Polystyrene-immobilised phenanthroline palladium(II) complex: A highly efficient and recyclable catalyst for oxidative Heck reactions

Article abstract of DOI:10.3184/174751912X13466942543952

Oxidative Heck coupling reactions of arylboronic acids with olefins were carried out in the presence of the polystyrene-immobilised phenanthroline palladium(II) complex using air as a co-oxidant to afford the Heck coupling products in high yields under base-free conditions. This heterogeneous palladium catalyst can be recovered by simple filtration and used for several times without loss of activity or selectivity.

Full text of DOI:10.3184/174751912X13466942543952

JOURNAL OF CHEMICAL RESEARCH 2012
NOVEMBER, 629–631
RESEARCH PAPER 629
Polystyrene-immobilised phenanthroline palladium(II) complex: a highly
efficient and recyclable catalyst for oxidative Heck reactions
a,b
a
a
Pingping Wang, Jiatao Zhang and Mingzhong Cai *
a
Department of Chemistry, Jiangxi Normal University, Nanchang 330022, P. R. China
bDepartment of Chemistry, Jiujiang University, Jiujiang 332000, P. R. China
Oxidative Heck coupling reactions of arylboronic acids with olefins were carried out in the presence of the polysty-
rene-immobilised phenanthroline palladium(II) complex using air as a co-oxidant to afford the Heck coupling prod-
ucts in high yields under base-free conditions. This heterogeneous palladium catalyst can be recovered by simple
filtration and used for several times without loss of activity or selectivity.
Keywords: oxidative Heck coupling, supported palladium catalyst, phenanthroline palladium complex, arylboronic acid,
heterogeneous catalysis
The palladium(II)-catalysed vinylic substitution reaction of
arylboronic acids with olefins, known as oxidative Heck coup-
ling, has received considerable attention of organic chemists
complex catalyst 4 as a light yellow powder, the palladium
content of the catalyst was determined by the ICP-AES to be
0.49 mmol/g.
1–9
in recent years. The large diversity of readily accessible
arylboronic acids, their relative stability in air and moisture,
their low toxicity and the ease of boron-derived by-products
removal have made oxidative Heck coupling useful tool for
carbon-carbon bond formation. Usually, a metal salt such as
In our initial screening experiments, the reaction between
phenylboronic acid (5a) and butyl acrylate (6a) was investi-
gated to optimise the reaction conditions, and the results are
listed in Table 1. At first, the temperature effect was examined,
and a significant temperature effect was observed. When the
reaction was carried out at 80 °C, a too long reaction time was
required although high yield and selectivity could be obtained
(entry 1). The reaction rate increased with increase in reaction
temperatures. For the temperatures evaluated [80, 90, 100, and
110 °C], 100 °C gave the best result (entry 3). Our next studies
focused on the effect of solvent on the model reaction. Among
the solvents examined, it turned out that DMF was the best
2,3
3–7
Cu(OAc)2 or molecular oxygen are used as co-oxidants to
reoxidise Pd(0) in the oxidative Heck reactions which, in turn,
produces a stoichiometric amount of metal waste or causes
problems associated with the use of handling pure oxygen gas.
9
Recently, Larhed et al. reported a base-free oxidative Heck
reaction in the presence of air using palladium catalysts and
nitrogen ligands.
The reported catalytic systems for the oxidative Heck
reaction generally involve the use of homogeneous palladium
choice (entry 3). While other solvents, such as CH CN, EtOH,
3
toluene and DMSO were substantially less effective (entries
5–8). Increasing the amount of palladium catalyst could
shorten the reaction time, but did not increase the yield of
butyl-(E)-cinnamate 7a (entry 9). Taken together, excellent
result was obtained when the oxidative coupling reaction was
carried out with 2.5 mol% of the palladium catalyst 4 in DMF
at 100 °C under aerobic conditions (entry 3).
