Self-supported thiourea-palladium complexes: Highly air-stable and recyclable catalysts for the suzuki reaction in neat water

Article abstract of DOI:10.1055/s-2006-942531

The synthesis of novel self-supported thiourea-PdCl₂ complexes is described. The heterogeneous catalysts exhibited high catalytic activities in the Suzuki coupling reaction of aryl bromides and aryl boronic acids in neat water under aerobic conditions. Moreover, the catalysts could be easily reused without diminishing the catalytic activity. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-942531

3058
PAPER
Self-Supported Thiourea–Palladium Complexes: Highly Air-Stable and
Recyclable Catalysts for the Suzuki Reaction in Neat Water
T
hiourea–Palladium-C
ae
i
uki
R
eaction
C
inWater hen,a Rui Li,b Yong Wu,a Li-Sheng Ding,b Ying-Chun Chen*a
a
Key Laboratory of Drug-Targeting of Education Ministry and Department of Medicinal Chemistry, West China School of Pharmacy,
Sichuan University, Chengdu 610041, P. R. of China
Fax +86(28)85502609; E-mail: ycchenhuaxi@yahoo.com.cn
Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, P. R. of China
b
Received 18 April 2006; revised 1 June 2006
Functional metal-organic assemblies, linked through co-
ordination to the metal, provide a facile strategy for the
synthesis of heterogeneous catalysts without using any
other supports. This approach has proven to be quite suc-
Abstract: The synthesis of novel self-supported thiourea-PdCl2
complexes is described. The heterogeneous catalysts exhibited high
catalytic activities in the Suzuki coupling reaction of aryl bromides
and aryl boronic acids in neat water under aerobic conditions. More-
over, the catalysts could be easily reused without diminishing the cessful for developing new heterogeneous metal cata-
lysts.4,5 Recently we reported that bulky thiourea
catalytic activity.
compounds can form robust complexes with PdCl2 in a
2:1 ratio (Figure 1, A),6 and that the complexes can act as
air-stable and efficient catalysts for some coupling reac-
tions.7 The ability of these catalysts to be recycled, how-
ever, was not investigated. We envisioned that the self-
supported thiourea–Pd complexes could be easily gener-
ated through the combination of rigid, bulky bis-thiourea
ligands and a Pd (II) salt (Figure 1, B). In this work, we
wish to report the synthesis of self-supported, heteroge-
neous, thiourea–PdCl2 catalysts and describe their appli-
cation to the Suzuki reaction of aryl bromides and aryl
boronic acids in neat water under aerobic conditions.
Key words: thiourea, palladium, self-supported, heterogeneous,
Suzuki reaction
The palladium-catalyzed Suzuki reaction, involving the
cross-coupling of sp2-halides or sp2-sulfonates with sp2-
boronic acids or their esters, is one of the most important
and straightforward tools for the synthesis of unsaturated
compounds such as biaryls.1 A variety of efficient palladi-
um catalysts, including electron-rich phosphine or car-
bene palladium complexes, palladacycles and others,
have been developed that are effective even for the cou-
pling of deactivated chloroarenes.2 On the other hand, the
development of stable and recyclable immobilized palla-
dium catalysts is also a current focus because of the in-
creasing importance of green chemistry.3 Various solid,
insoluble supports (inorganic or organic polymers) have
been applied for the immobilization of palladium cata-
lysts, however, problems are often encountered that arise
from the heterogeneous nature of these support materials:
tedious synthetic procedures, random anchoring of cata-
lytic units, unequal access to chemical reactions, and re-
duced catalytic activities. Therefore, the development of
more efficient protocols that enable the preparation of re-
usable palladium catalysts would be desirable.
