Visible Light Assisted Photocatalytic [3 + 2] AzideâAlkyne âClick

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Visible light assisted photocatalytic [3+2] azide-alkyne “click” reaction for the synthesis of 1,4- substituted 1, 2, 3-triazoles using a novel bimetallic Ru-Mn complex s Jain, Pawan Kumar, chetan Joshi, Ambrish Kumar Srivastava, Piyush gupta, and Rabah Boukherroub ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.5b00653 • Publication Date (Web): 02 Dec 2015 Downloaded from http://pubs.acs.org on December 2, 2015

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ACS Sustainable Chemistry & Engineering

Visible light assisted photocatalytic [3+2] azidealkyne “click” reaction for the synthesis of 1,4substituted 1, 2, 3-triazoles using a novel bimetallic Ru-Mn complex Pawan Kumar,a Chetan Joshi,a Ambrish K. Srivastavab Piyush Gupta,c Rabah Boukherroub,d and Suman L. Jain,a* a

Chemical Sciences Division; CSIR-Indian Institute of Petroleum, Mohkampur, Dehradun-

248005 India; *Email: [email protected]; Tel: 91-135-2525788; Fax: 91-135-2660202. b

Department of Physics, University of Lucknow, University road, Lucknow, Uttar Pradesh 226007, India

c

Anaytical Sciences Division, CSIR-Indian Institute of Petroleum, Mohkampur, Dehradun248005 India

d

Institute of Electronics, Microelectronics and Nanotechnology (IEMN), UMR CNRS8520, Lille1 University, Avenue Poincaré-BP60069, 59652 Villeneuve d’Ascq, France

ACS Paragon Plus Environment

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ABSTRACT A photoactive bimetallic complex comprising a photosensitizer ruthenium unit and a catalytic Mn(I) unit connected via bipyrimidine (bpm) bridging ligand is prepared and used for the first time for developing light-induced copper catalyzed [3+2] azide-alkyne “click” (CuAAC) reaction for the formation of 1,2,3-triazoles under visible light irradiation. The developed bimetallic complex exhibited enhanced activity as both photosensitizer ruthenium unit as well as manganese catalyst unit are attached in a single molecule, provided efficient electron transfer for the photochemical reduction of Cu(II) to Cu(I) in situ which subsequently used for the cycloaddition of azides with terminal alkynes to give 1,4-disubstituted 1,2,3-triazoles in the presence of triethylamine as a sacrificial donor.

KEYWORDS: Photocatalyst; click reaction; ruthenium; manganese; visible light; redox catalyst; triazoles


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Introduction Development of sustainable chemical synthesis in order to diminish the detrimental environmental impact associated with chemical industries is a prime objective in the present day chemistry. Sunlight, being an abundant, safe and easily available energy resource, holds a great potential in driving environmentally benign organic transformations [1]. Importantly, light induced reactions provide room temperature chemical synthesis, and also avoid thermally induced side reactions. However, simple organic molecules mainly absorb only ultraviolet (UV) light, which consists only 5% in the solar spectrum and require special reaction vessels to be performed. Owing to these limitations, development of visible light assisted photocatalytic reactions is receiving particular interest in current decades [2-3]. In this regard, a plethora of selective organic transformations on a semiconductor photocatalyst have been developed, which can be performed in common glass reactors [4-5]. However, lower efficiency and poor product yields are the common drawbacks of such catalytic systems. Transition metal complexes such as ruthenium or iridium metal complexes and metal free organic dyes have also been acknowledged as excellent homogeneous photocatalysts for a series of organic transformations under visible light irradiation [6-7]. The copper-catalyzed azide–alkyne cycloaddition (CuAAC) also known as “click reaction” is a well accepted, widely utilized, reliable, and straightforward approach to transform organic azides and terminal alkynes into the corresponding 1,4-disubstituted 1,2,3triazoles [8]. Owing to the unique features of the CuAAC reaction, such as high efficiency, high yields and mild reaction conditions, it has been established to be a powerful tool in organic synthesis, medicinal chemistry, polymer chemistry and surface modifications [9-10]. Furthermore, the products of CuAAC reactions, such as 1,4-disubstituted 1,2,3-triazoles, have been employed as ligands for catalysts and as building blocks for luminescent metal complexes.


