightly lower BE than
the corresponding ones in M(COD)Cl2, which confirmed the
coordination between metallic ions with the PPh2 or the PPh3
ligand instead of the COD ligand, making metallic ions more
electron-enriched owing to the stronger electron-donating
ability of PPh2 or PPh3 than that of COD. Moreover, the met-
allic ions in the M-PPh2-Ts (M = Pd2+, Rh+, and Ru2+) exhibited
slightly lower BE than the corresponding ones in M(PPh3)xCly,
implying the weaker electron-donation ability of the PPh3-
ligand than PPh2-CH2-CH2-ligand. This could be easily under-
stood by considering the conjugated system between one
P atom with three Ph groups. The PPh2-CH2-CH2-ligand con-
tains a conjugated system between one P atom and two Ph
rings, while the PPh3-ligand contains a bigger conjugated
system between one P atom and three Ph rings, which might
dilute the electron density on the P atom, leading to the lower
electron-donating ability.19 In comparison with the Ru-PPh2-
Ts, no significant BE shift was observed in the DPEN-Ru-PPh2-
Ts, suggesting the similar electron-donating ability of the
DPEN-ligand to that of the PPh2-CH2-CH2-ligand.
Scheme 1 Illustration of the catalyst preparation.
contents were determined by inductively coupled plasma
spectrometer (ICP, Varian VISTAMPX), while the C, N, and H
contents were detected by elemental analysis (Elementar Vario
ELIII, Germany). Some results are listed as follows (see the
structural formula of catalysts in Scheme S1†): (1) Pd-PPh2-Ts
= Pd(II)[PPh2CH2CH2Si(OEt)3]2Cl2: calculation values, C (51.64)
and H (6.28), experimental results, C (51.59) and H (6.22). (2)
Rh-PPh2-Ts
=
Rh(I)[PPh2CH2CH2Si(OEt)3]3Cl: calculation
values, C (56.84) and H (6.92), experimental results, C (56.64),
H (6.85). (3) Ru-PPh2-Ts = Ru(II)[PPh2CH2CH2Si(OEt)3]3Cl2:
calculation values, C (55.37), H (6.74), experimental results,
C (55.55) and H (6.74). (4) DPEN-Ru-PPh2-Ts = Ru(II)[(DPEN)/
PPh2CH2CH2Si(OEt)3]3Cl2: calculation value,
C (55.37), N
(1.85) and H (6.74), experimental results, C (55.31), N (1.81)
and H (6.75). The sample compositions and structures could
be further determined by NMR spectra (Fig. S1†). The 1H NMR
(CDCl3) spectra displayed characteristic peaks at 7.2–7.5,
7.6–7.7 (2 m, ArH), 3.71 (q, CH2CH2), 2.47 (m, CH2P), 1.13 (t,
CH3CH2), and 0.79 (m, SiCH2). The DPEN-Ru-PPh2-Ts dis-
played two new peaks around 4.1 and 5.2 ppm, indicative of
the H–N group.11 Meanwhile, the 13C NMR spectra exhibited
two peaks at 18 and 30 ppm, corresponding to two C atoms in
the ethyl group connecting with the PPh2 terminal. The peak
at 58 ppm was attributed to the Cb atom in the CaH3CbH2O–Si
group. An intense peak at 133 ppm was assigned to the
C atoms in the benzene ring.12 The DPEN-Ru-PPh2-Ts dis-
played two additional peaks around 29 and 62 ppm, character-
istic of two C atoms in the ethyl group connecting with the
NH2 terminal.13 The 29Si NMR spectra (Fig. S8†) of the PPh2-
Ts, and Pd-PPh2-Ts catalyst displayed an intense signal at
−47.1 ppm, which demonstrated that only one Si chemical
