Synthesis and Characterization of Metal Complexes

Chapter 3: Cell-Selective Biological Activity of Rhodium

3.2 Experimental Protocols

3.2.3 Synthesis and Characterization of Metal Complexes

The complexes [Rh(bpy)2(chrysi)]³⁺, [Rh(HDPA)2(chrysi)]³⁺, [Rh(NH₃)₄(chrysi)]³⁺, [Rh(DIP)₂(chrysi)]^3, [Rh(DPAE)₂(chrysi)]³⁺, and [Rh(PrDPA)2(chrysi)]³⁺ were prepared according to published procedures.^13-15

3.2.3.1 [Rh(chrysi)(phen)(NH₃)₂]Cl₃

[Rh(chrysi)(phen)(NH₃)₂]Cl₃ was prepared according to an adaptation of previously described procedures.¹⁶ A 1 L round bottomed flask was charged with [Rh(NH₃)₄(phen)][OTf]₃ (0.500 g, 0.626 mmol) and chrysene-5,6-dione (0.162 g, 0.626 mmol), and 1:9 H2O:MeCN was added (400 mL). A 1M solution of NaOH (1.5 mL) was added to the orange solution. Over the next hour, the solution changed color from orange to red, after which time a 1M solution of HCl (1.5 mL) was added to quench the reaction.

The MeCN was evaporated in vacuo and the resulting red solution was loaded onto a SPE cartridge, eluted with 25% acetonitrile in 0.1% TFA(aq), and lyophilized to give a red solid. The chloride salt can be obtained from a Sephadex QAE anion exchange column equilibrated with 0.1M MgCl2. Yield: 0.536 g, 94%. ¹H NMR (300 MHz, d6-DMSO): δ 13.59 (s, 1H); 13.43 (s, 1H); 9.56 (d, J =5.3 Hz, 1 H); 9.16 (m, 2H); 8.93 (d, J =8.3 Hz, 1H); 8.77 (d, J = 5.3 Hz, 1H); 8.35-8.57 (m, 7H); 8.23 (d, J =8.3 Hz, 1H); 7.99 (m, 2H);

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7.83 (m, 2H); 7.54 (t, J =7.6 Hz, 1H); 4.95 (s, 3H); 4.79 (s, 3H). ESI-MS (cation): m/z calc. 571.13 (M-2H⁺), obs. 570.9.

3.2.3.2 1,1-di(pyridin-2-yl)ethanol (DPE)

DPE was synthesized according to an adaptation of previously described procedures.¹⁷ A 250-mL oven dried schlenk flask was cooled to - in a ice/acetone bath and charged with di(pyridin-2-yl)methanone (0.508 g, 2.8 mmol).

Anhydrous Et₂O (50 mL) was added via cannula transfer, and the resulting yellow solution was allowed to stir for 10 m. A 1.6M solution of MeLi (5 mL) was then added dropwise over 15 m, during which time the solution turned deep purple. After 30 m of stirring at - , sat. NH4Cl (aq) (15 mL) was added. The resulting yellow solution was allowed to warm to ambient temperature, and was then extracted with Et2O (3 x 50 mL).

The organic fractions were combined and dried over magnesium sulfate, and the solvent was removed in vacuo. The ligand was further purified via flash chromatography (SiO2, 1:1 Et₂O:hexanes). Yield: 0.560 g, 100% . ¹H-NMR (CDCl₃, 300 MHz): δ .5 (d, J =5.1 Hz, 2H); 7.92 (d, J =6.9 Hz, 2H); 7.80 (m, 2H); 7.27 (m, 2H); 6.60 (s, 1H); 2.08 (s, 3H).

ESI-MS (cation): m/z calc. 201.09 (M+H⁺), obs. 201.0.

