Transition metal complexes of pentadentate ligands

The investigation of N,N'bis(salicylidene)-1,7-diamino-4-azaheptane, SALLDIPN, N,N'bis(salicylidene)-1,5-diamino-3-azaheptane, SALDIEN, and N,N'bis(salicylidene)-1,5-diamino-3-thiopentanane, SALUAES, as pentadentate ligands is logical in that they offer an analogy to the environment around the cobalt atom in Vitamin B₁₂, I [see Figure I], represented below. These complexes might be expected to give some insight as to the behavior and role of the metal ion as it interacts with the five-donor atoms and hence an insight into the role of the metal ion in Vitamin B₁₂.

[See Figure I]

Compounds formed by the reaction of Ni(XSAL)₂·2H₂0 with 1,5-diamino-3-azaheptane, DlEN, and Ni(OAc)₂·4H₂O with X-SALDAES were isolated and characterized. In addition to these, alkyl σ-bonded derivatives formed by the reaction of reduced Co(SALDIPN) with R-X were also isolated and characterized.

Mass spectra, magnetic moments; X-ray powder patterns, infrared, visible, and near infrared spectra were obtained on the majority of the compounds. Nuclear magnetic resonance spectra were obtained on the majority of the σ-bonded alkyl complexes.

It was concluded that the Ni(X-SALDIEN) complexes are square planar whereas the Ni(X-SALDAES) complexes are distorted square planar or possibly a five-coordinate species. Spin state changes were observed for both complexes when they were dissolvea in pyridine which is in contrast to Ni(X-SALEN).

The alkyl derivatives were all primary in nature and very stable to light, air, and H₂0 which in contrast to the alkyl derivatives of Co(X-SALEN) which happen to be photolabile. The geometry around the cobalt atom in R-Co-(SALDIPN) was concluded to be pseudo-octahedral.

Reasons for certain anomalies (i.e., magnetic moments, etc.) were discussed in detail.