Branch selective allylation of acetylacetone catalyzed by Water-soluble rhodium complex catalyst

Article abstract of DOI:10.1016/j.jorganchem.2010.10.037

[RhCl(1,5-cod)]₂/PTA is highly active branch-selective catalyst for C-allylation of acetylacetone by allylic carbonates in water/ethyl acetate biphasic system, where either crotyl or 1-methylallyl carbonates gives sterically congested branched allylation product, suggesting formation of a common allylrhodium intermediate.

Full text of DOI:10.1016/j.jorganchem.2010.10.037

Journal of Organometallic Chemistry 696 (2011) 1927e1930
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Journal of Organometallic Chemistry
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Communication
Branch selective allylation of acetylacetone catalyzed by Water-soluble rhodium
complex catalyst
*
Nobuyuki Komine, Kohtaro Ishiguro, Sachiyo Kanai, Masafumi Hirano, Sanshiro Komiya
Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
[RhCl(1,5-cod)]2/PTA is highly active branch-selective catalyst for C-allylation of acetylacetone by allylic
carbonates in water/ethyl acetate biphasic system, where either crotyl or 1-methylallyl carbonates gives
sterically congested branched allylation product, suggesting formation of a common allylrhodium
intermediate.
Received 2 August 2010
Received in revised form
16 October 2010
Accepted 19 October 2010
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Water-soluble rhodium complex
Branch-selective allylation
Biphasic Catalysis
1. Introduction
we found that [RhCl(1,5-cod)]2/PTA is highly active branch-selec-
tive water/AcOEt biphasic catalyst for C-allylation of acetylacetone
Biphasic catalysis using water/organic solvent attracts signifi-
cant attentions, since such processes benefits us more green
chemical transformation [1]. For example, if the catalyst can stay in
water phase, the hydrophobic organic products are easily separated
by simple decantation, providing highly cost saving chemical
processes due to easy recovery and reuse of the catalyst. Such
processes also save the amount of harmful organic solvent in
synthesis. We recently reported highly branch-selective allylation
of benzenethiols using allylic alcohol catalyzed by water-soluble
palladium catalyst (Pd(OAc)2/TPPTS) using water/hexane biphasic
system, where very unusual effect of interface area is also observed
[2]. Although sulfonated phosphine ligands such as TPPTS and
TPPMS are frequently used as water-soluble ligands in such catal-
yses, their ionic property might interfere their activity and reac-
tivity [3]. Non-ionic water-soluble phosphorus ligands such as PTA
[4] and DAPTA [5], which also have high solubility in water without
ionic property, are also considered as one of the promising ligands
for providing water-soluble transition metal catalysts. We extended
this Pd-catalyzed water/organic solvent biphasic allylation system
to Rh catalyst [6]. The high branch-selective C-allylation reaction
by a Rh catalyst using branch allylic carbonate in organic solvent
has been already reported by J. Tsuji et al. [6a]. On the other hand,
by both of branch and linear allylic carbonates. In this system,
allylic acetates can also be used for allylation even without stoi-
chiometric amount of base.
2. Experimental
2.1. Materials
All manipulations were carried out under a dry nitrogen or
argon atmosphere using standard Schlenk techniques. Water was
purified by ion-exchange column followed by distillation, and other
solvents were dried over and distilled from appropriate drying
agents under N2 and were stored under nitrogen before use. Ethyl
acetate were dried over and distilled from CaCl2 under N2. Crotyl,
1-methylallyl, prenyl, and cinnmamyl carbonate by the reaction
of corresponding allylic alcohol with methyl chloroformate [7].
[RhCl(1,5-cod)]2 [8], PTA [9], DAPTA [5] and THMP [10] were
prepared according to the literature methods. All other chemicals
were obtained from commercial sources and used directly without
further purification.
Abbreviations: TPPTS, trisodium 3,30,300-phosphinidynetris(benzenesulfonate;
PTA, 1,3,5-triaza-7-phosphaadamantane; DAPTA, 3,7-diacetyl-1,3,7-trisaza-5-phos-
phabicyclo[3.3.1]nonane; TPPMS, sodium diphenylphosphinobenzene-3-sulfonate.
* Corresponding author. Tel./fax: þ81 423 887 043.
E-mail address: komiya@cc.tuat.ac.jp (S. Komiya).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.10.037