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In this context, Bai et al. have recently reported the use of CuAAC reactions in the syntheses of nitrogen containing ligands such as pyridine, pyrazole and benzyltriazole hybridized 1,2,3triazole ligands and their application to support luminescent Cu(I) and Zn(II) clusters and polymeric complexes [11-12]. Click reaction is generally carried out by using a catalytic mixture containing Cu(II) with a reducing agent (usually sodium ascorbate). The direct use of Cu(I)/ metallic copper or its clusters is also possible, however the formation of undesirable alkynealkyne homocoupling products make such methods of limited synthetic utility. To overcome these limitations Bai et al. reported a number of hybrid nitrogen-sulfur ligands supported Cu(I)/(II) complexes as effective catalysts for azide-alkyne cycloaddition reaction [13-14]. Recently, photochemical CuAAC reactions using UV light have emerged to be promising approach for various applications in material synthesis [15-16]. In this context, Bowman and Yagci

reported

a

photoinduced

CuAAC

reaction

using

a

Cu(II)/N,N,N’,N’’,N’’-

pentamethyldiethylenetriamine (PMDETA) complex and a photoinitiator as catalyst under UV irradiation [17-19]. Subsequently, Guan et al. developed a Cu(II)/carboxylate complex for photoinduced CuAAC reaction under UV light irradiation [20]. However to the best of our knowledge there is no report on the visible light assisted photocatalytic azide-alkyne “click” reaction. In continuation to our recent research on visible light assisted photocatalytic transformations [21-22], herein we report the first successful example of visible light assisted photocatalytic [3+2] azide-alkyne “click” reaction using ruthenium-manganese (Ru-Mn) bimetallic complex as photocatalyst to give 1,4-substituted 1,2,3-triazoles in the presence of Cu(II) sulphate and triethyl amine (Figure 1, Scheme 1). The developed bimetallic complex was found to be more efficient as both photosensitizer (Ru unit) and photocatalyst (Mn unit) units are


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associated within the same molecule, which provide efficient electron transfer and therefore enhanced catalytic efficiency. Furthermore, Ru-Mn complex plays a major role and provides photoinduced insitu reduction of Cu(II) to Cu(I) for the CuAAC reaction.

Fig. 1. The photoredox catalyst [Ru(bpy)2(bpm)Mn(CO)3Br](PF6)2 (Ru-Mn complex).

Scheme 1. Photocatalytic “click” reaction between organic azides and terminal alkynes for the synthesis of 1, 4-substituted 1, 2, 3-triazoles.

Results and discussion At first, Mn(bpm)(CO)3Br complex was synthesized by following the literature procedure [23]. Subsequently, Ru-Mn bimetallic ([Ru(bpy)2(bpm)Mn(CO)3Br](PF6)2) complex was synthesized by the reaction of Ru(bpy)2Cl2 and Mn(bpm)(CO)3Br followed by precipitating the product with


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ammonium hexafluorophosphate (Scheme 2) [24]. As shown, bipyrimidine ligand provides a coordination site for the attachment of Ru(bpy)2Cl2 to Mn(bpm)(CO)3Br [25-26].

Scheme 2: Synthesis of [Ru(bpy)2(bpm)Mn(CO)3Br](PF6)2 (Ru-Mn complex 4). The successful synthesis of bimetallic complex 4 was confirmed with various techniques like MALDI-TOF-MS, FTIR, UV-Vis, 1H NMR,

13

C NMR and elemental analysis. The detailed

characterization of the bimetallic Ru-Mn catalyst 4 is given in the supporting information. Fig. 2 shows UV-Vis spectra of Mn(bpm)(CO)3Br 2, Ru(bpy)3Cl2 photosensitizer and Ru-Mn catalyst 4 in DMF. The UV-Vis spectrum of 2 displayed a weak absorption band at 276 nm due to bpm interligand transition, while a very weak shoulder at 429 nm due to Mn(dπ)→bpm(π*) transition was also observed (Fig. 2a) [27-28]. The UV-Vis spectrum of Ru(bpy)3Cl2 photosensitizer gave a strong absorption band at 285 nm due to interligand (π→π*) transition and a shoulder at 455


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nm due to MLCT(dπ→π*) transition (Fig. 2b) [29-30]. In the Ru-Mn complex the attachment of ruthenium unit to Mn unit through coordination with bipyrimidine ligand exhibited a significant enhancement in the absorbance (Fig. 2c). The peak at 286 nm in the UV-Vis spectrum of Ru-Mn complex was due to bipyridine interligand (π-π*) transition, while the broad hump at 420 nm was due to Ru(dπ)→bpy(π*) transition.

