Reinterpreting the Role of the Catalyst Formal Potential. the Case of Thiocyanate Electrooxidation Catalyzed by Con4-L

We report on the interaction of the thiocyanate ion (SCN -) with Co macrocyclics. In order to modulate the electron density located on the metal center, we used several phthalocyanine and macrocyclic molecules with electron-donating or electron-withdrawing groups located on the phthalocyanine ligand. We studied the following substituted Cobalt-macrocycles (CoPcâ s): cobalt-tetraamino-phthalocyanine (4?(NH 2)CoPc), cobalt-phthalocyanine (CoPc), cobalt-octahydroxyethylthio-phthalocyanine (8?(SC 2H 4OH)CoPc), cobalt-tetrapentylopyrrol- phthalocyanine (4?(PenPyr)CoPc), cobalt-tetrapyridino-phorphyrazine (4?(Pyr)CoPc), cobalt-octaethylhexyloxy-phthalocyanine (8?(EH)CoPc), cobalt-octamethoxyphthalocyanine (8?(OCH 3)CoPc), and cobalt-hexadecafluorophthalocyanine (16(F)CoPc). Our results for the formation of a CoPc-SCN adduct indicate that the electron-withdrawing groups favors the formation of an adduct between thiocyanate and the Co center, with an increase of the thiocyanate-binding energy. When the adducts are formed, they exhibit an increasing chemical potential, thus indicating the feasibility to produce the catalysis once the adducts are formed. The molecular hardness values suggest that the CoPc s with electron-withdrawing substituents will show low catalytic activity while those with electron-donor substituents will show an enhanced catalytic activity. The functionalized Co-phthalocyanine shows the highest catalytic activity for the thiocyanate electroxidation, which presents an appropriate energy gap (HOMOSCN --LUMO CoPc s) for the adduct formation and the subsequent electronic transfer. © 2012 American Chemical Society.