Amino-phosphanes in Rh(I)-catalyzed hydroformylation: hemilabile behavior of P,N ligands under high CO pressure and catalytic properties

International audienceThe catalytic properties of rhodium complexes containing the α-, β-, or γ-amino-phosphane ligands Ph2PCH2NEt2 (α-P,N-1), Ph2PCH(Ar)NHPh [α-P,N-2; Ar = η6(o-C6H4Cl)Cr(CO)3], Ph2PCH2NPh2 (α-P,N-3), Ph2PCH2CH(Ph)NHPh (β-P,N), Ph2PCH2(o-C6H4–NMe2) (γ-P,N-1), Ph2PCH(o-C6H4–CH2NHPh) (γ-P,N-2), and the α,β-diamino-phosphane ligand Et2NCH2P(Ph)CH2CH(Ph)NHPh (α,β-N,P,N), in styrene hydroformylation have been examined. The results show that the activity increases when the number of backbone carbon atoms linking P and N decreases from 3 to 1. IR and 31P HPNMR studies in solution show that all P,N ligands adopt exclusively a κ1-P coordination mode in rhodium chloride carbonyl complexes under high CO pressure. In the solid state a κ1-P-α-amino-phosphane coordination has been ascertained by X-ray methods in trans-[RhCl(CO)(γ-P,N-1)2]. In contrast, an equilibrium between the κ2-P,N and κ1-P-coordination modes has been observed as a function of the CO pressure for the complex containing the β-P,N ligand. The basicity of the dangling amino group also plays an important role on the catalytic activity and a mechanism involving the nitrogen function in the catalytic cycle is proposed