Alkane oxidation by an immobilized nickel complex catalyst: Structural and reactivity differences induced by surface-ligand density on mesoporous silica

Article abstract of DOI:10.1002/asia.201300165

Immobilized nickel catalysts SBA*-L-x/Ni (L=bis(2-pyridylmethyl)(1H- 1,2,3-triazol-4-ylmethyl)amine) with various ligand densities (L content (x)=0.5, 1, 2, 4 mol % Si) have been prepared from azidopropyl-functionalized mesoporous silicas SBA-N₃

Full text of DOI:10.1002/asia.201300165

FULL PAPER
DOI: 10.1002/asia.201300165
Alkane Oxidation by an Immobilized Nickel Complex Catalyst: Structural
and Reactivity Differences Induced by Surface-Ligand Density on
Mesoporous Silica
Jun Nakazawa,*[a] Tomoaki Hori,[a] T. Daniel P. Stack,[b] and Shiro Hikichi*[a]
Abstract: Immobilized nickel catalysts
SBA*-L-x/Ni (L=bis(2-pyridylme-
thyl)(1H-1,2,3-triazol-4-ylmethyl)a-
L/Ni ratio (0.9–1.7:1) in SBA*-L-x/Ni
suggests the formation of an inert
[NiL2] site on the surface at higher
ligand loadings. SBA*-L-x/Ni has been
applied to the catalytic oxidation of cy-
clohexane with m-chloroperbenzoic
acid (mCPBA). The catalyst with the
lowest loading shows high activity in its
initial use as the homogeneous LtBu/Ni
catalyst, with some metal leaching. As
the ligand loading increases, the activi-
ty and Ni leaching are suppressed. The
importance of site-density control for
the development of immobilized cata-
lysts has been demonstrated.
mine) with various ligand densities (L
content (x)=0.5, 1, 2, 4 mol% Si) have
been prepared from azidopropyl-func-
tionalized mesoporous silicas SBA-N3-
x. Related homogeneous ligand LtBu
Keywords: heterogeneous catalysis ·
immobilization · mesoporous mate-
rials · nickel · oxidation
and its NiII complexes, [Ni(LtBu
ACTHNUTRGENNUG )CAHTUNGTERN(NUNG OAc)2
ACHTUNGTRENNUNG ACHTUNGTRENNUGN
(H2O)] (LtBu/Ni) and [Ni(LtBu)2]BF4
(2LtBu/Ni), have been synthesized. The
Introduction
silica solid supports, by using a two-step synthetic procedure
that involves a copper(I)-catalyzed azide–alkyne cycloaddi-
tion reaction (CuAAC, also called a click reaction).[3] The
first step is the direct incorporation of a defined quantity of
an azide (e.g., 3-azidopropyltriethoxysilane) into the synthe-
sis of a material that exploits the discotic mesophase of non-
ionic surfactant Pluronic P-123 under acidic conditions and
the hydrolysis of tetraethylorthosilicate; this method is re-
ferred to as a direct synthesis, in which the organic azide
groups are preferentially oriented into the templated pores
once the surfactant is removed under soft conditions.[4]
Beyond providing control over the azide loading, the mate-
rial retains the advantageous properties of the original SBA-
15 mesoporous silica,[5] such as mechanical strength, which
results from the thick silica walls, and large surface areas,
which are accessible through well-defined mesopores. The
covalent attachment of ethynylated molecules onto the azi-
dopropyl tethers, as the second step in the synthetic proce-
dure, relies on the highly selective, high-yielding click reac-
tion that is widely applied in many research areas.[6] This
procedure not only provides reproducible attachment with
desired surface coverage, but also randomly distributed
functional groups on the solid surface. The use of these ma-
terials enables the investigation of the interactions between
surface-immobilized functionalities, with special focus on
the effects of metal-complex sites on the coordination struc-
ture and catalytic reactivity through interactions between
immobilized ligands.
Homogeneous metal catalysts hold great promise for chang-
ing the chemo- and regioselectivities in fine-chemical trans-
formations through simple ligand variation. The efficient
and well-defined immobilization of such catalysts on solid
supports provides additional advantages, such as facile sepa-
ration, reusability, and catalyst site-isolation.[1] However, the
translation of catalytic reactivity from a homogeneous cata-
lyst to a heterogenized analogue is often associated with
a decrease in activity, presumably owing to interactions of
the catalyst with itself or with ligands on the support sur-
face.[2] The ability to define the relevance of such interac-
tions with respect to the catalysis would facilitate the use of
heterogenized homogeneous catalysts. In fact, these interac-
tions with surface ligands might even be exploited to yield
new types of transformations, because site-isolation on the
surface could prevent the formation of the most thermody-
namically stable species, as is generally observed in a homo-
geneous solution.
It is now possible to immobilize a variety of useful dis-
crete molecules at a defined level of loading on mesoporous
[a] Dr. J. Nakazawa, T. Hori, Prof. Dr. S. Hikichi
Department of Material and Life Chemistry
Kanagawa University
Yokohama, Kanagawa 221-8686 (Japan)
Fax : (+81)45-413-9770
E-mail: jnaka@kanagawa-u.ac.jp
In 2006, Itoh and co-workers reported that [Ni2+
ACHTUNGTRENNUNG(tpa)]
[b] Prof. Dr. T. D. P. Stack
Department of Chemistry
Stanford University
(tpa=tris(2-pyridylmethyl)amine) complexes efficiently cat-
alyzed the oxidation of alkanes with m-chloroperbenzoic
acid (mCPBA) with high alcohol selectivity (Scheme 1).[7]
Stanford, CA, 94305-5080 (USA)
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Jun Nakazawa, Shiro Hikichi et al.
Herein, we compare the homogeneous and heterogeneous
reactivities of a related nickel complex with the N,N-bis(2-
pyridylmethyl)-N-{(1H-1,2,3-triazol-4-yl)methyl}amine (L)
ligand. This ligand is readily prepared and covalently at-
tached onto azide-functionalized SBA-15 by using CuAAC
reactions with various surface-ligand densities. The coordi-
nation of the surface-immobilized nickel complex was infer-
red by comparison with homogeneous analogues. A compar-
ison of the oxidation of cyclohexane with mCPBA and both
the homogeneous and immobilized nickel complexes pro-
vides insights into the nature of the active catalytic species.
Results and Discussion
Preparation and Characterization of the Homogeneous
Complexes
Scheme 1. a) Nickel-catalyzed oxidation of cyclohexane with mCPBA.
b) Reported Ni catalysts for the oxidation reactions.
N,N-Bis(2-pyridylmethyl)-N-{(1-tert-butyl-1H-1,2,3-triazol-4-
yl)methyl}amine (LtBu) was prepared from N-propargyl-N,N-
bis(2-pyridiylmethyl)amine (1)[6j–l] and tert-butylazide[8] by
using a click reaction (Scheme 2) as a homogeneous ana-
logue to evaluate the effect of triazole substitution of one of
the pyridine arms on the tpa ligand. The facile preparation
of ligands with potentially coordinating triazole groups is
called the “click-to-chelate” approach.[6p,9] Compound LtBu
was fully characterized (elemental analysis, MS (ESI), and
IR, UV/Vis, and NMR (1H, 13C) spectroscopy). The mixture
of equimolar amounts of LtBu and NiII acetate give [Ni2+-
ACHTUNGTRENNUNG(OAc)2ACHTUNGTRENNUNG(H2O)ACHTUNGTRENNUNG
(LtBu)], (=LtBu/Ni) as blue crystals, whilst the
addition of an excess of the ligand to nickel acetate also
gave LtBu/Ni in quantitative yield. In contrast, the addition
of Ni
ACHTUNGTRENNUNG(BF4)·6H2O, which had a noncoordinating counter
anion, to two equivalents of the ligand in EtOH afforded
purple crystals of [NiACTHNUGTRENNUG ACHUTNGTRENNGUN
(LtBu)2](BF4)2 (2LtBu/Ni). Both nickel
complexes (LtBu/Ni and 2LtBu/Ni) were fully characterized by
elemental analysis, MS (ESI), IR and UV/Vis spectroscopy,
and X-ray crystallography.
