Reactivity of TpMe2-Containing Hydride–Iridafurans with Alkenes, Alkynes, and H2

The TpMe2-containing hydride-iridafurans 2a,b (TpMe2 = hydrotris­(3,5-dimethylpyrazolyl)­borate) cleanly reacted with ethylene to give the bicyclic derivatives 6a,b. Formation of the latter complexes is a reversible process, and it is proposed to occur by an electrocyclic ring closure that takes place between C2H4 and the 16e unsaturated intermediates A, resulting from hydride migration to the α carbon of the metallacycle. Similar reactions were observed with a variety of alkynes RCCR (R = H, Ph, CO2Me) and R′CCH (R′= CO2Me, Ph, CMe3), with the regioselectivity observed for the latter substrates depending on the nature of R′. In the case of Me3SiCCH the structure of an unexpected byproduct indicates that an alkyne–vinylidene rearrangement has taken place on the metal coordination sphere during the reaction, and this observation suggests that in the mechanism of all these coupling processes the corresponding π adducts are active intermediates. Finally, complexes 2a,b reacted with H2 to give products derived from the hydrogenation of their alkenyl arms.含氢三(3,5-二甲基吡唑基)硼酸盐（hydrotris(3,5-dimethylpyrazolyl)borate, TpMe2）的氢化物-铱呋喃杂环化合物2a、b可与乙烯发生无副产物的专一反应，生成双环衍生物6a、b。该后述配合物的生成过程为可逆过程，其反应机理被认为是：乙烯与16电子不饱和中间体A发生电环闭环反应，而中间体A由氢化物迁移至金属杂环的α碳原子后形成。多种炔烃RC≡CR（R=H、苯基、甲氧羰基）与R'C≡CH（R'=甲氧羰基、苯基、叔丁基）均可发生类似反应，后一类底物的区域选择性取决于R'的结构性质。针对三甲基硅基乙炔（Me3SiC≡CH）的反应中，意外得到的副产物结构表明，反应过程中金属配位球内发生了炔烃-亚乙烯基重排反应；这一现象提示，在所有此类偶联反应的机理中，对应的π配位加合物均为活性中间体。最后，配合物2a、b与氢气反应，可得到其烯基侧链加氢生成的产物。