Design and Synthesis of Binucleating Macrocyclic Clefts Derived from Schiff‐Base Calixpyrroles

Abstract

The syntheses, characterisation and complexation reactions of a series of binucleating Schiff-base calixpyrrole macrocycles are described. The acid-templated [2+2] condensations between meso-disubstituted diformyldipyrromethanes and o-phenylenediamines generate the Schiff-base pyrrolic macrocycles H(4)L(1) to H(4)L(6) upon basic workup. The single-crystal X-ray structures of both H(4)L(3).2 EtOH and H(4)L(6).H2O confirm that [2+2] cyclisation has occurred, with either EtOH or H2O hydrogen-bonded within the macrocyclic cleft. A series of complexation reactions generate the dipalladium [Pd2(L)] (L=L(1) to L(5)), dinickel [Ni2(L(1))] and dicopper [Cu2(L)] (L=L(1) to L(3)) complexes. All of these complexes have been structurally characterised in the solid state and are found to adopt wedged structures that are enforced by the rigidity of the aryl backbone to give a cleft reminiscent of the structures of Pacman porphyrins. The binuclear nickel complexes [Ni2(mu-OMe)2Cl2(HOMe)2(H(4)L(1))] and [Ni2(mu-OH)2Cl2(HOMe)(H(4)L(5))] have also been prepared, although in these cases the solid-state structures show that the macrocyclic ligand remains protonated at the pyrrolic nitrogen atoms, and the Ni(II) cations are therefore co-ordinated by the imine nitrogen atoms only to give an open conformation for the complex. The dicopper complex [Cu2(L(3))] was crystallised in the presence of pyridine to form the adduct [Cu2(py)(L(3))], in which, in the solid state, the pyridine ligand is bound within the binuclear molecular cleft. Reaction between H(4)L(1) and [Mn(thf){N(SiMe(3))2}2] results in clean formation of the dimanganese complex [Mn2(L(1))], which, upon crystallisation, formed the mixed-valent complex [Mn2(mu-OH)(L(1))] in which the hydroxo ligand bridges the metal centres within the molecular cleft.

Dioxygen Reduction at Dicobalt Complexes of a Schiff Base Calixpyrrole Ligand

“…Both the cobalt cations are square pyramidal, with Co1 and Co2 displaced out of the N 4 -basal planes by 0.17 and 0.18 , respectively, and the apical sites are occupied by pyridine nitrogen atoms that are exo and endo to the cleft. The canted geometry of the endo-pyridine (Co2-N10-C46 161.708) is similar to that seen by us in [Cu 2 (endo-py)(L)], [14] and reflects the inability of the binuclear cleft to expand. In contrast, pacman diporphyrin and bis(corrole) complexes have the capacity to undergo considerable vertical expansion.…”

Synthesis and structures of transition metal pacman complexes of heteroditopic Schiff-base pyrrole macrocycles

“…Similar interactions between the pyrrole NH donors and imine N acceptors in H 4 L and solvent of crystallisation were seen previously, 22,23 and an analogous weak interaction between the fluorenyl substituent (C108) and the metal-bound hydroxide was seen in a related binuclear cobalt complex of the symmetric macrocycle (C fluorenyl -O 3.386 Å) and could play a role in any future catalytic chemistry. 17 The second pyrrolic nitrogen (N103) is not involved in any further bonding.…”

Determination of intermolecular copper–copper distances from the EPR half-field transitions and their comparison with distances from X-ray structures: applications to copper(II) complexes with biologically important ligands

“…There have since been only a limited number of applications of the Eatons' method in EPR spectroscopy of transition metal compounds. These include studies both of pure powders [13][14][15][16][17][18] and of frozen solutions [19][20][21][22][23][24]. The most studied compounds have been copper(II) systems, in which the distances between copper centers were known from X-ray analyses, but applications to other metals such as W(V) are found [19].…”