The molecular structures of compounds LtBu/Ni and 2LtBu
/
Ni, as obtained by X-ray crystallographic analysis, are
shown in Figure 1 and Figure 2 and selected bond lengths
and angles are collected in Table 1 and Table 2, respectively.
Scheme 2. Preparation of LtBu and its nickel(II) complexes, LtBu/Ni and
2LtBu/Ni. Reaction conditions: (i) tert-butylazide, Cu0 powder, N2, RT,
24 h; (ii) Ni
30 min; (iv) NiACTHNUGRTEN(NGU BF4)2·6H2O, EtOH, 30 min.
(OAc)2·4H2O, MeOH, 30 min; (iii) LtBu (2 equiv), MeOH,
ACHTUNGTRENNUNG
Abstract in Japanese:
Two independent isomers with similar geometries around
the nickel ions existed in the unit cells of both complexes.
Both [NiL(X)n] (X=solvent, anion, etc.) and [NiL2]-type
structures were also reported with the N,N-bis(2-pyridylme-
thyl)benzylamine ligand (BzPym2 or BzBPA in reference
compounds).[7b,10] In LtBu/Ni, the triazole group does not co-
ordinate to the Ni center (Ni–N>5 ꢁ). The coordination
environment (two pyridine groups, a tertiary amine, a water
molecule, and two monodentate acetate groups) is more
similar to that in [Ni2+
than in [Ni(tpa)(OAc)ACHTUGNTRENNNUG
G
(H2O)] (BzPym2/Ni)[7b]
ACHUTGTNRNENUG(OAc)2ACHTUNGTRENNUGN
E
N
donor atoms (N1, N2, N3) of the bis(2-pyridylmethyl)amine)
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Jun Nakazawa, Shiro Hikichi et al.
Table 1. Selected bond lengths [ꢁ] and angles [8] in the single crystal of
complex LtBu/Ni.[a]
Unit 1
Unit 2
Ni1(2)–N1(7)
2.102(2)
2.094(2)
Ni1(2)–N2(8)
Ni1(2)–N3(9)
Ni1(2)–O1(6)
Ni1(2)–O3(8)
Ni1(2)–O5(10)
O2(7)–O5(10)
O4(9)–O5(10)
N1(7)-Ni1(2)-N2(8)
N1(7)-Ni1(2)-N3(9)
N1(7)-Ni1(2)-O1(6)
N1(7)-Ni1(2)-O3(8)
N1(7)-Ni1(2)-O5(10)
N2(8)-Ni1(2)-N3(9)
N2(8)-Ni1(2)-O1(6)
N2(8)-Ni1(2)-O3(8)
N2(8)-Ni1(2)-O5(10)
N3(9)-Ni1(2)-O1(6)
N3(9)-Ni1(2)-O3(8)
N3(9)-Ni1(2)-O5(10)
O1(6)-Ni1(2)-O3(8)
O1(6)-Ni1(2)-O5(10)
O3(8)-Ni1(2)-O5(10)
2.060(2)
2.164(2)
2.080(2)
2.031(2)
2.099(2)
2.639(2)
2.679(3)
99.99(7)
78.02(7)
171.47(7)
93.54(7)
84.79(7)
81.64(7)
84.71(7)
89.99(7)
173.28(7)
95.77(7)
166.81(7)
94.85(7)
93.56(7)
89.97(7)
94.45(7)
2.061(2)
2.153(2)
2.075(2)
2.039(2)
2.097(2)
2.638(3)
2.633(2)
97.78(7)
78.07(7)
173.94(7)
94.75(7)
87.19(7)
81.51(7)
83.65(7)
94.13(7)
170.70(7)
96.37(7)
170.92(7)
91.91(6)
91.01(7)
90.60(7)
93.27(6)
Figure 1. Molecular structure of complex LtBu/Ni (unit 1). Two independ-
ent isomers exist in the unit cell. Ellipsoids are set at 30% probability;
hydrogen atoms on carbon atoms are omitted for clarity.
[a] Atom numbering in unit 2 is shown in parentheses.
Table 2. Selected bond lengths [ꢁ] and angles [8] in the single crystal of
complex 2LtBu/Ni.[a]
Unit 1
Unit 2
Ni1(2)–N1(7)
2.122(4)
2.118(3)
Ni1(2)–N2(8)
Ni1(2)–N3(9)
2.046(3)
2.165(3)
82.3(1)
79.6(1)
98.1(1)
102.6(1)
173.6(1)
83.1(1)
172.7(1)
92.3(1)
2.044(3)
2.181(3)
82.5(1)
79.7(1)
97.9(1)
102.7(1)
173.8(1)
82.6(1)
172.2(1)
92.5(1)
N1(7)-Ni1(2)-N2(8)
N1(7)-Ni1(2)-N3(9)
N1(7)-Ni1(2)-N1’(7’)
N1(7)-Ni1(2)-N2’(8’)
N1(7)-Ni1(2)-N3’(9’)
N2(8)-Ni1(2)-N3(9)
N2(8)-Ni1(2)-N2’(8’)
N2(8)-Ni1(2)-N3’(9’)
N3(9)-Ni1(2)-N3’(9’)
103.2(1)
103.4(1)
Figure 2. Molecular structure of complex 2LtBu/Ni (unit 1). Two inde-
pendent isomers exist in the unit cell. Ellipsoids are set at 30% probabili-
ty; hydrogen atoms on carbon atoms are omitted for clarity.
[a] Atom numbering in unit 2 is shown in parentheses.
other acetate group (O1=2.080 ꢁ) or the water molecule
(O5=2.099 ꢁ), which are located trans to the pyridine
groups.
unit occupy slightly distorted facial positions in the octahe-
dral geometry and the water donor atom (O5) occupies a po-
sition trans to one of the pyridine donor groups (N2). The
In the molecular structure of complex 2LtBu/Ni, the nickel
ion is located on a two-fold axis and two symmetrically
equivalent molecules of the LtBu ligand occupy the octahe-
dral coordination environment of the nickel. Each ligand is
coordinated in a facial and tridentate manner by two pyri-
dine groups and a tertiary amine moiety. The two tertiary
amine sites (N3, N3’) on the nickel atom occupy cis posi-
Ni–NACHTUNGTRENNUNG(pyridine) (N1, N2) bond lengths are shorter than the
Ni–N(tertiary amine) bond (N3=2.164 ꢁ). In addition, the
following differences in the bond lengths, which are derived
from the donating character of the trans-locating ligand,
have been observed: 1) In the two pyridine groups, the Ni–
N distance to the pyridine donor (N1=2.102 ꢁ) that is lo-
cated trans to an acetate group (O1) is longer than that of
the other pyridine group (N2=2.060 ꢁ), which is trans to
the water molecule (O5). 2) In terms of the Ni–O distances,
the distance to the acetate group (O3=2.031 ꢁ) that is lo-
cated trans to the tertiary amine is shorter than that to the
tions. The Ni–NACTHNUTRGNEUNG(pyridine) bond lengths (N1=2.122 ꢁ, N2=
2.046 ꢁ) are shorter than that of the Ni–N(tertiary amine)
bond (N3=2.165 ꢁ). Although there have been some very
recent reports of coordination structures between tightly co-
ordinating triazole groups and various metal ions,[9] the tria-
zole group in LtBu is not coordinated to the Ni center in this
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complex. The chelate geometry of the triazolylmethyl arm
in LtBu could be unsuitable for coordination, especially for
the nickel-coordination environment.
end-capped silica (SBA*-L-x). Then, the SBA*-L-x silicas
were treated with a solution of nickel(II) acetate in MeOH
to give the SBA*-L-x/Ni catalysts.
