Highest Recorded N–O Stretching Frequency for 6-Coordinate {Fe-NO}⁷ Complexes: An Iron Nitrosyl Model for His₃ Active Sites

Abstract

We report the synthesis, structure, and reactivity of [Fe(T1Et4iPrIP)(OTf)2] [1; T1Et4iPrIP = tris(1-ethyl-4-isopropylimidazolyl)phosphine]. Compound 1 reacts reversibly with nitric oxide to afford [Fe(T1Et4iPrIP)(NO)(THF)(OTf)](OTf) (2), which is the first example of a 6-coordinate {FeNO}(7) S = 3/2 complex containing a linear Fe-N-O group. 2 exhibits the highest ν(NO) for compounds in this class. Density functional theory studies reveal an enhanced degree of β-electron transfer from π*(NO) to the Fe d orbitals accounting for the large stretching frequency.

Assembly of a mononuclear ferrous site using a bulky aldehyde-imidazole ligand

“…The short bond is likely due to the participation of the aldehydic oxygen (O1) in the formation of a 5-membered chelate ring. The iron triflate Fe1-O2 distance is 2.101(2) Å which is in the range of other known high spin iron (II)-O(triflate) bond distances (2.025–2.211 Å) [18,37–48]. The Fe1-O1(aldehyde) bond distance is 2.189(2) Å which is quite long for an iron(II)-O(carbonyl) bond (2.009–2.183 Å) [49–55].…”

The versatile ruthenium(II/III) tetraazamacrocycle complexes and their nitrosyl derivatives

“…In a similar way, theoretical calculations and experimental data show that [Fe II NO + ] also predominates in ferric heme nitrosyls [141]. On the other hand, in many nonheme systems, the formation of paramagnetic nitrosyl iron centers {RuNO} 7 is also observed [64,141]. The nature of the equatorial ligands does not have any significant influence on the N O bond prior to the reduction of the {RuNO} 6 core.…”

“…Theoretical calculations have been used to provide deep insight into fundamental properties, such as stretching frequencies and geometries, as well as excited or photo-induced metastable states, thereby elucidating Ru NO bonding modes and allowing prediction of the relative stability of light-induced linkage isomers [55][56][57][58][59][60][61][62][63][64][65]. Recently, energy decomposition analysis (EDA) has revealed the nature of the Ru NO bond in tetraazamacrocycle complexes, allowing investigation of the influence of ring-size and N-appended methyl groups both prior to and following one-electron reduction [56].…”

Synthesis and reactivity of a 4His enzyme model complex

“…32-38 The iron triflate Fe1-O1 distance is 2.1843(13) Å which is in the range of other known high spin Fe II -Otriflate bond distances (2.025-2.211 Å). 20, 39-50 Hydrogen bonding (D…A: 2.995 Å) is observed between an imidazole hydrogen located on C1A and a coordinated triflate oxygen (O1). Close contacts between a triflate fluorines and phenyl carbons (F3…C7′: 3.320 Å; F3…C8′: 3.322 Å; F1…C19′ 3.133 Å; F1…C16′: 3.295 Å; F1…C18′: 3.120 Å) are observed.…”