Trapping of photogenerated group IV radicals by TEMPO: Potential new organometallic initiators for "living" free radical polymerization

A series of trialkyl and triaryl organometallic radicals from group IV gene rated by hydrogen abstraction by tert-butoxyl radical From the parent hydri des have been examined using laser flash photolysis. The rate constants for the trapping of the metal-centered radicals by the persistent radical TEMP O were measured and were found to be large and similar to those of the carb on-centered radical systems, yet below the diffusion controlled limit. The metal-centered radicals were found to be efficiently trapped by TEMPO and w ould appear to be candidates suitable for "living" free radical polymerizat ion similar to carbon analogue stoichiometric initiators. The radical trapp ing rate constants For the trialkyl series (M = Si, Ge, Sn) were Found to b e 8.9 x 10(8) M-1 s(-1) (M = Si), 7.2 X 10(8) M-1 s(-1) (M = Ce), and 6.2 X 108 M-1 s(-1) (M = Sn), respectively. The triaryl (Ph,M) series gave sligh tly slower rates of 1.6 X 10(8) M-1 s(-1) (M = Si). 3.4 x 10(8) M-1 s(-1) ( M = Ge), and 1.9 x 10(7) M-1 s(-1) (M = Sn), respectively. (C) 2000 John Wi ley & Sons, Inc.