Secondary Coordination Sphere Influence on the Reactivity of Nonheme Iron(II) Complexes: An Experimental and DFT Approach

Abstract

The new biomimetic ligands N4Py2Ph (1) and N4Py2Ph,amide (2) were synthesized and yield the iron(II) complexes [FeII(N4Py2Ph)(NCCH3)](BF4)2 (3) and [FeII(N4Py2Ph,amide)](BF4)2 (5). Controlled orientation of the Ph substituents in 3 leads to facile triplet spin reactivity for a putative FeIV(O) intermediate, resulting in rapid arene hydroxylation. Addition of a peripheral amide substituent within hydrogen-bond distance of the iron first coordination sphere leads to stabilization of a high-spin FeIIIOOR species which decays without arene hydroxylation. These results provide new insights regarding the impact of secondary coordination sphere effects at nonheme iron centers.

Thioether-ligated iron(ii) and iron(iii)-hydroperoxo/alkylperoxo complexes with an H-bond donor in the second coordination sphere

“…The key synthetic step, incorporation of the phenyl substituents onto the pyridine rings, was accomplished in high yield using Suzuki–Miyaura cross coupling reaction. 46 Metallation of the free ligand with Fe(BF 4 ) 2 was accomplished by stirring in MeCN, and single crystals of 8 were grown from vapor diffusion of Et 2 O into the solution. The light yellow crystals reveal Fe–N bond distances (2.1842–2.2267 Å, Table 6) consistent with a high-spin (hs) iron( ii ) center.…”

“…However, in the presence of an amide H-bond donor, [Fe III (N4-Py amide,2Ph )(OO t Bu)] 2+ is stabilized and only the alkylperoxoiron( iii ) complex is observed. 46 We also determined the influence of first and second coordination sphere modifications in a system in which an equatorial thioether donor was included in the first coordination sphere and an amide H-bond donor was included in the second coordination sphere. The [Fe II (N3-Py amide SR)](BF 4 ) 2 starting material was shown to react with O-atom donors to give [Fe IV (O)(N3Py amide SR)] 2+ in CH 3 CN at −40 °C.…”

Mono- and binuclear non-heme iron chemistry from a theoretical perspective

“…This is in line with the stabilization of the -dz2 and hence increased axial reactivity in going from S = 1 to S = 2 Fe IV =O. As a result, the electronic structure at the S = 2 TS is characterized as an early -attack (transfer of an -electron into dz2) that weakens both the Fe─oxo and trans-axial Figure 11), whereas a Brønsted acid (HClO4) would contribute to a direct OAT mechanism (top part of Figure 11) were synthesized [215,216] and shown to significantly enhance OAT reactivity. However, the detailed analysis of these effects on reactivity of such complexes was not provided.…”

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).…”