Fig. 2. UV-Vis absorption spectra of (a) Mn(bpm)(CO)3Br 2, (b) Ru(bpy)3Cl2 and (c) Ru-Mn complex 4. The synthesized bimetallic Ru-Mn complex was used for the copper catalyzed [3+2] azidealkyne cycloaddition “click” reaction of terminal alkynes with azides to give 1,4-substituted 1,2,3-triazoles under visible light irradiation using triethylamine as a sacrificial donor and 20 watt white cold LED light as a source of visible light. In the present study, copper (II) sulfate was used and underwent in situ photochemical reduction to give Cu(I) catalytic species. A variety of alkynes and azides were investigated and in all cases higher conversions and yields of


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the corresponding 1,4-substituted 1,2,3-triazoles were obtained in 5-7 h of irradiation period (Table 1). The obtained 1,4-disubstituted 1,2,3-triazoles were easily isolated by extraction with ethyl acetate, followed by recrystallization, and identified by comparing their physical and spectral data with those of authentic samples. Among the various alkynes, aromatic alkynes gave higher yields (Table 1, entry 1-14). Among the various aromatic alkynes, electron withdrawing groups such as (-Br, -Cl) containing substrates exhibited higher activity which is most likely due to the easy formation of intermediate copper acetylide during the reaction [31]. In case of various substituted azides, those having electron donating groups (methyl) were found to be somewhat sluggish towards the “click” chemistry as compared to the azides containing electron withdrawing groups (-Cl). Table 1: Photocatalytic “click” reaction of azides and alkynes by using Ru-Mn complex4.a

Time (h)

Yield

1

5.0

96

19.2

2

6.5

87

13.3

5.0

97

19.4

4

4.5

94

20.8

5

6.0

84

18.0

Entry

3

Alkyne

Br

Product


b

(%)

TOF (h-1)

8

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a

6

8.0

82

10.2

7

6.5

86

13.2

8

6.0

92

15.3

9

5.0

95

19.0

10

6.0

88

14.6

11

5.0

93

18.6

12

4.5

90

20.0

13

7.0

75

10.7

14

6.5

78

12.0

Reaction conditions: alkyne (1 mmol), azide (1.5 mmol), copper (II) sulfate (0.5 mmol), TEA

(0.5 mL), catalyst (5 mol %), ethanol (10 mL); Visible Light (20 Watt LED λ >400 nm). b

Isolated yield of the product.

Further, to establish the superiority of bimetallic Ru-Mn photocatalyst 4, we have checked various possible combinations of catalyst fragments for the photoinduced “click” reaction


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between alkynes and azides. Phenyl acetylene and benzyl azide were chosen as model substrates for this study. Blank reaction without any catalyst did not give any reaction product even after prolonged time of exposure to visible light (Table 2, entry 1). Moreover, the use of Mn(CO)5Br, Mn(bpm)(CO)3Br, Ru(bpy)2Cl2, or Ru(bpy)3Cl2 as catalyst also did not produce any reaction product even after 24 h of visible light irradiation (Table 2, entry 2-5). After that a combination of photosensitizer Ru(bpy)3Cl2 and catalyst Mn(bpm)(CO)3Br was tried, which afforded only 46 % yield of the desired product after 24 h irradiation period. However, the use of bimetallic (RuMn) complex 4 under identical experimental condition provided almost quantitative yield of the desired product within 5 h of irradiation period. These studies suggested that both photosensitizer ruthenium and catalyst Mn(I) are essential for this reaction and attachment of both units in one molecule (Ru-Mn bimetallic complex 4) through a bridging ligand enhanced the reaction rate significantly in comparison to the physical mixing of both units separately. This enhancement in bimetallic complex may be attributed due to efficient electron transfer by Ru photosensitizer unit to Mn catalyst unit without time delay [32-33]. To prove the essential role of visible light, we performed the blank experiment and no reaction was observed in the absence of light even after 12 h (Table 2, entry 7). Furthermore, the presence of Cu(II) sulphate and sacrificial donor triethylamine was found to be vital, which was confirmed by performing the reaction in the absence of copper (II) sulphate and triethyl amine respectively. No reaction occurred in the absence of these components (Table 2, entry 6-7). Based on these experiments, it was concluded that bimetallic Ru-Mn complex, Cu(II) sulphate, triethyl amine and visible light all were essentially required for this transformation. Furthermore, to establish the effect of photocatalyst, controlled experiments using copper (II) sulfate and Cu(II) sulphate with triethyl amine in the absence of photocatalyst under otherwise identical experimental conditions were performed


