High-Valent Imido Complexes of Manganese and Chromium Corroles

The oxidation reaction of M(tpfc) [M = Mn or Cr and tpfc = tris(pentafluorophenyl)corrole] with aryl azides under
photolytic or thermal conditions gives the first examples of mononuclear imido complexes of manganese(V) and
chromium(V). These complexes have been characterized by NMR, mass spectrometry, UV−vis, EPR, elemental
analysis, and cyclic voltammetry. Two X-ray structures have been obtained for Mn(tpfc)(NMes) and Cr(tpfc)(NMes)
[Mes = 2,4,6-(CH3)3C6H2]. Short metal−imido bonds (1.610 and 1.635 Å) as well as nearly linear M−N−C angles
are consistent with triple M⋮NR bond formation. The kinetics of nitrene [NR] group transfer from manganese(V)
corroles to various organic phosphines have been defined. Reduction of the manganese(V) corrolato complex
affords phosphine imine and MnIII with reaction rates that are sensitive to steric and electronic elements of the
phosphine substrate. An analogous manganese complex with a variant corrole ligand containing bromine atoms in
the β-pyrrole positions, Mn(Br8tpfc)(NAr), has been prepared and studied. Its reaction with PEt3 is 250× faster than
that of the parent tpfc complex, and its MnV/IV couple is shifted by 370 mV to a more positive potential. The EPR
spectra of chromium(V) imido corroles reveal a rich signal at ambient temperature consistent with CrV⋮NR (d1, S
= 1/2) containing a localized spin density in the dxy orbital, and an anisotropic signal at liquid nitrogen temperature.
Our results demonstrate the synthetic utility of organic aryl azides in the preparation of mononuclear metal imido
complexes previously considered elusive, and suggest strong σ-donation as the underlying factor in stabilizing
high-valent metals by corrole ligands.

M(tpfc) [M为锰(Mn)或铬(Cr)，tpfc为三(五氟苯基)咔咯（tris(pentafluorophenyl)corrole）]与芳基叠氮化物在光解或热解条件下发生氧化反应，首次得到了单核亚胺基锰(V)与铬(V)配合物。上述配合物均通过核磁共振波谱（NMR）、质谱、紫外-可见光谱（UV−vis）、电子顺磁共振波谱（EPR）、元素分析以及循环伏安法进行了表征。已获得Mn(tpfc)(NMes)与Cr(tpfc)(NMes)的两例X射线晶体结构[Mes为2,4,6-三甲基苯基（2,4,6-(CH3)3C6H2）]。金属-亚胺基键较短（1.610 Å与1.635 Å），且M−N−C键角接近线性，这与三键M⋮NR的形成特征相符。本研究阐明了亚氮宾（nitrene，[NR]）基团从锰(V)咔咯配合物向各类有机膦转移的反应动力学。该锰(V)咔咯配合物经还原后可生成膦亚胺与三价锰（MnIII），反应速率对膦底物的空间位阻与电子效应均具有依赖性。研究者还合成并研究了一种结构类似的锰配合物：其咔咯配体在β-吡咯位带有溴原子，即Mn(Br8tpfc)(NAr)。该配合物与三乙基膦（PEt3）的反应速率是母体tpfc配合物的250倍，且其Mn(V)/Mn(IV)氧化还原电对的电位正向偏移了370 mV。铬(V)亚胺基咔咯配合物的电子顺磁共振波谱显示，室温下存在特征信号，与CrV⋮NR（d¹，自旋S=1/2）的特征相符——该物种的dxy轨道存在定域自旋密度；而在液氮温度下则观测到各向异性信号。本研究结果证实了芳基叠氮化物在合成此前被认为难以获得的单核金属亚胺基配合物中的应用价值，并表明咔咯配体通过强σ给电子作用稳定高价金属物种是该类反应的核心机制。