Flash Communication: Stopping the Movement of Carbon\nAtoms Traveling in Organic Molecules by Pinacolboryl Substituents

When\nall substituents of bis(cyclopentadienyl)titanacyclopentadienes <b>5</b> are primary alkyl groups, coupling of a Cp ligand and the\ndiene moiety in <b>5</b> gave dihydroindenyl titanium complexes <b>2</b>. The intermediate complexes <b>1</b> were not obtained\nbecause complexes <b>2</b> are more thermodynamically stable\nthan complexes <b>1</b> as previously reported. To prevent this\nfurther transformation, the influence of the bulkiness of the substituents\nwas investigated. Pinacolboryl (Bpin) groups as substituents R<sup>1</sup> were found to be a key factor in disturbing the further transformation\nof complex <b>1</b> to <b>2</b>. Complex <b>1</b> bearing Bpin substituents as R<sup>1</sup> was confirmed by NMR.\nIts dihydroindenyl moiety was removed from the titanium and converted\nto a TCNE-adduct to verify the structure by X-ray diffraction.