3.2.3.3 N-alkyl-N-(pyridin-2-yl)pyridin-2-amine (alkyl = methyl or propyl; MeDPA, PrDPA)

To a slu of so ium h i e ( 0 mg, 2.9 mmol) in THF (10 mL) was a e HDPA (500 mg, 2.9 mmol) in THF (5 mL) at 0 ° un e 1 atm A . The eaction was pu ge with a gon fo 15 min, an the app op iate 1-b omoalkane (3. mmol) was a e opwise an wa me to ambient tempe atu e. The eaction was sti e an a itional 1 h un e a gon at eflux tempe atu e. The eaction mixtu e was ext acte with ilute so ium

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bica bonate, an the aqueous phase was ext acte with H2 l2 (3 x 40 mL). The o ganic f actions we e combine an ie ove magnesium sulfate, an the solvent was emove in vacuo. These ligan s we e pu ifie via flash ch omatog aph (SiO2, 1:9 EtOAc:hexanes).

MeDPA: Yield: 23%. ¹H-NMR (CDCl3, 300 MHz): δ .35 ( d, 2H); 7.54 (t, 2H);

7.17 (d, 2H); 6.86 (t, 2H), 3.62 (s, 3H). ESI-MS (cation): m/z calc. 186.1 (M+H⁺), obs.

186.

PrDPA: Yiel : 25%. ¹H NMR ( D l3, 300 MHz): δ .34 ( , J = . Hz, 2H);

.5 – .45 (m, 2H); .06 ( , J = 0. Hz, 2H); 6.90 – 6. 9 (m, 2H); 4.19 – 4.0 (m, 2H);

1. 9 – 1.65 (m, 2H); 0.99 – 0. 5 (m, 3H). ESI-MS (cation): m/z calc. 214.1 (M + H⁺), obs. 214.

3.2.3.4 [Rh(NH3)4(phzi)]Cl3

[Rh(NH3)6][OTf]3 (0.50 g, 0. mmol) an benzo[]phenazine-5,6- ione (0.200 g, 0. mmol) we e issolve in a 1:5 mixtu e of wate :acetonit ile (500 mL). A 1M solution of NaOH (1 mL) was a e to the ellow solution an the eaction was allowe to sti at ambient tempe atu e fo 45 min, at which time a 1M solution of H l (1 mL) was a e to neut alize the eaction mixtu e. The Me N was evapo ate in vacuo an the esulting ellow solution was loa e onto a SPE ca t i ge, elute with 25% acetonit ile in 0.1% TFA(aq), an l ophilize to give a ellow soli . The chlo i e salt can be obtaine f om a Sepha ex QAE anion exchange column equilib ate with 0.1M Mg l2. Yiel : 0.45 g, 6%. ¹H NMR (300 MHz, 6-DMSO): δ 13.9 (s, 1H); 13. (s, 1H); .96 ( , J

= . Hz, 1 H); .62 ( , J = .6 Hz, 1H); .34 (m, 2H); .92- .21 (m, 4H); 4.4 ( , J = 20.1 Hz, 6 H); 3. 9 (s, 6H). ESI-MS (cation): m/z calc. 524.0 (M-NH3+TFA⁺), obs.

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523. . UV-Vis (H2O, pH ): 250 nm (36, 00 M^-1 cm^-1), 310 nm (20, 00 M^-1, cm^-1), 340 nm (23,400 M^-1, cm^-1).

3.2.3.5 [Rh(chrysi)(phen)(L)]Cl₃ (L= HDPA, MeDPA, PrDPA) Rh(chrysi)(phen)(NH₃)₂]Cl₃ (25 mg, 0.02 mmol) was reacted with L (0.022 mmol) in a 4:1 mixture of ethanol:water (10 mL). The bright red solution was refluxed overnight. The solvent was removed in vacuo and the resulting red solid dissolved in 0.1% TFA_(aq) (10 mL). The red solution was loaded onto a SPE cartridge and rinsed with copious amount of 0.1% TFA(aq). The SPE cartridge was eluted with 10% acetonitrile in 0.1% TFA_(aq), and fractions were collected. The fractions containing product were identified by HPLC, combined, and lyophilized. The chloride salt can be obtained from a Sephadex QAE anion exchange column equilibrated with 0.1M MgCl2.

