Iron(II) Complexes with Bio‐Inspired N,N,O Ligands as Oxidation Catalysts: Olefin Epoxidation and cis‐Dihydroxylation

Abstract

The Rieske dioxygenases are a group of non‐heme iron enzymes, which catalyze the stereospecific cis‐dihydroxylation of its substrates. Herein, we report the iron(II) coordination chemistry of the ligands 3,3‐bis(1‐methylimidazol‐2‐yl)propionate (L1) and its neutral propyl ester analogue propyl 3,3‐bis(1‐methylimidazol‐2‐yl)propionate (PrL1). The molecular structures of two iron(II) complexes with PrL1 were determined and two different coordination modes of the ligand were observed. In [FeII(PrL1)2](BPh4)2 (3) the ligand is facially coordinated to the metal with an N,N,O donor set, whereas in [FeII(PrL1)2(MeOH)2](OTf)2 (4) a bidentate N,N binding mode is found. In 4, the solvent molecules are in a cis arrangement with respect to each other. Complex 4 is a close structural mimic of the crystallographically characterized non‐heme iron(II) enzyme apocarotenoid‐15–15′‐oxygenase (APO). The mechanistic features of APO are thought to be similar to those of the Rieske oxygenases, the original inspiration for this work. The non‐heme iron complexes [FeII(PrL1)2](OTf)2 (2) and [FeII(PrL1)2](BPh4)2 (3) were tested in olefin oxidation reactions with H2O2 as the terminal oxidant. Whereas 2 was an active catalyst and both epoxide and cis‐dihydroxylation products were observed, 3 showed negligible activity under the same conditions, illustrating the importance of the anion in the reaction.

Long-term, low temperature simulation of early diagenetic alterations of organic matter from conifers: Aliphatic hydrocarbons

“…IX calamenene,3,5,6,?,6,8,11,8,11,8,11,8,11, Simoneit and Mazurek, 1982;Simoneit et al, 1986;Otto and Simoneit, 2001). genation of cadinenes (Britovsek et al, 2002;Bruijnincx et al, 2008), which may distort the diagenetic pathways of sesquiterpenoids.…”

Mimicry of the 2‐His‐1‐Carboxylate Facial Triad Using Bulky N,N,O‐Ligands: Non‐Heme Iron Complexes Featuring a Single Facial Ligand and Easily Exchangeable Co‐Ligands

“…To this end, we have previously reported the development of the tripodal 3,3-bis(alkylimidazol-2-yl)propionate (BAIP) N,N,O-ligand BMIP nPr ( Figure 1). [33][34][35] This ligand and the corresponding carboxylate (BMIP) mimic the facial triad with two imidazole rings and a coordinating ester or carboxylate group, accurately modeling the two histidine and the aspartate or glutamate amino acids present in the enzymes.…”

“…[34,35] The latter is most probably facilitated by rearrangement and/or partial dissociation of the ligands in solution to create vacant sites on iron for catalysis to take place.…”

Oxidative Double Dehalogenation of Tetrachlorocatechol by a Bio‐Inspired CuII Complex: Formation of Chloranilic Acid

“…Geometry calculations and checking for higher symmetry were performed with the PLATON program. [52] X 14); a = 10.1857(4), b = 11.0587(3), c = 27.1239 (14) ; b = 109.560(2)8; V = 2878.9 (2) 3 ; Z = 2; 1 calcd = 1.428 g cm À3 ; m = 0.99 mm À1 . 55363 reflections were measured at 150 K, corrected for absorption, and scaled on the basis of multiple measured reflections with the program SADABS [53] (correction range 0.79-0.84).…”

“…Most of these deal with model compounds of catechol oxidase, [6][7][8][9][10][11] and they have recently been reviewed. [2] Some of us earlier reported copper [12,13] and iron [14,15] complexes of the family of monoanionic, substituted 3,3-bis(1-alkylimidazol-2-yl)propionate ligands as biomimetic oxidation catalysts. Homogeneous and immobilised copper(II) complexes of parent ligand L1 (Figure 1) have, for instance, been tested in the oxidation of benzyl alcohol.…”