environment existed in the two samples. No obvious Qn peaks
were observed, where Qn = Si(OSi)n-(OH)4−n, n = 2–4, indicating
that the Pd-PPh2-Ts catalyst did not undergo hydrolysis and
condensation reactions under the present conditions. There is
a very small wide peak at about −110 ppm (Q4), which was
attributed to the hydrolysis and condensation of very few
Si(OEt)3 groups, as it is very difficult to completely exclude air
when conducting the NMR experiments. The 31P NMR spectra
further showed the intense signals around 21.2, 39.2 and
38.7 ppm indicative of the Pd-PPh2, Rh-PPh2 and Ru-PPh2
coordination bonds in the Pd-PPh2-Ts, Rh-PPh2-Ts, and
Ru-PPh2-Ts samples,14 respectively. The different peak posi-
tions could be attributed to the different chemical environ-
ments of the P atoms due to the change of metallic ions. The
The catalytic performances of the as-prepared organometals
were examined in various organic reactions including Pd-cata-
lyzed Suzuki coupling reactions (Table 1),20 Rh-catalyzed alde-
hyde methylenation reactions (Table 2),21 Ru-catalyzed
homoallylic alcohol isomerization reactions (Table 3),22 DPEN/
Ru-catalyzed asymmetric hydrogenations of acetophenone
(Table 4),23 Pt-catalyzed carboselenation of alkynes by seleno-
esters (Table S1†), and Ir-catalyzed transfer hydrogenation
reactions (Table S2†). In these reactions, all the M-PPh2-Ts cat-
alysts and the DPEN-Ru-PPh2-Ts chiral catalyst could be com-
pletely dissolved in the THF, CH2Cl2 or toluene used as the
reaction media and precipitated at the end of organic reactions
by adding fresh pentane. The catalytic performance of the
Pd-PPh2-Ts was examined for the Suzuki coupling reactions in
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Table 1 Pd-catalyzed Suzuki coupling reactionsa
Table 3 Ru-catalyzed isomerization reactionsa
R1
R2
X
Yield (%)
Time Conversion Selectivity Yield
Entry
Catalyst
R
(h)
(%)
(%)
(%)
1
2
3
4
5
6
7
8
H
H
H
4-NO2
2-NO2
2-NO2
4-Me
2-Me
4-OMe
H
H
H
H
4-NO2
4-NO2
H
H
H
H
H
H
H
H
H
H
4-F
4-F
4-F
4-OMe
4-OMe
F
4-OMe
4-OMe
4-OMe
4-OMe
4-OMe
4-OMe
Cl
Br
I
I
Br
I
I
I
I
Cl
Br
I
Cl
I
I
I
Br
Br
I
I
I
41 (36)
89 (84)
Ru-PPh2-Ts
H
10
91
90
79
77
77
73
70
69
58
Ru(PPh3)3Cl2
92 (89)
Ru-PPh2-PMO(Ph)b
96 (98) 86c
88 (92)
Ru-PPh2-Ts
Ru(PPh3)3Cl2
CH3 12
94
94
75
76
71
71
90 (93)
80 (84)
78 (75)
82 (85)
30 (24)
60 (62)
72 (68)
a Reaction conditions: a catalyst with 0.032 mmol Ru(II), 25 µl of
homoallylic alcohol, 5.0 ml of CH2Cl2, 40 °C, 10 h. b Ru–PPh2–PMO-
(Ph) catalyst used from ref. 12.
9
10
11
12
13
14
15
16
17
18
19
20
21
34 (27)
91 (95) 93b 80c
61 (63)
Table 4 Ru-catalyzed asymmetric ketone hydrogenationsa
78 (77)
H
75 (72) 65c
Trace
4-CONH2
4-NH2
4-CO2C2H5
4-CN
29 (31) 33b
75 (76) 66c
93 (96) 82c
Catalyst
R
Conversion (%)
ee (%)
a Reaction conditions: 0.50 mmol arylhalide, 0.60 mmol
organoboronic acid, 1.0 mmol K2CO3, 5.0 ml of THF and a catalyst
containing 0.021 mmol Pd(II), 25 °C, 24 h. The data in brackets were
obtained from the Pd(PPh3)2Cl2 catalyst. b The Pd(PPh3)4 catalyst used.
c The Pd-PPh2-PMO(Ph) catalyst used from. ref. 12.
