Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with FeV=O and FeIV=O Units

Santanu Pattanayak; Andrew J. Jasniewski; Atanu Rana; Apparao Draksharapu; Kundan K. Singh; Andrew Weitz; Michael Hendrich; Lawrence Que; Abhishek Dey; Sayam Sen Gupta

doi:10.1021/acs.inorgchem.7b00448

Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with Fe^V=O and Fe^IV=O Units

Santanu Pattanayak, Andrew J. Jasniewski, Atanu Rana, Apparao Draksharapu, Kundan K. Singh, Andrew Weitz, Michael Hendrich, Lawrence Que, Abhishek Dey, Sayam Sen Gupta

Chemistry (Twin Cities)

Research output: Contribution to journal › Article › peer-review

55 Scopus citations

Abstract

In this report we compare the geometric and electronic structures and reactivities of [Fe^V(O)]⁻ and [Fe^IV(O)]^2- species supported by the same ancillary nonheme biuret tetraamido macrocyclic ligand (bTAML). Resonance Raman studies show that the FeO vibration of the [Fe^IV(O)]^2- complex 2 is at 798 cm^-1, compared to 862 cm^-1 for the corresponding [Fe^V(O)]⁻ species 3, a 64 cm^-1 frequency difference reasonably reproduced by density functional theory calculations. These values are, respectively, the lowest and the highest frequencies observed thus far for nonheme high-valent Fe=O complexes. Extended X-ray absorption fine structure analysis of 3 reveals an Fe=O bond length of 1.59 Å, which is 0.05 Å shorter than that found in complex 2. The redox potentials of 2 and 3 are 0.44 V (measured at pH 12) and 1.19 V (measured at pH 7) versus normal hydrogen electrode, respectively, corresponding to the [Fe^IV(O)]^2-/[Fe^III(OH)]^2- and [Fe^V(O)]⁻/[Fe^IV(O)]^2- couples. Consistent with its higher potential (even after correcting for the pH difference), 3 oxidizes benzyl alcohol at pH 7 with a second-order rate constant that is 2500-fold bigger than that for 2 at pH 12. Furthermore, 2 exhibits a classical kinteic isotope effect (KIE) of 3 in the oxidation of benzyl alcohol to benzaldehyde versus a nonclassical KIE of 12 for 3, emphasizing the reactivity differences between 2 and 3.

Original language	English (US)
Pages (from-to)	6352-6361
Number of pages	10
Journal	Inorganic chemistry
Volume	56
Issue number	11
DOIs	https://doi.org/10.1021/acs.inorgchem.7b00448
State	Published - Jun 5 2017

Bibliographical note

Funding Information:
The work performed at the CSIR-National Chemical Laboratory was supported by SERB, New Delhi (Grant No. SERB/EMR/2014/0016 to SSG). The work performed at the Univ. of Minnesota was supported by the U.S. National Science Foundation (Grant No. CHE-1361773 to L.Q.). XAS data were collected on Beamlines 7-3 and 9-3 at the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, which is supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. Use of Beamlines 7-3 and 9-3 is supported by the DOE Office of Biological and Environmental Research and by the National Institutes of Health, National Institute of General Medical Sciences (including P41GM103393). S.P. and K.K.S. thank UGC-India for a fellowships. S.P. and S.S.G. thank Dr. A. Das (CSIR-NCL) for use of the electrochemical facility at CSIR-NCL.

Publisher Copyright:
© 2017 American Chemical Society.

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10.1021/acs.inorgchem.7b00448

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5908480

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@article{a7b898b8d757496ea257c3b312989959,

title = "Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with FeV=O and FeIV=O Units",

abstract = "In this report we compare the geometric and electronic structures and reactivities of [FeV(O)]− and [FeIV(O)]2- species supported by the same ancillary nonheme biuret tetraamido macrocyclic ligand (bTAML). Resonance Raman studies show that the FeO vibration of the [FeIV(O)]2- complex 2 is at 798 cm-1, compared to 862 cm-1 for the corresponding [FeV(O)]− species 3, a 64 cm-1 frequency difference reasonably reproduced by density functional theory calculations. These values are, respectively, the lowest and the highest frequencies observed thus far for nonheme high-valent Fe=O complexes. Extended X-ray absorption fine structure analysis of 3 reveals an Fe=O bond length of 1.59 {\AA}, which is 0.05 {\AA} shorter than that found in complex 2. The redox potentials of 2 and 3 are 0.44 V (measured at pH 12) and 1.19 V (measured at pH 7) versus normal hydrogen electrode, respectively, corresponding to the [FeIV(O)]2-/[FeIII(OH)]2- and [FeV(O)]−/[FeIV(O)]2- couples. Consistent with its higher potential (even after correcting for the pH difference), 3 oxidizes benzyl alcohol at pH 7 with a second-order rate constant that is 2500-fold bigger than that for 2 at pH 12. Furthermore, 2 exhibits a classical kinteic isotope effect (KIE) of 3 in the oxidation of benzyl alcohol to benzaldehyde versus a nonclassical KIE of 12 for 3, emphasizing the reactivity differences between 2 and 3.",

author = "Santanu Pattanayak and Jasniewski, {Andrew J.} and Atanu Rana and Apparao Draksharapu and Singh, {Kundan K.} and Andrew Weitz and Michael Hendrich and Lawrence Que and Abhishek Dey and {Sen Gupta}, Sayam",