The physicochemical properties of the prepared silicas, as
well as their nickel and ligand loadings, are summarized in
Table 3. The surface area, pore volume, and pore diameter
of the silica materials were calculated from their nitrogen-
adsorption/desorption isotherms by using the Brunauer–
Emmett–Teller (BET)[11] and Barrett–Joyner–Halenda
Preparation and Characterization of the Immobilized Nickel
Complexes
The immobilized catalysts were prepared as shown in
Scheme 3. Azidopropyl-functionalized mesoporous silica
with controlled azide loadings, SBA-N3-x (x=molar content
of (EtO)3SiACHTUNGTRENNUNG(CH2)3N3 in the silica preparation; 0.5, 1, 2,
4 mol% Si), was synthesized according to a literature proce-
Table 3. Physicochemical properties of functionalized silicas.
Property
Silica
x
0.5
1
2
4
[a]
A [m2 gꢀ1
]
SBA-L-x
SBA*-L-x
SBA-L-x
SBA*-L-x
SBA-L-x
SBA*-L-x
SBA-L-x
SBA*-L-x
SBA*-L-x/Ni
used[f]
685
590
0.96
0.86
4.85
5.00
0.08
0.07
0.08
724
602
498
422
0.39
430
302
0.52
[b]
V [m3 gꢀ1
D [nm][c]
]
0.84
0.73
4.04
4.12
0.11
0.12
0.14
0.05
0.04
0.9
0.36
3.46
3.44
0.25
0.25
0.22
0.14
0.14
1.1
0.30
3.93
3.22
0.32
0.33
0.19
0.18
0.17
1.7
L loading
[d]
[mmolgꢀ1
]
Ni loading
[e]
[mmolgꢀ1
]
0.03 (0.06)
0.02 (0.05)
0.9
reused[f]
L/Ni ratio[g]
[a] BET surface area. [b] Pore volume (BJH method, desorption branch).
[c] Pore diameter (BJH method, desorption branch). [d] Determined
from the UV/Vis absorption spectrum after silica digestion. [e] Deter-
mined from the atomic absorption analysis after silica digestion. [f] Used
and re-used catalysts from the oxidation reactions after washing with
MeOH (CH2Cl2 in parentheses). [g] Calculated according to [L loading
of SBA*-L-x]/[Ni loading of SBA*-L-x/Ni].
(BJH) methods.[12] The nitrogen-adsorption isotherms of the
SBA*-L-x materials at all loadings of SBA-L-x show a type-
IV pattern, thus indicating that the mesoporous structure of
the SBA-N3-x material is maintained during the surface
modification by the click and end-capping reactions.[3] As
the loading (x) increases, the surface area, pore volume, and
pore diameter decrease, owing to the occupation of the pore
surface by the organic functionalities. The smooth access of
small molecules to the metal-complex sites is even allowed
in the mesopores of higher-loading samples, such as SBA-L-
4 (and also SBA-R-8 in a previous report[3]). This accessibili-
ty was previously confirmed by the complete removal of the
trapped copper catalyst from these materials by Na-ddtc
during the preparation of the materials.
The ligand loading in SBA-L-x and SBA-L*-x was quanti-
fied by UV/Vis spectrometry after silica digestion by treat-
ment with OHꢀ and Fꢀ, respectively. The ligand loading
showed an almost-linear increase with the initial azide con-
tent (x) during the silica preparation. The nickel loading in
the SBA-L*-x/Ni materials was quantified by atomic absorp-
tion analysis after silica digestion by treatment with OHꢀ.
In contrast to the ligand loading, the nickel loading on the
SBA*-L-x materials showed a different trend. The silica
with the lowest ligand loading, SBA*-L-0.5, retained a simi-
Scheme 3. Preparation of the heterogeneous SBA*-L-x/Ni catalysts. Re-
action conditions: (i) P123 polymer, HCl, water, 358C 24 h, then 1008C
24 h, then polymer removal on a Soxhlet apparatus, EtOH, 24 h; (ii) Cu-
SO4·5H2O, sodium ascorbate, DMF, N2, 24 h, RT; (iii) HMDS, toluene
508C, 1 h; (iv) NiACHTUNGTRENNUNG(OAc)2·4H2O, MeOH.
dure.[3] The click attachment of ligand precursor 1 onto the
SBA-N3-x support was also performed under the same con-
ditions, by using CuSO4/sodium ascorbate in DMF to afford
the ligand-immobilized silicas (SBA-L-x). The progress of
the click reaction was monitored by the decrease (>70%)
in the intensity of the azide peak (at 2110 cmꢀ1) in the IR
spectra. A stoichiometric amount of the copper catalyst was
required for the click immobilization, in contrast to the stan-
dard homogeneous-phase conditions (about 5 mol% Cu),
because the copper intermediate was captured by the in situ
generated immobilized ligand site, which prevented its mi-
gration onto other surface azide sites. Excess copper ions
were fully removed by washing with a solution of the chelat-
ing reagent (sodium N,N-diethyldithiocarbamate, Na-ddtc).
ꢀ
To simplify the reactivity study, the surface Si OH groups
were end-capped by treatment with 1,1,1,3,3,3-hexamethyl-
disilazane (HMDS) in toluene to give ligand-immobilized,
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lar amount of nickel ions to that of the loaded ligand (L=
0.07 and Ni=0.08 mmolgꢀ1), whereas the silica with the
highest ligand loading, SBA*-L-4, only retained roughly half
of the amount of nickel as that of the ligand (L=0.32 and
Ni=0.19 mmolgꢀ1).
To obtain further structural information on the immobi-
lized nickel complexes, the UV/Vis absorption spectra of the
SBA*-L-x/Ni materials were compared with those of their
homogeneous analogues, LtBu/Ni and 2LtBu/Ni (Figure 3).[13]
geneous and heterogeneous cases suggests the formation of
[NiL2] species on the ligand-rich silica surface. It should be
noted again that complex 2LtBu/Ni is not formed from [Ni-
AHCTUNGRTEG(NUNN OAc)2] in homogeneous solution. This result indicates that
the coordination equilibrium of the second ligand leans
toward the formation of [NiL2] in the ligand-rich environ-
ment on the solid support.