With this promising result in hand, we started to investigate
the scope of this reaction under the optimised conditions. The
scope of both arylboronic acids and olefins was explored, and
the results are summarized in Table 2. From Table 2, it can be
seen that the oxidative Heck coupling reactions of a variety of
arylboronic acids with butyl acrylate could proceed smoothly
under the optimised conditions to afford the corresponding
substituted butyl-(E)-cinnamates in good to excellent yields
(entries 2–9). The electronic effects of the substituents present
complexes such as Pd(OAc) , which makes the recovery of the
2
metal tedious if not impossible and might result in unaccept-
able palladium contamination of the product. From the
standpoint of green chemistry, the development of more envi-
ronmentally benign conditions for the reaction, for example,
the use of a heterogeneous palladium catalyst would be desir-
able. Heterogeneous catalysis also helps to minimise wastes
derived from reaction workup, contributing to the development
1
0–13
of green chemical processes.
So far, supported palladium
catalysts have successfully been used for the conventional
1
4–22
Heck coupling reaction of aryl halides,
however, the
heterogeneous palladium-catalysed oxidative Heck reaction
has received less attention. In continuing our efforts to develop
greener synthetic pathways for organic transformations, we
now report a highly efficient and reusable polystyrene-
immobilised phenanthroline palladium(II) complex catalyst
for the oxidative Heck coupling reactions of arylboronic acids
with olefins in the absence of external oxidants and under
base-free conditions.
The polystyrene-immobilised phenanthroline palladium(II)
complex was easily prepared starting from commercially avail-
able Merrifield resin according to Scheme 1. Firstly, Merrifield
resin was reacted with 4-hydroxybenzaldehyde in the presence
of NaH in anhydrous DMF in 90 °C to afford benzaldehyde-
functionalised resin 1. The resin 1 was subsequently treated
with 5-amino-1,10-phenanthroline (2) in ethanol at 80 °C for
24 h. After the organics were filtered, the solid was washed
with ethanol, diethyl ether and dried in vacuum to give
the phenanthroline-functionalised resin 3. Then the resin 3
was allowed to react with palladium acetate in acetone to gen-
erate the polystyrene-immobilised phenanthroline palladium
*
Correspondent. E-mail: caimzhong@163.com
Scheme 1

6
30 JOURNAL OF CHEMICAL RESEARCH 2012
Table 1 Optimisation of reaction conditions for the oxidative
reaction of phenylboronic acid with butyl acrylate. After
completion of reaction, the catalyst was separated by simple
filtration and washed with DMF and acetone. After being
air-dried, it can be reused directly without further purification.
The recovered catalyst was used in the next run and almost
consistent activity was observed for five consecutive cycles
(Table 3). The result is important from a practical point of
view.
In summary, we have described a novel polystyrene-
immobilised phenanthroline palladium(II) complex catalyst
whose preparation is simple and convenient. This heteroge-
neous palladium catalyst has not only high activity for the
open air oxidative Heck coupling reaction of olefins with aryl-
boronic acids under base-free conditions, but offers practical
advantages such as easy handling, separation from the product
and reuse.
Heck coupling of phenylboronic acid (5a) with butyl acrylate
a
(
6a)
b
c
Entry Solvent
Pd
Temperature Time Yield Selectivity
loading
/°C
/h
/%
(7a:8)
/
mol%
1
2
3
4
5
6
7
8
9
DMF
DMF
DMF
DMF
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
5
80
90
48
36
28
25
48
48
48
48
18
88
92
94
91
79
17
12
54
93
99:1
99:1
99:1
99:1
99:1
99:1
99:1
99:1
99:1
100
110
80
CH
3
CN
EtOH
80
Toluene
DMSO
DMF
110
110
100
Experimental
a
Reaction conditions: phenylboronic acid (1 mmol), butyl acryl-
1
b
H NMR spectra were recorded on a Bruker Avance (300 MHz) spec-
ate (0.5 mmol), solvent (2.5 mL) under air. Isolated yield of 7a
and 8. Determined by H NMR and GC.
c
1
trometer with TMS as an internal standard using CDCl as the solvent.
3
IR spectra were determined on an FTS-185 instrument as neat films.
−
1
Palladium acetate, Merrifield resin (1.0–1.3 mmol g ), arylboronic
acids, butyl acrylate and styrene were purchased from Sigma-Aldrich
and used as received. 5-Amino-1,10-phenanthroline (2) was prepared
Table 2 Oxidative Heck coupling of arylboronic acids with
olefins in the paresence of the polystyrene-immobilised
palladium catalyst
23
according to the literature procedure.
