Convergent (De)Hydrogenative Pathways via a Rhodium α-Hydroxylalkyl Complex

We report the convergent reaction pathways between [RhH(PPh₃)₄] and POP ketone (1) and alcohol (2) ligands that terminate in the formation of an α-hydroxylalkyl rhodium(I) complex (3), representing two halves of a formal reduction/oxidation pathway between 1 and 2. In the case of hydride transfer to 1, the formation of the α-hydroxylalkyl rhodium(I) complex (3) proceeds via a rare hydrido(²-carbonyl) complex (4). C-H activation in 2 at the proligand's central methine position, rather than O-H activation of the hydroxy motif, followed by loss of dihydrogen also generates the α-hydroxylalkyl rhodium(I) complex (3). The validity of the postulated reaction pathways is probed with DFT calculations. The observed reactivity supports α-hydroxylalkyl complexes as competent intermediates in ketone hydrogenation catalyzed by rhodium hydrides and suggest that ligands 1 and 2 may be "noninnocent" coligands in reported hydrogenation catalyst systems in which they are utilized.