@article {D5SC04700E,
	title = {Promoting selective electrochemical CO2 reduction under unconventionally acidic conditions through secondary coordination sphere positioning},
	journal = {Chem. Sci.},
	volume = {16},
	year = {2025},
	pages = {19226-19234},
	publisher = {The Royal Society of Chemistry},
	abstract = {While several studies have investigated the effects of protic secondary coordination sphere (SCS) groups on the kinetics of iron tetraphenylporphyrin (FeTPP) catalysed CO2 reduction{,} few have examined how a protic SCS might alter reaction selectivity. Under mildly acidic conditions{,} FeTPP-based catalysts are selective towards the 2e-/2H+ reduction of CO2 to CO; however{,} in the presence of more acidic proton donors{,} indiscriminate proton transfers often result in parasitic H2 evolution. This report investigates how SCS amide positioning alters CO versus H2 selectivity during CO2 reduction with a series of four FeTPP isomers bearing SCS amides at varying positions around the porphyrin core: NH donors are placed at either the meta or ortho position of the meso aryl porphyrin ring{,} as well as proximal (closer) or distal (farther away) to the porphyrin plane. In the presence of a conventional{,} weakly acidic proton source (phenol; pKa = 29.2 in MeCN){,} all isomers display the expected high faradaic efficiency (FE) towards CO (FECO = 67{\textendash}85\%) along with minimal H2 evolution (FEH2 = 3{\textendash}13\%). With a significantly stronger acid (3{,}5-bis(trifluoromethyl)phenol; pKa = 23.8 in MeCN){,} H2 becomes the major product when using the ortho-distal or both meta isomers (FEH2 = 45{\textendash}65\%) as well as unfunctionalized FeTPP (FEH2 = 78\%). Importantly{,} the ortho-proximal isomer shows dramatically rescued CO selectivity under these unconventionally acidic conditions (FECO = 83 {\textpm} 4\%). These results show how proper SCS placement impacts reaction selectivity during CO2 reduction{,} particularly with respect to minimizing indiscriminate proton transfers that lead to undesirable reactivity.},
	doi = {10.1039/D5SC04700E},
	url = {http://dx.doi.org/10.1039/D5SC04700E},
	author = {Teindl, Kaeden and Reid, Jolene P. and Nichols, Eva M.}
}
