Synthesis and Structural Characterization

Shematic representations of one, two and three metal systems are depicted in Figure 5.1.

Structure of single, double and triple metal cored thiophene dendrimers has been depicted in Figure 1.Three generations of thiophene dendrimers (G1,G2 and G3) has been synthesized by as shown in Scheme 5.1. Stille coupling of 4^/-(2-Bromo-5-thienyl)-2,2^/,6^/,2^//-terpyridine with G1-SnBu3, G2-SnBu3 and G3-SnBu3 produced G1-TPY, G2-TPY and G3-TPY respectively (scheme 5.2). The single metal systems ie. G1RuG1, G2RuG2 and G3RuG3 were prepared according to scheme 5.3. Core for the two metal systems was prepared by as shown in Scheme 5.4. Synthetic route for the preparation of the core for three metal system was depicted in scheme 5.4. The supramolecular ruthenium cored dendrimer series has got good solubility in common organic solvents such as DCM, THF, EA, DMF, DMA etc. The good solubility of these supramolecular macromolecules led these to have easy processing.

The compound structures were confirmed by NMR, UV characterization.

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Shematic representation:

One Metal System

Two Metal System

Three Metal System

Figure 5.1 Shematic representations of one, two and three metal systems.

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Scheme 5.1 Synthesis of The Dendrimers.

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Scheme 5.2 Synthesis of terpyridine derivatives

N

Scheme 5.3 Synthesis of one metal systems

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Scheme 5.4 Synthesis of core for two metal systems.

S S

Scheme 5.5 Synthesis of core for three metal systems.

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Figure 5.2 Final structures of one metal systems

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Figure 5.3 Final structures of two metal systems

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Figure 5.4 Final structures of three metal systems

5.2.3 Synthetic Procedures

G1-SnBu₃: G1 (2.1gm, 5.03 mmole) was dissolved in 25 ml THF and cooled to -78^°C. To it 2.5 M n-BuLi in hexane (2.41 ml, 6.04 mmole) was added drop wise.

The reaction was allowed stir at -78^°C for 1 hour. To it SnBu3Cl (1.96gm, 1.63ml, 6.03mmole) was added rapidly. The reaction mixture was allowed to warm to room temperature and stirred overnight. The reaction mixture was quenched by addition of 20 ml H₂O and extracted by ethyl acetate via three times water wash. The organic layer was dried

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over MgSO4, solvent was removed by rotary evaporation to get the crude product as pale-yellow oil. The crude product was used for next step without further purification.

1H NMR (CDCl3, 300 MHz): 7.10 (s, 1H) , 6.91 (d, 1H, 3.3 Hz), 6.87 (d, 1H, 3.6 Hz), 6.66 (d, 2H, 3.3 Hz), 2.77 (m, 4H), 1.64 (m, 4H) , 1.56 (m, 6H), 1.36 (t, 6H, 7.3Hz), 1.30 (m, 12H), 1.11 (t, 6H, 8.3 Hz), 0.90 (m, 15H).

G1-TPY : G1-SnBu3 (3.5 gm,4.95 mmole), Br-th-tpy (1.62 gm,4.13 mmole) and Pd(PPh3)4

(114 mg, 0.099 mmole) was taken in a two neck flask and degassed by nitrogen. 30 ml dry DMF was poured into it and the reaction mixture heated to 90^°C

overnight. 100 ml of water was added to it and the reaction mixture was extracted by EA.

Organic layer was dried over MgSO4 and the solvent was removed by rota vapour. Crude product was purified by neutral alumina column chromatography using hexane: EA = 15:1 to yield pure compound (2.02 gm, 67.1%). ¹H NMR (CDCl₃, 300MHz) : 8.75 (d, 2H, 6Hz), 8.67 (s, 2H), 8.65 (d, 2H, 6 Hz), 7.90 (dt, 2H, 9 Hz ,1.2 Hz), 7.71 (1H, 3.9 Hz), 7.38 (2H, 6 Hz), 7.27 (s, 1H), 7.23 (d, 1H, 3 Hz), 6.98 (d, 1H, 3 Hz), 6.92 (d, 1H, 3 Hz), 6.69 (d, 2H, 3 Hz), 2.82 (t, 4H, 7.5 Hz ), 1.70-1.61 (m, 4H), 1.39-1.26 (m, 12H), 0.94 (t, 6H, 6.5 Hz) . ¹³C NMR (CDCl3, 300MHz) : 155.98, 155.88, 149.07, 147.73, 146.41, 142.80, 140.45, 138.32, 136.78, 134.58, 134.28, 132.44, 131.94, 131.11, 127.52, 126.67, 126.57, 126.41, 124.68, 124.23, 124.08, 123.85, 121.24, 116.56, 31.55, 31.52, 31.47, 28.74, 26.81, 22.57, 17.48, 14.07 13.58 Elemental analysis for C43H43N3S4 : Calculated : (%) C, 70.74; H, 5.94; N, 5.76.

