Trace amount CuII (ppm) and mixture design of CuII/PdII catalyzed Suzuki cross-coupling reactions based on the cooperative interaction of metal with a conjugated pyridylspirobifluorene

Article abstract of DOI:10.1039/c5ta00222b

Self-assembly of Cu/psf sheets and layer-by-layer (LbL) growth of PEI-(Cu/psf)_n films were carried out and characterized (psf = 2,2′,7,7′-tetra(4-pyridyl)-9,9′-spirobifluorene). A mixture design was performed to evaluate the singular and combined catalytic effects of Cu(ii), Pd(ii) and psf ligands in the Suzuki cross-coupling reactions. The results showed that copper exhibited high catalytic activities in the presence of psf ligands. The (Cu^II/psf)_n films were used as the reservoirs of catalysts capable of gradually discharging highly active catalytic moieties to promote the coupling reactions with ultra low Cu-loadings (as low as 1.4 × 10^-5 mol%). This journal is

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Communications
Trace Amount CuII(ppm) and Mixture Design of CuII/PdII Catalyzed
Suzuki Cross-Coupling Reactions Based on Cooperative Interaction of
Metal with a Conjugated Pyridylspirobifluorene
Xing Li,*a Jie Zhang,a,b Yayun Zhao,a Xiuhua Zhao,a Feng Li,b Taohai Li,*b H. L. Lic and Liang Chenc
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
in which delocalized electrons of the organic ligand can be
transferred to dꢀorbits of metal ions to elevate the catalytic
50 performance of metal ions.20,21 For this purpose, we
synthesized a tetrapyridylspirobifluorene ligand (Scheme S1),
and assembled a kind multilayer film (Cu/psf)n as catalyst
reservoirs capable of progressively releasing amounts of high
catalytic active Cuꢀspecies to promote Suzuki crossꢀcoupling
55 reactions with ultra low Cuꢀloadings (1.4 x 10ꢀ5 mol%).
Self-assemble of the Cu/psf sheets and the layer-by-layer
(LbL) growth of PEI-(Cu/psf)n films were carried out and
characterized (psf
= 2,2',7,7'-tetra(4-pyridyl)-9,9'-spirobi-
10 fluorene). A mixture design was performed to evaluate the
singular and combined catalytic effects of Cu(II), Pd(II) and
psf ligands in the Suzuki cross-coupling reactions. The results
showed that copper exhibited high catalytic activities in the
presence of psf ligands. The (CuII/psf)n films were used as the
15 reservoirs of catalysts capable of gradually discharging high
active catalytic moieties to promote the coupling reactions
with ultra low Cu-loadings (as low as 1.4 x 10-5 mol%).
Palladium or its compounds are widely used as the catalysts to
promote a variety of CꢀC bond formation because of their high
20 catalytic activity in organic synthesis.1ꢀ5 Copper in place of
the more toxic and expensive palladium, as the catalyst to
perform various coupling reactions, is much more attractive
for industry syntheses.6ꢀ8 For example, copperꢀcatalyzed CꢀN,
CꢀO and CꢀC Ullmannꢀtype coupling reactions are key routes
Fig. 1 (a) Space filling representation of the R configuration; (b) R and S
configurations of the psf ligand.
