Characterization of a Ferryl Flip in Electronically Tuned Nonheme Complexes. Consequences in Hydrogen Atom Transfer Reactivity

Abstract

Two oxoiron(IV) isomers ( R 2a and R 2b) of general formula [Fe IV (O)( R PyNMe 3 )(CH 3 CN)] 2 + are obtained by reaction of their iron(II) precursor with NBu 4 IO 4 . The two isomers differ in the position of the oxo ligand, cis and trans to the pyridine donor. The mechanism of isomerization between R 2a and R 2b has been determined by kinetic and computational analyses uncovering an unprecedented path for interconversion of geometrical oxoiron(IV) isomers. The activity of the two oxoiron(IV) isomers in hydrogen atom transfer (HAT) reactions shows that R 2a reacts one order of magnitude faster than R 2b, which is explained by a repulsive noncovalent interaction between the ligand and the substrate in R 2b. Interestingly, the electronic properties of the R substituent in the ligand pyridine ring do not have a significant effect on reaction rates. Overall, the intrinsic structural aspects of each isomer define their relative HAT reactivity, overcoming changes in electronic properties of the ligand.

Electrocatalytic Atom Transfer Radical Addition with Turbocharged Organocopper(II) Complexes

“…The ligand L1, including its analogues bearing various N -alkyl groups and pyridyl ring substituents, forms 6-coordinate distorted octahedral complexes with Mn IV , Fe II , ,, Fe III , , Co II , Co III , Ni II (high-spin), and Ni III . Interestingly, and also found here, Cu II only forms 5-coordinate complexes with L1 and its derivatives. ,,, When coordinated to metals enforcing square planar geometries (e.g., low-spin Ni II ), L1 has been found to bind in an interesting didentate mode, which is an important feature in terms of its ability to reversibly attach to or detach from a metal, as will be discussed later.…”

“…30 Interestingly, and also found here, Cu II only forms 5coordinate complexes with L1 and its derivatives. 14,16,29,31 When coordinated to metals enforcing square planar geometries (e.g., low-spin Ni II ), L1 has been found to bind in an interesting didentate mode, which is an important feature in terms of its ability to reversibly attach to or detach from a metal, 30 as will be discussed later.…”

Synchronous and basic asynchronous hydrogen-atom abstraction of benzylic substrates by high-valent iron–oxo porphyrin species

“…Recent work by Company and his colleagues has investigated the impact of the R substituent on the ligand pyridine ring in non-heme iron-oxo complexes ([Fe IV (O)( R PyNMe 3 ) (CH 3 CN)] 2+ , R = MeO, H, Cl, Br, CO 2 Me, and CF 3 ) regarding the HAA reaction. 36 The results indicate that the electronic properties of the R substituents did not significantly influence the HAA reaction. The η values for [Fe IV (O)( R PyNMe 3 )(CH 3 CN)] 2+ were approximately 500 mV, suggesting a synchronous HAT mechanism.…”

Kinetic and Product Study of the S‐oxidation vs HAT Chemoselectivity in Reactions Promoted by Nonheme Iron(IV)‐oxo Complex/NHPI Mediator System

“…The C−H oxidation mechanism by iron‐oxo complexes and N ‐oxyl radicals has been thoroughly investigated in the past decades. Several studies, including kinetic and isotope effect studies and theoretical calculations, clearly point to the operation of a hydrogen atom transfer (HAT) process as shown in Figure 1a and 1b for the reactions promoted by [(N4Py)Fe IV (O)] 2+[2] and PINO, respectively [13,23,24–39] …”

“…Several studies, including kinetic and isotope effect studies and theoretical calculations, clearly point to the operation of a hydrogen atom transfer (HAT) process as shown in Figure 1a and 1b for the reactions promoted by [(N4Py)Fe IV -(O)] 2 + [2] and PINO, respectively. [13,23,[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] In this context, we have recently reported a novel way to modify and control the selectivity of CÀ H bond oxidations of hydrocarbons and alcohols, combining the two systems, using nonheme iron(IV) À oxo complex [(N4Py)Fe IV (O)] 2 + as oxidant and N-hydroxyphthalimide (NHPI) as a HAT mediator. [40] [(N4Py)Fe IV (O)] 2 + , is able to promote the oxidation of NHPI to the phthalimide-N-oxyl radical (PINO) which, in turn, abstracts a hydrogen atom from the substrate as shown in Figure 2 for HAT from a benzylic CÀ H bond.…”