A Heteroleptic Palladium(II) Complex Containing a Bidentate Carbene/Amido Ligand and 3-(Trifluoromethyl)-5-(2-pyridyl)pyrazolate: Fast Catalyst Activation in the Heck Coupling Reaction

A multicomponent reaction between PdCl2, fppzH, and [(LHH2)-H-1]Cl in the presence of K2CO3 (L = bidentate amido/carbene; fppzH = 3-(trifluoromethyl)-5-(2-pyridyl)pyrazole) allows the preparation of PdL(fppz) in good yield. The analogous platinum complex, however, needs to be prepared by a two-step procedure. The new palladium(II) and platinum(II) complexes were characterized by 1D and 2D NMR spectroscopy, X-ray crystallography, electrospray ionization mass spectrometry, and elemental analyses. X-ray photoelectron spectroscopy indicates the high electron richness of the palladium atoms in PdL(fppz). These palladium complexes are efficient in catalyzing Heck coupling reactions with challenging aryl halide substrates. The catalyst activation in PdL(fppz) is significantly faster than that in cis-PdL2. A mere 0.5 mol % of palladium loading is enough to afford a 82% yield of coupled product from 4-chloroanisole and styrene in 24 h.