Homogeneous Oxidation Catalysis
The homogeneous oxidation of cyclohexane by mCPBA in
the presence of the LtBu/Ni catalyst was initially examined
under literature conditions to compare the reactivity and re-
action mechanisms with those of the tpa/Ni and BzPym2/Ni
catalysts (Table 4, entries 1–3).[7] The yields of cyclohexanol
(2), cyclohexanone (3), e-caprolactone (4; as the Baeyer–
Villiger reaction product from the reaction between com-
pound 3 and mCPBA), and chlorobenzene (5; as an oxidant
byproduct) were quantified by GC. The progress of product
formation in the reaction with the LtBu/Ni catalyst indicates
that the reaction is complete within 1 h, as in the tpa/Ni and
BzPym2/Ni cases (Figure 4). The reactivity of the LtBu/Ni cat-
Figure 3. UV/Vis spectra of the nickel complexes. a) Solid-state diffusion
reflectance spectra of immobilized metal complexes SBA*-L-x/Ni (x=
0.5, 1, 2, 4), with SBA*-L-0.5 as a reference. b) UV/Vis spectra of homo-
geneous complexes LtBu/Ni and 2LtBu/Ni in CH2Cl2 (0.01 moldmꢀ3).
Figure 4. Progress of product formation in the oxidation of cyclohexane
catalyzed by LtBu/Ni under standard conditions; cyclohexanol 2 (*), cy-
clohexanone 3 (~), e-caprolactone 4 (+), and chlorobenzene 5 (X);
(TON=[product]/[Ni]).
In CH2Cl2, the homogeneous LtBu/Ni complex shows a peak
at 1005 nm (e=14 molꢀ1 dm3 cmꢀ1), owing to a d–d band,
which is similar to the reported values of [Ni
(OAc)2A
(H2O)] (1010 nm, e=13 molꢀ1 dm3 cmꢀ1 in CH2Cl2)
and [Ni
(BzPym2)-
ACHTUNGTRENNUNG
A
CHTUNGTRENNUNG
N
tBuPym2)
G
alyst is closer to that of tpa/Ni than BzPym2/Ni in terms of
two factors: 1) the catalyst turnover number (TON=[prod-
uct]/[Ni]) and 2) the selectivity for alcohol 2 versus ketone 3.
The triazole group on the LtBu ligand probably serves as a co-
ordination donor or a base. Roughly half of the amount of
chlorobenzene (5), as a byproduct from mCPBA, was de-
tected, based on the sum of the cyclohexane-oxidation prod-
MeCN).[7b,10] In contrast, the corresponding band of complex
2LtBu/Ni is observed at 973 nm (e=19 molꢀ1 dm3 cmꢀ1),
whereas that of [NiACTHNUGTRENNUG ACHUTGNTREN(NUNG ClO4)2 is at 958 nm (e=
(BzPym2)2]
16 molꢀ1 dm3 cmꢀ1 in MeCN).[10] In our homogeneous com-
plexes, the difference between the peak maxima of LtBu/Ni
and 2LtBu/Ni is 32 nm. On the other hand, the immobilized
nickel complexes, SBA*-L-x/Ni, also show a 28 nm peak
shift of the d–d band in the solid-state diffusion reflectance
spectra from 970 (x=0.5) to 942 nm (x=4) upon increasing
the ligand loading. This similarity in the shifts of the homo-
ucts. This result suggests that the reaction with the LtBu/Ni
II
ꢀ
system may also proceed through a Ni OC radical species,
followed by mCPBA coordination and O O homolysis, as
ꢀ
suggested for the tpa/Ni system.[7] The following two experi-
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Jun Nakazawa, Shiro Hikichi et al.
ments indicated that some of the active species survived
under the original conditions (Table 4, entry 3): 1) The addi-
tion of an oxidant (2 mmol) into the reacted mixture (to
entry 3) at 90 min induced a partial increase in the yield of
the products. 2) Decreasing the amount of catalyst to
0.2 mmol caused the reaction rate to slow, but the final TON
of compound 2 reached 3395 (Table 4, entry 4).
In the case of complex 2LtBu/Ni, the reaction afforded
similar amounts of the products as in the case of LtBu/Ni
after a longer period of time (2 h), thus suggesting that the
reactive [NiL(X)n] species was supplied in situ by the disso-
ciation equilibrium of one of the LtBu ligands (Table 4,
entry 6).
Heterogeneous Oxidation Catalysis
Heterogeneous catalysis with the SBA*-L-x/Ni materials
was also performed under the same conditions (Table 4 and
Figure 5). The SBA*-L-0.5/Ni catalyst exhibited a TON of
534 for compound 2 after 3 h with activity saturation, whilst
Figure 5. Progress of cyclohexanol formation in the oxidation of cyclo-
hexane catalyzed by SBA*-L-x/Ni under standard conditions (x=0.5: *,
1: ~, 2: +, 4: X) and the filtration test (x=0.5 filtered at t=1 h: *,
dashed line).
Table 4. Catalyzed oxidation of cyclohexane with mCPBA as an oxidan-
t.[a]
nickel complex. Nam et al. also reported that NiACHTUNGTRENNUNG(ClO4)
TON
showed no catalytic activity for the oxidation of alkanes
Entry
Catalyst
t [h]
2
3
4
5
2/ACTHNGUTERNN(UG 3+4)
with mCPBA.[15]
1
2
3
4
5
6
7
8
tpa/Ni[b]
1
1
1
1
1
2
3
3
3
3
3
3
3
3
3
587
455
616
69
69
49
–
–
31
–
–
8.5
6.6
7.7
BzPym2/Ni[b]
The relationship between catalytic activity and surface en-
vironment has been investigated (Table 4, entries 5, 7–10).
The addition of SBA*-L-4 to the homogeneous LtBu/Ni cat-
alysis does not cause a loss of activity (Table 4, entry 5).
L
L
L
tBu/Ni
340
tBu/Ni[c]
tBu/Ni[d]
3395 162 164 1769 10.4
599
647
534
377
261
251
121
45
56
56
17
14
10
10
16
4
25
20
34
22
11
10
7
1
1
2
7
323
377
247 10.5
180 10.5
119 12.4
117 12.6
7.4
8.5
2LtBu/Ni[e]
SBA*-L-0.5/Ni
SBA*-L-1/Ni
SBA*-L-2/Ni
SBA*-L-4/Ni
SBA*-L-0.5/Ni[f]
SBA*-L-1/Ni[f]
SBA*-L-2/Ni[f]
SBA*-L-4/Ni[f]
SBA*-L-0.5/Ni[g]
ꢀ
ꢀ ꢀ
This result indicates that the functionalities (Si OH, Si O
SiMe3) and the extra ligand (1 equiv for Ni) on the silica
support have no significant effect on the catalysis. In hetero-
geneous catalysis, the yield and selectivity of compound 2
decrease upon an increase in the ligand loading (x) of the
immobilized catalyst (Table 4, entries 7–10). This de-activa-
tion effect upon the increase in ligand loading might be cor-
related with the formation of the [NiL2] site at higher ligand
densities on the support surface. In contrast to the homoge-
neous 2LtBu/Ni catalyst, which shows catalytic reactivity
owing to smooth ligand dissociation, the two closely fixed
Py2N sites on the solid support may act as a hexadentate
chelate and force the formation of an “inert [NiL2]” site. By
using our facile method for loading control with high repro-
ducibility, we have successfully observed a relationship be-
tween the reactivity and the structure of the active site on
the surface in this catalyst system.
