Photochemistry of Trimethyltin Iodide in Polar Media:  Orbital Parentage and Observed Reactivity

• Published in: Inorganic chemistry 2002-01, Vol.41 (1), p.11-18
• Main Authors: Dong, Jinquan, Devi, P. Sujatha, Sunil, D, Mendoza, Edgar, Gafney, Harry D
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic010051c

(CH3)3SnI exists as individual tetrahedral molecules in hexane but reacts with the silanol moieties present on the surface of porous glass and with the hydroxyl group of ethanol and hexanol to form five-coordinate adducts. With the exception of slight shifts to higher energy, formation of the adduct has little effect on the electronic spectrum of the complex, and the wavelength and O2 dependencies of the quantum yield of (CH3)3SnI disappearance indicate that the photochemistry of the complex initiates from the ligand-to-metal charge-transfer (LMCT) state populated on absorption in each medium. Nevertheless, 254 nm excitation in hexane leads to I2 and ((CH3)3Sn)2, whereas excitation of the five-coordinate adduct on the glass surface leads to I2, I3 -, ((CH3)3Sn)2 , and (CH3)3Sn−OSi⋮ (OSi⋮ represents a surface siloxyl), while in ethanol, I3 - is the only detectable product. Regardless of the medium, the ground state is polarized and population of the LMCT state creates a more uniform charge distribution from which homolytic cleavage of the (CH3)3Sn−I bond is the dominant reaction pathway in each medium. In hexane, the (CH3)3Sn• and I• radicals couple to form ((CH3)3Sn)2 and I2, whereas adsorbed onto the glass, a fraction of the radical pairs thermalize via electron transfer to form I3 - and a surface-bound (CH3)3Sn−OSi⋮ species. In ethanol, excitation of the solvent adduct (CH3)3Sn−OHC2H5 leads to homolytic cleavage and I2 formation, which reacts thermally with (CH3)3Sn−OHC2H5 to form an [(CH3)3Sn+, I3 -] ion pair.