Preparation of tethered palladium catalysis supported on gold(111) and its surface characterization by X-ray photoelectron spectroscopy (XPS)

Article abstract of DOI:10.1246/bcsj.81.1012

Chelated tethering ligands were confined on a Au(111) substrate, and the confinement of the ligands was confirmed by X-ray photoelectron spectroscopy (XPS). Palladium was anchored to the ligands to construct heterogeneous (Pd)-L-Au(111) catalysts (L = lig

Full text of DOI:10.1246/bcsj.81.1012

1012 Bull. Chem. Soc. Jpn. Vol. 81, No. 8, 1012–1018 (2008)
ꢀ 2008 The Chemical Society of Japan
Preparation of Tethered Palladium Catalysis Supported
on Gold(111) and Its Surface Characterization
by X-ray Photoelectron Spectroscopy (XPS)
Rabbani M. Gulam,1 Masahiro Hamada,2 Ikuko Takamiya,2 Masahiko Shimoda,3
ꢀ1;2
Satoshi Shuto,1 Atsushi Nishida,2 Shiro Tsukamoto,4 and Mitsuhiro Arisawa
1Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita 12, Nishi 6, Kita-ku, Sapporo 060-0812
2Graduate School of Pharmaceutical Sciences, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522
3National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047
4The Anan National College of Technology, 265 Aoki, Minoubayashi-cho, Anan 774-0017
Received March 12, 2008; E-mail: arisawa@pharm.hokudai.ac.jp
Chelated tethering ligands were confined on a Au(111) substrate, and the confinement of the ligands was confirmed
by X-ray photoelectron spectroscopy (XPS). Palladium was anchored to the ligands to construct heterogeneous {Pd}–L–
Au(111) catalysts (L = ligand). A {Pd}–Au(111) catalyst was also prepared by adsorbing the Pd complex directly on the
Au(111) substrate without a tethering ligand. Both types of catalysts were used in the Mizoroki–Heck reaction to eval-
uate their catalytic activities. The tether-ligated Pd catalyst {Pd}–L–Au(111) activity decreased with recycling, whereas
the {Pd}–Au(111) catalyst was quite stable upon reuse. The surfaces of both catalyst types were evaluated using XPS to
determine the presence of tethering ligands and/or Pd on the Au(111). The ligands of the tether-ligated Pd catalysts
could not be detected on the Au(111) surface after the Mizoroki–Heck reaction, which suggests weak bonding of the
S–Au by which the ligand is bound to the Au(111) substrate.
The development of efficient methods to facilitate the recov-
ery and reuse of organometallic catalysts is an important goal in
catalytic organic chemistry. Organopalladium catalysts are
widely used to yield a wide variety of organic compounds.1
The Pd-catalyzed Mizoroki–Heck reaction2 has received con-
siderable attention as it offers a versatile method for carbon–
carbon bond formation.3 For this reaction to be industrially fea-
sible, it is particularly important to reduce both the loss and
presence of Pd catalysts in the product solution due to the ex-
pense and toxicity. Heterogeneous catalysis is a promising op-
tion for solving these problems and a variety of heterogeneous
Pd catalysts have been developed.4 Polymer- or silica-support-
ed tether ligands containing P, S, or nitrogen-containing hetero-
cyclic carbene (NHC) donor centers are well-defined candi-
dates for the construction of heterogeneous Pd catalysts and
they have been used as recyclable catalysts for cross-coupling
reactions.5 Recently, we reported the development of novel het-
erogeneous Pd catalysts supported on a sulfur-terminated semi-
conductor GaAs(001) and evaluated their catalytic activities in
cross-coupling reactions.6 This catalyst was easily recovered
and handled in aerobic conditions, and exhibited high activity
and stability during recycling in the Mizoroki–Heck reaction.6d
However, its surface is complicated due to the existence of sev-
eral S and Pd species and it was rather difficult to know the
actual active species of this catalyst. On the other hand, immo-
bilization of molecular catalyst onto crystalline Si(111) surface
has also been used to the surface-attached polymerizaton.6e
Tethered palladium catalyst onto crystalline silicon, Si(111)–
BOX–Pd, has been reported as a recyclable catalyst in the aero-
bic oxidation of benzylic alcohols.6f These findings prompted
us to construct the much more simplified heterogeneous cata-
lyst by anchoring the Pd to the metal substrate functionalized
with P-, S-, or N-containing chelating tethering ligands.