Found: (%) C, 70.29; H, 5.93; N, 5.90. MS (FAB): m/z 730 (calcd (M)⁺).

G2-SnBu3: G1 (1.8 gm, 1.97 mmole) was dissolved in 25 ml THF and cooled to -78⁰C. To it 2.5 M n-BuLi in hexane (0.94 ml, 2.36 mmole) was added drop wise.

The reaction was allowed stir at -78⁰C for 1 hour. To it SnBu3Cl (0.83 gm, 0.69 ml, 2.56 mmole) was added rapidly. The reaction mixture was allowed to warm to room temperature and stirred overnight. The reaction mixture was quenched by addition of 20 ml H₂O and

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extracted by ethyl acetate via three times water wash. The organic layer was dried over MgSO₄, solvent was removed by rotary evaporation to get the crude product as pale-yellow oil. The crude product was used for next step without further purification. ¹H NMR (CDCl3, 300 MHz): 7.19 (s, 1H), 7.18 (s, 1H), 7.15 (s, 1H), 6.93 (t, 2H, 3Hz), 6.87 (d, 2H, 3Hz), 6.65 (m, 4H), 2.76 (t, 8H, 6.9 Hz),1.69-1.57 (m, 14H), 1.36-1.29 (m, 30H), 1.11 (t, 6H, J=8.2 Hz), 0.89 (m, 21H).

G₂-TPY: G₂-SnBu₃ (2.3 gm,1.91 mmole), Br-th-tpy (0.62 gm, 1.59 mmole) and Pd(PPh₃)₄ (44 mg, 0.038 mmole) was taken in a two neck flask and degassed by nitrogen .25 ml dry DMF was poured into it and the reaction mixture heated to 90^°C

overnight. 100 ml of water was added to it and the reaction mixture was extracted by EA.

Organic layer was dried over MgSO4 and the solvent was removed by rota vapour. Crude product was purified by neutral alumina column chromatography using (hexane: EA = 20:1) to yield pure compound (1.27 gm, 54.2%).

1H NMR (CDCl3, 300 MHz): 8.75 (d, 2H, 6Hz), 8.67 (s, 2H), 8.65 (d, 2H ,6Hz), 7.90 (dt, 2H, 9 Hz, 1.2 Hz), 7.71 (1H, 3.9 Hz), 7.38 (2H, 6 Hz), 7.27 (s, 1H), 7.23 (d, 1H, 3 Hz), 6.98 (d, 1H, 3 Hz), 6.92 (d, 1H, 3 Hz) 6.69 (d, 2H, 3 Hz), 2.82 (t, 4H, 7.5 Hz), 1.70-1.61 (m, 4H), 1.39-1.26 (m, 12H), 0.94 (t, 6H, 6.5 Hz). ¹³C NMR (CDCl₃, 300 MHz): 155.76 , 155.72 , 148.97, 147.62, 147.41 146.27, 146.09,142.43, 140.79, 137.65, 136.67, 135.61, 134.75, 134.48, 134.39, 132.19, 131.91, 131.87, 131.81, 130.24, 129.70, 127.59, 127.49, 126.51, 126.44, 126.26, 124.19, 124.05, 123.77, 121.16, 116.39, 116.20, 31.61, 31.51, 30.16, 28.82, 28.80, 27.83, 26.86, 25.60, 22.71, 22.63, 14.35, 13.64. Elemental analysis for C71H75N3S8: Calculated: (%) C, 69.51; H, 6.16; N, 3.42. Found: (%) C, 69.32; H, 6.63; N, 3.41. MS (FAB):

m/z 1227 (calcd (m)⁺).

