Synthesis and Characterization of Cyclopentadienyl Transition Metal Complexes Bearing Tetrafluoropyridyl Substituents

Abstract

Three new tetrafluoropyridyl-substituted cyclopentadienes were synthesized. Reactions of pentafluoropyridine (C5F5N) with sodium cyclopentadienide (NaCp) in THF with excess NaH present afforded mixtures of (4-tetrafluoropyridyl)cyclopentadiene (1), 1,3-bis(tetrafluoropyridylcyclopentadiene) (2), and 1,2-bis(tetrafluoropyridylcyclo-pentadiene) (3). Selectivity for mono- and diarylation was controlled by varying the reaction time. Each of the three cyclopentadienes (1, 2, and 3) was converted to its corresponding substituted sodium cyclopentadienide (4, 5, and 6, respectively) by treatment with NaH in THF.

Reaction of the monoarylated sodium cyclopentadienide (4) with M(CO)5Br in THF (M = Mn, Re) afforded the corresponding substituted CpM(CO)3 complexes (7Mn and 7Re). The diarylated sodium cyclopentadienides (5 and 6) likewise afforded the diarylated complexes 8Mn, 8Re, 9Mn, and 9Re. Infrared spectroscopic measurements of [(C5F4N)nC5H5-n]M(CO)3 (M = Mn, Re; n = 0 - 2) revealed an increase of about 6 cm-1 in the A-symmetric C-O stretching mode per C5F4N group, which is significantly higher than the average increase (4 cm-1) found earlier for C6F5 groups.

Reaction of 2 equiv of 4 with FeBr2 in THF afforded the 1,1'-diarylated ferrocene (10). Analogous reactions starting with 5 and 6 afforded tetraarylated ferrocenes (11 and 12, respectively).

Reaction of 2 equiv of 4 with ZrCl4 afforded (C5F4NCp)2ZrCl2 (13), whereas the reaction of CpZrCl3 with 1 equiv of 4 afforded (C5F4NCp)CpZrCl2 (14). Metallocene (13) was found to be moderately active for ethylene/1-hexene copolymerization (1 atm of C2H4, toluene solvent, methylalumoxane cocatalyst).