Hydrolytic cleavage of both CS₂ carbon-sulfur bonds by multinuclear Pd(II) complexes at room temperature

Developing homogeneous catalysts that convert CS₂ and COS pollutants into environmentally benign products is important for both fundamental catalytic research and applied environmental science. Here we report a series of air-stable dimeric Pd complexes that mediate the facile hydrolytic cleavage of both CS₂ carbon-sulfur bonds at 25 °C to produce CO₂ and trimeric Pd complexes. Oxidation of the trimeric complexes with HNO₃ regenerates the dimeric starting complexes with the release of SO₂ and NO₂. Isotopic labelling confirms that the carbon and oxygen atoms of CO₂ originate from CS₂ and H₂O, respectively, and reaction intermediates were observed by gas-phase and electrospray ionization mass spectrometry, as well as by Fourier transform infrared spectroscopy. We also propose a plausible mechanistic scenario based on the experimentally observed intermediates. The mechanism involves intramolecular attack by a nucleophilic Pd-OH moiety on the carbon atom of coordinated µ-OCS₂, which on deprotonation cleaves one C-S bond and simultaneously forms a C-O bond. Coupled C-S cleavage and CO₂ release to yield [(bpy)₃Pd₃(µ₃-S)₂](NO₃)₂ (bpy, 2,2'-bipyridine) provides the thermodynamic driving force for the reaction.