9
10
11
12
13
14
15
83
30
5
9
41
48
282
2
6
13
22 14
31
174 14
6
[a] General conditions: catalyst (2 mmol), cyclohexane (15 mmol),
mCPBA (2 mmol), CH2Cl2 (3 mL), MeCN (1 mL), RT. [b] Taken from
reference [7]; the TONs of compound 5 in runs 1 and 2 were estimated
to be about 300. [c] Catalyst (0.2 mmol). [d] With the addition of SBA*-L-
4 (6 mg, 2 mmol of the immobilized ligand). [e] This system required
a longer reaction time for the saturation of product formation. [f] Reused
after washing the recovered catalyst with MeOH. [g] Reused after wash-
ing the recovered catalyst with CH2Cl2.
homogeneous catalyst LtBu/Ni showed a TON of 616 for
compound 2 (Table 4, entries 3 versus 7). A filtration test
was performed to check whether the catalysis occurred on
the immobilized complex or on the leached metal ions.[1g,14]
Under the standard conditions, with the SBA*-L-0.5/Ni cata-
lyst, the reaction mixture was passed through a syringe filter
(ADVANTEC DISMIC-13 PTFE 0.2 mm) under an Ar at-
mosphere for 1 h. GC analysis of the eluent showed no fur-
ther increase in the yield of the products, thus suggesting
that the oxidation was only catalyzed by the immobilized
To confirm that the catalyst was reusable, the nickel load-
ing in the recovered catalysts was analyzed by atomic ab-
sorption spectrometry after filtration of the reaction mixture
and subsequent washing of the recovered catalysts with
MeOH (Table 3). Lower ligand loadings in SBA*-L-x/Ni
systems (x=0.5, 1, and 2) show significant metal leaching,
whereas the material with the highest ligand loading (x=4)
almost maintains its initial metal loading at a L/Ni ratio of
2:1. This result also supports the conclusion that the coordi-
nation equilibrium shifts toward the formation of [NiL2] spe-
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Jun Nakazawa, Shiro Hikichi et al.
cies upon increasing the amount of ligand on the silica sur-
face. Metal leaching was partially suppressed by using
CH2Cl2, which is a typical unpolar and uncoordinating sol-
vent for NiII or NiIII, instead of MeOH in the washing pro-
cess during the recovery of the catalysts (initial SBA*-L-0.5/
Ni: Ni=0.08 mmolgꢀ1, recovered catalyst: Ni=0.06
(CH2Cl2) and 0.03 (MeOH) mmolgꢀ1; Table 3 and Table 4,
entries 7, 11, and 15). This result suggests that the metal
leaching is enhanced by protic and polar solvents during
washing in the presence of the products, such as cyclohexa-
nol and m-chlorobenzoic acid, with some contribution from
ligand loss through oxidative decomposition. The replace-
ment of the reaction solvent (MeCN/CH2Cl2 with CH2Cl2)
in addition to that of the washing solvent did not further im-
prove nickel leaching (0.06 mmolgꢀ1).
A catalyst-reuse experiment was performed with the re-
covered catalysts. Owing to the loss of material and nickel
leaching during the filtration step, the scale of the reaction
was decreased based on the quantity of recovered nickel
ions to maintain the same concentrations and ratios of re-
agents as in the initial run. The results were normalized to
the TON. The results for the catalysts that were recovered
by washing with MeOH (entries 11–14) or CH2Cl2 (entry 15)
are shown in Table 4. The MeOH-recovered catalysts
showed no activity, although some nickel ions remained. In
contrast, the CH2Cl2-recovered SBA*-L-0.5/Ni catalyst ex-
hibited some reactivity. The reuse run also indicated that
nickel ions were easily displaced from the reactive
[NiL(X)n] species under polar conditions, whereas any inac-
tive nickel species remained on the catalyst support. The
real deactivation process remains unknown.
nally, this result clearly demonstrates the importance of the
interactions between the surface sites for constructing de-
sired catalysts on solid supports.
Experimental Section
Instrumentation and Materials
Atomic absorption analysis was performed on a Shimadzu AA-6200. Ele-
mental analysis was performed on a Perkin–Elmer CHNS/O Analyzer
2400II. MS (ESI) spectra were recorded on a JEOL JMS-T100LC “Accu-
TOF” mass spectrometer. GC analysis was performed on a Shimadzu
GC2010 gas chromatograph with an Rtx-5 column (Restek, length=
30 m, i.d.=0.25 mm, thickness=0.25 mm). IR spectra were recorded on
a JASCO FTIR 4200 spectrometer. NMR spectra were recorded on
a
JEOL ECA-500 spectrometer. UV/Vis spectra were recorded on
a JASCO V650 spectrometer with a PIN-757 integrating-sphere attach-
ment for solid reflectance. Nitrogen-sorption studies were performed at
77 K on a Micromeritics TriStar 3000. Before the adsorption experiments,
the samples were degassed under reduced pressure for 3 h at 333 K. All
of the commercial reagents and solvents were used as received.
Synthesis of N,N-bis(2-pyridylmethyl)-N-{(1-tert-butyl-1H-1,2,3-triazol-4-
yl)methyl}amine (LtBu
)
[8]
A
mixture of compound 1[6j–l] (500 mg, 2.1 mmol), tBuN3 (500 mg,
5.0 mmol), and copper(0) powder (1 g) was stirred in 2-methyl-2-propa-
nol (10 mL) for 24 h under a N2 atmosphere at RT. The copper powder
was removed by filtration and the solvent was then evaporated under re-
duced pressure. The product was purified by column chromatography on
alumina (EtOAc) to give the product as a yellow solid (566 mg, 80%
yield). M.p. 90–928C; 1H NMR (300 MHz, CDCl3, 258C, TMS): d=8.52
(d, J
N
ACHTUNGERTN(NUNG H,H)=7.8, 1.7 Hz, 2H; Py-
4), 7.59 (s, 1H; triazole), 7.58 (d, JAHCUTNGTRENNUNG
2H; Py-5), 3.87 (s, 2H; NCH2Tz), 3.85 (s, 4H; NCH2Py), 1.64 ppm (s,
9H; tBu); 13C NMR (75 MHz, CDCl3, 258C, TMS): d=159.4, 149.1,
143.6, 136.5, 123.4, 122.0, 120.0, 59.8, 59.2, 48.9, 30.1 ppm; IR (KBr): n˜ =
3111, 3061, 2977, 2935, 2872, 2814, 1590, 1570, 1472, 1434, 1371, 1326,
1302, 1235, 1211, 1137, 1050, 979, 962, 898, 866, 772, 753 cmꢀ1; UV/Vis
(HCl/water): lmax (e)=263 nm (11700 molꢀ1 dm3 cmꢀ1); MS (ESI+,
MeOH): m/z=337.12 [M+H+]; elemental analysis calcd (%) for
C19H24N6: C 67.83, H 7.19, N 24.98; found: C 67.99, H 7.40, N 25.23.
Conclusions
In summary, polypyridylamine-type ligand L has been im-
mobilized onto silica supports with various surface densities.