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(Table 2, entry 8). In both cases, no conversion was observed, suggesting that the presence of Ru-Mn photocatalyst 4 was essential to promote the CuAAC reaction under visible light irradiation. Table 2: “Click” reaction using various catalyst combinations under different experimental conditions a b

Yield

TOF(h-1)

Entry

Catalyst

Time (h)

1

-

24

-

-

2

Mn(CO)5Br

24

-

-

3

Mn(bpm)(CO)3Br

24

-

-

4

Ru(bpy)2Cl2

24

-

-

5

Ru(bpy)3Cl2

24

-

-

6

Ru(bpy)3Cl2 + Mn(bpm)(CO)3Br

24 16 12 12

46 c (-) d (-) e (-)

1.9 -

7

Ru-Mn complex 4

8

CuSO4 CuSO4 + TEA

5 16 10 8 24 24

96 (4) d (6) e (14) (-)

19.2 0.25 0.6 1.7 -

c

a

Reaction conditions: phenyl acetylene (1 mmol), benzyl azide (1.5 mmol), Cu(II) sulphate (0.5 mmol), TEA (0.5 mL), catalyst (5 mol%), ethanol (10 mL); Visible light (20 Watt LED λ >400 nm); room temperature (25 ᵒC). bisolated yield. cin the absence of light. dwithout CuSO4. ein the absence of TEA.


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The effect of solvent on light-induced “click” reaction was studied in detail by varying the different solvents for “click” reaction between phenyl acetylene and benzyl azide under described reaction conditions. The results of these experiments are summarized in Table 3. As shown the reaction was found to be sluggish in highly polar solvents such as DMF, DMSO, etc. The yield % (TOF) of product in various solvents i.e. DMF, DMSO, THF and water was determined to be 52 % (10.4), 76 % (15.2), 87 % (15.8) and 89 % (17.8), respectively. Furthermore, the % yield (TOF) of the product in methanol (MeOH), acetonitrile (ACN) and dichloromethane (DCM) was found to be 78% (15.6), 64% (6.4) and 48% (6.0), respectively. Ethanol was the best solvent for the photo induced “click” reaction with 96 % (19.2) yield of triazoles (Table 3, entry 4). It can be concluded from Table 3 that solvents with moderate polarity were optimum for this reaction. Table 3: Effect of solvent on photoinduced “click” reactiona b

Yield

TOF(h-1)

Entry

Solvent

Time (h)

1

DMF

5.0

52

10.4

2

DMSO

5.0

76

15.2

3

Water

5.5

87

15.8

4

THF

5.0

89

17.8

5

EtOH

5.0

96

19.2

6

MeOH

5.0

78

15.6

7

CH3CN

10.0

64

6.4


12

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8

CH2Cl2

8.0

48

6.0

a

Reaction conditions: phenyl acetylene (1 mmol), benzyl azide (1.5 mmol), Cu(II) sulphate (0.5 mmol), TEA (0.5 mL), catalyst 4 (5 mol%), solvent (10 mL); visible light (20 Watt LED λ>400 nm); room temperature (25 ᵒC). bisolated yield.

In order to explain the photocatalytic “click” reaction, a plausible reaction mechanism is proposed as depicted in Scheme 3. After absorption of visible light, ruthenium sensitizer unit of photocatalyst is excited and electrons move from its HOMO to LUMO. The excited ruthenium unit transfers electrons to the Mn catalyst unit through bipyrimidine bridging ligand [34]. After that one electron reduced (OER) Mn catalyst unit transfers electron to Cu(II), which is subsequently reduced in situ to give Cu(I) catalytic species for the “click” reaction [35]. In contrast to the existing literature reports, in the present work, no reducing agent like sodium ascorbate for reducing Cu(II) to Cu(I) is required. Triethylamine acts as a sacrificial donor and provides necessary electrons for this process [36-37]. The increase in catalytic activity of the catalyst was assumed to be due to the fast electron transfer from Ru unit to Mn unit because of attachment of both units through bipyrimidine bridging ligand. Ru-Mn + hν → Ru*-Mn Ru*-Mn → Ru+-MnRu+-Mn- + Cu(II) → Cu(I) +Ru+-Mn Ru+-Mn + (C2H5)3N: → Ru-Mn + (C2H5)3No+ Cu(I) + R-C≡CH + R-N3 → R-(C=CH-N=N-N)-R + Cu(II)


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Scheme 3: Plausible mechanism of visible light induced “click” reaction by Ru-Mn complex.

