Amino-phosphanes in RhI-Catalyzed Hydroformylation: Hemilabile Behavior of P,N Ligands under High CO Pressure and Catalytic Properties

The catalytic properties of rhodium complexes containing the ?-, ?-, or ?-amino-phosphane ligands Ph2PCH2NEt2 (?-P,N- 1), Ph2PCH(Ar)NHPh [?-P,N-2; Ar = ?6(o-C6H4Cl)Cr(CO)3], Ph2PCH2NPh2 (?-P,N-3), Ph2PCH2CH(Ph)NHPh (?-P,N), Ph2PCH2(o-C6H4-NMe2) (?-P,N-1), Ph2PCH(o-C6H4-CH2NHPh) (?-P,N-2), and the ?,?-diamino-phosphane ligand Et2NCH2P(Ph)CH2CH(Ph)NHPh (?,?-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 k1-P coordination mode in rhodium chloride carbonyl complexes under high CO pressure. In the solid state a ?1-P-?-amino-phosphane coordination has been ascertained by X-ray methods in trans-[RhCl(CO)(?-P,N-1)2]. In contrast, an equilibrium between the ?2-P,N and ?1-P-coordination modes has been observed as a function of the CO pressure for the complex containing the ?-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.