Reactions of Zirconocene Bis(trimethylsilyl)acetylene Complexes with Fluorinated Pyridines: C–H vs. C–F Bond Activation

Abstract

AbstractThe zirconocene complexes Cp2Zr(L)(η2‐Me3SiC2SiMe3) (1a: L = THF; 1b: L = pyridine) and the ethylene bis(tetrahydroindenyl) complex rac‐(ebthi)Zr(η2‐Me3SiC2SiMe3) (2) react with 2,3,5,6‐tetrafluoropyridine with C–H bond activation to produce the 4‐substituted pyridyl complexes with agostic alkenyl groups Cp'2Zr(4‐C5NF4)[–C(SiMe3)=CH(SiMe3)] (Cp'2 = Cp2) (3) and (Cp'2 = ebthi) (4). With 2,3,4,6‐tetrafluoropyridine, after C–H bond activation, complex 2 yields two isomers of the 5‐substituted pyridyl complex rac‐(ebthi)Zr(3‐C5NF4)[–C(SiMe3)=CH(SiMe3)] with agostic alkenyl groups, 5a and 5b. With pentafluoropyridine complex 1b gives, after dissociation of the bis(trimethylsilyl)acetylene (btmsa), C–F bond activation at the 4‐position and formation of Cp2Zr(4‐C5NF4)F (6). Complex 1b reacts with 3‐chloro‐2,4,5,6‐tetrafluoropyridine by means of a preferred C–Cl activation to give Cp2Zr(3‐C5NF4)Cl (7). These results are in contrast to the reactions of the titanium complex Cp2Ti(η2‐Me3SiC2SiMe3) which, with 2,3,5,6‐tetrafluoropyridine, gaveC–F activation in preference to C–H activation. With pentafluoropyridine, C–F bond activation at the 2‐position was found rather than at the 4‐position. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)