Polystyrene supported thiopseudourea Pd(II) complex: Applications for Sonogashira, Suzuki-Miyaura, Heck, Hiyama and Larock heteroannulation reactions Srinivas Keesara, Saiprathima Parvathaneni, Govardhan Dussa, Mohan Rao Mandapati * I & PC Division, Indian Institute of Chemical Technology, Taranaka, Hyderabad 500607, India article info Article history: Received 19 November 2013 Received in revised form 3 April 2014 Accepted 19 April 2014 Keywords: Thiopseudourea CeC coupling reactions Larock indolization Palladium abstract A new polystyrene supported thiopseudourea palladium(II) complex (3) is found to be a highly active catalyst for the copper-free Sonogashira, Suzuki, Heck, Hiyama and Larock heteroannulation reactions of aryl halides. All the reactions proceeded well affording the corresponding cross-coupling products in good to excellent yields. Further, the catalyst showed excellent recyclability without any significant loss in its activity. Ó 2014 Elsevier B.V. All rights reserved. Introduction The palladium catalyzed Sonogashira [1], Suzuki-Miyaura [2], Heck [3], Hiyama [4] and Larock heteroannulation [5] reactions have emerged as powerful methods in organic synthesis. These cross coupling reactions are having importance in the synthesis of natural products and fine chemicals [6]. Most of the reported Sonogashira [7], Suzuki [8], Heck [9], Hiyama [10] and Larock het- eroannulation [11] reactions proceeded under homogeneous con- ditions. However, many homogeneous systems cannot be commercialized because of difficulties associated with the recovery of the catalyst. In order to achieve environmentally benign condi- tions, immobilization of homogeneous catalysts onto polymeric organic or inorganic insoluble supports [12]. The immobilization of homogeneous catalysts is generally more attractive from an industrial point of view and polystyrene- supported palladium catalysts have successfully been used for a variety of organic reactions [13]. C. Najera et al. have reported resin supported and unsupported palladacycle oxime complexes for CeC coupling reactions [14]. The development of efficient heteroge- neous palladium catalyst systems that could be simultaneously catalyzing the CeC coupling reactions and obtaining Pd-free pure products is the most important for the pharmaceutical industry. In view of this, several heterogeneous Pd-catalysts have been re- ported [15]. However, polymer-supported palladium catalyst cata- lyzed Hiyama and Larock heteroannulation reactions have received less attention. Very few efficient reusable palladium catalytic sys- tems have been reported for Hiyama couplings [16]. C. L. Drian has described very recently efficient reusable polystyrene-supported palladium catalyst for Hiyama cross-coupling [17]. Laurent Djako- vitch has reported heterogeneous Pd catalysts for different heter- oannulation reactions [18]. Herein, we describe the synthesis and application of polystyrene supported thiopseudourea palladium(II) complex (3) [abbreviated as PS-tsu-Pd(II)] catalyst to CeC cross- couplings (Sonogashira, Suzuki-Miyaura, Heck & Hiyama) and Larock heteroannulation reactions. Recently, we have reported homogeneous thiopseudourea pal- ladium(II) complex (4) as catalysts for the above cross-coupling reactions (Fig. 1) [19]. Although it showed significant catalytic ac- tivity for all the cross-coupling reactions of aryl halides, the dis- advantages associated with it are overwhelmed by our polymer supported heterogeneous system. Results and discussion Synthesis and characterization of PS-tsu-Pd(II) complex In Scheme 1 , We have given the steps involved in the preparation of a new polystyrene supported thiopseudourea palladium(II) complex 3. A 1-(2-Picolyl)-3-(4-fluorobenzoyl)-2-benzyl-2- * Corresponding author. Tel.: þ91 40 27193181; fax: þ91 40 27160921. E-mail addresses: [email protected], [email protected](M.R. Mandapati). Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem http://dx.doi.org/10.1016/j.jorganchem.2014.04.020 0022-328X/Ó 2014 Elsevier B.V. All rights reserved. Journal of Organometallic Chemistry 765 (2014) 31e38
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Journal of Organometallic Chemistry 765 (2014) 31e38
http://dx.doi.org/10.1016/j.jorganchem.2014.04.0200022-328X/� 2014 Elsevier B.V. All rights reserved.
