Simple Alkaline-Earth Metal Catalysts for Effective Alkene Hydrogenation
Simple Alkaline-Earth Metal Catalysts for Effective Alkene Hydrogenation
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DOI：
10.1002/anie.201810026
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发表时间：
2018-11-12
影响因子：
16.6
通讯作者：
Harder, Sjoerd
中科院分区：
文献类型：
--
作者：
Bauer, Heiko;Alonso, Mercedes;Harder, Sjoerd
碱土金属酰胺（AeN“（2）：Ae = Ca，Sr，Ba，N "= N（SiMe 3）（2））催化烯烃氢化（80-120 ℃，1-6巴H-2，1-10摩尔%催化剂），活性随金属尺寸而增加。可以还原各种活化的C=C键（苯乙烯、p-MeO-苯乙烯、α-Me-苯乙烯、Ph 2C = CH 2、反式-芪、环己二烯、1-Ph-环己烯）、半活化的C=C键（Me 3SiCH = CH 2、降冰片二烯）或非活化的（分离的）C= C键（异戊烯、4-乙烯基环己烯、1-己烯）。结果表明，中性Ca或Ba催化剂在具有挑战性的孤立双键的氢化中具有活性。对于活化的烯烃（例如苯乙烯），由于高反应性苄基中间体被N "H（在催化剂引发中形成）快速质子化，聚合被完全抑制。首次报道了以环己二烯为氢源，Ae金属催化的氢转移氢化反应。用CaN“（2）对苯乙烯加氢反应的DFT计算表明，苯乙烯齐聚反应与苯乙烯加氢反应存在竞争.计算还表明，质子化的苄基钙中间体与N“' H是一个低能量的逃逸路线，从而避免低聚。
Alkaline earth metal amides (AeN ''(2): Ae = Ca, Sr, Ba, N '' = N(SiMe3)(2)) catalyze alkene hydrogenation (80-120 degrees C, 1-6 bar H-2, 1-10 mol% cat.), with the activity increasing with metal size. Various activated C=C bonds (styrene, p-MeO-styrene, alpha-Me-styrene, Ph2C=CH2, trans-stilbene, cyclohexadiene, 1-Ph-cyclohexene), semi-activated C=C bonds (Me3SiCH=CH2, norbornadiene), or non-activated (isolated) C= C bonds (norbornene, 4-vinylcyclohexene, 1-hexene) could be reduced. The results show that neutral Ca or Ba catalysts are active in the challenging hydrogenation of isolated double bonds. For activated alkenes (e.g. styrene), polymerization is fully suppressed due to fast protonation of the highly reactive benzyl intermediate by N '' H (formed in the catalyst initiation). Using cyclohexadiene as the H source, the first Ae metal catalyzed H-transfer hydrogenation is reported. DFT calculations on styrene hydrogenation using CaN ''(2) show that styrene oligomerization competes with styrene hydrogenation. Calculations also show that protonation of the benzylcalcium intermediate with N '' H is a low-energy escape route, thus avoiding oligomerization.