A Monomeric Diarylstannanone with a Sn=O Double Bond: Synthesis and Characterization

A series of diarylstannylenes, (Rind)₂Sn: (1) [Rind=1,1,7,7-tetra-R¹-3,3,5,5-tetra-R²-s-hydrindacen-4-yl: EMind (a: R¹=Et, R²=Me), Eind (b: R¹=R²=Et), and MPind (c: R¹=Me, R²=ⁿPr)], has been obtained as purple to blue crystals by the reaction of SnX₂ ⋅ dioxane (X=Br or Cl) with two equiv. of (Rind)Li. The less bulky EMind-based stannylene, (EMnd)₂Sn: (1 a), reacted with N₂O gas to afford a 1,3,2,4-dioxadistannetane, (EMind)₄Sn₂(μ-O)₂ (3 a), through the dimerization of a stannanone, (EMind)₂Sn=O (2 a). In contrast, a similar oxidation reaction using the bulkier MPind-based stannylene, (MPind)₂Sn: (1 c), produced a hitherto unknown acid-base free monomeric diarylstannanone, (MPind)₂Sn=O (2 c), with an authentic Sn=O double bond. The stannanone 2 c was highly sensitive to air and moisture but remained thermally stable at room temperature. Isolating 2 c as a pure single crystalline material proved challenging due to its highly-reactive nature; however, its structural characteristics and bonding properties were discussed based on both experimental findings and computational results. The Sn=O double bond in 2 c exhibits a weaker and more polarized character compared to the Ge=O double bond in the diaryl-germanone, (Eind)₂Ge=O (A).