Hydrophenylation of internal alkynes with boronic acids catalysed by a Ni-Zn hydroxy double salt-intercalated anionic rhodium(III) complex

Article abstract of DOI:10.1039/c5cy01139f

[Rh(OH)₆]^3- intercalated Ni-Zn mixed basic salt (Rh/NiZn) acts as an efficient catalyst for the hydrophenylation of internal alkynes with arylboronic acids under mild conditions. The turnover number per Rh site approached 740 in the reaction between 4-octyne and phenylboronic acid. The catalytic monomeric Rh(iii) complex is stabilised within the NiZn interlayers, attributable to a strong electrostatic interaction, promoting its re-use.

Full text of DOI:10.1039/c5cy01139f

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Hydrophenylation of internal alkynes with boronic
acids catalysed by a Ni–Zn hydroxy double salt-
intercalated anionic rhodiumIJIII) complex†
Cite this: DOI: 10.1039/c5cy01139f
Takayoshi Hara,a Nozomi Fujita,a Nobuyuki Ichikuni,a Karen Wilson,b Adam F. Leeb
a
*
and Shogo Shimazu
[RhIJOH)6]3− intercalated Ni–Zn mixed basic salt (Rh/NiZn) acts as an efficient catalyst for the
hydrophenylation of internal alkynes with arylboronic acids under mild conditions. The turnover number
per Rh site approached 740 in the reaction between 4-octyne and phenylboronic acid. The catalytic
monomeric RhIJIII) complex is stabilised within the NiZn interlayers, attributable to a strong electrostatic
interaction, promoting its re-use.
Received 21st July 2015,
Accepted 27th August 2015
DOI: 10.1039/c5cy01139f
www.rsc.org/catalysis
exchange to create a Rh/NiZn catalyst8b which exhibited
extremely high activity for the 1,4-addition reaction between
Introduction
The regio- and stereoselective synthesis of multi-substituted
alkenes is an important synthetic approach for constructing
complex molecules from relatively simple precursors. Multi-
substituted alkenes are commonly derived from PdIJII)
catalysed cross-coupling reactions between simple arenes and
activated olefins in acetic acid (Fujiwara–Moritani reaction)1,2
or aryl halides and alkenes (Mizoroki–Heck reaction).1,3 Tran-
sition metal catalysed hydrophenylation of carbon–carbon
triple bonds is also an efficient route to form such products.4
In 2001, Hayashi and co-workers reported the rhodiumIJI)-
catalysed hydrophenylation of internal alkynes with
arylboronic acids via a 1,4-shift promoted by rhodium.5 There-
after, rhodium-catalysed hydrophenylation has proven chal-
lenging for the general synthesis of multi-substituted alkenes.6
Recently, it was reported that a Zn–Al hydrotalcite docked Rh-
IJI) complex (Rh-m-TPPTC/Zn–Al LDH) was able to catalyse this
type of hydrophenylation; however, the reaction was carried
out under stoichiometric conditions (S/C ratio was 1).7
α,β-unsaturated ketones and phenylboronic acids, with Turn-
over Frequencies (TOFs) reaching 920 h−1. Here, we report
the efficient hydrophenylation of internal alkynes with
phenylboronic acids to form multi-substituted alkenes. The
present catalytic methodology is particularly attractive, featur-
ing a facile catalyst synthesis via a simple intercalation proce-
dure and high Turnover Numbers (TONs).