O
i
NH2
H2N
+
Ar NH
OH
( )m
O
2
1
O
ii
NH
HN
NH
Ar
Ar
HN
N
( )m
3
iii
N
N
Ar
Ar
N
S
N
S
( )m
Ar
Ar
N
N
4
N
N
Cl
Pd
Cl
N
N
N
linker
N
Ar
Ar
N
N
S
S
S
S
Cl
n
Cl
Cl
N
Cl
S
S
Pd
Pd
Cl
( )m
Cl
Ar
Ar
Cl
Cl
Pd
Pd
Ar = mesityl
5
n
A
B
5a Ar = mesityl, m = 0
5b Ar = 2,5-tBu2C6H3, m = 1
5c Ar = mesityl, m = 1
Figure 1 Structures of thiourea–PdCl2 complexes
Scheme 1 Synthesis of rigid bis-thiourea ligands and the self-sup-
ported thiourea–PdCl2 complexes. Reagents and conditions: (i)
EDCI, HOBt, Et3N, CH2Cl2, 90–98%; (ii) BH3–SMe2, then CSCl2,
Na2CO3, THF, 36–40%; (iii) PdCl2(MeCN)2, toluene, 90–95%
SYNTHESIS 2006, No. 18, pp 3058–3062
Advanced online publication: 02.08.2006
x
x.
x
x
.
2
0
0
6
DOI: 10.1055/s-2006-942531; Art ID: F06206SS
© Georg Thieme Verlag Stuttgart · New York

PAPER
Thiourea–Palladium-Catalyzed Suzuki Reaction in Water
3059
We have reported the preparation of some flexible bis- thermore, the palladium loadings could be reduced with-
thiourea ligands.7a Here, the novel, bulky and rigid bis- out significantly affecting the yield (entries 2 and 3). We
thiourea ligands 4a–c were synthesized in reasonable total then tested the catalytic activities of the self-supported
yields in a similar fashion (Scheme 1). Subsequently the heterogeneous thiourea-PdCl2 complexes 5. All the brown
ligand 4 was dissolved in toluene, and a solution of polymeric complexes remained as finely divided suspen-
PdCl2(MeCN)2 in dichloromethane was added. The re- sions throughout the reaction and quickly darkened to
sulting brown precipitate, which appeared upon stirring black solids due to the formation of the active Pd(0)–thio-
and removal of the dichloromethane, could be isolated by urea complexes. We found that results comparable to
filtration to give the heterogeneous, brown catalysts 5a–c. those using monomeric catalyst were achieved for the cat-
After drying the solids under high vacuum, ICP analysis alysts 5a–c (entry 4–6). The substrate scope of the reac-
confirmed that the palladium composition of the resulting tion was studied in regard to the aryl bromides and aryl
solids were consistent with the structures of 5a–c. In addi- boronic acids, catalyzed by heterogeneous catalysts 5a–c.
tion, SEM images revealed that the solids were composed Excellent yields were obtained in the Suzuki reaction of a
of micrometer particles (Figure 2). The polymeric com- range of activated aryl bromides and phenyboronic acid
plexes 5a–c were insoluble in water and organic solvents (entries 7–10). In the case of deactivated p-bromoanisole,
such as ethyl acetate, toluene and diethyl ether, while they better results were obtained using NaOH as the base, but
were soluble in dichloromethane and chloroform.
without adding tetrabutylammonium bromide (TBAB;
entry 11), and a high yield was still observed at 0.01
mol% of palladium loading (entry 12). These results were
significantly better than those obtained in organic solvents
catalyzed by thiourea–palladium complex in the absence
of TBAB.7a Excellent yields were also obtained using oth-
er boronic acids with either electron-withdrawing or
-donating substituents on the aryl ring (entries 13–17). At
1 mol% of palladium loading, the Suzuki coupling of 2-
bromopyridine with p-methoxyphenylboronic acid was
successful, and the product was isolated in 89% yield after
12 hours (entry 18). Unfortunately, aryl chlorides were
unreactive in this catalytic system.
O2N
O2N
5a (0.2 mol%)
+
PhB(OH)2
Br
Ph
Figure 2 SEM images of self-supported catalyst 5a
H2O, K2CO3
100 °C
Equation 2 Recycling of 5a for the Suzuki reaction in neat water
From the standpoint of green chemistry, the use of water
instead of organic solvents would be highly desirable.