[Rh(chrysi)(phen)(HDPA)]Cl₃: Yield: 17-28%. ESI-MS (cation): m/z calc 708.14 (M-2H⁺), obs. 708.2. UV-Vis (H2O, pH 7): 303 nm (34,200 M^-1 cm^-1), 391 nm (8,000 M^-1, cm^-1), 440 nm (3,600 M^-1, cm^-1).

[Rh(chrysi)(phen)(MeDPA)]Cl3: Yield: 12-32%. ¹H NMR (500 MHz, DMSO- d6) δ 12.45 (s, 1H), 10.4 (s, 1H), 9.34 – 6.83 (m, 26H), 3.87 (s, 3H). ESI-MS (cation):

m/z calc. 722.15 (M-2H⁺) 361.6 (M-H²⁺), obs. 722, 362. UV-Vis (H₂O, pH 7): 303 nm (55,500 M^-1 cm^-1), 391 nm (13,800 M^-1, cm^-1), 440 nm (5,700 M^-1, cm^-1).

[Rh(chrysi)(phen)(PrDPA)]Cl3: Yield: 10-22%. ESI-MS: calc. 750.18 (M-2H⁺), 375.6 (M-H²⁺), obs. 750, 376. UV-Vis (H₂O, pH 7): 303 nm (53,500 M^-1 cm^-1), 391 nm (13,900 M^-1, cm^-1), 440 nm (9,900 M^-1, cm^-1).

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3.2.3.6 [Rh(chrysi)(phen)(DPE)]Cl₂

A 125 mL round-bottomed flask was charged with

[Rh(chrysi)(phen)(NH3)2]TFA3 (62.0 mg, 0.068 mmol) and DPE (25.6 mg, 0.128 mmol) in ethanol (50 mL) to give a red solution. The reaction was heated to reflux (80° C) and stirred for 48 h. The ethanol solution was evaporated to dryness and dissolved in 0.1%

TFA(aq)(50 mL). The red solution was loaded onto a SPE cartridge and rinsed with copious amount of 0.1% TFA_(aq). The SPE cartridge was eluted with 10% acetonitrile in 0.1% TFA(aq), and fractions were collected. The fractions containing product were identified by HPLC, combined, and lyophilized. The chloride salt can be obtained from a Sephadex QAE anion exchange column equilibrated with 0.1M MgCl2. Yield: 30%. ESI- MS (cation): m/z calc. 737.15 (M-H⁺), 369.1 (M²⁺), obs. 737, 369. UV-Vis (H2O, pH 7):

272 nm (102,100 M^-1 cm^-1), 303 nm (35,400 M^-1, cm^-1), 440 nm (10,600 M^-1, cm^-1). ¹H NMR (CD3 N, 500 MHz): δ 15.10 (s, 1 H); 11.30 (s, 1 H); 9.62 ( , J = 5.5 Hz, 1H); 8.98 (d, J = 7.0 Hz, 1H); 8.92 (d, J = 8.0 Hz, 1H); 8.88 (m, 2H); 8.36 (m, 4H); 8.27 (d, J = 8.5 Hz, 1H); 8.21 (m, 1H); 8.13 (d, J = 8.5 Hz, 1H); 8.00 (m, 2H); 7.94 (d, J = 8.5 Hz, 1H);

7.73-7.78 (m, 4H); 7.62 (t, J = 8.0 Hz, 1H); 7.57 (d, J = 8.0 Hz, 1H); 7.50 (t, J = 7.0 Hz, 1H); 7.32 (d, J = 6.5 Hz, 1H); 7.14 (m, 1H); 6.95 (t, J = 7.5 Hz, 1H); 6.33 (t, J = 6.0 Hz, 1H); 1.98 (s, 3H).