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. (η5-C5Me5)2ThMe2 reacts with 2 equiv of TEMPO to generate 1-methoxy-2,2,6,6-tetramethylpiperidine (Me-TEMPO) and (η5-C5Me5)2ThMe­(η1-TEMPO), which contains a TEMPO– anion coordinated to thorium through oxygen only. (η5-C5Me5)2Th­(η1-C3H5)­(η3-C3H5), synthesized from (η5-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 (η5-C5Me5)2Th­(η1-C3H5)­(η1-TEMPO). Although bis­(TEMPO) metallocenes were not obtained in these reactions, the methyl group in (η5-C5Me5)2ThMe­(η1-TEMPO) is reactive with 1 equiv of CuBr to form (η5-C5Me5)2ThBr­(η1-TEMPO). The bis­(TEMPO) metallocene (η5-C5Me5)2Th­(η1-TEMPO)2 is accessible in the reaction of [(η5-C5Me5)2ThH2]2 with 4 equiv of TEMPO. In contrast, (η5-C5Me5)2ThBr2 reacts with 2 equiv of TEMPO by loss of C5Me5 to form (C5Me5)2 and (η2-TEMPO)2ThBr2, in which the TEMPO– anions bind through oxygen and nitrogen. The bromide ions in (η2-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(η1-TEMPO)2(η2-TEMPO)2. ThBr4(THF)4 reacts with TEMPO to form ThBr4(THF)2(η1-TEMPO), which contains an oxygen-bound TEMPO radical. The Th3+ complex (η5-C5Me4H)3Th is oxidized in the presence of TEMPO, without ligand loss, to afford the Th4+ species (η5-C5Me4H)3Th­(η1-TEMPO). The reactions show that TEMPO can react with organothorium complexes in several ways including coordination, anion substitution, and cyclopentadienyl replacement.本研究考察了2,2,6,6-四甲基哌啶氮氧自由基（2,2,6,6-tetramethylpiperidin-1-oxyl radical，TEMPO）与茂钍配合物的反应，以期同时探究有机钍配合物的自由基反应模式，以及TEMPO与钍的配位化学特性。二(五甲基环戊二烯基)二甲基钍[(η⁵-C₅Me₅)₂ThMe₂]与2当量的TEMPO反应，生成1-甲氧基-2,2,6,6-四甲基哌啶（Me-TEMPO）以及仅通过氧原子与钍配位的单齿TEMPO配合物[(η⁵-C₅Me₅)₂ThMe(η¹-TEMPO)]；由二(五甲基环戊二烯基)二溴化钍[(η⁵-C₅Me₅)₂ThBr₂]与烯丙基溴化镁[(C₃H₅)MgBr]合成得到的二(五甲基环戊二烯基)(η¹-烯丙基)(η³-烯丙基)钍[(η⁵-C₅Me₅)₂Th(η¹-C₃H₅)(η³-C₃H₅)]，与2当量的TEMPO反应，生成1-(2-丙烯-1-基氧基)-2,2,6,6-四甲基哌啶（烯丙基-TEMPO）与[(η⁵-C₅Me₅)₂Th(η¹-C₃H₅)(η¹-TEMPO)]。尽管上述两类反应均未获得双(TEMPO)取代的茂钍配合物，但[(η⁵-C₅Me₅)₂ThMe(η¹-TEMPO)]中的甲基可与1当量溴化亚铜（CuBr）反应，生成[(η⁵-C₅Me₅)₂ThBr(η¹-TEMPO)]。双(TEMPO)取代的茂钍配合物[(η⁵-C₅Me₅)₂Th(η¹-TEMPO)₂]可通过二聚二(五甲基环戊二烯基)二氢化钍{[(η⁵-C₅Me₅)₂ThH₂]₂}与4当量的TEMPO反应制备得到。与之相对，二(五甲基环戊二烯基)二溴化钍[(η⁵-C₅Me₅)₂ThBr₂]与2当量的TEMPO反应时会发生五甲基环戊二烯基配体解离，生成二(五甲基环戊二烯基)（(C₅Me₅)₂）以及双齿TEMPO配合物[(η²-TEMPO)₂ThBr₂]，该配合物中的TEMPO⁻阴离子通过氧原子与氮原子共同与钍配位；[(η²-TEMPO)₂ThBr₂]中的溴离子可在2当量石墨酸钾（KC₈）存在下，与额外2当量的TEMPO发生取代反应，生成全(TEMPO)配位配合物Th(η¹-TEMPO)₂(η²-TEMPO)₂。四(四氢呋喃)合四溴化钍[ThBr₄(THF)₄]与TEMPO反应，生成仅通过氧原子配位的TEMPO自由基配合物ThBr₄(THF)₂(η¹-TEMPO)。三价钍配合物[(η⁵-C₅Me₄H)₃Th]在TEMPO存在下发生氧化反应，且无配体解离，得到四价钍物种[(η⁵-C₅Me₄H)₃Th(η¹-TEMPO)]。上述反应结果表明，TEMPO可通过配位、阴离子取代以及环戊二烯基配体取代等多种途径与有机钍配合物发生反应。