A 2,2',7,7'ꢀtetra(4ꢀpyridyl)ꢀ9,9'ꢀspirobifluorene (psf) was
25 for creating new molecules of pharmaceuticals, natural 60 synthesized by the reaction of pyridineꢀ4ꢀboronic acid and
products, and organic functional materials, in which Ullmannꢀ
Hurtley reactions present the C(sp2)ꢀC(sp3) condensations of
aryl halides (ArI and ArBr) with activated methylene
compounds (dialkyl malonate and βꢀketoesters).8,9 Copperꢀ
2,2',7,7'ꢀtetrabromoꢀ9,9'ꢀspirobifluorene in the presence of
K2CO3 and Pd(PPh3)4 in the solution of toluene / EtOH / H2O,
purified by column chromatography and characterized by IR,
MS, NMR (Fig. S1ꢀ4 in ESI). Single crystal Xꢀray diffraction
30 mediated Stilleꢀtype crossꢀcoupling of ArylꢀI with R4Sn 65 analysis revealed that compound crystallized in triclinic
(organostannane) can take place under mild reaction
conditions to develop new CꢀC bonds.10,11 CuIꢀcatalyzed
Clickꢀtype coupling reactions of azideꢀalkyne cyclizations are
important approaches for preparation of new useful
system, space group Pꢀ1 (Table S1 and S2 for crystal data in
ESI). The dihedral angle between the two spiroꢀlinked aryl
branches was measured to be 86.6o for Rꢀtype, and 86.7o for
Sꢀtype configuration. Four pyridyl rings were greatly twisted
35 compounds.12,13 However, previous studies on the coupling 70 from the planes of the fluorine units with various dihedral
reactions were mainly focused on C(sp2)ꢀN, C(sp2)ꢀO, C(sp2)ꢀC
condensations and Cu(I)ꢀcatalyzed Suzuki and Sonogashira
coupling reactions.14ꢀ17 Reports on Cu(0)ꢀcatalyzed Suzuki
couplings of aryl halides with arylboronic acids were very
40 limited in the past decades.18,19
angles of 31.8, 38.8, 46.4 and 46.9o for Rꢀtype; 34.5, 38.9,
49.3 and 52.6o for Sꢀtype. The different twisted angles
resulted in that the psf molecule was chiral, and a racemic
mixture was isolated from DMF solution. As shown in Fig.1,
75 the psf structure was close to be “X”ꢀlike orthogonal mode, of
which four terminal pyridine N atoms facilely link metal ions
to form polymeric metalꢀorganic framework complexes.22 In
addition, the delocalized π electrons of the psf could be
transfered to d orbits of metal ions to activate the catalytic
Interestingly, as far as we known, Cu(II)ꢀcatalyzed Suzukiꢀ
type C(aryl)ꢀC(aryl
) crossꢀcoupling reactions are scarcely
reported up to now, which possibly result from Cu(II) ion
inactivity of 3d9 electrons for those catalytic system. A larger
45 πꢀconjugated organic ligand may enhance the catalytic activity 80 activities of transition metal ions. Based on the strongpoint
of Cu(II) ions to promote the CꢀC coupling information based
on synergistic effect of metal ions and πꢀconjugated moieties,
above, the organic ligand psf was synthesized to act as a
useful building unit for the assembly of multilayer films.
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Fig. 2 TEM images, inset: EDS spectra; (a): (Pd/psf), (b): (Cu/psf), (c): (Cu/Pd/psf) composites.
5
Combination designs 4-7 were prepared by mixing 50 surfaces (Fig. S11). TEM confirmed the amorphous structure
predetermined quantificational solution of Cu(II), Pd(II) and
psf ligands (Fig. S5), and characterized by SEM, TEM and
EDS to understand the morphologies, sizes and structures of
the composites. The tubular structure (Fig. S6) of the free psf
of the Cu/Pd/psf complex and the element maps gave all of
the expected elements C, N, O, Cu, Pd and Cl measured by
EDS spectra (Fig. 2c), indicating that the composite of 7
should be composed of Cu(NO3)2, PdCl2 and psf ligands.
PEIꢀ[Cu(NO3)2/psf]n multilayer films were assembled by
alternately immersing a quartz slide preꢀcoated with a PEI
layer in Cu(NO3)2 and psf solutions, respectively. PEI firstly
formed a layer on the quartz substrate (Fig. S12), and then the
substrate absorbed copper ions through coordination bonding
10 ligand was different with the pattern of the metalꢀpsf
composites. SEM of the combination of PdCl2/psf (5) showed
that nanoscale particles of (Pd/psf) complex (NPs) were
generally quite homogeneous with significant agglomeration
(Fig. S7a), in which statistical calculations were used to
55
15 determine the particle size distribution in the measured SEM 60 after it was preꢀcoated with a PEI layer.24,25 UVꢀvis spectra
images. Mean size of the particles was recorded with high
accuracy over 100 particles of each sample measured.23 The
diameters of Pd/psf complex particles ranged from 24 to 67
nm with mean values of 38.8 ± 3.1 nm (Fig. S7b).