By using our facile ligand-immobilization method, with con-
trolled loading and high reproducibility, we have observed
the relationship between the reactivity and structure of the
active sites on the support surface. In addition, two related
Synthesis of [Ni
(LtBu (H2O)] (LtBu/Ni)
ACHTUNGTRNENNUG )ACHTUNREGTG(NNUN OAc)2ACHTNUGTRENNUGN
A solution of LtBu (288 mg, 0.86 mmol) in MeOH (10 mL) was added to
a solution of Ni(OAc)2·4H2O (214 mg, 0.86 mmol) in MeOH (10 mL)
ACHTUNGTRENNUNG
with stirring, after which the solvent was evaporated. The crude mixture
was dissolved in CH2Cl2 (10 mL) and filtrated to remove the inorganic
salts. n-Hexane (30 mL) was layered onto the solution, which was al-
lowed to stand for 3 days to give LtBu/Ni as blue crystals (222 mg, 49%
yield). IR (KBr): n˜ =3398, 2983, 2940, 1606, 1567, 1410, 1209, 1023, 901,
771, 731, 661 cmꢀ1; UV/Vis (CH2Cl2): lmax (e)=608 (14), 771 (4), 1005 nm
homogeneous model complexes, [Ni
(LtBu
ACHTUNGTRENNGUN )ACHTUNRTGEN(NGUN OAc)2ACHTNUGTERN(NUGN H2O)] and
[Ni (BF4)2, have been prepared to determine the
A
ACHTUNGTRENNUNG
structure of the immobilized complex species. Disappoint-
ingly, the “click-to-chelate” approach was not successful in
this investigation, but the triazole group could serve as
a good anchor for attaching additional functionalities. Heter-
ogeneous nickel SBA*-L-x/Ni catalysts retained the activity
of homogeneous analogue LtBu/Ni and other reported tpa/Ni
systems for alkane oxidation. Increasing the ligand density
(x) decreases the catalytic activity. The site-isolated condi-
tions, which occur when the ligand loading is low, is effective
for preventing unwanted interactions between the active
sites, such as the formation of [ML2] species as reported
herein. On the other hand, [ML2] species that are formed
under site-dense (ligand-rich) surfaces show inert character
in comparison with the related homogeneous complex. Fi-
(14 molꢀ1 dm3 cmꢀ1); MS (ESI+, MeCN): m/z=453.13 [Ni
elemental analysis calcd (%) for [Ni(OAc)2A(H2O)
(LtBu)]·0.5H2O: C 49.20,
H 5.80, N 14.65; found: C 49.31, H 5.62, N 14.82.
ACHUTGTNRENNUG(OAc)ACHTUNGTRENNUNG
(LtBu)]+;
A
U
ACHTUNGTRENNUNG
Synthesis of [Ni
A
ACHTUNGTRENNUNG
Purple crystals of the title complex (340 mg, 72% yield) were obtained
after several days by the slow diffusion of a solution of LtBu (370 mg,
1.1 mmol) in EtOH (3 mL) into a solution of NiACTHNUTGRNEG(UN BF4)·6H2O (170 mg,
0.5 mmol) in EtOH (6 mL) in a test tube. The crystal was corrected by
filtration and washed with EtOH. Instead of the slow-diffusion proce-
dure, rapid mixing of the two solutions gave the title complex as a purple
powder within 30 min. IR (KBr): n˜ =3161, 3077, 2984, 2936, 1610, 1450,
1054, 770, 758 cmꢀ1; UV/Vis (CH2Cl2): lmax (e)=568 (23), 818 (8), 973 nm
(19 molꢀ1 dm3 cmꢀ1); MS (ESI+, MeCN): m/z=817.29 [Ni
elemental analysis calcd (%) for [Ni (BF4)2·2H2O: C 48.49, H 5.57,
(LtBu)2]
N 17.86; found: C 48.45, H 5.30, N 17.83.
(LtBu (BF4)]+;
ACHTUNGTRENNUGN )2ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
7
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Jun Nakazawa, Shiro Hikichi et al.
Preparation of SBA-L-x: General Procedure for Click Attachment
Table 5. Crystallographic data of complexes LtBu/Ni and 2LtBu/Ni.
L
tBu/Ni
2LtBu/Ni
The starting material, SBA-N3-x (x=0.5, 1, 2, 4), was prepared according
to a literature procedure.[3] A suspension of SBA-N3-x (1.0 g) in DMF
(100 mL), N-propargyl-N,N-bis(2-pyridylmethyl)amine (about 2 equiv for
N3 loading), and copper(II) sulfate (about 2 equiv for N3 loading) was de-
gassed under a flow of Ar for 30 min at RT. Then, sodium ascorbate
(5 equiv for N3 loading in 5 mL water) was added to the suspension and
the mixture was stirred for 24 h under an Ar atmosphere. The silica was
recovered by filtration and washed with DMF and water. To remove the
copper catalyst, the silica was repeatedly washed with a solution of
sodium N,N-diethyldithiocarbamate (Na-ddtc, 0.1 molꢀ1 dm3) in MeOH,
DMF, and MeOH until the brownish color of the silica had disappeared.
formula
Mw
C23H32N6NiO5·CH2Cl2
616.18
C38H48B2F8N12Ni·
932.24
ACHTUNGTRENNUNG(H2O)1.5
crystal color, shape
crystal size [mm]
crystal system
space group
a [ꢁ]
blue, block
0.2ꢃ0.3ꢃ0.4
monoclinic
P21/n (#14)
11.913(3)
14.014(4)
34.872(9)
92.034(3)
5818(3)
purple, platelet
0.15ꢃ0.35ꢃ0.45
tetragonal
I4122 (#98)
18.0581(2)
18.0581(2)
57.3310(11)
90
18695.3(5)
16
2.84–54.92
7760
113
1.325
0.492
0.0757, 0.2142
0.0769, 0.2162
1.092
b [ꢁ]
c [ꢁ]
b [8]
V [ꢁ3]
Finally, the silica was rinsed with
a solution of sodium acetate
(0.01 molꢀ1 dm3) in MeOH and in MeOH, before being vacuum-dried at
Z
8
RT for 24 h to yield SBA-L-x.
2q range [8]
FACTHNUTRGNE(UNG 000)
2.34–55.00
2576
113
1.407
0.894
0.0503, 0.1283
0.0559, 0.1245
1.153
Preparation of SBA*-L-x: General Procedure for End-Capping with
trimethylsilyl (TMS) Groups
T [K]
1calcd [gcmꢀ3
]
m
G
]
SBA-L-x (0.8 g) was suspended in toluene (50 mL) under an Ar atmos-
phere. Then, the suspension was heated at 508C with 1,1,1,3,3,3-hexame-
thyldisilazane (HMDS, 0.37 mL, 1.7 mmol) for 1 h and the silica was re-
covered by membrane filtration. The silica was washed with toluene and
vacuum-dried at RT for 24 h to give end-capped silica SBA*-L-x as
a pale-yellow powder.
R, Rw (I>2s(I))[a]
R, Rw (all data)[a]
GOF on S[b]
2
2
[a] R=ꢀj jFo jꢀjFc j j/ꢀjFo j. Rw ={ꢀ[w
{ꢀ[w
(Fo ꢀFc2)2]/ꢀ[w
N
.
[b] S=
2
A
ACHTUNGTRENNUNG
the total number of refined parameters.
General Procedure for the Preparation of SBA*-L-x/Ni
SBA*-L-x (0.5 g) was suspended into
a solution of NiACHTUNTGNRUEGN(OAc)2·4H2O
was recorded in a cell (path length: 1 cm). The ligand loading was calcu-
lated by using the homogeneous analogue, LtBu (l=263 nm, e=
11700 molꢀ1 dm3 cmꢀ1 in aqueous HCl), as a reference.
(1.5 equiv for ligand) in MeOH (50 mL) and the mixture was stirred for
30 min. The silica powder was recovered by membrane filtration, washed
with MeOH, and vacuum-dried at RT for 24 h to give SBA*-L-x/Ni.