Gold is a fascinating metal substrate for the adsorption of
organic molecules due to the fact that it does not form a sur-
face oxide under atmospheric conditions and its surface is sat-
isfactorily inert to many chemicals, but it easily chemisorbs
thiols (RSH), disulfides (RSSR), and dialkylsulfides (RSR),
which spontaneously organize into self-assembled monolayers,
and it has thus been investigated extensively in recent years.7,8
The self-assembled monolayers of functionalized tether mole-
cules on gold are capable of undergoing chemical reactions un-
der mild conditions.9 Some transition-metal complexes teth-
ered on gold powder are also catalytically active.10 However,
as far as we know, experiments to know the strength of S–
Au bonding have not been reported.
In the present study, we attempted to confine the P, S, or
NHC donor center-containing chelating tethering ligands on
Au(111) film. These ligand-modified Au(111) films were re-
acted with Pd sources to prepare tethered Pd complexes
supported on Au(111) substrate and then applied to the
Mizoroki–Heck reaction to evaluate their catalytic activity.
The existence of the tether ligands on the gold surface was
also examined by X-ray photoelectron spectroscopy (XPS).
Published on the web August 11, 2008; doi:10.1246/bcsj.81.1012

R. M. Gulam et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 8 (2008) 1013
Br
1) BnBr, toluene
100 °C, 3 h
( )2
Br
Grubbs cat. 2nd gen.
H2, Pd/C
2) NaH, PhCHO
THF, rt, 12 h
84% (2 steps)
Ph2P
Ph2P
Ph2P
CH2Cl2, reflux, 1 h
76%
EtOH,
100 °C, 6 h
91%
O
2A
O
1A
1) (NH2)2CS, EtOH
120 °C, 3 h
( )4
( )4
( )4
HSiCl3, Et3N
Br
S
S
toluene
reflux, 3 h
55%
2) aq. NaOH,
120 °C, 2 h
93% (2 steps)
Ph2P
Ph2P
Ph2P
O
O
2
2
3A
4A
A
Scheme 1. Synthesis of ligand A.
O
O
Cl
Cl
OH
1) LiAlH4, THF
reflux, 15 h
OMe
OMe
NaSPh, THF
SOCl2 , pyridine
AcHN
AcHN
H2N
reflux, 19 h
76%
CH2Cl2, rt, 18 h
86%
2) Ac2O, Et3N
THF, rt, 4 h
57% (2 steps)
OH
1B
2B
O
SPh
SPh
SPh
SPh
O
S
OH
2
NaOH (aq.)
H2N
S
N
H
AcHN
MeOH
DCC, HOBt
reflux, 22 h
2
SPh
CH2Cl2, DMF
rt, 24 h
SPh
4B
76%
3B
B
98%
Scheme 2. Synthesis of ligand B.
O
1) EtOH,
Br
Br
( )12
Br
Br
( )12
( )12
aq. NaOH
KSCOCH3
( )12
S
SH
N
N
N
N
N
N
N
N
0 °C, 1 h
Br
Br
CH2Cl2
reflux, 12 h
80%
THF
reflux, 6 h
97%
2C
2) 2M HBr
88%(2 steps)
1C
C
Scheme 3. Synthesis of ligand C.
ligand B [L(B)–Au(111)] was prepared by immersing the
Au(111) plate in 1 mmol dmꢁ3 ligand B solution in chloro-
form–methanol (19:1) at 50 ꢂC for 12 h.8b The plate was re-
moved from the solution and rinsed with the same solvent mix-
ture and dried under a stream of Ar gas. The Au(111) film
modified with ligand C [L(C)–Au(111)] was prepared by im-
mersing the Au(111) plate in 1 mmol dmꢁ3 thiol-terminated
ligand C solution in absolute ethanol at room temperature
for 3 h.11 The plate was removed from the solution and rinsed
with ethanol and dried under a stream of Ar gas. These ligand-
modified Au(111) films [L–Au(111)] were examined by XPS.
Surface Characterization by XPS 1. The surface of the
L–Au(111) films was characterized by XPS (Figure 1). Spectra
a, b, c, and d correspond to L(A)–Au(111), L(B)–Au(111),
L(C)–Au(111), and pure Au(111) films, respectively. A clear
peak due to C 1s was observed in spectra a, b, and c, which
suggests the presence of organic molecules on the Au(111)
surface. Characteristic peaks due to P, S, or N atoms were con-
sidered as the evidence of ligand confinement on the Au(111)
surface. The peak due to P for ligand A was not detected in
Results and Discussion
Preparation of Tethering Ligands and Adsorption of
Ligands on Au(111) Substrate. The tethering ligands con-
taining P, S, and NHC donor centers were synthesized accord-
ing to Schemes 1, 2, and 3, respectively, and are referred to as
ligand A, B, and C, respectively. The ligands were allowed to
adsorb onto the Au(111) substrate to prepare ligand-modified
Au(111) film (L–Au(111)) and then reacted with the Pd source
to obtain the expected catalysts {Pd}–L–Au(111).