were used to monitor the growth process of the multilayer
films. As shown in Fig. S13, two highꢀenergy peaks centered
at 223 and 262 nm could be attributed to n→σ* transition, and
the absorption peaks centered at 321 and 345 nm tentatively
20
The morphologies of Pd/psf NPs were confirmed by TEM 65 ascribed to πꢀπ* transitions in the psf ligand. The UVꢀvis
(Fig. 2a), which displayed that the particles were almost
spherical in shape and comparatively uniform in size with the
average diameter of 25 ~ 60 nm. The elemental maps on the
samples were detected by EDS, which showed all of the
absorbance spectrogram of PEIꢀ(Cu(NO3)2/psf)n was similar
with one of the free psf ligand with some redꢀshift changes of
the absorption peaks (Fig. S14), which could result from the
Cu(II)ꢀpsf coordination interaction, probably along with some
25 expected elements C, N, O, Pd and Cl in the spectra, 70 d(Cu2+)→π*(pyridyl) MLCT (Metalꢀtoꢀligand charge transfer)
indicating the nanocomposite consisted of PdCl2 and psf
ligands (Fig. 2a, inset). It needs to be reminded that reaction
times, temperatures, solvents and concentration of metal ions
and psf ligands exerted important effects on the morphologies
character.26,27 Upon adding film layers, Cu2+ ions deposition
resulted in the absorbance increase. The absorbance increases
were close to linear with R2 = 0.9803 between the optical
absorption at λmax = 345 nm and the number of bilayers,
30 of combination composites. When decreasing reaction time 75 suggesting that the psf ligands were incorporated in the
and temperature (down to 40 oC for 1.0 h), stickꢀlike
structures of combination (Pd/psf) were separated from
EtOH/H2O (Fig. S8). When EtOH solvents were replaced by
DMF or CH2Cl2, the (Pd/psf) NPs patterns or agglomerated
35 particles were observed, respectively (Fig. S9).
The morphological patterns of combination Cu/psf (6)
provided some valuable information. The different
dimensional Cuꢀpsf NPs were separated from various reaction
conditions including the reaction solvents, temperatures or
multilayer films PEIꢀ(Cu2+/psf)n for the first ten layers. Thus,
metalꢀpyridyl coordination interactions were responsible for
the LbL deposition between Cu(II) ions and the psf.24,25
The desorption experimental tests were carried out to
80 determine the Cuꢀloadings in the multilayer film of PEIꢀ
(Cu2+/psf)10. The quartz slide coated with PEIꢀ(Cu2+/psf)10
film was immersed in a mixed solution of K2CO3, EtOH and
H2O for 20, 40, 60, 80 and 100 min, respectively, to study the
release behavior of Cuꢀpsf complex, in which UVꢀvis spectra
40 times (Fig. S10). It was interesting that regular hexagons were 85 were employed to monitor the absorbance change of films.
clearly found in the TEM images of Cu/psf samples with the
size ranging from 2.1 to 3.5ꢁm (Fig. 2b). The element maps
presented all of the expected constituents of C, N, O and Cu
detected by EDS spectra (inset in Fig. 2b), confirming the
45 components of the Cu/psf composites.
After (Cu2+/psf)10 components were completely desorbed into
the aqueous solution, the Cu(II) concentration of 0.87 ppm in
the solution (10mL) was determined by inductively coupled
plasmaꢀatomic emission spectroscopy (ICPꢀAES), namely, 8.7
90 µg (1.4 x 10ꢀ5 mol%).