Synthesis of benzaldehyde-functionalised resin (1)
A 100 mL, two-necked, round-bottom flask equipped with a magnetic
stir bar, and argon was charged sequentially with dry DMF (35 mL),
4
-hydroxybenzaldehyde (1.20 g) and sodium hydride (0.45 g). After
Entry
Ar
Y
Time Product Yield Selectivity
b c
the mixture was stirred at room temperature for 1 h, the Merrifield
resin (4.0 g) was added and the reaction mixture was stirred at 90 °C
for 6 h, cooled to room temperature and filtered. The solid product
was washed with DMF (10 mL), distilled water (10 mL), and ethanol
(3 × 10 mL) and dried under vaccum to afford 4.3 g of benzaldehyde-
functionalised resin (1).
/h
/%
/%
1
2
3
4
5
6
7
8
9
Ph
CO
CO
CO
CO
CO
CO
CO
CO
CO
2
Bu 28
2
Bu 28
2
Bu 28
2
Bu 30
2
Bu 28
2
Bu 28
2
Bu 28
2
Bu 28
2
Bu 28
7a
7b
7c
7d
7e
7f
7g
7h
7i
7j
7k
7l
7m
7n
94
93
96
88
91
93
89
88
91
85
84
88
81
87
99
92
6 4
4-MeC H
4-ClC
6
H
6
4
98
4-MeOC
H
4
98
4-O
3-O
2
NC
NC
6
H
6
4
96
2
H
4
97
Synthesis of phenanthroline-functionalised resin (3)
4-BrC
4-FC
6
H
4
97
A 50 mL, two-necked, round-bottom flask equipped with a magnetic
stir bar, and argon was charged sequentially with dry ethanol (25 mL),
benzaldehyde-functionalised resin 1 (2.0 g), and 5-amino-1,10-
phenanthroline 2 (0.41 g, 5 mmol). The reaction mixture was refluxed
for 24 h, cooled to room temperature and filtered. The solid product
was washed with ethanol (10 mL), diethyl ether (10 mL), and dried
under vaccum to give 2.11 g of phenanthroline-functionalised resin
6
H
4
98
4-MeCOC
Ph
6
H
4
99
1
1
1
1
1
0
1
2
3
4
Ph
Ph
Ph
Ph
Ph
40
40
40
45
38
100
100
100
100
100
4-MeC
4-ClC
4-MeOC
4-O NC
6
H
4
6
H
4
6
H
4
2
6 4
H
3
as a light yellow powder. The nitrogen content of the resin 3 was
a
Reaction conditions: arylboronic acid (1 mmol), olefin (0.5
mmol), palladium catalyst 4 (2.5 mol%), DMF (2.5 mL) at 100 °C
under air. b Isolated yield. Selectivity of Heck coupling product
determined to be 2.24 mmol/g by CHN microanalysis.
c
Synthesis of polystyrene-immobilised phenanthroline palladium
catalyst (4)
1
determined by H NMR and GC.
Phenanthroline-functionalised resin 3 (1.5 g) was added to a solution
of Pd(OAc) (0.9 mmol) in acetone (50 mL). The mixture was heated
2
at reflux under argon for 72 h. The solid product was filtered by suc-
tion, washed with acetone, distilled water and acetone successively
and dried at 70 °C/26.7 Pa under argon for 3 h to give 1.51 g of the
light yellow polymeric palladium catalyst 4. The nitrogen and palla-
on the arylboronic acids do not have a significant effect on
the reaction yields (entries 1–9). The selectivity to the Heck
product varies between 92 and 99%, but we were not able
to observe any direct relationship with the electronic nature of
the arylboronic acids. The optimised reaction conditions were
also applied to the oxidative Heck coupling of styrene with
arylboronic acids. When we employed styrene in the oxidative
Heck coupling reaction with phenylboronic acid, trans-
stilbene was formed exclusively in high yield without any
−1
−1
dium content was 2.03 mmol g and 0.49 mmol g , respectively.
Oxidative Heck coupling reaction; general procedure
In an oven-dried 15 mL round-bottomed flask, arylboronic acid
(1 mmol), olefin (0.5 mmol), palladium catalyst 4 (2.5 mol%) and
DMF (2.5 mL) were charged and the reaction mixture was stirred at
1
,4-addition product, but a longer reaction time was required
(
entry 10). A variety of arylboronic acids with electron-
Table 3 Reusability study of the palladium catalyst 4 in
oxidative Heck reaction of phenylboronic acid with butyl
acrylatea
withdrawing or electron-donating groups were also coupled
smoothly with styrene to afford the corresponding substituted
trans-stilbenes in high yields with excellent selectivity (entries
Cycle
1
2
3
4
5
1
0–14).