Therefore, the development of efficient catalysts to per-
form Suzuki cross-coupling reactions in aqueous media
continues to attract significant attention.8 Previously, we
showed that the thiourea-Pd complexes were active and
robust homogeneous catalysts for both Heck and Suzuki
reactions in organic solvents.6,7a In the present study, we
extended this operationally simple use of the heteroge-
neous, air-stable thiourea–Pd complexes, to the Suzuki re-
action in neat water.9
The reusability of the self-supported heterogeneous thio-
urea-Pd catalysts was then investigated. Recycling proce-
dures were found to be straightforward: upon completion
of the cross-coupling reaction, diethyl ether was added to
the mixture and the black, solid catalyst was recovered by
filtration. Subsequent reactions were run after addition of
more water, base and substrate. All the procedures could
be conducted under aerobic conditions. Catalyst recycling
of 5a (0.2 mol% of Pd loading) was successful for the Su-
zuki reaction of m-nitrobromobenzene and phenylboronic
acid (Equation 2), with no apparent deterioration of activ-
ity in the recovered catalyst. Quantitative yields (99%)
were still obtained after six runs in one hour. Moreover,
ICP analysis of the reaction mixture filtrate indicated that
the concentration of palladium was less than 2 ppm for
each round of reaction, which further confirmed that the
self-supported heterogeneous thiourea-Pd complexes
were robust in the present reaction systems.
PdCl2–thiourea
N
N
ArBr
+
Ar1B(OH)2
Ar-Ar1
Mes
Mes
H2O, base
100 °C
S
6
Equation 1 Suzuki reaction of aryl bromides and aryl boronic acids
catalyzed by Pd (II)-thiourea in neat water
In an initial study, we investigated the Suzuki reaction of
activated m-nitrobromobenzene and phenylboronic acid,
catalyzed by PdCl2–monothiourea 6 in neat water at
100 °C under aerobic conditions (Equation 1). We were
pleased to find that the coupled product was obtained
quantitatively within 30 minutes (Table 1, entry 1). Fur-
In summary, we have designed and synthesized the bulky
and rigid bis-thiourea ligands, and used them to generate
self-supported thiourea–PdCl2 complexes 5a–c. All acted
as efficient heterogeneous catalysts in the Suzuki reaction
Synthesis 2006, No. 18, 3058–3062 © Thieme Stuttgart · New York

3060
W. Chen et al.
PAPER
Table 1 Pd(II)–Thiourea Catalyzed Suzuki Reactions in Neat Watera
Entry
1
ArBr
Ar1B(OH)2
PhB(OH)2
Base
Catalyst
Pd (mol%) Time (h)
Yieldb (%)
99
O2N
K2CO3
PdCl2-(6)2
0.1
0.5
3
Br
Br
Br
Br
O2N
O2N
O2N
2
PhB(OH)2
PhB(OH)2
PhB(OH)2
K2CO3
K2CO3
K2CO3
PdCl2-(6)2
PdCl2-(6)2
5a–5c
0.001
0.0001
0.1
99
72
99
3
24
4–6
0.5
7
8
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
K2CO3
K2CO3
K2CO3
K2CO3
NaOH
NaOH
5a
5a
5a
5a
5a
5a
0.1
0.5
1
99
99
97
93
80
75
MeOC
MeOC
MeOOC
OHC
Br
Br
0.01
0.1
9
0.5
0.5
Br
10
11c
12c
0.1
Br
0.1
12
MeO
Br
Br
PhB(OH)2
0.01
20
5
MeO
O2N
F
13
K2CO3
5a
0.1
99
B(OH)2
Br
F
14
15
K2CO3
K2CO3
5b
5c
0.1
0.1
0.5
99
99
MeOC
MeOC
Br
B(OH)2
0.5
4
Br
Br
MeO
MeS
B(OH)2
16
K2CO3
5b
0.1
99
MeOC
B(OH)2
B(OH)2
17c
18
NaOH
K2CO3
5b
5b
0.1
1
10
86
89
MeO
N
Br
12
MeO
B(OH)2
Br
a The reactions were conducted in neat water under aerobic conditions. ArBr/Ar1B(OH)2/K2CO3 = 1:1.2:1.5.
b Isolated yield.
c ArBr/Ar1B(OH)2/NaOH = 1:1.5:2.0.
