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Papers by Asmita Singha

Research paper thumbnail of Interplay of Electronic Cooperativity and Exchange Coupling in Regulating the Reactivity of Diiron(IV)-oxo Complexes towards C-H and O-H Bond Activation

Chemistry: A European Journal, 2017

Activationo fi nert CÀHb onds such as those of methane are extremely challenging for chemists but... more Activationo fi nert CÀHb onds such as those of methane are extremely challenging for chemists but in nature, the soluble methane monooxygenase (sMMO) enzyme readily oxidizes methane to methanol by using adiir-on(IV) species. This has prompted chemists to look for similar model systems. Recently,a(m-oxo)bis(m-carboxamido)diir-on(IV) ([Fe IV 2 O(L) 2 ] 2 + L = N,N-bis-(3',5'-dimethyl-4'-methoxy-pyridyl-2'-methyl)-N'-acetyl-1,2-diaminoethane) complex has been generated by bulk electrolysis and this species activates inert CÀHb ondsa lmost1 000 times faster than mono-nuclear Fe IV =Os peciesa nd at the same time selectively activates OÀHb onds of alcohols. The very high reactivity and selectivity of this speciesi sp uzzlinga nd herein we use extensive DFT calculations to shed light on this aspect. We have studied the electronic and spectralf eatures of diiron {Fe III-m(O)-Fe III } + 2 (complex I), {Fe III-m(O)-Fe IV } + 3 (II), and {Fe IV-m(O)-Fe IV } + 4 (III)c omplexes. Strong antiferromagnetic coupling between the Fe centers leads to spin-coupled S = 0, S = 3/2, and S = 0g round state for species I-III respectively. The mechanistic study of the CÀHa nd OÀHb ond activation reveals am ultistater eactivity scenario where CÀHb ond activation is found to occur through the S = 4s pin-coupled state corresponding to the high-spin state of individual Fe IV centers.T he OÀHb ond activation on the other hand, occurs through the S = 2s pin-coupled state corresponding to an intermediate state of individual Fe IV centers. Molecular orbital analysisr eveals s-p/p-p channels for the reactivity.T he nature of the magnetic exchange interaction is found to be switched during the course of the reactiona nd this offers lower energy pathways. Significant electronic cooperativity between two metal centers during the course of the reaction has been witnessed and this uncovers the reason behind the efficiency and selectivity observed. The catalyst is found to prudently choose the desired spin states based on the natureo ft he substrate to effect the catalytic transformations. These findings suggestt hat the presence of such factors play ar ole in the reactivity of dinuclear metalloenzymes such as sMMO.

Research paper thumbnail of Interplay of Electronic Cooperativity and Exchange Coupling in Regulating the Reactivity of Diiron(IV)-oxo Complexes towards C-H and O-H Bond Activation

Chemistry: A European Journal, 2017

Activationo fi nert CÀHb onds such as those of methane are extremely challenging for chemists but... more Activationo fi nert CÀHb onds such as those of methane are extremely challenging for chemists but in nature, the soluble methane monooxygenase (sMMO) enzyme readily oxidizes methane to methanol by using adiir-on(IV) species. This has prompted chemists to look for similar model systems. Recently,a(m-oxo)bis(m-carboxamido)diir-on(IV) ([Fe IV 2 O(L) 2 ] 2 + L = N,N-bis-(3',5'-dimethyl-4'-methoxy-pyridyl-2'-methyl)-N'-acetyl-1,2-diaminoethane) complex has been generated by bulk electrolysis and this species activates inert CÀHb ondsa lmost1 000 times faster than mono-nuclear Fe IV =Os peciesa nd at the same time selectively activates OÀHb onds of alcohols. The very high reactivity and selectivity of this speciesi sp uzzlinga nd herein we use extensive DFT calculations to shed light on this aspect. We have studied the electronic and spectralf eatures of diiron {Fe III-m(O)-Fe III } + 2 (complex I), {Fe III-m(O)-Fe IV } + 3 (II), and {Fe IV-m(O)-Fe IV } + 4 (III)c omplexes. Strong antiferromagnetic coupling between the Fe centers leads to spin-coupled S = 0, S = 3/2, and S = 0g round state for species I-III respectively. The mechanistic study of the CÀHa nd OÀHb ond activation reveals am ultistater eactivity scenario where CÀHb ond activation is found to occur through the S = 4s pin-coupled state corresponding to the high-spin state of individual Fe IV centers.T he OÀHb ond activation on the other hand, occurs through the S = 2s pin-coupled state corresponding to an intermediate state of individual Fe IV centers. Molecular orbital analysisr eveals s-p/p-p channels for the reactivity.T he nature of the magnetic exchange interaction is found to be switched during the course of the reactiona nd this offers lower energy pathways. Significant electronic cooperativity between two metal centers during the course of the reaction has been witnessed and this uncovers the reason behind the efficiency and selectivity observed. The catalyst is found to prudently choose the desired spin states based on the natureo ft he substrate to effect the catalytic transformations. These findings suggestt hat the presence of such factors play ar ole in the reactivity of dinuclear metalloenzymes such as sMMO.

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