Calcium Hydride Catalyzed Highly 1,2-Selective Pyridine Hydrosilylation
Calcium Hydride Catalyzed Highly 1,2-Selective Pyridine Hydrosilylation
复制标题
DOI：
10.1002/chem.201501072
复制
发表时间：
2015-08-03
影响因子：
4.3
通讯作者：
Harder, Sjoerd
中科院分区：
文献类型：
--
作者：
Intemann, Julia;Bauer, Heiko;Harder, Sjoerd
与相应的氢化镁配合物(DIPPnacnac = [(2,6- ipr (2)C(6)H(3))NC（Me)](2)CH）相比，氢化钙配合物（DIPPnacnac- cahthf）(2)与吡啶的反应速度更快，选择性更强。在一系列吡啶、吡啶和喹啉底物中，观察到氢化物配体完全转移到2位，并且在较高温度下也没有发现1,21,4异构化。异感产物dippnacac - ca（1,2-二氢吡啶）（吡啶）表现出快速的配体交换成同感钙配合物，因此不能被分离。异喹啉氢化钙还原得到性质明确的同感产物Ca（1,2-二氢异喹啉）(2)（异喹啉）(4)和Ca-3（1,2-二氢异喹啉）(6)（异喹啉）(6)。Mg和Ca配合物对吡啶脱芳化反应的选择性差异可以用DFT理论解释，并应用于催化。在氢化钙催化剂下，吡啶与蒎醇硼烷的硼氢化反应转化率很小，而吡啶和喹啉与PhSiH3的硅氢化反应只产生1,2-二氢吡啶和1,2-二氢喹啉硅烷，转化率为80-90%。使用催化剂Ca[N(SiMe3)(2)](2)(THF)(2)也可以获得类似的结果。这些钙配合物代表了吡啶的1,2-选择性硅氢化反应的第一个催化剂。
Reaction of the calcium hydride complex (DIPPnacnac-CaHTHF)(2) with pyridine is much faster and selective than that of the corresponding magnesium hydride complex (DIPPnacnac = [(2,6-iPr(2)C(6)H(3))NC(Me)](2)CH). With a range of pyridine, picoline and quinoline substrates, exclusive transfer of the hydride ligand to the 2-position is observed and also at higher temperatures no 1,21,4 isomerization is found. The heteroleptic product DIPPnacnac-Ca(1,2-dihydropyridide)(pyridine) shows fast ligand exchange into homoleptic calcium complexes and therefore could not be isolated. Calcium hydride reduction of isoquinoline gave well-defined homoleptic products which could be characterized by X-ray diffraction: Ca(1,2-dihydroisoquinolide)(2)(isoquinoline)(4) and Ca-3(1,2-dihydroisoquinolide)(6)(isoquinoline)(6). The striking selectivity difference in the dearomatization of pyridines by Mg or Ca complexes could be explained by DFT theory and was utilized in catalysis. Whereas hydroboration of pyridine with pinacol borane with a calcium hydride catalyst gave only minor conversion, the hydrosilylation of pyridine and quinolines with PhSiH3 yields exclusively 1,2-dihydropyridine and 1,2-dihydroquinoline silanes with 80-90% conversion. Similar results can be achieved with the catalyst Ca[N(SiMe3)(2)](2)(THF)(2). These calcium complexes represent the first catalysts for the 1,2-selective hydrosilylation of pyridines.