Developing five-membered heterocycle substituted phosphinous acids as ligands for palladium-catalyzed Suzuki–Miyaura and Catellani reactions

Abstract

A new category of secondary phosphine oxides (SPOs) (5a–5j) with/without benzo-fused five-membered heterocyclic substituents were prepared. These new compounds are air- and moisture-stable ligands and have the advantage of long-term storage. Some of the ligands as well as ligand coordinated palladium complexes (6f′ and 6f′′) and platinum complexes (7b_trans & 7i_trans) were prepared and their structures were determined using single crystal X-ray diffraction methods. The crystal structure of 6f′ revealed the formation of diamond shape di-palladium complexes with a Pd₂Cl₂ core. As for the structures of 7b_trans & 7i_trans, the processes for the generation of the trans-form of the bis-phosphine ligand coordinated platinum complexes are shown. These SPOs exhibit notable efficiencies in palladium-catalyzed Suzuki–Miyaura reactions. Moreover, organic compounds (9k and 10c) with unexpected conformations were obtained from Heck-type Catellani reactions. Reaction pathways are proposed to accommodate the probable routes for the formation of all organic products.