PHOTOCHEMICAL-REACTIONS OF ARYL-SUBSTITUTED CATENATES OF GROUP 4B ELEMENTS, PHME2E-E'ME3 (E,E'=SI AND GE) - FORMATION OF A RADICAL PAIR

Photochemical reactions of phenyl substituted catenates of group 4B elements, PhMe2E-E'Me3 (E,E' = Si and Ge) have been investigated by chemical trapping experiments and laser flash-photolysis. On irradiation, the phenylated group 4B catenate undergoes E-E' bond homolysis to give a pair of radicals (PhMe2E. and Me3E'.). In CCl4, these radicals are converted to the corresponding chlorides by abstraction of a chlorine atom. In a nonhalogenated solvent, the radical pair couples at the ipso-position of the phenyl group of the pairing radical (PhMe2E.) to yield the corresponding diradical. This undergoes either elimination of a divalent species (Me2E:) with concomitant formation of trimethylphenyl group 4B element (PhMe3E') or intramolecular 1,2-group 4B element migration to yield group 4B metal-carbon double bonded species. The radical escapes from the solvent cage coupled to the metal atom of the radical to yield the dimetallic product. The reaction path observed is highly dependent on the nature of the group 4B element comprising the phenyl substituted catenate.