Conclusion In conclusion, we have demonstrated first successful visible light induced copper catalyzed [3+2] cycloaddition (CuAAC) “click” reaction between azides and terminal alkynes to give 1,4-disubstituted 1,2,3-triazoles in high yields using a novel bimetallic Ru-Mn complex as photocatalyst. In the synthesized photocatalyst ruthenium photosensitizer unit is attached to manganese carbonyl complex by bipyrimidine bridging ligand, which provided rapid electron transfer without delay in contact time and resulted in enhanced reaction rate in comparison to the physical mixing of photosensitizer and Mn complex in the reaction mixture. Furthermore, copper (II) sulfate has been used for CuAAC reaction which is converted in situ to active Cu(I) catalytic species through photochemical reduction without need of reducing agent like sodium ascorbate. To the best of our knowledge this is the first report on the visible light induced CuAAC “click” reaction which can be further used for various applications including in material science as well as surface functionalization.


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Experimental Materials 2, 2’-bipyridine (99%), 2, 2’-bipyrimidine (95%), ruthenium chloride trihydrate were purchased from Sigma Aldrich and used without further purification. Mn(CO)5Br (98%), ammonium hexafluorophosphate (99.9 %), dimethylformamide (DMF, HPLC grade), acetonitrile (HPLC grade) were of analytical grade and procured from Alfa Aesar. All other chemicals were of A.R. grade and used without further purification. Characterization Techniques Absorption spectra in the UV-Vis region of Mn(bpm)(CO)3Br and Ru-Mn complex were collected in DMF on Perkin Elmer lambda-19 UV-VIS-NIR spectrophotometer using a 10 mm quartz cell, using BaSO4 as reference. Fourier Transform Infrared (FTIR) spectra were recorded on Perkin–Elmer spectrum RX-1 IR spectrophotometer using potassium bromide window. 1HNMR and

13

C NMR spectra of metal complexes were taken at 500 MHz by using Bruker

Avance-II 500 MHz instrument. MALDI-TOF-MS analysis for confirming the synthesis of RuMn complex was conducted on Thermo Exactive Orbitrap system in HESI mode. Ru and Mn metal contents of Mn(bpm)(CO)3Br and Ru-Mn complex were determined with ICP-AES analysis by Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES, DRE, PS3000UV, Leeman Labs Inc, USA). Samples for ICP AES analysis were prepared by oxidizing 50 mg catalyst by HNO3 and heating at 70 ᵒC for 15 min. The final volume was made up to 5 mL by adding deionized water. Elemental contents of (bpm)(CO)3Br and Ru-Mn complex were determined on CHN analyzer (Vario micro cube elementar). Photoirradiation was carried out under visible light by using 20 W white cold LED flood light (model no. HP-FL-20W-F-Hope


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LED Opto-Electric Co., Ltd.). Intensity of the light at vessel was measured by intensity meter and was found to be 75 W m-2. Synthesis of Mn(bpm)(CO)3Br Mn complex was synthesized by following a literature procedure. [23] Briefly, a mixture of 2, 2’-bipyrimidine (120.2 mg, 0.76 mmol) and Mn(CO)5Br (199.6 mg, 0.72 mmol) was refluxed in 40 mL diethyl ether for 3 h in the dark. The obtained orange Mn(bpm)(CO)3Br was collected by filtration, and washed with diethyl ether and dried in vacuum. Yield: 185.1 mg (68.4%). 1HNMR spectrum (500 MHz, DMSO-d6) was in accordance with literature values (Fig. S1). UVVis; λmax = 276 nm(s), 429 nm(w), FT-IR: v(CO)/cm–1, 2028, 1943, 1922 (Fig. S2). Elemental analysis, C11H6BrMnN4O3; calculated (found) C%, 35.04(35.34); H%, 1.60(1.58); N%, 14.86(14.73); Mn% by ICP-AES, 14.57(14.38). Synthesis of Ru-Mn complex [Ru(bpy)2(bpm)Mn(CO)3Br](PF6)2 A mixture of Ru(bpy)2Cl2.2H2O [38] (130.05 mg, 0.25 mmol) and Mn(bpm)(CO)3Br (93.98 mg, 0.25 mmol) was refluxed in 15 mL of ethanol for 12 h under nitrogen atmosphere. After cooling to room temperature, the reaction mixture was filtered through membrane filter. The filtrate was dried under vacuum by rotary evaporation to getting crude catalyst. The purification of the catalyst was carried out by dissolving in minimum amount of ethanol and the reprecipitation with diethyl ether. This process was repeated three times. Yield: 107.43 mg (54.4%). The product was identified by MALDI-TOF-MS; [M+]-2CO(1023.9), [M+]-3CO(995.9), [M+]-Br-F-H(979.0), [M+]-Br-CO-F-3H(949.3), [M+]-PF6(935.0), [M+]-PF6-Br(856.9), [M+]-PF6-3CO(851.2), [M+]PF6-Br-CO(825.9),

