Probing the Coordination Chemistry of N-2-Pyridylimidoyl-2-pyridylamidine: A Versatile Ligand with Multiple Coordination Sites

Abstract

The research presented herein focuses on controlling the coordination environment of Mn, Fe, and Co in coordination complexes with the ligand N-2-pyridylimidoyl-2-pyridylamidine (Py 2 ImAm), which possesses both a bidentate and tridentate coordinating site. The synthesis and characterization of seven new metallic complexes are described, and these results indicate that the key factor dictating which coordination site of Py 2 ImAm the metal ion prefers is the presence (or absence) of a weak acid. More specifically, the presence of a weak acid directs the metal ion to the tridentate site of Py 2 ImAm, while neutral or basic conditions lead to coordination complexes in which the metal center is bound to the bidentate pocket.

Rational Design of Tetranuclear Complexes Employing N‐Imidoylamidine Based Ligands

“…As previously reported, the coordination environment of first row transition metals in either a bidentate or tridentate fashion with Py 2 ImAm can be controlled by tailoring the reaction conditions . Following a similar procedure, coordination to the tridentate pocket of the pyrimidyl analogue Pm 2 ImAm can also be achieved.…”

“…In the case of Mn2, since it is located in a general position, it is reproduced by symmetry (e.g., Mn2 ′ ). Previously, we published the tridentate mononuclear complex [Mn II (Py 2 ImAm)Cl 2 ] , which has the same coordination environment as Mn2, as highlighted in the overlay of both structures shown in Figure b. On the other hand, Mn3 is unique and located on the C 2 axis.…”

“…S1 and Table S1). Interestingly, when the pyrimidyl ligand is employed a dimeric complex with bridging chloride ions is isolated, contrary to a mononuclear complex that was obtained with the Py 2 ImAm ligand (i.e., [Mn II (Py 2 ImAm)Cl 2 ] ); however, similar to the pyridyl analogue, the Mn II ions coordinate exclusively in a tridentate fashion to Pm 2 ImAm under acidic conditions. As well, the N ‐imidoylamidine ligand in [Mn II 2 ( µ ‐Cl) 2 (Pm 2 ImAm) 2 Cl 2 ] is neutral, since there is a hydrogen atom located at the imino nitrogen atom N5, which was refined isotropically without any constraints.…”

“…In [Mn III Mn II 3 (Pm 2 ImAm) 3 Cl 6 ] , which crystallizes in the monoclinic C2/c space group, each Pm 2 ImAm ligand is anionic and coordinates to two Mn ions resulting in two distinct Mn moieties – one coordinated in a bidentate fashion, the other in the tridentate pocket of the ligand. The central Mn ion, which is bound to three anionic Pm 2 ImAm ligands in a bidentate fashion, adopts a nearly ideal octahedral environment (Figure S2) that is very similar to that of the mononuclear complex [Mn III (Py 2 ImAm) 3 ] , as highlighted in the overlay of the two structures (Figure a). Comparing the Mn–N distances of the central metal in [Mn III Mn II 3 (Pm 2 ImAm) 3 Cl 6 ] to those of [Mn III (Py 2 ImAm) 3 ] reveal a slight elongation of these bond lengths upon development of the polynuclear complex (e.g., 1.94227(4) – 1.95932(3) Å for [Mn III (Py 2 ImAm) 3 ] ; 1.954(4) – 1.969(5) for [Mn III Mn II 3 (Pm 2 ImAm) 3 Cl 6 ] ).…”

“…Mononuclear [Fe III (Pm 2 ImAm)Cl 3 ] was synthesized using the same approach as its pyridyl analogue [Fe III (Py 2 ImAm)Cl 3 ] , by reacting a dichloromethane (DCM) solution of the ligand ( Pm 2 ImAm ) with a DCM solution of pyridinium tetrachloroferrate(III) ( [PyH][FeCl 4 ] ), as outlined in Scheme . Here, the acidic environment achieved through the use of [PyH][FeCl 4 ] affords [Fe III (Pm 2 ImAm)Cl 3 ] , as confirmed through single‐crystal X‐ray analysis (Figure a).…”