Synthesis of Os(II) Bipyridine Complex

The synthesis of [Os(dmebpy)₂Cl(ampy)]⁺ was based on previously reported protocols.^{30,31 (link)} However, in this work, we substituted the bipyridyl ligands for dmebpy to decrease the redox potential of the final complex, ensuring that it falls within a voltage window below the surface oxidation of gold (<0.3 V vs. Ag/AgCl).^{32 (link)} The synthesis of this complex involves two straightforward steps (Fig. S1, ESI†). First, we reacted 200 mg of (NH₄)₂OsCl₆ with 180 mg dmebpy in 5 mL of DMF under reflux and N₂ atmosphere for 1 hour. After cooling down the mixture for 30 min, the product was filtered to separate the NH₄Cl precipitate, and 3 mL of MeOH was added to the mixture. Then, 200 mL of diethyl ether was slowly added under vigorous stirring, causing the precipitation of the intermediate complex (Os(dmebpy)₂Cl)Cl. This complex was isolated by vacuum filtering and washed with diethyl ether. In the second step, 200 mg of the (Os(dmebpy)₂Cl)Cl were reacted with 40 mg of ampy in 5 mL of ethylene glycol under reflux and N₂ atmosphere for 3 hours. After cooling down the product to 25 °C for 1 hour, 5 mL of a saturated NH₄PF₆ aqueous solution was slowly added to the mixture while vigorously stirring, observing the precipitation of [Os(dmebpy)₂Cl(ampy)]PF₆ (dark solid). The final product was vacuum filtered, washed with deionized water, and air-dried overnight at 25 °C. For both steps, we obtained yields higher than 85%.