Using para hydrogen induced polarization to study steps in the hydroformylation reaction

A range of iridium complexes, Ir(eta(3)-C3H5)(CO)(PR2R')(2) (1a-1e) [where 1a, PR2R' = PPh3, 1b P(p-tol)(3), 1c PMePh2, 1d PMe2Ph and 1e PMe3] were synthesized and their reactivity as stoichiometric hydroformylation precursors studied. Para-hydrogen assisted NMR spectroscopy detected the following intermediates: Ir(H)(2)(eta(3)-C3H5)(CO)(PR2R') (2a-e), Ir(H) 2(eta(1)-C3H5)(CO)(PR2R')(2) (4d-e), Ir(H)(2)(eta(1)-C3H5)(CO)(2)(PR2R') (10a-e), Ir(H)(2)(CO-C3H5)(CO)(2)(PR2R') (11a-c), Ir(H)(2)(CO-C3H7)(CO)(2)(PR2R') (12a-c) and Ir(H)(2)(CO-C3H5)(CO) (PR2R')(2) (13d-e). Some of these species exist as two geometric isomers according to their multinuclear NMR characteristics. The NMR studies suggest a role for the following 16 electron species in these reactions: Ir(eta(3)-C3H5)(CO)(PR2R'), Ir(eta(1)-C3H5)(CO)(PR2R')(2), Ir(eta(1)-C3H5)(CO)(2)(PR2R'), Ir(CO-C3H5)(CO)(2)(PR2R'), Ir(CO-C3H7)(CO)(2)(PR2R') and Ir(CO-C3H5)(CO)(PR2R')(2). Their role is linked to several 18 electron species in order to confirm the route by which hydroformylation and hydrogenation proceeds.