Vallina Ana Tesouro, Stoeckli-Evans Helen, Neels Antonia, Ensling Jürgen, Decurtins Silvio
Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3012 Bern, Switzerland.
Inorg Chem. 2003 May 19;42(10):3374-82. doi: 10.1021/ic026079l.
We report here three examples of the reactivity of protic nucleophiles with diimine-type ligands in the presence of Fe(II) salts. In the first case, the iron-promoted alcoholysis reaction of one nitrile group of the ligand 2,3-dicyano-5,6-bis(2-pyridyl)-pyrazine (L1) permitted the isolation of an stable E-imido-ester, Fe(L1')(2)(2) (1), which has been characterized by spectroscopic studies (IR, ES-MS, Mössbauer), elemental analysis, and crystallographically. Compound 1 consists of mononuclear octahedrally coordinated Fe(II) complexes where the Fe(II) ion is in its low-spin state. The iron-mediated nucleophilic attack of water to the asymmetric ligand 2,3-bis(2-pyridyl)pyrido[3,4-b]pyrazine (L2) has also been studied. In this context, the crystal structures of two hydration-oxidation Fe(III) products, Fe(L2')(2)(3).3CH(3)CN (2) and trans-[FeL2"Cl(2)] (3), are described. Compounds 2 and 3 are both mononuclear Fe(III) complexes where the metals occupy octahedral positions. In principle, L2 is expected to coordinate to metal ions through its bipyridine-type units to form a five-membered ring; however, this is not the case in compounds 2 and 3. In 2, the ligand coordinates through its pyridines and through the hydroxyl group attached to the pyrazine imino carbon after hydration, that is, in an N,O,N tridentate manner. In compound 3, the ligand has suffered further transformations leading to a very stable diamido complex. In this case, the metal ion achieves its octahedral geometry by means of two pyridines, two amido N atoms, and two axial chlorine atoms. Magnetic susceptibility measurements confirmed the spin state of these two Fe(III) species: compounds 2 and 3 are low-spin and high-spin, respectively.
我们在此报告了三例质子亲核试剂在Fe(II)盐存在下与二亚胺型配体反应的实例。在第一个例子中，配体2,3 - 二氰基 - 5,6 - 双(2 - 吡啶基)吡嗪(L1)的一个腈基发生铁促进的醇解反应，得到了一种稳定的E - 亚氨基酯Fe(L1')(2)(2) (1)，通过光谱研究(红外光谱、电喷雾质谱、穆斯堡尔谱)、元素分析和晶体学对其进行了表征。化合物1由单核八面体配位的Fe(II)配合物组成，其中Fe(II)离子处于低自旋态。还研究了铁介导的水对不对称配体2,3 - 双(2 - 吡啶基)吡啶并[3,4 - b]吡嗪(L2)的亲核进攻。在此背景下，描述了两种水合氧化Fe(III)产物Fe(L2')(2)(3).3CH(3)CN (2)和反式 - [FeL2"Cl(2)] (3)的晶体结构。化合物2和3均为单核Fe(III)配合物，其中金属占据八面体位置。原则上，预计L2会通过其二吡啶型单元与金属离子配位形成五元环；然而，在化合物2和3中并非如此。在2中，配体通过其吡啶以及水合后连接在吡嗪亚氨基碳上的羟基进行配位，即以N,O,N三齿方式配位。在化合物3中，配体发生了进一步的转化，形成了一种非常稳定的二酰胺配合物。在这种情况下，金属离子通过两个吡啶、两个酰胺N原子和两个轴向氯原子实现其八面体几何构型。磁化率测量证实了这两种Fe(III)物种的自旋态：化合物2和3分别为低自旋和高自旋。