Synthesis 2006, No. 18, 3058–3062 © Thieme Stuttgart · New York

PAPER
Thiourea–Palladium-Catalyzed Suzuki Reaction in Water
3061
1H NMR (300 MHz, CDCl3): d = 9.24 (s, 2 H), 7.54 (d, J = 8.4 Hz,
4 H), 7.17 (d, J = 8.4 Hz, 4 H), 6.86 (s, 4 H), 3.95 (s, 2 H), 3.70 (s,
4 H), 2.28 (s, 12 H), 2.25 (s, 6 H).
13C NMR (50 MHz, CDCl3): d = 169.2, 142.1, 137.3, 135.6, 132.9,
129.8, 129.5, 119.8, 52.6, 40.8, 20.5, 18.3.
of aryl bromides and aryl boronic acids in neat water un-
der aerobic conditions. Moreover, facile recovery of the
heterogeneous catalysts was demonstrated with no appar-
ent palladium leaching. Currently the application of these
catalysts to other transformations is under investigation in
this laboratory.
MS (ESI): m/z (%) = 547.4 (100) [M – 1].
HRMS (ESI): m/z calcd for C35H40N4O2 + H: 549.3230; found:
549.3242.
All chemicals were purchased from commercial sources and used
without further purification. Melting points were determined in
open capillaries and were uncorrected. H NMR spectra were re-
Synthesis of Bis-Thiourea Ligands 4; General Procedures
To a solution of 3 (0.9 mmol) in THF (20 mL) was added BH3-SMe2
(2 M in THF, 3.6 mL, 7.2 mmol, 8 equiv) at 0 °C. The solution was
refluxed overnight then, after cooling to r.t., MeOH was added
dropwise in order to destroy the excess BH3. The solvent was re-
moved, and the resulting tetraamine was directly used in the next
step.
1
corded at 300 MHz or 400 MHz, and 13C NMR spectra were record-
ed at 50 MHz or 100 MHz on Bruker Avance spectrometers.
Chemical shifts (d) are reported in ppm downfield from CDCl3 (d =
7.27 ppm) for 1H NMR and relative to the central CDCl3 resonance
(d = 77.0 ppm) for 13C NMR spectroscopy. Coupling constants (J)
are given in Hz. IR spectra were recorded using a Perkin-Elmer
1600 Series FTIR. ESI-mass spectra were measured with a Finnigan
LCQDECA ion trap mass spectrometer.
To a stirred mixture of tetraamine obtained above and Na2CO3 (580
mg, 5.4 mmol) in dry THF (20 mL) was added a dilute solution of
thiophosgene (510 mL, 2.25 mmol) in THF (10 mL) over about 8 h.
After stirring at r.t. overnight, THF was removed under vacuum,
and H2O (15 mL) and EtOAc (20 mL) were added. The organic lay-
er was washed with brine (10 mL), dried (Na2SO4) and concentrat-
ed. The pure bis-thiourea was obtained as a white solid through
flash chromatography and recrystallization from ethanol.
Synthesis of Bis-Amides 3; General Procedure
Diamine 1 (1 mmol), amino acid 27a (2.2 mmol), 1-(3-dimethylami-
nopropyl)-3-ethylcarbodiimide hydrochloride (460 mg, 2.4 mmol)
and 1-hydroxybenzotriazole (135 mg, 1 mmol) were stirred in
CH2Cl2 (20 mL) at 0 °C for 5 min. Et3N (0.42 mL, 3 mmol) was then
added and the reaction was stirred at r.t. under argon and monitored
by TLC. Upon completion, the organic layer was washed with sat-
urated NaHCO3 (2 × 10 mL) and brine (10 mL), dried and concen-
trated. Pure compounds 3 were obtained after flash chromatography
or recrystallization from ethanol.
4a
Yield: 36% (two steps); white solid; mp >200 °C.
IR (KBr): 1608, 1500, 1272 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.75 (d, J = 8.3 Hz, 4 H), 7.64 (d,
J = 8.3 Hz, 4 H), 6.98 (s, 4 H), 4.29 (t, J = 8.9 Hz, 4 H), 3.94 (t,
J = 8.9 Hz, 4 H), 2.31 (s, 6 H), 2.30 (s, 12 H).
3a
Yield: 90%; white solid; mp >200 °C.
IR (KBr): 3377, 3304, 1665 cm–1.
1H NMR (300 MHz, DMSO-d6): d = 10.10 (s, 2 H), 7.70 (d, J = 8.1
Hz, 4 H), 7.60 (d, J = 8.1 Hz, 4 H), 6.75 (s, 4 H), 4.34 (s, 2 H), 3.74
(d, J = 5.1 Hz, 4 H), 2.24 (s, 12 H), 2.14 (s, 6 H).
