Crystal structure of a chiral nitrido-manganese salen complex. The nitrogen analogue to the intermediate in the Jacobsen epoxidation reaction

Jepsen, A.; Roberson, Mark; Hazell, Rita G.

doi:10.1039/a802592d

Cited by 23 publications

(27 citation statements)

References 17 publications

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“…Such polymeric nitrido-metal complexes have been observed for V, Mo, W, and Re [84][85][86][87][88]. However, this is the first report of the 1D chain form of Mn(V) N. The nitrido-Mn(V) complexes are diamagnetic due to the formation of frontier orbitals between d-orbitals of Mn(V) ion and p-orbitals of nitrogen [29,31,89].…”

Section: Compoundmentioning

confidence: 80%

“…The nitrido-metal complexes are of great interest in research on metal-assisted nitrogen-transfer reactions. To date, several mono-Mn(V) complexes based on salen complexes have been synthesized for this purpose [28][29][30][31][32]. Among these complexes, Tsuchimoto et al reported a rare 1D chain form repeating a [ Mn V N ] unit: [Mn V N(salpn)] (Fig.…”

Section: Compoundmentioning

confidence: 97%

“…The Mn(IV) [22,23] and Mn(V) species are obtained by oxidation of the Mn(III) species (such compounds as di--oxo-Mn(IV) dimers will be described in Section 3). In particular, the Mn(V) species are exceptionally stabilized in two forms as oxo-Mn(V) complexes [24][25][26][27] (Scheme 3a) or as nitrido-Mn(V) complexes [28][29][30][31][32] (Scheme 3b). Meanwhile, the Mn(II) species are generally stable in anaerobic conditions [33].…”

Section: Introductionmentioning

confidence: 99%

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Magnetic assemblies based on Mn(III) salen analogues

Miyasaka

Saitoh

Abe

2007

Coordination Chemistry Reviews

365

204

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Section: Compoundmentioning

confidence: 80%

Section: Compoundmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Magnetic assemblies based on Mn(III) salen analogues

Miyasaka

Saitoh

Abe

2007

Coordination Chemistry Reviews

365

204

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“…Numerous studies assume the Mn V -oxo species postulated by Kochi and coworkers (20) to be the enantioselective oxidant. Although the Mn V -oxo species has not been detected experimentally, its geometric and electronic structure, as well as the mechanism of the epoxidation, have been the focus of several theoretical investigations (5)(6)(7)(8)(9)(10)(11)(21)(22)(23)(24)(25).…”

mentioning

confidence: 99%

Epoxidation of unfunctionalized olefins by Mn(salen) catalyst using organic peracids as oxygen source: A theoretical study

Khavrutskii

Musaev

Morokuma

2004

Proc. Natl. Acad. Sci. U.S.A.

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The mechanism and origin of asymmetric induction in the Mn III Highly enantioselective Kochi-Jacobsen-Katsuki epoxidation of unfunctionalized olefins with Mn III (salen)-based chiral catalyst provides an efficient route to optically active epoxides (1-4). Understanding the mechanism of the epoxidation and the origin of asymmetric induction can lead to the development of new efficient catalysts and therefore is actively pursued (5-19). Numerous studies assume the Mn V -oxo species postulated by Kochi and coworkers (20) to be the enantioselective oxidant. Although the Mn V -oxo species has not been detected experimentally, its geometric and electronic structure, as well as the mechanism of the epoxidation, have been the focus of several theoretical investigations (5)(6)(7)(8)(9)(10)(11)(21)(22)(23)(24)(25).The predicted electronic structure of the trans-Mn V -oxo species is controversial due to small energetic differences between various electronic states. Without an axial ligand, the singlet, triplet, and quintet states of the square pyramidal complex are nearly degenerate. In the presence of axial ligands, the singlet state is strongly destabilized, whereas the triplet and quintet states remain nearly degenerate in energy. The mechanism of the epoxidation by the trans-Mn V -oxo species has been predicted to depend on the spin state and presence of an axial ligand. Without an axial ligand, epoxidation is predicted to be concerted for the quintet and singlet states but stepwise (through a radical intermediate) for the triplet state (5, 6). Axial Cl Ϫ ligand alters epoxidation by the quintet state from concerted to stepwise (5, 7-9).The origin of the asymmetric induction is a separate issue from the epoxidation mechanism and is poorly understood (1-4, 11, 26-29). For the trans-Mn V -oxo species, Jacobsen and Cavallo (11) and Houk et al. (28) computationally studied the asymmetric induction, describing only the small core part of the catalyst by quantum mechanics. To describe crucial noncovalent interactions between the olefin and the substituted salen, they used empirical force fields. Both agreed that olefin could approach the reactive MnO moiety in a side-on manner from multiple directions. However, Houk et al. (28) indicated olefin approach along the oxygen side of the salen ligand, whereas Jacobson and Cavallo (11) suggested a perpendicular approach to be the most favorable. Both studies demonstrated that olefin adds to the Mn V -oxo species regioselectively, forming the most stable radical intermediate. Although the trans-Mn V -oxo hypothesis can successfully explain most of the experimental data, in certain cases enantioselectivity depends on the oxygen source and reaction conditions, suggesting alternative oxygenating species (17,18,(30)(31)(32)(33)(34). The most dramatic enantioselectivity variations are observed for a synthetically important class of oxidants, organic peracids (30-34). In particular, in the presence of N-alkyl imidazole or N-oxide axial ligands, high enantioselectivity is realized,...

