*3.1. Materials*

Palladium chloride, sodium chloride, and sodium borohydride were used as received. Pyridine (Py), 2-methylpyridine (2-MePy), 3-methylpyridine (3-MePy), 4-methylpyridine (4-MePy), 2,6-dimethylpyridine (2,6-Me2Py), 2,4-dimethylpyridine (2,4-Me2Py), 3,5-dimethylpyridine (3,5-Me2Py), 2-chloropyridine (2-ClPy), 3-chloropyridine (3-ClPy), 2,4-dichloropyridine (2,4-Cl2Py), aniline, and ethanol were distilled (or fractionally distilled) over drying agen<sup>t</sup> and stored under argon. 2,6-dichloropyridine (2,6-Cl2Py), 3,5-dichloropyridine (3,5-Cl2Py), iron powder, and iodine were used as received. Ultrapure (Milli-Q, 18.2 MΩ·cm resistivity at 25 ◦C) water was used in all experiments.

### *3.2. Synthesis of Palladium Nanoparticles*

PdNPs were prepared according to the method described elsewhere [48,55]. NaCl (0.188 mmoL; 0.11 g) and PdCl2 (0.084 mmoL; 0.015 g) were dissolved in 6 mL of ultrapure water and stirred at room temperature to form water soluble PdCl4<sup>2</sup>− species. Then, a freshly prepared solution of ligand (derivative of pyridine; 0.628 mmoL in 9 mL of water) was added, stirred for 20 min, and reduced by NaBH4 (1% w/v, 1.1 mL) added in 20 μL portions. The progress of reaction was observed as an immediate darkening of the mixture from light orange to dark brown (almost black). The resulting PdNPs were stirred for 30 min. In some experiments, for comparison purposes, nanoparticles were synthesized in ethanol instead of water. The size of centrifuged NPs as well as centrifuged and dried NPs was measured by transmission electron microscopy (TEM). The composition of Pd/ligand expressed as a percentage of the organic ligand and the metal in the centrifuged and dried palladium nanoparticles stabilized by 4-methylpyridine (PdNPs/4MePy) was determined by thermogravimetry (TG) under nitrogen atmosphere, with the heating rate = 10 K/min (see Figure S1 in Supplementary Information).