Ru(PPh3)3Cl2+DPEN
DPEN-Ru-PPh2-Ts
H
99
97
68
70
Ru(PPh3)3Cl2+DPEN
DPEN-Ru-PPh2-Ts
CH3
98
98
71
72
Table 2 Rh-catalyzed aldehyde methylenation reactionsa
Ru(PPh3)3Cl2+DPEN
DPEN-Ru-PPh2-Ts
CH3O
99
98
72
73
a Reaction conditions: a catalyst with 5.0 μmol Ru(II), 0.50 mmol
ketone, 1.0 ml of propanol, 0.10 mmol potassium tert-butoxide, 5.0 ml
of CH2Cl2, 50 °C, 36 h.
Time
(h)
Conversion
(%)
Selectivity
(%)
Yield
(%)
Entry
R
1
2
3
4
5
6
7
8
9
Ph
1
4
4
1
2
2
6
8
8
96 (95)
97 (94)
89 (89)
94 (92)
72 (78)
76 (79)
93 (90)
68 (60)
88 (94)
84 (86)
90 (94)
90 (88)
87 (90)
96 (96)
93 (94)
91 (92)
96 (97)
89 (88)
85 (83)
84 (87)
86 (89)
87 (83)
77 (80)
90 (88)
67 (73)
69 (73)
89 (87)
61 (53)
75 (78)
71 (75)
Ts exhibited comparable catalytic activities owing to the
similar coordination model and chemical micro-environment
of the Pd(II) active sites. The Suzuki reactions with chloro-
benzene exhibited much lower product yields than either
those with bromobenzene or iodobenzene since the activation
of the C–Cl bond was much more difficult than that of either
the C–Br or the C–I bond. The electron withdrawing groups on
the aryl halides promoted the reactions while the electron
donating groups disfavored the reactions. Similarly, the elec-
tron contributing groups on the arylboronic acids were also
detrimental to the reaction.
4-Cl–Ph
2-Cl–Ph
Ph–CvC
4-CH3–Ph
4-CH3O–Ph
C–C
2-OH–Ph
4-OH–Ph
4-NO2–Ph
10
12
a Reaction
conditions:
1.0
mmol
aldehydes,
1.4
mmol
trimethylsilyldiazomethane, 1.1 mmol iPrOH, 1.1 mmol PPh3, 5.0 ml
of THF and a catalyst with 0.030 mmol Rh(I), 25 °C. The data in
brackets were obtained from the Rh(PPh3)Cl catalyst.
As shown in Tables 2 and 3, both the Rh-PPh2-Ts and the
Ru-PPh2-Ts catalysts displayed almost identical activities and
selectivities with their corresponding Rh(PPh3)Cl and Ru-
(PPh3)3Cl2 homogeneous catalysts in THF-medium aldehyde
methylenation reactions and CH2Cl2-medium homoallylic
alcohol isomerization reactions, respectively, which further
confirms the similar coordination models and chemical micro-
environment of the metal active sites. In the aldehyde
methylenation reactions, both the benzaldehyde and the cin-
namaldehyde displayed much higher activities than the pro-
THF solution (Table 1). Non-silylated Pd(PPh3)2Cl2 and
Pd(PPh3)4 (entries 14 and 19, Table 1) and the Pd-PPh2-PMO
(Ph) catalyst12 (entries 4, 14, 17, 20 and 21, Table 1) were used
in parallel for comparison under the same reaction conditions
and the yields are provided in brackets. All these reactions
were absolutely selective for the target products under the
present conditions since no significant side products were
identified by GC-MS. As homogeneous catalysts, the Pd-PPh2-
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Table 5 Catalyst recycling efficiencies by adding pentanea
paldehyde, possibly owing to the conjugated system, which
favored the formation of the carbon cation connecting with
the O atom and thus facilitated the attack by the trimethylsilyl-
diazomethane molecule. The presence of either the electron-
withdrawing or the electron-donating groups on the Ph ring
connecting with the CvO greatly decreased the activity,
obviously due to the steric hindrance for the attack of the
trimethylsilyldiazomethane molecule with very large size.
