Reactivity of organothorium complexes with TEMPO

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