Au(111) film deposited on a mica support was used as the
substrate for adsorption of the ligands. The Au(111) plate
was used as purchased or cleaned with piranha solution prior
to use for ligand adsorption. We prepared the Au(111) film
modified with ligand A [L(A)–Au(111)] by immersing the
Au(111) plate in 1 mmol dmꢁ3 ligand A solution in CHCl3 at
60 ꢂC for 12 h in Ar atmosphere. The plate was removed from
the solution and rinsed with CHCl3 and then dried under a
stream of Ar gas. Thereafter, the plate was kept in a glovebox
to avoid the oxidation of P. The Au(111) film modified with

1014 Bull. Chem. Soc. Jpn. Vol. 81, No. 8 (2008)
Tethered Pd Catalysis on Au(111) and Its XPS
Table 1. Catalytic Activities of the {Pd}–L(C)–Au(111) and {Pd}–Au(111) Catalysts in the Mizoroki–Heck Reaction
Entry Catalyst
Pd adsorption
Yield/%aÞ
1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th mean
1
2
3
4
5
6
7
C1
C1
C1
C2
C3
C4
WdÞ
Pd(OAc)2, THF, 50 ꢂC, 4 h
Pd(OAc)2, THF, 50 ꢂC, 4 h
Pd(OAc)2, THF, 50 ꢂC, 4 h
Pd(OAc)2, THF, 80 ꢂC, 4 h
Pd(OAc)2, THF, 50 ꢂC, 12 h
Pd(OAc)2, THF, 80 ꢂC, 12 h
100
12
82
93
73
61
75
6
47
35
87
81
73
—
37
29
93
98
68
—
20
58
72
99
69
—
22
37
56
89
51 79 61 75
58
—
—
37
30
67
83
71
—
15 19 23
—
—
—
—
9bÞ
33cÞ
41
59
86
27 28 32 35
49 59 34 32
99 87 86 89
Pd(dba)2, xylene, 85 ꢂC, 4 h 100 100 100 100 100 100 94 79 87
94
a) Yields were determined by NMR analysis. b) The Mizoroki–Heck reaction was performed at 50 ꢂC and the average
yield of two runs is shown. c) The Mizoroki–Heck reaction was performed at 80 ꢂC and the average yield of eight runs
is shown. d) Pd was directly adsorbed onto the Au(111) substrate without a tethering ligand.
Intensity/Arb.Unit
O
Catalyst
Et3N (1.25 equiv)
O
I
O
O
MeCN, (3 mL)
100 °C, 12 h
(0.5 mmol)
(1.25 equiv)
Scheme 4. Mizoroki–Heck reaction.
Preparation of Pd Catalysts. Based on the above results,
the adsorbed imidazolium ligand C was converted to a car-
bene-type ligand in the glovebox by treating the L(C)–
Au(111) film with potassium tert-butoxide (tBuOK) in
THF12 and then Pd was anchored by immersing the film in a
solution of Pd(OAc)2 in THF. The prepared catalyst, hereafter
called {Pd}–L(C)–Au(111), was rinsed with MeCN and dried
under a stream of Ar gas. Pd catalyst supported on Au(111),
{Pd}–Au(111), was also prepared by the direct adsorption of
Pd(dba)2 in xylene.
Catalytic Activity. The catalytic activities of the {Pd}–
L(C)–Au(111) and {Pd}–Au(111) catalysts in the Mizoroki–
Heck reaction of iodobenzene and methyl acrylate as a model
reaction were examined (Scheme 4). At the end of reaction,
the catalyst was removed from the reaction mixture and rinsed
several times with MeCN. The reaction mixture was concen-
trated in vacuo to obtain a residue. The yield of methyl
trans-cinnamate, which is the desired product of the reaction,
Binding Energy/eV
Figure 1. XPS spectra for the ligand-modified gold sur-
face. Spectra a, b, c, and d correspond to L(A)–Au(111),
L(B)–Au(111), L(C)–Au(111), and pure Au(111), respec-
tively.
spectrum a of the L(A)–Au(111) film. Although very weak
peaks at around 229 eV (S 2s) and 165 eV (S 2p) due to S were
observed in spectrum b, no peak due to N was detected for the
Au(111) film modified with ligand B. On the other hand, a
clear peak due to N 1s was observed at around 402 eV in spec-
trum c for the L(C)–Au(111) film. Notably, the N 1s peak for
L(C)–Au(111) was observed when the Au(111) film was used
without prior piranha treatment or after treatment with piranha
for 1 min or 1 h (some spectra not shown). Intense peaks due to
Au were observed for all three ligand-modified Au(111) films.
