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Ambidentate bonding and electrochemical implications of pincer-type pyridylidene amide ligands in complexes of nickel, cobalt and zinc.
Dalton Transactions ( IF 4 ) Pub Date : 2020-08-21 , DOI: 10.1039/d0dt02482a
Philipp Melle 1 , Nathalie Ségaud 1 , Martin Albrecht 1
Affiliation  

Pincer-type tridentate pyridyl bis(pyridylidene amide) (pyPYA2) ligand systems were coordinated to the Earth-abundant first row transition metals nickel, cobalt and zinc. A one-pot synthesis in water/ethanol afforded octahedral homoleptic bis-PYA complexes, [M(pyPYA2)2](PF6)2, whereas five-coordinate mono-PYA dichloride complexes, [M(pyPYA2)Cl2], were obtained upon slow addition of the ligand to the metal chlorides in DMF. Electrochemical measurements further revealed a facile oxidation of the metal centers from Ni2+ to Ni4+ and Co2+ to Co3+, respectively, while the Zn2+ system was redox inactive. These experiments further allowed for quantification of the much stronger electron donor properties of neutral N,N,N-tridentate pyPYA2 pincer ligands as compared to terpy. Remarkably, ortho-PYA pincer ligands feature amide coordination to the metal center via oxygen or nitrogen. This ambidentate ligand binding constitutes another mode of donor flexibility of the PYA ligand system, complementing the resonance structure dynamics established previously. NMR spectroscopic and MS analysis reveal that the meta-PYA ligand undergoes selective deuteration when coordinated to cobalt. This reactivity suggests the potential of this ligand as a transient proton reservoir for HX bond activation and, moreover, indicates the relevance of several resonance structures and therefore supports the notion that meta-PYA ligands are mesoionic.

中文翻译:

镍,钴和锌络合物中的钳型吡啶亚酰胺配体的精确键合和电化学含义。

钳型三齿吡啶基双(亚吡啶基酰胺)(pyPYA 2)配体体系与地球上第一排过渡金属镍,钴和锌配位。在水/乙醇中一锅合成得到八面体均相双-PYA配合物[M(pyPYA 22 ](PF 62,而五配位单-PYA二氯化物配合物[M(pyPYA 2)Cl 2 ]通过将配体缓慢加到DMF中的金属氯化物上得到α,β。电化学测量进一步揭示了金属中心从Ni 2+到Ni 4+以及Co 2+到Co 3+的容易氧化,而Zn 2+系统是氧化还原惰性的。这些实验还允许定量与中毒相比,中性NNN-三齿的pyPYA 2钳型配体的更强的电子供体性质。值得注意的是,-PYA钳形配体的特征是酰胺通过氧或氮与金属中心配位。这种歧义的配体结合构成了PYA配体系统供体柔性的另一种模式,补充了先前建立的共振结构动力学。NMR光谱和质谱分析表明,该-PYA配体与钴配位时会经历选择性氘化。该反应性表明该配体作为HX键活化的瞬时质子储库的潜力,此外,表明了几种共振结构的相关性,因此支持间位-PYA配体是介离子的。
更新日期:2020-09-22
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