a b s t r a c t
A new polystyrene supported thiopseudourea palladium(II) complex (3) is found to be a highly activecatalyst for the copper-free Sonogashira, Suzuki, Heck, Hiyama and Larock heteroannulation reactions ofaryl halides. All the reactions proceeded well affording the corresponding cross-coupling products ingood to excellent yields. Further, the catalyst showed excellent recyclability without any significant lossin its activity.
� 2014 Elsevier B.V. All rights reserved.
Introduction
The palladium catalyzed Sonogashira [1], Suzuki-Miyaura [2],Heck [3], Hiyama [4] and Larock heteroannulation [5] reactionshave emerged as powerful methods in organic synthesis. Thesecross coupling reactions are having importance in the synthesis ofnatural products and fine chemicals [6]. Most of the reportedSonogashira [7], Suzuki [8], Heck [9], Hiyama [10] and Larock het-eroannulation [11] reactions proceeded under homogeneous con-ditions. However, many homogeneous systems cannot becommercialized because of difficulties associated with the recoveryof the catalyst. In order to achieve environmentally benign condi-tions, immobilization of homogeneous catalysts onto polymericorganic or inorganic insoluble supports [12].
The immobilization of homogeneous catalysts is generally moreattractive from an industrial point of view and polystyrene-supported palladium catalysts have successfully been used for avariety of organic reactions [13]. C. Najera et al. have reported resinsupported and unsupported palladacycle oxime complexes for CeCcoupling reactions [14]. The development of efficient heteroge-neous palladium catalyst systems that could be simultaneouslycatalyzing the CeC coupling reactions and obtaining Pd-free pureproducts is the most important for the pharmaceutical industry. In
view of this, several heterogeneous Pd-catalysts have been re-ported [15]. However, polymer-supported palladium catalyst cata-lyzed Hiyama and Larock heteroannulation reactions have receivedless attention. Very few efficient reusable palladium catalytic sys-tems have been reported for Hiyama couplings [16]. C. L. Drian hasdescribed very recently efficient reusable polystyrene-supportedpalladium catalyst for Hiyama cross-coupling [17]. Laurent Djako-vitch has reported heterogeneous Pd catalysts for different heter-oannulation reactions [18]. Herein, we describe the synthesis andapplication of polystyrene supported thiopseudourea palladium(II)complex (3) [abbreviated as PS-tsu-Pd(II)] catalyst to CeC cross-couplings (Sonogashira, Suzuki-Miyaura, Heck & Hiyama) andLarock heteroannulation reactions.
Recently, we have reported homogeneous thiopseudourea pal-ladium(II) complex (4) as catalysts for the above cross-couplingreactions (Fig. 1) [19]. Although it showed significant catalytic ac-tivity for all the cross-coupling reactions of aryl halides, the dis-advantages associated with it are overwhelmed by our polymersupported heterogeneous system.