The procedure for determining the Ni loadings of SBA*-L-x/Ni was as
follows: SBA*-L-x/Ni (5 mg) was dissolved in a 10% aqueous solution of
KOH (1 mL) with heating for 5 min. Then, the solution was acidified
with a concentrated aqueous solution of HNO3 (2 mL) and diluted with
water to a total volume of 10 mL. The solution was passed through a sy-
ringe filter prior to its introduction into an atomic absorption spectrome-
ter.
Crystallography
The preparation of single crystals of complexes LtBu/Ni and 2LtBu/Ni was
discussed in the synthesis section. Diffraction data for all single crystals
were collected on a Rigaku Saturn 70 CDD area-detector system with
graphite-monochromated MoKa radiation. Crystals were mounted onto
loops with liquid paraffin and then flash cooled to 113 K. Data collection
and processing were performed by using Rigaku CrystalClear software.[16]
Oxidation of Cyclohexane
Structural solution was performed by using direct methods (SIR-92[17]
)
Cyclohexane was oxidized at RT under an Ar atmosphere. In a typical re-
action,[7] a solution (or suspension) of the homogeneous (or heterogene-
ous) nickel complex (2.0 mmol) in MeCN (1.0 mL) and CH2Cl2 (1.0 mL)
was added to a mixture of cyclohexane (15 mmol, 1.6 mL), mCPBA
(345 mg, 2.0 mmol), and nitrobenzene (10 mL, 100 mmol, as a GC stan-
dard) in CH2Cl2 (2.0 mL). To monitor the product formation, an aliquot
of the reaction mixture (0.2 mL) was extracted at certain times and
and refinements were performed by using full-matrix least-squares
(SHELXL-97[18]) against F2; all reflections were performed by using
WinGX software.[19] For complex 2LtBu/Ni, racemic twin refinement was
applied by using SHELEX-97. All nonhydrogen atoms were refined ani-
sotropically. Hydrogen atoms that were adjacent to carbon atoms were
placed at calculated positions. Hydrogen atoms on oxygen atoms were lo-
cated by using difference Fourier synthesis and were refined isotropically.
The molecular structures were visualized by using the ORTEP-3 pro-
gram.[20] Crystallographic data are summarized in Table 5. CCDC 860009
(LtBu/Ni) and CCDC 860010 (2LtBu/Ni) contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif.
quenched with
a solution of triphenylphosphine (10 mg) in CH2Cl2
(0.5 mL), after which the solution was subjected to GC analysis. The re-
ported data are averages of three independent measurements. No change
in reactivity was observed under shaking instead of mechanical stirring
with a Teflon-coated magnetic stirrer bar.
Quantification of the Loadings of the Immobilized Ligand and Nickel
Acknowledgements
The procedure for the determination of the ligand loadings of SBA-L-
x was as follows: SBA-L-x (5 mg) was dissolved in an aqueous solution of
potassium hydroxide (10%, 1 mL) and the mixture was boiled for 5 min.
Then, the solution was diluted with an aqueous solution of HCl (about
0.1 molꢀ1 dm3) to a total volume of 100 mL and a UV/Vis spectrum was
recorded in a cell (path length: 1 cm). The ligand loading was calculated
by using the homogeneous analogue, LtBu (l=263 nm, e=
11700 molꢀ1 dm3 cmꢀ1 in aqueous HCl), as a reference.
This work was supported by a Grant in-Aid for Scientific Research
(20360367), the Cooperative Research Program of the Network Joint Re-
search Center for Materials and Devices (2011169, 2012216, and
2012348), the Strategic Development of Research Infrastructure for Pri-
vate Universities and a Scientific Frontier Research Project from the
Ministry of Education, Culture, Sports, Science, and Technology of Japan,
and by the Stanford Global Climate and Energy Project (GCEP).
The procedure for determining the ligand loadings of SBA*-L-x was as
follows: SBA*-L-x (5 mg) and acidic NH4F (18 mg) were dissolved in
MeOH (5 mL) under gentle heating (508C) for several hours. Then, the
solution was diluted with MeOH and a concentrated aqueous solution of
HCl (about 1 mL) to a total volume of 100 mL and a UV/Vis spectrum
[1] a) D. E. De Vos, M. Dams, B. F. Sels, P. A. Jacobs, Chem. Rev. 2002,
102, 3615–3640; b) Q.-H. Xia, H.-Q. Ge, C.-P. Ye, Z.-M. Liu, K.-X.
Su, Chem. Rev. 2005, 105, 1603–1662; c) E. Brulꢂ, Y. R. de Miguel,
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&
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www.chemasianj.org
Jun Nakazawa, Shiro Hikichi et al.
Org. Biomol. Chem. 2006, 4, 599–609; d) S. Minakata, M. Komatsu,
Chem. Rev. 2009, 109, 711–724; e) A. Zamboulis, N. Moitra, J. J. E.
Moreau, X. Cattçen, M. W. C. Man, J. Mater. Chem. 2010, 20, 9322–
9338; f) S. Shylesh, M. J. Jia, W. R. Thiel, Eur. J. Inorg. Chem. 2010,
4395–4410; g) C. W. Jones, Top. Catal. 2010, 53, 942–952.
2010, 49, 4278–4287; l) J. Rosenthal, S. J. Lippard, J. Am. Chem.
Soc. 2010, 132, 5536–5537; m) J. M. Lee, J. Kim, Y. Shin, C. E.
Yeom, J. E. Lee, T. Hyeon, B. M. Kim, Tetrahedron: Asymmetry
2010, 21, 285–291; n) B. S. Rana, S. L. Jain, B. Singh, A. Bhaumik,
B. Sain, A. K. Sinha, Dalton Trans. 2010, 39, 7760–7767; o) C. M.
Fu, H. Y. Shi, G. S. Qian, Z. W. Li, Chin. Chem. Lett. 2009, 20,
1345–1347; p) T. L. Mindt, H. Struthers, B. Spingler, L. Brans, D.
Tourwꢂ, E. Garcꢄa-Garayoa, R. Schibli, ChemMedChem 2010, 5,
2026–2038; q) G. Zhang, Y. Wang, X. Wen, C. Ding, Y. Li, Chem.
Commun. 2012, 48, 2979–2981.
[2] a) M. Tada, T. Taniike, L. M. Kantam, Y. Iwasawa, Chem. Commun.
2004, 2542–2543; b) J. C. Hicks, R. Dabestani, A. C. Buchanan,
C. W. Jones, Chem. Mater. 2006, 18, 5022–5032; c) J. C. Hicks, C. W.
Jones, Langmuir 2006, 22, 2676–2681; d) M. Tada, R. Coquet, J.
Yoshida, M. Kinoshita, Y. Iwasawa, Angew. Chem. 2007, 119, 7358–
7361; Angew. Chem. Int. Ed. 2007, 46, 7220–7223; e) K. Cheng,
C. C. Landry, J. Am. Chem. Soc. 2007, 129, 9674–9685; f) G. Grigor-
opoulou, K. C. Christoforidis, M. Louloudi, Y. Deligiannakis, Lang-
muir 2007, 23, 10407–10418; g) T. J. Terry, G. Dubois, A. Murphy,
T. D. P. Stack, Angew. Chem. 2007, 119, 963–965; Angew. Chem. Int.
Ed. 2007, 46, 945–947; h) T. J. Terry, T. D. P. Stack, J. Am. Chem.
