Synthesis and Isolation of Di-<i>n</i>-butylhafnocene and Its Application as a Versatile Starting Material for the Synthesis of New Hafnacycles

The previously described hafnocene alkyne complexes are of limited applicability for the generation of the hafnocene fragment in stoichiometric and catalytic reactions. For this reason di-n-butylhafnocene (1-Hf) was fully characterized and used as a hafnocene source in reactions with alkynes and diynes. With bis(trimethylsilyl)acetylene and pyridine the alkyne complex Cp2Hf(py)(η2-Me3SiC2SiMe3) (2-Hf) was obtained and coordination of di-tert-butylbutadiyne yielded the first structurally characterized hafnacyclocumulene, Cp2Hf(η4-t-BuC4-t-Bu) (4-Hf). By the coupling of 2 equiv of the 1,3-butadiyne RC4R at the hafnocene center, hafnacyclopentadienes were formed regioselectively (R = t-Bu, 5-t-Bu-Hf; R = SiMe3, 5-SiMe3-Hf). In the case of 1,4-diphenylbutadiyne the hafnocene-substituted [4]radialene 6-Hf was formed. Treatment of the latter with acid gave the free [4]radialene 7. In the reaction of 4-Hf with diphenylacetylene, the alkyne inserted into the Hf−Cα bond to give the hafnacyclopentadiene 8.此前报道的二茂铪（hafnocene）炔配合物，在通过化学计量反应与催化反应制备二茂铪活性片段时，应用范围较为有限。鉴于此，研究人员对二正丁基二茂铪（1-Hf）完成了全表征，并将其作为二茂铪源，用于与炔烃、二炔的反应当中。当以双(三甲基硅基)乙炔与吡啶为底物时，可得到炔配合物Cp₂Hf(py)(η²-Me₃SiC₂SiMe₃)（2-Hf）；而二叔丁基丁二炔经配位后，得到首例经结构表征的铪杂累积多烯烃（hafnacyclocumulene）Cp₂Hf(η⁴-t-BuC₄-t-Bu)（4-Hf）。在二茂铪中心上，2当量的1,3-丁二炔RC₄R发生偶联反应，区域选择性地生成铪杂环戊二烯类化合物：当R为叔丁基时得到5-t-Bu-Hf，当R为三甲基硅基时得到5-SiMe₃-Hf。针对1,4-二苯基丁二炔，反应生成二茂铪取代的[4]轮烯（[4]radialene）6-Hf。将该产物经酸处理后，可得到游离态[4]轮烯7。在4-Hf与二苯基乙炔的反应中，炔烃插入Hf−Cα键，得到铪杂环戊二烯8。