Results and discussion
Synthesis and characterization of PS-tsu-Pd(II) complex
In Scheme 1,We have given the steps involved in the preparationof a new polystyrene supported thiopseudourea palladium(II)complex 3. A 1-(2-Picolyl)-3-(4-fluorobenzoyl)-2-benzyl-2-
S. Keesara et al. / Journal of Organometallic Chemistry 765 (2014) 31e3832
thiopseudourea functionalized polystyrene resin (2% DVB) wasformed by heating a mixture of chloromethylated polystyrene and1-(2-Picolyl)-3-(4-fluorobenzoyl)-thiourea in DMF at 120 �C for24 h. This solid polymer-supported thiopseudourea is insoluble incommon organic solvents. Reaction of polymer-bound thio-pseudourea with chloroform and Pd(OAc)2 in 1 : 1 molar ratio for12 h at room temperature resulted in covalent attachment ofpalladium to give functionalized polymer. The exact complex for-mation was confirmed by FT-IR analysis. In the FT-IR spectrum ofpolymer-bound thiopseudourea, the absence of sharp CeCl peak(due to CH2Cl groups) at 1263 cm�1 of starting polymer, indicatesthe introduction of thiourea on the polymer. The stretching vibra-tion of the C]N and C]O double bond peaks observed at 1600 and1724 cm�1 corresponds to the formation of polystyrene-supportedthiopseudourea palladium complex [19a,20]. Scanning electronmicrographs (SEM) were reported for pure chloromethylatedpolystyrene, and polymer supported thiopseudourea-Pd(II) com-plex to observe themorphological changes. The complete change inthemorphology indicates the formation of desired complex Fig. 2(a)& (b). Thermal stability of the complexwas investigated by TGA. Thenegligibleweight loss below200 �C is due to the physically adsorbedsolvent molecules. Thermogravimetric analysis shows stability of
Scheme 1. Preparation of the polymer supp
the PS-tsu-Pd(II) complex (3) up to 320 �C and further weight loss ata higher temperature (above 320 �C) was attributed to the decom-position of complex. The amount of palladium incorporated into thepolymer was also determined by atomic absorption spectroscopy(AAS), which showed the value of about 5.55% (0.52 mmol/g).
Sonogashira reaction
From the preliminary investigations, we examined the catalyticactivity of PS-tsu-Pd(II) complex (3) for Sonogashira reaction. Wechoose the reaction of 4-iodobenzene and phenylacetylene as amodel to optimize the reaction conditions. The results are sum-marized in Table 1. For the optimization of base, we tested severalinorganic and organic bases inwater using 0.001mmol of catalyst 3at room temperature. The best experimental results were observedby employing the organic amine bases (entries 4e6). Among thetested amine bases, Et3N proved to be efficient for Sonogashirareaction under aqueous conditions (entry 4). Best results were alsoobtained under solvent free conditions (entry 7). The scope andlimitations of the reaction were studied with different aryl iodidesand terminal alkynes by using the optimal solvent and base.Excellent yields were obtained for both deactivated and activatedaryl iodides (Table 2, entries 2e12) and the substituent effect in thearyl iodides appeared to be less significant. However, it could not beextended for the bromobenzene coupling reaction.
Suzuki cross-coupling reactions
The catalytic activity of PS-tsu-Pd(II) complex (3) for the Suzuki-Miyaura cross coupling reaction was studied in water (Table 3).Initially, we examined the coupling of 4-iodotoluene and phenyl-boronic acid in the presence of 0.001 mmol of catalyst 3 at 80 �C for6 h. Among the bases screened, LiOH.H2O found to be the best(entry 1). Further, we studied the temperature effect on the cata-lytic activity of PS-tsu-Pd(II) complex. The yield of coupled biphenyl
orted thiopseudourea-Pd(II) complex 3.
Fig. 2. Scanning electron micrograph of (a) chloromethylated polystyrene; (b) PS-tsu-Pd(II) complex (3).
S. Keesara et al. / Journal of Organometallic Chemistry 765 (2014) 31e38 33
product decreased from 98% to 54%, while decreasing the temper-ature from 80 to 50 �C (entry 6). The reactions of aryl halides withvarious phenylboronic acids were carried under optimized reactionconditions as shown in Table 4. All the reactions of aryl iodidesproceeded well with high yields of desired products even with0.001 mmol of catalyst 3 (entries 2e6). The substituent effect onphenyl ring is almost negligible, with electron-donating group (Me,
Table 1PS-tsu-Pd(II) complex (3) catalyzed Sonogashira reactions of iodobenzene with phenylac
Entry Base
1 LiOH.H2O2 K3PO4
3 Na2CO3
4 Et3N5 piperidine6 pyrrolidine7c Et3N
a Reaction conditions: 1 mmol of iodobenzene, 1.2 mmol of phenylaetylene, 2.0 mmob Isolated yield.c Solvent free reaction.