Results and discussion
Acetate anion-intercalated NiZn (CH3COO−/NiZn) was
synthesised according to a previously reported procedure.9
The composition and anion-exchange capacity of the parent
NiZn were Ni0.63Zn0.37IJOH)2IJCH3COO)0.37·1.93H2O (i.e. Ni : Zn
= 2.2) and 2.44 mmol g−1, respectively, based on X-ray fluores-
cence (XRF) and thermogravimetric-differential thermal anal-
ysis (TG-DTA). The RhIJIII) hydroxyl complex was intercalated
into NiZn interlayers via a simple anion-exchange reaction in
water at 50 °C for 8 h. The resulting Rh/NiZn catalyst, a green
powder, contained 0.034 mmol g−1 of Rh species as deter-
mined by atomic absorption spectrometry (AAS). Rh 3d X-ray
photoelectron spectroscopy (XPS) and Rh K-edge X-ray
absorption fine structure (XAFS) measurements confirmed
the presence of RhIJIII) as a monomeric hexahydroxy rhodate
[RhIJOH)6]3− anion, which is proposed to reside within the
NiZn interlayer accompanied by intercalated OH−.8b
We have recently developed novel heterogeneous intercala-
tion catalysts based on Ni–Zn hydroxy double salts (NiZn),
Ni1−x2+Zn2x2+(OH)2A2x/nn−·mH2O (0.15 < x < 0.25), where An−
represents various anions, as heterogeneous base catalysts
and/or hosts for catalytically active anions.8 In particular, a
monomeric hexahydroxy rhodateIJIII) complex, [RhIJOH)6]3−
,
could be intercalated into NiZn interlayers by simple anion-
a Department of Applied Chemistry and Biotechnology, Graduate School of
Engineering, Chiba University, 1-33, Yayoi, Inage, Chiba 263-8522, Japan.
E-mail: shimazu@faculty.chiba-u.jp
The catalytic investigations first optimised the reaction
solvent for the hydrophenylation of internal alkynes with
phenylboronic acid (2a) over Rh/NiZn in the presence of a
catalytic amount of 1,5-cyclooctadiene (1,5-COD). 4-Octyne
(1a) and 2a were chosen as model substrates for this optimi-
zation process (Table 1). The initial reaction conditions
b European Bioenergy Research Institute, School of Engineering and Applied
Science, Aston University, Birmingham B4 7ET, UK
† Electronic supplementary information (ESI) available: Experimental details,
EXAFS, FTIR, and NMR data. See DOI: 10.1039/c5cy01139f
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Table 1 Solvent effect on hydrophenylation between 1a and 2a with the
Rh/NiZn catalysta
resulting in 89% yield of 3aa (entry 3). It should be noted
that the catalytic reaction did not proceed in water alone
(entry 7).
The catalytic activity was strongly dependent upon the use
of olefins as ligands (Table 3), with no hydrophenylation
occurring without such ligands (entry 1). While hydro-
phenylation only occurred in the presence of 1,5-COD and
2,5-norbornadiene (entries 3 and 4), 2,5-norbornadiene was
found to be less effective. Other dienes such as 1,3-cyclo-
pentadiene and 1,4-cyclohexadiene did not promote hydro-
phenylation (entries 2 and 5), and neither did trienes such as
1,5,9-cyclododecatriene or monoenes such as cyclooctene,
2-norbornene and cyclohexene (entries 6–9). This observation
suggests that 1,5-COD may coordinate to Rh under reaction
conditions to form an activated catalytic complex in situ. We
speculate that 1,5-COD acts as a weak electron-donating
ligand on the Rh catalytic centre. Variation of the 1,5-COD
amount up to seven equivalents relative to the amount of Rh
(entries 10–15) revealed that the optimum 1,5-COD level was
four equivalents, which yielded 71% of 3aa over 1.5 h of reac-
tion (entry 13).
Yieldb (%)
Conv.b
Entry
Solvent
(%)
3aa
4aa
1
Toluene
1,2-Dichloroethane
Ethanol
Tetrahydrofuran
1,4-Dioxide
N,N-Dimethylformamide
>99
45
71
27
8
3
2c
3c
4c
5
8
Trace
Trace
Trace
n.d.
Trace
Trace
Trace
n.d.
Trace
Trace
n.d.
6
a
Rh/NiZn catalyst (Rh: 0.34 mol%), 1a (1 mmol), 2a (3 mmol),
1,5-COD (3 eq. relative to Rh), solvent (4 mL), H2O (0.9 mL), 100 °C,
5 h. Determined by GC using an internal standard technique.
b
c
Reaction was carried out in a sealed tube.
The catalytic activity for hydrophenylation over Rh/NiZn
was subsequently compared with that over Rh catalysts under
identical conditions (Table 4). Rh/NiZn exhibited the highest
catalytic activity (entry 1), achieving 71% yield over 1.5 h ver-
sus 45% for Na3RhCl6·12H2O (ref. 10) over 5 h (entry 7). The
Rh/NiZn catalyst showed almost identical activity under air,
O2 and N2 atmospheres (entries 2–4). Control reactions in the
absence of any catalyst, or in the presence of CH3COO−/NiZn
or OH−/NiZn unfunctionalised by Rh, were completely inac-
tive (entries 5, 6, and 11). RhIJOH)3, Rh2O3, and Rh0/carbon
were also ineffective catalysts (entries 8–10). We conclude
that anionic [RhIJOH)6]3− intercalated into NiZn interlayers is
a highly efficient catalyst for hydrophenylation under mild
conditions.
