A series of mixed P(OR) 3 /NHC Pd complexes was synthesized and fully characterized. The steric properties of both types of ligands were computationally determined using X-ray data. These structural studies clearly show that N-heterocyclic carbenes modulate their bulkiness with respect to the steric requirements of the coligands. Catalytic studies were performed using this new class of complexes for the Suzuki-Miyaura reaction. It was found that alkoxide or hydroxide bases and/or alcohols were necessary to achieve good catalytic activity. Mechanistic studies were undertaken in order to gain insights into the role of alkoxide groups. These studies suggest that alcohols or alkoxide groups play a major role in the activation of the precatalyst to generate the catalytically active species. Catalytic studies proved these systems to be efficient using 0.1 mol % of Pd loading for the coupling of aryl, benzyl, and heterocyclic chlorides with boronic acids.

The [Pd(SIPr)(PCy3)] complex efficiently promotes a tandem process involving dehydrogenation of formic acid and hydrogenation of C-C multiple bonds using H2 formed in situ. The isolation of a key catalytic hydridoformatopalladium species, [Pd{OC(O)H}(H)(IPr)(PCy3)], is reported. The complex plays a key role in the Pd(0)-mediated formation of hydrogen from formic acid. Mechanistic and computational studies delineate the operational role of the palladium complex in this efficient tandem sequence.

An even split: In sharp contrast with the general behavior of Pd0 complexes, [Pd(IPr)(PCy3)] is able to activate the HH bond. The resulting trans‐[Pd(H)2(IPr)(PCy3)] is the first isolated mononuclear dihydride palladium compound. Its formation is supported by multinuclear NMR spectroscopy, density functional calculations, and X‐ray diffraction studies. The stability and reactivity of this new species are examined.magnified image

[Pd(NHC)(PR(3))] complexes were shown to be active catalysts in the dehydrogenation of ammonia borane and the subsequent hydrogenation of unsaturated compounds at very low catalyst loadings (0.05 mol% for some substrates).