A LASER FLASH-PHOTOLYSIS STUDY OF THE PHOTOCHEMISTRY OF (PHENYLETHYNYL)PENTAMETHYLDISILANE - ABSOLUTE RATE CONSTANTS FOR TRAPPING OF A REACTIVE 1-SILAALLENE BY NUCLEOPHILES

Laser flash photolysis of nitrogen-saturated hexane solutions of penta methyl(phenylethynyl)disilane affords a mixture of three transient spe cies and a product which is stable on the millisecond time scale. Thes e are assigned to the triplet state of the disilane (tau similar to 5 mu s), -dimethyl-3-phenyl-3-(trimethylsilyl)-1-silaallene (tau similar to 25 mu s), dimethylsilylene (tau similar to 100 ns), and hyl-2-phen yl-3-(trimethylsilyl)-1-silacyclopropene (tau > 100 ms), respectively, on the basis of their UV spectra and reactivity toward various reagen ts. While previous work has shown that the 1-silaallene is formed in l ess than 25% yield, it can be readily observed in transient absorption experiments in spite of extensive spectral overlap with the alkynyldi silane triplet and the 1-silacyclopropene. Absolute rate constants for reaction of the silaallene with methanol, acetone, acetic acid, and o xygen in hexane solution are reported and compared to data for a relat ed compound.