The hydrophenylation between 1a and 2a catalysed by Rh/
NiZn was also successfully undertaken on a preparative scale.
For example, 1a (0.66 g; 6 mmol) and 2a (1.83 g; 15 mmol)
successfully gave 3aa (0.95 g; 84% of isolated yield) in the
presence of the Rh/NiZn catalyst (0.2 g, Rh: 6.8 μmol) for 16 h
(Scheme 1). The TON per Rh atom approached 740, an order
of magnitude higher than previous reports for homogeneous
Rh complexes: RhIJacac)IJCO)2 = 18;6a RhIJacac)IJCO)2/Janaphos =
46;6b [RhIJ1,5-COD)IJOH)]2/m-TPPTC = 59;6c,d [RhIJ1,5-COD)Cl]2/
TPPDS = 43;6e and RhIJacac)IJC2H4)2/dppb = 32.5
Deactivation, whether arising from structural changes in
the active metal species or support architecture, or leaching
of the active metal species into the reaction mixture, pro-
foundly influences the prospect of catalyst commercializa-
tion. In order to establish whether deactivation occurred
under our reaction conditions, additional reactants 1a and 2a
were added to the reaction mixture after 1.5 h of initial reac-
tion (without additional 1,5-COD). Fig. 1 shows that hydro-
phenylation immediately recommenced at the same rate as
during the first reaction cycle, evidencing no loss of catalytic
activity.11
utilised 0.1 g of Rh/NiZn catalyst (i.e. 3.4 μmol of Rh), 1
mmol of 1a, 3 mmol of 2a, and three equivalents of 1,5-COD
relative to Rh in a solvent mixture comprising 4 mL of tolu-
ene and 0.9 mL of water at 100 °C under air for 5 h. Solvent
screening revealed toluene as the most effective, affording
the highest yield (71%) of the hydrophenylation product, (E)-
4-phenyl-4-octene (3aa), accompanied by a small amount of
(4Z,6E)-4-phenyl-5,6-dipropyl-4,6-decadiene (4aa) (entry 1).
Although 1,2-dichloroethane also afforded 3aa, the resulting
yield was low (entry 2). Solvents such as ethanol, tetrahydro-
furan, 1,4-dioxane and N,N-dimethylformamide did not yield
any products (entries 3–6).
Water addition proved essential to obtain high yields of
the hydrophenylation product (Table 2), with neither 3aa nor
4aa obtained in its absence (entry 1). When the reaction was
conducted in toluene–water biphasic solvents, catalysis
proceeded efficiently (entries 2–6), with the optimum solvent
mixture comprising 4 mL of toluene and 0.45 mL of water,
Table 2 Effect of water on hydrophenylation between 1a and 2a with
the Rh/NiZn catalysta
Yieldb (%)
Toluene
(mL)
H2O
(mL)
Conv.b
(%)
Entry
3aa
4aa
1
2
3
4
5
6
7
4
4
4
4
2
1
—
—
n.d.
14
n.d.
6
89
87
82
n.d.
Trace
5
7
7
5
n.d.
0.09
0.45
0.90
0.45
0.45
4.45
>99
>99
>99
>99
n.d.
82
n.d.
a
Rh/NiZn catalyst (Rh: 0.68 mol%), 1a (0.5 mmol), 2a (1.5 mmol),
b
1,5-COD (3 eq. relative to Rh), 100 °C, 5 h. Determined by GC using
an internal standard technique.
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Table 3 Ligand effect on hydrophenylation between 1a and 2a with the Rh/NiZn catalysta
Entry
Ligand (eq. relative to Rh)
Time (h)
Conv.b (%)
Yield of 3aab (%)
1
2
3
4
5
6
7
8
None (–)
5
5
5
5
5
5
5
5
Trace
Trace
99
Trace
Trace
89
1,3-Cyclopentadiene (3)
1,5-Cyclooctadiene (3)
2,5-Norbornadiene (3)
1,4-Cyclohexadiene (3)
Cyclooctene (3)
23
17
Trace
Trace
Trace
Trace
Trace
24
19
44
84
74
Trace
Trace
Trace
Trace
n.d.