The presence of the Au peak does not necessarily indicate a
bare gold surface. Possible reasons for an intense Au signal
are as follows: The ligands covered the surface completely
but the layer was thin enough to allow photoelectrons to pen-
etrate through the film; or the ligands covered the surface par-
tially and the Au atoms were exposed. Based on the clear N 1s
peak, the above XPS results suggest that ligand C was surely
bound to the gold surface, whereas the results were ambiguous
for ligands A and B. The L(C)–Au(111) film was then applied
for preparation of the Pd catalysts.
1
was determined by H NMR spectroscopy. The recovered cat-
alyst was subjected to another reaction as a second run and this
procedure was repeated at least 10 times to evaluate the stabil-
ity of the catalyst. The catalytic activities for each run are
shown in Table 1.
The catalytic activities of the {Pd}–L(C)–Au(111) catalysts
depended on the Pd adsorption step as well as the Mizoroki–
Heck reaction temperature. Catalyst C1 prepared by Pd adsorp-
tion at 50 ꢂC for 4 h gave a 71% average yield from 10 succes-
sive Mizoroki–Heck reactions at 100 ꢂC (Entry 1). The yield
was considerably lower, however, for C1 at a lower reaction
temperature (Entries 2 and 3). Increasing the Pd adsorption
temperature did not promote the catalytic activities. Catalyst
C2 prepared by Pd adsorption at 80 ꢂC gave a 41% average
yield (Entry 4). The activities of both catalysts C1 and C2 de-
creased considerably after the second run. On the other hand,
catalysts C3 and C4, prepared by increasing the Pd adsorption
time, had increased activity at first and then decreased activity
(Entries 5 and 6). The surface characteristics of these catalysts

R. M. Gulam et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 8 (2008) 1015
Intensity/Arb.Unit
ent on the Pd adsorption step. The drastic decrease in catalytic
activity after the second run (Entries 1–4) suggested that the
S–Au bonds were cleaved during the Mizoroki–Heck reaction
and the tethered Pd complexes were washed away during the
first run. The increase in catalytic activities of the catalyst pre-
pared with a longer Pd adsorption time, however, suggests the
adsorption of excess nontethered Pd, which may possess lower
catalytic activity. After desorption of nontethered Pd, the cat-
alytic activity increased. This may indirectly suggest the cov-
erage of the tether ligand by excess Pd. If this is the case, then
the absence of a ligand for catalyst C1 before applied to
Mizoroki–Heck reaction according to the XPS measurements
(spectrum e in Figure 2) is not surprising.
Although our previously reported catalyst {Pd}–S–GaAs
was stable enough to survive the Mizoroki–Heck reaction,
the mechanistic approach appeared to be simpler for the teth-
ered Pd catalyst, {Pd}–L(C)–Au(111). Since the catalytic Pd
center is far away from the metal support in {Pd}–L(C)–
Au(111) catalyst, the reaction can proceed like a homogeneous
reaction. In this approach, however, varieties of tethering
ligands can be adsorbed on the Au(111) substrate to make
highly functionalized catalyst. These are not possible in
{Pd}–S–GaAs catalyst in which the Pd is directly adsorbed
to the sulfur-terminated GaAs(001). The surface inertness of
Au(111) also makes it a better candidate as a solid substrate
compared to GaAs(001) surface which oxidizes upon atmo-
spheric condition.6a
Binding Energy/eV
Figure 2. XPS spectra of catalysts {Pd}–L(C)–Au(111)
and {Pd}–Au(111). Spectra e and f correspond to catalyst
C1 before and after application to the Mizoroki–Heck re-
action, respectively, and spectrum g corresponds to cata-
lyst W after application to the Mizoroki–Heck reaction.
observed by XPS measurements will be useful for understand-
ing these activities.
Conclusion
Catalyst {Pd}–Au(111) (Entry 7), prepared by the direct ad-
sorption of Pd(dba)2 on the Au(111) substrate without a tether,
had the best performance among the catalysts. The activity
slightly decreased after the 7th run, but it had an impressive
94% average yield for 10 successive runs.
