Coordination Versatility and Amide Shift in Mononuclear Fe super(II) Complexes with the Asymmetrical Tripod [(6-Bromo-2-pyridyl)methyl][(6-pivaloylamido-2-pyridyl)methyl](2-p y ridylmethyl)amine (BrMPPA)

We report in this communication the preparation of the BrMPPA ligand, a new tris(2-pyridylmethyl)amine-type tripod in which di- alpha -substitution by an amido group and a bromine atom, respectively, provide functionality and sterically induced ligand flexibility. The coordination versatility of this tripod is evidenced by the complete characterization of two dichlorido and di-triflato Fe super(II) complexes in the solid state and in solution. The new tripod can potentially act as a Kappa super(5) ligand with coordination of the carbonyl group of the amide function. This is true when there is little steric hindrance at the coordination site. With bulky chlorido ligands, however, decoordination occurs, and the tripod becomes a Kappa super(4) chelate. In this case, a state-dependent coordination mode is reported: A dangling pyridyl group is observed in solution, whereas the carbonyl group is noncoordinated in the solid state, the three pyridine groups remaining bound. In the new BrMPPA tripod, di- alpha -substitution by an amido group and a bromine atom, respectively, provide functionality and sterically induced ligand flexibility in Fe super(II) complexes. Three different coordination modes of the tripod are described, the occurrence of which depends on the nature of the ancillary ligands.