Abstract
Alternative synthesis of ferrocenylacetylenes and the synthesis and full spectral and solid-state structures characterization of their titanocene complexes are described. The reduction of (η(5)-C5H5-Me-n(n))(2)TiCl2 (n = 0, 4, and 5) complexes by magnesium metal in tetrahydrofuran and in the presence of [(trimethylsilyl)ethynyl]ferrocene (2) or [(phenyl)ethynyl]ferrocene (3) affords the (η(5)-C5H5-nMen)(2)Ti(η(2)-FcC equivalent to CR) complexes [Fe = (η(5)-C5H5)Fe(η(5)-C5H4), R = SiMe3 (4-6) and Ph (7-9)].
Crystal structures of 5 and 9 show a titanacyclopropene-like mode of coordination of the acetylenes 2 and 3. Bonding of the acetylenes to the titanocene unit results in a remarkable downfield shift of C-13 NMR resonances of the acetylenic carbon atoms and in a large red shift of the v(C equivalent to C) wavenumbers.
Testing the complexes 6 and 9 toward head-to-tail dimerization of HC equivalent to CSiMe3 showed that compound 9 induces dimerization to give exclusively 2,4-bis(trimethylsilyl)but-1-en-3-yne (10), whereas complex 6 is inactive.