The original goal of this investigation was to evaluate the
feasibility of using solid-supported tethering ligands to con-
struct heterogeneous tether-ligated Pd catalysts. We attempted
to confine the functionalized tether ligands on a gold surface
through S–Au bonding and then Pd was anchored to the
ligands. To the best of our knowledge, this is the first report
of XPS analysis the S–Au bonds are not strong enough to
maintain the ligands on the gold substrate under the standard
Mizoroki–Heck reaction. We previously reported that sulfur-
termination of GaAs(001) is essential for the preparation of
stable Pd catalysts and the resultant catalyst {Pd}–S–GaAs is
reusable in the Mizoroki–Heck reaction many times without
the loss of catalytic activity.6b,6d The present report, thus, indi-
cates that the S–GaAs bond is stronger than the S–Au bond.
These studies, however, demonstrated that the transition-metal
catalysts tethered on a gold substrate may be appropriate
for mild reaction conditions. The results also demonstrated
that it is possible to form effective catalysts by adsorbing
the Pd complexes directly onto the Au surface and it can be
used in high-temperature reactions. The catalysts are easy to
recover and transferred under aerobic conditions using a pair
of tweezers.
Surface Characterization by XPS 2. XPS was used to
evaluate the fate of the ligands and the state of the Pd after
the Mizoroki–Heck reaction. The XPS results for {Pd}–
L(C)–Au(111) (catalyst C1) and {Pd}–Au(111) (catalyst W)
are shown in Figure 2. Spectra e and f are for the catalyst
C1 before and after application to the Mizoroki–Heck reaction,
respectively, and spectrum g is for catalyst W after application
to the Mizoroki–Heck reaction. Clear peaks of Pd 3d core-lev-
el photoemission were observed for all catalysts, indicating
that Pd was definitely immobilized to the surface. No peak
due to the N of ligand C was observed for catalyst {Pd}–
L(C)–Au(111) either before or after the Mizoroki–Heck reac-
tion. The absence of a peak due to N 1s for {Pd}–L(C)–
Au(111) was surprising, because the peak was clearly observed
for L(C)–Au(111). One possibility is that the S–Au bond by
which the ligands are bound to the gold surface was too weak
to survive the Mizoroki–Heck reaction conditions or even the
Pd adsorption step. It is also possible that the peaks could not
be detected due to the low signal intensity and the presence
of immobilized Pd on top of the ligand. Similar results were
reported for the sulfur-terminated {Pd}–S–GaAs catalyst in
which S 2p photoemission peaks could not be detected by
XPS and was ascribed due to the immobilization of Pd on
top of the S.6c
Experimental
General. All moisture-sensitive reactions were performed un-
der an Ar atmosphere unless cited. Solvents were dried using mo-
lecular sieves. Reagents were obtained from commercial sources
and were used without further purification. Mica-supported
Au(111) film plate was purchased from Agilent and was cleaned
The results shown in Table 1 demonstrate that the catalytic
activity for catalyst {Pd}–L(C)–Au(111) was mainly depend-
1
with piranha solution prior to use in some cases. H NMR spectra

1016 Bull. Chem. Soc. Jpn. Vol. 81, No. 8 (2008)
Tethered Pd Catalysis on Au(111) and Its XPS
were recorded in CDCl3 at 25 ꢂC unless otherwise noted, at
400 MHz, with TMS as an internal standard. 13C NMR spectra
were recorded in CDCl3 at 25 ꢂC unless otherwise noted, at
100 MHz. 31P NMR spectra were recorded at 25 ꢂC unless other-
wise noted at 161 MHz, with 80% H3PO4 (ꢀ 0) as an external
standard. XPS measurement was carried out using Mg Kꢁ radia-
tion (K.E. ¼ 1253 eV) and Al Kꢁ radiation (K.E. ¼ 1487 eV).
The energy shift due to sample charging was corrected by using
Au 4f7=2 (84.0 eV) as an internal standard. Syntheses of air-unsta-
ble chemicals were carried out in a glovebox (Miwa, DBO-1NKP-
TA) containing less than 1 ppm of oxygen and water. Flash col-
umn chromatographies were performed with silica gel 60 N
(spherical, neutral, 40–50 mm, Kanto Chemical Co., Inc.).
