Modulating Sonogashira Cross‐Coupling Reactivity in Four‐Coordinate Nickel Complexes by Using Geometric Control

Abstract

AbstractHerein, we present the synthesis of nickel complexes with tripodal phosphine ligands, CH3Si(CH2PPh2)3 and CH3C(CH2PPh2)3, and their application as catalysts in Sonogashira cross‐coupling reactions in water. Although both types of nickel complexes are based on similar tripodal ligands, the Si‐derived compounds adopt stable tetrahedral coordination geometries, whereas the C‐derived counterparts adopt a square‐planar coordination environment. This structural and electronic difference has an important effect on the catalytic properties of the complexes. Our study demonstrates that C‐derived complexes are catalytically inactive, whereas the complexes [CH3Si(CH2PPh2)3NiX2] (X = Cl–, Br–) are competent catalysts for cross‐coupling reactions of aryl halides with phenylacetylenes. This investigation reveals the importance of structural tuning on catalysis and strongly supports the theory that tetrahedral (PR3)2NiCl2 complexes are the active species in Sonogashira cross‐coupling reactions.