Diastereoselective Assembly of Helicates Incorporating a Hexadentate Chiral Scaffold
Diastereoselective Assembly of Helicates Incorporating a Hexadentate Chiral Scaffold
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结合六齿手性支架的螺旋的非对映选择性组装
DOI：
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发表时间：
2010
期刊：
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通讯作者：
Jennifer A. Zampese
中科院分区：
文献类型：
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作者：
E. Constable;Guoqi Zhang;C. Housecroft;M. Neuburger;Jennifer A. Zampese
对映纯(1R,2R)-(-)-1,2-二氨基环己烷与两个当量的2,2 ' -联吡啶-6-乙醛缩合，然后用NaBH4还原，可以很容易地合成对映纯六齿配体（R，R）-3。（R，R）-3中的每个三齿金属结合域都表现出一定程度的灵活性，这是由胺氮中心的反转和N-C和C-C单键的旋转引起的。这导致形成M-[M{(R，R)-3}]2+或P-[M{(R，R)-3}]2+。铜（II）、铁（II）和锌（II）配合物（R，R）-3的固态结构均表现出对M-[M{(R，R)-3}]2+的偏好。在溶液中，[Fe{(R，R)-3}]2+主要以一种非对映异构体存在（假设为m型）。M-型优于p -型的原因是：在M-型中，nh1和环己烷-1,2-二烷基CH氢原子具有有利的反构型，而在p -型中具有不利的同构构型。当（R，R）-3的希夫碱类似物（R，R）-4与锌（II）或银(I)结合时，具有m -手性的[2+2]双螺旋在固态中聚集。与（S，S）-4一起，铁（II）也组装成具有m手性的双核双螺旋结构。在溶液中观察到完全立体选择性，核磁共振光谱数据表明存在一种非对映异构体。对双核螺旋构型的偏爱可以追溯到配体从3（饱和主链）到4（不饱和亚胺主链）的柔韧性下降。
The condensation of enantiopure (1R,2R)-(–)-1,2-diaminocyclohexane with two equivalents of 2,2′-bipyridine-6-carbaldehyde followed by reduction with NaBH4 allows the facile synthesis of the enantiopure hexadentate ligand (R,R)-3. Each tridentate metal-binding domain in (R,R)-3 exhibits a degree of flexibility arising from inversion at the amine nitrogen centre and rotation about N–C and C–C single bonds. This leads to the formation of either M-[M{(R,R)-3}]2+ or P-[M{(R,R)-3}]2+. The solid-state structures of the copper(II), iron(II) and zinc(II) complexes of (R,R)-3 all show a preference for M-[M{(R,R)-3}]2+. In solution, [Fe{(R,R)-3}]2+ exists predominantly as one diastereoisomer (assumed to be the M-form). The preference for the M- over P-form is rationalized in terms of a favourable anti configuration of the NH and cyclohexane-1,2-diyl CH hydrogen atoms in the M-form, and an unfavourable syn-configuration in the P-form. When (R,R)-4, the Schiff base analogue of (R,R)-3, combines with zinc(II) or silver(I), [2+2] double helicates with M-chirality assemble in the solid state. With (S,S)-4, iron(II) also assembles into a dinuclear, double helicate with M-handedness. Complete stereoselectivity is observed in solution with NMR spectroscopic data indicating the presence of one diastereoisomer. The preference for a dinuclear over mononuclear helicate can be traced to a decrease in ligand flexibility on going from 3 (saturated backbone) to 4 (unsaturated imine backbone).