Synthesis of Tethering Ligand A and Adsorption of Ligand
on Au(111) Substrate. The ligand A was synthesized in six steps
as described in Scheme 1. The details for the synthesis of ligand
A and the adsorption of ligand A on Au(111) substrate are given
below.
ture was refluxed at 100 ꢂC for 6 h under H2 atmosphere. After
cooling to rt, the mixture was filtered through a Celite pad. The
filtrate was concentrated in vacuo and then purified by column
chromatography on silica gel (hexane:EtOAc = 1:2) to afford
3A (91 mg, 91%) as a viscous solid. 1H NMR (400 MHz, CDCl3):
ꢀ 1.75–1.92 (4H, m), 2.69 (2H, t, J ¼ 7:6 Hz), 3.41 (2H, t, J ¼
6:4 Hz), 7.26–7.69 (14H, m); 13C NMR (100 MHz, CDCl3):
ꢀ 29.4, 32.1, 33.3, 34.9, 128.4, 128.5, 128.6, 130.4, 131.8,
131.9, 132.1, 132.2, 132.2, 146.1, 146.2 (overlapped); 31P NMR
(100 MHz, CDCl3): ꢀ 29.7; IR (neat): ꢂ 3447, 3053, 2930,
2856, 1600, 1436, 1182, 1116 cmꢁ1; LRMS (EI) m=z 411
ðM ꢁ HÞþ; HRMS (FAB) calcd for C22H23Br1O1P1 413.0652
ðM þ HÞþ, found 413.0660.
Synthesis of Bis[4-(4-diphenylphosphinoyl)butyl] Sulfide
(4A): To a solution of 3A (32.0 mg, 0.077 mmol) in EtOH
(7.0 mL) was added thiourea (6.0 mg, 0.077 mmol). The resulting
mixture was refluxed at 120 ꢂC for 3 h and then aq NaOH (5 mg,
0.11 mmol in 1.5 mL H2O) was added and refluxed again at
120 ꢂC for 2 h. After cooling to rt, the reaction mixture was
quenched with H2SO4 and extracted with ether. The organic layer
was dried over Na2SO4. After filtration, the filtrate was concen-
trated in vacuo and then purified by column chromatography on
silica gel (EtOAc:MeOH = 5:1) to afford 4A (26.0 mg, 93%) as
a viscous solid. 1H NMR (400 MHz, CDCl3): ꢀ 1.60 (4H, tt,
J ¼ 7:2, 7.2 Hz), 1.72 (4H, tt, J ¼ 7:2, 7.2 Hz), 2.50 (4H, t,
J ¼ 7:2 Hz), 2.66 (4H, t, J ¼ 7:2 Hz), 7.25–7.69 (28H, m);
13C NMR (100 MHz, CDCl3): ꢀ 28.9, 30.0, 31.7, 35.3, 128.2,
128.3, 128.4, 128.5, 128.9, 129.9, 131.7, 131.7, 131.8, 131.9,
132.0, 132.0, 132.1, 133.0, 146.5, 146.5 (overlapped); 31P NMR
(100 MHz, CDCl3): ꢀ 29.6; IR (neat): ꢂ 3054, 2929, 2854,
Synthesis of Diphenyl(4-vinylphenyl)phosphine Oxide (1A):
mixture of diphenyl(4-vinylphenyl)phosphine (490 mg,
A
1.7 mmol) and benzyl bromide (0.23 mL, 1.9 mmol) in toluene
(10.0 mL) was stirred at 100 ꢂC for 3 h under Ar atmosphere. After
cooling to rt, the precipitate was filtered and washed with cool tol-
uene and then dried under vacuum to get (bromobenzyl)diphen-
yl(4-vinylphenyl)phosphonium salt (700 mg, 1.5 mmol) as a white
solid. The resulting salt was mixed with NaH (68.0 mg, 60% in oil,
1.7 mmol) and benzaldehyde (0.17 mL, 1.7 mmol) and then THF
(8.0 mL) was added. The resulting mixture was stirred at rt for
12 h and then quenched with saturated aq NH4Cl. The mixture
was extracted with CH2Cl2. The organic layer was washed with
brine, and then dried over Na2SO4. After filtration, the solvent
was removed in vacuo and the residue was purified by column
chromatography on silica gel (hexane:EtOAc = 20:1, then 1:1)
to afford 1A (436 mg, 84% for 2 steps) as a viscous solid. 1H NMR
(400 MHz, CDCl3): ꢀ 5.38 (1H, d, J ¼ 10:8 Hz), 5.85 (1H, d,
J ¼ 17:6 Hz), 6.74 (1H, dd, J ¼ 10:8, 17.6 Hz), 7.46–7.70 (14H,
m); 13C NMR (100 MHz, CDCl3): ꢀ 116.5, 126.1, 126.2, 128.4,
128.5, 131.0, 131.9, 131.9, 131.9, 132.0, 132.0, 132.3, 132.4,
133.0, 135.8, 135.8, 140.9, 140.9; 31P NMR (100 MHz, CDCl3):
ꢀ 29.3; IR (neat): ꢂ 3054, 2967, 159þ8, 1436, 1395, 1182,
1115 cmꢁ1; LRMS (EI) m=z 303 ðM ꢁ HÞ ; HRMS (FAB) calcd
for C20H18O1P1 305.1095 ðM þ HÞþ, found 305.1077.