A texture was observed for the composite of Combination
Cu/Pd/psf (7) with the thickness of 10~15 nm, in which the
composites performed selfꢀcrimp to form agaricꢀlike
structures with various hollows or pools on the material
The AFM images of the multilayer films were taken to
provide detailed information about the surface morphology
and homogeneity of the deposited film. The height images of
PEIꢀ(Cu2+/psf)n showed that the aggregated nanoꢀparticulates
2
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were compactly distributed on the quartz sheets with vague
boundaries among particles. As shown in Fig. S15a, the scan
area is 1.0 × 1.0 ꢁm for typical AFM image of the PEIꢀ
(Cu2+/psf)5 film, in which some aggregated particles as islets
molecular Cuꢀspecies or nanoparticulates as high active
catalysts to promote the Suzuki crossꢀcoupling reactions.
The Suzuki coupling reactions were carried out to evaluate
the catalytic effects of the singular and combined composites
5
were unevenly distributed on the surface of the film with rootꢀ 55 from Cu(II), Pd(II) and psf ligands. The crossꢀcoupling of 4ꢀ
meanꢀsquare (RMS) roughness being 0.430 nm. The
stereoscopic graphic visually displayed the surface rugged
morphology of the film PEIꢀ(Cu2+/psf)5 and the maximum
peak height (Rmax) could reach up to 6.615 nm. With the
ethoxyꢀ4ꢀiodobenzenes and 4ꢀmethylphenylꢀboronic acids was
used as a model reaction, and the results were listed in Table 1.
As expected, complex 2 (PdCl2) displayed high catalytic
o
activity, affording quantitative yield at 90 C for 10 h (Table 1,
10 increase in the number of layers, more particle aggregates 60 entry 2), but 1 (Cu(NO3)2) and 3 (psf) were inactive (Table 1,
were observed and the islandꢀshaped nanostructures were
dispensed on the film surface (Fig. S15b). The height image
of PEIꢀ(Cu2+/psf)10 showed the rough, and uneven degrees
were obviously raised on the film surface with the RMS
entries 1 and 3). Biꢀcomponent combination, 4 (Cu/Pd) NPs
gave a satisfied yield (85%, Table 1, entry 4). However, Biꢀ or
tricomponent combinations exhibited considerably high
catalytic activity in the presence of the psf ligand (Table 1,
15 roughness of 1.134 nm for ten layer film PEIꢀ(Cu2+/psf)10 65 entries 5ꢀ7). The results above shown that the high catalytic
upon increasing the film number. The stereoscopic graphic
provided the clear view of the rough surface and the
maximum peak height (Rmax) reached up to 16.325 nm. For the
film PEIꢀ(Cu2+/psf)15, the surface of the film became much
activity of Cuꢀcomponents could result from the synergistic
interaction of dꢀπ electrons between the psf ligands and Cu(II)
ions.28ꢀ30 If Cuꢀpsf components as active catalysts can be used
for Suzuki coupling reactions instead of palladiums, the cost
20 more rougher with RMS roughness of 1.293 nm (Fig. S15c), 70 will be reduced greatly in the industrial organic synthesis.
and larger islandꢀshaped or valleyꢀlike structures were
Table 1. Filtrating of monoꢀ or multiꢀcomponent catalysts for the Suzuki
reaction of aryl iodides with aryl boronic acids.
observed and the maximum peak height (Rmax) reached up to
25.461 nm. The results above showed that PEIꢀ(Cu2+/psf)n
multilayer films could be assembled with layerꢀbyꢀlayer
25 fashion on the surface of the preceding deposition layer to
Entry
Catalyst
T/oC
Time/h Yield / %
form islandꢀshaped nanostructure through the coordination
bonding interaction.
1
2
3
4
5
1 [Cu(NO3)2]
2 (PdCl2)
3 (psf)
4 (Cu/Pd) NPs
5 (Pd/psf) NPs
90
90
90
90
90
10
10
10
10
10
0
100
0
85
100
6
7
6 (Cu/psf) sheets
90
90
10
10
95
98
7 (Cu/Pd/psf) composites
Procedure: 1.0 mmol of aryl iodobe, 1.2 mmol of aryl boronic acid, 3.0
mmol of K2CO3, 4.0 mL of EtOH and 3.0 mL of H2O in the air.