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N. Komine et al. / Journal of Organometallic Chemistry 696 (2011) 1927e1930
2.2. Instrumentation
3. Results and discussion
GC analysis was performed on a Shimadzu GC-14B using a GL
Science 30 m ꢀ 0.25 mm TC-WAX capillary column.
Table 1 shows the results of catalytic allylation promoted by
water-soluble Rh complex in biphasic system under various
conditions. Treatment of allyl methyl carbonate (1) with acetyla-
cetone in the presence of 2 mol% [RhCl(1,5-cod)]2 with 6 equiva-
lents of PTA at room temperature for 3.5 h under nitrogen
atmosphere in water/ethyl acetate biphasic media smoothly gave
an allylated product (10) quantitatively (Entry 1). Other allylating
reagents such as allyl acetate (2) can also be used with less activity
(Entry 2). Unfortunately, allyl alcohol (3) could not be used in this
reaction (Entry 3), the result being in sharp contrast to Pd/TPPTS
system [2]. In these reactions, simple separation of allylated prod-
ucts from catalyst was easily achieved by decantation and the
catalyst can be reused with some catalytic activity loss. Both crotyl-
(4) and 1-methylallyl carbonates (6) also gave corresponding ally-
lated products (11,12) in high yields at 40 ꢁC (Entries 4,6). One
interesting point is that both reactions gave high branch selectivity
(98%), suggesting involvement of the common intermediate in
2.3. Catalytic allylation
Typical procedure for catalytic allylation is shown as follows. In
a 25-mL Schlenk tube, [RhCl(1,5-cod)]2 (12.5 mg, 0.025 mmol) and
PTA (24.3 mg, 0.155 mmol) were placed under nitrogen atmo-
sphere. Degassed pure water (2.0 mL) was introduced, and the
mixture was stirred vigorously for several minutes, then the
aqueous solution became a clear yellow solution. AcOEt (2.0 mL),
allylic carbonate (68.9 mg, 0.529 mmol) and acetylacetone
(50.0 mg, 0.499 mmol) were added to the solution. Biphenyl
(15.3 mg, 0.0992 mmol) was added as an internal standard to
the solution. After reaction the organic layer was quantitatively
analyzed by GLC. All the prepared compounds are known and
compared with authentic samples.
Table 1
Allylation of Acetylacetone Catalyzed by Water-soluble Rhodium Complex Catalyst.a
Entry
Substrate
Time
Product (ratio)
Total yield%
1b
3.5
97
2
24
11
10
10
71
0
3b
4
3
94
11, 12
(98/2)
5
6
24
48
84
89
11, 12
(98/2)
7
74
64

