| Abstract
| - The photochemistry of 1,1-dimethyl- and 1,1,3,4-tetramethylstannacyclopent-3-ene (4a and 4b,respectively) has been studied in the gas phase and in hexane solution by steady-state and 193-nm laserflash photolysis methods. Photolysis of the two compounds results in the formation of 1,3-butadiene (from4a) and 2,3-dimethyl-1,3-butadiene (from 4b) as the major products, suggesting that cycloreversion toyield dimethylstannylene (SnMe2) is the main photodecomposition pathway of these molecules. Indeed,the stannylene has been trapped as the Sn−H insertion product upon photolysis of 4a in hexane containingtrimethylstannane. Flash photolysis of 4a in the gas phase affords a transient absorbing in the 450−520-nm range that is assigned to SnMe2 by comparison of its spectrum and reactivity to those previously reportedfrom other precursors. Flash photolysis of 4b in hexane solution affords results consistent with the initialformation of SnMe2 (λmax ≈ 500 nm), which decays over ∼10 μs to form tetramethyldistannene (5b; λmax≈ 470 nm). The distannene decays over the next ca. 50 μs to form at least two other longer-lived species,which are assigned to higher SnMe2 oligomers. Time-dependent DFT calculations support the spectralassignments for SnMe2 and Sn2Me4, and calculations examining the variation in bond dissociation energywith substituent (H, Me, and Ph) in disilenes, digermenes, and distannenes rule out the possibility thatdimerization of SnMe2 proceeds reversibly. Addition of methanol leads to reversible reaction with SnMe2to form a transient absorbing at λmax ≈ 360 nm, which is assigned to the Lewis acid−base complex betweenSnMe2 and the alcohol.
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