Catalysts 3.0% (metal or metalꢀligand nanoparticles relative to aryl
halide). IR, NMR and MS of products in ESI.
Fig. 3 SEM images of the [Cu(NO3)2/psf]10 film, inset: EDS; (b) particle
30 size distribution.
To further investigate the catalytic activity of copper, a
75 series of comparative experiments were performed in the
similar conditions. It was found that Cu powders as catalysts
presented very low activity (Table S3, entry 1). When the psf
ligands were added into the above reaction, the yield
increased to 47% at 90 oC for 10h (entry 2). Similarly, CuI
80 was low active as a catalyst in absence of the psf ligand (entry
3), once the psf ligands were added and the catalysts (CuI/psf)
displayed wondrously high activity with the yield up to 99%
(entry 4). Likewise, Cu(NO3)2 was inactive (entry 5), and
Cu(NO3)2/psf nanoparticulates (NP) as catalysts exhibited
85 considerably high activity (entry 6). Comprehensibly, CuSO4
and CuCl2 were inactive (entries 7 and 9). Strangely, when
CuSO4 or CuCl2 replaced Cu(NO3)2, the catalysts of Cu(II)ꢀ
psf NPs exhibited low catalytic activity in the similar reaction
SEM image of [Cu(NO3)2/psf]10 film also confirmed the
rough surface texture. The agglomerated particles were
irregularly scattered on the film surface with indistinct
borderline among the particulates (Fig. 3a), which supported
35 the morphology what was observed in AFM. EDS spectrum
confirmed all the expected elements on the film (Fig. 3a,
inset), indicating that Cu(NO3)2 and psf were adsorbed on the
substrates. Statistic calculations in SEM image were used to
measure the particle size distribution, and results showed the
40 particle sizes ranged from 25.5 to 78.5 nm with average value
49.3 ± 2.8nm (Fig. 8b). The above SEM exhibited that the
analogous morphologies for the films and Cu(II)ꢀpsf
components. Powder Xꢀray diffraction (PXRD) analyses
displayed that Cuꢀpsf NPs and PEIꢀ(Cu/psf)n films had similar
45 PXRD patterns (Fig. S16), indicating that the films and
nanoparticulates possessed the analogous composition. The
similar morphologies and components may promise analogous
physical or chemical properties. The delaminated texture of
the above Cuꢀpsf complex also confirmed that the Cuꢀpsf
50 multilayer films, sheets or colloids could release the soluble
system (Table S3, entries 8 and 10), which could result from
2ꢀ
90 that the anions of SO4
and Clꢀ gave the different
coordination interaction to Cu(II) ions, compared with the
ꢀ
NO3 , resulting in the Cu(II) ions showed different catalytic
activity for the coupling reactions.31
In addition, particle sizes and morphologies exerted
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o
important effect on the conversion yields, which was
confirmed by using Cu/psf composites as catalysts in the
respectively, but a very low yield (≤5.0%) at 50 C (Fig. 5,
for 3). The higher yields may originate from that the psf
coupling reactions. The different yields of 71%, 83%, 65% 45 ligand could easily transfer its π electrons to 3dꢀorbits of
and 58% corresponded to the different dimensional sizes
(Table S4), respectively, indicating catalytic activity increased
with the decrease of Cuꢀpsf sheet sizes in this reaction
system.32 Notably, the fresh precipitates of the Cu(NO3)2/psf
Cu(II) ions for promoting the catalytic performance at
corresponding the temperatures, comparing with bpy ligand.
