Synthesis and Characterization of Terphenyl Phosphine Ligands and Their Palladium Catalyst Precursors

Abstract

Terphenyl phosphines are rising as powerful supporting ligands for palladium-catalyzed C–N coupling reactions. Sixteen terphenyl phosphines L1–16 with varying electronic and steric properties and their precatalysts of 2′-aminobiphenyl-2-yl-η²-C,N palladium(II) triflates (tP1–16) and allyl palladium triflates (tA1–16) were synthesized and characterized by ¹H, ¹³C, and ³¹P nuclear magnetic resonance (NMR) spectroscopy, and the complexes [(L3)(2′-aminobiphenyl-2-yl-η²-C,N)Pd]OTf (tP3), [(L7)(2′-aminobiphenyl-2-yl-η²-C,N)Pd]OTf (tP7), and [(L4)(allyl)Pd]OTf (tA4) were confirmed by single-crystal X-ray diffraction. The cross-coupling of 4-chloroanisole and 4-methoxyphenyl amine by tP1–16 suggests that the combination of 2,4,6-triisopropyl groups on the terphenyl skeleton and the two cyclohexyl groups on the phosphorus atoms is important for the excellent catalytic performance of the palladium-catalyzed C–N cross-coupling reaction.