Similarly, the Pt-PPh2-Ts catalyst also exhibited equivalent
efficiencies with the traditional Pt(PPh3)2Cl2 homogeneous cata-
lyst in the toluene-medium cyclization of propargylic esters (see
Table S1†), while the Ir-PPh2-Ts displayed nearly the same
efficiencies as the [Ir(COD)Cl]2 and phosphine homogeneous
catalyst system in the toluene-medium transfer hydrogenation
reactions of ketones (see Table S2†). Moreover, Table 4 further
indicates that, during the CH2Cl2-medium asymmetric hydro-
genation of ketones, the DPEN-Ru-PPh2-Ts chiral catalyst also
displayed comparable conversion and ee value to the traditional
homogeneous system comprised of soluble RuCl2(PPh3)3 and
DPEN chiral reagent. These results clearly demonstrated the
general properties of the as-prepared homogeneous catalysts.
The most important advantage of the present family of sily-
Separation
efficiency (%)
Metal leaching
(ppm)
Catalyst
Solvent
Pd-PPh2-Ts
Rh-PPh2-Ts
Pt-PPh2-Ts
Ir-PPh2-Ts
Ru-PPh2-Ts
DPEN-Ru-PPh2-Ts
THF
THF
Toluene
Toluene
CH2Cl2
CH2Cl2
99.4
99.6
99.1
98.7
98.4
99.0
2.5
2.4
2.0
2.6
2.8
1.4
a Reaction conditions: see Tables 1–4, and Tables S1, S2 respectively.
lated organometals (M-PPh2-Ts and DPEN-Ru-PPh2-Ts) is that Fig. 2 Recycling test of catalysts in Suzuki reaction of 4-nitroiodo-
benzene with phenylboronic acid, methylenation reaction of cinnamal-
dehyde with trimethylsilyldiazomethane, and isomerization reaction of
1-phenyl-3-buten-1-ol.
they could be used as homogeneous catalysts with high
efficiencies in various organic reactions using THF, CH2Cl2 or
toluene solvent as the reaction medium. After reaction, they
could be totally settled down by adding fresh pentane for reuse
in subsequent runs of the reactions. Fig. 1 clearly demon-
catalyst could also be reused (see Table S3†). Besides the high
recycling efficiency of the catalysts with negligible loss of
strated that the Pd-PPh2-Ts, Rh-PPh2-Ts, Ru-PPh2-Ts, and
metal active sites (see Table 5), the identical XPS spectra
DPEN-Ru-PPh2-Ts catalysts could be absolutely dissolved in
1
(Fig. S5†), H NMR spectra (Fig. S6†), FTIR spectra (Fig. S7†),
THF or CH2Cl2 and could then be completely precipitated by
adding fresh pentane. Similarly, we also found that both the
Pt-PPh2-Ts and the Ir-PPh2-Ts catalysts could be totally dis-
microenvironment of metal active sites after being reused,
solved in toluene and could then be completely settled down
by adding fresh pentane. From Table 5, one could see the high
catalyst separation efficiencies of the as-prepared silylated
29Si NMR and 31P NMR spectra (Fig. S8†) clearly demonstrated
the preservation of the catalyst structure and the chemical
which could sufficiently account for the excellent durability of
the catalysts upon recycling.
organometals from the THF, CH2Cl2 or toluene solutions with
the neglected metal leaching by adding fresh pentane,
showing excellent catalyst recycling efficiencies. An increase in
Conclusions
the solvent quantity or decrease in the temperature could
further decrease the metal leaching.
In summary, this work developed a general way to design Pd-,
Rh-, Ru-, Pt-, and Ir-based silylated organometals as a new
As shown in Fig. 2, the Pd-PPh2-Ts, Rh-PPh2-Ts and
family of recyclable homogeneous catalysts, since they could
Ru-PPh2-Ts catalysts could be used repeatedly more than
be used as homogeneous catalysts in THF-, CH2Cl2- or
6
times without significant deactivation. Similarly, the
toluene-medium organic reactions and could be easily recycled
by adding pentane after the reactions. The catalysts could be
used repeatedly without significant deactivation. Other sily-
lated organometals could also be synthesized, which may
enlarge the catalyst family and thus offer more opportunities
for industrial applications.
