[(CO)3(dppe)Mn(OH2)]BF4 (1). A synthetically versatile compound and its use as a probe for determining the preferred site of coordination on ambident ligands

Previous work in this laboratory has shown that the Mn(I) octahedral complex, [(CO)3(dppe)Mn(OH2)]BF4 (1), may be used for the synthesis of many related complexes by the ready replacement of the aqua ligand by neutral and anionic ligands, leading to new complexes having a variety of functional groups sigma (η1) bonded to the Mn atom. This procedure has now been extended to ligands possessing phenolic and carboxylic acid groups, including amino acids. Compound 1 is used as a probe to compare the relative coordinating ability of different heteroatoms on ambident ligands. The 1H NMR spectra of the resulting complexes show two signals at room temperature for the four protons (each 2H m) of the dppe-Mn metallacyle whose position depends on the specific atom of the ligand that is attached to the metal. The spectrum of 1, however, shows only one signal (4H m). On cooling to −53 °C this signal is split in two (both 2H, m) owing to a slowing of the rapid reversible dissociation of the aqua ligand.

Graphical abstractThe aqua ligand in the titled compound, 1, is readily replaced by many other neutral or anionic ligands. Polydentate ligands react at every coordination site. Ambident ligands react selectively. 1H NMR and IR spectra indicate which atom of the K1 complexed ambident ligand is attached to the Mn atom.Figure optionsDownload full-size imageDownload as PowerPoint slide