Mechanism of Coordination-site Exchange Reaction of the Cobalt(III) Complexes Containing Multidentate Ligands

[Co（edda）（en）]^+、[Co（edda）（gly）]、[Co（edda）（beta-ala）]和[Co（eddp）（en）]^+配合物的异构体被制备和光学拆分。通过吸收光谱、圆二色谱、~ 1H-NMR和~ 1C-NMR数据以及部分X射线分析研究了这些配合物的立体化学<13>。[Co（eddp）（en）]^+的两个β异构体β（e-1）和β（e-2）是由于配位eddp配体中一个不对称N原子手性不同而产生的非对映异构体。在[Co（edda）（en）]&lt;@D1+@&gt;D1体系中，LAMBDA（R）-β异构体异构化为光学纯度（o. p.）为约百分之四十五在[Co（edda）（gly）]的三种异构体的反应中，LAMBDA（R）-beta-fac（O）异构化为LAMBDA（R）-betamer（O）（o. p.：约100%）和LAMBDA（S，S）-α-聚体（O）（o. p.：约33%），LAMBDA（R）-β-聚体（O）至LAMBDA（R） 关于我们 - β-fac（O）（o.p.：约65%）和LAMBDA（S，S）-α-聚体（O）（o. p.：约40%）和LAMBDA（S，S）-α-mer（O）至LAMBDA（R）-β-fac（O）（o.p.：约50%）和LAMBDA（R）-β-mer（O）（o. p.：约65%）。[Co（edda）（beta-ala）]体系的异构化行为与[Co（edda）（gly）]体系相似，不同之处在于beta-fac（O）* beta-mer（O）的立体选择性较低。在[Co（eddp）（en）]&lt;@D1+@&gt;D1体系中，β（e-1）（] SY. [）β（E-2）变化是在配位eddp的面内β-丙氨酸环上的不对称sec-N原子上发生的反转反应，反应速率较慢。alpha（] SY.tautm. [）β（e-1，或2）变化（配位位点交换反应）是立体选择性的：LAMBDA（R，R）-α * LAMBDA（S，S）-β（e-1）（o. p.：约40%），LAMBDA（R，R）-α * LAMBDA（S，R）-β（e-2）（o.p.：约45%）。这些结果被解释的基础上的Co-O键断裂机制：的edda或eddp配体的sec-N和O原子之间的配位交换发生占主导地位，因此，在sec-N中心的不对称性被逆转。少

The isomers of the [Co(edda)(en)]^+, [Co(edda)(gly)], [Co(edda)(beta-ala)], and [Co(eddp)(en)]^+ complexes were prepared and optically resolved. The stereochemistry of these complexes was studied on the basis of absorption, CD, ^1H-NMR and ^<13>C-NMR data and partially on the basis of X-ray analysis. Two beta isomers, beta(e-1) and beta(e-2), of [Co(eddp)(en)]^+ were comformational diastereomers arising from a difference of the chirality around one of the asymmetric N atoms in a coordinated eddp ligand.Coordination-site exchange (isomerization and racemization) reactions of the complexes described above were studied in a basic aqueous solution. In the [Co(edda)(en)]<@D1+@>D1 system, LAMBDA(R)-beta isomer isomerized to LAMBDA(S,S)-alpha isomer with an optical purity (o.p.) of ca. 45%. In the reactions of three isomers of [Co(edda)(gly)], LAMBDA(R)-beta-fac(O) isomerized to LAMBDA(R)-betamer(O) (o.p.:ca.100%) and LAMBDA(S,S)-alpha-mer(O) (o.p.:ca. 33%), LAMBDA(R)-beta-mer(O) to LAMBDA(R) … More -beta-fac(O) (o.p.:ca.65%) and LAMBDA(S,S)-alpha-mer(O) (o.p.: ca.40%), and LAMBDA(S,S)-alpha-mer(O) to LAMBDA(R)-beta-fac(O) (o.p.:ca.50%) and LAMBDA(R)-beta-mer(O) (o.p.:ca.65%). The isomerization behavior of the [Co(edda)(beta-ala)] system was similar to that of the [Co(edda)(gly)] system except for the low stereoselectivity of the beta-fac(O) * beta-mer(O) change. In the [Co(eddp)(en)]<@D1+@>D1 system, the beta(e-1) (] SY.tautm.[) beta(E-2) change was an inversion reaction at the asymmetric sec-N atom in the in-plane beta-alaninate ring of the coordinated eddp, and the rate was slow. The alpha (] SY.tautm.[) beta(e-1,or2) change (coordination-site exchange reaction) was stereoselective: LAMBDA(R,R)-alpha * LAMBDA(S,S)-beta(e-1) (o.p.:ca.40%), LAMBDA(R,R)-alpha * LAMBDA(S,R)-beta(e-2) (o.p.:ca.45%). These results were explained on the basis of a Co-O bond rupture mechanism: the coordination-site exchange between the sec-N and O atoms of the edda or eddp ligand occurred predominantly; consequently, the asymmetry at the sec-N center was inverted. Less