Jonas Robert T., Stack T. D. P.
Department of Chemistry, Stanford University Stanford, California 94305-5080.
Inorg Chem. 1998 Dec 28;37(26):6615-6629. doi: 10.1021/ic9713487.
An efficient modular protocol for synthesizing a series of facial-capping tris-pyridyl ligands, based on the tris(2-pyridyl)methoxymethane backbone, has been developed which allows for systematic variations of the steric demands at the periphery of the ligand. The coordination chemistry of one such family of ligands that positions 0-->3 methoxy groups at the periphery with Cu(I) and Cu(II) is presented. The ligands are tris(2-pyridyl)methoxymethane (L(0)()), bis(2-pyridyl)(2-(6-methoxy)pyridyl)methoxymethane (L(1)()), bis(2-(6-methoxy)pyridyl)(2-pyridyl)methoxymethane (L(2)()), and tris(2-(6-methoxy)pyridyl)methoxymethane (L(3)()). The ligand exchange behavior and, to a lesser extent, the structures of the these complexes vary dramatically given the small perturbation of introducing methoxy substituents. Two distinct coordination modes are observed for the Cu(I) complexes, both in solution and the solid state. One is a pseudo-tetrahedral coordination comprised of the facial-capping, tris-pyridyl ligand and a monodentate ligand such as CH(3)CN, CO, or PPh(3). The other structural type is also a pseudo-tetrahedral Cu(I) monomer formed by two tris-pyridyl ligands coordinated in a bidentate manner with preferable binding by the nonmethoxy pyridyl subunits. With the exception of the most sterically hindered ligand, L(3)(), which only displays monoligation to Cu(I), all ligands form both types of Cu(I) complexes, and the formation is controlled by stoichiometry. Both competitive ligand binding experiments and ligand substitution with CO(g) show that the (L(0)())(2)Cu and (L(1)())(2)Cu complexes have nearly equivalent stability in aprotic solvent, and greater stability than the (L(2)())(2)Cu complex due to inclusion of bulky methoxypyridines into the Cu(I) coordination sphere. The Cu(II) complexes of the ligand series generate "bis-tris", (L(0)()(-->)(3)())(2)Cu, complexes, with the Cu(II) ligated in a tetragonally distorted octahedral coordination environment. The degree of bulk at the ligand periphery dictates the Cu(II)-ligand bond lengths both in solution and the solid state. In these complexes, the bulky pyridyl ring prefers to bind in the axial position. For the most sterically encumbered ligand, L(3)(), the bisligated Cu(II) complex is moisture sensitive, reacting to give a monoligated, tris-aqua species, L(3)()Cu(H(2)O)(3).
已开发出一种高效的模块化协议，用于合成一系列基于三（2 - 吡啶基）甲氧基甲烷主链的面封端三吡啶配体，该协议允许在配体外围系统地改变空间需求。本文介绍了一类这样的配体家族与Cu（I）和Cu（II）在其外围带有0至3个甲氧基的配位化学。这些配体分别是三（2 - 吡啶基）甲氧基甲烷（L(0)()）、双（2 - 吡啶基）（2 - （6 - 甲氧基）吡啶基）甲氧基甲烷（L(1)()）、双（2 - （6 - 甲氧基）吡啶基）（2 - 吡啶基）甲氧基甲烷（L(2)()）和三（2 - （6 - 甲氧基）吡啶基）甲氧基甲烷（L(3)()）。鉴于引入甲氧基取代基的微小扰动，这些配合物的配体交换行为以及在较小程度上其结构有显著变化。在溶液和固态中，Cu（I）配合物观察到两种不同的配位模式。一种是由面封端的三吡啶配体和单齿配体（如CH(3)CN、CO或PPh(3)）组成的假四面体配位。另一种结构类型也是由两个以双齿方式配位的三吡啶配体形成的假四面体Cu（I）单体，非甲氧基吡啶亚基优先配位。除了空间位阻最大的配体L(3)()仅与Cu（I）形成单配位外，所有配体都形成两种类型的Cu（I）配合物，且形成过程由化学计量比控制。竞争性配体结合实验和用CO(g)进行的配体取代实验均表明，(L(0)())(2)Cu和(L(1)())(2)Cu配合物在非质子溶剂中具有几乎相等的稳定性，并且由于在Cu（I）配位球中包含庞大的甲氧基吡啶，其稳定性高于(L(2)())(2)Cu配合物。该配体系列的Cu（II）配合物生成“双三”型(L(0)()(-->)(3)())(2)Cu配合物，其中Cu（II）以四方畸变的八面体配位环境配位。配体外围的空间位阻程度决定了溶液和固态中Cu（II） - 配体键长。在这些配合物中，庞大的吡啶环比更喜欢在轴向位置配位。对于空间位阻最大的配体L(3)()，双配位的Cu（II）配合物对水分敏感，反应生成单配位的三水合物种L(3)()Cu(H(2)O)(3)。