Yield/%b
94
92
93
92
90
For a heterogeneous catalyst, it is important to examine its
ease of separation, good of recoverability and reusability. The
reusability of the polystyrene-immobilised phenanthroline
palladium(II) catalyst 4 was tested through the repeated
a
Reaction conditions: phenylboronic acid (1 mmol), butyl acryl-
ate (0.5 mmol), palladium catalyst 4 (2.5 mol%), DMF (2.5 mL)
at 100 °C for 28 h under air. b Isolated yield.

JOURNAL OF CHEMICAL RESEARCH 2012 631
3
0
1
00 °C under air. After completion of the reaction, as monitored by
7n: Yellow solid, m.p. 156–157 °C (lit. m.p. 157 °C). IR (KBr): ν
−
1
1
TLC, the catalyst was filtered, washed with DMF (3 × 10 mL) and
acetone (2 × 10 mL), and reused in the next run. The filtrate was
diluted with ethyl acetate and washed with 10% NaOH solution,
followed by a saturated NaCl solution. The combined organic layer
was concentrated under reduced pressure to give the crude product
which was purified by flash chromatography on silica gel.
(cm ) 3046, 1590, 1516, 1500, 1340, 840, 760, 690; H NMR (CDCl ):
δ 8.32–8.18 (m, 2H), 7.78–7.25 (m, 7H), 7.18 (s, 2H).
3
We thank the National Natural Science Foundation of China
Project No. 20862008) and the Natural Science Foundation
of Jiangxi Province of China (2008GQH0034) for financial
support.
(
2
4
−1
7
a: Oil. IR (film): ν (cm ) 3060, 2925, 2870, 1710, 1630, 1170,
1
8
5
4
25; H NMR (CDCl ): δ 7.63 (d, J = 16.0 Hz, 1H), 7.53–7.17 (m,
3
H), 6.34 (d, J = 16.0 Hz, 1H), 4.12 (t, J = 6.4 Hz, 2H), 1.94–1.18 (m,
H), 0.95 (t, J = 7.2 Hz, 3H).
Received 7 August 2012; accepted 20 August 2012
Paper 1201452 doi: 10.3184/174751912X13466942543952
Published online: 12 November 2012
2
4
−1
7
b: Oil. IR (film): ν (cm ) 3030, 2930, 2860, 1715, 1640, 1175,
1
8
30; H NMR (CDCl ): δ 7.69 (d, J = 16.0 Hz, 1H), 7.42 (d, J =
3
8
.4 Hz, 2H), 7.16 (d, J = 8.4 Hz, 2H), 6.37 (d, J = 16.0 Hz, 1H), 4.21
(
3
t, J = 6.4 Hz, 2H), 2.37 (s, 3H), 1.93–1.17 (m, 4H), 0.96 (t, J = 7.2 Hz,
References
H).
c: Oil. IR (film): ν (cm ) 3060, 2930, 2865, 1725, 1643, 1173,
1
2
3
C.S. Cho and S. Uemura, J. Organomet. Chem., 1994, 465, 85.
X. Du, M. Suguro, K. Hirabayashi and A. Mori, Org. Lett., 2001, 3, 3313.
J.P. Parrish, Y.C. Jung, S.I. Shin and K.W. Jung, J. Org. Chem., 2002, 67,
7127.
2
4
−1
7
1
8
8
(
50; H NMR (CDCl ): δ 7.68 (d, J = 16.0 Hz, 1H), 7.49 (d, J =
3
.0 Hz, 2H), 7.36 (d, J = 8.0 Hz, 2H), 6.43 (d, J = 16.0 Hz, 1H), 4.22
4
5
6
7
8
9
0
M.M.S. Andappan, P. Nilsson and M. Larhed, Chem. Commun., 2004,
218.
K.S. Yoo, C.H. Yoon and K.W. Jung, J. Am. Chem. Soc., 2006, 128,
t, J = 6.4 Hz, 2H), 1.90–1.19 (m, 4H), 0.94 (t, J = 7.2 Hz, 3H).