Pt-PPh2-Ts, Ir-PPh2-Ts as well as the DPEN-Ru-PPh2-Ts chiral
Experimental section
General
Fig. 1 Representative pictures indicating the alternative dissolving and
precipitating of (a) Pd-PPh2-Ts, (b) Rh-PPh2-Ts, (c) Ru-PPh2-Ts, and (d)
DPEN-Ru-PPh2-Ts in THF or CH2Cl2 solvent and pentane.
The following general procedures were applied for all experi-
ments in this work. Unless specifically stated, all organic reac-
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tions were performed under water-free atmosphere with absol- used were of spectrophotometric purity, dried over a molecular
ute exclusion of moisture from all reagents, solvents and glass- sieve, degassed, and stored under argon. In order to determine
ware. The reproducibility was checked by repeating each the catalyst durability, any solids in the reaction system were
experiment at least three times and was found to be within first filtered after each reaction run and the solids were
acceptable limits ( 5%).
washed more than two times with dry solvent. After being con-
centrated to about 2.0 ml, 2 times volume of dry pentane
(about 4.0 ml) was added and then the silylated organometal-
Catalyst preparation
In a typical synthesis run, 2.7 g of PPh2CH2CH2Si(OEt)3 was lic catalyst in the solution was precipitated, typically at 25 °C,
added dropwise into a suspension comprised of 1.0 g of Pd- using 4.0 ml of pentane for about 2 min (if at 5 °C, 2.0 ml of
(COD)Cl2 (COD = 1,5-cyclooctadiene) and 25 ml of toluene. pentane for about 30 s), followed by decanting the solvents,
The mixture was kept stirring until it reached a clear orange washing with fresh pentane and vacuum drying at 60 °C over-
solution. After being concentrated to 5.0 ml, 25 ml of pentane night. Then, the catalyst was re-used with fresh THF, CH2Cl2
was added, leading to the Pd-PPh2-Ts catalyst in yellow solid, or toluene and reactants for subsequent runs of reactions
which was washed thoroughly with pentane more than three under identical conditions.
times. The remaining yellow solid was dried at 60 °C and 0.10
Torr to remove residual solvents, leading to the Pd-PPh2-Ts
catalyst. The preparation of M-PPh2-Ts (M = Rh+, Pt2+, Ir+ and
Acknowledgements
Ru2+) and the chiral catalyst DPEN-Ru-PPh2-Ts followed
similar procedures. Detailed preparation procedures are This work was supported by the National Natural Science
described in the ESI.†
Foundation of China (21237003, 21202136, 21261140333),
Shanghai Key Lab of Rare-Earth Functional Materials, the
National Natural Science Foundation of China (21403274,
Characterization
The carbon and hydrogen contents in the samples were deter- Y5JJ7A1771) and Young Research Fund of Institute of Coal
mined by elemental analysis on a CHN analyzer (Elementar Chemistry, Chinese Academy of Sciences (2014SCXQT01).
Vario ELIII, Germany). Contents of palladium, ruthenium,
rhodium, silica, nitrogen, and phosphor were determined by
inductively coupled plasma spectrometer (ICP, Varian VIS-
TAMPX). The catalyst structure was characterized by FTIR
Notes and references
spectra (Nicolet Magna 550), NMR spectra (Bruker AV-400) and
thermogravimetry (TG, Shimadzu DT-60). The surface elec-
tronic states were analyzed by X-ray photoelectron spectroscopy
(XPS, PerkinElmer PHI 5000C). All the binding energy (BE)
values were calibrated using the standard BE value of contami-
nant carbon (C1S = 284.8 eV) as a reference.
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Activity test
Generally, the catalytic performances were examined in
various organic reactions including Pd-catalyzed Suzuki coup-
ling reactions (Table 1), Rh-catalyzed aldehyde methylenation
reactions (Table 2), Ru-catalyzed homoallylic alcohol isomeri-
zation reactions (Table 3), Pt-catalyzed carboselenations of
alkynes by selenoesters (Table S1†), Ir-catalyzed transfer hydro-
genation reactions (Table S2†), and DPEN/Ru-catalyzed asym-
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specially stated, all organic reactions were performed under a
water-free atmosphere with absolute exclusion of moisture
from all reagents, solvents and glassware. The reaction con-
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products were analyzed by GC, GC-MS and HPLC-MS. The
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