17
16
40
71
63
2-Norbornene (3)
Cyclohexene (3)
9
1,5,9-Cyclododecatriene (3)
1,5-Cyclooctadiene (1)
1,5-Cyclooctadiene (2)
1,5-Cyclooctadiene (3)
1,5-Cyclooctadiene (4)
1,5-Cyclooctadiene (6)
1,5-Cyclooctadiene (7)
5
10
11
12
13
14
15
1.5
1.5
1.5
1.5
1.5
1.5
74
62
a
b
Rh/NiZn catalyst (0.1 g, Rh: 0.68 mol%), 1a (0.5 mmol), 2a (1.5 mmol), ligand, toluene (4 mL), H2O (0.45 mL), 100 °C. Determined by GC
using an internal standard technique.
AAS analysis of the reaction filtrate confirmed that negligi-
ble Rh was leached under our conditions (below 0.4 μmol).
In order to further demonstrate the requirement of the
heterogeneous Rh/NiZn catalyst, the catalyst was removed by
hot filtration when hydrophenylation between 1a and 2a had
reached almost 35% conversion (Fig. S1†).12 After removal of
the catalyst, the reaction was monitored for an additional
hour; however, almost no formation of 3aa was observed.13
The Rh K-edge XANES and k3-weighted Rh K-edge EXAFS
spectra of the fresh and spent Rh/NiZn catalysts (Fig. 2) con-
firmed no change in either Rh oxidation or coordination
environment, suggesting that Rh species in the NiZn matrix
remained in a trivalent monomeric state throughout the reac-
tion, likely due to the strong electrostatic interactions
between the anionic [RhIJOH)6]3− species and the NiZn lamel-
lar host, which appears to inhibit the aggregation of hydrated
rhodium oxide species such as RhIJOH)3. However, the pow-
der XRD profiles revealed the expansion of the interlayer
spacing of the recovered Rh/NiZn catalyst from 0.42 to 0.66
nm (Fig. 3), which may reflect the incorporation of water
and/or a reactively-formed product alongside [RhIJOH)6]3− and
OH− anions during reaction.14
The scope of the hydrophenylation reaction was examined
using a variety of alkynes and phenylboronic acids (Table 5)
using the optimised amount of 1,5-COD and toluene/H2O
mixed solvent. p-Substituted phenylboronic acids such as
electron-donating
4-methylphenylboronic
acid
(2d),
4-methoxyphenylboronic acid (2e), and electron-withdrawing
4-chlorophenylboronic acid (2f) gave the corresponding
hydrophenylation products (3ad, 3ae, and 3af) in high yields
(entries 7–12). For short reaction times, electron-donating
phenylboronic acids generally reacted with alkynes more
readily, while the electron-withdrawing analogue provided a
relatively lower yield. Steric hindrance in the boronic acid
aromatic ring strongly influenced the hydrophenylation. For
example, the reaction between 1a and 2-methylphenylboronic
acid (2b) did not proceed effectively, with only 52% yield of
3ab obtained after 24 h (entries 3 and 4), possibly due to the
strong inhibition of transmetalation by o-substituents. In
Table 4 Effects of catalyst on hydrophenylation between 1a and 2aa
comparison,
3-methylphenylboronic
acid
(2c)
and
Entry
Catalyst
Time (h)
Conv.b (%)
Yieldb (%)
p-substituted 2d reacted more readily with 1a (entries 5–8).
However, a low product yield was obtained over our Rh/NiZn
catalyst for the reaction between 1-phenyl-1-propyne (1b) and
1
2
Rh/NiZn
Rh/NiZn
Rh/NiZn
Rh/NiZn
1.5
1
1
1
5
5
5
5
5
84
62
63
60
n.d.
n.d.
54
Trace
Trace
Trace
n.d.
71
52
50
48
n.d.
n.d.
45
Trace
Trace
Trace
n.d.
3c
4d
5e
6e
7
CH3COO−/NiZn
OH−/NiZn
Na3RhCI6·nH2O
RhIJOH)3
8
9
Rh2O3
RhIJ0)/carbon
—
10f
11
5
5
a
Rh catalyst (Rh: 0.68 mol%), 1a (0.5 mmol), 2a (1.5 mmol), 1,5-COD
(4 eq. relative to Rh), toluene (4 mL), H2O (0.45 mL), 100 °C.
