Palladium acetate efficiently catalyzes the addition of an H-spirophosphorane (pinacolato)2PH to alkynes to give Markovnikov addition products highly selectively. The addition products can be easily converted to the corresponding alkenylphosphonates and phosphonic acids via simple hydrolysis or thermal decomposition. This new reaction is a general method for the introduction of phosphorus functionality to the internal carbons of terminal alkynes, resolving the problem of the regioselectivity associated with hydrophosphorylation reactions so far reported. Mechanistic studies confirmed that (a) palladium acetate was reduced to metallic palladium by H-spirophosphorane, (b) the P–H bond of H-spirophosphorane could be activated by zero-valent platinum complexes to give the corresponding hydridoplatinum complexes, and (c) an alkenylpalladium species was identified from the reaction of palladium acetate with H-spirophosphorane and diphenylacetylene. These results support a reaction mechanism that palladium acetate was first reduced by H-spirophosphorane to give zero-valent palladium. This zero-valent palladium might insert into the P–H bond of the H-spirophosphorane to give a hydridopalladium species which then added to alkyne via the addition of H–Pd bond to form an alkenylpalladium species with the hydrogen atom added to the terminal carbon of alkynes. Reductive elimination of the alkenylpalladium affords the addition product.
乙酸钯能高效催化H-螺
磷烷(pinacolato)2PH与
炔烃反应,高选择性地得到马氏加成产物。该加成产物通过简单的
水解或热分解即可转化为相应的
烯基
膦酸盐和
膦酸。这一新反应为解决端炔的内
碳原子亲核膦化反应的区域选择性问题提供了一般性的方法。机理研究表明:(a)
乙酸钯被H-螺
磷烷还原为
金属
钯;(b)零价
铂配合物可活化H-螺
磷烷的P-H键,生成相应的
氢铂配合物;(c)
乙酸钯与H-螺
磷烷和
二苯基乙炔反应生成了
烯基
钯物种。这些结果支持下列反应机理:
乙酸钯首先被H-螺
磷烷还原为零价
钯,后者插入H-螺
磷烷的P-H键生成
氢钯物种,该
氢钯物种与
炔烃反应时, H-Pd键加成形成
烯基
钯物种,其中的
氢原子加成到
炔烃的末端
碳原子上,最后经还原消除生成加成产物。