John W. Sibert

Synthesis and coordination chemistry of unsymmetrical tetraazaporphyrins containing single oxathia- and thiacrown substituents

Abstract Singly crowned porphyrazines containing oxathia- and thiacrown ethers were prepared from a mixed condensation of 1,2-dicyanobenzene or its 3,4-dibutyl analog and the appropriate crowned maleonitrile precursor. Peripheral metal-binding to each porphyrazine was examined spectrophotometrically. The oxathiaether-crowned porphyrazines were found to coordinate Ag(I) and HgCl 2 , though all complexes suffered from poor solubility and complexes with the latter were unstable in polar media. With an interest in the formation of comparatively more stable and soluble heavy and transition metal complexes, two new sets of thiaether-crowned porphyrazines were examined. In these cases, coordination of Hg(II), Ag(I), Cu(I) and Cu(II) was observed with no evidence for complexation of Tl(I), Pb(II) or CdCl 2 .

Wurster-type ureas as redox-active receptors for anions

Four redox-active receptors, 1-4, based on the incorporation of p-phenylenediamine(s) within a urea framework, were synthesized, and the affinities of two for a series of anions were quantified through UV-vis and NMR spectroscopic studies. The structure of 1 was confirmed by X-ray crystallography. For the oxoanions studied, complex stabilities approached 10(6) M(-1) in acetonitrile and decreased with the decreasing basicity of the anion (CH(3)COO(-) > C(6)H(5)COO(-) > H(2)PO(4)(-) > NO(2)(-) > NO(3)(-)). The presence of the urea functionality caused an increase in the oxidation potential of the p-phenylenediamine subunit compared to that of free p-phenylenediamine. Electrochemical studies of the anion complexes revealed two-wave behavior with the appearance of a second oxidation wave cathodic to that in the free receptors and characteristic of the bound anion. Ab initio DFT studies of a representative acetate complex revealed the consequences of host oxidation state on complex structure.

Macrocyclic dithiomaleonitrile derivatives containing sulfur and nitrogen heteroatoms

Abstract A general synthetic method for incorporation of the dithiomaleonitrile unit into macrocycles containing sulfur, oxygen, and nitrogen heteroatoms is presented along with the single-crystal X-ray structures of the thiacrowns. In addition to being new ligands, these macrocycles are direct precursors to peripherally crown functionalized porphyrazines capable of coordinating multiple metal ions.

Lipophilic derivatives of cyclam as new inhibitors of tumor cell growth

Two new lipophilic tetraazamacrocycles were prepared and, in contrast to non-lipophilic analogs, found to be potent inhibitors of tumor cell growth in vitro with IC50 values below 10 micromolar.

On the synthesis of unsymmetrical bis(macrocyclic) ligands

Abstract The syntheses of novel three and four carbon-bridged unsymmetrical bis(macrocyclic) ligands have been investigated. Suitable functionalization of a selectively protected 1,4,7-triazacyclononane macrocycle allows for the coupling of this well-studied ligand to either 1,4-diazacyclononane or 4,7-diaza-1-oxacyclononane.

Bulky substituent effects on the iron(III) complexation of 1,4,7-triazacyclononane

Abstract The synthesis of two sterically encumbered macrocycles, N,N′,N″-triisopropyl-1,4,7-triazacyclononane (1) and N,N′,N″-triisobutyl-1,4,7-triazacyclononane (2), and their reactions with iron(III) have been investigated. In alcoholic solvents, a 1:1 mixture of either 1 or 2 and FeCl3·6H2O does not result in complex formation. Instead, the macrocycles are singly protonated with the iron being incorporated into the anion. The structure of (1·H)+(FeCl4)− was determined by single crystal X-ray methods. Crystals are orthorhombic, space group Pbca (No. 61), with the following unit cell parameters: a=14.921(2), b=17.765(2), c=17.414(2) A, V=4616.0(10) A3 and Z=8. The structure of (2·H)+2(Fe2OCl6)2− was also determined. Crystals are triclinic, space group P 1 (No. 2) with the following unit cell parameters: a=9.3543(10), b=10.1002(11), c=14.4167(14) A, α=85.185(8), β=73.395(8), γ=73.198(8)°, V =1246.6(2) A3 and Z=2. The reactivity of 1 and 2 with iron(III) is then compared to that of the well-studied macrocycles, 1,4,7-triazacyclononane and N,N′,N″-trimethyl-1,4,7-triazacyclononane. The inability of 1 and 2 to serve as ligands to iron(III) in protic media is attributed to steric interactions involving the bulky alkyl appendages of the macrocycles.

Unusual coordination of HgCl2 by a mixed oxathioether crown

The oxathioether crown 1,4,7,10-tetraoxa-13,16-dithiacyclooctadec-14-en-14,15-dicarbonitrile reacts with HgCl2 to give an endocyclic complex in which macrocylic coordination to HgII in the solid state is through only the O donor atoms.

‘meta-Wurster's crowns’: The synthesis and properties of meta-Phenylenediamine-based macrocycles

Abstract meta-Wursters crowns are a new class of hosts that incorporate the meta-phenylenediamine moiety within a macrocyclic framework. We have used a Pd-catalyzed amination procedure in the synthesis of representative m-Wursters crown members containing aza-12-crown-4, aza-15-crown-5 and aza-18-crown-6 macrocycles and bis/tris(macrocycles) containing aza-15-crown-5 units with yields ranging from 70 to 86%. Competitive alkali metal ion binding experiments, monitored by electrospray mass spectrometry, revealed that the monocyclic crowns form 1:1 complexes with the cation that best matches the crown topology. 13C NMR studies confirm the results from mass spectrometry and show the m-phenylenediamine moiety to interact with the bound ions, thus, establishing its participation as a direct link in the stabilization of the complexes. The bis and tris(macrocycles) were shown by cyclic voltammetry and 13C NMR spectroscopy to coordinate two and three sodium ions, respectively. Anodic shifts in the oxidation potentials of the ligands upon complexation were driven by complex stability, not charge density, with the largest shifts resulting from the cation that appears to best fit the crown.

Synthesis and crystal structure of the 1:1 Pd(II) complex of 1,4,7,10-tetraoxa-13,16,19,22-tetraazacyclotetracosane

Abstract The synthesis and structural characterization of [1·Pd](PF6)2, complex 3, where 1=1,4,7,10-tetraoxa-13,16,19,22-tetraazacyclotetracosane, are reported. The palladium atom in the complex is coordinated by the four ligand nitrogen atoms in an essentially square planar structure (average PdN bond length=2.040(1) A). A further weak apical interaction exists (2.98 A) to one O atom of the ligand. The pale yellow crystals of Pd(C16H36N4O4) (PF6)2 are monoclinic with unit-cell dimensions a=15.222(7), b=20.480(9), c=8.733(4) A,β=91.53(4)°, V=2722(2) A3, space group P21/c (No. 14) and Z=4. Crystals of [1·Pd](PF6)2 are, thus, isomorphous with those of a Cu(PF6)2 salt of 1, complex 2, reported earlier (J. L. Sessler, J. W. Sibert, J. D. Hugdahl and V. Lynch, Inorg. Chem., 28 (1989) 1417–1419). The coordination around Cu, however, is better described as square pyramidal with a long CuO axial contact (2.47(2)).