Isolable Tin(II) Hydrides Featuring Sterically Undemanding Pincer-Type Ligands and Their Dehydrogenative Sn–Sn Bond Forming Reactions to Distannynes Promoted by Lewis Acidic Tri-sec-butylborane

Abstract

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 LPhSnH (1-H) and MeLSnH (2-H) stabilized by sterically undemanding N,N,N-coordinating pincer-type ligands (LPh = 2,5-dipyridyl-3,4-diphenylpyrrolato; MeL = 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 BsBu3, generated upon delivering hydride from commonly used hydride reagents M[BsBu3H] ("selectrides", M = Li or K). This study details compelling experimental evidence and theoretical results of the role played by BsBu3, which catalyzes the dehydrocoupling reactions of 1-H and 2-H to yield tin(I) distannynes LPhSn-SnLPh (12) and MeLSn-SnMeL (22) with the liberation of H2. To avoid the interference of BsBu3, 1-H and 2-H can be isolated in pure forms using pinacolborane as the hydride donor with LPhSnOMe (1-OMe) and MeLSnOMe (2-OMe) as reactants, respectively. DFT calculations and experimental observations indicate that the coordination of the Sn-H bond of 1-H to BsBu3 leaves an electrophilic tin center, rendering the nucleophilic attack by the second equivalent of 1-H forming a Sn-Sn bond.