N. Komine et al. / Journal of Organometallic Chemistry 696 (2011) 1927e1930
1929
Table 1 (continued )
Entry
Substrate
Time
68
Product (ratio)
Total yield%
,c
8b
7
13, 14
(98/2)
13, 14
(98/2)
16
,d
9b
7
393
0
10
48
0
0
15, 16
(ꢂ)
11
48
a
Reaction conditions: [RhCl(1,5-cod)]2 (0.025 mmol), PTA (0.15 mmol), allylic carbonate (0.50 mmol), acetylacetone (0.50 mmol), solvent ¼ water 2.0 mL, AcOEt 2.0 mL,
30 ꢁC.
b
c
Reactions were carried out at room temperature.
PTA (0.10 mmol).
PTA (0.30 mmol).
d
these reactions. Cinnamyl carbonate (7) was less reactive in
comparison with crotyl derivative, but exclusively gave the
branched allylation product (13) (Entry 7). Unusual effect of inter-
face area on branch/linear ratio of the products by changing stirring
speed was not observed in these reactions [2b]. On the other hand,
trisubstituted allyl carbonate such as prenyl carbonate (8) showed
no reactivity in this allylation reaction (Entry 10). Such a trend was
also observed for allylic acetates (Entry 11). These reactivity
differences are probably due to the large steric hindrance of the
trisubstituted allylic moiety, discouraging pre-requisite coordina-
tion of the C]C double bond to rhodium leading to a common
allylrhodium intermediate to which nucleophilic reaction of ace-
tylacetone takes place. Importance of prior coordination of C]C
double bond has been proposed [11]. The low reactivity of acetates
compared to that of carbonate may be attributed to the difficulty in
oxidative addition.
The ratio of PTA to Rh was also important. When using 2 equivs
of PTA per mole of Rh, the yield of allylation products significantly
decreased in comparison with the result using 3 equivs of PTA
(Table 1, entry 8). On the other hand, addition of 6 equivs of PTA/Rh
completely inhibited the reaction, suggesting the prior dissociation
of PTA (Table 1, entry 9). The results suggest that active interme-
diate needs PTA as a ligand, but excess PTA compete with prior
coordination of allyl carbonate.
By analogy of previously reported branch-selective allylation,
following mechanism is proposed for this catalytic allylation
(Scheme 1) [2b]. An allylrhodium(III) species initially formed by
oxidative addition of allylic carbonate or acetate to Rh(I), followed
by nucleophilic reaction of acetylacetone to give the corresponding
allylation product. Exclusive formation of the branched product
from both 1-methylallyl and crotyl carbonates suggests the
involvement of a common allylrhodium intermediate. It is unlikely
(1)
We also examined some other water-soluble phosphorus
ligands for comparison and the results are also shown in Table 2.
Use of DAPTA as ligands gave a similar selectivity and reactivity in
H2O/AcOEt biphasic system. Unfortunately the combinations with
other well-known water-soluble phosphine ligands such as TPPTS,
TPPMS, and tris(hydroxylmethyl)phosphine showed very low
catalytic activity.
to suppose h
3-allylrhodium(III) intermediate, since less-hindered
side is generally allylated by the steric reason, though electronic
effect of substitutents and ligand effect are also important factors
[6d,12]. Initially formed
h
3-allylrhodium(III) probably rearranges to
the
h
1-allylrhodium(III) by coordination of three trimethylphos-
phine ligands, where methyl substituents in the allylmetal inter-
mediate would stay in the remote position from Rh metal center to
(2)

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N. Komine et al. / Journal of Organometallic Chemistry 696 (2011) 1927e1930
Table 2
Acknowledgements
Effect of water-soluble phosphine.a
This work was financially supported by a Grant-in-Aid for
Scientific Research from the Ministry of Education, Sports, Culture,
Science and Technology of Japan.
Entry
L
Time
Yield%
11:12
1
2
3
4
5
6
DAPTA
PTA
THMP
TPPTS
TPPMS
P(OCH2OH)3
3
3
24
48
44
24
92
94
4
1
1
98/2
98/2
e
e
e
trace
e
Reference
a
Reaction conditions: [RhCl(1,5-cod)]2 (0.025 mmol), Water-soluble phosphine
ligand (0.15 mmol), crotyl carbonate (0.50 mmol), acetylacetone (0.50 mmol),
solvent ¼ water 2.0 mL, AcOEt 2.0 mL, 40 ꢁC.
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avoid steric repulsion with other ligands. Thus the 3-methylallyl
structure would be favored in comparison with the 1-methylallyl.
SN20 reaction of the acetylacetone nucleophile to this 1-allyl ligand
h
selectively gives branched product. Facile oxidative addition of
allylic carbonate promoted by highly electoron-donating PTA
ligand may also be an important factor for the present allylation
process.
4. Conclusion
[RhCl(1,5-cod)]2/PTA is highly active branch-selective water/
ethyl acetate biphasic catalyst for C-allylation of acetylacetone by
allylic carbonates.
(d) C. Amatore, E. Genin, A. Jutand, L. Mensh, Organometallics 26 (2007) 1875;
(e) N. Kanbayashi, K. Onitsuka, J. Am. Chem. Soc. 132 (2010) 1206.