Phosphonium-based aminophosphines as bifunctional ligands for sequential catalysis of one-pot hydroformylation-acetalization of olefins

A series of ionic phosphonium-based aminophosphines L1-L3 were prepared and fully characterized, in each of which the involved bifunctional moieties of the phosphine fragment and Lewis acidic phosphonium were linked together by stable chemical bonds and bridged by one N-atom. The molecular structure of the L2-ligated Rh-complex (Rh-L2) indicated that such bifunctionalities were well retained without incompatibility problems. Investigations on co-catalysis over L1-L3 showed that L3 exhibited the best sequential catalysis for both hydroformylation and acetalization. The phosphine fragment in L3 was responsible for hydroformylation together with the Rh-complex and the phosphonium acted as the Lewis acidic catalyst in charge of acetalization. The L3-Rh(acac)(CO)₂ system also exhibited good generality to hydroformylation-acetalization of a wide range of olefins in different alcohols.