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

Inorg Chem. 2022 Apr 25;61(16):6026-6036. doi: 10.1021/acs.inorgchem.1c04019. Epub 2022 Apr 8.

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.