G3-SnBu3: G3 (1.5 gm, 0.78 mmole) was dissolved in 20 ml THF and cooled to -78^°C. To it 2.5 M n-BuLi in hexane (0.37 ml, 0.93 mmole) was added drop wise.

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The reaction was allowed stir at -78^°C for 1 hour. To it SnBu3Cl (0.33 gm, 0.27 ml, 1.04 mmole) was added rapidly. The reaction mixture was allowed to warm to room temperature and stirred overnight. The reaction mixture was quenched by addition of 20 ml H2O and extracted by ethyl acetate via three times water wash. The organic layer was dried over MgSO₄, solvent was removed by rotary evaporation to get the crude product as pale-yellow oil. The crude product was used for next step without further purification.

G₃-TPY: G₂-SnBu₃ (1.7 gm,0.77 mmole), Br-th-tpy (0.25 gm, 0.64 mmole) and Pd(PPh₃)₄ (17.8 mg, 0.015 mmole) was taken in a two neck flask and degassed by nitrogen .15 ml dry DMF was poured into it and the reaction mixture heated to 90^°C

overnight. 100 ml of water was added to it and the reaction mixture was extracted by EA.

Organic layer was dried over MgSO4 and the solvent was removed by rota vapor. Crude product was purified by neutral alumina column chromatography using (hexane: EA = 20:1) to yield pure compound (0.82 g , 48.2%). ¹H NMR (CDCl3,300MHz): 8.72 (d, 2H, 6Hz), 8.65 (s, 2H), 8.62 (d, 2H, 9Hz),7.77 (t, 2H, 9Hz), 7.59 (d, 3Hz), 7.29-7.24 (m, 7H), 7.18 (s, 1H),7.12 (d, 1H, 2.7Hz), 7.02 (s, 1H),6.97 (m, 4H), 6.91 (m, 4H), 6.65 (m, 8H), 2.74 (t, 16H, 7.4Hz), 1.63 (m, 16H), 1.34 (m, 48H), 0.96 (t, 24H, 5.4Hz). ¹³C NMR (CDCl3,300 MHz):

155.98, 155.82, 149.06, 147.60, 147.35, 147.29, 146.23, 146.19, 146.06, 146.02, 142.66, 141.13, 137.65, 136.79, 136.11, 135.30,134.76, 134.46, 134.42, 134.36, 133.17, 133.08, 132.95, 132.58, 132.31, 132.21, 132.16, 131.95, 131.86, 131.72, 131.37, 131.31,130.47, 130.39, 130.26, 129.73, 129.59, 127.64, 127.52, 126.66, 126.43, 126.39,126.25, 125.26, 124.10, 123.94, 121.25, 116.65, 31.54,31.46, 30.14, 30.10, 28.77, 22.57, 14.05 .Elemental analysis for C127,H139,N3,S16 : Calculated : (%) C, 68.69; H, 6.31; N, 1.89 . Found: (%) C, 67.86; H, 6.75; N, 1.73. MS (MALDI-TOF): m/z 2220.7 (calcd (M)⁺) .

G1-TPY-RuCl3: G1-TPY (600 mg, 0.822 mmole) and RuCl3 .xH2O (236.46 mg, 0.906 mmole) were taken in MeOH: THF/ 5:1 under N₂ atmosphere. The mixture was refluxed

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overnight. The solid residue was filtered, washed in excess methanol and dried to get the product as shiny black solid (746.04 mg, 97%).

G2-TPY-RuCl3: G1-TPY (500 mg, 0.407 mmole) and RuCl3.xH2O (117 mg, 0.448 mmole) were taken in MeOH: THF /5:1 (100 ml) under N2 atmosphere. The mixture was refluxed overnight. The solid residue was filtered, washed in excess methanol and dried to get the product as black solid (574.28 mg, 98.5%).

G2-TPY-RuCl₃: G2-TPY (400 mg, 0.18 mmole) and RuCl₃.xH₂O (51.15 mg, 0.196 mmole) were taken in MeOH: THF /5:1 (100 ml) under N2 atmosphere. The mixture was refluxed overnight. The solid residue was filtered, washed in excess methanol and dried to get the product as black solid (420.52 mg, 96.4%).

