Abstract
A detailed experimental analysis of the 1,4‐selective reduction of pyridine with hydrosilanes catalyzed by a coordinatively unsaturated RuII thiolate complex is reported. The previously suggested intermediates, N‐silylpyridinium ions and a neutral RuII hydride, have been independently synthesized and do indeed participate in the catalytic cycle. The resting state is not the cationic RuII complex initially used as the catalyst but its pyridine‐coordinated congener. All RuII complexes, including the one resulting from hydrosilane activation, are in equilibrium with each other. The N‐silylated 1,4‐dihydropyridine together with the cationic RuII complex convert back into the corresponding N‐silylpyridinium ion and the neutral RuII hydride (retro‐hydrosilylation), followed by further backward reaction into the hydrosilane and the pyridine adduct of the cationic complex. These steps prove the overall reversibility of the transformation.
There and back again: The 1,4‐hydrosilylation of pyridines catalyzed by a RuII thiolate complex is mechanistically investigated. Stoichiometric experiments with independently synthesized intermediates made it possible to refine the initial proposal; equilibria between three different RuII complexes are part of this reversible (retro‐)hydrosilylation.