Analysis of Reaction Channels for Alkane Hydroxylation by Nonheme Iron(IV)–Oxo Complexes

Abstract

New high‐spin pathways: All four feasible reaction pathways for alkane hydroxylation by nonheme iron(IV)–oxo complexes have been investigated by computational methods. The triplet σ path is too high in energy to be involved in CH bond activation, but the reactivity of the quintet π channel competes with the triplet path and may thus offer a new approach for specific control of CH bond activation by iron(IV)–oxo species (see scheme).

Dichotomous Hydrogen Atom Transfer vs Proton-Coupled Electron Transfer During Activation of X–H Bonds (X = C, N, O) by Nonheme Iron–Oxo Complexes of Variable Basicity

“…Underneath this orbital occupation diagram we show the electron-shift from σ CH to σ* z2 that is responsible for the enrichment of the d-block by one spin-up electron in σ* z2 . 24,28,45b,46,47,48 …”

Insights into enzymatic halogenation from computational studies

“…This pushes against the practicability limits of modern electronic-structure methods, despite the ever-continuing increase in computing power and the methodical and algorithmic advances, notably, the broad availability of highly efficient explicitly correlated “R12” or “F12” coupled-cluster methods (Ten-no and Noga, 2012). Even if an (F12-)CCSD(T) calculation with a decent-size basis set is just about feasible (for recent examples of applications of coupled-cluster methods to NHFe systems, see, e.g., Chen et al, 2010a, 2011; Geng et al, 2010; Ye et al, 2012), one needs to interpret the results with care (Harvey, 2011; Neese et al, 2011). The close-lying electronic states, for which first-row transition metal complexes are notorious, may cause the coupled-cluster calculation to converge to the wrong electronic state, depending on the initial reference wave function used (e.g., HF, CASSCF, or DFT), yielding a qualitatively incorrect description of the electronic structure.…”

“…side-ways attack of the C–H bond on the Fe=O unit, has been studied in detail for various small [Fe IV =O] complexes (Chen et al, 2010a; Geng et al, 2010; Janardanan et al, 2010; Ye and Neese, 2011) using B3LYP and CCSD(T) methods. In brief, the actual reactive form, which evolves as the Fe=O bond is slightly stretched as the transition state is approached, is best described as [Fe III −O • ].…”

Applications of density functional theory to iron-containing molecules of bioinorganic interest

“…Theoretical studies of such biomimetic models may not only identify the key elements that determine their chemical reactivities, but may also provide insight into intermediates and reactivities of parent enzymes (Shaik et al, 2007a; de Visser et al, 2013). To date, DFT calculations have been applied extensively to various types of non-heme iron species (Scheme 1) (Bassan et al, 2002, 2005a,b; Roelfes et al, 2003; Decker and Solomon, 2005; Kumar et al, 2005; Quinonero et al, 2005; Berry et al, 2006; Bernasconi et al, 2007, 2011; de Visser, 2006, 2010; Hirao et al, 2006a, 2008a,b, 2011; Rohde et al, 2006; Decker et al, 2007; de Visser et al, 2007, 2011; Johansson et al, 2007; Noack and Siegbahn, 2007; Sastri et al, 2007; Sicking et al, 2007; Bernasconi and Baerends, 2008, 2013; Comba et al, 2008; Dhuri et al, 2008; Fiedler and Que, 2009; Klinker et al, 2009; Wang et al, 2009a, 2013b; Cho et al, 2010, 2012a, 2013; Geng et al, 2010; Chen et al, 2011; Chung et al, 2011b; Seo et al, 2011; Shaik et al, 2011; Vardhaman et al, 2011; Wong et al, 2011; Ye and Neese, 2011; Gonzalez-Ovalle et al, 2012; Gopakumar et al, 2012; Latifi et al, 2012; Mas-Ballesté et al, 2012; McDonald et al, 2012; Van Heuvelen et al, 2012; Ansari et al, 2013; Kim et al, 2013; Lee et al, 2013; Sahu et al, 2013; Tang et al, 2013; Ye et al, 2013; Hong et al, 2014; Sun et al, 2014). The intriguing reactivity patterns of these complexes are the result of active involvement of electrons in d-type MOs, which gives rise to multi-state scenarios (Shaik et al, 1998; Schröder et al, 2000; Schwarz, 2011).…”