Soc. 2008, 130, 4945–4953; i) J. M. Fraile, J. I. Garcꢄa, C. I. Herrerꢄas,
J. A. Mayoral, E. Pires, Chem. Soc. Rev. 2009, 38, 695–706; j) J. M.
Fraile, J. I. Garcꢄa, J. A. Mayoral, Chem. Rev. 2009, 109, 360–417.
[3] a) J. Nakazawa, T. D. P. Stack, J. Am. Chem. Soc. 2008, 130, 14360–
14361; b) J. Nakazawa, B. J. Smith, T. D. P. Stack, J. Am. Chem. Soc.
2012, 134, 2750–2759.
[4] a) D. J. Macquarrie, Chem. Commun. 1996, 1961–1962; b) S. Huh,
J. W. Wiench, J.-C. Yoo, M. Pruski, V. S.-Y. Lin, Chem. Mater. 2003,
15, 4247–4256; c) V. Matsura, Y. Guari, J. Larionova, C. Guꢂrin, A.
Caneschi, C. Sangregorio, E. Lancelle-Beltran, A. Mehdi, R. J. P.
Corriu, J. Mater. Chem. 2004, 14, 3026–3033; d) R. J. P. Corriu, A.
Mehdi, C. Reyꢂ, C. Thieuleux, Chem. Mater. 2004, 16, 159–166; e) J.
Alauzun, A. Mehdi, C. Reyꢂ, R. Corriu, New J. Chem. 2007, 31,
911–915; f) C.-T. Tsai, Y.-C. Pan, C.-C. Ting, S. Vetrivel, A. S. T.
Chiang, G. T. K. Fey, H.-M. Kao, Chem. Commun. 2009, 5018–5020.
[5] D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson,
B. F. Chmelka, G. D. Stucky, Science 1998, 279, 548–552.
[6] a) V. V. Rostovtsev, L. G. Green, V. V. Fokin, K. B. Sharpless,
Angew. Chem. 2002, 114, 2708–2711; Angew. Chem. Int. Ed. 2002,
41, 2596–2599; b) V. O. Rodionov, S. I. Presolski, D. D. Diaz, V. V.
Fokin, M. G. Finn, J. Am. Chem. Soc. 2007, 129, 12705–12712;
c) W. H. Binder, C. Kluger, Curr. Org. Chem. 2006, 10, 1791–1815;
d) Z. M. Guo, A. W. Lei, X. M. Liang, Q. Xu, Chem. Commun.
2006, 4512–4514; e) M. Ortega-MuÇoz, J. Lopez-Jaramillo, F. Her-
nandez-Mateo, F. Santoyo-Gonzalez, Adv. Synth. Catal. 2006, 348,
2410–2420; f) J. P. Collman, N. K. Devaraj, T. P. A. Eberspacher,
C. E. D. Chidsey, Langmuir 2006, 22, 2457–2464; g) J. P. Collman, L.
Zeng, H. J. H. Wang, A. Lei, J. I. Brauman, Eur. J. Org. Chem. 2006,
2707–2714; h) A. Devadoss, C. E. D. Chidsey, J. Am. Chem. Soc.
2007, 129, 5370–5371; i) D. E. Bergbreiter, P. N. Hamilton, N. M.
Koshti, J. Am. Chem. Soc. 2007, 129, 10666–10667; j) S. Huang, R. J.
Clark, L. Zhu, Org. Lett. 2007, 9, 4999–5002; k) H. A. Michaels,
C. S. Murphy, R. J. Clark, M. W. Davidson, L. Zhu, Inorg. Chem.
[7] a) T. Nagataki, Y. Tachi, S. Itoh, Chem. Commun. 2006, 4016–4018;
b) T. Nagataki, K. Ishii, Y. Tachi, S. Itoh, Dalton Trans. 2007, 1120–
1128; c) T. Nagataki, S. Itoh, Chem. Lett. 2007, 36, 748–749.
[8] J. C. Bottaro, P. E. Penwell, R. J. Schmitt, Synth. Commun. 1997, 27,
1465–1467.
[9] a) D. Schweinfurth, R. Pattacini, S. Strobel, B. Sarkar, Dalton Trans.
2009, 9291–9297; b) M. Ostermeier, M.-A. Berlin, R. M. Meudtner,
S. Demeshko, F. Meyer, C. Limberg, S. Hecht, Chem. Eur. J. 2010,
16, 10202–10213; c) O. Fleischel, N. Wu, A. Petitjean, Chem.
Commun. 2010, 46, 8454–8456; d) S. Zanarini, M. Felici, G. Valenti,
M. Marcaccio, L. Prodi, S. Bonacchi, P. Contreras-Carballada, R. M.
Williams, M. C. Feiters, R. J. M. Nolte, L. De Cola, F. Paolucci,
Chem. Eur. J. 2011, 17, 4640–4647; e) C. H. Zhang, X. D. Shen, R.
Sakai, M. Gottschaldt, U. S. Schubert, S. Hirohara, M. Tanihara, S.
Yano, M. Obata, N. O. Xiao, T. Satoh, T. Kakuchi, J. Polym. Sci.
Part A 2011, 49, 746–753.
[10] J. P. Wikstrom, A. S. Filatov, R. J. Staples, C. R. Guifarro, E. V.
Rybak-Akimova, Inorg. Chim. Acta 2010, 363, 884–890.
[11] S. Brunauer, P. H. Emmett, E. Teller, J. Am. Chem. Soc. 1938, 60,
309–319.
[12] E. P. Barrett, L. G. Joyner, P. P. Halenda, J. Am. Chem. Soc. 1951,
73, 373–380.
[13] G. Tꢅrkoglu, C. P. Ulldemolins, R. Mꢅller, E. Hꢅbner, F. W. Heine-
mann, M. Wolf, N. Burzlaff, Eur. J. Inorg. Chem. 2010, 2962–2974.
[14] a) M. Ghorbanloo, H. H. Monfared, C. Janiak, J. Mol. Catal. A 2011,
345, 12–20; b) M. Weck, C. W. Jones, Inorg. Chem. 2007, 46, 1865–
1875.
[15] W. Nam, J. Y. Ryu, I. Kim, C. Kim, Tetrahedron Lett. 2002, 43,
5487–5490.
[16] Rigaku corporation, 1999.
[17] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, J. Appl.
Crystallogr. 1993, 26, 343–350.
[18] G. M. Sheldrick, Acta Crystallogr. Sect. A 2008, 64, 123–134.
[19] L. J. Farrugia, J. Appl. Crystallogr. 1999, 32, 837–838.
[20] L. J. Farrugia, J. Appl. Crystallogr. 1997, 30, 565.
Received: February 6, 2013
Published online: && &&, 0000
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Chem. Asian J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
These are not the final page numbers! ÞÞ

FULL PAPER
Heterogeneous Catalysis
Jun Nakazawa,* Tomoaki Hori,
T. Daniel P. Stack,
Shiro Hikichi*
&&&& — &&&&
Alkane Oxidation by an Immobilized
Nickel Complex Catalyst: Structural
and Reactivity Differences Induced by
Surface-Ligand Density on Mesopo-
rous Silica
Going nowhere fast: An immobilized
SBA*-L-x/Ni complex was prepared
with various ligand loadings and used
in the oxidation of cyclohexane. The
importance of site-density control for
the development of immobilized cata-
lysts has been demonstrated.
&
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10
Chem. Asian J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!