P-Stereogenic threonine derived Ir–P,N complexes. Reversible cyclometallation and asymmetric hydrogenation reactions

A threonine-derived phosphine-oxazoline iridium catalyst is reported, showcasing excellent selectivity in the hydrogenation of N-Boc-2,3-diarylallylamines. The reversible cyclometallation process between the square planar Ir(I) complex and the corresponding octahedral Ir(III) species is thoroughly investigated, while considering the influence of substitution at the phenyl group of the oxazoline on this equilibrium. X-Ray analysis reveals that the cyclometallated tridentate ligand adopts a fac coordination mode. Furthermore, the catalytic performance of these complexes in the asymmetric hydrogenation is evaluated and the utilization of Ir(III) pre-catalysts or Ir(I)/Ir(III) mixtures in hydrogenation reactions is proposed based on the observed equilibrium dynamics.