Pd/S cooperativity: from stoichiometric activation of Si−H bonds to catalytic hydrosilylation

With the aim to explore metal-ligand cooperation across Pd−S linkages, we designed a quinoline-based PNS tridentate ligand and prepared Pd(II) complexes thereof. Optimal solubility and stability of the dicationic complex [(PNS)Pd(II)]₂²⁺ IV₂ were achieved with B(C₆F₅)₄^– as counter-anion. It adopts a thiolate-bridged dimeric structure with a (PdS)₂ core, but readily activates hydrosilanes across the Pd−S linkage. The resulting mononuclear Pd(II) hydride [(PNS^SiR3)Pd(II)H]⁺ VI was characterized by multi-nuclear NMR spectroscopy and the Si−H bond coordination/activation was studied computationally. Complex IV₂ was found to efficiently catalyze the hydrosilylation of alkynes, internal as well as terminal, with good stereo and regioselectivity.