Selective C-H and C-F Bond Activation Reactions of Pyridine and Fluoropyridines - Formation of Binuclear mu-X Titanocene Complexes(X = H,F)with alpha-Functionalized N-Heterocycles

摘要

Titanocene synthons react with pyridine(2),fluorosubsti-tuted pyridines[pentafluoropyridine(3),2-fluoropyridine(4)]and cyanuric fluoride,by C-H and C-F bond activation,respectively,to afford interesting novel binuclear titanium(III)complexes.C-H bond activation requires high temperatures(110 degC),whereas C-F bond activation occurs at room temperature.X-ray structure analysis showed that the two titani-um(III)centres are hydride-bridged when pyridine was reacted with the titanocene fragment and fluoride-bridged if a 2-fluoro-substituted derivative of pyridine was used.The reactivities of a C-F and a C-H bond in the 2-position toward the titanocene fragment have been compared in a competition experiment using 2-fluoropyridine - revealing a preference for C-F bond cleavage.Primary mononuclear C-F bond activation products have been proved in solution by NMR measurements using[Cp*_2Ti(eta~2-C_2(SiMe_3)_2}]instead of the non-methylated titanocene source.