OMe) (entry 5 & 6) or electron-withdrawing groups (Cl, & NO2)(entries 3 & 4). When the catalyst loading was increased to0.005 mmol for the coupling reactions of aryl bromides, the yieldswere good irrespective of the position of the substituent on phenylring (entries 7e17). However, product formation was not observedin case of low reactive chlorobenzene under the same reactionconditions (entry 18).
Heck reactions
The catalytic activity of the PS-tsu-Pd(II) complex 3(0.001 mmol) was studied with iodobenzene and styrene byemploying several bases at 100 �C for 10 h (Table 5). We observedthat the reactions were not preceded well under aqueous condi-tions (entries 1e4). Excellent yield (96%) of coupled product wasobtained with K3PO4 in DMF solvent (entry 6). Further, we appliedspecified optimal reaction conditions to various aryl iodides andstyrenes (Table 6). All the activated (Cl, F, COCH3 and NO2) anddeactivated (CH3 and OCH3) aryl iodides gave excellent yields at100 �C using complex 3 (entries 2e10). Next we applied this reac-tion conditions to aryl bromides with increasing catalyst loading,higher temperature and longer times. The Heck reactions of a va-riety of aryl bromides with styrenes could go on smoothly at 130 �Cto give the resultant coupling products in high yields on longerreaction times (entries 11e19).
Hiyama reactions
The reaction of 4-iodotoluene with trimethoxy(phenyl)silanewas studied by applying catalyst (3) in presence of various basesand solvents at 100 �C (Table 7). We found that 0.005 mmol cata-lyst, LiOH.H2O base and water as solvent is the best system to studythe reactivity of different aryl halides (entries 7e9).
Larock heteroannulation reactions
Finally, we extended the activity studies of PS-tsu-Pd(II) com-plex (3) for the heteroannulation reactions. We have chosen thecoupling reaction of 2-iodoanilinewith diphenylacetylene asmodelto optimize the reaction conditions. Several bases and solventswere screened with 0.005 mmol of catalyst at 100 �C for about 30 h(Table 8). Among the studied bases and solvents, K2CO3 and DMFgave the best results (entry 3).
etylene.a
Cat (mmol) Yield (%)b
0.001 e
0.001 e
0.001 e
0.001 960.001 900.001 880.001 74
l of base, 0.001 mmol of catalyst 3, 3 mL of H2O at room temperature for 8 h.
2 C6H5 H 943 4-ClC6H4 H 974 4-CF3C6H4 H 955 4-CF3C6H4 OCF3 946 4-NO2C6H4 H 947 4-COCH3C6H4 H 928 4-CH3C6H4 H 889 4-CH3OC6H4 H 9610 3-CH3C6H4 H 9311 2-CHOC6H5 H 9212 2-CH3OC6H5 H 80
a Reaction conditions: 1 mmol of Aryl halide, 1.2 mmol of phenylacetylene,2.0 mmol of Et3N, 0.001mmol of catalyst 3, 3 mL of H2O at room temperature for 8 h.
b Isolated yield.c Reaction with 0.5 mol% of Pd complex (4).
Table 4PS-tsu-Pd(II) complex (3) catalyzed Suzuki reaction of aryl halides with arylboronicacids.a
Entry Ar X R Yield (%)b
1 C6H5 I H 80d
2 C6H5 I H 943 4-ClC6H4 I H 954 4-NO2C6H4 I H 925 4-CH3C6H4 I H 946 4-CH3OC6H4 I H 907 C6H5 Br H 92c
8 4-CH3C6H4 Br H 92c
9 4-CH3OC6H4 Br H 96c
10 4-CH3SC6H4 Br H 90c
11 4-CF3C6H4 Br CH3 86c
12 4-CH3C6H4 Br CH3 92c
13 4-CH3OC6H4 Br CH3 90c
14 4-CH3SC6H4 Br CH3 88c
15 4-CH3OC6H4 Br 3-OEt 72c
16 2-CH3OC6H4 Br H 82c
17 3-pyridyl Br H 84c
18 C6H5 Cl H ec
a Reaction conditions: 1 mmol of Aryl halide, 1.2 mmol of Arylboronic acid,2.0 mmol of LiOH.H2O, 0.001 mmol of catalyst 3, 3 mL of H2O at 80 �C for 6 h.
b Isolated yield.c 0.005 mmol of catalyst 3.d Reaction with 0.5 mol% of Pd complex (4).
