Controlling Selectivity in Alkene Oxidation: Anion Driven Epoxidation or Dihydroxylation Catalysed by [Iron(III)(Pyridine‐Containing Ligand)] Complexes

Abstract

A highly reactive and selective catalytic system comprising Fe (III) and macrocyclic pyridine-containing ligands (Pc-L) for alkene oxidation by using hydrogen peroxide is reported herein. Four new stable iron(III) complexes have been isolated and characterized. Importantly, depending on the anion of the iron(III) metal complex employed as catalyst, a completely reversed selectivity was observed. When X = OTf, a selective dihydroxylation reaction took place. On the other hand, employing X = Cl resulted in the epoxide as the major product.The reaction proved to be quite general, tolerating aromatic and aliphatic alkenes as well as internal or terminal double bonds and both epoxides and diol products were obtained in good yields with good to excellent selectivities (up to 93 % isolated yield and d.r. = 99 : 1). The catalytic system proved its robustness by performing several catalytic cycles, without observing catalyst deactivation. The use of acetone as a solvent and hydrogen peroxide as terminal oxidant renders this catalytic system appealing.

Catalytic Selective Oxidation of Primary and Secondary Alcohols Using Nonheme [Iron(III)(Pyridine‐Containing Ligand)] Complexes

“…[28] Among the Fe-N distances, the Fe-N1 bond length is the shortest one, indicating that the strongest metal-ligand interaction occurs with the pyridinic nitrogen. [24] All the structural parameters are in good agreement with those previously reported in the literature for similar complexes. [24,28,29] A comparison with the analogous chloride complex [Fe(III)(Cl) 2 (Pc-L)]Cl (CSD refcode JIKPAX) [28b] reveals similar…”

“…[27] These values have to be compared with those of complexes 3a•H 2 O and 3b, which at room temperature possess lower magnetic moments, in agreement with a mixture of low spin and high spin states as already reported by us. [24] Detailed EPR studies showed that for complex 3a•H 2 O both low (S = 1/2) and high (S = 5/2) spin iron(III) species are present at r.t. while lowering the T, the populated spin state 5/2 increases.…”

“…In order to further test the selectivity of our system, several alcohols having both -CH 2 OH and C=C units were considered. Since we have already studied the reactivity of alkenes to give epoxide or diols in the presence of Fe(III)Pc-L complexes using hydrogen peroxide as oxidant, [24] it was interesting to evaluate the possibility of competitive reactions. When cinnamyl alcohol, 5r, was used as a substrate, we observed a good conversion (60 %), but a poor selectivity towards the expected cinnamaldehyde, 6r (17 %).…”

“…Last year, we reported the synthesis and characterization of robust [iron(III)(pyridine-Containing Ligand)] complexes, [Fe(III)(Pc-L)], highly active and selective for the alkene oxidation using hydrogen peroxide as the terminal oxidant, in the absence of any additive. [24] Depending on the anion, X -, of the iron(III) metal complex employed as a catalyst, we observed the selective formation of epoxide (X = Cl), or a clean dihydroxylation reaction (X = OTf ) ( Figure 1a). The rationale for this reversal of selectivity could be traced to the influence of the counteranion on the spin state of the iron center (low spin for X = Cl, high spin for X = OTf ) although a possible role of hidden HOTf in the opening of the epoxide cannot be ruled out.…”

[Ag(PcL)]‐Catalyzed Domino Reactions of 2‐Alkynylbenzaldehydes with Electron‐Poor Anilines: Synthesis of 1‐Aminoisochromenes

“…The synthesis of ligand (PcL 1 ) and the corresponding silver complex [Ag(PcL 1 )] have been already described. [22] The synthesis of ligands (PcL 2 ), [23] and (PcL 3 ), [23] have been already reported. Details for the preparation of [Ag(PcL 2 )] and [Ag(PcL 3 )] complexes are reported below.…”