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

Abstract

We report the convergent reaction pathways between [RhH(PPh 3 ) 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(η 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.