S. Keesara et al. / Journal of Organometallic Chemistry 765 (2014) 31e3834
Catalytic activity of the heterogeneous and the homogeneouscatalyst
We conducted the below described cross coupling reactionsunder the same reaction conditions by using PS-tsu-Pd(II) complex(3) and homogeneous Pd complex (4) (Table 9). Homogeneouscomplex is active only for Sonogashira, Suzuki and Heck couplingreactions. Complex 4 gave high yields for Heck reaction comparedto heterogeneous complex 3.
Temperature studies for Suzuki and Heck coupling reactions
The Suzuki reaction of iodobenzene with phenylboronic acidwas conducted at different temperatures. The reaction reached99.5% conversion after 1 h at 100 �C, whereas for a temperature of80 �C it took 6 h for 97% conversion. We observe 90% conversionafter 10 h where the reaction at 60 �C. The conversion of substrateto product was high at 100 �C (Fig. 3). Further we study the tem-perature effect in Heck reaction of iodobenzene with styrene. Herewe observed 97% conversion after 10 h at 100 �C and the reaction
Table 3PS-tsu-Pd(II) complex (3) catalyzed Suzuki reaction of 4-iodotoluene with phenylboroni
Entry Base
1 LiOH.H2O2 K3PO4
3 K2CO3
4 Na2CO3
5 Et3N6 LiOH.H2O
a Reaction conditions: 1 mmol of 4-iodotoluene, 1.2 mmol of phenylboronic acid, 2.0b Isolated yield.c Reaction temperature at 50 �C.
reached 42% after 20 h at 80 �C. Where the reaction at 120 �C weobtained 99% conversion within 4 h only. The conversion of sub-strate to product was high at 120 �C. This indicates that an oxidativeaddition of palladium species to aryl iodide is the rate-limiting stepof both Suzuki and Heck coupling reactions, it follows that fasteraddition is associated at higher temperatures (Fig. 4). As expected,aryl bromides are low reactive compare to aryl iodides, which haveobserved the highest yield at high temperature and catalyst loadingon longer reaction times.
Recyclability of the catalyst
In view of industrial application, reusability of the catalyst is avery important factor to be considered. Therefore the reusability of
c acid.a
Cat (mmol) Yield (%)b
0.001 980.001 880.001 940.001 900.001 e
0.001 54c
mmol of base, 0.001 mmol of catalyst 3, 3 mL of H2O at 80 �C for 6 h.
Table 5PS-tsu-Pd(II) complex (3) catalyzed Heck reaction of iodobenzene with styrene.a
Entry Base Solvent Yield (%)b
1 LiOH.H2O H2O e
2 K3PO4 H2O e
3 Na2CO3 H2O e
4 Et3N H2O e
5 LiOH.H2O DMF 906 K3PO4 DMF 967 Na2CO3 DMF e
8 Et3N DMF 34
a Reaction conditions: 1 mmol of Aryl halide, 2 mmol of styrene, 2.0 mmol of base,0.001 mmol of catalyst 3, 2 mL of solvent at 100 �C for 10 h.
b Isolated yield.
Table 7PS-tsu-Pd(II) complex (3) catalyzed Hiyama reactions of aryl halides with trime-thoxy(phenyl)silane.a
a Reaction conditions: 1 mmol of aryl halide, 1.2 mmol of trimethoxy(phenyl)silane, 2.0 mmol of base, 0.005 mmol of catalyst 3, 2 mL of solvent at 100 �C for 10 h.
b Isolated yield.c Reaction with 0.5 mol% of Pd complex (4).
