Selective C-H and C-F bond activation reactions of pyridine and fluoropyridines - formation of binuclear μ-X titanocene complexes (X = H, F) with α-functionalized N-heterocycles

I. M. Piglosiewicz, S. Kraft, R. Beckhaus, W. Saak, D. Haase
Eur. J. Inorg. Chem .
, 2005, 5, 938-945.

Reactions of the titanocene synthons with pyridine, fluorosubstituted pyridines (pentafluoropyridine, 2-fluoropyridine) and cyanuric fluoride lead by C-H bond and C-F bond activation, respectively, to interesting novel binuclear titanium(III) complexes. The C-H bond activation reaction requires high temperatures (110°C), whereas C-F bond activations are found at room temperature. X-ray structure analysis showed that the two titanium(III) centres are hydride-bridged in case that pyridine was reacted with the titanocene fragment and fluoride-bridged if a 2-fluoro-substituted derivative of pyridine was used. To compare the reactivities of α C-F and α C-H bond in 2-position towards the titanocene fragment, a competition experiment using 2-fluoropyridine was performed, exhibiting the preference of α C-F bond cleavage. The primary mononuclear C-F bond activation products are proved in solution by NMR measurements using [Cp*2Ti{ η2 -C2(SiMe3)2}] instead of the non-methylated titanocene source.

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