Efficient hydroaminomethylation of olefins catalyzed by Rh-complex ligated by P,O-hybrid ligand with chelating effect

Tandem hydroaminomethylation (HAM) represents one of the most important catalytic protocols for the one-pot synthesis of amines using low-cost and widely available olefins, syngas and amines as starting materials. In this work, the applied P,O-hybrid ligand containing phosphino-fragment and carboxylic group [L1, 2-(diphenylphosphino)benzoic acid] could stoichiometrically react with Rh(acac)(CO)₂ to afford a stable Rh-complex of Z [dicarbonyl-2-(diphenylphosphino)benzoato rhodium(I)], wherein the more substantial P,O-chelation derived from L1 as a bidental pincer upon deprotonation as well as the thermodynamically favored six-membered ring structure warranted its stability. It was found that Z could serve as a highly active catalyst to accelerate the reaction rate of each individual step in the HAM, advantageous with the completely inhibited side-reaction of olefin-hydrogenation. The in situ high-pressure FT-IR spectral analysis demonstrated, for the first time, that the involvement of L1 greatly facilitated the formation of two kinds of the active Rh-H intermediates (A′ and A, v 2012 and 2043 cm⁻¹) with well-maintained longevity. And the DFT calculations further confirmed that the Rh-complex of Z exhibited exclusive ability to activate H₂, resulting in the efficient formation of Rh-H intermediates of A′ and A, the later (A) was responsible for rapid olefin-hydroformylation, and the former (A′) was in charge of imine-hydrogenation.