S. Keesara et al. / Journal of Organometallic Chemistry 765 (2014) 31e38 35
the catalyst was examined for all CeC cross coupling and hetero-annulation reactions. The catalyst was easily recovered from thereaction mixture by simple filtration, washing with acetonitrile anddrying for further use.
Leaching studiesTo determine the degree of leaching of the palladium from the
heterogeneous catalyst, the catalyst was removed by filtration andthe palladium content of the filtrate was determined by AAS. Dur-ing the course of Suzuki and Sonogashira reactions, only 0.2% ofpalladium was lost into solution after the first run. After five re-cycles loss of 5% was observed, which shows the average amount ofleaching of palladium per cycle is about 1.0%. In case of Heck,
Table 6PS-tsu-Pd(II) complex (3) catalyzed Heck reactions of aryl halides with styrenes.a
a Reaction conditions: 1 mmol of aryl halide, 2 mmol of olefin, 2.0 mmol of K3PO4, 0.0b Isolated yield.c 0.005 mmol of catalyst 3, reaction temperature 130 �C, reaction time 15 h.d Reaction with 0.5 mol% of Pd complex (4).
Hiyama and Larock heteroannulation reactions leaching of palla-dium per cycle was observed to be 5% approximately.
Conclusions
A new polystyrene-supported thiopseudourea-Pd(II) complex issynthesized and characterized. This complex acts as an efficientcatalyst in the Sonogashira, Suzuki, Heck, Hiyama and Larock
R Yield (%)b
H 98d
H 94H 92H 95H 94H 90H 92H 884-CH3 964-CH3 93H 96c
H 92c
4-CH3 94c
H 83c
H 88c
H 90c
H 84c
4-CH3 80c
4-CH3 82c
01 mmol of catalyst 3, 2 mL of DMF at 100 �C for 10 h.
Table 8PS-tsu-Pd(II) complex (3) catalyzed heteroannulation of 2-iodoaniline with diphenyl acetylene.a
Entry Base Solvent Yield (%)b
1 LiOH.H2O DMF 682 K3PO4 DMF e
3 K2CO3 DMF 864 Na2CO3 DMF 825 K2CO3 DMA e
6 K2CO3 NMP e
7 K2CO3 H2O e
8 K2CO3 DMF 10c
a Reaction conditions: 1 mmol of 2-iodoaniline, 1.5 mmol of diphenylacetylene, 2.0 mmol of base, 0.005 mmol of catalyst 3, 2 mL of solvent at 100 �C for 30 h.b Isolated yield.c Reaction with 0.5 mol% of Pd complex (4).
80
90
100
(%)
S. Keesara et al. / Journal of Organometallic Chemistry 765 (2014) 31e3836
heteroannulation reactions of aryl halides. This versatile hetero-geneous palladium catalyst proved to be potential one with broadapplicability, high efficiency and recyclability. The catalyst gaveexcellent results with a slight decrease in the activity even after tencycles for Sonogashira and Suzuki cross coupling reactions.
Experimental section
All materials were commercial reagent grade. Chloromethylatedpolystyrene (4e5% Cl and 2% cross-linked with divinylbenzene)was a product of Alfaacer. Alkyne and aryl halide compounds wereobtained from Aldrich.
Preparation of polymer supported thiopseudourea-Pd(II) complex(3)
To a 250-mL round bottom flask containing DMF (50 mL),equippedwithmagnetic stirrer bar is addedwith chloromethylatedpolystyrene (5 g, 1.25 mmol/g of Cl) and 1-(2-Picolyl)-3-(4-fluorobenzoyl)-thiourea (10.0 mmol). The reaction mixture wasstirred for 24 h at 120 �C and was subsequently filtered and washedthoroughly with DMF, dried in oven at 80 �C for 24 h. The poly-styrene supported thiopseudourea 2 (5 mmol) was treated withchloroform (50mL). After for 10min Pd(OAc)2 (5 mmol) was added,and the resulting mixture was allowed to stir at room temperaturefor 24 h. This mixture was filtered and washed with chloroform toobtain PS-tsu-Pd(II) complex 3 (Scheme 1).
