Evidence that steric factors modulate reactivity of tautomeric iron–oxo species in stereospecific alkane C–H hydroxylation

Abstract

A new iron complex mediates stereospecific hydroxylation of alkyl C-H bonds with hydrogen peroxide, exhibiting excellent efficiency. Isotope labelling studies provide evidence that the relative reactivity of tautomerically related oxo-iron species responsible for the C-H hydroxylation reaction is dominated by steric factors.

X-ray absorption spectroscopic characterization of the diferric-peroxo intermediate of human deoxyhypusine hydroxylase in the presence of its substrate eIF5a

“…A particularly useful diiron(II) complex for comparison is [Fe II 2 ( μ -OH)( μ -OH 2 )(TPA) 2 ] 3+ (TPA = tris(2-pyridylmethyl)amine) [74], which was found to have respective Fe II - μ -OH and Fe II - μ -OH 2 bonds averaging 2.07 and 2.17 Å, values that support our proposed assignment of the 2.07-Å scatterer in hDOHH- R as a hydroxo bridge. The remaining two scatterers at 2.18 Å have Fe–O distances consistent with either terminal (2.04 – 2.16 Å, Table S8) [51, 77, 79–83] or bridging water ligands (2.13 – 2.40 Å) [77, 78], but the Fe•••Fe distance of 3.22 Å observed for [Fe II 2 ( μ -OH)( μ -OH 2 )(TPA) 2 ] 3+ is too short to match the distance deduced for hDOHH- R .…”

Oxidationsreaktionen mit bioinspirierten einkernigen Nicht‐Häm‐Oxidometallkomplexen

“…Eine alternative Strategie zur Erhöhung der Reaktivität von Oxidoeisen(IV)‐Komplexen beruht auf dem Austausch der äquatorialen Pyridinliganden durch N ‐Methylbenzimidazolyl‐Substituenten. Der durch den sp 2 ‐Charakter und die Starrheit dieser Substituenten erzwungene sterische Anspruch im äquatorialen Bereich sollte größer sein als derjenige der α‐H‐Substituenten an den senkrechten Pyridindonoren . Andererseits können die relativen Donorfähigkeiten von Pyridinen und Benzimidazolen anhand der p K a ‐Werte ihrer konjugierten Säuren als sehr ähnlich eingeschätzt werden (5.22 für Pyridin und 5.41 für Benzimidazol).…”

Highly enantioselective epoxidation of olefins by H2O2 catalyzed by a non-heme Fe(ii) catalyst of a chiral tetradentate ligand

“…1). 18 We have previously observed that an (N-methyl)benzimidazolyl-containing ligand can enhance the catalytic reactivity of an Fe(II) complex in stereospecific C-H hydroxylation reactions, 27 and were therefore interested in investigating the influence of a chiral ligand containing (N-methyl)benzimidazolyl donor moieties on Fe(II)-catalyzed asymmetric epoxidation. For this purpose we have employed the tetradentate chiral ligand, Fig.…”