Understanding the Origin of the Regioselectivity in Cyclopolymerizations of Diynes and How to Completely Switch It
Understanding the Origin of the Regioselectivity in Cyclopolymerizations of Diynes and How to Completely Switch It
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DOI：
10.1021/jacs.7b11968
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发表时间：
2018-01-17
影响因子：
15
通讯作者：
Baik, Mu-Hyun
中科院分区：
文献类型：
--
作者：
Jung, Hoimin;Jung, Kijung;Baik, Mu-Hyun
已知格拉布型烯烃复分解催化剂可使1,6-庚二炔进行环聚合，得到含有五元或六元碳环的共轭多烯。虽然以前在五元环的形成中观察到高达bbb99:1的高区域选择性，但既不可能故意获得具有相似选择性水平的六元环，也不理解为什么某些催化剂选择性地表现出这种选择性。结合实验和计算方法，什么控制这些环聚合的区域化学提出了一个新的和一般的理论。钌基费雪碳烯的电子需求被发现天生倾向于形成五元环。通过加强钌的三角-双锥体结构来降低卡宾的亲电性，其中更强的pi-反给体增加了卡宾上的电子密度，预计会逆转区域选择性。随后的实验为新概念提供了强有力的支持，并且可以将区域选择性完全切换到比率
Grubbs-type olefin metathesis catalysts are known to cyclopolymerize 1,6-heptadiynes to afford conjugated polyenes containing five- or six-membered carbocycles. Although high levels of regioselectivity up to >99:1 were observed previously for the formation of five-membered rings, it was neither possible to deliberately obtain six-membered rings at similar levels of selectivity nor understood why certain catalysts showed this selectively. Combining experimental and computational methods, a novel and general theory for what controls the regiochemistry of these cyclopolymerizations is presented. The electronic demands of the ruthenium-based Fischer carbenes are found to innately prefer to form five-membered rings. Reducing the electrophilicity of the carbene by enforcing a trigonal-bipyramidal structure for the ruthenium, where stronger pi-backdonation increases the electron density on the carbene, is predicted to invert the regioselectivity. Subsequent experiments provide strong support for the new concept, and it is possible to completely switch the regioselectivity to a ratio of