[M+]-2PF6-CO-F+3H(745.1),

[M+]-2PF6-3CO(705.2),

[M+]-2PF6-

Mn(CO)3Br(572.1) (Fig S3–Fig S5). UV-Vis: λmax=286 nm(s) and 420 nm(s); Elemental analysis. C31H22BrMnN8O3RuP2F12; Calculated (Found) C%, 34.44(35.08); H%, 2.03(1.97); N%,


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10.37(10.24); Mn% by ICP-AES, 5.08(4.97); Ru% by ICP-AES, 9.35(9.22), 1H-NMR (500 MHz, DMSO-d6); δ = 7.00-8.10 (m, 5H), 8.10-8.50 (m, 1H), 9.15-9.45 (m, 2H), 9.45-9.80 (m, 3H). 13C NMR (500 MHz, DMSO-d6); δ = 124.09, 138.00, 160.16, 161.58 (Fig S6-Fig S7), FTIR: v(CO)/cm–1, 2030, 1995, 1924 (Fig. S8). Typical experimental procedure for visible light promoted “click” reaction In a round bottom flask containing 10 mL ethanol, alkyne (1mmol), azide (1.5 mmol), Cu(II)sulphate (0.5 mmol) and triethylamine (0.5 mL) was added the catalyst 4 (5 mol%). The flask was sealed with a septum and irradiated with stirring by using a 20 Watt white cold LED (Model - HP-FL-20W-F-Hope LED Opto-Electric Co., Ltd) for a desired time period. After completion of reaction, monitored by TLC, the reaction mixture was filtered and the product was extracted using DCM and washed with water, brine and dried over Na2SO4. The solvent was removed under vacuum and the product having some catalyst was isolated. The product was purified by dissolving in minimum amount of DCM, followed by addition of hexane to precipitate the catalyst, filtration and drying under vacuum. Further purification was performed by using column chromatography on silica gel. The product was identified with FTIR, 1H NMR and 13C NMR.

Acknowledgement Authors would like to thanks Director IIP for granting permission to publish these finding. Analytical department is acknowledged for kind support in analysis of samples. PK is also thankful to CSIR for providing fellowships to conduct research. CJ is thankful to CSIR, New Delhi for funding in CSC-0117 12th five year projects.

Supporting Information


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Characterization data of synthesized catalysts (MALDI-TOF, 1HNMR, 13C NMR, FTIR etc) and analysis of reaction products (FTIR, 1HNMR,

13

C NMR) are given in supporting information.

This material is available free of charge via the Internet at http://pubs.acs.org


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For Table of content entry Visible light assisted photocatalytic [3+2] azide-alkyne “Click” reaction for the synthesis of 1,4-substituted 1, 2, 3-triazoles using a novel bimetallic Ru-Mn complex Pawan Kumar,a Chetan Joshi,a Ambrish K. Srivastava,b Piyush Gupta,c Rabah Boukherroubd and Suman L. Jaina* First successful example of visible light induced copper catalyzed [3+2] azide-alkyne “click” (CuAAC) reaction for the formation of 1,2,3-tiazoles using a novel bimetallic complex having photosensitizer ruthenium unit and catalytic Mn(I) unit connected via bipyrimidine (bpm) bridging ligand is described.


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Visible Light Assisted Photocatalytic [3 + 2] AzideâAlkyne âClick

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