Nonheme iron complexes are emerging as effective catalysts for reliable aliphatic C-H bond oxidation in organic synthesis.[1] Catalyst’s activity and selectivity are highly affected by the nature of the ligand. Elaborated ligand structures are usually required to achieve good regioselectivities. This feature often leads to expensive and difficult to obtain complexes, thus hampering the diffusion of this synthetic methodology.[2] In this context, we prepared a simple nonheme iron complex (3) which can be assembled directly in the reaction vessel from cheap and commercially available reagents (Figure 1). Complex 3 shows good activity in C-H bond oxidation, comparable to that reported for several amine-based Fe(II) complexes, albeit with a simpler structure.[3] Tuning of oxidation selectivity can be achieved by modifying the electronic properties of the pyridine ligands. From a mechanistic point of view, complex 3 acts as a pentadentate, metal-based oxidant without involvement of free radical species, and the only oxygen source is H2O2. The first step of the catalytic cycle is the oxidation of the Fe(II) present in complex 3 to Fe(III). Then, the oxidized complex looses a pyridine arm in order to make a coordination site free for H2O2 binding and activation. Eventually the oxidative degradation pathway of the catalytic species has been determined.[4] Catalytic activity of complex 3 in some hydrocarbon oxidations together with the full mechanistic investigation of complex 3 will be here reported. [1] L. Que, Jr. and W. B. Tolman Nature, 2008, 455, 333-340. [2] Gómez, L.; Garcia-Bosch, I.; Company, A. Benet-Buchholz, J. Polo, A.; Sala, X.; Ribas, X.; Costas, M. Angew. Chem. Int. Ed. 2009, 48, 5720-5723. Gorminsky, P. E.; White, M. C. J. Am. Chem. Soc. 2013, 135, 14052-14055. [3] G. Olivo, G. Arancio, L. Mandolini, O. Lanzalunga, S. Di Stefano, Catal. Sci. Tech. 2014, 4, 2900-2903. [4] G. Olivo, M. Nardi, A. Barbieri, A. Lapi, O. Lanzalunga, M. Costas, S. Di Stefano, submitted.
C-H bond oxidations catalyzed by an imine-based nonheme iron complex: a mechanistic insight / Olivo, Giorgio; Nardi, Martina; Vìdal, Diego; Lanzalunga, Osvaldo; Costas, Miquel; DI STEFANO, Stefano. - STAMPA. - (2015). (Intervento presentato al convegno Organometallic Chemistry directed towards Organic Synthesis (OMCOS 18) tenutosi a Sitges (Spagna) nel 28/06/2015-03/0772015).
C-H bond oxidations catalyzed by an imine-based nonheme iron complex: a mechanistic insight
OLIVO, GIORGIO;NARDI, MARTINA;LANZALUNGA, Osvaldo;DI STEFANO, Stefano
2015
Abstract
Nonheme iron complexes are emerging as effective catalysts for reliable aliphatic C-H bond oxidation in organic synthesis.[1] Catalyst’s activity and selectivity are highly affected by the nature of the ligand. Elaborated ligand structures are usually required to achieve good regioselectivities. This feature often leads to expensive and difficult to obtain complexes, thus hampering the diffusion of this synthetic methodology.[2] In this context, we prepared a simple nonheme iron complex (3) which can be assembled directly in the reaction vessel from cheap and commercially available reagents (Figure 1). Complex 3 shows good activity in C-H bond oxidation, comparable to that reported for several amine-based Fe(II) complexes, albeit with a simpler structure.[3] Tuning of oxidation selectivity can be achieved by modifying the electronic properties of the pyridine ligands. From a mechanistic point of view, complex 3 acts as a pentadentate, metal-based oxidant without involvement of free radical species, and the only oxygen source is H2O2. The first step of the catalytic cycle is the oxidation of the Fe(II) present in complex 3 to Fe(III). Then, the oxidized complex looses a pyridine arm in order to make a coordination site free for H2O2 binding and activation. Eventually the oxidative degradation pathway of the catalytic species has been determined.[4] Catalytic activity of complex 3 in some hydrocarbon oxidations together with the full mechanistic investigation of complex 3 will be here reported. [1] L. Que, Jr. and W. B. Tolman Nature, 2008, 455, 333-340. [2] Gómez, L.; Garcia-Bosch, I.; Company, A. Benet-Buchholz, J. Polo, A.; Sala, X.; Ribas, X.; Costas, M. Angew. Chem. Int. Ed. 2009, 48, 5720-5723. Gorminsky, P. E.; White, M. C. J. Am. Chem. Soc. 2013, 135, 14052-14055. [3] G. Olivo, G. Arancio, L. Mandolini, O. Lanzalunga, S. Di Stefano, Catal. Sci. Tech. 2014, 4, 2900-2903. [4] G. Olivo, M. Nardi, A. Barbieri, A. Lapi, O. Lanzalunga, M. Costas, S. Di Stefano, submitted.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
