Isolable Tin(II) Hydrides Featuring Sterically Undemanding Pincer-Type Ligands and Their Dehydrogenative Sn-Sn Bond...

Unlike isolable tin(II) hydrides supported by bulky ligands reported in the literature, this research describes the synthesis and characterization of thermally stable tin(II) hydrides LSnH (1-H) and LSnH (2-H) stabilized by sterically undemanding N,N,N-coordinating pincer-type ligands (L = 2,5-dipyridyl-3,4-diphenylpyrrolato; L = 2,5-bis(6-methylpyridyl)pyrrolato). The results from previous reports reveal that attempts to access tin(II) hydrides containing less-bulky ligands have had limited success, and decomposition to tin(I) distannynes often occurs. The key to the successful isolation of 1-H and 2-H is the identification of the role of Lewis acidic BBu₃, generated upon delivering hydride from commonly used hydride reagents M[BBu₃H] ("selectrides", M = Li or K). This study details compelling experimental evidence and theoretical results of the role played by BBu₃, which catalyzes the dehydrocoupling reactions of 1-H and 2-H to yield tin(I) distannynes LSn-SnL (1) and LSn-SnL (2) with the liberation of H₂. To avoid the interference of BBu₃, 1-H and 2-H can be isolated in pure forms using pinacolborane as the hydride donor with LSnOMe (1-OMe) and LSnOMe (2-OMe) as reactants, respectively. DFT calculations and experimental observations indicate that the coordination of the Sn-H bond of 1-H to BBu₃ leaves an electrophilic tin center, rendering the nucleophilic attack by the second equivalent of 1-H forming a Sn-Sn bond.