Synthesis and structure of piano stool complexes derived from the tetrakis(pentafluorophenyl)cyclopentadienyl ligand

The reaction of NaCp (Cp = C5H5) With excess C6F6 and excess NaH in refluxing diglyme afforded a 57% yield of 1,2,3,4-tetrakis(pentafluorophenyl)cyclopentadiene (1). Treatment of 1 with NaH in THF afforded sodium tetrakis(pentafluorophenyl)cyclopentadienide (2) in 89% yield. Reactions of 2 with M(CO)(5)Br (M = Mn, Re) yielded [(C6F5)(4)C5H]M(CO)(3) complexes (3, M = Mn, 33%, and 4, M = Re, 28%). Reactions of 2 with various iron(II) salts and with CoBr2 however failed to afford the corresponding octaarylated metallocenes. Infrared spectroscopic analysis of 3 and 4 revealed an increase of 16(1) cm(-1) relative to CpM(CO)(3) in the A-symmetric C-O stretching frequency, suggesting that the C6F5 groups have a highly electron-withdrawing effect on the coordinated M(CO)(3) moieties. Crystal structures of 1, 1.(1)/2C6D6, 2, and 3 display a propeller-like arrangement of the C5F5 groups. Complexes 2 and 3 show elongation of the Cs(centroid)-M bond distances relative to CpMn(CO)(3) and CpRe(CO)(3), which is attributed to steric effects.