1601, 1436, 1184, 1116 cmꢁ1
; LRMS (FAB) m=z 699
ðM þ HÞþ; HRMS (FAB) calcd for C44H45O2P2S 699.2616
ðM þ HÞþ, found 699.2585.
Synthesis of Bis[4-(4-diphenylphosphino)butyl] Sulfide
(Ligand A): To a solution of 4A (56.0 mg, 0.15 mmol) in toluene
(7.0 mL) was added Et3N (0.070 mL, 0.66 mmol) and trichloro-
silane (0.070 mL, 0.64 mmol). The resulting mixture was refluxed
at 130 ꢂC for 3 h under Ar atmosphere and then 30 wt % aq NaOH
(10.0 mL) was added and stirred at 60 ꢂC for 1 h. After cooling
down the reaction mixture to rt, 5.0 mL of H2O was added and ex-
tracted with toluene (15:0 mL ꢃ 3). The organic layer was washed
with brine and then dried over Na2SO4. After filtration, the filtrate
was concentrated in vacuo and then purified by flash column
chromatography on silica gel (hexane:EtOAc = 20:1, and then
hexane:CHCl3 = 4:1 using PTLC) to afford ligand A (31 mg,
55%) as a viscous solid. 1H NMR (400 MHz, CDCl3): ꢀ 1.56–
1.74 (8H, m), 2.49 (4H, t, J ¼ 7:2 Hz), 2.61 (4H, t, J ¼ 7:2 Hz),
7.13–7.33 (28H, m); 13C NMR (100 MHz, CDCl3): ꢀ 29.2, 30.3,
31.9, 35.3, 128.4, 128.4, 128.5, 128.6, 128.6, 128.7, 132.0,
132.1, 133.5, 133.7, 133.8, 133.9, 134.0, 137.4, 137.5, 143.0
(overlapped); 31P NMR (100 MHz, CDCl3): ꢀ ꢁ5:8; IR (neat): ꢂ
3067, 3051, 3013, 2923, 2853, 1597, 1584, 1477, 1432, 1090,
741, 693 cmꢁ1; LRMS (FAB) m=z 667 ðM þ HÞþ; HRMS
(FAB) calcd for C44H45P2S 667.2717 ðM þ HÞþ, found 667.2673.
Synthesis of {4-[(E)-4-Bromo-1-butenyl]phenyl}diphenyl-
phosphine Oxide (2A):
To a solution of 1A (183 mg,
0.60 mmol) in CH2Cl2 (8.0 mL) was added Grubbs catalyst second
generation (5.8 mg, 0:69 ꢃ 10ꢁ2 mmol) and 4-bromo-1-butene
(0.1 mL, 1.0 mmol). The resulting mixture was refluxed at 50 ꢂC
for 1 h under Ar atmosphere. After cooling to rt, the solvent was
removed in vacuo and then purified by column chromatography
on silica gel (hexane:EtOAc = 20:1, then 1:2) to afford 2A
(189 mg, 76%) as a viscous solid. 1H NMR (400 MHz, CDCl3):
ꢀ 2.80 (2H, dt, J ¼ 6:8, 6.8 Hz), 3.48 (2H, t, J ¼ 6:8 Hz), 6.30
(1H, dt, J ¼ 16:0, 6.8 Hz), 7.43–7.69 (15H, m); 13C NMR (100
MHz, CDCl3): ꢀ 31.8, 36.0, 126.0, 126.1, 128.3, 128.4, 129.5,
130.5, 131.6, 131.6, 131.6, 131.8, 131.8, 131.9, 132.0, 132.3,
132.4, 133.0, 140.4, 140.4 (overlapped); IR (neat): ꢂ 3430,
3054, 2960, 1597, 1436, 1181, 1115, 967 cmꢁ1; LRMS (EI) m=z
409 ðM ꢁ HÞþ; HRMS (FAB) calcd for C22H21Br1O1P1
411.0513 ðM þ HÞþ, found 411.0496.
