Characteristics of organic transformations in a confined dendritic core: studies on the AIBN-initiated reaction of dendrimer cobalt(II) porphyrins with alkynes.
Characteristics of organic transformations in a confined dendritic core: studies on the AIBN-initiated reaction of dendrimer cobalt(II) porphyrins with alkynes.
复制标题
受限树突核中有机转化的特征：AIBN引发的树枝状钴(II)卟啉与炔烃的反应研究。
作者：
M. Uyemura;T. Aida
钴（II）配合物的聚（芳基酯）树枝状大分子卟啉[（m-[Gn]TPP）Co（II）]（代数n=0-4），在偶氮二异丁腈（AIBN）的存在下，在60 ℃，进行烯基化与几个炔的金属中心。观察到[（m-[Gn]TPP）Co（II）]（n=3和4）完全抑制双键迁移（二次转化），这仅产生[（m-[Gn]TPP）Co（III）-C（=CH（2））R]（n=3和4）。[（m-[Gn]TPP）Co（II）]（n=0-3）的总反应速率几乎不依赖于树枝状取代基的大小，而对于最大的树枝状聚合物[（m-[G4]TPP）Co（II）]观察到显著的延迟。纯[（m-[Gn]TPP）Co（III）-C（=CH（2））Bu]（n=0-4）的双键迁移机理研究表明，二次转化涉及[（m-[Gn]TPP）Co（III）H]（n=0-4）的参与，衍生自[（m-[Gn]TPP）Co（II）]和AIBN，而不是单独的[（m-[Gn]TPP）Co（II）]。使用[（m-[Gn]TPP）Co（III）-C（=CH（2））Bu]（n=2-4）与非树枝状[（m-[G 0]TPP）Co（II）]和AIBN组合的交叉实验表明，通过稳健的[G4]-树枝状笼对活性中心具有高水平的空间保护，如m-[G4]TPPH（2）的（1）H NMR脉冲弛豫时间曲线所示。
Cobalt(II) complexes of poly(aryl ester) dendrimer porphyrins [(m-[Gn]TPP)Co(II)] (generation number n=0-4), in the presence of azobisisobutyronitrile (AIBN) at 60 degrees C, underwent alkenylation with several alkynes at the metal center. A complete inhibition of double-bond migration (secondary transformation) was observed for [(m-[Gn]TPP)Co(II)] (n=3 and 4), which gave [(m-[Gn]TPP)Co(III)-C(=CH(2))R] (n=3 and 4) exclusively. Overall reaction rates for [(m-[Gn]TPP)Co(II)] (n=0-3) were hardly dependent on the size of the dendritic substituents, while a notable retardation was observed for the largest dendrimer, [(m-[G4]TPP)Co(II)]. Mechanistic studies on double-bond migration with pure [(m-[Gn]TPP)Co(III)-C(=CH(2))Bu] (n=0-4) demonstrated that the secondary transformation involves participation of [(m-[Gn]TPP)Co(III)H] (n=0-4), derived from [(m-[Gn]TPP)Co(II)] and AIBN, rather than [(m-[Gn]TPP)Co(II)] alone. Crossover experiments using [(m-[Gn]TPP)Co(III)-C(=CH(2))Bu] (n=2-4), in combination with nondendritic [(m-[G0]TPP)Co(II)] and AIBN, indicated a high level of steric protection of the active center by a robust [G4]-dendritic cage, as suggested by a (1)H NMR pulse relaxation time profile of m-[G4]TPPH(2).