note = "Funding Information: The work performed at the CSIR-National Chemical Laboratory was supported by SERB, New Delhi (Grant No. SERB/EMR/2014/0016 to SSG). The work performed at the Univ. of Minnesota was supported by the U.S. National Science Foundation (Grant No. CHE-1361773 to L.Q.). XAS data were collected on Beamlines 7-3 and 9-3 at the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, which is supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. Use of Beamlines 7-3 and 9-3 is supported by the DOE Office of Biological and Environmental Research and by the National Institutes of Health, National Institute of General Medical Sciences (including P41GM103393). S.P. and K.K.S. thank UGC-India for a fellowships. S.P. and S.S.G. thank Dr. A. Das (CSIR-NCL) for use of the electrochemical facility at CSIR-NCL. Publisher Copyright: {\textcopyright} 2017 American Chemical Society.",

year = "2017",

month = jun,

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doi = "10.1021/acs.inorgchem.7b00448",

language = "English (US)",

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T1 - Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with FeV=O and FeIV=O Units

AU - Pattanayak, Santanu

AU - Jasniewski, Andrew J.

AU - Rana, Atanu

AU - Draksharapu, Apparao

AU - Singh, Kundan K.

AU - Weitz, Andrew

AU - Hendrich, Michael

AU - Que, Lawrence

AU - Dey, Abhishek

AU - Sen Gupta, Sayam

N1 - Funding Information: The work performed at the CSIR-National Chemical Laboratory was supported by SERB, New Delhi (Grant No. SERB/EMR/2014/0016 to SSG). The work performed at the Univ. of Minnesota was supported by the U.S. National Science Foundation (Grant No. CHE-1361773 to L.Q.). XAS data were collected on Beamlines 7-3 and 9-3 at the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, which is supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. Use of Beamlines 7-3 and 9-3 is supported by the DOE Office of Biological and Environmental Research and by the National Institutes of Health, National Institute of General Medical Sciences (including P41GM103393). S.P. and K.K.S. thank UGC-India for a fellowships. S.P. and S.S.G. thank Dr. A. Das (CSIR-NCL) for use of the electrochemical facility at CSIR-NCL. Publisher Copyright: © 2017 American Chemical Society.

PY - 2017/6/5

Y1 - 2017/6/5

N2 - In this report we compare the geometric and electronic structures and reactivities of [FeV(O)]− and [FeIV(O)]2- species supported by the same ancillary nonheme biuret tetraamido macrocyclic ligand (bTAML). Resonance Raman studies show that the FeO vibration of the [FeIV(O)]2- complex 2 is at 798 cm-1, compared to 862 cm-1 for the corresponding [FeV(O)]− species 3, a 64 cm-1 frequency difference reasonably reproduced by density functional theory calculations. These values are, respectively, the lowest and the highest frequencies observed thus far for nonheme high-valent Fe=O complexes. Extended X-ray absorption fine structure analysis of 3 reveals an Fe=O bond length of 1.59 Å, which is 0.05 Å shorter than that found in complex 2. The redox potentials of 2 and 3 are 0.44 V (measured at pH 12) and 1.19 V (measured at pH 7) versus normal hydrogen electrode, respectively, corresponding to the [FeIV(O)]2-/[FeIII(OH)]2- and [FeV(O)]−/[FeIV(O)]2- couples. Consistent with its higher potential (even after correcting for the pH difference), 3 oxidizes benzyl alcohol at pH 7 with a second-order rate constant that is 2500-fold bigger than that for 2 at pH 12. Furthermore, 2 exhibits a classical kinteic isotope effect (KIE) of 3 in the oxidation of benzyl alcohol to benzaldehyde versus a nonclassical KIE of 12 for 3, emphasizing the reactivity differences between 2 and 3.

AB - In this report we compare the geometric and electronic structures and reactivities of [FeV(O)]− and [FeIV(O)]2- species supported by the same ancillary nonheme biuret tetraamido macrocyclic ligand (bTAML). Resonance Raman studies show that the FeO vibration of the [FeIV(O)]2- complex 2 is at 798 cm-1, compared to 862 cm-1 for the corresponding [FeV(O)]− species 3, a 64 cm-1 frequency difference reasonably reproduced by density functional theory calculations. These values are, respectively, the lowest and the highest frequencies observed thus far for nonheme high-valent Fe=O complexes. Extended X-ray absorption fine structure analysis of 3 reveals an Fe=O bond length of 1.59 Å, which is 0.05 Å shorter than that found in complex 2. The redox potentials of 2 and 3 are 0.44 V (measured at pH 12) and 1.19 V (measured at pH 7) versus normal hydrogen electrode, respectively, corresponding to the [FeIV(O)]2-/[FeIII(OH)]2- and [FeV(O)]−/[FeIV(O)]2- couples. Consistent with its higher potential (even after correcting for the pH difference), 3 oxidizes benzyl alcohol at pH 7 with a second-order rate constant that is 2500-fold bigger than that for 2 at pH 12. Furthermore, 2 exhibits a classical kinteic isotope effect (KIE) of 3 in the oxidation of benzyl alcohol to benzaldehyde versus a nonclassical KIE of 12 for 3, emphasizing the reactivity differences between 2 and 3.

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