Iron-Catalyzed Dehydrocoupling/Dehydrogenation of Amine-Boranes
Iron-Catalyzed Dehydrocoupling/Dehydrogenation of Amine-Boranes
复制标题
DOI：
10.1021/ja410129j
复制
发表时间：
2014-02-26
影响因子：
15
通讯作者：
Manners, Ian
中科院分区：
文献类型：
--
作者：
Vance, James R.;Schaefer, Andre;Manners, Ian
人们发现，容易获得的铁羰基配合物 [CpFe(CO)(2)](2) (1) 和 CpFe(CO)(2)I (2) (Cp = eta-C5H5) 是胺-硼烷 Me2NH 中心点 BH3 (3) 脱氢偶联/脱氢的有效预催化剂，得到环二硼烷 [Me2N-BH2](2) (4)、在环境温度下进行UV光照射。通过 B-11 NMR 光谱对反应混合物进行的原位分析表明，在每种情况下都存在不同的两步机制。因此，预催化剂 1 通过氨基硼烷 Me2N=BH2 (5) 将 3 脱氢偶联，然后通过脱金属工艺环二聚化得到 4。相比之下，与预催化剂 2 的反应通过 Me2NH-BH2-NMe2-BH3 (6) 作为关键中间体进行，在第二个金属介导步骤后得到 4 作为最终产物。相关络合物 Cp2Fe2(CO)(3)(MeCN) (7) 是由 1 在 MeCN 中光照射形成的，被发现是一种活性更高的脱氢偶联催化剂，不需要光活化，但通过类似于 1 的两步机制进行操作。值得注意的是，详细的机理研究表明，由预催化剂 7 生成的活性催化剂本质上是非均相的，并且由小的铁纳米粒子组成（
The readily available iron carbonyl complexes, [CpFe(CO)(2)](2) (1) and CpFe(CO)(2)I (2) (Cp = eta-C5H5), were found to be efficient precatalysts for the dehydrocoupling/ dehydrogenation of the amine-borane Me2NH center dot BH3 (3) to afford the cyclodiborazane [Me2N-BH2](2) (4), upon UV photoirradiation at ambient temperature. In situ analysis of the reaction mixtures by B-11 NMR spectroscopy indicated that different two-step mechanisms operate in each case. Thus, precatalyst 1 dehydrocoupled 3 via the aminoborane Me2N=BH2 (5) which then cyclodimerized to give 4 via an off-metal process. In contrast, the reaction with precatalyst 2 proceeded via Me2NH-BH2-NMe2-BH3 (6) as the key intermediate, affording 4 as the final product after a second metal-mediated step. The related complex Cp2Fe2(CO)(3)(MeCN) (7), formed by photoirradiation of 1 in MeCN, was found to be a substantially more active dehydrocoupling catalyst and not to require photoactivation, but otherwise operated via a two-step mechanism analogous to that for 1. Significantly, detailed mechanistic studies indicated that the active catalyst generated from precatalyst 7 was heterogeneous in nature and consisted, of small iron nanoparticles (