Diverse reactions of nitroxide-radical adducts of silylene, germylene, and stannylene

The results of the thermolysis of 1:2 adducts of stable group-14 element divalent compounds [R2M:, R2=1,1,4,4-tetrakis(trimethylsilyl)butane-1,4-diyl; 1b, M=Ge; 1c, M=Sn] to TEMPO radical are discussed in detail. Whereas the thermal reactions of the 1:2 adducts [R2M(OR′)2, R′=2,2,6,6-tetramethylpiperidin-N-yl; 3b, M=Ge; 3c, M=Sn] are understood to proceed by the initial homolysis of an M–O bond to give the corresponding aminoxy-substituted group-14 element radicals [R2(R′O)Mradical dot; 2b, M=Ge; 2c, M=Sn] and TEMPO, the subsequent reactions of 2b and 2c were remarkably different to each other; 2b favors the N–O bond fission (path b) to give the corresponding germanone, while 2c prefers the M–O bond fission (path a) to give stannylene (1c). In combining with our previous results for aminoxysilyl radical (2a) [R2(R′O)Siradical dot], the origin of the remarkable differences in the reactivity among group-14 element radicals 2a–2c is discussed on the basis of the theoretical calculations for model reactions. Improved syntheses of the precursor dichlorogermane and dichlorostannane of germylene (1b) and stannylene (1c), respectively, are described in Section 3.