Reactions of zirconocene bis(trimethylsilyl)acetylene complexes with fluorinated pyridines:: C-H vs. C-F bond activation

The zirconocene complexes Cp2Zr(L)(eta(2)-Me3SiC2SiMe3) (1a: L = THF; 1b: L = pyridine) and the ethylene bis(tetrahydroindenyl) complex rac-(ebthi)Zr(eta(2)-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'Zr-2(4-C5NF4)[-C(SiMe3)=CH(SiMe3)] (Cp'(2) = Cp-2) (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(eta(2)-Me-3-SiC2SiMe3) which, with 2,3,5,6-tetrafluoropyridine, gave C-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. (c) Wiley-VCH Verlag GmbH & Co.