Synthesis and Reactivity of Manganese Imido and Nitrido Complexes Bearing Tetradentate Trianionic and Tetraanionic Ligands

具有四齒三陰離子和四陰離子配體的錳亞胺和氮雜配合物的合成和反應性

Student thesis: Doctoral Thesis

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Award date8 Jan 2020

Abstract

The chemistry of high valent manganese imido and nitrido with tetradentate trianionic and tetraanionic ligand and iron nitrido with tetradentate tetraanionic ligand was explored. Manganese(V) mesitylimido complexes of a series of tetraamido macrocylic ligands (TAML) were prepared. Structural and spectroscopic characterization of the MnV imido complexes show that they have a Mn≡N bond with a d2 low spin electronic configuration. Electrochemical experiments reveal that all MnV imido complexes exhibit a reversible oxidation, while EPR spectroscopy and theoretical studies show that the oxidation is Mn based. The MnV imido complexes are relatively stable towards various organic substrates, but the one electron oxidized MnVI imido species can achieve HAT reaction with hydrocarbons and imido group transfer to thioanisoles to produce sulfilimine.

MnV nitrido complexes of a series of TAML have also been synthesized. Structural and spectroscopic characterization of these MnV nitrido complexes show that they have a Mn≡N bond and adopt a d2 low spin electronic structure. Electrochemical experiments reveal a reversible oxidation, and EPR spectroscopy and theoretical studies indicate that the oxidation is Mn based. MnV nitrido of TAML is relatively stable towards alkenes, phosphines and amines, but the one electron oxidized MnVI nitrido undergoes slow bimolecular nitrido ligand N–N coupling reaction to produce N2 with a second order reaction rate 136 M−1 s−1. At low concentration, the MnVI nitrido can undergo N atom transfer to styrene to form 2-phenylaziridine with 45 % yield.

A new MnV nitrido complex, [PPh4][MnV(N)(TTPPC3−)] with a bulky trianionic corrole ligand (TTPPC = 5,10,15-tris(2,4,6-triphenylphenyl) corrole) has been synthesized and characterized by IR spectroscopy, ESI-MS, cyclic voltammetry, NMR, UV-Vis spectroscopy and X-ray crystallography. Cyclic voltammetry of [PPh4][MnV(N)(TTPPC)] exhibits two reversible redox waves centered at –0.573 and +0.228 V in CH2Cl2 (vs FeCp20/+). The one electron oxidized MnV corrole nitrido complex [MnV(N)(TTPPC•2−)] and the two electron oxidized MnV corrole nitrido complex ([MnV(N)(TTPPC)][B(C6F5)4] have also been synthesized and characterized by IR, CV, ESI-MS and X-ray crystallography. UV-Vis, EPR spectroscopy, X-ray crystallography as well as theoretical studies indicate both one- and two-electron oxidation are corrole ligand-based. Both one-electron and two-electron oxidized MnV corrole nitrido complexes can undergo N atom transfer to styrene.

A series of terminal iron(VI) nitrido complexes can also be generated by intermetal N transfer between FeIII TAML complexes and MnV Salen nitrido complexes. 1H NMR spectroscopy reveals that these FeVI nitrido species are diamagnetic. Theoretical studies show that the FeVI nitrido species adopt a d2 low spin (S = 0) electronic structure. Preliminary reactivity studies reveal that these FeVI nitrido complexes undergo N–N coupling reaction to generate N2 and the corresponding FeIII TAML complexes. N-atom transfer to triphenylphosphine and styrene could also be achieved at relatively low Fe(VI) nitrido concentrations. FeIII TAML is able to catalyse the aziridination of styrene to 2-phenylaziridine by [MnV(N)(Salen)].