Intriguingly, the PEIꢀ(Cu2+/psf)10 film was submerged to
the reaction mixture in a small pressureꢀproof vial with a
5
combination as catalysts showed high catalytic activity (yield 50 magnetic bar, in which the multilayer film as a catalyst
95%), and the dry bulk powders of the Cu(NO3)2/psf
reservoir was capable of progressively releasing amounts of
high catalytic active Cuꢀspecies to promote Suzuki coupling
reactions with ultra low Cuꢀloadings (down to 1.4 x 10ꢀ5
mol%), and gave higher yields (Fig. 5, for 4), comparing with
10 combination as catalysts demonstrated low activity (yield <
58%). Still, the reaction, displaying high yield by using the
combination of the CuI/psf as catalyst, was understandable, in
which CuI could be progressively oxidized to be Cu(II) in 55 ones of Cu(NO3)2/psf sheets as catalysts in the respective
presence of K2CO3 and O2, and immobilized by the pyridyl
15 groups of the psf ligand, and the reaction was a homogeneous
process.33 Although Cu powder was also oxidized to be Cu(II)
in presence of K2CO3 and O2, and to formed the Cu(II)/psf
corresponding temperatures. As expected, the released Cuꢀpsf
components from the film were highly active for the Suzuki
crossꢀcoupling reactions under mild reaction conditions (Fig.
5 and Table S6, entry 4). It should be noted that when
composite with the psf ligand as the catalyst, it was too few to 60 Cu(NO3)2 and psf were put together in H2OꢀEtOH solutions,
availably promote the coupling in the similar reaction.
the Cuꢀpsf precipitate nanoparticulates or colloids were
formed immediately, which were not separated and directly
acted as the catalysts, and gave high yield (95%). However,
the Cuꢀpsf precipitates were separated, dried and acted as the
20
As shown in Fig. 4, the amount of Cuꢀcatalysts exerted
great effects on the Suzuki crossꢀcoupling reactions. The
catalystꢀloadings from 2.9 x 10ꢀ2 to 2.9 mmol%, the reactions
gave high yields by using Cu(II)/psf nanoparticulates (Cu : psf 65 catalysts, the reaction gave only 82% yield. Therefore, we
= 1:1, mmol / mmol) as catalysts. On the quantity of the
have reason to assume that the released Cuꢀsfp species from
the film are the soluble molecules or nanoparticulates, which
act as the active constituents in the coupling reactions.34
25 catalyst being less than 2.9 ×10ꢀ2 mmol%, the reaction gave
o
very low yield at 90 C for 10 h (Table S5).
Fig. 4 Effect of amount of Cu(II)/psf NP catalysts on the reactions.
70 Fig. 5 Effect of the coꢀcatalysts and temperatures on the reactions. 1:
Cu(II)/PPh3 NPs; 2: Cu(II)/bpy NPs; 3: Cu(II)/psf sheets; 4: (Cu(II)/psf)10
film. Cuꢀcatalyst loading 3.0 mol% for Cu(II)/PPh3, Cu(II)/bpy NPs and
Cu(II)/psf sheets; 1.4 x 10ꢀ5 mol% for (Cu(II)/psf)10 film.
Further studies revealed that the reaction temperatures and
30 coꢀcatalysts of metal ions and organic ligands exerted a great
effect on catalytic active of Cuꢀcomponents for these coupling
systems (Fig. 5). It was observed that Cu(II)/PPh3
combination was inactive in the crossꢀcoupling reaction
(Table S6, entry 1). A aqueous solution of Cu(NO3)2 was
35 added to a EtOH solution of 4,4’ꢀbipyridine (bpy), resulting in
the formation of Cu(II)/bpy NPs, which acted as the catalysts
To further test the catalytic activity of Cu(NO3)2/psf NPs,
75 some contrast experiments of the Suzuki crossꢀcoupling
reactions of aryl iodides and arylboronic acid derivatives were
curried out under ambient atmosphere, and favorable yields
were obtained (Table 2, entries 1 and 2). A medium yield was
gotten in the similar condition if 3ꢀcyanophenylboronic acids
80 replaced arylboronic acids in the reaction above (entry 3).
However, when aryl bromides instead of aryl iodides, the
reactions gave low yields under similar condition (entries 4
and 6), indicating that the catalysts were not strong enough to
promote the coupling reactions in these systems, even higher
o
and the reactions gave low yields at 50 and 70 C, respectively,
o
even the temperature raised up to 90 C it only gave the 31%
yield (Fig. 5, for 2). In contrast, when the psf replaced the bpy
40 in the reactions above, Cu(II)/psf fresh NPs precipitates
formed rapidly without separation, were directly acted as the
catalysts and reactions gave high yields at 70 and 90 oC,
4
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reaction temperature was performed in the same reaction
system, it was considerably difficult to obtained a favorable
yield (Table 2, entries 5 and 7), comparing with one of entry 1
in Table 2 with 0.3% catalystꢀloading.
