Palladium (II) complexes with the unsymmetrical H-spirophosphorane ligand HP(OCMe2CMe2O)(OCH2CMe2NH): Synthesis, structural and catalytic studies

We have investigated the reactivity of the unsymmetrical H-spirophosphorane (HSP) ligand HP(OCMe2CMe2O)(OCH2CMe2NH) 1 towards different palladium(II) precursors and synthesised the mononuclear complexes [PdCl2{P(OCMe2CMe2O)OCH2CMe2NH2}] 2 and [PdCl(C3H5){P(OCMe2CMe2O)OCH2CMe2NH2}] 3. The structural features of the compounds are characterised by spectroscopic methods as well as single crystal X-ray diffraction studies. The complexes are shown to be remarkably active precatalysts for the Heck and Hiyama cross-coupling reactions. The products of the C–C bond formation reactions were obtained with high conversion and stereoselectivity. Mechanistic studies of the Heck reaction reveal that, besides homogenous precatalysts, also heterogeneous Pd(0) nanoparticles are involved in the catalytic process.

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► Pd complexes with unsymmetrical H-spirophosphorane ligand as catalyst precursors.
► Remarkably active precatalyst for Heck and Hiyama cross-coupling reactions.
► Homogenous catalyst and Pd nanoparticles formed in situ operate in the Heck reaction.