(IP)2GaIII Complexes Facilitate Net Two |
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(IP)2GaIII Complexes Facilitate Net Two
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Reaction of M+[(IP2-)2Ga]− (IP = iminopyridine, M = Bu4N, 1a; (DME)3Na, 1b) with pyridine N-oxide affords two-electron-oxidized (IP–)2Ga(OH) (2) in reactions where the product outcome is independent of the cation identity, M+. In a second example of net two-electron chemistry, outer sphere oxidation of M+[(IP2-)2Ga]− using either 1 or 2 equiv of the one-electron oxidant ferrocenium afforded [(IP–)2Ga]+ (3) in either 44 or 87% yield, respectively. Reaction with 1 equiv of TEMPO, a one-electron oxidant, afforded the two-electron-oxidized product (IP–)2Ga(TEMPO) (4). Reduction of 2IP by 3Na and subsequent reaction with GaCl3 yielded a 1:1 mixture of (IP–)2GaCl and 1. Most remarkably, all of these reactions are overall two-electron processes and only the (IP–)2GaX and [(IP2-)2Ga]− oxidation states are thermodynamically accessible to us. Analogous aluminum chemistry previously afforded either one-electron or two-electron reactions and mixed-valent states. The thermodynamic accessibility of the mixed-valent states of (IP2-)(IP–)E, where E = Al or Ga, can be compared using cyclic voltammetry measurements. These measurements indicated that the mixed-valent state [(IP2-)(IP–)Ga]+ is not significantly stabilized with respect to disproportionation on the time scale of the electrochemistry experiment. The electrochemically observed differences in thermodynamic stability of the mixed-valent state [(IP2-)(IP–)E]+ can be rationalized by the observation that the dihedral angle between the ligand planes containing the π-system of IP is roughly 5° larger in all gallium complexes compared with aluminum analogs. Presumably, a larger dihedral angle provides weaker electronic coupling between the π-systems of IP via the E–X σ* orbital. Alternatively, the observed difference may be a result of the “inert pair effect”: a contracted Ga component in the E–X σ* orbital would also afford weaker electronic coupling.
中文翻译：
M + [（IP 2-）2 Ga] -（IP =亚氨基吡啶，M = Bu 4 N，1a ;（DME）3 Na，1b）与吡啶N-氧化物反应，得到两电子氧化（IP –）2 Ga（OH）（2）在反应中，产物的结果独立于阳离子同一性M +。在净双电子化学的第二个示例中，M + [（IP 2-）2 Ga] -的外球氧化使用1或2当量的单电子得到氧化剂的二茂铁[（IP - ）2镓] +（3分别）在屈服或者44或者87％。与1个当量的单电子氧化剂TEMPO反应，得到双电子氧化产物（IP –）2 Ga（TEMPO）（4）。用3Na还原2IP，然后与GaCl 3反应，得到（IP –）2 GaCl和1的1：1混合物。最值得注意的是，所有这些反应都是整体的两电子过程，只有（IP –）2 GaX和[（IP 2-）2Ga] -氧化态是我们热力学上可及的。以前类似的铝化学方法提供了一个电子或两个电子反应以及混合价态。可以使用循环伏安法比较（IP 2-）（IP –）E（E = Al或Ga）的混合价态的热力学可及性。这些测量结果表明，在电化学实验的时间尺度上，混合价态[（IP 2-）（IP –）Ga] +对于歧化作用并没有显着稳定。电化学观察到的混合价态[（IP 2-）（IP –）E]的热力学稳定性差异通过观察发现，与铝类似物相比，在所有镓络合物中，包含IPπ系统IP的配体平面之间的二面角大约大5°，可以使+合理化。据推测，较大的二面角会通过E-Xσ*轨道在IP的π系统之间提供较弱的电子耦合。或者，观察到的差异可能是“惰性对效应”的结果：在E-Xσ*轨道中收缩的Ga组分也将提供较弱的电子耦合。 |
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