G1RuG1: G1-TPY-RuCl3 (360 mg, 0.385 mmole) and AgBF4 (300 mg, 1.54 mmole) were taken in acetone (60 ml) and refluxed 18 hrs under N₂ atmosphere. The solution was filtered to remove AgCl salt. The filtrate was evaporated and to it G1-TPY (280 mg, 0.385 mmole) was added. The mixture was dissolved in 5 ml Dimethyl acetamide and 50 ml of n-BuOH and refluxed for 24 hours. The product was cooled and added drop wise into a beaker containing 500 ml MeOH under stirring. The solid was filtered, washed in MeOH and 5:1 mixture of MeOH: acetone. The residue was dried to get dark red solid (560.04 mg, 93.2%). ¹H NMR (DMSO-d6, 300MHz): 9.33 (s, 4H), 9.11 (d, 4H, 8.1 Hz), 8.48 (d, 2H, 3.9 Hz), 8.07 (t, 4H, 7.5 Hz), 7.82 (d, 2H, 3.6 Hz), 7.72 (s, 2H), 7.60 (d, 4H, 6 Hz), 7.28 (t, 4H, 6.2 Hz), 7.12 (d, 4H, 3.6 Hz), 6.87 (d, 2H, 3.6 Hz), 6.85 (d, 2H, 3.3 Hz), 2.78 (t, 8H, 7.5 Hz), 1.60-1.57 (m, 8H), 1.35-1.24 (m, 24H), 0.86 (t, 12H, 6.6 Hz).

G2RuG2: G2-TPY-RuCl3 (340 mg, 0.237 mmole) and AgBF₄ (194.67 mg, 0.949 mmole) were taken in acetone (50 ml) and refluxed 20 hrs under N2 atmosphere. The solution was filtered to remove AgCl salt. The filtrate was evaporated and to it G2-TPY (290.3 mg, 0.237 mmole) was added. The mixture was dissolved in 5 ml Dimethyl acetamide and 50 ml of n-BuOH and refluxed for 24 hours. The product was cooled and added drop wise into a beaker

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containing 500 ml MeOH under stirring. The solid was filtered, washed in MeOH and 6:1 mixture of MeOH: acetone. The residue was dried to get dark red solid (559.77 mg, 94.1%). ¹H NMR (DMSO-d6, 300MHz): 9.35-9.28 (br, 4H), 9.11 (d, 4H, 8.1 Hz), 8.50-8.43 (br, 2H), 8.07 (br, 4H), 7.90-7.83 (br, 4H), 7.58-7.49 (br, 10H), 7.38-7.28 (br, 4H), 7.05-7.02 (br, 8H), 6.82-6.78 (br, 8H), 2.77-2.74 (br, 16H), 1.57-1.55 (br, 16H), 1.27 (br, 48H), 0.85 (br, 24H).

G3RuG3: G3-TPY-RuCl3 (7.2 mg, 0.18 mmole) and AgBF₄ (140 mg, 0.721 mmole) were taken in acetone (50 ml) and refluxed 20 hrs under N2 atmosphere. The solution was filtered to remove AgCl salt. The filtrate was evaporated and to it G3-TPY (400 mg, 0.18 mmole) was added. The mixture was dissolved in 5 ml Dimethyl acetamide and 50 ml of n-BuOH and refluxed for 24 hours. The product was cooled and added drop wise into a beaker containing 500 ml MeOH under stirring. The solid was filtered, washed in MeOH and 6:1 mixture of MeOH: acetone. The residue was dried to get dark red solid (749.72 mg, 91.7%). ¹H NMR (CDCl3, 300 MHz): 8.85 (br, 4H), 8.70-8.62 (br, 4H), 8.16 (br, 2H), 7.86 (br, 4H), 7.41 (br, 4H), 7.24-7.05 (br, 20H), 6.90-6.82 (br, 16H), 6.61-6.57 (br, 16H), 2.73-2.69 (br, 32H), 1.65-1.58 (br, 32H), 1.26 (br, 96H), 0.85 (br, 48H).

5.3 Results and Discussion