Scheme 1 Large-scale reaction with the Rh/NiZn catalyst. Reaction
conditions: Rh/NiZn catalyst (0.2 g, Rh: 6.8 μmol), 1a (0.66 g; 6 mmol),
2a (1.83 g; 15 mmol), 1,5-COD (27.2 μmol), toluene (20 mL), H2O (2.25
mL), 100 °C, 16 h. 0.13 g of (4Z,6E)-4-phenyl-5,6-dipropyl-4,6-
decadiene (4aa) was also isolated.
b
Determined by GC analysis using an internal standard technique.
c
e
f
d
Reaction was carried out under O2 atmosphere.
Under N2.
CH3COO−/NiZn (0.1 g) or OH−/NiZn (0.1 g) was used as a catalyst.
5 wt% Rh, purchased from Aldrich.
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Fig. 3 XRD profiles of (a) CH3COO−/NiZn, (b) fresh Rh/NiZn, and (c)
recovered Rh/NiZn.
Fig. 1 Time profile of hydrophenylation of 1a and 2a with the Rh/NiZn
catalyst. Reaction conditions: Rh/NiZn catalyst (Rh: 0.68 mol%), 1a (0.5
mmol), 2a (1.5 mmol), 1,5-COD (4 eq. relative to Rh), toluene (4 mL),
H2O (0.45 mL), 100 °C.
Rh leaching was not observed by AAS, nor any changes in
the Rh chemical environment by XAS (Fig. 2). Since neither
2a (entry 13), in which phenyl addition occurred exclusively
at the β position of the phenyl group in 1b with no other iso-
mer detectable by GC. Terminal alkynes such as
1-phenylethyne (1c) did not react at all (entry 14). Our Rh/
NiZn catalyst was also able to promote the hydrophenylation
of 1,2-diphenylethyne (1d) with 2a (entry 15); however, no
hydrophenylation product was formed with the electron-
deficient alkynes such as 1,2-bisIJmethoxycarbonyl) ethyne
(1e), a well-known acceptor (entry 16). It therefore seems that
the diester group in 1e may strongly coordinate to, and hence
deactivate, the catalytic rhodium species.
Table 5 Substrate scope on alkyne hydrophenylation with the Rh/NiZn
catalysta
Boronic
acid
Time
(h)
Conv.b Yieldb
Entry Alkyne
Product (%)
(%)
1
1a: R1 =
R2 = C3H7
1a
2a: R3 = H 1.5
3aa
84
71
2
3
2a
3
3aa
3ab
>99
Trace
90
Trace
1a
2b: R3 =
2-Me
2b
1.5
4
5
1a
1a
24
3ab
3ac
53
60
52
55
2c: R3 =
3-Me
2c
1.5
6
7
1a
1a
3
3ac
3ad
92
12
88
10
2d: R3 =
4-Me
2d
1.5
8
9
1a
1a
24
3ad
3ae
>99
55
95
52
2e:R3 =
3-MeO
2e
1.5
10
11
1a
1a
6
3ae
3af
96
40
94
38
2f: R3 =
4-CI
1.5
12
13
1a
2f
2a
9
12
3af
3ba
92
20
89
20
1b: R1 = Me,
R2 = Ph
14
15
16
1c: R1 = Ph,
R2 = H
1d: R1 =
R2 = Ph
1e: R1 =
R2 = CO2Me
2a
2a
2a
24
12
24
3ca
3da
3ea
n.d.
>99
n.d.
n.d.
98
n.d.
a
Fig. 2 XAFS analysis of (a) fresh Rh/NiZn and (b) recovered Rh/NiZn:
(A) Rh K-edge XANES spectra, (B) FT of k3-weighted Rh K-edge EXAFS
spectra, and (C) results of curve fitting.
Rh/NiZn catalyst (Rh: 0.68 mol%), 1 (0.5 mmol), 2 (1.5 mmol),
1,5-COD (4 eq. relative to Rh), toluene (4 mL), H2O (0.45 mL), 100 °C.
