Synthesis and Reactivity of Neutral Palladium(II) Alkyl Complexes that Contain Phosphinimine-Arenesulfonate Ligands

The synthesis and characterization of ortho-phosphiniminium-arenesulfonate zwitterions 1a-1d, the corresponding sodium salts 3a-3d, methyl(pyridine)palladium-(II) complex 4a, and methyl(4-tert-butylpyridine)palladium-(II) 5a-5d complexes are reported. Complex 4a suffers from limited solubility in aromatic hydrocarbons, while 5a-5d are soluble in benzene and toluene. Complex 5a forms a tridentate orthopalladated species 6a upon heating to 80 degrees C in toluene. Introduction of alkyl substituents on the phosphinimine phosphorus atom retards orthopalladation, and the (Bu-n)(3)P functionalized complex 5d does not undergo orthopalladation after heating at 80 degrees C for 24 h. The Pd-C bond in the orthopalladated complex 6a is inert toward ethylene insertion. Complexes 5a-5d do not react with ethylene at 80 degrees C and decompose to Pd-0 and zwitterions 1a-1d.