Oxygen-Atom Transfer from Iodosylarene Adducts of a Manganese(IV) Salen Complex: Effect of Arenes and Anions on I(III) of the Coordinated Iodosylarene

Abstract

This paper reports preparation, characterization, and reactivity of iodosylarene adducts of a manganese(IV) salen complex. In order to systematically investigate steric and electronic factors that control reactivity and selectivity, we prepared iodosylarene adducts from iodosylbenzene, iodosylmesitylene, 2,4,6-triethyliodosylbenzene, and pentafluoroiodosylbenzene. We also investigated the effect of anions on I(III) by using chloride, benzoate, and p-toluenesulfonate. Spectroscopic studies using (1)H NMR, electron paramagnetic resonance, infrared spectroscopy, and electrospray ionization mass spectrometry show that these iodosylarene adducts are manganese(IV) complexes bearing two iodosylarenes as external axial ligands. Reactions with thioanisole under the pseudo-first-order conditions show that the electron-withdrawing pentafluorophenyl group and the p-toluenesulfonate anion on I(III) significantly accelerate the oxygen-atom transfer. The high reactivity is correlated with a weakened I-OMn bond, as indicated by IR spectroscopy and mass spectrometry. Stoichiometric reactions with styrenes show that both enantioselectivity and diastereoselectivity are dependent on the arenes and anions on I(III) of the coordinate iodosylarenes. Notably, the pentafluorophenyl group and the p-toluenesulfonate anion suppress the cis-to-trans isomerization in the epoxidation of cis-β-methylstyrene. The present results show that iodosylarene adducts of manganese(IV) salen complexes are indeed active oxygen-atom-transfer reagents and that their reactivity and selectivity are regulated by steric and electronic properties of the arenes and anions on I(III) of the coordinated iodosylarenes.

Oxygen-Atom Transfer Reactivity of Axially Ligated Mn(V)–Oxo Complexes: Evidence for Enhanced Electrophilic and Nucleophilic Pathways

“…23 The effects of axial donors on nonheme Mn(O) complexes such as Mn(O)(salen)(X) have been reported. 31−34 However, direct structural, spectroscopic, or reactivity information on these complexes is in general quite limited because of the transient nature of these species. 31 …”

“…31−34 However, direct structural, spectroscopic, or reactivity information on these complexes is in general quite limited because of the transient nature of these species. 31 …”

Highly Reactive Nonheme Iron(III) Iodosylarene Complexes in Alkane Hydroxylation and Sulfoxidation Reactions

“…For example, Fujii and co-workers reported that iron(III)-OCl porphyrin and manganese(IV) iodosylarene salen complexes are competent oxidants in OAT reactions. [5] McKenzie and Lennartson reported a crystal structure of a nonheme iron(III) iodosylbenzene complex and used it in a sulfoxidation reaction. [6] Lei and coworkers reported spectroscopic evidence for a manganese iodosylarene porphyrin adduct.…”

“…The reactivities of the iron(III)-iodosylarene adducts, 2 and 3, were investigated in the CÀH bond activation of hydrocarbons at À40 8C. Upon addition of cumene to a solution of 2, the intermediate was converted into a new species (5) which gives rise to an isosbestic point at l = 537 nm (Figure 2 a). First-order rate constants, determined by the pseudo-first-order fitting of the kinetic data for the decay of 2 (Figure 2 a, inset), increased linearly with increasing cumene concentration, giving rise to a second-order rate constant of 2.1 10 À1 m À1 s À1 at À40 8C.…”

Advances in Engineered Hemoproteins that Promote Biocatalysis

“…Metal-salen complexes are known to be powerful and robust catalysts and their planar structures make them an ideal choice to mimic the structure of porphyrins so that the active sites of the hemoproteins stay relatively unchanged [61][62][63][64][65]. Figure 6 shows the comparison of protoporphyrin IX and two salen metal complexes that have been utilized as surrogates for the heme cofactor.…”