[A] Reaction with Heterogeneous PS-tsu-Pd(II) complex (3).[B] Reaction with Homogeneous Pd complex (4).
General procedure for the Sonogashira coupling reaction
An aryl halide (1.0mmol) and a terminal alkyne (1.2mmol) wereadded to a mixture of PS-tsu-Pd(II) complex (3) (0.001 mmol),triethylamine (2.0 mmol), and water (3 mL) in a round bottom flaskunder vigorous stirring. The mixture was stirred at room temper-ature for 8 h under aerobic conditions. After completion of thereaction, the mixture was filtered to recover the catalyst. Thepolymer was washed with water, acetonitrile and subjected tovacuum drying for the next run. Further, the reaction mixture wasextractedwith ethyl acetate and dried overMgSO4. The solvent wasremoved under reduced pressure and the residue was purified bycolumn chromatography on silica gel using ethyl acetate/hexane asthe eluent to give the corresponding coupling products.
General procedure for the Suzuki of aryl halides
A mixture of aryl halide (1.0 mmol), phenyl boronic acid(1.2 mmol), PS-tsu-Pd(II) complex (3) (0.005 mmol), LiOH.H2O
0 2 4 6 8 10
40
50
60
70
Con
vers
ion
Time (hours)
Reaction at 60 ºC Reaction at 80 ºC Reaction at 100 ºC
Fig. 3. The kinetics of Suzuki reaction catalyzed by PS-tsu-Pd(II) complex usingiodobenzene with phenylboronic acid.
2 4 6 8 10 12 14 16
40
50
60
70
80
90
100
Con
vers
ion
(%)
Time (hours)
Reaction at 80 ºC Reaction at 100 ºC Reaction at 120 ºC
Fig. 4. The kinetics of Heck reaction catalyzed by PS-tsu-Pd(II) complex using iodo-benzene with styrene.
S. Keesara et al. / Journal of Organometallic Chemistry 765 (2014) 31e38 37
(2 mmol), and water (2 mL) was stirred at 80 �C for 6 h. Aftercompletion of the reaction, the mixture was filtered to recoverthe catalyst. Then the experimental procedure was same asabove.
General procedure for the Heck reaction of aryl halides
A mixture of aryl halide (1.0 mmol), styrene (2 mmol), PS-tsu-Pd(II) complex (3) (0.005 mmol), K3PO4 (2.0 mmol), and DMF(2 mL) was stirred at 100 �C for 10 h. After completion of the re-action, the mixture was filtered to recover the catalyst. Then theexperimental procedure was same as above.
General procedure for Hiyama reaction of aryl halides
The 25 mL RB-flask was charged with aryl bromide (1 mmol),trimethoxy(phenyl)silane (1.2 mmol), LiOH.H2O (2 mmol) andcatalyst (3) (0.005mmol) inwater (2 mL). The reaction mixture wasstirred at 100 �C for 10 h. After completion of the reaction, themixture was filtered to recover the catalyst. Then the experimentalprocedure was same as above.
General procedure for the Larock heteroannulation reaction
The 25 mL RB-flask was charged with 2-iodoaniline (1 mmol),diphenylacetylene (1.5 mmol), K2CO3 (2 mmol) and PS-tsu-Pd(II)complex (3) (0.005 mmol) in DMF (2 mL). The reaction mixturewas stirred at 100 �C for 30 h. After completion of the reaction, thereaction mixture was cooled to room temperature and filtered torecover the catalyst. Then the experimental procedure was same asabove.
Acknowledgments
K.S., D. G., and P. S. P. thank CSIR, India for their fellowships.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.jorganchem.2014.04.020.
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