Rath Sankar Prasad, Kalish Heather, Latos-Grazyński Lechosław, Olmstead Marilyn M, Balch Alan L
Department of Chemistry, University of California, Davis, California 95616, USA.
J Am Chem Soc. 2004 Jan 21;126(2):646-54. doi: 10.1021/ja0384431.
Pyridine solutions of ClFe(III)(meso-NH(2)-OEP) undergo oxidative ring opening when exposed to dioxygen. The high-spin iron(III) complex, ClFe(III)(meso-NH(2)-OEP), has been isolated and characterized by X-ray crystallography. In the solid state, it has a five-coordinate structure typical for high-spin (S = 5/2) iron(III) complex. In chloroform-d solution, ClFe(III)(meso-NH(2)-OEP) displays an (1)H NMR spectrum characteristic of a high-spin, five-coordinate complex and is unreactive toward dioxygen. However, in pyridine-d(5) solution a temperature-dependent equilibrium exists between the high-spin (S = 5/2), six-coordinate complex, [(py)ClFe(III)(meso-NH(2)-OEP)], and the six-coordinate, low spin (S = 1/2 with the less common (d(xz)d(yz))(4)(d(xy))(1) ground state)) complex, (py)(2)Fe(III)(meso-NH(2)-OEP). Such pyridine solutions are air-sensitive, and the remarkable degradation has been monitored by (1)H NMR spectroscopy. These studies reveal a stepwise conversion of ClFe(III)(meso-NH(2)-OEP) into an open-chain tetrapyrrole complex in which the original amino group and the attached meso carbon atom have been converted into a nitrile group. Additional oxidation at an adjacent meso carbon occurs to produce a ligand that binds iron by three pyrrole nitrogen atoms and the oxygen atom introduced at a meso carbon. This open-chain tetrapyrrole complex itself is sensitive to attack by dioxygen and is converted into a tripyrrole complex that is stable to further oxidation and has been isolated. The process of oxidation of the Fe(III) complex, ClFe(III)(meso-NH(2)-OEP), is compared with that of the iron(II) complex, (py)(2)Fe(II)(meso-NH(2)-OEP); both converge to form identical products.
ClFe(III)(内消旋 - NH₂ - OEP)的吡啶溶液在暴露于氧气时会发生氧化开环反应。高自旋铁(III)配合物ClFe(III)(内消旋 - NH₂ - OEP)已通过X射线晶体学进行了分离和表征。在固态下，它具有高自旋(S = 5/2)铁(III)配合物典型的五配位结构。在氘代氯仿溶液中，ClFe(III)(内消旋 - NH₂ - OEP)显示出高自旋五配位配合物的¹H NMR谱，并且对氧气无反应。然而，在氘代吡啶 - d₅溶液中，高自旋(S = 5/2)的六配位配合物[(py)ClFe(III)(内消旋 - NH₂ - OEP)]与六配位、低自旋(S = 1/2，基态为较少见的(d(xz)d(yz))⁴(d(xy))¹)配合物[(py)₂Fe(III)(内消旋 - NH₂ - OEP)]⁺之间存在温度依赖性平衡。这种吡啶溶液对空气敏感，其显著降解过程已通过¹H NMR光谱进行监测。这些研究揭示了ClFe(III)(内消旋 - NH₂ - OEP)逐步转化为开链四吡咯配合物的过程，其中原来的氨基和相连的中位碳原子已转化为腈基。相邻中位碳原子发生进一步氧化，生成一种通过三个吡咯氮原子和在中位碳原子引入的氧原子与铁结合的配体。这种开链四吡咯配合物本身对氧气攻击敏感，会转化为对进一步氧化稳定的三吡咯配合物，且已被分离出来。将Fe(III)配合物ClFe(III)(内消旋 - NH₂ - OEP)的氧化过程与铁(II)配合物(py)₂Fe(II)(内消旋 - NH₂ - OEP)的氧化过程进行了比较；两者都收敛形成相同的产物。
