Factors Affecting the Carboxylate Shift Upon Formation of Nonheme Diiron‑O₂ Adducts

Several [Fe^II₂(N-EtHPTB)­(μ-O₂X)]²⁺ complexes (<b>1</b>·O₂X) have been synthesized, where N-EtHPTB is the anion of <i>N,N,N′N′</i>-tetrakis­(2-benzimidazolylmethyl)-2-hydroxy-1,3-diaminopropane and O₂X is an oxyanion bridge. Crystal structures reveal five-coordinate (μ-alkoxo)­diiron­(II) cores. These diiron­(II) complexes react with O₂ at low temperatures in CH₂Cl₂ (−90 °C) to form blue-green O₂ adducts that are best described as triply bridged (μ–η¹:η¹-peroxo)­diiron­(III) species (<b>2</b>·O₂X). With one exception, all <b>2</b>·O₂X intermediates convert irreversibly to doubly bridged, blue (μ–η¹:η¹-peroxo)­diiron­(III) species (<b>3</b>·O₂X). Where possible, <b>2</b>·O₂X and <b>3</b>·O₂X intermediates were characterized using resonance Raman spectroscopy, showing respective ν_O–O values of ∼850 and ∼900 cm^–1. How the steric and electronic properties of O₂X affect conversion of <b>2</b>·O₂X to <b>3</b>·O₂X was examined. Stopped-flow analysis reveals that oxygenation kinetics of <b>1</b>·O₂X is unaffected by the nature of O₂X, and for the first time, the benzoate analog of <b>2</b>·O₂X (<b>2</b>·O₂CPh) is observed

Factors Affecting the Carboxylate Shift Upon Formation of Nonheme Diiron‑O₂ Adducts

Several [Fe^II₂(N-EtHPTB)­(μ-O₂X)]²⁺ complexes (<b>1</b>·O₂X) have been synthesized, where N-EtHPTB is the anion of <i>N,N,N′N′</i>-tetrakis­(2-benzimidazolylmethyl)-2-hydroxy-1,3-diaminopropane and O₂X is an oxyanion bridge. Crystal structures reveal five-coordinate (μ-alkoxo)­diiron­(II) cores. These diiron­(II) complexes react with O₂ at low temperatures in CH₂Cl₂ (−90 °C) to form blue-green O₂ adducts that are best described as triply bridged (μ–η¹:η¹-peroxo)­diiron­(III) species (<b>2</b>·O₂X). With one exception, all <b>2</b>·O₂X intermediates convert irreversibly to doubly bridged, blue (μ–η¹:η¹-peroxo)­diiron­(III) species (<b>3</b>·O₂X). Where possible, <b>2</b>·O₂X and <b>3</b>·O₂X intermediates were characterized using resonance Raman spectroscopy, showing respective ν_O–O values of ∼850 and ∼900 cm^–1. How the steric and electronic properties of O₂X affect conversion of <b>2</b>·O₂X to <b>3</b>·O₂X was examined. Stopped-flow analysis reveals that oxygenation kinetics of <b>1</b>·O₂X is unaffected by the nature of O₂X, and for the first time, the benzoate analog of <b>2</b>·O₂X (<b>2</b>·O₂CPh) is observed