50
55
5
Table 2. The crossꢀcoulping reactions of ArꢀX and ArꢀB(OH)2 derivatives
using Cu(NO3)2/psf NPs as catalysts under ambient atmosphere.
Entry
X
I
I
R1
R2
H
4ꢀF
3ꢀCN
H
H
H
H
T/ oC
90
90
90
90
140
90
140
Yield(%)
87 ± 3
82 ± 3
56 ± 3
22 ± 5
46 ± 3
13 ± 5
31 ± 5
1
2
3
4
5
6
7
4ꢀOEt
4ꢀOEt
4ꢀOEt
4ꢀOMe
4ꢀOMe
4ꢀCF3
4ꢀCF3
10 G. D. Allred and L. S. Liebeskind, J. Am. Chem. Soc., 1996, 118,
2748–2749.
I
60 11 P. Espinet and A. M. Echavarren, Angew. Chem. Int. Ed., 2004, 43,
4704–4734.
12 V. V. Rostovtsev, L. G. Green, V. V. Fokin and K. B. Sharpless,
Angew. Chem. Int. Ed., 2002, 41, 2596–2599.
Br
Br
Br
Br
13 F. Himo, T. Lovell, R. Hilgraf, V. V. Rostovtsev, L. Noodleman, K.
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The experimental results above indicated that Cu(II)ꢀpsf
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10 reactions of ArꢀI and ArꢀB(OH)2 derivatives and low active for
ArꢀBr replaced ArꢀI. However, those existing stateꢀofꢀtheꢀart Pdꢀ
catalysts displayed high catalytic active for the couplings of ArꢀI
and ArꢀBr with ArꢀB(OH)2 derivatives.35 The first Cu(II) species
in this report as catalysts exhibit merits including cheapness, low
15 loadings, high stability without inert gas protection, which would
be very attractive to organic industrial synthesis.
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In this work, the PEIꢀ(Cu/psf)n films were facilely prepared
and applied for the Suzuki reaction with highly catalytic
efficiency. The low cost Cuꢀcatalysts would be a fascinating
20 alternative to noble metal systems. On the other hand, the
ultraꢀlow Cuꢀloading (down to 1.4 x 10ꢀ5 mol%) for the PEIꢀ
(Cu/psf)n multilayer films, is in favor of reducing the catalysts
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Acknowledgements
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25 Authors acknowledge the financial support by the NSFC
(20971075, 61275153 and 61320106014), the NSF of
Zhejiang province (LY12B01005), the Ningbo Science and
Technology Bureau (2014C50037 and 2014A610106) and
sponsored K. C. Wong Magna Fund in Ningbo University.
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30 Notes and references
100
a
Faculty of Materials Science and Chemical Engineering, Ningbo
University, Ningbo, 315211, China. Fax: +86ꢀ574ꢀ87609987. Eꢀmail:
lixing@nbu.edu.cn or and lix905@126.com.cn
b College of Chemistry, Xiangtan University, Xiangtan 411105, China.
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Journal of Materials Chemistry A
Page 6 of 6
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DOI: 10.1039/C5TA00222B
Trace Amount CuII(ppm) and Mixture Design of CuII/PdII Catalyzed Su-
zuki Cross-Coupling Reactions Based on Cooperative Interaction of Metal
with a Conjugated Pyridylspirobifluorene
Xing Li, Jie Zhang, Yayun Zhao, Xiuhua Zhao, Feng Li, Taohai Li, H. L. Li and Liang Chen
The multilayers of PEI-(Cu/psf)n could be capable of gradually discharging high active catalytic moieties
to promote the C-C coupling reactions with ultra low Cu-loadings of 1.4 x 10-5 mol%.