13C NMR (100 MHz, CDCl3): d = 180.8, 140.0, 138.4, 137.8, 136.4,
134.7, 129.5, 127.2, 124.3, 49.5, 47.2, 21.1, 17.9.
MS (ESI): m/z (%) = 589.8 (21) [M – 1], 555.1 (100).
HRMS (ESI): m/z calcd for C36H38N4S2 + H: 591.2616; found:
591.2611.
13C NMR (50 MHz, DMSO-d6): d = 170.1, 143.8, 138.0, 134.8,
129.9, 129.4, 128.5, 126.7, 119.8, 51.8, 20.4, 18.6.
4b
MS (ESI): m/z (%) = 533.4 (100) [M – 1].
Yield: 40% (two steps); white solid; mp 140–142 °C.
IR (KBr): 1611, 1513, 1282 cm–1.
HRMS (ESI): m/z calcd for C34H38N4O2 + H: 535.3073; found:
535.3055.
1H NMR (300 MHz, CDCl3): d = 7.55 (d, J = 8.3 Hz, 4 H), 7.46 (d,
J = 8.5 Hz, 2 H), 7.36 (dd, J = 2.0, 8.5 Hz, 2 H), 7.20 (d, J = 7.8 Hz,
4 H), 7.11 (d, J = 2.0 Hz, 2 H), 4.17–3.93 (m, 10 H), 1.47 (s, 18 H),
1.32 (s, 18 H).
13C NMR (75 MHz, CDCl3): d = 184.4, 150.4, 145.0, 139.6, 139.2,
138.8, 129.2, 128.2, 127.5, 125.4, 125.0, 52.6, 49.6, 41.0, 35.4,
34.3, 31.9, 31.2.
3b
Yield: 98%; white solid; mp 104–106 °C.
IR (KBr): 3449, 3339, 1671 cm–1.
1H NMR (300 MHz, CDCl3): d = 8.52 (s, 2 H), 7.38 (d, J = 8.4 Hz,
4 H), 7.24 (d, J = 8.3 Hz, 2 H), 7.09 (d, J = 8.4 Hz, 4 H), 6.86 (d,
J = 8.3 Hz, 2 H), 6.66 (s, 2 H), 4.02 (s, 4 H), 3.87 (s, 2 H), 1.48 (s,
18 H), 1.24 (s, 18 H).
13C NMR (50 MHz, CDCl3): d = 169.1, 150.6, 145.0, 137.5, 135.4,
131.9, 129.5, 126.4, 120.5, 116.4, 110.6, 50.4, 40.9, 34.5, 34.0,
31.4, 30.4.
MS (ESI): m/z (%) = 745.4 (100) [M + 1].
HRMS (ESI): m/z calcd for C47H60N4S2 + Na: 767.4157; found:
767.4152.
4c
MS (ESI): m/z (%) = 687.6 (100) [M – 1].
Yield: 40% (two steps); white solid; mp 110–112 °C.
IR (KBr): 1609, 1514, 1273 cm–1.
HRMS (ESI): m/z calcd for C45H60N4O2 + Na: 711.4614; found:
711.4612.
1H NMR (300 MHz, CDCl3): d = 7.55 (d, J = 8.4 Hz, 4 H), 7.24 (d,
J = 8.4 Hz, 4 H), 6.96 (s, 4 H), 4.22 (t, J = 8.3 Hz, 4 H), 3.98 (s,
2 H), 3.90 (t, J = 8.3 Hz, 4 H), 2.30 (s, 6 H), 2.28 (s, 12 H).
13C NMR (75 MHz, CDCl3): d = 180.9, 138.9, 138.5, 138.2, 136.3,
134.7, 129.4, 129.1, 124.4, 49.5, 47.1, 40.9, 21.0, 17.8.
3c
Yield: 95%; white solid; mp 138–140 °C.
IR (KBr): 3353, 3314, 1673 cm–1.
MS (ESI): m/z (%) = 605.4 (12) [M + 1].
Synthesis 2006, No. 18, 3058–3062 © Thieme Stuttgart · New York

3062
W. Chen et al.
PAPER
HRMS (ESI): m/z calcd for C37H40N4S2 + H: 605.2773; found:
605.2767.
