Ligand-to-metal ratio controls stereoselectivity: Highly functional-group-tolerant, iridium-based, (E)-selective alkyne transfer semihydrogenation

Herein, we present (E)-selective transfer semihydrogenation of alkynes based on an iridium complex in situ generated from [Ir(COD)Cl]2 and unsymmetrical (bearing two different phosphorous centers), ferrocene-based phosphine ligand utilizing formic acid as a hydrogen donor. Interestingly, ligand-to-metal ratio may be used to control the stereoselectivity process: 1:1 led formation (Z)-alkene major product, whereas 1:2 gave exclusively (E)-alkene. The latter catalytic system is distinguished by its unprecedented chemoselectivity exceptional stereoselectivity, which substantiated broad scope tested substrates, including natural product derivatives. intriguing difference activity between symmetrical ligands was attributed divergent coordination steric hindrance. presented methodology constitutes solution common limitations known systems for semihydrogenation.