O-H and (CO)N-H bond weakening by coordination to Fe(II)

摘要

New N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)-ethane-1,2-diamine derivatives bearing covalently linked OH and (CO) NH groups have been synthesized. The coordination of those pendant hydroxyl/amide groups to a Fe(II) metal center is demonstrated both in solution, even in the presence of chloride as the counterion, and in solid state, by means of X-ray diffraction crystal structures. As a result of this coordination, the experimental bond dissociation free energies (BDFE) of O-H and (CO) N-H bonds are remarkably diminished down to 76.0 and 80.5 kcal mol(-1) respectively, which is also in agreement with DFT-based theoretical calculations. These BDFE values are in the range of commonly used hydrogen-atom donor reagents. The strategy presented here allows an unequivocal evaluation of the influence of metal coordination in X-H bond weakening in organic solvents which could be easily extended to other metal centers.