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 L Ph SnH (1-H) and Me LSnH (2-H) stabilized by sterically undemanding N,N,N-coordinating pincer-type ligands (L Ph = 2,5-dipyridyl-3,4-diphenylpyrrolato; Me 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 B s Bu 3 , generated upon delivering hydride from commonly used hydride reagents M[B s Bu 3 H] ("selectrides", M = Li or K). This study details compelling experimental evidence and theoretical results of the role played by B s Bu 3 , which catalyzes the dehydrocoupling reactions of 1-H and 2-H to yield tin(I) distannynes L Ph Sn−SnL Ph (1 2 ) and Me LSn−Sn Me L (2 2 ) with the liberation of H 2 . To avoid the interference of B s Bu 3 , 1-H and 2-H can be isolated in pure forms using pinacolborane as the hydride donor with L Ph SnOMe (1-OMe) and Me LSnOMe (2-OMe) as reactants, respectively. DFT calculations and experimental observations indicate that the coordination of the Sn−H bond of 1-H to B s Bu 3 leaves an electrophilic tin center, rendering the nucleophilic attack by the second equivalent of 1-H forming a Sn−Sn bond.

Access to Monomeric Lead(II) Hydrides with Remarkable Thermostability and Their Use in Catalytic Hydroboration of Carbonyl Derivatives

“…Our recent report indicated that the bulkier d Me pp [2,5-bis(6methylpyridyl)pyrrolato] ligand significantly stabilizes its tin(II) hydride (t 1/2 ∼ 20 days) as compared to smaller dpp Ph (2,5-dipyridyl-3,4-diphenylpyrrolato) ligand (t 1/2 ∼ 4 days) at 25 °C. 34 Second, dihydrogen-bonding (DHB) interactions 35−37 between the ortho-hydrogens on the five phenyl rings of the pyrrolyl donors (H Ph ) and hydride ligand (H Pb ) may have stabilized the Pb−H moiety. In the density functional theory-optimized structure, two H Ph were pointing toward H Pb at a short distance of 2.317 Å (Figure 5a), which was less than the sum of the van der Waals radii of H (2r H = 2.4 Å).…”

“…The kinetic stabilization provided by the phenyl groups on the pyrrolyl donor should not be neglected in [1-H] – . Our recent report indicated that the bulkier d Me pp [2,5-bis­(6-methylpyridyl)­pyrrolato] ligand significantly stabilizes its tin­(II) hydride ( t 1/2 ∼ 20 days) as compared to smaller dpp Ph (2,5-dipyridyl-3,4-diphenylpyrrolato) ligand ( t 1/2 ∼ 4 days) at 25 °C . Second, dihydrogen-bonding (DHB) interactions − between the ortho-hydrogens on the five phenyl rings of the pyrrolyl donors (H Ph ) and hydride ligand (H Pb ) may have stabilized the Pb–H moiety.…”

One-Electron (2c/1e) Tin···Tin Bond Stabilized by ortho-Phenylenediamido Ligands

“…Meanwhile, using a smaller amount of reducing agent did not yield the 1e-reduced species in the case of germylene reduction. Compound 1 shows a very long Sn···Sn distance (3.2155(9) Å) compared to a typical Sn–Sn single bond in distannylenes, − even longer by 0.11 Å than the longest one (3.1013(7) Å) ever reported, thus suggesting a different bonding mode. From the crystal structure, computations, EPR spectroscopy, and chemical reactions of 1 , this bonding is proven to be a 2c/1e Sn···Sn bond with a bond order of 0.5, as described below.…”

“…The calculated bond dissociation energy (Δ E ) of [LSn···SnL] •– to [LSn] and [LSn] •– is 43.5 kcal mol –1 in the gas phase (31.9 kcal mol –1 in THF; Table S2), which is larger than that for some of the Sn–Sn single bond in LSnSnL compounds (from ca. 10 to 30 kcal mol –1 ), − suggesting a rather strong bonding. The spin density plot (Figure b,c) demonstrates that the unpaired electron is largely delocalized on the two Sn atoms (0.68 e) with a smaller distribution on the two ligands (0.32 e).…”

“…Unexpectedly, the dinuclear complex [K(THF) 6 ][LSn:•••Sn:L] (1) was obtained with a monoanionic [LSnSnL] − moiety and a separated K(THF) 6 + countercation (Figure 1). In contrast, the desired two-electron (2e) reduced distannylene, [LSn:−Sn:L] 2− , similar to the digermylene 26 was not obtained even when an excess of 32 ever reported, thus suggesting a different bonding mode. From the crystal structure, computations, EPR spectroscopy, and chemical reactions of 1, this bonding is proven to be a 2c/1e Sn•••Sn bond with a bond order of 0.5, as described below.…”