Determined by GC using an internal standard technique.
b
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the parent CH3COO−/NiZn nor OH−/NiZn materials were able
to catalyse the reaction (Table 4, entries 5 and 6), we specu-
late the following reaction pathway for hydrophenylation over
Rh/NiZn (Scheme S1†), which is in agreement with previous
proposals for homogeneous Rh catalysts:15 initial trans-
metallation between the interlayer Rh species and the
arylboronic acid16 occurs to generate a Rh–Ar species. The
internal alkyne triple bond then inserts into the Rh–Ar bond,
yielding a 2-(alkynyl)phenylrhodium species which is subse-
quently readily hydrolysed by water. Finally, the desired addi-
tion product is obtained, accompanied by the regeneration of
the initial Rh species. At present, the precise nature of the
active Rh species is unclear. Although it is possible that a low
valent RhIJI) species could form in situ via the reduction of the
RhIJIII) species we observed by XAS, our catalytic system
proved inactive towards the well-known RhIJI)-catalysed
1,2-addition of 2a to benzaldehyde17 under our reaction con-
ditions. Moreover, biphenyl was not observed as a by-product
of our Rh/NiZn catalyst in the hydrophenylation process.18
Together, these observations demonstrate that neither reduc-
tive elimination from Ar–RhIJIII)–Ar to RhIJI) nor indicative
RhIJI)-catalysed homocoupling of 2a occurred. Furthermore,
hydrophenylation under O2 proceeded at almost the same
rate as under N2 (Table 4, entries 3 and 4), suggesting that
the re-oxidation of RhIJI) formed in situ to RhIJIII) by molecular
oxygen cannot occur.
Piao, J. Oyamada, W. Lu, T. Kitamura and Y. Fujiwara,
Science, 2000, 287, 1992; (d) C. Jia, T. Kitamura and Y.
Fujiwara, Acc. Chem. Res., 2001, 34, 633.
3 (a) T. Mizoroki, K. Mori and A. Ozaki, Bull. Chem. Soc. Jpn.,
1971, 44, 581; (b) R. F. Heck and J. P. Nolley Jr., J. Org.
Chem., 1972, 37, 2320; (c) R. F. Heck, Org. React., 1982, 27,
345; (d) L. Yin and J. Liebscher, Chem. Rev., 2007, 107, 133.
4 (a) Y. Yamamoto, Chem. Soc. Rev., 2014, 43, 1575; (b) X. Xu,
J. Chen, W. Gao, H. Wu, J. Ding and W. Su, Tetrahedron,
2010, 66, 2433; (c) Y. Yamamoto, N. Kirai and Y. Harada,
Chem. Commun., 2008, 2010; (d) P.-S. Lin, M. Jeganmohan
and C.-H. Cheng, Chem. – Eur. J., 2008, 14, 11296; (e) A. K.
Gupta, K. S. Kim and C. H. Oh, Synlett, 2005, 457; ( f ) C. H.
Oh, H. H. Jung, K. S. Kim and N. Kim, Angew. Chem., Int.
Ed., 2003, 42, 805; (g) N. Tsukada, T. Mitsuboshi, H.
Setoguchi and Y. Inoue, J. Am. Chem. Soc., 2003, 125, 12102;
(h) E. Shirakawa, G. Takahashi, T. Tsuchimoto and Y.
Kawakami, Chem. Commun., 2001, 2688; (i) C. Jia, W. Lu, J.
Oyamada, T. Kitamura, K. Matsuda, M. Irie and Y. Fujiwara,
J. Am. Chem. Soc., 2000, 122, 7252.
5 T. Hayashi, K. Inoue, N. Taniguchi and M. Ogasawara, J. Am.
Chem. Soc., 2001, 123, 9918.
6 (a) W. Zhang, M. Liu, H. Wu, J. Ding and J. Cheng,
Tetrahedron Lett., 2008, 49, 5214; (b) R. Jana and J. A. Tunge,
J. Org. Chem., 2011, 76, 8376; (c) E. Genin, V. Michelet and
J.-P. Genêt, Tetrahedron Lett., 2004, 45, 4157; (d) E. Genin, V.
Michelet and J.-P. Genêt, J. Organomet. Chem., 2004, 689,
3820; (e) M. Lautens and M. Yoshida, J. Org. Chem.,
2003, 68, 762; ( f ) M. Lautens and M. Yoshida, Org. Lett.,
2002, 4, 123; (g) K. Fagnou and M. Lautens, Chem. Rev.,
2003, 103, 169.
