Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry, UK CV4 7AL.
Dalton Trans. 2011 Oct 28;40(40):10416-33. doi: 10.1039/c1dt10588d. Epub 2011 Jul 11.
One-pot reactions of 2-pyridinecarboxaldehyde, chiral phenylethanamines and Fe(II) give single diastereomer fac diimine complexes at thermodynamic equilibrium so that no chiral separations are required (d.r. > 200 : 1). The origins of this stereoselectivity are partly steric and partly a result of the presence of three sets of inter-ligand parallel-offset π-stacking interactions. Mn(II), Co(II), Co(III), Ni(II) and Zn(II) give similar fac structures, alongside the imidazole analogues for Fe(II). While most of the complexes are paramagnetic, the series of molecular structures allows us to assess the influence of the π-stacking present, and there is a strong correlation between this and the M-N bond length. Fe(II) is close to optimal. For the larger Zn(II) ion, very weak π-stacking leads to poorer measured stereoselectivity (NMR) but this is improved with increased solvent polarity. The mechanism of stereoselection is further investigated via DFT calculations, chiroptical spectroscopy and the use of synthetic probes.
一锅法反应 2-吡啶甲醛、手性苯乙胺和 Fe(II)，在热力学平衡时得到单一非对映异构体的面式二亚胺配合物，因此无需进行手性分离（dr>200:1）。这种立体选择性的起源部分是空间位阻的，部分是由于存在三组配体平行交错的π堆积相互作用。Mn(II)、Co(II)、Co(III)、Ni(II)和 Zn(II) 也得到了类似的面式结构，以及 Fe(II)的咪唑类似物。虽然大多数配合物都是顺磁性的，但这一系列分子结构使我们能够评估存在的π堆积的影响，并且这与 M-N 键长之间存在很强的相关性。Fe(II)接近最佳。对于较大的 Zn(II)离子，非常弱的π堆积导致较差的立体选择性（NMR），但随着溶剂极性的增加，这种情况得到改善。通过密度泛函理论计算、圆二色光谱和使用合成探针进一步研究了立体选择性的机制。
