The binding behavior of the bifunctional Lewis acid (η 5 -C 5 H 5 Fe) 2 [μ-(C 5 H 3 (BPh)) 2 ] ( 3 ) toward different pyridine derivatives as the Lewis base has been investigated. The 1:1 and 1:2 adducts, 3 ·D and 3 ·D 2 (donor, D = 4- tert -butylpyridine ( t Bupy) and 4-dimethylaminopyridine (DMAP)), were obtained by low-temperature crystallization or slow solvent evaporation techniques. The complexes were fully characterized by multinuclear NMR, IR, and elemental analysis. Single-crystal X-ray diffraction data were collected for the 1:1 adduct with DMAP and for both 1:2 adducts, and the marked structural changes upon pyridine binding are discussed in detail. In solution, the 1:2 adducts were found to readily undergo dissociation with formation of the 1:1 adducts as the dominant species at room temperature. Variable-temperature NMR and UV−visible titration studies demonstrate that the first binding process is more than 5 orders of magnitude more favorable than the second binding process.
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Pakkirisamy et al. (2008) studied this question.