Badiei Yosra M, Jiang Yunbo, Widger Leland R, Siegler Maxime A, Goldberg David P
Department of Chemistry, Johns Hopkins University, Baltimore, Maryland, 21218, USA.
Inorganica Chim Acta. 2012 Mar 15;382:19-26. doi: 10.1016/j.ica.2011.09.056.
Treatment of an unsymmetrical bis(imino)pyridyl-thiolate zinc(II) complex [Zn(II)(LN(3)S)(OTf)] (1) with LiAlH(4) results in the double reduction of the two imino groups in the ligand backbone, and at the same time causes a rare transmetalation reaction to occur. The products formed in this reaction are two novel aluminium(III) bis(amido)pyridyl-thiolate complexes [(R,S/S,R-[Al(III)(LH(2)N(3)S)(THF)] (2a) and [(R,R/S,S-[Al(III)(LH(2)N(3)S)(THF)] (2b), which are diastereomers of each other. These complexes have been characterized by single-crystal X-ray diffraction and (1)H NMR spectroscopy. Single crystal X-ray structure analysis shows that the Al(III) ion is bound in an almost idealized square pyramidal geometry in 2a, while being held in a more distorted square pyramidal geometry in 2b. The major difference between 2a and 2b arises in the orientation of the terminal methyl groups of the ligand backbone in relation to the Al(III)N(3)S plane. These two complexes are crystallized at different temperatures (room temperature vs -35 °C), allowing for their separate isolation. Structural analysis shows that these complexes are reduced by the formal addition of one hydride ion to each imino group, resulting in a deprotonated bis(amido)pyridyl-thiolate ligand. A detailed analysis of metrical parameters rules out the possibility of pure one- or two-electron reduction of the π-conjugated bis(imino)pyridine framework. (1)H NMR spectra reveal a rich pattern in solution indicating that the solution state structures for 2a and 2b match those observed in the solid-state crystal structures, and reveal that both complexes are severely conformationally restricted. Direct organic synthetic methods failed to produce the reduced bis(amino)pyridyl-thiol ligand in pure form, but during the course of these efforts an unusual unsymmetrical aminopyridyl ketone, 1-(6-(1-(2,6-diisopropylphenylamino)ethyl)pyridin-2-yl)ethanone was synthesized in good yield and can be used as a possible precursor for further ligand development.
用氢化铝锂（LiAlH₄）处理不对称双（亚氨基）吡啶硫醇锌（II）配合物[Zn(II)(LN(3)S)(OTf)]（1），会导致配体主链中的两个亚氨基发生双还原反应，同时引发罕见的金属转移反应。该反应生成的产物是两种新型铝（III）双（酰胺基）吡啶硫醇配合物[(R,S/S,R-[Al(III)(LH(2)N(3)S)(THF)]（2a）和[(R,R/S,S-[Al(III)(LH(2)N(3)S)(THF)]（2b），它们是彼此的非对映异构体。这些配合物已通过单晶X射线衍射和¹H NMR光谱进行了表征。单晶X射线结构分析表明，Al(III)离子在2a中以几乎理想化的四方锥几何构型配位，而在2b中以更扭曲的四方锥几何构型配位。2a和2b之间的主要差异在于配体主链末端甲基相对于Al(III)N(3)S平面的取向。这两种配合物在不同温度下结晶（室温与-35°C），从而得以分别分离。结构分析表明，这些配合物通过向每个亚氨基正式添加一个氢负离子而被还原，生成去质子化的双（酰胺基）吡啶硫醇配体。对测量参数的详细分析排除了π共轭双（亚氨基）吡啶骨架发生纯单电子或双电子还原的可能性。¹H NMR光谱显示溶液中有丰富的图谱，表明2a和2b的溶液态结构与固态晶体结构中观察到的结构相符，并表明两种配合物在构象上都受到严重限制。直接的有机合成方法未能以纯形式制备出还原的双（氨基）吡啶硫醇配体，但在这些尝试过程中，一种不寻常的不对称氨基吡啶酮，1-(6-(1-(2,6-二异丙基苯基氨基)乙基)吡啶-2-基)乙酮以良好的产率合成出来，可作为进一步配体开发的可能前体。
