Interplay between Cationic and Neutral Species in the Rhodium-Catalyzed Hydroaminomethylation Reaction

The reactivity of [Rh(CO)2{(R,R)-Ph?BPE}]BF4 (2) toward amine, CO and/or H2 was examined by high-pressure NMR and IR spectroscopy. The two cationic pentacoordinated species [Rh(CO)3{(R,R)-Ph?BPE}]BF4 (4) and [Rh(CO)2(NHC5H10){(R,R)-Ph-BPE}]BF4 (8) were identified. The transformation of 2 into the neutral complex [RhH(CO)2{(R,R)-Ph?BPE}] (3) under hydroaminomethylation conditions (CO/H2, amine) was investigated. The full mechanisms related to the formation of 3, 4 and 8 starting from 2 are supported by DFT calculations. In particular, the pathway from 2 to 3 revealed the deprotonation by the amine of the dihydride species [Rh(H)2(CO)2{(R,R)-Ph?BPE}]BF4 (6), resulting from the oxidative addition of H2 on 2.