7 F. Neaţu, M. Ciobanu, L. E. Ştoflea, L. Frunză, V. I.
Pârvulescu and V. Michelet, Catal. Today, 2015, 247, 155.
8 (a) T. Hara, J. Kurihara, N. Ichikuni and S. Shimazu, Catal.
Sci. Technol., 2015, 5, 578; (b) T. Hara, N. Fujita, N. Ichikuni,
K. Wilson, A. F. Lee and S. Shimazu, ACS Catal., 2014, 4,
4040; (c) T. Hara, J. Sawada, Y. Nakamura, N. Ichikuni and
S. Shimazu, Catal. Sci. Technol., 2011, 1, 1376; (d) T. Hara, J.
Kurihara, N. Ichikuni and S. Shimazu, Chem. Lett., 2010, 39,
304; (e) T. Hara, M. Ishikawa, J. Sawada, N. Ichikuni and S.
Shimazu, Green Chem., 2009, 11, 2034.
Conclusions
In conclusion, Rh/NiZn is an effective heterogeneous catalyst
for the hydrophenylation of internal alkynes with
phenylboronic acids in the presence of 1,5-COD. X-ray
spectroscopy measurements confirm the catalytically active
species as a hydroxo-rhodiumIJIII) complex stabilised within
the NiZn interlayers by strong electrostatic interactions. Re-
use experiments evidence no loss of hydrophenylation cata-
lytic activity over Rh/NiZn.
Acknowledgements
Financial support from a Grant-in-Aid for Scientific Research
from the Ministry of Education, Culture, Sports, Science, and
Technology of Japan (25420824) is acknowledged. Rh K-edge
XAFS experiments were conducted at a facility in the Photon
Factory (KEK-PF, Proposal no. 2012G596). A. F. L. thanks the
9 S. Yamanaka, K. Ando and M. Ohashi, Mater. Res. Soc. Symp.
Proc., 1995, 371, 131.
10 Rh/NiZn pretreated with 1,5-COD showed no catalytic activity
for the hydrophenylation of 1a with 2a.
EPSRC for the award of
G007594/4), and K. W. thanks the Royal Society for the award
of an Industry Fellowship.
a
Leadership Fellowship (EP/
11 M. Lederer, E. Leipzig-Pagani, T. Lumini and R. J. Roulet,
J. Chromatogr. A, 1997, 769, 325.
12 Significant loss of activity was observed following the
recovery and recycle of our Rh/NiZn heterogeneous catalyst
via filtration, washing and drying (the yield decreased to
20%) relative to that obtained through the addition of an
extra substrate to a spent catalyst solution, shown in Fig. 1.
This deactivation is therefore likely associated with the
washing and/or drying protocols.
Notes and references
1 In Handbook of Organopalladium Chemistry for Organic
Synthesis, ed. E. Negishi, Wiley-Interscience, New York, 2002.
2 (a) I. Moritani and Y. Fujiwara, Tetrahedron Lett., 1967, 1119;
(b) Y. Fujiwara, I. Moritani, S. Danno, R. Asano and S.
Teranishi, J. Am. Chem. Soc., 1969, 91, 7166; (c) C. Jia, D.
13 M. T. Reetz and E. Westermann, Angew. Chem., Int. Ed.,
2000, 39, 165.
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14 In the FT-IR spectra of the recovered Rh/NiZn catalyst, weak
peaks based on ν(CH2) of the product accompanied by a
small shift were observed, see ESI,† Fig. S3.
16 K. Motokura, N. Hashimoto, T. Hara, T. Mitsudome, T.
Mizugaki, K. Jitsukawa and K. Kaneda, Green Chem.,
2011, 13, 2416.
15 To further clarify the catalytically active species, FTIR and
Rh K-edge XAS experiments were conducted using the Rh/
NiZn catalyst with 1,5-COD in toluene/water solvent; how-
ever, no significant spectral changes were observed.
17 M. Sakai, M. Ueda and N. Miyaura, Angew. Chem., Int. Ed.,
1998, 37, 3279.
18 T. Vogler and A. Studer, Adv. Synth. Catal., 2008, 350,
1963.
Catal. Sci. Technol.
This journal is © The Royal Society of Chemistry 2015