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 C6F6 in THF to afford mostly (C6F5Cp)(2)Fe (2), accompanied by the diiron complex (C6F5 Cp)FeCp(1,4-C6F4)CpFe(CpC6F5) (3). The reaction of 1 with 1.0 equiv of C6F6 affords a mixture of sparingly soluble step-growth oligomers assigned to [ -FeCp(1,4-C6F4)(-)](n) (4). [1-Li-2-(RCp)-Cp-N]FeCp (6, R-N = CH2-NMe2) rea cts with 1 equiv of C6F6 to afford [1-(C6F5)-2-(RCp)-Cp-N]FeCp (7). Complex 6 reacts with 0.5 equiv of C6F6 to afford CpFe[2-(RCp)-Cp-N](1,4-C6F4)[2-( RCp)-Cp-N]FeCp as a mixture of two diastereomers (meso-8, major and dl-8, m inor). The relative stereochemistry of meso-8 is established by crystallogr aphic analysis of the corresponding bis(methiodide) (12). [1-Li-2-(RCp)-Cp- N]Fe(CpLi) (9) reacts with excess C6F6 to afford mainly the diarylated ferr ocene [1-(C6F5)2-(RCp)-Cp-N]Fe(CpC6F5) (10). The reaction of 9 instead with 1.0 equiv of C6F6 affords a mixture of oligomeric species assigned to the formula [-(2-(RCp)-Cp-N)FeCp(1,4-C6F4)-](n) (11). In contrast to 4, 11 is s ufficiently 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 diffra ction. Crystalline 3 exhibits infinite ct-stacking interactions composed of intramolecular "triple-decker" C6F5-C6F4-C6F5 stacking and intermolecular Cp-C6F5 stacking. The crystal structure of 10 also shows intramolecular are ne stacking, but intermolecular Cp-C6F5 interaction is interrupted by the d imethylaminomethyl substituent. None of these complexes show intermolecular stacking among the various C6F5 and C6F4 groups. Extensive intermolecular C-H ... F-C interactions in the crystallographic packing diagrams of 3, 7, 10, 12, and CpFeCpC6F4C6F4CpFeCp (13) are characterized as either "purposef ul" or "diffuse" by examining correlations of their respective H ... F dist ances 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.