Nickel(II) complexes stabilized by bis[N-(6-pivalamido-2-pyridylmethyl)]benzylamine: Synthesis and characterization of complexes stabilized by a hydrogen bonding network

Abstract

Hydrogen bonds in metalloproteins are key in directing reactivity yet to be achieved in synthetic systems. We have been developing a synthetic system that uses hydrogen-bonding interactions to modulate the secondary coordination around a transition metal ion. This was accomplished with the ligand bis[N-(6-pivalamido-2-pyridylmethyl)]benzylamine (H2pmb), which contains two carboxyamido units appended from pyridine rings. Several nickel complexes were prepared and structurally characterized. In particular, we found that the appended carboxyamido groups either provide intramolecular H-bond donors or can be converted to bind directly to a metal center. We established that the complex NiIIH2pmb(Cl)2 can be sequentially deprotonated with potassium tert-butoxide, causing coordination of the carboxyamido oxygen atoms and concomitant loss of the chloro ligands. The chloro ligands were also removed with silver(I) salts—in the presence of acetate ions, the complex NiIIH2pmb(κ2-OAc)(κ1-OAc) was isolated, in which an intramolecular H-bonding network occurs between the H2pmb ligand and the coordinate acetato ligands.

Structural Diversity in Metal Complexes with a Dinucleating Ligand Containing Carboxyamidopyridyl Groups

“…However, there are several situations in which differing metal coordination geometries would be beneficial for function. , For example, the reduced form of the respiratory protein hemerthyrin contains one six-coordinate and one five-coordinate ferrous center: dioxygen binding occurs at the coordinately unsaturated site . Our group and others have been utilizing (carboxyamido)pyridyl units in the design of multidentate ligands because they potentially coordinate to metal ions in two distinct modes. In one case, the carboxyamido group is deprotonated and functions as a bidentate ligand through coordination of the pyridyl nitrogen and carbonyl oxygen atoms (Figure A).…”

Coordination Versatility and Amide Shift in Mononuclear FeII Complexes with the Asymmetrical Tripod [(6‐Bromo‐2‐pyridyl)methyl][(6‐pivaloylamido‐2‐pyridyl)methyl](2‐pyridylmethyl)amine (BrMPPA)

“…[1] Tripodal nitrogen-containing ligands of the tris(2-pyridylmethyl)amine (TPA) type substituted at the α-position by pivaloylamido (NHCOtBu) groups are well known, [2][3][4] and their coordination chemistry studied in detail with various metal centers, such as copper, [5][6][7][8][9] iron, [10][11][12] zinc, [13,14] cobalt, [13] nickel, [13,[15][16][17] or ruthenium, [18,19] to cite a few examples. [1] Tripodal nitrogen-containing ligands of the tris(2-pyridylmethyl)amine (TPA) type substituted at the α-position by pivaloylamido (NHCOtBu) groups are well known, [2][3][4] and their coordination chemistry studied in detail with various metal centers, such as copper, [5][6][7][8][9] iron, [10][11][12] zinc, [13,14] cobalt, [13] nickel, [13,[15][16][17] or ruthenium, [18,19] to cite a few examples.…”