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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 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.

SUBMITTER: Pattanayak S 

PROVIDER: S-EPMC5908480 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature

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Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with Fe<sup>V</sup>═O and Fe<sup>IV</sup>═O Units.

Pattanayak Santanu S   Jasniewski Andrew J AJ   Rana Atanu A   Draksharapu Apparao A   Singh Kundan K KK   Weitz Andrew A   Hendrich Michael M   Que Lawrence L   Dey Abhishek A   Sen Gupta Sayam S  

Inorganic chemistry 20170508 11


In this report we compare the geometric and electronic structures and reactivities of [Fe<sup>V</sup>(O)]<sup>-</sup> and [Fe<sup>IV</sup>(O)]<sup>2-</sup> species supported by the same ancillary nonheme biuret tetraamido macrocyclic ligand (bTAML). Resonance Raman studies show that the Fe═O vibration of the [Fe<sup>IV</sup>(O)]<sup>2-</sup> complex 2 is at 798 cm<sup>-1</sup>, compared to 862 cm<sup>-1</sup> for the corresponding [Fe<sup>V</sup>(O)]<sup>-</sup> species 3, a 64 cm<sup>-1</sup> f  ...[more]

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