Adsorption of Ligand A on Au(111) Substrate:
The
Au(111) plates either cleaned with piranha solution (a mixture
of concd H2SO4 and 30% H2O2 in 3:1 ratio) or without cleaning,
both types were used for adsorption of ligands. In piranha treat-
ment, the Au(111) plate was immersed in piranha solution for
1 min and rinsed exhaustively with distilled, deionized water
and absolute ethanol and then dried with a stream of Ar gas.
The clean Au(111) plate was immersed in 1 mM solution of ligand
Synthesis of [4-(4-Bromobutyl)phenyl]diphenylphosphine
Oxide (3A): To a solution of 2A (100 mg, 0.25 mmol) in EtOH
(7.0 mL) was added Pd/C (26.0 mg, 10% wt). The resulting mix-

R. M. Gulam et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 8 (2008) 1017
A in CHCl3 at 60 ꢂC for 12 h under an Ar atmosphere. The ligand-
modified Au(111) plate was rinsed with CHCl3 and then dried
under a stream of Ar gas and kept in glovebox.
Synthesis of Tethering Ligand B and Adsorption of Ligand
on Au(111) Substrate. The ligand B was synthesized in six steps
as described in Scheme 2. Species 1B, 2B, 3B, and 4B were syn-
thesized according to a previously reported procedure.5g The de-
tails for the synthesis of ligand B from species 4B and the adsorp-
tion of ligand B on Au(111) substrate are given below.
This research was supported by a Grant-in-Aid for Explor-
atory Research and the Encouragement of Young Scientists
(A) from the Ministry of Education, Culture, Sports, Science
and Technology, Japan. M. A. is also grateful for financial sup-
port from the Iketani Foundation, Yazaki Memorial Founda-
tion for Science and Technology, and a Mitsui Chemical
Ltd. Award in Synthetic Organic Chemistry.
References
Synthesis of N,N0-3,5-Bis[(phenylthio)methyl]phenyl-3,30-
dithiopropanamide (Ligand B): To a solution of 3,30-dithiodi-
propionic acid (21 mg, 0.10 mmol) in CH2Cl2 (2.0 mL) and DMF
(0.1 mL) was added HOBt (28 mg, 0.21 mmol). The mixture was
stirred at rt for 15 min, and then added DCC (43 mg, 0.21 mmol)
and 3,5-bis(phenylthiomethyl)aniline (4B) (71 mg, 0.21 mmol).
The solution was stirred at rt for 24 h, and then filtered through
a Celite pad. The filtrate was concentrated in vacuo. The residue
was purified by column chromatography on silica gel (hexane:
EtOAc = 3:1) to afford ligand B (83 mg, 98% with respect to
3,30-dithiodipropionic acid) as a yellow solid. 1H NMR (400
MHz, CDCl3): ꢀ 2.71 (t, J ¼ 6:8 Hz, 4H), 3.05 (t, J ¼ 6:6 Hz,
4H), 3.97 (s, 8H), 6.96 (s, 2H), 7.14–7.26 (m, 20H), 7.40
(s, 4H), 7.71 (s, 2H); LRMS (EI) m=z 849 ðM ꢁ HÞþ.
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¨
¨
C. Ni, O. Buyukgungor, E. Ozkal, J. Organomet. Chem. 2006,
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¨
¨
in THF (3.00 mL) was immersed the ligand-modified Au(111) film
L(C)–Au(111) and stirred gently at rt for 20 min.12 The plate was
rinsed with THF and then immersed in a solution of Pd(OAc)2
(4.0 mg) in THF (3.00 mL). The solution was stirred gently at
50 ꢂC for 4 h. Catalyst was also prepared for longer adsorption
period as well as changing the temperature. After cooling to rt,
plate was rinsed with MeCN and dried under a stream of Ar gas
to get the catalyst {Pd}–L(C)–Au(111).
Preparation of {Pd}–Au(111) Catalyst. The Au(111) plate
was immersed in a solution of Pd(dba)2 (10.0 mg) in xylene
(3.00 mL) and stirred gently at 85 ꢂC for 4 h. The plate was then
rinsed with MeCN and dried under stream of Ar gas to get the
catalyst {Pd}–Au(111).
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A
mixture of iodobenzene (56.0 mL, 0.500 mmol), methyl methacry-
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MeCN (3.00 mL) was heated in the presence of catalyst at
100 ꢂC (bath temperature) for 12 h under an argon atmosphere
without stirring. After the reaction mixture was cooled to rt, the
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7
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