Preparation of Secondary Phosphine Oxide Ligands through Nucleophilic Attack on Imines and Their Applications in Palladium‐Catalyzed Catellani Reactions. Issue 19 (19th May 2016)

• Record Type: Journal Article
• Authors: Hu, Chan‐Yu; Chen, Ya‐Qian; Lin, Guan‐Yu; Huang, Ming‐Kai; Chang, Yu‐Chang; Hong, Fung‐E
• Is Part Of: European journal of inorganic chemistry. Issue 19(2016)
• Page Start: 3131
• Page End: 3142
• Publication Date: 2016-05-19
• Subjects: Secondary phosphine oxides -- Ligand design -- Catellani reactions -- C–H activation -- Palladium -- P ligands; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201600181
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract : Several new amino‐type secondary phosphine oxide (SPO) pre‐ligands (3a –3h ) that contain P–N bonds were synthesized and characterized. SPOs3a –3h can tautomerize to phosphinous acids (PA, 3a –3h ) as genuine ligands. The formation of SPOs3a –3h occurred first through nucleophilic attack on the imine carbon atom, then by the addition of RPCl2 (R = Ph, Cy, t Bu, or i Pr), and work‐up under acidic conditions. The P–N bond in the newly prepared SPOs is evident from the crystal structures of SPOs3d and3h . Reactions of SPOs3f, 3g, or3h with Pd(COD)Cl2 (COD = cyclooctadiene) yielded palladium complexes6f, 6g, or6h . In these crystal structures, PAs3f, 3g, and3h act as didentate ligands through P and N donors. Intriguingly, the reaction of SPO3f with Pd(COD)Cl2 also gave rise to palladium complexes7fa, 7fb, and8f . The crystal structures of7fa and7fb show that the palladium atom is chelated by PA3f and coordinated by a phosphine‐like ligand fragmented from SPO3f through C–N bond dissociation. Finally, the syntheses of carbazole derivatives were pursued in Catellani reactions with SPOs3g and3h as pre‐ligands. A mechanism is proposed to account for the catalytic reaction (see the Supporting Information). The optimized conditions for Suzuki reactions using selected SPO ligands are also reported. Abstract : Several new secondary phosphine oxide (SPO) type ligands, 3a –3n, were prepared. In addition, some SPOs as well as coordinated palladium complexes of ligand3f, that is, 7fa, 7fb, and8f, with fascinating bonding modes were characterized by X‐ray diffraction methods. Some of these ligands were chosen to assist in palladium‐catalyzed Catellani reactions.