Synthesis and Structure of Piano Stool Complexes Derived from the Tetrakis(pentafluorophenyl)cyclopentadienyl Ligand

The reaction of NaCp (Cp = C 5 H 5 ) with excess C 6 F 6 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 [(C 6 F 5 ) 4 C 5 H]M(CO) 3 complexes ( 3, M = Mn, 33%, and 4, M = Re, 28%). Reactions of 2 with various iron(II) salts and with CoBr 2 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 C 6 F 5 groups have a highly electron-withdrawing effect on the coordinated M(CO) 3 moieties. Crystal structures of 1, 1 · 1 / 2 C 6 D 6, 2, and 3 display a propeller-like arrangement of the C 6 F 5 groups. Complexes 2 and 3 show elongation of the C 5 (centroid)−M bond distances relative to CpMn(CO) 3 and CpRe(CO) 3, which is attributed to steric effects.