HOMOLYTIC REACTIVITY OF GROUP-14 ORGANOMETALLIC HYDRIDES TOWARD NITROXIDES

The spontaneous reactions of Et3SiH, Ph3GeH, Bu3SnH, and (Me3Si)(3)SiH with 2,2,6,6-tetramethyl-1-piperidinoxyl (TEMPO) and related nitroxid es have been investigated. Metal hydrides characterized by relatively weak metal-hydrogen bonds, like Ph3GeH and Bu3SnH, reduce TEMPO to the corresponding hydroxylamine while no reaction is observed with Et3SiH and Ph3SiH. Tris(trimethylsilyl)silane, on the other hand, is able to reduce the nitroxide to the corresponding hydroxylamine and amine in a ca. 1:1 ratio. By repeating the above reactions in the presence of t hermal or photochemical radical initiators, deoxygenation of TEMPO was obtained in high yield with (Me3Si)(3)SiH and (Me3Si)(2)Si(H)Ne, but not with other silanes, germanes, and stannanes. A mechanism for the r eduction of TEMPO by the two trimethylsilyl-substituted silanes is pro posed, and kinetic data for the various steps of the overall reaction are reported. In particular rate constants and activation parameters h ave been measured for the hydrogen transfer reaction from several sila nes to the hindered aminyl radical 2,2,6,6-tetramethylpiperidinyl.