When Philicity Fails: Mechanistic Control of Ambiphilic Metal–Superoxo Reactivity
- 1Department of Chemistry
- 2Indian Institute of Technology Bombay
Abstract
A fundamental challenge in oxygen activation chemistry is understanding the factors that govern the switch between electrophilic and nucleophilic reactivity in metal–superoxo intermediates. Notably, only four ambiphilic metal–superoxo systems have been reported to date, yet the origins of their ambiphilic behavior remain poorly understood, limiting the rational design of catalysts with predictable and tunable reactivity. Here, we systematically investigate these four reported complexes, [(L 1 ) •+ Co II –O2 •⁻ ] – ( 1b ) (where L1 = (N • ( o -PhNC(O) i Pr) 2 ) 2– ) , [(L 2 )Mn III –O 2 •– ] ( 2b ) (where L 2 = BDP Br P = 2,6-bis((2-( S )-di(4-bromo)phenylhydroxylmethyl-1-pyrrolidinyl)methyl)pyridine) 2– ), [(L 3 )Fe III (O 2 •⁻ )] 2− ( 3b ) (where L 3 = TAML = Tetra Amido Macrocyclic Ligand) 4- and [(L 4 )Co III –O 2 •⁻ ] ( 4b ) (where L 4 = BDPP = 2,6-bis((2-(S)diphenylhydroxylmethyl-1-pyrrolidinyl)methyl)pyridine) 2– ) , using density functional theory to elucidate their O 2 activation and reactivity toward electrophilic and nucleophilic substrates. O 2 activation preferentially proceeds through inner-sphere pathways, in which electron transfer and M–O 2 bond formation occurs concomitantly, with ligand-to-O 2 electron transfer for 1a and metal-to-O 2 electron transfer for 2a – 4a . For PPA deformylation, coordinatively saturated complex 2b favor α-hydrogen atom abstraction, whereas the open, four-coordinate 1b preferentially undergoes nucleophilic addition. In contrast, oxygen-atom-transfer reactivity toward triphenylphosphine does not follow electrophilicity alone: despite the higher intrinsic electrophilicity of [(L 5 )Cu II –O 2 •– ] + (L 5 =TMPA = tris(2-pyridyl methyl)amine); ( 5b ), 1b exhibits a lower activation barrier (68.4 vs 81.4 kJ/mol) owing to stronger orbital interactions and reduced deformation requirements. Collectively, these results establish that metal–superoxo reactivity is governed by the interplay of coordination environment, philicity, orbital interactions, steric effects, and deformation energy. These insights provide a framework for rational catalyst design in which reactivity can be tuned by optimizing the complete electronic and structural reaction landscape rather than maximizing philicity alone.
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BibTeX
@misc{nettem2026when,
title = {{When Philicity Fails: Mechanistic Control of Ambiphilic Metal–Superoxo Reactivity}},
author = {Chandrasekhar Nettem and Abitha Periyasamy and Manjeet Kumar and Gopalan Rajaraman},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15009918/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009918/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - When Philicity Fails: Mechanistic Control of Ambiphilic Metal–Superoxo Reactivity
AU - Chandrasekhar Nettem
AU - Abitha Periyasamy
AU - Manjeet Kumar
AU - Gopalan Rajaraman
PY - 2026
DA - 2026/10/05
PB - ChemRxiv
DO - 10.26434/chemrxiv.15009918/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009918/v1
AB - A fundamental challenge in oxygen activation chemistry is understanding the factors that govern the switch between electrophilic and nucleophilic reactivity in metal–superoxo intermediates. Notably, only four ambiphilic metal–superoxo systems have been reported to date, yet the origins of their ambiphilic behavior remain poorly understood, limiting the rational design of catalysts with predictable and tunable reactivity. Here, we systematically investigate these four reported complexes, [(L 1 ) •+ Co II –O2 •⁻ ] – ( 1b ) (where L1 = (N • ( o -PhNC(O) i Pr) 2 ) 2– ) , [(L 2 )Mn III –O 2 •– ] ( 2b ) (where L 2 = BDP Br P = 2,6-bis((2-( S )-di(4-bromo)phenylhydroxylmethyl-1-pyrrolidinyl)methyl)pyridine) 2– ), [(L 3 )Fe III (O 2 •⁻ )] 2− ( 3b ) (where L 3 = TAML = Tetra Amido Macrocyclic Ligand) 4- and [(L 4 )Co III –O 2 •⁻ ] ( 4b ) (where L 4 = BDPP = 2,6-bis((2-(S)diphenylhydroxylmethyl-1-pyrrolidinyl)methyl)pyridine) 2– ) , using density functional theory to elucidate their O 2 activation and reactivity toward electrophilic and nucleophilic substrates. O 2 activation preferentially proceeds through inner-sphere pathways, in which electron transfer and M–O 2 bond formation occurs concomitantly, with ligand-to-O 2 electron transfer for 1a and metal-to-O 2 electron transfer for 2a – 4a . For PPA deformylation, coordinatively saturated complex 2b favor α-hydrogen atom abstraction, whereas the open, four-coordinate 1b preferentially undergoes nucleophilic addition. In contrast, oxygen-atom-transfer reactivity toward triphenylphosphine does not follow electrophilicity alone: despite the higher intrinsic electrophilicity of [(L 5 )Cu II –O 2 •– ] + (L 5 =TMPA = tris(2-pyridyl methyl)amine); ( 5b ), 1b exhibits a lower activation barrier (68.4 vs 81.4 kJ/mol) owing to stronger orbital interactions and reduced deformation requirements. Collectively, these results establish that metal–superoxo reactivity is governed by the interplay of coordination environment, philicity, orbital interactions, steric effects, and deformation energy. These insights provide a framework for rational catalyst design in which reactivity can be tuned by optimizing the complete electronic and structural reaction landscape rather than maximizing philicity alone.
ER -