Heterogeneous Hydrothiolation of Alkynes with Thiols
139
the Suzuki–Miyaura reaction, the Sonogashira reaction,
and the Stille reaction, etc. [23–25]. However, carbon–
carbon bond or carbon-heteroatom bond formation reac-
tions catalyzed by heterogeneized rhodium complexes have
received less attention.
with benzene (5 9 10 mL), and dried at 70 °C/26.7 Pa
under an argon atmosphere for 3 h to give 2.34 g of the
light yellow rhodium complex [MCM-41-2P-RhCl(PPh3)].
The phosphine and rhodium content was 1.74 mmol/g and
0.39 mmol/g, respectively.
Developments on the mesoporous material MCM-41
provided a new possible candidate for a solid support for
immobilization of homogeneous catalysts [26]. MCM-41
has a regular pore diameter of ca.5 nm and a specific surface
area [ 700 m2g-1 [27]. Its large pore size allows passage of
large molecules such as organic reactants and metal com-
plexes through the pores to reach to the surface of the channel
[28–30]. Shyu et al. [31] reported phosphinated MCM-41-
supported rhodium complex for catalytic hydrogenation of
olefins and found that it is an excellent hydrogenation cata-
lyst with turnover frequency (TOF) three times higher than
that of RhCl(PPh3)3 in the hydrogenation of cyclohexene.
However, to the best of our knowledge, no hydrothiolation
reaction of alkynes with thiols catalyzed by a heterogeneized
rhodium complex has been reported until now. In this paper,
we wish to report the synthesis of diphosphino-functiona-
lized MCM-41 anchored rhodium complex [abbreviation:
MCM-41-2P-RhCl(PPh3)] and its catalytic properties in the
hydrothiolation reaction of alkynes with thiols.
2.2 General Procedure for the Hydrothiolation
of Alkynes with Thiols
In a 20 mL two-necked glass flask with a magnetic stirring
bar under an argon atmosphere were placed MCM-41-2P-
RhCl(PPh3) (77 mg, 0.03 mmol), EtOH (2 mL), and
alkyne (1.0 mmol). Then thiol (1.1 mmol) was added
dropwise to the solution over 1 h at 40 °C. The reaction
was continued with magnetic stirring for 24 h at 40 °C.
The mixture was diluted with Et2O (30 mL). The MCM-
41-2P-RhCl(PPh3) catalyst was separated from the mixture
by filtration, washed with EtOH (2 9 10 mL), Et2O
(2 9 10 mL) and reused in the next run. The solvent was
removed in vacuo, and the residue was purified by Flash
chromatography on silica gel to give the desired product.
3 Results and Discussion
The novel diphosphino-functionalized MCM-41 anchored
rhodium complex [MCM-41-2P-RhCl(PPh3)] was conve-
niently synthesized by the reaction of diphosphino-func-
tionalized MCM-41 (MCM-41-2P) with RhCl(PPh3)3
(Scheme 1). Small angle X-ray powder diffraction (XRD)
analysis of the MCM-41-2P-RhCl(PPh3) indicated that, the
100 reflection of MCM-41-2P-RhCl(PPh3) had lower
intensity compared to that of the parent MCM-41, while
the 110 and 200 reflections became weak and diffuse,
which could be due to contrast matching between the sil-
icate framework and organic moieties which are located
inside the channels of MCM-41. Therefore, the basic
structure of the parent MCM-41 was not damaged in the
whole process of catalyst preparation. Elemental analyzes
and solid state 31P NMR were used to characterize the
supported rhodium complex [MCM-41-2P-RhCl(PPh3)].
The P:Rh mole ratio of the MCM-41-2P-RhCl(PPh3) was
determined to be 4:5. Blumel et al. [33, 34] investigated the
silica-supported phosphine rhodium complexes by solid
state 31P NMR spectroscopy. Solid state 31P NMR of
MCM-41-2P showed a signal at d -23.1 ppm, which fur-
ther indicates that the mesoporous material MCM-41-2P
contains phosphorus. Solid state 31P NMR of MCM-41-2P-
RhCl(PPh3) showed three signals at d -23.1, 12.2, and
31.3 ppm, respectively (Fig. 1b). One of these corresponds
to the unreacted anchoring ligand while the other two are
assigned to the anchoring ligand and triphenylphosphine
ligand coordinated to the Rh complex since they are shifted
2 Experimental
The diphosphino-functionalized mesoporous material
MCM-41-2P was prepared according to our previous pro-
cedure, the phosphine content was 1.44 mmol/g [32]. Other
reagents were obtained from commercial suppliers and
purified by distillation. All hydrothiolation products were
characterized by comparison of their spectra and physical
data with authentic samples. IR spectra were determined on
a Perkin–Elmer 683 instrument. 1H NMR spectra were
recorded on a Bruker AC-P400 (400 MHz) spectrometer
with TMS as an internal standard in CDCl3 as solvent.
13C NMR spectra were recorded on a Bruker AC-P400
(100 MHz) spectrometer in CDCl3 as solvent. X-ray
powder diffraction patterns were obtained on Damx-rA
(Rigaku). 31P one-pulse experiments were performed on a
Bruker AMX 400 spectrometer at a 31P frequency of
161.98 MHz at room temperature. Chemical shifts were
referenced to Na2HPO4 at 0 ppm. Microanalyses were
obtained using a Perkin–Elmer 240 elemental analyzer.
2.1 Preparation of MCM-41-2P-RhCl(PPh3)
To a solution of RhCl(PPh3)3 (1.109 g, 1.2 mmol) in
benzene (50 mL) was added MCM-41-2P (2.04 g). The
mixture was stirred under an argon atmosphere at 25 °C for
48 h. The solid product was filtered by suction, washed
123