Aziridination Reactivity of a Manganese(II) Complex with a Bulky Chelating Bis(Alkoxide) Ligand

Abstract

Treatment of Mn(N(SiMe3)2)2(THF)2 with bulky chelating bis(alkoxide) ligand [1,1′:4′,1′′-terphenyl]-2,2′′-diylbis(diphenylmethanol) (H2[O-terphenyl-O]Ph) formed a seesaw manganese(II) complex Mn[O-terphenyl-O]Ph(THF)2, characterized by structural, spectroscopic, magnetic, and analytical methods. The reactivity of Mn[O-terphenyl-O]Ph(THF)2 with various nitrene precursors was investigated. No reaction was observed between Mn[O-terphenyl-O]Ph(THF)2 and aryl azides. In contrast, the treatment of Mn[O-terphenyl-O]Ph(THF)2 with iminoiodinane PhINTs (Ts = p-toluenesulfonyl) was consistent with the formation of a metal-nitrene complex. In the presence of styrene, the reaction led to the formation of aziridine. Combining varying ratios of styrene and PhINTs in different solvents with 10 mol% of Mn[O-terphenyl-O]Ph(THF)2 at room temperature produced 2-phenylaziridine in up to a 79% yield. Exploration of the reactivity of Mn[O-terphenyl-O]Ph(THF)2 with various olefins revealed (1) moderate aziridination yields for p-substituted styrenes, irrespective of the electronic nature of the substituent; (2) moderate yield for 1,1′-disubstituted α-methylstyrene; (3) no aziridination for aliphatic α-olefins; (4) complex product mixtures for the β-substituted styrenes. DFT calculations suggest that iminoiodinane is oxidatively added upon binding to Mn, and the resulting formal imido intermediate has a high-spin Mn(III) center antiferromagnetically coupled to an imidyl radical. This imidyl radical reacts with styrene to form a sextet intermediate that readily reductively eliminates the formation of a sextet Mn(II) aziridine complex.

Efficient carbene transfer reactivity mediated by Fe(ii) complexes supported by bulky alkoxides

“…This quintet corresponds to high-spin Fe iii antiferromagnetically coupled to carbene radical anion. Significant ligand radical character is consistent with our earlier work on Co carbene, 27 Fe/Mn nitrenes, 21,29 and Fe azide/diazoester complexes in this ligand environment. 20,26 Upon addition of styrene, either directly or through attempted coordination to Fe, significant rearrangement of the carbene during geometry optimization resulted in one or both of the esters coordinated to Fe and the carbene uncoordinated.…”

“…[16][17][18][19] We previously reported the synthesis and group-transfer reactivity of middle and late 3d metal complexes in weak-field bis(alkoxide) ligand environments. [20][21][22][23][24][25][26][27][28][29][30] The reaction of Co(OR) 2 (THF) 2 (OR¼OC t Bu 2 Ph) with diphenyldiazomethane formed high-valent, low-spin cobalt-carbene Co(OR) 2 (¼CPh 2 ) with an electronic structure intermediate between cobalt(IV)alkylidene and carbene(III)-carbene radical. 22 One-electron reduction of this compound produced high-spin Co(II) weakly coupled with a carbene radical.…”

Synthesis, Characterization, and the Effect of Lewis Bases on the Nuclearity of Iron Alkoxide Complexes

“…Fewer studies have examined weaker-field alkoxides as supporting ligands for late, first-row transition metals, primarily due to the propensity of alkoxides to form cluster compounds , if not carefully tuned. Nevertheless, several groups have made use of either fluorinated alkoxides to minimize the π-donicity of the ligand and thus inhibit clustering − or sterically encumbering alkoxides to enable the formation of well-defined mononuclear complexes. ,− These investigations have revealed that alkoxide complexes can accommodate unique electronic configurations (e.g., high-spin square planar complexes ,− ) and indeed allow access to high-spin metal–ligand multiply bonded intermediates (e.g., an iron–oxo example as well as iron–imido complexes − not directly detected, but proposed based on reactivity and computational support).…”