Phosphine-free Heck reaction: mechanistic insights and catalysis “on water” using a charge-tagged palladium complex†
A novel Pd-complex with a charge tag (imidazolium cation) was applied for online monitoring of the neutral Heck reaction by electrospray ionization (tandem) mass spectrometry – ESI-MS(/MS). The results shed light on the mechanism of the reaction, whereas the charge-tagged ligand also allowed the unprecedented MS monitoring of Pd2+ reduction to Pd0. Key reaction intermediates associated with Pd catalysis could also be detected and characterized due to the presence of the charge tag on the Pd-complex. DFT calculations supported the proposed mechanism. The new charge-tagged Pd-complex is also shown to function as an active catalyst “on water” with the advantage of using cheaper and less reactive aryl chloride substrates in a phosphine-free version of the Heck reaction.