Photochemistry of trimethyltin iodide in polar media: orbital parentage and observed reactivity.
(CH(3))(3)SnI 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 O(2) dependencies of the quantum yield of (CH(3))(3)SnI 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 I(2) and ((CH(3))(3)Sn)(2), whereas excitation of the five-coordinate adduct on the glass surface leads to I(2), I(3)(-), ((CH(3))(3)Sn)(2), and (CH(3))(3)Sn-OSi[triple bond](OSi[triple bond]represents a surface siloxyl), while in ethanol, I(3)(-) 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 (CH(3))(3)Sn-I bond is the dominant reaction pathway in each medium. In hexane, the (CH(3))(3)Sn(*) and I(*) radicals couple to form ((CH(3))(3)Sn)(2) and I(2), whereas adsorbed onto the glass, a fraction of the radical pairs thermalize via electron transfer to form I(3)(-) and a surface-bound (CH(3))(3)Sn-OSi[triple bond] species. In ethanol, excitation of the solvent adduct (CH(3))(3)Sn-OHC(2)H(5) leads to homolytic cleavage and I(2) formation, which reacts thermally with (CH(3))(3)Sn-OHC(2)H(5) to form an [(CH(3))(3)Sn(+), I(3)(-)] ion pair.
Dong
Jinquan
J
Department of Chemistry, City University of New York, Queens College, Flushing, New York 11367, USA.
Devi
P Sujatha
PS
Sunil
D
D
Mendoza
Edgar
E
Gafney
Harry D
HD