In contrast to the titanium and zirconium analogs, first hafnocene alkyne complexes were prepared only recently. Spectroscopic and structural data revealed that in these complexes the alkyne is bound strongly to the metal center resulting in a hafnacyclopropene structure.However, investigation of the reaction of the bridged alkyne complex rac-(ebthi)Hf(?2-Me3SiC2SiMe3) with ethylene has shown that the alkyne can be replaced in this case to form a hafnacyclopentane.The reaction proceeds in three steps with a bis-p-complex and a hafnacyclopentene intermediate. Investigation of the reaction by UV/vis spectroscopy (stopped flow) has shown that the former species, which is only present for a short time (<2 s) can be detected by spectroscopic methods. This has not been achieved before by common NMR techniques.The results are compared with the reactions of the corresponding similar titanocene and zirconocene complexes with ethylene.

Formation of group 4 metallacyclopentanes from metallacyclopropenes: Investigation of the reactions with ethylene by <i>in situ</i> NMR and UV/vis spectroscopy

240th National Meeting (2010)

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Formation of group 4 metallacyclopentanes from metallacyclopropenes: Investigation of the reactions with ethylene by in situ NMR and UV/vis spectroscopy