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

摘要

The zirconocene complexes Cp_2Zr(L)(eta~2-Me_3SiC_2SiMe_3) (la: L = THF;1b: L = pyridine) and the ethylene bis(tetrahydroin-denyl) complex rac-(ebthi)Zr(eta~2-Me_3SiC_2SiMe_3) (2) react with 2,3,5,6-tetrafluoropyridine with C-H bond activation to produce the 4-substituted pyridyl complexes with agostic al-kenyl groups Cp'_2Zr(4-C_5NF_4)[-C(SiMe_3)=CH(SiMe_3)] (Cp'_2 = Cp_2) (3) and (Cp'_2 = ebthi) (4).With 2,3,4,6-tetrafluoropyri-dine,after C-H bond activation,complex 2 yields two iso-mers of the 5-substituted pyridyl complex rac-(ebthi)Zr(3-C_5NF_4)[-C(SiMe_3)=CH(SiMe_3)] 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-C_5NF_4)F (6).Complex 1b reacts with 3-chloro-2,4,5,6-tetra-fluoropyridine by means of a preferred C-C1 activation to give Cp_2Zr(3-C_5NF_4)Cl (7).These results are in contrast to the reactions of the titanium complex Cp_2Ti(eta~2-Me_3-SiC_2SiMe_3) 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.