24
−1
7
d: Oil. IR (film): ν (cm ) 3050, 2930, 2860, 1710, 1635, 1170,
1
8
8
(
3
30; H NMR (CDCl ): δ 7.56 (d, J = 16.0 Hz, 1H), 7.38 (d, J =
3
1
6384.
.8 Hz, 2H), 6.80 (d, J = 8.8 Hz, 2H), 6.22 (d, J = 16.0 Hz, 1H), 4.13
C. Adamo, C. Amatore, I. Ciofini, A. Jutand and H. Lakmini, J. Am. Chem.
Soc., 2006, 128, 6829.
P.A. Enquist, P. Nilsson, P. Sjoberg and M. Larhed, J. Org. Chem., 2006,
71, 8779.
t, J = 6.8 Hz, 2H), 3.68 (s, 3H), 1.93–1.18 (m, 4H), 0.96 (t, J = 7.2 Hz,
H).
e: Yellow solid, m.p. 68-69 °C (lit. m.p. 68–70 °C). IR (KBr): ν
24
7
−
1
1
P.A. Enquist, J. Lindh, P. Nilsson and M. Larhed, Green Chem., 2006, 8,
(
cm ) 3070, 2920, 2860, 1710, 1640, 1515, 1340, 840; H NMR
3
38.
J. Lindh, P.A. Enquist, A. Pilotti, P. Nilsson and M. Larhed, J. Org. Chem.,
007, 72, 7957.
(
CDCl ): δ 8.18 (d, J = 8.8 Hz, 2H), 7.66 (d, J = 16.0 Hz, 1H), 7.65 (d,
3
J = 8.8 Hz, 2H), 6.52 (d, J = 16.0 Hz, 1H), 4.18 (t, J = 6.8 Hz, 2H),
1
2
.96–1.27 (m, 4H), 0.98 (t, J = 7.2 Hz, 3H).
1
M. Poliakoff, J.M. Fitzpatrick, T.R. Farren and P.T. Anastas, Science, 2002,
297, 807.
25
−1
7
f: Yellow oil. IR (film): ν (cm ) 3065, 2923, 2865, 1712, 1638,
1
1
520, 1356, 970; H NMR (CDCl ): δ 8.12-7.47 (m, 5H), 6.62 (d,
11 A. Kirschnig, H. Monenschein and R. Wittenberg, Angew. Chem. Int. Ed.,
2001, 40, 650.
3
J = 16.0 Hz, 1H), 4.23 (t, J = 6.4 Hz, 2H), 1.94–1.20 (m, 4H), 0.96 (t,
J = 7.2 Hz, 3H).
1
2
N.E. Leadbeater and M. Marco, Chem. Rev., 2002, 102, 3217.
26
−1
1
13 L. Yin and J. Liebscher, Chem. Rev., 2007, 107, 133.
7
g: Oil. IR (film): ν (cm ) 3058, 2960, 2875, 1699, 1173, 851; H
1
1
1
4
5
6
P.-W. Wang and M.A. Fox, J. Org. Chem., 1994, 59, 5358.
M.-Z. Cai, C.-S. Song and X. Huang, Synthesis, 1997, 521.
S.I. Khan and M.W. Grinstaff, J. Org. Chem., 1999, 64, 1077.
NMR (CDCl ): δ 7.64 (d, J = 16.0 Hz, 1H), 7.52 (d, J = 8.4 Hz, 2H),
7
2
3
.40 (d, J = 8.4 Hz, 2H), 6.44 (d, J = 16.0 Hz, 1H), 4.23 (t, J = 6.8 Hz,
H), 1.92-1.18 (m, 4H), 0.97 (t, J = 7.2 Hz, 3H).
17 J.H. Clark, D.J. Macquarrie and E.B. Mubofu, Green Chem., 2000, 2, 53.
18 K. Yu, W. Sommer, J.M. Richardson, M. Week and C.W. Jones, Adv. Synth.
Catal., 2005, 347, 161.
2
7
−1
7
h: Oil. IR (film): ν (cm ) 3062, 2957, 2874, 1712, 1645, 1173,
1
8
2
2
50; H NMR (CDCl ): δ 7.52 (d, J = 15.6 Hz, 1H), 7.44–7.40 (m,
3
1
2
9
0
V. Farina, Adv. Synth. Catal., 2004, 346, 1553.
S.S. Prockl, W. Kleist, M.A. Gruber and K. Koehler, Angew. Chem. Int.
