Navarro Miquel, Smith Christene A, Albrecht Martin
Department of Chemistry and Biochemistry, University of Bern , Freiestrasse 3, CH-3012 Bern, Switzerland.
Inorg Chem. 2017 Oct 2;56(19):11688-11701. doi: 10.1021/acs.inorgchem.7b01654. Epub 2017 Sep 12.
A set of aryl-substituted pyridylideneamide (PYA) ligands with variable donor properties owing to a pronounced zwitterionic and a neutral diene-type resonance structure were used as electronically flexible ligands at a pentamethylcyclopentadienyl (Cp*) iridium center. The straightforward synthesis of this type of ligand allows for an easy incorporation of donor substituents such as methoxy groups in different positions of the phenyl ring of the C,N-bidentate chelating PYA. These modifications considerably enhance the catalytic activity of the coordinated iridium center toward the catalytic aerobic transfer hydrogenation of carbonyls and imines as well as the hydrosilylation of phenylacetylene. Moreover, these PYA iridium complexes catalyze the base-free transfer hydrogenation of aldehydes, and to a lesser extent also of ketones. Under standard transfer hydrogenation conditions including base, aldehydes are rapidly oxidized to carboxylic acids rather than reduced to the corresponding alcohol, as is observed under base-free conditions.
由于具有明显的两性离子和中性二烯型共振结构，一组具有可变给体性质的芳基取代吡啶叉酰胺（PYA）配体被用作五甲基环戊二烯基（Cp*）铱中心的电子柔性配体。这类配体的直接合成使得在C，N - 双齿螯合PYA的苯环不同位置容易引入供电子取代基，如甲氧基。这些修饰显著增强了配位铱中心对羰基和亚胺的催化需氧转移氢化以及苯乙炔的硅氢化反应的催化活性。此外，这些PYA铱配合物催化醛的无碱转移氢化反应，对酮的催化作用较小。在包括碱的标准转移氢化条件下，醛会迅速氧化为羧酸而不是还原为相应的醇，这与无碱条件下的情况不同。
