Amino‐phosphanes in Rh^I‐Catalyzed Hydroformylation: Hemilabile Behavior of P,N Ligands under High CO Pressure and Catalytic Properties

Abstract

Abstract The catalytic properties of rhodium complexes containing the α‐, β‐, or γ‐amino‐phosphane ligands Ph 2 PCH 2 NEt 2 ( α ‐P,N‐1 ), Ph 2 PCH(Ar)NHPh [ α‐P,N‐2 ; Ar = η 6 ( o ‐C 6 H 4 Cl)Cr(CO) 3 ], Ph 2 PCH 2 NPh 2 ( α ‐P,N‐3 ), Ph 2 PCH 2 CH(Ph)NHPh ( β ‐P,N ), Ph 2 PCH 2 ( o ‐C 6 H 4 –NMe 2 ) ( γ ‐P,N‐1 ), Ph 2 PCH( o ‐C 6 H 4 –CH 2 NHPh) ( γ‐P,N‐2 ), and the α,β‐diamino‐phosphane ligand Et 2 NCH 2 P(Ph)CH 2 CH(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 31 P HPNMR studies in solution show that all P,N ligands adopt exclusively a κ 1 ‐ P coordination mode in rhodium chloride carbonyl complexes under high CO pressure. In the solid state a κ 1 ‐ 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 κ 2 ‐ P , N and κ 1 ‐ 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.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)