Catalytic activity of halogenated iron porphyrins in alkene and alkane oxidations by iodosylbenzene and hydrogen peroxide

Abstract

Uma ferro porfirina poli-clorada, Fe(PCl 8 )Cl, foi sintetizada e usada como catalisador em reações de oxidação de hidrocarbonetos por iodosilbenzeno e peróxido de hidrogênio, em solução e ancorado covalentemente na aminopropilsilica. Embora a Fe(PCl 8 )Cl tenha mostrado a mesma eficiência da ferro porfirina precursora, Fe(P)Cl, na epoxidação de alcenos, foi um catalisador mais eficiente na hidroxilação de alcanos por iodosilbenzeno, com preferência por carbonos secundários na oxidação do adamantano e primário na oxidação do pentano. Essa seletividade reflete o impedimento estéreo da espécie ferro-oxo ou, alternativamente, a grande reatividade do oxidante ativo gerado da Fe(PCl 8 )Cl. A Fe(PCl 8 )Cl ancorada mostrou baixa atividade catalítica quando comparada com o catalisador homogêneo e com a Fe(P)Cl ancorada. Peróxido de hidrogênio foi um oxidante pobre para este sistema. A excessiva substituição dos hidrogênios por grupos sacadores de elétrons na periferia do anel porfirínico dificulta a formação do intermediário ativo na reação de oxidação. O mecanismo alternativo de oxidação envolve a participação de radicais.A poly-halogenated iron porphyrin, Fe(PCl 8 )Cl, has been synthesised and used as a catalyst in hydrocarbon oxidations by iodosylbenzene and hydrogen peroxide both in solution and covalently bound to aminopropylated silica. The poly-chlorinated iron porphyrin shows the same efficiency of the related Fe(P)Cl, in the epoxidation of alkenes but higher efficiency in the hydroxylation of alkanes by iodosylbenzene, with increased preference for the oxidation of secondary carbon in adamantane and primary carbon in the oxidation of pentane. These selectivities may reflect the steric constraints around the oxo-iron species or, alternatively, it may arise from the greater reactivity of the active oxidant from Fe(PCl 8 )Cl. The supported iron(III) porphyrin showed lower activity as compared with the homogeneous analogue and the related supported Fe(P)Cl. The poly-chlorinated iron porpyrin is a poor catalyst with hydrogen peroxide. Excessive substitutuion by electron withdrawing groups on the porphyrin periphery eventually prohibits the formation of the key intermediate in catalytic oxidations. The alternative oxidation mechanism could involve radical participation.Keywords: poly-halogenated iron porphyrins, catalysis, supported catalysts, hydrocarbon oxidation IntroductionAbout 25 years have passed since an iron(III) porphyrin, [iron(III) tetraphenylporphyrin] with iodosylbenzene was first used as a functional model for cytochrome P-450 for hydrocarbon oxidation. 1 The success of this pioneering work led to the synthesis of other metallo tetraarylporphyrins and the development of three generations of catalysts, which differ depending on the degree of substitution on the porphyrin ring. 2 Although the syntheses of the second and third generation porphyrins involve more expensive starting materials and are more time consuming, their improved robustness towards oxidative degradation and greater catalytic efficiency...

Nanofibrous and nanotubular supports for the immobilization of metalloporphyrins as oxidation catalysts

“…Metalloporphyrins, other complexes and transition metal ions either in solution or immobilized have been used for oxidation of linear alkanes such as n-heptane [62,[66][67][68][69][70]. The regioselectivity in the oxidation process using metalloporphyrins and in the absence of steric restraints is essentially under thermodynamic control [71].…”

“…The site could even be located in pores obtained by the single layer agglomeration with a "castle of cards" morphology, resulting from the exfoliation process. Another possibility could be that the fifth and sixth coordinative positions of the iron are bound to the support, which avoids the interaction with the oxidant iodosylbenzene and consequently deactivate the catalytic site [66,88]. Yet another possibility is the coordination of the iron porphyrin to hexylamine/urea, which can also deactivate the catalyst.…”

Ab initio simulations of the intercalation of iron(III) porphyrinates in Zn 2 Al-LDH: Structural analysis and evaluation of their basic and acid sites

“…Their fluorescence properties and the production of cytotoxic singlet O 2 ( 1 Δ g ) make them great photosensitizers to be used in photodynamic therapy (Lang et al, 2007;Kafunkova et al, 2010). The catalytic activity of porphyrins has also been reported for the oxidation reactions of alkane and alkene by iodosylbenzene and hydrogen peroxide as the oxygen donors (Guedes et al, 2005;Wypych et al, 2005;Stephenson and Bell, 2007a,b;Halma et al, 2008;Halma et al, 2009;Nakagaki et al, 2014).…”

“…The mechanistic features of these oxidation reactions are also of great interest since the oxygen donor seems to affect the catalytic activity (Bell et al, 1991;In et al, 2003;Guedes et al, 2005). For example, in the case of the use of hydrogen peroxide, the oxygen radical released by the oxygen donor is captured by the iron(III) center and a homolytic or heterolytic path may occur (Goh and Nam, 1999;Nam et al, 2000;Nam, 2007;Stephenson and Bell, 2007b).…”

Chemoselective epoxidation of electron rich and electron deficient olefins catalyzed by meso-tetraarylporphyrin iron(iii) chlorides in imidazolium ionic liquids

“…5,6 The meso substituents and axial ligands of metalloporphyrins influence the oxidative potential of the reactive intermediates formed by the reaction of mono oxygen donors with TAPFe(III)Cl in different reaction conditions. 7,8 Solvents constitute a major factor in deciding the efficacy of an environmentally friendly technology to develop new products and processes. 9 Room-temperature ionic liquids (RTILs) are potentially environmentally benign solvents for various organic and biochemical transformations.…”