S.; Whang, D.; Lee, H.; Jun, S. I.; Oh, J.; Jeon, Y. J.; Kim,
K. Nature 2000, 404, 982. (b) Takizawa, S.; Somei, H.;
Jayaprakash, D.; Sasai, H. Angew. Chem. Int. Ed. 2003, 42,
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(d) Ding, K.; Wang, Z.; Wang, X.; Liang, Y.; Wang, X.
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Synthesis of Thiourea–PdCl2 Complexes 5; General Procedure
To a stirred solution of bis-thiourea ligand 4 (0.5 mmol) in toluene
(10 mL) was added a solution of PdCl2(MeCN)2 (130 mg, 0.6
mmol) in CH2Cl2 (5 mL). The mixture was heated at 40 °C for 3 h,
then the solvent was removed under vacuum and the brown solids
were filtered and washed thoroughly with toluene and Et2O. After
drying under high vacuum, the Pd loadings were determined by ICP
analysis. The Pd values for 5a, 5b and 5c were 1.08, 1.04 and 1.15
mmol/g, respectively.
Suzuki Reaction Catalyzed by Heterogeneous 5; General Proce-
dure
Aryl bromides (1.15 mmol), aryl boronic acid (1.38 mmol), K2CO3
(240 mg, 1.73 mmol), the calculated amount of self-supported cat-
alyst 5 and H2O (1 mL) were added to a flask under aerobic condi-
tions. The mixture was heated to 100 °C during which the brown
complexes quickly darkened to black solids. Upon completion, the
mixture was extracted with Et2O (15 mL), washed with brine (2 × 5
mL), and dried. The solvent was removed and the residue was puri-
fied by flash chromatography on silica gel to give the coupling
product.
(5) For the cross-linked dendritic or star-shaped catalysts, see:
(a) Reetz, M. T.; Giebel, D. Angew. Chem. Int. Ed. 2000, 39,
2498. (b) Rigaut, S.; Delville, M.-H.; Losada, J.; Astruc, D.
Inorg. Chim. Acta 2002, 334, 225. (c) Harada, T.;
Nakatsugawa, M. Synlett 2006, 321. (d) Liu, Q.-P.; Chen,
Y.-C.; Wu, Y.; Zhu, J.; Deng, J.-G. Synlett 2006, 1503.
(e) For self-supported amphiphilic polymeric Pd catalyst,
see: Yamada, Y. M. A.; Takeda, K.; Takahashi, H.; Ikegami,
S. Org. Lett. 2002, 4, 3371.
The 1H NMR and 13C NMR spectral data of the coupling products
(6) Yang, D.; Chen, Y.-C.; Zhu, N.-Y. Org. Lett. 2004, 6, 1577.
(7) For recent work on thiourea-Pd catalysts, see: (a) Chen, W.;
Li, R.; Han, B.; Li, B.-J.; Chen, Y.-C.; Wu, Y.; Ding, L.-S.;
Yang, D. Eur. J. Org. Chem. 2006, 1177. (b) Dai, M.;
Liang, B.; Wang, C.; Chen, J.; Yang, Z. Org. Lett. 2004, 6,
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Dong, G.; Chen, J.; Yang, Z. Adv. Synth. Catal. 2004, 346,
1669. (d) For furancarbo-thioamide-based palladacycles,
see: Xiong, Z.; Wang, N.; Dai, M.; Li, A.; Chen, J.; Yang, Z.
Org. Lett. 2004, 6, 3337.
were found to be identical to those reported in the literature.7a
Acknowledgment
The project was sponsored by SRF for ROCS, SEM, China. We are
grateful for the financial support from Sichuan University.
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(1) For recent reviews on Suzuki coupling, see: (a) Bai, L.;
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Angew. Chem. Int. Ed. 2004, 43, 2201. (c) Hassan, J.;
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(2) (a) Littke, A. F.; Fu, G. C. Angew. Chem. Int. Ed. 2002, 41,
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(3) For a review, see: Cole-Hamilton, D. J. Science 2003, 299,
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(4) For self-supported metal-organic catalysts, see: (a) Seo, J.
Synthesis 2006, No. 18, 3058–3062 © Thieme Stuttgart · New York