Ed., 2004, 43, 1881.
H), 6.97–6.93 (m, 2H), 6.27 (d, J = 15.6 Hz, 1H), 4.13 (t, J = 6.8 Hz,
H), 1.95–1.16 (m, 4H), 0.95 (t, J = 7.2 Hz, 3H).
2
8
−1
7
i: Oil. IR (film): ν (cm ) 3057, 2964, 2878, 1714, 1694, 1634,
2
1
A. Cwik, Z. Hell and F. Figueras, Adv. Synth. Catal., 2006, 348, 523.
1
1
1
2
173, 830; H NMR (CDCl ): δ 7.98–7.94 (m, 2H), 7.69 (d, J = 15.6 Hz,
3
22 M.L. Kantam, K.B.S. Kumar, P. Srinivas and B. Sreedhar, Adv. Synth.
Catal., 2007, 349, 1141.
23 D. Stephanie, D. Eric, M. Cecile, K.-D.M. Andree and D. Pascal,
Tetrahedron Lett., 2003, 44, 8379.
24 M. Miura, H. Hashimoto, K. Itoh and M. Nomura, J. Chem. Soc., Perkin
Trans. 1, 1990, 2207.
H), 7.63–7.60 (m, 2H), 6.51 (d, J = 15.6 Hz, 1H), 4.22 (t, J = 6.4 Hz,
H), 2.62 (s, 3H), 1.95–1.19 (m, 4H), 0.97 (t, J = 7.2 Hz, 3H).
2
9
−1
7
j: White solid, m.p. 124 °C (lit. m.p. 124 °C). IR (KBr): ν (cm )
1
3
7
020, 1600, 1498, 760, 690; H NMR (CDCl ): δ 7.69–7.13 (m, 10H),
3
.09 (s, 2H).
2
5
P.R. Likhar, M. Roy, S. Roy, M.S. Subhas, M.L. Kantam and B. Sreedhar,
30
7
k: White solid, m.p. 117-118 °C (lit. m.p. 120 °C). IR (KBr):
Adv. Synth. Catal., 2008, 350, 1968.
26 E.J. Farrington, J.M. Brown, C.F.J. Barnard and E. Rowsell, Angew. Chem.,
Int. Ed., 2002, 41, 169.
27 M. Feuerstein, H. Doucet and M. Santelli, J. Org. Chem., 2001, 66, 5923.
28 M.M.S. Andappan, P. Nilsson and M. Larhed, Molecular Diversity, 2003,
−
1
1
ν (cm ) 3030, 1596, 1490, 940, 825, 710; H NMR (CDCl ): δ 7.65–
7
3
.04 (m, 9H), 7.02 (s, 2H), 2.32 (s, 3H).
3
1
7
l: White solid, m.p. 126–127 °C (lit. m.p. 129 °C). IR (KBr):
−1
1
ν (cm ) 3060, 1590, 1495, 940, 814, 700; H NMR (CDCl ): δ 7.47–
7
3
7
, 97.
Z.Y. Zhang, H.W. Hu and T.Y. Kao, React. Polym., Ion Exch., Sorbents,
990, 12, 229.
.16 (m, 9H), 7.08 (s, 2H).
m: White solid, m.p. 134–135 °C (lit. m.p. 136 °C). IR (KBr):
2
9
32
7
1
−1
1
ν (cm ) 3050, 1601, 1500, 1250, 1170, 820, 750; H NMR (CDCl ):
δ 7.58–7.20 (m, 7H), 7.02 (s, 2H), 6.86 (d, J = 8.8 Hz, 2H), 3.83 (s,
3
3
30 F. Bergmann and D. Schapira, J. Org. Chem., 1947, 12, 57.
31 A. Sekiguchi and W. Ando, J. Org. Chem., 1979, 44, 413.
32 A.R. George and R.G.W. Spickett, J. Chem. Soc., 1949, 2724.
H).

Copyright of Journal of Chemical Research is the property of Science Reviews 2000 Ltd. and its content may
not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written
permission. However, users may print, download, or email articles for individual use.