Synthesis and Structural Trends in Pentafluorophenyl-Substituted Ferrocenes, 1,4-Tetrafluorophenylene-Linked Diferrocenes, and 1,1‘-Ferrocenylene−1,4-Tetrafluorophenylene Co-oligomers

1,1‘-Dilithioferrocene, or (CpLi) 2 Fe ( 1 ), reacts with excess C 6 F 6 in THF to afford mostly (C 6 F 5 Cp) 2 Fe ( 2 ), accompanied by the diiron complex (C 6 F 5 Cp)FeCp(1,4-C 6 F 4 )CpFe(CpC 6 F 5 ) ( 3 ). The reaction of 1 with 1.0 equiv of C 6 F 6 affords a mixture of sparingly soluble step-growth oligomers assigned to [−FeCp(1,4-C 6 F 4 )−] n ( 4 ). [1-Li-2-R N Cp]FeCp ( 6, R N = CH 2 NMe 2 ) reacts with 1 equiv of C 6 F 6 to afford [1-(C 6 F 5 )-2-R N Cp]FeCp ( 7 ). Complex 6 reacts with 0.5 equiv of C 6 F 6 to afford CpFe[2-R N Cp](1,4-C 6 F 4 )[2-R N Cp]FeCp as a mixture of two diastereomers ( meso -8, major and dl -8, minor). The relative stereochemistry of meso- 8 is established by crystallographic analysis of the corresponding bis(methiodide) ( 12 ). [1-Li-2-R N Cp]Fe(CpLi) ( 9 ) reacts with excess C 6 F 6 to afford mainly the diarylated ferrocene [1-(C 6 F 5 )-2-R N Cp]Fe(CpC 6 F 5 ) ( 10 ). The reaction of 9 instead with 1.0 equiv of C 6 F 6 affords a mixture of oligomeric species assigned to the formula [−(2-R N Cp)FeCp(1,4-C 6 F 4 )−] n ( 11 ). In contrast to 4, 11 is sufficiently soluble for characterization by solution NMR spectroscopy (end group analysis), and under optimized conditions a number-averaged degree of oligomerization corresponding to a linear Fe 9 species is determined. The complexes 3, 7, 10, and 12 are characterized by single-crystal X-ray diffraction. Crystalline 3 exhibits infinite π-stacking interactions composed of intramolecular “triple-decker” C 6 F 5 −C 6 F 4 −C 6 F 5 stacking and intermolecular Cp−C 6 F 5 stacking. The crystal structure of 10 also shows intramolecular arene stacking, but intermolecular Cp−C 6 F 5 interaction is interrupted by the dimethylaminomethyl substituent. None of these complexes show intermolecular stacking among the various C 6 F 5 and C 6 F 4 groups. Extensive intermolecular C−H···F−C interactions in the crystallographic packing diagrams of 3, 7, 10, 12, and CpFeCpC 6 F 4 C 6 F 4 CpFeCp ( 13 ) are characterized as either “purposeful” or “diffuse” by examining correlations of their respective H···F distances and C−H···F angles. Solution voltammetry of 3 shows two unresolved, reversible Fe II |Fe III couples, suggesting weak electronic communication between the two iron centers despite the fully conjugated structure.