Reactions of the 2,2,6,6-tetramethylpiperidin-1-oxyl radical (TEMPO) with thorium metallocenes have been examined to investigate both the radical reaction patterns for organothorium complexes and the coordination chemistry of TEMPO with thorium. (eta(5)-C5Me5)(2)ThMe2 reacts with 2 equiv of TEMPO to generate 1-methoxy-2,2,6,6-tetramethylpiperidine (Me-TEMPO) and (eta(5)-C5Me5)(2)ThMe(eta(1)-TEMPO), which contains a TEMPO- anion coordinated to thorium through oxygen only. (eta(5)-C5Me5)(2)Th(eta(1)-C3H5)(eta(3)-C3H5), synthesized from (eta(5)-C5Me5)(2)ThBr2 and (C3H5)MgBr, reacts with 2 equiv of TEMPO to form 1-(2-propen-1-yloxy)-2,2,6,6-tetramethylpiperidine (allyl-TEMPO) and (eta(5)-C5Me5)(2)Th(eta(1)-C3H5)(eta(1)-TEMPO). Although bis(TEMPO) metallocenes were not obtained in these reactions, the methyl group in (eta(5)-C5Me5)(2)ThMe(eta(1)-TEMPO) is reactive with 1 equiv of CuBr to form (eta(5)-C5Me5)(2)ThBr(eta(1)-TEMPO). The bis(TEMPO) metallocene (eta(5)-C5Me5)(2)Th(eta(1)-TEMPO)(2) is accessible in the reaction of [(eta(5)-C5Me5)(2)ThH2](2) with 4 equiv of TEMPO. In contrast, (eta(5)-C5Me5)(2)ThBr2 reacts with 2 equiv of TEMPO by loss of C5Me5 to form (C5Me5)(2) and (eta(2)-TEMPO)(2)ThBr2, in which the TEMPO- anions bind through oxygen and nitrogen. The bromide ions in (eta(2)-TEMPO)(2)ThBr2 can be replaced by an additional 2 equiv of TEMPO in the presence of 2 equiv of KC8 to form the per(TEMPO) complex Th(eta(1)-TEMPO)(2)(eta(2)-TEMPO)(2). ThBr4(THF)(4) reacts with TEMPO to form ThBr4(THF)(2)(eta(1)-TEMPO), which contains an oxygen-bound TEMPO radical. The Th3+ complex (eta(5)-C5Me4H)(3)Th is oxidized in the presence of TEMPO, without ligand loss, to afford the Th4+ species (eta(5)-C5Me4H)(3)Th(eta(1)-TEMPO). The reactions show that TEMPO can react with organothorium complexes in several ways including coordination, anion substitution, and cyclopentadienyl replacement.