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“…Thus, the ability of an auxiliary ligand in a Mn(III)-salen complex to adopt a "reduced state"-like square-planar structure may facilitate electron transfer. Crystal structures of Mn(III)-salen complexes have demonstrated that salen ligands twist slightly when binding to manganese ions with their tert-butyl groups arranged in equatorial conformation with respect to the ligand, rendering the two unoccupied axial sites available for the peptide to interact freely with the Mn(III) ion [43,44] Figure 6), which, although not quite at the same abundance as that provided by the 5,5=(NO 2 ) 2 -salen ligand, was a significant improvement over the effect of the o-phenylenediamine-containing ligand. In addition to their electronic effects, a simple interpretation of the enhanced degree of [M Ϫ 2H] ·Ϫ formation is that the rigid confirmations of the salophen and dsn ligands lead to their [Mn III (L)(M Ϫ 2H)] ·Ϫ complexes adopting more sterically constrained square-planar geometries; as a result, the relatively preorganized structures of the reduced [Mn II (L)] · species facilitates the electron transfer (Table 1, Reaction a) [45,46].…”

Section: Ligand Effects On the Formation Of [M ϫ 2h] ·ϫ : Steric Effementioning

confidence: 99%

Formation of Anionic Peptide Radicals In Vacuo

Lam

Chu

2006

J. Am. Soc. Mass Spectrom.

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In this paper, we demonstrate for the first time the formation of radical anionic peptides [M - 2H]*- through a one-electron transfer mechanism upon low-energy collision-induced dissociation (CID) of gas-phase singly charged [Mn(III)(salen)(M - 2H)]*- complex ions [where salen is N,N'-ethylenebis(salicylideneiminato) and M is an angiotensin III derivative]. The types of fragment ions formed from [M - 2H]*- share some similarities with those from the cationic radical peptides M*+ and [M + H]*2+, but differ significantly from those of the corresponding deprotonated peptides [M - H]-. Fragmentation of [M - 2H]*- radical anionic angiotensin III derivatives leads preferentially to product ions of side-chain cleavage of amino acid residues, z-type and minor x-type fragment ions, most of which are types rarely observed in low-energy CID spectra of deprotonated analogs. The degree of competitive dissociation of the complexes is highly dependent on the nature of the substituted salen derivatives. The yields of anionic peptide radicals were enhanced to the greatest extent when electron withdrawing groups were positioned at the 5 and 5' positions, but the effect was rather modest when such groups resided at the 3 and 3' positions. Substituting a cyclohexyl unit of a salen with phenyl or naphthyl moieties at the 8 and 8' positions also facilitated electron-transfer pathways.

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Crystal structure of a chiral nitrido-manganese salen complex. The nitrogen analogue to the intermediate in the Jacobsen epoxidation reaction

Cited by 23 publications

References 17 publications

Magnetic assemblies based on Mn(III) salen analogues

Magnetic assemblies based on Mn(III) salen analogues

Epoxidation of unfunctionalized olefins by Mn(salen) catalyst using organic peracids as oxygen source: A theoretical study

Formation of Anionic Peptide Radicals In Vacuo

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