N-hydroxymethylation of ethylene-bridged glycine metal(II) complexes by formaldehyde

The (N,N′-ethylenediglycinato)metal(II) complexes, M(edg) (M=Cu, Zn, Ni, Co) undergo N-hydroxymethylation with formaldehyde in the pH range ∼3.5–9.5 to yield the respective [N,N′-ethylenedi(N-hydroxymethyl-glycinato)]metal(II), ML·xH2O (L=N,N′-ethylenedi(N-hydroxymethylglycinate); x=4, 4.5). The crystal and molecular structures of the Ni(edg)·3H2O and ML·4H2O (M=Ni, Cu, Co) complexes have been determined; all the complexes have distorted octahedral geometries and their tetradentate ligands have α-cis configuration. Analysis of these structures also shows that the N-hydroxymethylated ligands are stereospecifically coordinated. However, M(edg) do not undergo Mannich aminomethylation with formaldehyde and ammonia. In the reactions studied, the α-carbon of M(edg) is unaffected by formaldehyde attack. No further condensation of the N-hydroxymethyl substituents and their potential reactivity are also explained.