Structural and electronic effects of pentafluorophenyl substituents on cyclopentadienyl complexes of Fe, Co, Mn, and Re

The reaction of CpNa(Cp = C5H5) With C6F6 (diglyme, 110 degrees C, 14 h) af forded a mixture of products, from which two new triarylated cyclopentadien es, 1,2,4-Ar3C5H3 (3) and 1,2,3-Ar3C5H3 (4), were separated by silica gel c hromatography (Ar = C6F5) The dienes 3 and 4 were readily converted (NaH, T HF) to the corresponding triarylated sodium cyclopentadienides, (1,2,4-Ar3C 5H2)Na (7) and (1,2,3-Ar3C5H2)Na (8). Reactions of the ligands 7 and 8 with FeBr2 afforded the ferrocenes (1,2,4-Ar3C5H2)(2)Fe (11) and (1,2,3-Ar3C5H2 )2Fe (12), respectively. The cobaltocenes (ArC5H4)(2)CO (13), (1,3-Ar2C5H3) (2)CO (14), (1,2,4-Ar3C5H2)(2)CO (15), and (1,2,3-Ar3C5H2)(2)Co (16) were p repared from CoBr2 and (ArC5H4)Na (5), (1,3-Ar2C5H3)Na (6), 7, and 8, respe ctively. Oxidation of 13 lair, dilute aqueous HC1) followed by precipitatio n with KPF6 afforded [(ArC5H4)(2)Co](+)PFG(6)(-) (17). The homologous cobal tocenium ions [1,3-Ar2C5H3](2)Co+ (18), (1,2,4- Ar3C5H2)(2)Co+ (19), and (1 ,2,3-Ar3C5H2)(2)Co+ (20) were observed (NMR) only after dissolving the corr esponding Co-II: species 14-16 in D2SO4; efforts to isolate 18-20 as hexafl uorophosphates failed. Reactions of the ligands 5-8 with M(CO)(5)Br (M = Mn , Re) afforded the piano stool complexes (ArCp)Mn(CO)(3) (21), (1,8-Ar2Cp)M n(CO)(3) (22), (1,2,4-Ar3C5H2)M(CO); (2, M =Mn; 27, M = Re), and (1,2,3-Ar3 C5H2)M(CO)(3) (24, M = Mn; 28, M = Re). Both the voltammetric oxidation pot entials (E-1/2) Of the substituted metallocenes 9-16 and the carbonyl stret ching wavenumbers of the substituted piano stool complexes 21-24 and 25-28 increased linearly with increasing number of C6F5 substituents. Crystal str uctures were obtained for 2 (two polymorphs), 4, 11, 16, 23, 26, and 27. No teworthy features of these structures include C6F5-C6F5 arene stacking, C6F 5 stacking with benzene solvate molecules, C6F5 O dropC-M interactions, and extensive C-H F-C interactions. Barriers toward CP-C6F5 rotationand Cp-Fe- Cp rotation were quantified for several of the complexes using dynamic F-19 and H-1 NMR spectroscopy.