N,O- vs N,C-Chelation in Half-Sandwich Iridium Complexes: A Dramatic Effect on Enantioselectivity in Asymmetric Transfer Hydrogenation of Ketones
作者:Gang Zhou、Ahmed H. Aboo、Craig M. Robertson、Ruixia Liu、Zhenhua Li、Konstantin Luzyanin、Neil G. Berry、Weiping Chen、Jianliang Xiao
DOI:10.1021/acscatal.8b02068
日期:2018.9.7
to a N,C- or N,O-chelated Cp*Ir(III) complex, depending on whether or not water was present in the reaction. While derived from the same precursor, these two complexes behaved in a dramatically different manner in asymmetric transfer hydrogenation (ATH) of ketones by formic acid, with the N,O-chelated complex being much more selective and active. The sense of asymmetric induction is also different, with
[Cp * IrCl 2 ] 2的环金属化在NaOAc存在下与(S)-2-苯基-4,5-二氢恶唑-4-羧酸甲酯一起选择性地导致N,C-或N,O螯合的Cp * Ir(III)络合物,具体取决于反应中没有水。尽管这两种配合物均来自相同的前体,但在甲酸的酮的不对称转移氢化(ATH)中表现出明显不同的方式,其中N,O螯合的配合物具有更高的选择性和活性。不对称感应的感觉也不同,N,O-络合物提供S,而N,C-类似物R醇。进一步的研究表明,基础添加剂的性质极大地影响对映选择性和有效的HCOOH /胺比。这些观察结果表明配体配位模式和为ATH反应使用正确的碱基的重要性。